Friday, February 5, 2010
Fundamental physics
While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well described. General relativity has not yet been unified with the other fundamental descriptions.
preparasi material
Metallography Material
1. Tujuan Preparasi Sampel
1.1 Cutting
Mengetahui prosedur proses pemotongan sampel dan menentukan teknik pemotongan yang tepat dalam pengambilan sampel metalografi, sehingga didapat benda uji yang representatif
1.2 Mounting
Menempatkan sampel pada suatu media, untuk memudahkan penanganan sampel yang berukuran kecil dan tidak beraturan tanpa merusak sampel
1.3 Grinding
Meratakan dan menghaluskan permukaan sampel dengan cara menggosokkan sampel pada kain abrasif / amplas
1.4 Pemolesan / Polishing
Mendapatkan permukaan sampel yang halus dan mengkilat seperti kaca tanpa gores
Memperoleh permukaan sampel yang halus bebas goresan dan mengkilap seperti cermin
Menghilangkan ketidakteraturan sampel hingga orde 0.01 μm
1.5 Etsa / Etching
Mengamati dan mengidentifikasi detil struktur logam dengan bantuan mikroskop optik setelah terlebih dahulu dilakukan proses etsa pada sampel
Mengetahui perbedaan antara etsa kimia dengan elektro etsa serta aplikasinya
Dapat melakukan preparasi sampel metalografi secara baik dan benar
2. Tujuan Pengamatan Struktur Makro dan Mikro
Menganalisa struktur mikro dan sifat-sifatnya
1. Tujuan Preparasi Sampel
1.1 Cutting
Mengetahui prosedur proses pemotongan sampel dan menentukan teknik pemotongan yang tepat dalam pengambilan sampel metalografi, sehingga didapat benda uji yang representatif
1.2 Mounting
Menempatkan sampel pada suatu media, untuk memudahkan penanganan sampel yang berukuran kecil dan tidak beraturan tanpa merusak sampel
1.3 Grinding
Meratakan dan menghaluskan permukaan sampel dengan cara menggosokkan sampel pada kain abrasif / amplas
1.4 Pemolesan / Polishing
Mendapatkan permukaan sampel yang halus dan mengkilat seperti kaca tanpa gores
Memperoleh permukaan sampel yang halus bebas goresan dan mengkilap seperti cermin
Menghilangkan ketidakteraturan sampel hingga orde 0.01 μm
1.5 Etsa / Etching
Mengamati dan mengidentifikasi detil struktur logam dengan bantuan mikroskop optik setelah terlebih dahulu dilakukan proses etsa pada sampel
Mengetahui perbedaan antara etsa kimia dengan elektro etsa serta aplikasinya
Dapat melakukan preparasi sampel metalografi secara baik dan benar
2. Tujuan Pengamatan Struktur Makro dan Mikro
Menganalisa struktur mikro dan sifat-sifatnya
Radiasi Benda Hitam
Dalam fisika, benda hitam (black body) adalah obyek yang menyerap seluruh radiasi elektromagnetik yang jatuh kepadanya. Tidak ada radiasi yang dapat keluar atau dipantulkannya. Namun demikian, dalam fisika klasik, secara teori benda hitam haruslah juga memancarkan seluruh panjang gelombang energi yang mungkin, karena hanya dari sinilah energi benda itu dapat diukur.
Meskipun namanya benda hitam, dia tidaklah harus benar-benar hitam karena dia juga memancarkan energi. Jumlah dan jenis radiasi elektromagnetik yang dipancarkannya bergantung pada suhu benda hitam tersebut. Benda hitam dengan suhu di bawah sekitar 700Kelvin hampir semua energinya dipancarkan dalam bentuk gelombang inframerah, sangat sedikit dalam panjang gelombang tampak. Semakin tinggi temperatur, semakin banyak energi yang dipancarkan dalam panjang gelombang tampak dimulai dari merah, jingga, kuning dan putih.
Istilah "benda hitam" pertama kali diperkenalkan oleh Gustav Robert Kirchhoff pada tahun 1862. Cahaya yang dipancarkan oleh benda hitam disebut radiasi benda hitam
9FEB
Teori Radiasi Benda Hitam
Distribusi kerapatan radiasi yang terkandung dalam increment sebesar df adalah sesuai dengan hukum planck sebagai berikut
………………………..(1)
Element g(f) adalah kerapatan radiasi per satuan frekuensi dengan satuan Js/cm3, k adalah konstanta Bolzmann, c adalah kelajuan cahaya. Distribusi spectral tersebut akan bernilai nol untuk f = 0 dan f = serta memiliki puncak tertinggi (peak) yang berbeda- beda tergantung temperaturnya.
Radiasi benda hitam
Dalam fisika, benda hitam (bahasa Inggris black body) adalah obyek yang menyerap seluruh radiasi elektromagnetik yang jatuh kepadanya. Tidak ada radiasi yang dapat keluar atau dipantulkannya. Namun demikian, dalam fisika klasik, secara teori benda hitam haruslah juga memancarkan seluruh panjang gelombang energi yang mungkin, karena hanya dari sinilah energi benda itu dapat diukur.
Setiap benda secara kontinu memancarkan radiasi panas dalam bentuk gelombang
elektromagnetik. Bahkan sebuah kubus es pun memancarkan radiasi panas, sebagian kecil dari
radiasi panas ini ada dalam daerah cahaya tampak. Walaupun demikian kubus es ini tak dapat
dilihat dalam ruang gelap. Serupa dengan kubus es, badan manusia pun memancarkan radiasi
panas dalam daerah cahaya tampak, tetapi intensitasnya tidak cukup kuat untuk dapat dilihat
dalam ruang gelap.
Setiap benda memancarkan radiasi panas, tetapi umunya benda terlihat oleh kita karena
benda itu memantulkan cahaya yang dating padanya, bukan karena ia memacarkan radiasi
panas. Benda baru terlihat karena meradiasikan panas jika suhunya melebihi 1000 K. Pada suhu
ini benda mulai berpijar merah sepeti kumparan pemanas sebuah kompor listrik. Pada suhu di
atas 2000 K benda berpijar kuning atau keputih-putihan, seperti besi berpijar putihatau pijar
putih dari filamen lampu pijar. Begitu suhu benda terus ditingkatkan, intensitas relatif dari
spectrum cahaya yang dipancarkannya berubah. Ini menyebabkan pergeseran dalam warnawarna
spektrum yang diamati, yang dapat digunakan untuk menaksir suhu suatu benda
Intensitas energi radiasi yang dipancarkan benda hitam dinyatakan sebagai
Hukum pergeseran Wien menyatakan bahwa panjang gelombang dengan intensitas maksimumyang dipancarkan benda hitam selalu berbanding terbalik dengan suhu benda hitam tersebut.
Hubungannya adalah
•
Dalam teori klasik dinyatakan bahwa kerapatan energi yang dipancarkan sebuah benda adalah
u(λ, T) = 8.phi.kTλ^-4
Pada persamaan tersebut terlihat bila lambda mendekati nol maka kerapatan energinya tak terhingga. Ini disebut bencana ultraviolet.
Dalam persamaan Planck, persamaan dalam teori klasik tersebut dikoreksi menjadi
sehingga ketika lambda mendekati nol, kerapatan energi tidak tak terhingga.
Meskipun namanya benda hitam, dia tidaklah harus benar-benar hitam karena dia juga memancarkan energi. Jumlah dan jenis radiasi elektromagnetik yang dipancarkannya bergantung pada suhu benda hitam tersebut. Benda hitam dengan suhu di bawah sekitar 700Kelvin hampir semua energinya dipancarkan dalam bentuk gelombang inframerah, sangat sedikit dalam panjang gelombang tampak. Semakin tinggi temperatur, semakin banyak energi yang dipancarkan dalam panjang gelombang tampak dimulai dari merah, jingga, kuning dan putih.
Istilah "benda hitam" pertama kali diperkenalkan oleh Gustav Robert Kirchhoff pada tahun 1862. Cahaya yang dipancarkan oleh benda hitam disebut radiasi benda hitam
9FEB
Teori Radiasi Benda Hitam
Distribusi kerapatan radiasi yang terkandung dalam increment sebesar df adalah sesuai dengan hukum planck sebagai berikut
………………………..(1)
Element g(f) adalah kerapatan radiasi per satuan frekuensi dengan satuan Js/cm3, k adalah konstanta Bolzmann, c adalah kelajuan cahaya. Distribusi spectral tersebut akan bernilai nol untuk f = 0 dan f = serta memiliki puncak tertinggi (peak) yang berbeda- beda tergantung temperaturnya.
