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Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexagonal form corresponding to graphite is the most stable and soft among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic variety analogous to diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior. The rare wurtzite BN modification is similar to lonsdaleite but slightly softer than the cubic form.
Graphite is a crystalline allotrope (form) of the element carbon. It consists of many stacked layers of graphene, typically in the excess of hundreds of layers. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on a large scale for uses in many critical industries including refractories (50%), lithium-ion batteries (18%), foundries (10%), lubricants (5%), among others (17%). Under extremely high pressures and extremely high temperatures it converts to diamond. Graphite's low cost, thermal and chemical inertness and characteristic conductivity of heat and electricity finds numerous applications in high energy and high temperature processes.
Stainless steel, also known as inox, corrosion-resistant steel (CRES), and rustless steel, is an alloy of iron that is resistant to rusting and corrosion. It contains iron with chromium and other elements such as molybdenum, carbon, nickel and nitrogen depending on its specific use and cost. Stainless steel's resistance to corrosion results from the 10.5%, or more, chromium content which forms a passive film that can protect the material and self-heal in the presence of oxygen.
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
In physical chemistry and engineering, passivation is coating a material so that it becomes "passive", that is, less readily affected or corroded by the environment. Passivation involves creation of an outer layer of shield material that is applied as a microcoating, created by chemical reaction with the base material, or allowed to build by spontaneous oxidation in the air. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shield against corrosion. Passivation of silicon is used during fabrication of microelectronic devices. Undesired passivation of electrodes, called "fouling", increases the circuit resistance so it interferes with some electrochemical applications such as electrocoagulation for wastewater treatment, amperometric chemical sensing, and electrochemical synthesis.
Heat treating is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.
Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.
Case-hardening or carburization is the process of introducing carbon to the surface of a low-carbon iron, or more commonly a low-carbon steel object, in order to harden the surface.
Titanium nitride is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties.
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.
Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms or a non-living substance (inorganic). Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system, or plant performing a defined and useful function and that the fouling process impedes or interferes with this function.
Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. It is a process for growing crystalline layers to create complex semiconductor multilayer structures. In contrast to molecular-beam epitaxy (MBE), the growth of crystals is by chemical reaction and not physical deposition. This takes place not in vacuum, but from the gas phase at moderate pressures. As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys, and it has become a major process in the manufacture of optoelectronics, such as light-emitting diodes, its most widespread application. It was first demonstrated in 1967 at North American Aviation Autonetics Division in Anaheim CA by Harold M. Manasevit.
Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr3C2, Cr7C3, and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.
Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si
3N
4 is the most thermodynamically stable and commercially important of the silicon nitrides, and the term ″Silicon nitride″ commonly refers to this specific composition. It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot H
3PO
4. It is very hard. It has a high thermal stability with strong optical nonlinearities for all-optical applications.
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.
Ferritic nitrocarburizing or FNC, also known by the proprietary names "Tenifer", "Tufftride", Melonite, and "Arcor", is a range of proprietary case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures during a salt bath. Other methods of ferritic nitrocarburizing include gaseous processes such as Nitrotec and ion (plasma) ones. The processing temperature ranges from 525 °C (977 °F) to 625 °C (1,157 °F), but usually occurs at 565 °C (1,049 °F). Steel and other ferrous alloys remain in the ferritic phase region at this temperature. This allows for better control of the dimensional stability that would not be present in case hardening processes that occur when the alloy is transitioned into the austenitic phase. There are four main classes of ferritic nitrocarburizing: gaseous, salt bath, ion or plasma, and fluidized-bed.
Alonizing is a diffusion metallizing process in that it is a thermochemical treatment that involves enriching the surface layer of an object with one or more metallic elements. Specifically, alonizing is the diffusion of aluminum into the surface of a base metal through high temperature vapors. The types of metals that can be alonized include all types of wrought and cast steels. This process results in an alloy with the surface properties of aluminum while retaining the base metal's inherent strength and rigidity. Therefore, alonizing does not change the high-temperature mechanical properties of the base metal, which is the advantage of alonizing over simply creating an aluminum alloy.
Filamentous carbon is a carbon-containing deposit structure that refers to several allotropes of carbon, including carbon nanotubes, carbon nanofibers, and microcoils. It forms from gaseous carbon compounds. Filamentous carbon structures all contain metal particles. These are either iron, cobalt, or nickel or their alloys. Deposits of it also significantly disrupt synthesis gas methanation. Acetylene is involved in a number of method of the production of filamentous carbon. The structures of filamentous carbon are mesoporous and on the micrometer scale in dimension. Most reactions that form the structures take place at or above 280 °C (536 °F).
References
- ↑ Fischer-Tropsch Archive
- 1 2 On the Mechanism of Metal Dusting Corrosion (no date) C.M. Chun, J.D. Mumford and T.A. Ramanarayanan
- ↑ "Metal dusting: impacts, causes and prevention | Diffusion Alloys Ltd". www.diffusion-alloys.com. Archived from the original on 2014-10-12.
- ↑ Corrosion by Carbon and Nitrogen - Metal Dusting, Carburisation and Nitridation; Grabke, H.J., Schütze, M.; Woodhead Publishing 2007
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