A cermet is a composite material composed of ceramic and metal materials.
A cermet can combine attractive properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation. The metal is used as a binder for an oxide, boride, or carbide. Generally, the metallic elements used are nickel, molybdenum, and cobalt. Depending on the physical structure of the material, cermets can also be metal matrix composites, but cermets are usually less than 20% metal by volume.
Cermets are used in the manufacture of resistors (especially potentiometers), capacitors, and other electronic components which may experience high temperature.
Cermets are used instead of tungsten carbide in saws and other brazed tools due to their superior wear and corrosion properties. Titanium nitride (TiN), titanium carbonitride (TiCN), titanium carbide (TiC) and similar can be brazed like tungsten carbide if properly prepared, however they require special handling during grinding.
Composites of MAX phases, an emerging class of ternary carbides or nitrides with aluminium or titanium alloys have been studied since as high-value materials exhibiting favourable properties of ceramics in terms of hardness and compressive strength alongside ductility and fracture toughness typically associated with metals. Such cermet materials, including aluminium-MAX phase composites,[1] have potential applications in automotive and aerospace applications.[2][1]
Some types of cermets are also being considered for use as spacecraft shielding as they resist the high velocity impacts of micrometeoroids and orbital debris much more effectively than more traditional spacecraft materials such as aluminum and other metals.
History
[
edit
]
Source:[3]
After World War II, the need to develop high temperature and high stress-resistant materials became clear. During the war, German scientists developed oxide base cermets as substitutes for alloys. They saw a use for this for the high-temperature sections of new jet engines as well as high temperature turbine blades. Today ceramics are routinely implemented in the combuster part of jet engines because it provides a heat-resistant chamber. Ceramic turbine blades have also been developed. These blades are lighter (less massive) than steel and allow for greater rotational acceleration (&#;spool-up time&#;) of the blade assemblies.
The United States Air Force saw potential in the material technology and became one of the principal sponsors for various research programs in the US. Some of the first universities to research were Ohio State University, University of Illinois, and Rutgers University.
The word cermet was actually coined by the United States Air Force, the idea being that they are a combination of two materials, a metal and a ceramic. Basic physical properties of metals include ductility, high strength, and high thermal conductivity. Ceramics possess basic physical properties such as a high melting point, chemical stability, and especially oxidation resistance.
The first ceramic metal material developed used magnesium oxide (MgO), beryllium oxide (BeO), and aluminum oxide (Al2O3) for the ceramic part. Emphasis on high stress rupture strengths was around 980 °C.[4] Ohio State University was the first to develop Al2O3 based cermets with high stress rupture strengths around °C. Kennametal, a metal-working and tool company based in Latrobe, PA, USA, developed the first titanium carbide cermet with a 19 megapascals (2,800 psi) and 100-hour stress-to-rupture strength at 980 °C. Jet engines operate at this temperature and further research was invested on using these materials for components.
Quality control in manufacturing these ceramic metal composites was hard to standardize. Production had to be kept to small batches and within these batches, the properties varied greatly. Failure of the material was usually a result of undetected flaws usually nucleated during processing.
The existing technology in the s reached a limit for jet engines where little more could be improved. Subsequently, engine manufactures were reluctant to develop ceramic metal engines. Interest was renewed in the s when silicon nitride and silicon carbide were looked at more closely. Both materials possessed better thermal shock resistance, high strength, and moderate thermal conductivity.
Cermet production, Helipot Division of Beckman Instruments,
[
edit
]
1. Steatite Ingredients Being Weighed
2. Steatite Granulation Process
3. Steatite Chip Pressing
4. High Temperature Firing of Steatite Chip
5. Beckman Model 61 Potentiometer (Cermet Screening)
6. Final Firing of Cermet
7. Checking electrical resistance
8. Final Assembly
[5]
Applications
[
edit
]
Ceramic-to-metal joints and seals
[
edit
]
Cermets were first used extensively in ceramic-to-metal joint applications. Construction of vacuum tubes was one of the first critical systems, with the electronics industry employing and developing such seals. German scientists recognized that vacuum tubes with improved performance and reliability could be produced by substituting ceramics for glass. Ceramic tubes can be outgassed at higher temperatures. Because of the high-temperature seal, ceramic tubes withstand higher temperatures than glass tubes. Ceramic tubes are also mechanically stronger and less sensitive to thermal shock than glass tubes.[6] Today, cermet vacuum tube coatings have proved to be key to solar hot water systems.