Radiasi benda hitam
Dalam fisika, benda hitam (bahasa Inggris black body) adalah obyek yang menyerap seluruh radiasi elektromagnetik yang jatuh kepadanya. Tidak ada radiasi yang dapat keluar atau dipantulkannya. Namun demikian, dalam fisika klasik, secara teori benda hitam haruslah juga memancarkan seluruh panjang gelombang energi yang mungkin, karena hanya dari sinilah energi benda itu dapat diukur.
Setiap benda secara kontinu memancarkan radiasi panas dalam bentuk gelombang
elektromagnetik. Bahkan sebuah kubus es pun memancarkan radiasi panas, sebagian kecil dari
radiasi panas ini ada dalam daerah cahaya tampak. Walaupun demikian kubus es ini tak dapat
dilihat dalam ruang gelap. Serupa dengan kubus es, badan manusia pun memancarkan radiasi
panas dalam daerah cahaya tampak, tetapi intensitasnya tidak cukup kuat untuk dapat dilihat
dalam ruang gelap.
Setiap benda memancarkan radiasi panas, tetapi umunya benda terlihat oleh kita karena
benda itu memantulkan cahaya yang dating padanya, bukan karena ia memacarkan radiasi
panas. Benda baru terlihat karena meradiasikan panas jika suhunya melebihi 1000 K. Pada suhu
ini benda mulai berpijar merah sepeti kumparan pemanas sebuah kompor listrik. Pada suhu di
atas 2000 K benda berpijar kuning atau keputih-putihan, seperti besi berpijar putihatau pijar
putih dari filamen lampu pijar. Begitu suhu benda terus ditingkatkan, intensitas relatif dari
spectrum cahaya yang dipancarkannya berubah. Ini menyebabkan pergeseran dalam warnawarna
spektrum yang diamati, yang dapat digunakan untuk menaksir suhu suatu benda
Intensitas energi radiasi yang dipancarkan benda hitam dinyatakan sebagai
Hukum pergeseran Wien menyatakan bahwa panjang gelombang dengan intensitas maksimumyang dipancarkan benda hitam selalu berbanding terbalik dengan suhu benda hitam tersebut.
Hubungannya adalah
•
Dalam teori klasik dinyatakan bahwa kerapatan energi yang dipancarkan sebuah benda adalah
u(λ, T) = 8.phi.kTλ^-4
Pada persamaan tersebut terlihat bila lambda mendekati nol maka kerapatan energinya tak terhingga. Ini disebut bencana ultraviolet.
Dalam persamaan Planck, persamaan dalam teori klasik tersebut dikoreksi menjadi
sehingga ketika lambda mendekati nol, kerapatan energi tidak tak terhingga.
Logam-logam nonferro dan paduannya
Logam-logam nonferro dan paduannya tidak diproduksi secara besar-besaran seperti logam besi, tetapi cukup vital untuk kebutuhan industri karena memiliki sifat sifat yang tidak ditemukan pada logam besi dan baja. Sifat-sifat paduan logam nonferro adalah :
• -mampu dibentuk dengan baik
• -massa jenisnya rendah
• -penghantar panas dan listrik yang baik
• -mempunyai warna yang menarik
• -tahan karat
• -kekuatan dan kekakuannya umumnya lebih rendah dari pada logam ferro
• -sukar dilas
1. Paduan aluminium (aluminium alloy)
Paduan aluminium banyak dipakai dalam industri yang dapat dibagi dalam dua golongan utama:
a) Wrought alloy: dibuat dengan jalan rooling, (paduan tempa)forming, drawing, forging dan press working.
b) Casting alloy: dibuat berdasarkan pengecoran (paduan tuang) Paduan aluminium tempa mempunyai kekuatan mekanik yang tinggi mendekati baja.
Paduan ini dibedakan lagi berdasarkan:
a. dapat di heat treatment
b. tak dapat di heat treatment
Paduan aluminum yang tak dapat di heat treatment yaitu Al – Mn (1,3% Mn) dan Al – Mg Mn (2,5% Mg dan 0,3% Mn), memiliki kekuatan mekanik yang tinggi, ductil, tahan korosi dan dapat dilas.Paduan aluminium tuang merupakan paduan yang komplek dari aluminium dengan tembaga, nikel, besi, silikon dan unsur lain.
Duraluminium (dural) adalah paduan Al – Cu – Mg, dimana Mg dapat ditambahkan (meningkatkan kekuatan, dan ketahanan korosi) dan begitu juga dengan penambahan Si & Fe.Komposisi ducal : 2,2-5,2% Cu, diatas 1,75 % Mg, di atas 1% Si,diatas 1% Fe, dan diatas 1% Mn. Paduan aluminium yang terdiri dari 8-14% Si disebut silumin. Paduan aluminium dengan (10 – 13% Si & 0,8% Cu) dan (8 -10% Si, 0,3% Mg & 0,5% Mn)mempunyai sifat-sifat dapat dituang dengan baik dan tahan korosi serta ductile.
2.Paduan Magnesium
Sifat-sifat mekanik magnesium terutama memiliki kekuatan tarik yang sangat rendah. Oleh karena itu magnesium murni tidak dibuat dalam teknik.Paduan magnesium memiliki sifat-sifat mekanik yang lebih baik serta banyak digunakan Unsur-unsur paduan dasar magnesium adalah aluminium, seng dan mangan.Penambahan AI diatas 11%, meningkatkan kekerasan, kuat tarik dan fluidity (keenceran) Panambahan seng meningkatkan ductility (perpanjangan relatif dan castability (mampu tuang) .
Penambahan 0,1 – 0,5 % meningkatkan ketahanan korosi.Penambahan sedikit cerium, zirconium dan baryllium dapat membuat struktur butir yang halus dan meningkatkan ductility dan tahan oksidasi pada peningkatan suhu.Ada dua kelompok besar magnesium paduan a) Wrought alloy : (0,3% Al, 1,3% – 2,5% Mn ) dan (3 – 4% Al, 0,6% Zn & 0,5% Mn).b) casting allay : (5 – 7% Al, 2 – 3% Zn & 0,5% Mn) dan (8 % Al, 0,6 % Zn & 0,5 % Mn).
3. Paduan Tembaga
Ada dua kelompok besar yaitu : brass dan bronze Brass (kuningan) Paduan tembaga dan seng dinamakan brass. Penambahan sedikit timah, nikel, mangan, aluminium, dan unsur-unsur lain dalam paduan tembaga seng dapat mempertinggi kekerasan dan kekuatan serta tahan korosi (special – brass).Bronze (perunggu) .
Paduan tembaga dan timah dengan penambahan sedikit aluminium, silikon, mangan, besi dan beryllium disebut bronze.Dalam prakteknya yang paling banyak digunakan adalah perunggu dengan 25 – 30% Sn.
Wrought bronze, terdiri dari paling tinggi 6% Sn dan casting bronze lebih dari 6% Sn.Special bronze, yaitu paduan dengan dasar tembaga dicampur Ni,Al, Mn, Si, Fe, Be dll.Aluminium bronze, terdiri dari 4 – 11% Al, mempunyai sifat-sifat mekanik yang tinggi dan tahan korosi serta mudah dituang.
Bronze dengan penambahan besi dan nikel memiliki kekuatan mekanik yang tinggi, tahan panas, digunakan untuk fitting dapur dan bagian-bagian mesin yang permukaannya bersinggungan dengan metal, yaitu perunggu dengan penambahan seng.Phosphor bronze terdiri dari – 95% Cu, 5% Sn dan 0,2% P, di gunakan untuk saringan kawat, koil dan pegas pelat.Silikon bronze, memiliki sifat-sifat mekanik yang tinggi, tahan aus dan anti korosi dan mudah dituang maupun dilas. Beryllium bronze, memiliki sifat mekanik yang tinggi tahan koros, tahan aus dan ductil, daya hantar panas/listrik yang tinggi.Monel, komposisinya 31% Cu, 66% Ni, 1,35% Fe, 0,9% dan 0,12% C sifat tertarik bagus dan ductil, tahan korosi dalam air lautan Iarutan kimia.
4. Paduan tahan aus (anti friction alloy).
Bahan paduan tahan aus terutama digunakan untuk permukaan bantalan (bearing).Logam bantalan harus memenuhi syarat, koefisien gesek antara poros dan bantalan harus serendah mungkin mampu menahan panas akibat gesekan, tahan tekanan beban, dll.
