Alumina ceramics and zirconia ceramics
Special ceramics, also known as fine ceramics, are a type of inorganic non-metallic materials made from high-purity inorganic non-metallic raw materials through precise forming and sintering processes. Unlike traditional ceramics, they do not use natural minerals such as clay as the main raw materials. Instead, relying on artificially synthesized high-purity raw materials and advanced preparation technologies, they occupy an irreplaceable important position in the fields of modern industry and science and technology.
Special ceramics can be divided into a wide variety of types according to their chemical composition, including oxide ceramics (such as alumina, zirconia, etc.), nitride ceramics (such as silicon nitride, aluminum nitride, etc.), carbide ceramics (such as silicon carbide, boron carbide, etc.), boride ceramics (such as zirconium boride, lanthanum boride, etc.), as well as composite ceramics composed of multiple compounds and cermets with added metals. According to their application functions, they can be roughly divided into two categories: high-strength, high-temperature resistant and composite structural ceramics, and electrical and electronic functional ceramics.
From high-temperature resistant components in the aerospace field to chip packaging and sensor elements in the electronics industry; from fuel cell components in the energy sector to artificial joints and dental restoration materials in the biomedical field, special ceramics are everywhere. It is like an unsung hero, silently driving the progress of modern science and technology and changing our lives.
Alumina Ceramics: Properties and Applications
(1) Performance Characteristics
Alumina ceramics, with alumina (Al₂O₃) as the main component, occupy an important position in the field of special ceramics due to their excellent performance. They have extremely high hardness, with a Rockwell hardness of HRA80 - 90, second only to diamond, which makes them perform excellently in wear-resistant applications. In wear resistance tests, the wear resistance of alumina ceramics is 266 times that of manganese steel and 171.5 times that of high-chromium cast iron. Under the same working conditions, they can extend the service life of equipment by at least ten times or more.
The density of alumina ceramics is approximately 3.8g/cm³, which is only half that of steel, effectively reducing the load on equipment. It also has excellent chemical stability, being able to resist corrosion from chemicals such as strong acids and alkalis, thus finding wide application in corrosive environments like the chemical industry. Its high-temperature resistance is also very prominent, capable of withstanding temperatures up to 1600℃ or even higher, and it can be used as a lining for high-temperature furnaces and refractory materials.
(2) Application Fields
In the mechanical field, due to its high hardness and wear resistance, alumina ceramics are used to manufacture cutting tools, bearings, seals, etc. The cutting speed of alumina ceramic cutting tools is higher than that of general cemented carbide cutting tools, which can greatly improve cutting efficiency. Composite Al₂O₃ ceramic cutting tools can also process various materials such as hardened steel and alloy steel.
In the field of electronics and electric power, alumina ceramics are widely used. They have good insulation and thermal conductivity, and can be made into ceramic substrates, wafers, ceramic films, transparent ceramics and insulating devices, etc. For example, alumina ceramic substrates, with high mechanical strength, good insulation and high light-shielding property, are often used in multi-layer wiring ceramic substrates, electronic packaging and high-density packaging substrates.
In the chemical industry, alumina ceramics can be used to make linings of reaction kettles, pipelines, valves, etc. With their chemical stability and corrosion resistance, they can resist erosion from various chemical media, ensuring the safe and stable operation of chemical production.
Zirconia Ceramics: Properties and Applications
(1) Performance Characteristics
Zirconia ceramics, with zirconia (ZrO₂) as the main component, have excellent performance. They have relatively high hardness, with a Mohs hardness of 7 - 8, and perform excellently in wear-resistant applications. Under the same friction conditions, the wear loss of zirconia ceramics is only one-tenth of that of ordinary metal materials.
Its toughness is also very prominent, with a fracture toughness of 7 - 15 MPa・m¹/², which is much higher than that of ordinary ceramics. It can effectively resist crack propagation and is not easy to break. Its wear resistance is excellent, being more than 200 times that of stainless steel, and it has significant advantages in high-wear environments.
Zirconia ceramics also possess good insulating properties. They are excellent insulators at room temperature and can meet the insulation requirements in the electronic and electrical fields. Their high-temperature resistance is also noteworthy, with a melting point as high as 2700℃, enabling them to be used stably in high-temperature environments.
(2）Application Scope
In the field of structural ceramics, zirconia ceramics are often used to manufacture cutting tools, bearings, valves, etc. Zirconia ceramic cutting tools are sharp and durable, with excellent cutting performance. They can process a variety of difficult-to-cut materials and do not react with food, so they can be used to make table knives, surgical knives, etc. Zirconia ceramic bearings have the advantages of high temperature resistance, corrosion resistance and wear resistance, and are widely used in high-speed and high-precision equipment.
In terms of functional ceramics, zirconia ceramics can be made into oxygen sensors, solid oxide fuel cell electrodes, etc. Oxygen sensors, utilizing their conduction characteristics for oxygen ions, can quickly and accurately detect the oxygen content in the environment, and are widely used in fields such as automobile exhaust detection and industrial combustion control.