Ceramic-to-metal mechanical seals have also been used. Traditionally they have been used in fuel cells and other devices that convert chemical, nuclear, or thermionic energy to electricity. The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven generators designed to operate in corrosive liquid-metal vapors.[6]
Bioceramics
[
edit
]
Bioceramics play an extensive role in biomedical materials. The development of these materials and diversity of manufacturing techniques has broadened the applications that can be used in the human body. They can be in the form of thin layers on metallic implants, composites with a polymer component, or even just porous networks. These materials work well within the human body for several reasons. They are inert, and because they are resorbable and active, the materials can remain in the body unchanged. They can also dissolve and actively take part in physiological processes, for example, when hydroxylapatite, a material chemically similar to bone structure, can integrate and help bone grow into it. Common materials used for bioceramics include alumina, zirconia, calcium phosphate, glass ceramics, and pyrolytic carbons.
One important use of bioceramics is in hip replacement surgery. The materials used for the replacement hip joints were usually metals such as titanium, with the hip socket usually lined with plastic. The multiaxial ball was tough metal ball but was eventually replaced with a longer-lasting ceramic ball. This reduced the roughening associated with the metal wall against the plastic lining of the artificial hip socket. The use of ceramic implants extended the life of the hip replacement parts.[7]
Dental cermets are also used in dentistry as a material for fillings and prostheses.
Transportation
[
edit
]
Ceramic parts have been used in conjunction with metal parts as friction materials for brakes and clutches.[6]
Electrical heaters
[
edit
]
Cermets are used as heating elements in electric resistance heaters. One construction technique starts with the cermet material formulated as an ink which is printed on a substrate then cured with heat. This technique allows manufacture of complex shapes of heating elements. Examples of applications for cermet heating elements include thermostat heaters, heat sources for bottle sterilization, coffee carafe warmers, heaters for oven control, and laser printer fuser heaters.[8]
Other applications
[
edit
]
The United States Army and British Army have had extensive research in the development of cermets. These include the development of lightweight ceramic projectile-proof armor for soldiers and also Chobham armor.
Cermets are also used in machining on cutting tools.
Cermets are also used as the ring material in high-quality line guides for fishing rods.
A cermet of depleted fissile material (e.g. uranium, plutonium) and sodalite has been researched for its benefits in the storage of nuclear waste.[9] Similar composites have also been researched for use as a fuel form for nuclear reactors [10] and nuclear thermal rockets.[citation needed]
As nanostructured cermet, this material is used in the optical field, such as solar absorbers/selective surface. Thanks to the size of the particles (~5 nm), surface plasmons on the metallic particles are generated and enable the heat transmission.
See also
[
edit
]
Notes
[
edit
]
Further reading
[
edit
]
by Chris Woodford. Last updated: July 11, .
Humans have been shuffling round Earth for a couple of million years now&#;and you'd think, in all that time, we'd have discovered every material our planet has to offer. Not so! Our lives are still evolving, technologically much more quickly than biologically, and that means we constantly need to invent new materials and improve old ones. Some of the most exciting materials of recent decades are composites: combinations of two or more existing materials that combine the best properties of each. Cermets are composites in which ceramic materials and metals join together, typically to give something with the high temperature performance or wear resistance of a ceramic and the toughness, flexibility, or electrical conductivity of a metal. Let's take a closer look at what they are, how they work, and some of the ways we can use them!
Photo: Testing cermets in military armor at Lawrence Livermore National Laboratory. Photo by courtesy of US Department of Energy Digital Photo Archive (DOE).