Beberapa logam bantalan :
• -babbit
• -bronze tahan aus
• -besi tuang tahan aus
• -non logam tahan aus
Babbit
Babbit terdiri dari timah, antirron, timbal dan tembaga serta unsur lain yang memilliki sifat tahan aus. Bahan dasar babbit yang digunakan di industri adalah timbal atau logam lain sebagai pengganti timah yang mahal.Calcium babbit terdiri dari : 0,8-1,1 % Ca dan 0,75 – 1% Ni
sisanya, adalah Pb.
Bronze tahan aus
Digunakan untuk bantalan biasa dengan beban spesifik yang
tinggi.
Besi tuang tahan aus
Cocok untuk bantalan biasa yang bekerja dengan tekanan spesifik tinggi, tetapi kecepatan/putaran dari poros rendah.Komposisinya : 3,2 – 3,6% C, 2,2 – 2,4% Si, 0,6 – C,9% Mn, dan memiliki struktur pearlit dengan sejumlah grafit normal (HB = 170 – 229),
Paduan titanium (titanium: alloy)
Sebagai bahan teknik titanium banyak penggunaannya. Titanium adalah logam dengan warna putih keperak-perakan, titik lebur 1668°C dan masa jenisnya 4,505 kg/dm3 Titanium tidak murni/campuran dalam perdagangan dapat digolongkan.
• -unsur-unsur yang membentuk interstisi larutan padat (solid solution ) O2 , N, C dan H2 dan lain lain
• -Unsur-unsur yang membentuk substitusi larutan padat (Fe dan unsur-unsur logam lain ).Oksigen dan nitrogen dengan persentase kecil dalam titanium alloy dapat mengurangi ductility secara drastis. Kandungan karbon dengan lebih dari 0,2% menurunkan ductility dan kekuatan pukul dan titanium alloy. Paduan titanium alloy.Paduan titanium terdiri dari vanadium, molibden, chrom, mangan,aluminium timah, besi dll.Memiliki sifat-sifat mekanik yang tinggi dengan masa jenis yang rendah, sangat tahan korosi, banyak digunakan dalam industri pesawat terbang.
• -mampu dibentuk dengan baik
• -massa jenisnya rendah
• -penghantar panas dan listrik yang baik
• -mempunyai warna yang menarik
• -tahan karat
• -kekuatan dan kekakuannya umumnya lebih rendah dari pada logam ferro
• -sukar dilas
1. Paduan aluminium (aluminium alloy)
Paduan aluminium banyak dipakai dalam industri yang dapat dibagi dalam dua golongan utama:
a) Wrought alloy: dibuat dengan jalan rooling, (paduan tempa)forming, drawing, forging dan press working.
b) Casting alloy: dibuat berdasarkan pengecoran (paduan tuang) Paduan aluminium tempa mempunyai kekuatan mekanik yang tinggi mendekati baja.
Paduan ini dibedakan lagi berdasarkan:
a. dapat di heat treatment
b. tak dapat di heat treatment
Paduan aluminum yang tak dapat di heat treatment yaitu Al – Mn (1,3% Mn) dan Al – Mg Mn (2,5% Mg dan 0,3% Mn), memiliki kekuatan mekanik yang tinggi, ductil, tahan korosi dan dapat dilas.Paduan aluminium tuang merupakan paduan yang komplek dari aluminium dengan tembaga, nikel, besi, silikon dan unsur lain.
Duraluminium (dural) adalah paduan Al – Cu – Mg, dimana Mg dapat ditambahkan (meningkatkan kekuatan, dan ketahanan korosi) dan begitu juga dengan penambahan Si & Fe.Komposisi ducal : 2,2-5,2% Cu, diatas 1,75 % Mg, di atas 1% Si,diatas 1% Fe, dan diatas 1% Mn. Paduan aluminium yang terdiri dari 8-14% Si disebut silumin. Paduan aluminium dengan (10 – 13% Si & 0,8% Cu) dan (8 -10% Si, 0,3% Mg & 0,5% Mn)mempunyai sifat-sifat dapat dituang dengan baik dan tahan korosi serta ductile.
2.Paduan Magnesium
Sifat-sifat mekanik magnesium terutama memiliki kekuatan tarik yang sangat rendah. Oleh karena itu magnesium murni tidak dibuat dalam teknik.Paduan magnesium memiliki sifat-sifat mekanik yang lebih baik serta banyak digunakan Unsur-unsur paduan dasar magnesium adalah aluminium, seng dan mangan.Penambahan AI diatas 11%, meningkatkan kekerasan, kuat tarik dan fluidity (keenceran) Panambahan seng meningkatkan ductility (perpanjangan relatif dan castability (mampu tuang) .
Penambahan 0,1 – 0,5 % meningkatkan ketahanan korosi.Penambahan sedikit cerium, zirconium dan baryllium dapat membuat struktur butir yang halus dan meningkatkan ductility dan tahan oksidasi pada peningkatan suhu.Ada dua kelompok besar magnesium paduan a) Wrought alloy : (0,3% Al, 1,3% – 2,5% Mn ) dan (3 – 4% Al, 0,6% Zn & 0,5% Mn).b) casting allay : (5 – 7% Al, 2 – 3% Zn & 0,5% Mn) dan (8 % Al, 0,6 % Zn & 0,5 % Mn).
3. Paduan Tembaga
Ada dua kelompok besar yaitu : brass dan bronze Brass (kuningan) Paduan tembaga dan seng dinamakan brass. Penambahan sedikit timah, nikel, mangan, aluminium, dan unsur-unsur lain dalam paduan tembaga seng dapat mempertinggi kekerasan dan kekuatan serta tahan korosi (special – brass).Bronze (perunggu) .
Paduan tembaga dan timah dengan penambahan sedikit aluminium, silikon, mangan, besi dan beryllium disebut bronze.Dalam prakteknya yang paling banyak digunakan adalah perunggu dengan 25 – 30% Sn.
Wrought bronze, terdiri dari paling tinggi 6% Sn dan casting bronze lebih dari 6% Sn.Special bronze, yaitu paduan dengan dasar tembaga dicampur Ni,Al, Mn, Si, Fe, Be dll.Aluminium bronze, terdiri dari 4 – 11% Al, mempunyai sifat-sifat mekanik yang tinggi dan tahan korosi serta mudah dituang.
Bronze dengan penambahan besi dan nikel memiliki kekuatan mekanik yang tinggi, tahan panas, digunakan untuk fitting dapur dan bagian-bagian mesin yang permukaannya bersinggungan dengan metal, yaitu perunggu dengan penambahan seng.Phosphor bronze terdiri dari – 95% Cu, 5% Sn dan 0,2% P, di gunakan untuk saringan kawat, koil dan pegas pelat.Silikon bronze, memiliki sifat-sifat mekanik yang tinggi, tahan aus dan anti korosi dan mudah dituang maupun dilas. Beryllium bronze, memiliki sifat mekanik yang tinggi tahan koros, tahan aus dan ductil, daya hantar panas/listrik yang tinggi.Monel, komposisinya 31% Cu, 66% Ni, 1,35% Fe, 0,9% dan 0,12% C sifat tertarik bagus dan ductil, tahan korosi dalam air lautan Iarutan kimia.
4. Paduan tahan aus (anti friction alloy).
Bahan paduan tahan aus terutama digunakan untuk permukaan bantalan (bearing).Logam bantalan harus memenuhi syarat, koefisien gesek antara poros dan bantalan harus serendah mungkin mampu menahan panas akibat gesekan, tahan tekanan beban, dll.
Beberapa logam bantalan :
• -babbit
• -bronze tahan aus
• -besi tuang tahan aus
• -non logam tahan aus
Babbit
Babbit terdiri dari timah, antirron, timbal dan tembaga serta unsur lain yang memilliki sifat tahan aus. Bahan dasar babbit yang digunakan di industri adalah timbal atau logam lain sebagai pengganti timah yang mahal.Calcium babbit terdiri dari : 0,8-1,1 % Ca dan 0,75 – 1% Ni
sisanya, adalah Pb.
Bronze tahan aus
Digunakan untuk bantalan biasa dengan beban spesifik yang
tinggi.
