Ultra high temperature ceramics (UHTCs) are materials rarely found in nature, characterized by high melting points, hardness, thermal conductivities (if compared to other ceramics), good wear resistance and mechanical strength.1,2,3 Besides, they are chemically and thermally stable under a variety of conditions due to their high negative free energy of formation.1,3
The materials that fit in these criteria are ceramics compounds made of borides, nitrides and carbides. As a result of having those properties, this class of material can be applied in extreme environments such as extreme temperatures, chemical reactivity and erosive attack. Because of that, in the 1950’s, studies started to analyze the possibility of using them to coat nuclear reactor but they also have the ability to work as electrode for electric arc furnaces, handling of molten metals and for aerospace usage (e.g. rocket propulsion, atmospheric re-entry, hypersonic flight), this last application leaded to further investigations on UHTCs.3,4,5
Nitrides and carbides tend to have lower thermal conductivity if compared to borides (diborides have thermal conductivity similar to copper at room temperature), which means that borides compounds usually have higher thermal shock stability and good thermal stress response, because of that this essay will focus on this type of UHTC.3
ZrB2 is a diboride UHTC that have hexagonal crystal structure, as shown in the figure 1. According to Fahrenholtz et al., the crystal is arranged by layers of Zr hexagonally packed together alternating with layers of B atoms disposed in 2D graphite-like rings.1
Figure 1 – Representation of ZrB2 crystal structure1
A summary of ZrB2 properties are presented in Table 1.
Table 1 – Prope...
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...M. Gasch, J. W. Lawson, M. I. Gusman, M. M. Stackpoole, “Recent Developments in Ultra High Temperature Ceramics at NASA Ames” American Institute of Aeronautics and Astronautics (2009).
4 A. Paul, D.D. Jayaseelan, S. Venugopal, E. Zapata-Solvas, J. Binner, B. Vaidhyanathan, A. Heaton, P. Brown, W.E. Lee, “UHTC composites for hypersonic applications” American Ceramics Society Bulletin, 91 [1] 22–30 (2012).
5 E. Wuchina, E. Opila, M. Opeka, W. Fahrenholtz, I. Talmy, “UHTCs: Ultra-High Temperature Ceramic Materials for Extreme Environment Applications” The Electrochemical Society,30-37 (2007).
6 J. R. Fenter, ‘‘Refractory Diborides as Engineering Materials,’’ SAMPE Quarter., 2, 1–15 (1971).
7 A. L. Chamberlain, W. G. Fahrenholtz, G. E. Hilmas, and D. T. Ellerby, ‘‘High Strength ZrB2-Based Ceramics,’’ Journal of the American Ceramics Society, 87 [6] 1170–2 (2004).
Other materials used for the Canadarm are aramid fibers [1] such as Kevlar [7]. This aerospace material is also used in bulletproof vests [12]. These aramid fibers are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bond can be exploited [1]. Kevlar is also flame resistant [12] which bolds well in space due to the extreme heat from the solar winds. Kapton is another one of the materials used by spacecrafts. This material has the ability to sustain itself and be stable in many different temperatures such as -269 to 400 °C. Since Space is a vacuum the temperature is intense, therefore this material is well suited for counter...
Ceramic-on-Ceramic is a good combination alongside longevity and reliability. In this hip combined a high-strength ceramic bearing that has the standing for ultra-low wear performance. Ceramic is the har...
Some ceramics are used in orthopaedic applications such as bone repair, bone augmentation and joint replacement but their use in this field is not as extensive or widespread as metals and polymers because ceramics have poor fracture toughness. This severely limits the use of ceramics in load bearing applications (Davis, 2003).
"Production of Refractory Metal Powders," in Powder Metal Technologies and Applications, vol. 7, 1998, pp. 188-201.
It has a molar volume of 9.38 ×10-6 m3/mol. Molybdenum has an atomic weight of 95.94 amu. Its atomic number is 42. The atomic radius is 145 pm and the covalent radius is 145 pm also. Its electron configuration is [Kr]4d^5 5s^1.
