Metallography Material1. 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.
Tisu merupakan benda pembersih praktis yang dapat dibawa kemana–mana. Tujuan penelitian ini untuk mengidentifikasi potensi perbedaan kuat tarik dan daya. Fungsional seperti membran elektrolit yang berpotensi untuk penghantar litium. Data struktur mikro dan sifat listrik memperlihatkan bahwa termistor dari. Kawat penghantar 6201 ini biasanya digunakan untuk bahan kabel dari jenis All Aluminium Alloy Conductor (AAAC). Disamping persyaratan sifat listrik seperti konduktivitas listrik diatas, kriteria mutu lainnya yang juga harus dipenuhi meliputi seluruh atau sebagian dari sifat – sifat atau kondisi berikut ini, yaitu: a. Komposisi kimia.
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 hitam9FEBTeori Radiasi Benda HitamDistribusi 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 hitamDalam 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 gelombangelektromagnetik.
Bahkan sebuah kubus es pun memancarkan radiasi panas, sebagian kecil dariradiasi panas ini ada dalam daerah cahaya tampak. Walaupun demikian kubus es ini tak dapatdilihat dalam ruang gelap. Serupa dengan kubus es, badan manusia pun memancarkan radiasipanas dalam daerah cahaya tampak, tetapi intensitasnya tidak cukup kuat untuk dapat dilihatdalam ruang gelap.Setiap benda memancarkan radiasi panas, tetapi umunya benda terlihat oleh kita karenabenda itu memantulkan cahaya yang dating padanya, bukan karena ia memacarkan radiasipanas. Benda baru terlihat karena meradiasikan panas jika suhunya melebihi 1000 K. Pada suhuini benda mulai berpijar merah sepeti kumparan pemanas sebuah kompor listrik.
Pada suhu diatas 2000 K benda berpijar kuning atau keputih-putihan, seperti besi berpijar putihatau pijarputih dari filamen lampu pijar. Begitu suhu benda terus ditingkatkan, intensitas relatif darispectrum cahaya yang dipancarkannya berubah. Ini menyebabkan pergeseran dalam warnawarnaspektrum yang diamati, yang dapat digunakan untuk menaksir suhu suatu bendaIntensitas energi radiasi yang dipancarkan benda hitam dinyatakan sebagaiHukum 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 adalahu(λ, T) = 8.phi.kTλ^-4Pada 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 menjadisehingga ketika lambda mendekati nol, kerapatan energi tidak tak terhingga. 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 dilas1. 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 treatmentb. Tak dapat di heat treatmentPaduan 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 MagnesiumSifat-sifat mekanik magnesium terutama memiliki kekuatan tarik yang sangat rendah.
FREEZING POINT DEPRESSIONRepresents 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 asThe 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.
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, isWhere 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 = 11.300Actually 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 RULEIn 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 DIAGRAMConsider 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 BAccording 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). 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 CURVESIf 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.
![Mengidentifikasi sifat benda penghantar listrik Mengidentifikasi sifat benda penghantar listrik](/uploads/1/2/5/5/125599176/484906886.jpg)
![Penghantar Penghantar](/uploads/1/2/5/5/125599176/311610499.gif)
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). 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.