Besi tuang tahan aus
Cocok untuk bantalan biasa yang bekerja dengan tekanan spesifik tinggi, tetapi kecepatan/putaran dari poros rendah.Komposisinya : 3,2 – 3,6% C, 2,2 – 2,4% Si, 0,6 – C,9% Mn, dan memiliki struktur pearlit dengan sejumlah grafit normal (HB = 170 – 229),
Paduan titanium (titanium: alloy)
Sebagai bahan teknik titanium banyak penggunaannya. Titanium adalah logam dengan warna putih keperak-perakan, titik lebur 1668°C dan masa jenisnya 4,505 kg/dm3 Titanium tidak murni/campuran dalam perdagangan dapat digolongkan.
• -unsur-unsur yang membentuk interstisi larutan padat (solid solution ) O2 , N, C dan H2 dan lain lain
• -Unsur-unsur yang membentuk substitusi larutan padat (Fe dan unsur-unsur logam lain ).Oksigen dan nitrogen dengan persentase kecil dalam titanium alloy dapat mengurangi ductility secara drastis. Kandungan karbon dengan lebih dari 0,2% menurunkan ductility dan kekuatan pukul dan titanium alloy. Paduan titanium alloy.Paduan titanium terdiri dari vanadium, molibden, chrom, mangan,aluminium timah, besi dll.Memiliki sifat-sifat mekanik yang tinggi dengan masa jenis yang rendah, sangat tahan korosi, banyak digunakan dalam industri pesawat terbang.
phase diagram
FREEZING POINT DEPRESSION
Represents one line in phase diagram of a condensed system, the line corresponding to pure A. At the temperature Tm, the two phases, solid and liquid, are in equilibrium. Because we will be interested in the temperature region below Tm, let us take pure solid A as the standar state. For the reaction (or phase transformation) from solid A to liquid A, we can write the gibbs free energy change as follows :
At the melting temperature Tm, the two phases are in equilibrium : hence the value for the gibbs free energy change in the reaction is zero. The activity of the liquid is therefore l, the same as the solid. At temperatures lower than Tm, the value of gibbs free energy change for the melting of pure A can be written as
The term L (laten heat of fusion) is introduced for the enthalpy of melting to avoid confusion with the notation for mixing. For simplicity, assume that there is no difference in heat capacity between liquid and solid . in this case, the enthalpy change and entropy change of melting are each independent of temperature. Noting that at the melting temperature,
Based on this equation, it is apparent that the activity of pure liquid A is greater than one at temperatures below Tm, with the solid being considered the standard state. Note that the standard state is defined for each temperature.
Now let us deal with the addition of material B to A. at some temperature T (below Tm). The activity of A in an ideal A-B solution as a function of composition in shown in figure 9.2. consider the case in which A and B are immiscible in the solid state, but form ideal solutions in the liquid state. Liquid of composition is in equilibrium with pure solid A at temperature T. consider now the dissolving of pure, liquid A in the liquid solution.
The dissolution of pure, solid A in the liquid solution is the sum of the two processes above : the melting of pure A, and the dissolution of pure liquid A in the liquid solution.
The gibbs free energy change is the sum . furthermore. If the liquid solution is in equilibrium with the pure solid, then the G = 0 .
In the region of small Xb, therefore, the relationship between xb, the composition of the liquid, and the melting point depression, is
Where T = Tm – T. the melting point depression.
This expression can be plotted on a phase diagram in which temperature is the ordinate and composition is the abscissa. A region of such a diagram is shown as figure 9.3. in the portion of the diagram labeled liquid, the equilibrium phase is a liquid A-B solution. In the two phase region labeled “L + S” (liquid plus solid). Pure solid A is in equilibrium with a liquid solution of composition Xb.
As an example, let us calculate the lowering of the melting point of silver caused by the addition of one mole of lead. The conditions assumed in the derivation of eq.9.4 are followed by the silver-lead system, although there is small solubility of lead in solid silver.
For silver : Tm = 1234 K and L = 11.300
Actually the measured melting point depression is about 10K for an addition of one mole percent lead . considering the slight solubility of lead in silver, the agreement between the calculated and measured values is not bad.
Considering the phase rule in the liquid + solid region (condensed phases)
Because there are two components, A and B, and two phases, liquid and solid. There is only one degree of freedom. Once the temperature has been specified, the composition of the phases at equilibrium is specified. It is important to note that the relative amounts of the phases present (liquid and solid) are not determined by the phase rule. Only the composition of the phases is determined. We show next that if the overall composition of the A-B combination is given, the quantities of the various phases can be calculated using the lever rule.
THE LEVEL RULE
In the two phase region illustrated by figure 9.4. xb represents the overall composition of a system. At temperature T, the phase diagram tell us that the equilibrium liquid composition is xb. Given the overall composition and the composition of the two phases, we can calculate the relative quantities of fractions of liquid and solid using a mass balance.
SIMPLE EUTECTIC DIAGRAM
Consider a system in which materials A and B are immiscible in the solid state, but completely miscible in the liquid state. As shown in section 9.1. the addition of B to A lowers the melting point of A. the reverse is also true. The addition of A to B lowers the melting point of B. this relationship Is illustrated in figure 9.5. although the linear relationship between composition and temperature derived as eq.9.4. may no longer exist, the melting point depressions will continue. When the melting point depression lines intersect, the material will solidify totally into solid A and solid B (figure 9.5). the temperature at which the two curves intersect, called the eutectic temperature, is the lowest temperature at which a liquid solution of A and B may exist at equilibrium with solid A and solid B. the composition at which they intersect is the eutectic composition. At the eutectic point, the phase change may be represented by :
Liquid = solid A + solid B
According to the phase rule, there are two degrees of freedom in the liquid region ; that is, temperature and composition may be arbitrarily fixed. In the region labeled A + liquid, there is only one degree of freedom. Once the temperature has been fixed, the composition of each phase is fixed. The same is true of the region B + liquid.
At the eutectic temperature there are no degrees of freedom because there are two components (A and B) and three phases (solid A, solid B, liquid). Thus F = 0. if all three phases (liquid, solid A, and solid B) are present, one must, at equilibrium, be at the eutectic temperature and the liquid will have the eutectic composition.
COOLING CURVES
If a pure material-pure A. for example-is cooled from a temperature Tm (its melting temperature) to below Tm by removing thermal energy at a constant rate, the temperature of the material as a function of time follows a pattern illustrated in figure 9.6. assuming that equilibrium is maintained at all times. When material A is above T, in the liquid state, the removal of thermal energy lowers its temperature. When the melting point is reached, the removal of thermal energy result in solidification. During solidification, liquid A and solid A are in equilibrium and the temperature of the system does not change. This condition is called a thermal arrest in the cooling curve. Once all of material A has solidified, the temperature decrease resumes.
The same type of cooling curve, with a thermal arrest at the melting temperature, is observed if one cools a liquid of eutectic composition. As temperature drops, liquid will exist until the eutectic temperature is reached. At that temperature, all of the liquid solidifies into solid A and B. when all is solid, the cooling resumes as energy is removed from the system.
At compositions other than the eutectic composition, such as composition Xb in figure 9.7. the cooling rate of the material changes when temperature T is reached. At temperatures below T some pure, solid A is formed upon cooling, and the rate of temperature change is diminished, because to solidify A. energy must be removed from the system. After the material has reached the eutectic temperature, all the remaining liquid solidifies at a constant temperature, causing a thermal arrest at T (figure 9.8).
Represents one line in phase diagram of a condensed system, the line corresponding to pure A. At the temperature Tm, the two phases, solid and liquid, are in equilibrium. Because we will be interested in the temperature region below Tm, let us take pure solid A as the standar state. For the reaction (or phase transformation) from solid A to liquid A, we can write the gibbs free energy change as follows :
At the melting temperature Tm, the two phases are in equilibrium : hence the value for the gibbs free energy change in the reaction is zero. The activity of the liquid is therefore l, the same as the solid. At temperatures lower than Tm, the value of gibbs free energy change for the melting of pure A can be written as
The term L (laten heat of fusion) is introduced for the enthalpy of melting to avoid confusion with the notation for mixing. For simplicity, assume that there is no difference in heat capacity between liquid and solid . in this case, the enthalpy change and entropy change of melting are each independent of temperature. Noting that at the melting temperature,
Based on this equation, it is apparent that the activity of pure liquid A is greater than one at temperatures below Tm, with the solid being considered the standard state. Note that the standard state is defined for each temperature.
Now let us deal with the addition of material B to A. at some temperature T (below Tm). The activity of A in an ideal A-B solution as a function of composition in shown in figure 9.2. consider the case in which A and B are immiscible in the solid state, but form ideal solutions in the liquid state. Liquid of composition is in equilibrium with pure solid A at temperature T. consider now the dissolving of pure, liquid A in the liquid solution.