These include, high strength, low weight, high chemical resistance and high cut resistance. This material does not corrode or rust and is also unaffected when placed in or under water.
Silicon carbide (SiC) devices have received increased attention for high power, high speed, high temperature applications due to their superior properties, including wide band gap, high saturated electron velocity, high breakdown electric field strength, and high thermal conductivity. The high breakdown field allows SiC devices to operate at much higher voltages than Si or GaAs devices and...
of a zwitterion is made possible due to the basic properties of the NH2 group
Thin film coatings of ceramic materials are widely used to safeguard materials against corrosion, wear resistance, and thermal conductivity [1, 2]. The objective of this work is to increase the thermal resistivity and thereby improve the mechanical properties of the materials. In this work thin film of Ceria stabilized Zirconia was formed and is applied on the area where the heat transfer occurs the most and is used to reduce its effect of temperature. These coatings are used to protect parts from big and prolonged heat loads by utilizing thermally insulated materials which can undergo a significant temperature difference between the initial material and the coating surface [3]. Many new materials have been developed, but steel remains the principal construction material for automobiles appliances, and industrial machinery. Since steels are vulnerable to aggressive chemical environments or atmospheric oxidation, metal coating is necessary to provide various degrees of protection through hot-dipped and electroplating process to tough polymers and flame-sprayed ceramics. In general corrosive atmospheres contain more than one active material, and the coating must resist dissemination by a combination of oxidizers, solvents, or both. Thus, the best hurdle is one that resists corrosion [4]. The obligatory thin films have been attained by using spray pyrolysis coating method. Spray pyrolysis technique involves spraying of a solution containing soluble salts of the desired compound on to preheated substrates, where the constituents react to form a chemical compound [8, 9]. Both, dense and porous structures can be deposited by spray pyrolysis which can also be achieved on large substrates by scaling up the equipment. It has capability to...
Shiho Kanzaki had an influence on the history and development of Ceramics. Shiho’s work shows the purpose of what it means for a pottery to be really appealing to people. He got a hold of all details of the use of the completed product into account in the foundation of his pieces. His jars, bowls, urns, and teapots have a simple beauty where the form meets the purpose of the mission, featured by a beautiful glazing. These works of his continue an unharmed line of tradition culture that is as important throughout the globe as it is for the people of Shigaraki, where he grew up.
Also, they need to be so strong and rigid that the railgun does not sag while firing and buckle under its own weight. The obvious choice for high electrical conductivity is copper. However, the railguns made out of copper wear out much too quickly due to the erosion of the rails by the hypervelocity projectiles and they lack high-temperature strength. The wear and erosion of copper rails necessitate inordinately frequent barrel replacements. In order to satisfy these requirements, a nanocrystalline composite material made of tungsten, copper, and titanium diboride is being evaluated as a potential candidate. This nanocomposite possesses the requisite electrical conductivity, adequate thermal conductivity, excellent high strength, high rigidity, hardness, and wear/erosion resistance. This results in longer-lasting, wear-resistant, and erosion-resistant railguns, which can be fired more frequently and often than their conventional
Due to its good inherent structural properties it is widely used in industry, It can be used as an insulator to electrical wiring. It is
Drilling is a very significant and common activity which is used in many fields and industries in our everyday life; such as oil drilling and construction. Drilling requires large mechanical devices that dig deep into the ground and sometimes through several layers of rock and mineral. Drilling machines have a rotating mechanical tool attached to them known as drill bits which are used to cut and remove materials in order to penetrate deep below the ground. Drill bits come in different shapes, materials and sizes, and can create different kinds of holes in many different materials. Because of their vital role in drilling, it is hence very important that the material of the drill bits is strong. A common material for drill bits is steel. However, they proved to be inefficient as they have difficulty going through hard rocks because the metal is not strong enough. Moreover, they tend to overheat and collapse when used for a period of time. This is because the Metals are better conductors of heat than any other solids, as the electrons
Kinard, William H. "Technical Discipline Area: Materials." Long Duration Exposure Facility (LDEF) Archive System. NASA Langley Research Center, 04 Apr. 2001. Web. 21 Apr. 2014.