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Ceramic Matrix Composites
In materials science ceramic matrix composites (CMCs) are a subgroup of composite materials and a subgroup of ceramics. They consist of ceramic fibers embedded in a ceramic matrix. The fibers and the matrix both can consist of any ceramic material, including carbon and carbon fibers. Introduction The motivation to develop CMCs was to overcome the problems associated with the conventional technical ceramics like alumina, silicon carbide, aluminum nitride, silicon nitride or zirconia – they fracture easily under mechanical or thermo-mechanical loads because of cracks initiated by small defects or scratches. The crack resistance is very low, as in glass. To increase the crack resistance or fracture toughness, particles (so-called monocrystalline ''whiskers'' or ''platelets'') were embedded into the matrix. However, the improvement was limited, and those products found application only in some ceramic cutting tools. The integration of long multi-strand fibers has drastically in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monocrystalline Whisker
A monocrystalline whisker is a filament of material that is structured as a single, defect-free crystal. Some typical whisker materials are graphite, alumina, iron, silicon carbide and silicon. Single-crystal whiskers of these (and some other) materials are known for having very high tensile strength (on the order of 10–20 GPa). Whiskers are used in some composites, but large-scale fabrication of defect-free whiskers is very difficult. Prior to the discovery of carbon nanotubes, single-crystal whiskers had the highest tensile strength of any materials known, and were featured regularly in science fiction as materials for fabrication of space elevators, arcologies, and other large structures. Despite showing great promise for a range of applications, their usage has been hindered by concerns over their effects on health when inhaled. See also * Whisker (metallurgy) – Self-organizing metallic whisker-shaped structures that cause problems with electronics. *Laser-heated pedes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Machining
Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which utilizes machine tools, in contrast to ''additive manufacturing'' (e.g. 3D printing processes, 3D printing), which uses controlled addition of material. Machining is a major process of the manufacture of many metal products, but it can also be used on other materials such as wood, plastic, ceramic, and composite material, composites. A person who specializes in machining is called a machinist. As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing primary machine tools. Although a machine shop can be a standalone operation, many businesses maintain internal machine shops or tool rooms that support their specialized needs. Much modern-day machining uses Numerical control, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anisotropy
Anisotropy () is the structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit very different physical or mechanical properties when measured along different axes, e.g. absorbance, refractive index, conductivity, and tensile strength. An example of anisotropy is light coming through a polarizer. Another is wood, which is easier to split along its grain than across it because of the directional non-uniformity of the grain (the grain is the same in one direction, not all directions). Fields of interest Computer graphics In the field of computer graphics, an anisotropic surface changes in appearance as it rotates about its geometric normal, as is the case with velvet. Anisotropic filtering (AF) is a method of enhancing the image quality of textures on surfaces that are far away and viewed at a shallow angle. Older ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compound (chemistry), compounds, produces unique physical property, physical properties including toughness, high rubber elasticity, elasticity, viscoelasticity, and a tendency to form Amorphous solid, amorphous and crystallization of polymers, semicrystalline structures rath ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultra High Temperature Ceramic Matrix Composite
Ultra-high temperature ceramic matrix composites (UHTCMC) are a class of refractory ceramic matrix composites (CMCs) with melting points significantly higher than that of typical CMCs. Among other applications, they are the subject of extensive research in the aerospace engineering field for their ability to withstand extreme heat for extended periods of time, a crucial property in applications such as thermal protection systems (TPS) for high heat fluxes (> 10 MW/m2) and rocket nozzles. Carbon fiber-reinforced carbon (C/C) maintains its structural integrity up to 2000 °C; however, C/C is mainly used as an ablative material, designed to purposefully erode under extreme temperatures in order to dissipate energy. Carbon fiber reinforced silicon carbide matrix composites ( C/SiC) and Silicon carbide fiber reinforced silicon carbide matrix composites ( SiC/SiC) are considered reusable materials because silicon carbide is a hard material with a low erosion and it forms a silica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultra-high Temperature Ceramic
Ultra-high-temperature ceramics (UHTCs) are a type of refractory ceramics that can withstand extremely high temperatures without degrading, often above 2,000 °C. They also often have high Thermal conductivity, thermal conductivities and are highly resistant to thermal shock, meaning they can withstand sudden and extreme changes in temperature without cracking or breaking. Chemically, they are usually borides, carbides, nitrides, and oxides of early transition metals. UHTCs are used in various high-temperature applications, such as Thermal protection system, heat shields for spacecraft, Industrial furnace, furnace linings, Hypersonic flight, hypersonic aircraft components and nuclear reactor components. They can be fabricated through various methods, including hot pressing, spark plasma sintering, and chemical vapor deposition. Despite their advantages, UHTCs also have some limitations, such as their brittleness and difficulty in machining. However, ongoing research is focu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abnormal Grain Growth
In materials science, abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon in which certain energetically favorable grains (crystallites) grow rapidly in a matrix of finer grains, resulting in a bimodal distribution of grain size. In ceramic materials, this phenomenon can result in the formation of elongated prismatic, acicular (needle-like) grains in a densified matrix. This microstructure has the potential to improve fracture toughness by impeding the propagation of cracks. Mechanisms Abnormal grain growth (AGG) is encountered in metallic or ceramic systems exhibiting one or more of several characteristics: # Systems with secondary phase inclusions, precipitates or impurities above a certain threshold concentration. # Systems with a highly anisotropic surface energy. # Systems far from chemical equilibrium. Abnormal grain growth occurs due to very high local rates of interface ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mullite
Mullite or porcelainite is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3 Al2 O32 SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, there are three different aluminium sites: two distorted tetrahedral and one octahedral. Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Argyllshire, Scotland. Porcellanite Mullite (porcelainite) can be found as a constituent mineral in a type of thermally-metamorphosed rock called porcellanite. Use in porcelain Mullite is present in the form of needles in porcelain. It is produced during various melting and firing processes, and is used as a refractory material,H. Schneider & S. Komarneni (2005) Mullite. Wiley, VCH, 5 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 electrons. It belongs to group 14 of the periodic table. Carbon makes up about 0.025 percent of Earth's crust. Three Isotopes of carbon, isotopes occur naturally, carbon-12, C and carbon-13, C being stable, while carbon-14, C is a radionuclide, decaying with a half-life of 5,700 years. Carbon is one of the timeline of chemical element discoveries#Pre-modern and early modern discoveries, few elements known since antiquity. Carbon is the 15th abundance of elements in Earth's crust, most abundant element in the Earth's crust, and the abundance of the chemical elements, fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual abi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metal Matrix Composite
In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carbide) or another metal (such as steel). They are typically classified according to the type of reinforcement: short discontinuous fibers (whiskers), continuous fibers, or particulates. There is some overlap between MMCs and cermets, with the latter typically consisting of less than 20% metal by volume. When at least three materials are present, it is called a hybrid composite. MMCs can have much higher strength-to-weight ratios, stiffness, and ductility than traditional materials, so they are often used in demanding applications. MMCs typically have lower thermal and electrical conductivity and poor resistance to radiation, limiting their use in the very harshest environments. Composition MMCs are made by dispersing a reinforcing mater ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