The dissolution of pure, solid A in the liquid solution is the sum of the two processes above : the melting of pure A, and the dissolution of pure liquid A in the liquid solution.
The gibbs free energy change is the sum . furthermore. If the liquid solution is in equilibrium with the pure solid, then the G = 0 .
In the region of small Xb, therefore, the relationship between xb, the composition of the liquid, and the melting point depression, is
Where T = Tm – T. the melting point depression.
This expression can be plotted on a phase diagram in which temperature is the ordinate and composition is the abscissa. A region of such a diagram is shown as figure 9.3. in the portion of the diagram labeled liquid, the equilibrium phase is a liquid A-B solution. In the two phase region labeled “L + S” (liquid plus solid). Pure solid A is in equilibrium with a liquid solution of composition Xb.
As an example, let us calculate the lowering of the melting point of silver caused by the addition of one mole of lead. The conditions assumed in the derivation of eq.9.4 are followed by the silver-lead system, although there is small solubility of lead in solid silver.
For silver : Tm = 1234 K and L = 11.300
Actually the measured melting point depression is about 10K for an addition of one mole percent lead . considering the slight solubility of lead in silver, the agreement between the calculated and measured values is not bad.
Considering the phase rule in the liquid + solid region (condensed phases)
Because there are two components, A and B, and two phases, liquid and solid. There is only one degree of freedom. Once the temperature has been specified, the composition of the phases at equilibrium is specified. It is important to note that the relative amounts of the phases present (liquid and solid) are not determined by the phase rule. Only the composition of the phases is determined. We show next that if the overall composition of the A-B combination is given, the quantities of the various phases can be calculated using the lever rule.
THE LEVEL RULE
In the two phase region illustrated by figure 9.4. xb represents the overall composition of a system. At temperature T, the phase diagram tell us that the equilibrium liquid composition is xb. Given the overall composition and the composition of the two phases, we can calculate the relative quantities of fractions of liquid and solid using a mass balance.
SIMPLE EUTECTIC DIAGRAM
Consider a system in which materials A and B are immiscible in the solid state, but completely miscible in the liquid state. As shown in section 9.1. the addition of B to A lowers the melting point of A. the reverse is also true. The addition of A to B lowers the melting point of B. this relationship Is illustrated in figure 9.5. although the linear relationship between composition and temperature derived as eq.9.4. may no longer exist, the melting point depressions will continue. When the melting point depression lines intersect, the material will solidify totally into solid A and solid B (figure 9.5). the temperature at which the two curves intersect, called the eutectic temperature, is the lowest temperature at which a liquid solution of A and B may exist at equilibrium with solid A and solid B. the composition at which they intersect is the eutectic composition. At the eutectic point, the phase change may be represented by :
Liquid = solid A + solid B
According to the phase rule, there are two degrees of freedom in the liquid region ; that is, temperature and composition may be arbitrarily fixed. In the region labeled A + liquid, there is only one degree of freedom. Once the temperature has been fixed, the composition of each phase is fixed. The same is true of the region B + liquid.
At the eutectic temperature there are no degrees of freedom because there are two components (A and B) and three phases (solid A, solid B, liquid). Thus F = 0. if all three phases (liquid, solid A, and solid B) are present, one must, at equilibrium, be at the eutectic temperature and the liquid will have the eutectic composition.
COOLING CURVES
If a pure material-pure A. for example-is cooled from a temperature Tm (its melting temperature) to below Tm by removing thermal energy at a constant rate, the temperature of the material as a function of time follows a pattern illustrated in figure 9.6. assuming that equilibrium is maintained at all times. When material A is above T, in the liquid state, the removal of thermal energy lowers its temperature. When the melting point is reached, the removal of thermal energy result in solidification. During solidification, liquid A and solid A are in equilibrium and the temperature of the system does not change. This condition is called a thermal arrest in the cooling curve. Once all of material A has solidified, the temperature decrease resumes.
The same type of cooling curve, with a thermal arrest at the melting temperature, is observed if one cools a liquid of eutectic composition. As temperature drops, liquid will exist until the eutectic temperature is reached. At that temperature, all of the liquid solidifies into solid A and B. when all is solid, the cooling resumes as energy is removed from the system.
At compositions other than the eutectic composition, such as composition Xb in figure 9.7. the cooling rate of the material changes when temperature T is reached. At temperatures below T some pure, solid A is formed upon cooling, and the rate of temperature change is diminished, because to solidify A. energy must be removed from the system. After the material has reached the eutectic temperature, all the remaining liquid solidifies at a constant temperature, causing a thermal arrest at T (figure 9.8).
Application and influence
Applied physics is a general term for physics research which is intended for a particular use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. It usually differs from engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.
The approach is similar to that of applied mathematics. Applied physicists can also be interested in the use of physics for scientific research. For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics.
Physics is used heavily in engineering. For example, Statics, a subfield of mechanics, is used in the building of bridges and other structures. The understanding and use of acoustics results in better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic flight simulators, video games, and movies, and is often critical in forensic investigations.
With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty. For example, in the study of the origin of the Earth, one can reasonably model Earth's mass, temperature, and rate of rotation, over time. It also allows for simulations in engineering which drastically speed up the development of a new technology.
But there is also considerable interdisciplinarity in the physicist's methods, and so many other important fields are influenced by physics: e.g. presently the fields of econophysics plays an important role, as well as sociophysics.
The approach is similar to that of applied mathematics. Applied physicists can also be interested in the use of physics for scientific research. For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics.
Physics is used heavily in engineering. For example, Statics, a subfield of mechanics, is used in the building of bridges and other structures. The understanding and use of acoustics results in better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic flight simulators, video games, and movies, and is often critical in forensic investigations.
With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty. For example, in the study of the origin of the Earth, one can reasonably model Earth's mass, temperature, and rate of rotation, over time. It also allows for simulations in engineering which drastically speed up the development of a new technology.
But there is also considerable interdisciplinarity in the physicist's methods, and so many other important fields are influenced by physics: e.g. presently the fields of econophysics plays an important role, as well as sociophysics.
Physics
Physics (Greek: physis – φύσις meaning "nature") is a natural science; it is the study of matter[1] and its motion through spacetime and all that derives from these, such as energy and force.[2] More broadly, it is the general analysis of nature, conducted in order to understand how the world and universe behave.[3][4]
Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[5] Over the last two millennia, physics had been considered synonymous with philosophy, chemistry, and certain branches of mathematics and biology, but during the Scientific Revolution in the 16th century, it emerged to become a unique modern science in its own right.[6] However, in some subject areas such as in mathematical physics and quantum chemistry, the boundaries of physics remain difficult to distinguish.
Physics is both significant and influential, in part because advances in its understanding have often translated into new technologies, but also because new ideas in physics often resonate with the other sciences, mathematics and philosophy.
For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society (e.g., television, computers, domestic appliances, and nuclear weapons); advances in thermodynamics led to the development of motorized transport; and advances in mechanics inspired the development of calculus.
Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[5] Over the last two millennia, physics had been considered synonymous with philosophy, chemistry, and certain branches of mathematics and biology, but during the Scientific Revolution in the 16th century, it emerged to become a unique modern science in its own right.[6] However, in some subject areas such as in mathematical physics and quantum chemistry, the boundaries of physics remain difficult to distinguish.
Physics is both significant and influential, in part because advances in its understanding have often translated into new technologies, but also because new ideas in physics often resonate with the other sciences, mathematics and philosophy.
For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society (e.g., television, computers, domestic appliances, and nuclear weapons); advances in thermodynamics led to the development of motorized transport; and advances in mechanics inspired the development of calculus.
Atomic, molecular, and optical physics
Atomic, molecular, and optical physics (AMO) is the study of matter-matter and light-matter interactions on the scale of single atoms or structures containing a few atoms. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of the energy scales that are relevant. All three areas include both classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).
Atomic physics studies the electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics, the collective behavior of atoms in weakly interacting gases (Bose-Einstein Condensates and dilute Fermi degenerate systems), precision measurements of fundamental constants, and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the nucleus (see, e.g., hyperfine splitting), but intra-nuclear phenomenon such as fission and fusion are considered part of high energy physics.
Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light. Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects, but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.