Ceramic plus metal = cermet. It's really that simple! Why would you want to combine a metal and a ceramic? Metals, though versatile, aren't capable of withstanding the incredibly high temperatures you typically encounter in airplane jet engines or space rockets. Ceramics are brilliant at high temperatures and able to resist attack by chemicals and things like oxygen in the air, but their sheer inertness means they're just pretty boring most of the time. Brilliant for teapots and false teeth, but fairly hopeless when it comes to doing interesting things like conducting electricity or heat or bending and flexing. If you want something that can survive in really tough environments and still behave in interesting ways, you need to switch your attention to things like alloys, composites&#;and cermets.
"Cermet" is a generic name for a whole range of different composites. Sometimes the ceramic is the biggest ingredient and acts as the matrix (effectively the base or binder) to which particles of the metal are attached. Cermets used for electrical applications are typically made this way (in other words, they are examples of ceramic matrix composites or CMCs). But the metal component (typically an element such as cobalt, molybdenum, or nickel) can also be the matrix, giving what's called a metal matrix composite (MMC), in which hard ceramic particles are held together by a tough but ductile metal. Cermets used in things like cutting tools are made this way.
Artwork: What's a cermet like inside? Here's a simplified cermet microstructure (the fine inner, structure you'll see if you look at a cermet with a powerful microscope). In the type of cermet used in cutting tools, the core (gray) might be made of a ceramic such as tungsten carbide, while the binder (black stipples) could be made of a nickel alloy. The scale shown in red is approximately 20μm (20 microns). Most modern cermets designed for tools have a core material that's a carbide or nitride of titanium, tantalum, tungsten, niobium, or molybdenum, and a binder of nickel or cobalt.
Like other composites, cermets "work" by producing a material with a microstructure that has certain things in common with each of its different constituents. For example, the metal ingredient effectively allows electrons to flow through the material, enabling what would otherwise be a ceramic insulator to conduct electricity. That suggests cermets are relatively stable structures in which the metal and the ceramic are fixed in place&#;but that's not always the case. Under some conditions, cermets behave as though they have a dynamic surface layer, with metal particles constantly detaching and reattaching themselves. This effectively forms a smoother, harder, and more wear-resistant upper layer that makes a metal behave more like a ceramic.
Artwork: How do cermets conduct electricity? Here's the structure of a typical cermet made from particles of ceramic alumina (red), each of which is surrounded by platinum metal (blue). Although electricity doesn't normally flow through a ceramic, it can flow through a cermet (yellow arrowed line) by following a circuit through the platinum. Artwork based on a drawing from US Patent 4,183,746: Cermets by Stephen L. Pearce and Gordon L. Selman, Johnson, Matthey & Co., Limited, courtesy of US Patent and Trademark Office.
Apart from better electrical properties, the metal component of a cermet makes it more ductile (capable of being drawn thin into strands or wires). It also gives better resistance against thermal shock: often, if one part of a ceramic material (such as glass) is hotter than another, it will crack fatally or even shatter; the metal part of a cermet helps to avoid this by conducting the excess heat and dissipating it safely through the material.
Electrical components are one obvious application. Because they can get extremely hot, they need to behave like ceramics but, since they also need to conduct electricity, it helps if they work like metals. Cermets offer a perfect solution in components such as resistors and vacuum tubes (valves). Crudely, we can think of cermet resistors as a mixture of an insulator (the ceramic matrix) and a conductor (the metal particles), with the type and relative proportions of the two "ingredients" (ceramic and metal) determining the ultimate resistance.[1]
Artwork: An early design for a cermet-based electrical resistor from the s. The cermet (red, 10) is made from a nonconducting glass binder and conducting metal particles, mounted on a ceramic, insulating base (blue, 11), and connected to a circuit through two electrodes (green, 12/13). Artwork from US Patent 2,950,995: Electrical resistance element by Thomas M. Place, Sr. and Thomas M. Place, Jr., Beckman Coulter Inc., courtesy of US Patent and Trademark Office.