Atomic physics studies the electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics, the collective behavior of atoms in weakly interacting gases (Bose-Einstein Condensates and dilute Fermi degenerate systems), precision measurements of fundamental constants, and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the nucleus (see, e.g., hyperfine splitting), but intra-nuclear phenomenon such as fission and fusion are considered part of high energy physics.
Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light. Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects, but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.
Astrophysics
Astrophysics (Greek: Astro - meaning "star", and Greek: physis – φύσις - meaning "nature") is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as galaxies, stars, planets, exoplanets, and the interstellar medium, as well as their interactions. The study of cosmology is theoretical astrophysics at scales much larger than the size of particular gravitationally-bound objects in the universe.
Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. In practice, modern astronomical research involves a substantial amount of physics. The name of a university's department ("astrophysics" or "astronomy") often has to do more with the department's history than with the contents of the programs. Astrophysics can be studied at the bachelors, masters, and Ph.D. levels in aerospace engineering, physics, or astronomy departments at many universities.
Although astronomy is as ancient as recorded history itself, it was long separated from the study of physics. In the Aristotelian worldview, the celestial world tended towards perfection—bodies in the sky seemed to be perfect spheres moving in perfectly circular orbits—while the earthly world seemed destined to imperfection; these two realms were not seen as related.
Aristarchus of Samos (c. 310–250 BC) first put forward the notion that the motions of the celestial bodies could be explained by assuming that the Earth and all the other planets in the Solar System orbited the Sun. Unfortunately, in the geocentric world of the time, Aristarchus' heliocentric theory was deemed outlandish and heretical. For centuries, the apparently common-sense view that the Sun and other planets went round the Earth nearly went unquestioned until the development of Copernican heliocentrism in the 16th century AD. This was due to the dominance of the geocentric model developed by Ptolemy (c. 83-161 AD), a Hellenized astronomer from Roman Egypt, in his Almagest treatise.
The only known supporter of Aristarchus was Seleucus of Seleucia, a Babylonian astronomer who is said to have proved heliocentrism through reasoning in the 2nd century BC. This may have involved the phenomenon of tides,[1] which he correctly theorized to be caused by attraction to the Moon and notes that the height of the tides depends on the Moon's position relative to the Sun.[2] Alternatively, he may have determined the constants of a geometric model for the heliocentric theory and developed methods to compute planetary positions using this model, possibly using early trigonometric methods that were available in his time, much like Copernicus.[3] Some have also interpreted the planetary models developed by Aryabhata (476-550), an Indian astronomer,[4][5][6] and Albumasar (787-886), a Persian astronomer, to be heliocentric models.[7]
In the 9th century AD, the Persian physicist and astronomer, Ja'far Muhammad ibn Mūsā ibn Shākir, hypothesized that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth.[8] He also proposed that there is a force of attraction between "heavenly bodies",[9] vaguely foreshadowing the law of gravity.[10]
In the early 11th century, the Arabic Ibn al-Haytham (Alhazen) who is considered by some people as the first scientist in the history wrote the Maqala fi daw al-qamar (On the Light of the Moon) some time before 1021. This was the first successful attempt at combining mathematical astronomy with physics, and the earliest attempt at applying the experimental method to astronomy and astrophysics. He disproved the universally held opinion that the moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." In order to prove that "light is emitted from every point of the moon's illuminated surface," he built an "ingenious experimental device." Ibn al-Haytham had "formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up."[11]
In the 14th century, Ibn al-Shatir produced the first model of lunar motion which matched physical observations, and which was later used by Copernicus.[12] In the 13th to 15th centuries, Tusi and Ali Kuşçu provided the earliest empirical evidence for the Earth's rotation, using the phenomena of comets to refute Ptolemy's claim that a stationery Earth can be determined through observation. Kuşçu further rejected Aristotelian physics and natural philosophy, allowing astronomy and physics to become empirical and mathematical instead of philosophical. In the early 16th century, the debate on the Earth's motion was continued by Al-Birjandi (d. 1528), who in his analysis of what might occur if the Earth were rotating, develops a hypothesis similar to Galileo Galilei's notion of "circular inertia", which he described in the following observational test:[13][14]
"The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba). And this perpendicular is away from the tangent point of the Earth’s sphere and the plane of the perceived (hissi) horizon. This point moves with the motion of the Earth and thus there will be no difference in place of fall of the two rocks."
After heliocentrism was revived by Nicolaus Copernicus in the 16th century, Galileo Galilei discovered the four brightest moons of Jupiter in 1609, and documented their orbits about that planet, which contradicted the geocentric dogma of the Catholic Church of his time, and escaped serious punishment only by maintaining that his astronomy was a work of mathematics, not of natural philosophy (physics), and therefore purely abstract.
The availability of accurate observational data (mainly from the observatory of Tycho Brahe) led to research into theoretical explanations for the observed behavior. At first, only empirical rules were discovered, such as Kepler's laws of planetary motion, discovered at the start of the 17th century. Later that century, Isaac Newton bridged the gap between Kepler's laws and Galileo's dynamics, discovering that the same laws that rule the dynamics of objects on Earth rule the motion of planets and the moon. Celestial mechanics, the application of Newtonian gravity and Newton's laws to explain Kepler's laws of planetary motion, was the first unification of astronomy and physics.
After Isaac Newton published his book, Philosophiæ Naturalis Principia Mathematica, maritime navigation was transformed. Starting around 1670, the entire world was measured using essentially modern latitude instruments and the best available clocks. The needs of navigation provided a drive for progressively more accurate astronomical observations and instruments, providing a background for ever more available data for scientists.
At the end of the 19th century, it was discovered that, when decomposing the light from the Sun, a multitude of spectral lines were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique chemical elements. In this way it was proved that the chemical elements found in the Sun (chiefly hydrogen) were also found on Earth. Indeed, the element helium was first discovered in the spectrum of the Sun and only later on Earth, hence its name. During the 20th century, spectroscopy (the study of these spectral lines) advanced, particularly as a result of the advent of quantum physics that was necessary to understand the astronomical and experimental observations.[15]
See also:
Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
Timeline of white dwarfs, neutron stars, and supernovae
Timeline of black hole physics
Timeline of gravitational physics and relativity
[edit]Observational astrophysics
The majority of astrophysical observations are made using the electromagnetic spectrum.
Radio astronomy studies radiation with a wavelength greater than a few millimeters. Radio waves are usually emitted by cold objects, including interstellar gas and dust clouds. The cosmic microwave background radiation is the redshifted light from the Big Bang. Pulsars were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.
Infrared astronomy studies radiation with a wavelength that is too long to be visible but shorter than radio waves. Infrared observations are usually made with telescopes similar to the usual optical telescopes. Objects colder than stars (such as planets) are normally studied at infrared frequencies.
Optical astronomy is the oldest kind of astronomy. Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae.
Ultraviolet, X-ray and gamma ray astronomy study very energetic processes such as binary pulsars, black holes, magnetars, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well. There are two possibilities to observe this part of the electromagnetic spectrum—space-based telescopes and ground-based imaging air Cherenkov telescopes (IACT). Observatories of the first type are RXTE, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory. IACTs are, for example, the High Energy Stereoscopic System (H.E.S.S.) and the MAGIC telescope.
Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere.
Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.
The study of our own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Our understanding of our own sun serves as a guide to our understanding of other stars.
The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the Hertzsprung-Russell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction. The material composition of the astronomical objects can often be examined using:
Spectroscopy
Radio astronomy
Neutrino astronomy (future prospects)
[edit]Theoretical astrophysics
Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.[16][17]
Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.
Theorists also try to generate or modify models to take into account new data, In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.
Topics studied by theoretical astrophysicists include: stellar dynamics and evolution; galaxy formation; magnetohydrodynamics; large-scale structure of matter in the Universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Astrophysical relativity serves as a tool to gauge the properties of large scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.
Some widely accepted and studied theories and models in astrophysics, now included in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, dark energy and fundamental theories of physics.
Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. In practice, modern astronomical research involves a substantial amount of physics. The name of a university's department ("astrophysics" or "astronomy") often has to do more with the department's history than with the contents of the programs. Astrophysics can be studied at the bachelors, masters, and Ph.D. levels in aerospace engineering, physics, or astronomy departments at many universities.
Although astronomy is as ancient as recorded history itself, it was long separated from the study of physics. In the Aristotelian worldview, the celestial world tended towards perfection—bodies in the sky seemed to be perfect spheres moving in perfectly circular orbits—while the earthly world seemed destined to imperfection; these two realms were not seen as related.
Aristarchus of Samos (c. 310–250 BC) first put forward the notion that the motions of the celestial bodies could be explained by assuming that the Earth and all the other planets in the Solar System orbited the Sun. Unfortunately, in the geocentric world of the time, Aristarchus' heliocentric theory was deemed outlandish and heretical. For centuries, the apparently common-sense view that the Sun and other planets went round the Earth nearly went unquestioned until the development of Copernican heliocentrism in the 16th century AD. This was due to the dominance of the geocentric model developed by Ptolemy (c. 83-161 AD), a Hellenized astronomer from Roman Egypt, in his Almagest treatise.
The only known supporter of Aristarchus was Seleucus of Seleucia, a Babylonian astronomer who is said to have proved heliocentrism through reasoning in the 2nd century BC. This may have involved the phenomenon of tides,[1] which he correctly theorized to be caused by attraction to the Moon and notes that the height of the tides depends on the Moon's position relative to the Sun.[2] Alternatively, he may have determined the constants of a geometric model for the heliocentric theory and developed methods to compute planetary positions using this model, possibly using early trigonometric methods that were available in his time, much like Copernicus.[3] Some have also interpreted the planetary models developed by Aryabhata (476-550), an Indian astronomer,[4][5][6] and Albumasar (787-886), a Persian astronomer, to be heliocentric models.[7]
In the 9th century AD, the Persian physicist and astronomer, Ja'far Muhammad ibn Mūsā ibn Shākir, hypothesized that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth.[8] He also proposed that there is a force of attraction between "heavenly bodies",[9] vaguely foreshadowing the law of gravity.[10]
In the early 11th century, the Arabic Ibn al-Haytham (Alhazen) who is considered by some people as the first scientist in the history wrote the Maqala fi daw al-qamar (On the Light of the Moon) some time before 1021. This was the first successful attempt at combining mathematical astronomy with physics, and the earliest attempt at applying the experimental method to astronomy and astrophysics. He disproved the universally held opinion that the moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." In order to prove that "light is emitted from every point of the moon's illuminated surface," he built an "ingenious experimental device." Ibn al-Haytham had "formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up."[11]
In the 14th century, Ibn al-Shatir produced the first model of lunar motion which matched physical observations, and which was later used by Copernicus.[12] In the 13th to 15th centuries, Tusi and Ali Kuşçu provided the earliest empirical evidence for the Earth's rotation, using the phenomena of comets to refute Ptolemy's claim that a stationery Earth can be determined through observation. Kuşçu further rejected Aristotelian physics and natural philosophy, allowing astronomy and physics to become empirical and mathematical instead of philosophical. In the early 16th century, the debate on the Earth's motion was continued by Al-Birjandi (d. 1528), who in his analysis of what might occur if the Earth were rotating, develops a hypothesis similar to Galileo Galilei's notion of "circular inertia", which he described in the following observational test:[13][14]
"The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba). And this perpendicular is away from the tangent point of the Earth’s sphere and the plane of the perceived (hissi) horizon. This point moves with the motion of the Earth and thus there will be no difference in place of fall of the two rocks."
After heliocentrism was revived by Nicolaus Copernicus in the 16th century, Galileo Galilei discovered the four brightest moons of Jupiter in 1609, and documented their orbits about that planet, which contradicted the geocentric dogma of the Catholic Church of his time, and escaped serious punishment only by maintaining that his astronomy was a work of mathematics, not of natural philosophy (physics), and therefore purely abstract.
The availability of accurate observational data (mainly from the observatory of Tycho Brahe) led to research into theoretical explanations for the observed behavior. At first, only empirical rules were discovered, such as Kepler's laws of planetary motion, discovered at the start of the 17th century. Later that century, Isaac Newton bridged the gap between Kepler's laws and Galileo's dynamics, discovering that the same laws that rule the dynamics of objects on Earth rule the motion of planets and the moon. Celestial mechanics, the application of Newtonian gravity and Newton's laws to explain Kepler's laws of planetary motion, was the first unification of astronomy and physics.
After Isaac Newton published his book, Philosophiæ Naturalis Principia Mathematica, maritime navigation was transformed. Starting around 1670, the entire world was measured using essentially modern latitude instruments and the best available clocks. The needs of navigation provided a drive for progressively more accurate astronomical observations and instruments, providing a background for ever more available data for scientists.
At the end of the 19th century, it was discovered that, when decomposing the light from the Sun, a multitude of spectral lines were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique chemical elements. In this way it was proved that the chemical elements found in the Sun (chiefly hydrogen) were also found on Earth. Indeed, the element helium was first discovered in the spectrum of the Sun and only later on Earth, hence its name. During the 20th century, spectroscopy (the study of these spectral lines) advanced, particularly as a result of the advent of quantum physics that was necessary to understand the astronomical and experimental observations.[15]
See also:
Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
Timeline of white dwarfs, neutron stars, and supernovae
Timeline of black hole physics
Timeline of gravitational physics and relativity
[edit]Observational astrophysics
The majority of astrophysical observations are made using the electromagnetic spectrum.
Radio astronomy studies radiation with a wavelength greater than a few millimeters. Radio waves are usually emitted by cold objects, including interstellar gas and dust clouds. The cosmic microwave background radiation is the redshifted light from the Big Bang. Pulsars were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.
Infrared astronomy studies radiation with a wavelength that is too long to be visible but shorter than radio waves. Infrared observations are usually made with telescopes similar to the usual optical telescopes. Objects colder than stars (such as planets) are normally studied at infrared frequencies.
Optical astronomy is the oldest kind of astronomy. Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae.
Ultraviolet, X-ray and gamma ray astronomy study very energetic processes such as binary pulsars, black holes, magnetars, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well. There are two possibilities to observe this part of the electromagnetic spectrum—space-based telescopes and ground-based imaging air Cherenkov telescopes (IACT). Observatories of the first type are RXTE, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory. IACTs are, for example, the High Energy Stereoscopic System (H.E.S.S.) and the MAGIC telescope.
Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere.
Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.
The study of our own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Our understanding of our own sun serves as a guide to our understanding of other stars.
The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the Hertzsprung-Russell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction. The material composition of the astronomical objects can often be examined using:
Spectroscopy
Radio astronomy
Neutrino astronomy (future prospects)
[edit]Theoretical astrophysics
Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.[16][17]
Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.
Theorists also try to generate or modify models to take into account new data, In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.
Topics studied by theoretical astrophysicists include: stellar dynamics and evolution; galaxy formation; magnetohydrodynamics; large-scale structure of matter in the Universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Astrophysical relativity serves as a tool to gauge the properties of large scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.
Some widely accepted and studied theories and models in astrophysics, now included in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, dark energy and fundamental theories of physics.
Scope and aims
Physics covers a wide range of phenomena, from the smallest sub-atomic particles (protons, neutrons and electrons), to the largest galaxies. Included in this are the very most basic objects from which all other things are composed, and therefore physics is sometimes said to be the "fundamental science".[7]
Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things we see around us to root causes, and then to try to connect these causes together in the hope of finding an ultimate reason for why nature is as it is.
For example, the ancient Chinese observed that certain rocks (lodestone) were attracted to one another by some invisible force. This effect was later called magnetism, and was first rigorously studied in the 17th century.
A little earlier than the Chinese, the ancient Greeks knew of other objects such as amber, that when rubbed with fur would cause a similar invisible attraction between the two. This was also first studied rigorously in the 17th century, and came to be called electricity.
Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force – electromagnetism. This process of "unifying" forces continues today (see section Current research for more information).
Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things we see around us to root causes, and then to try to connect these causes together in the hope of finding an ultimate reason for why nature is as it is.
For example, the ancient Chinese observed that certain rocks (lodestone) were attracted to one another by some invisible force. This effect was later called magnetism, and was first rigorously studied in the 17th century.
A little earlier than the Chinese, the ancient Greeks knew of other objects such as amber, that when rubbed with fur would cause a similar invisible attraction between the two. This was also first studied rigorously in the 17th century, and came to be called electricity.
Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force – electromagnetism. This process of "unifying" forces continues today (see section Current research for more information).
Gallium
Gallium (pronounced /ˈɡæliəm/, GAL-ee-əm) is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium(III) salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies slightly above room temperature, it will melt in the hand. Its melting point is used as a temperature reference point, and from its discovery in 1875 to the semiconductor era, its primary uses were in high-temperature thermometric applications and in preparation of metal alloys with unusual properties of stability, or ease of melting; some being liquid at room temperature or below. The alloy Galinstan (68.5% Ga, 21.5% In, 10% Sn) has a melting point of about −19 °C (−2.2 °F).