Machine tools are another increasingly common use for cermets, which offer greater toughness and wear resistance than more traditional materials. Titanium carbide (TiC), from which many cutting and drilling tools are made, is a popular choice of cermet for tools used in milling, turning and boring, and for making threads and grooves. Typically cermet tools are made from either titanium carbide alone, titanium carbide and titanium nitride (TiN), or titanium carbonitride (TiCN). Generally, cermets provide higher cutting-tool speeds, better surface finish, and last much longer than traditional tool parts. Unlike tools coated in carbide, cermet-coated tools do not wear in the same way but effectively regenerate themselves. [2]
Photo: Cutting tools made from cermets last longer and produce a better surface finish than traditional carbide tools. Photo by Eduardo Zaragoza courtesy of US Navy and Wikimedia Commons.
The interesting surface properties of cermets also make them useful for reducing friction in machine parts. Some companies sell "ceramic metal conditioners" for engines that simultaneously make metal surfaces both smoother and tougher, reducing friction and wear at the same time, giving the dual benefits of greater fuel economy and longer engine life. Products such as this provide similar benefits to lubricants but work in an entirely different way by effectively modifying the surface structure of metal machine parts to make them behave more like ceramics. Since the particles involved are atoms and molecules, what we have here is a perfect example of nanotechnology in action.
Military applications of cermets include their use as lightweight protective coatings on clothing and friction-reducing surface layers on nuclear submarines.
Fuel cells (which work a bit like batteries, only making electrical power from a steady supply of fuel&#;maybe a tank of hydrogen or a solid fuel) are another exciting application. Because fuel cells work at high temperatures, cermets based on nickel metal (such as nickel yttria stabilized zirconia, Ni&#;YSZ, and nickel titania, NiTiO2) have long been the material of choice for their anodes (electrochemical terminals). [3] Cermets have also been used as a kind of nuclear fuel&#;in the shape of tungsten uranium dioxide (uranium dioxide in a tungsten matrix).[4]
What else will we use them for in future? Watch this space!
A cermet is a composite material composed of ceramic and metal materials.
A cermet can combine attractive properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation. The metal is used as a binder for an oxide, boride, or carbide. Generally, the metallic elements used are nickel, molybdenum, and cobalt. Depending on the physical structure of the material, cermets can also be metal matrix composites, but cermets are usually less than 20% metal by volume.
Cermets are used in the manufacture of resistors (especially potentiometers), capacitors, and other electronic components which may experience high temperature.
Cermets are used instead of tungsten carbide in saws and other brazed tools due to their superior wear and corrosion properties. Titanium nitride (TiN), titanium carbonitride (TiCN), titanium carbide (TiC) and similar can be brazed like tungsten carbide if properly prepared, however they require special handling during grinding.
Composites of MAX phases, an emerging class of ternary carbides or nitrides with aluminium or titanium alloys have been studied since as high-value materials exhibiting favourable properties of ceramics in terms of hardness and compressive strength alongside ductility and fracture toughness typically associated with metals. Such cermet materials, including aluminium-MAX phase composites,[1] have potential applications in automotive and aerospace applications.[2][1]
Some types of cermets are also being considered for use as spacecraft shielding as they resist the high velocity impacts of micrometeoroids and orbital debris much more effectively than more traditional spacecraft materials such as aluminum and other metals.
History
[
edit
]
Source:[3]
After World War II, the need to develop high temperature and high stress-resistant materials became clear. During the war, German scientists developed oxide base cermets as substitutes for alloys. They saw a use for this for the high-temperature sections of new jet engines as well as high temperature turbine blades. Today ceramics are routinely implemented in the combuster part of jet engines because it provides a heat-resistant chamber. Ceramic turbine blades have also been developed. These blades are lighter (less massive) than steel and allow for greater rotational acceleration (&#;spool-up time&#;) of the blade assemblies.
The United States Air Force saw potential in the material technology and became one of the principal sponsors for various research programs in the US. Some of the first universities to research were Ohio State University, University of Illinois, and Rutgers University.
The word cermet was actually coined by the United States Air Force, the idea being that they are a combination of two materials, a metal and a ceramic. Basic physical properties of metals include ductility, high strength, and high thermal conductivity. Ceramics possess basic physical properties such as a high melting point, chemical stability, and especially oxidation resistance.
The first ceramic metal material developed used magnesium oxide (MgO), beryllium oxide (BeO), and aluminum oxide (Al2O3) for the ceramic part. Emphasis on high stress rupture strengths was around 980 °C.[4] Ohio State University was the first to develop Al2O3 based cermets with high stress rupture strengths around °C. Kennametal, a metal-working and tool company based in Latrobe, PA, USA, developed the first titanium carbide cermet with a 19 megapascals (2,800 psi) and 100-hour stress-to-rupture strength at 980 °C. Jet engines operate at this temperature and further research was invested on using these materials for components.
Quality control in manufacturing these ceramic metal composites was hard to standardize. Production had to be kept to small batches and within these batches, the properties varied greatly. Failure of the material was usually a result of undetected flaws usually nucleated during processing.
The existing technology in the s reached a limit for jet engines where little more could be improved. Subsequently, engine manufactures were reluctant to develop ceramic metal engines. Interest was renewed in the s when silicon nitride and silicon carbide were looked at more closely. Both materials possessed better thermal shock resistance, high strength, and moderate thermal conductivity.
Cermet production, Helipot Division of Beckman Instruments,
[
edit
]
1. Steatite Ingredients Being Weighed
2. Steatite Granulation Process
3. Steatite Chip Pressing
4. High Temperature Firing of Steatite Chip
5. Beckman Model 61 Potentiometer (Cermet Screening)
6. Final Firing of Cermet
7. Checking electrical resistance
8. Final Assembly
[5]
Applications
[
edit
]
Ceramic-to-metal joints and seals
[
edit
]
Cermets were first used extensively in ceramic-to-metal joint applications. Construction of vacuum tubes was one of the first critical systems, with the electronics industry employing and developing such seals. German scientists recognized that vacuum tubes with improved performance and reliability could be produced by substituting ceramics for glass. Ceramic tubes can be outgassed at higher temperatures. Because of the high-temperature seal, ceramic tubes withstand higher temperatures than glass tubes. Ceramic tubes are also mechanically stronger and less sensitive to thermal shock than glass tubes.[6] Today, cermet vacuum tube coatings have proved to be key to solar hot water systems.
Ceramic-to-metal mechanical seals have also been used. Traditionally they have been used in fuel cells and other devices that convert chemical, nuclear, or thermionic energy to electricity. The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven generators designed to operate in corrosive liquid-metal vapors.[6]
Bioceramics
[
edit
]
Bioceramics play an extensive role in biomedical materials. The development of these materials and diversity of manufacturing techniques has broadened the applications that can be used in the human body. They can be in the form of thin layers on metallic implants, composites with a polymer component, or even just porous networks. These materials work well within the human body for several reasons. They are inert, and because they are resorbable and active, the materials can remain in the body unchanged. They can also dissolve and actively take part in physiological processes, for example, when hydroxylapatite, a material chemically similar to bone structure, can integrate and help bone grow into it. Common materials used for bioceramics include alumina, zirconia, calcium phosphate, glass ceramics, and pyrolytic carbons.
One important use of bioceramics is in hip replacement surgery. The materials used for the replacement hip joints were usually metals such as titanium, with the hip socket usually lined with plastic. The multiaxial ball was tough metal ball but was eventually replaced with a longer-lasting ceramic ball. This reduced the roughening associated with the metal wall against the plastic lining of the artificial hip socket. The use of ceramic implants extended the life of the hip replacement parts.[7]
Dental cermets are also used in dentistry as a material for fillings and prostheses.
Transportation
[
edit
]
Contact us to discuss your requirements of Epoxy Coated Steel Strand. Our experienced sales team can help you identify the options that best suit your needs.