In semiconductors, an important application is in the compounds gallium arsenide and gallium nitride, used most notably in light-emitting diodes (LEDs). Semiconductor use is now almost the entire (> 95%) world market for gallium, but new uses in alloys and fuel cells continue to be discovered.
Gallium is not known to be essential in biology, but because of the biological handling of gallium's primary ionic salt gallium(III) as though it were iron(III), the gallium ion localizes to and interacts with many processes in the body in which iron(III) is manipulated. As these processes include inflammation, which is a marker for many disease states, several gallium salts are used, or are in development, as both pharmaceuticals and radiopharmaceuticals in medicine.
Elemental gallium is not found in nature, but it is easily obtained by smelting. Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands by 3.1 percent when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing. Gallium shares the higher-density liquid state with only a few materials like silicon, germanium, bismuth, antimony and water.
Gallium attacks most other metals by diffusing into their metal lattice. Gallium for example diffuses into the grain boundaries of Al/Zn alloys[1] or steel,[2] making them very brittle. Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy in the core of the second nuclear bomb to help stabilize the plutonium crystal structure.[3]
The melting point of 302.9146 K (29.7646°C, 85.5763°F) is near room temperature. Gallium's melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990 (ITS-90) established by BIPM.[4] [5] [6] The triple point of gallium of 302.9166 K (29.7666°C, 85.5799°F), is being used by NIST in preference to gallium's melting point.[7]
Gallium is a metal that will melt in one's hand. This metal has a strong tendency to supercool below its melting point/freezing point. Seeding with a crystal helps to initiate freezing. Gallium is one of the metals (with caesium, rubidium, francium and mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low vapor pressure at high temperatures. Unlike mercury, liquid gallium metal wets glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions). For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers.
Crystallization of gallium from the melt
Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Each atom has only one nearest neighbor (at a distance of 244 pm) and six other neighbors within additional 39 pm. Many stable and metastable phases are found as function of temperature and pressure.
The bonding between the nearest neighbors is found to be of covalent character, hence Ga2 dimers are seen as the fundamental building blocks of the crystal. This explains the drop of the melting point compared to its neighbour elements aluminium and indium. The compound with arsenic, gallium arsenide is a semiconductor commonly used in light-emitting diodes.
High-purity gallium is dissolved slowly by mineral acids.
Gallium has no known biological role, although it has been observed to stimulate metabolism.[8]
[edit]History
Gallium (the Latin Gallia means "Gaul", essentially modern France) was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two violet lines) in an examination of a zinc blende from the Pyrenees.[9] Before its discovery, most of its properties had been predicted and described by Dmitri Mendeleev (who had called the hypothetical element "eka-aluminium" on the basis of its position in his periodic table). Later, in 1875, Lecoq obtained the free metal by electrolysis of its hydroxide in potassium hydroxide solution. He named the element "gallia" after his native land of France. It was later claimed that, in one of those multilingual puns so beloved of men of science in the early 19th century, he had also named gallium after himself, as his name, "Le coq", is the French for "the rooster", and the Latin for "rooster" is "gallus"; however, in an 1877 article Lecoq denied this supposition. (The supposition was also noted in Building Blocks of the Universe, a book on the elements by Isaac Asimov; cf. the naming of the J/ψ meson.)
[edit]Occurrence
Gallium does not exist in free form in nature, and the few high-gallium minerals such as gallite (CuGaS2) are too rare to serve as a primary source of the element or its compounds. Its abundance in the Earth's crust is approximately 16.9 ppm.[10] Gallium is found and extracted as a trace component in bauxite and to a small extent from sphalerite. The amount extracted from coal, diaspore and germanite in which gallium is also present is negligible. The United States Geological Survey (USGS) estimates gallium reserves to exceed 1 million tonnes, based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores.[11][12] Some flue dusts from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.[13][14][15][16]
[edit]Production
The only two economic sources for gallium are as byproduct of aluminium and zinc production, while the sphalerite for zinc production is the minor source. Most gallium is extracted from the crude aluminium hydroxide solution of the Bayer process for producing alumina and aluminium. A mercury cell electrolysis and hydrolysis of the amalgam with sodium hydroxide leads to sodium gallate. Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[17] An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling.[11]
In semiconductors, an important application is in the compounds gallium arsenide and gallium nitride, used most notably in light-emitting diodes (LEDs). Semiconductor use is now almost the entire (> 95%) world market for gallium, but new uses in alloys and fuel cells continue to be discovered.
Gallium is not known to be essential in biology, but because of the biological handling of gallium's primary ionic salt gallium(III) as though it were iron(III), the gallium ion localizes to and interacts with many processes in the body in which iron(III) is manipulated. As these processes include inflammation, which is a marker for many disease states, several gallium salts are used, or are in development, as both pharmaceuticals and radiopharmaceuticals in medicine.
Elemental gallium is not found in nature, but it is easily obtained by smelting. Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands by 3.1 percent when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing. Gallium shares the higher-density liquid state with only a few materials like silicon, germanium, bismuth, antimony and water.
Gallium attacks most other metals by diffusing into their metal lattice. Gallium for example diffuses into the grain boundaries of Al/Zn alloys[1] or steel,[2] making them very brittle. Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy in the core of the second nuclear bomb to help stabilize the plutonium crystal structure.[3]
The melting point of 302.9146 K (29.7646°C, 85.5763°F) is near room temperature. Gallium's melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990 (ITS-90) established by BIPM.[4] [5] [6] The triple point of gallium of 302.9166 K (29.7666°C, 85.5799°F), is being used by NIST in preference to gallium's melting point.[7]
Gallium is a metal that will melt in one's hand. This metal has a strong tendency to supercool below its melting point/freezing point. Seeding with a crystal helps to initiate freezing. Gallium is one of the metals (with caesium, rubidium, francium and mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low vapor pressure at high temperatures. Unlike mercury, liquid gallium metal wets glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions). For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers.
Crystallization of gallium from the melt
Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Each atom has only one nearest neighbor (at a distance of 244 pm) and six other neighbors within additional 39 pm. Many stable and metastable phases are found as function of temperature and pressure.
The bonding between the nearest neighbors is found to be of covalent character, hence Ga2 dimers are seen as the fundamental building blocks of the crystal. This explains the drop of the melting point compared to its neighbour elements aluminium and indium. The compound with arsenic, gallium arsenide is a semiconductor commonly used in light-emitting diodes.
High-purity gallium is dissolved slowly by mineral acids.
Gallium has no known biological role, although it has been observed to stimulate metabolism.[8]
[edit]History
Gallium (the Latin Gallia means "Gaul", essentially modern France) was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two violet lines) in an examination of a zinc blende from the Pyrenees.[9] Before its discovery, most of its properties had been predicted and described by Dmitri Mendeleev (who had called the hypothetical element "eka-aluminium" on the basis of its position in his periodic table). Later, in 1875, Lecoq obtained the free metal by electrolysis of its hydroxide in potassium hydroxide solution. He named the element "gallia" after his native land of France. It was later claimed that, in one of those multilingual puns so beloved of men of science in the early 19th century, he had also named gallium after himself, as his name, "Le coq", is the French for "the rooster", and the Latin for "rooster" is "gallus"; however, in an 1877 article Lecoq denied this supposition. (The supposition was also noted in Building Blocks of the Universe, a book on the elements by Isaac Asimov; cf. the naming of the J/ψ meson.)
[edit]Occurrence
Gallium does not exist in free form in nature, and the few high-gallium minerals such as gallite (CuGaS2) are too rare to serve as a primary source of the element or its compounds. Its abundance in the Earth's crust is approximately 16.9 ppm.[10] Gallium is found and extracted as a trace component in bauxite and to a small extent from sphalerite. The amount extracted from coal, diaspore and germanite in which gallium is also present is negligible. The United States Geological Survey (USGS) estimates gallium reserves to exceed 1 million tonnes, based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores.[11][12] Some flue dusts from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.[13][14][15][16]
[edit]Production
The only two economic sources for gallium are as byproduct of aluminium and zinc production, while the sphalerite for zinc production is the minor source. Most gallium is extracted from the crude aluminium hydroxide solution of the Bayer process for producing alumina and aluminium. A mercury cell electrolysis and hydrolysis of the amalgam with sodium hydroxide leads to sodium gallate. Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[17] An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling.[11]
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