Ceramic parts have been used in conjunction with metal parts as friction materials for brakes and clutches.[6]
Electrical heaters
[
edit
]
Cermets are used as heating elements in electric resistance heaters. One construction technique starts with the cermet material formulated as an ink which is printed on a substrate then cured with heat. This technique allows manufacture of complex shapes of heating elements. Examples of applications for cermet heating elements include thermostat heaters, heat sources for bottle sterilization, coffee carafe warmers, heaters for oven control, and laser printer fuser heaters.[8]
Other applications
[
edit
]
The United States Army and British Army have had extensive research in the development of cermets. These include the development of lightweight ceramic projectile-proof armor for soldiers and also Chobham armor.
Cermets are also used in machining on cutting tools.
Cermets are also used as the ring material in high-quality line guides for fishing rods.
A cermet of depleted fissile material (e.g. uranium, plutonium) and sodalite has been researched for its benefits in the storage of nuclear waste.[9] Similar composites have also been researched for use as a fuel form for nuclear reactors [10] and nuclear thermal rockets.[citation needed]
As nanostructured cermet, this material is used in the optical field, such as solar absorbers/selective surface. Thanks to the size of the particles (~5 nm), surface plasmons on the metallic particles are generated and enable the heat transmission.
See also
[
edit
]
Notes
[
edit
]
Further reading
[
edit
]
by Chris Woodford. Last updated: July 11, .
Humans have been shuffling round Earth for a couple of million years now&#;and you'd think, in all that time, we'd have discovered every material our planet has to offer. Not so! Our lives are still evolving, technologically much more quickly than biologically, and that means we constantly need to invent new materials and improve old ones. Some of the most exciting materials of recent decades are composites: combinations of two or more existing materials that combine the best properties of each. Cermets are composites in which ceramic materials and metals join together, typically to give something with the high temperature performance or wear resistance of a ceramic and the toughness, flexibility, or electrical conductivity of a metal. Let's take a closer look at what they are, how they work, and some of the ways we can use them!
Photo: Testing cermets in military armor at Lawrence Livermore National Laboratory. Photo by courtesy of US Department of Energy Digital Photo Archive (DOE).
Ceramic plus metal = cermet. It's really that simple! Why would you want to combine a metal and a ceramic? Metals, though versatile, aren't capable of withstanding the incredibly high temperatures you typically encounter in airplane jet engines or space rockets. Ceramics are brilliant at high temperatures and able to resist attack by chemicals and things like oxygen in the air, but their sheer inertness means they're just pretty boring most of the time. Brilliant for teapots and false teeth, but fairly hopeless when it comes to doing interesting things like conducting electricity or heat or bending and flexing. If you want something that can survive in really tough environments and still behave in interesting ways, you need to switch your attention to things like alloys, composites&#;and cermets.
"Cermet" is a generic name for a whole range of different composites. Sometimes the ceramic is the biggest ingredient and acts as the matrix (effectively the base or binder) to which particles of the metal are attached. Cermets used for electrical applications are typically made this way (in other words, they are examples of ceramic matrix composites or CMCs). But the metal component (typically an element such as cobalt, molybdenum, or nickel) can also be the matrix, giving what's called a metal matrix composite (MMC), in which hard ceramic particles are held together by a tough but ductile metal. Cermets used in things like cutting tools are made this way.
Artwork: What's a cermet like inside? Here's a simplified cermet microstructure (the fine inner, structure you'll see if you look at a cermet with a powerful microscope). In the type of cermet used in cutting tools, the core (gray) might be made of a ceramic such as tungsten carbide, while the binder (black stipples) could be made of a nickel alloy. The scale shown in red is approximately 20μm (20 microns). Most modern cermets designed for tools have a core material that's a carbide or nitride of titanium, tantalum, tungsten, niobium, or molybdenum, and a binder of nickel or cobalt.
Like other composites, cermets "work" by producing a material with a microstructure that has certain things in common with each of its different constituents. For example, the metal ingredient effectively allows electrons to flow through the material, enabling what would otherwise be a ceramic insulator to conduct electricity. That suggests cermets are relatively stable structures in which the metal and the ceramic are fixed in place&#;but that's not always the case. Under some conditions, cermets behave as though they have a dynamic surface layer, with metal particles constantly detaching and reattaching themselves. This effectively forms a smoother, harder, and more wear-resistant upper layer that makes a metal behave more like a ceramic.
Artwork: How do cermets conduct electricity? Here's the structure of a typical cermet made from particles of ceramic alumina (red), each of which is surrounded by platinum metal (blue). Although electricity doesn't normally flow through a ceramic, it can flow through a cermet (yellow arrowed line) by following a circuit through the platinum. Artwork based on a drawing from US Patent 4,183,746: Cermets by Stephen L. Pearce and Gordon L. Selman, Johnson, Matthey & Co., Limited, courtesy of US Patent and Trademark Office.
Apart from better electrical properties, the metal component of a cermet makes it more ductile (capable of being drawn thin into strands or wires). It also gives better resistance against thermal shock: often, if one part of a ceramic material (such as glass) is hotter than another, it will crack fatally or even shatter; the metal part of a cermet helps to avoid this by conducting the excess heat and dissipating it safely through the material.
Electrical components are one obvious application. Because they can get extremely hot, they need to behave like ceramics but, since they also need to conduct electricity, it helps if they work like metals. Cermets offer a perfect solution in components such as resistors and vacuum tubes (valves). Crudely, we can think of cermet resistors as a mixture of an insulator (the ceramic matrix) and a conductor (the metal particles), with the type and relative proportions of the two "ingredients" (ceramic and metal) determining the ultimate resistance.[1]
Artwork: An early design for a cermet-based electrical resistor from the s. The cermet (red, 10) is made from a nonconducting glass binder and conducting metal particles, mounted on a ceramic, insulating base (blue, 11), and connected to a circuit through two electrodes (green, 12/13). Artwork from US Patent 2,950,995: Electrical resistance element by Thomas M. Place, Sr. and Thomas M. Place, Jr., Beckman Coulter Inc., courtesy of US Patent and Trademark Office.
Machine tools are another increasingly common use for cermets, which offer greater toughness and wear resistance than more traditional materials. Titanium carbide (TiC), from which many cutting and drilling tools are made, is a popular choice of cermet for tools used in milling, turning and boring, and for making threads and grooves. Typically cermet tools are made from either titanium carbide alone, titanium carbide and titanium nitride (TiN), or titanium carbonitride (TiCN). Generally, cermets provide higher cutting-tool speeds, better surface finish, and last much longer than traditional tool parts. Unlike tools coated in carbide, cermet-coated tools do not wear in the same way but effectively regenerate themselves. [2]
Photo: Cutting tools made from cermets last longer and produce a better surface finish than traditional carbide tools. Photo by Eduardo Zaragoza courtesy of US Navy and Wikimedia Commons.
The interesting surface properties of cermets also make them useful for reducing friction in machine parts. Some companies sell "ceramic metal conditioners" for engines that simultaneously make metal surfaces both smoother and tougher, reducing friction and wear at the same time, giving the dual benefits of greater fuel economy and longer engine life. Products such as this provide similar benefits to lubricants but work in an entirely different way by effectively modifying the surface structure of metal machine parts to make them behave more like ceramics. Since the particles involved are atoms and molecules, what we have here is a perfect example of nanotechnology in action.
Military applications of cermets include their use as lightweight protective coatings on clothing and friction-reducing surface layers on nuclear submarines.
Fuel cells (which work a bit like batteries, only making electrical power from a steady supply of fuel&#;maybe a tank of hydrogen or a solid fuel) are another exciting application. Because fuel cells work at high temperatures, cermets based on nickel metal (such as nickel yttria stabilized zirconia, Ni&#;YSZ, and nickel titania, NiTiO2) have long been the material of choice for their anodes (electrochemical terminals). [3] Cermets have also been used as a kind of nuclear fuel&#;in the shape of tungsten uranium dioxide (uranium dioxide in a tungsten matrix).[4]
What else will we use them for in future? Watch this space!
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