Zirconium boride is a relatively common material in boride, and there are three types of zirconium boride in the boron-zirconium system, namely zirconium boride (ZrB), zirconium diboride (ZrB2) and dodecaboron Zirconium dichloride (ZrB12), but zirconium diboride has good stability in a wide temperature range, so most of the zirconium boride produced in industrial production is mainly composed of zirconium diboride.
1. Characteristics of zirconium diboride ceramic material
Zirconium diboride has extremely high melting point, strength, hardness and electrical conductivity (and the temperature coefficient of electrical conductivity is positive), as well as a low coefficient of thermal expansion, good electrical and thermal conductivity and chemical stability.
2. Preparation of zirconium diboride ceramic material
① Preparation of ZrB2 powder
The preparation of ZrB2 powder mainly uses zirconium or high oxide for boronization. The traditional synthesis method is to realize the oxide carbon thermal reduction process in a high temperature induction furnace or resistance furnace. This method has a simple process, but the temperature is generally higher (about 1800 ℃), the purity of the synthetic powder is lower, and the average particle size is larger , Poor sintering activity. At present, carbon thermal reduction method, high temperature self-propagating method, mechanical alloying method, ceramic precursor cracking method, liquid phase method, etc. are mostly used.
②ZrB2 ceramic molding method
There are many molding methods for ZrB2, such as isostatic pressing molding, dry pressing molding, grouting molding, and injection molding. People can choose different molding methods according to their needs and actual conditions. In order to increase the density of the product and reduce the sintering temperature, most people use hot pressing sintering, which is a process of forming and sintering at the same time, but only ZrB2 ceramic products with simple shapes can be obtained.
③ZrB2 ceramic sintering method
The traditional sintering methods of ZrB2 materials include pressureless sintering and hot pressing sintering, and the new sintering methods include in-situ reaction hot pressing, high temperature self-propagating sintering and spark plasma sintering.
3. Application examples of zirconium diboride ceramic materials
Zirconium diboride ceramics are valued and applied in the fields of high-temperature structural ceramic materials, composite materials, refractory materials, electrode materials, and nuclear control materials because of their high melting point and hardness, good electrical and thermal conductivity, and strong neutron control capabilities. Such as: turbine blades, magnetic fluid power generation electrodes in the aviation industry. In addition, compared with many ceramic materials, it has better electrical conductivity, and can produce complex-shaped parts by wire cutting technology.
①Refractory
ZrB2 ceramics are excellent special refractory materials, which can be used as high temperature thermocouple protection sleeves, casting molds, metallurgical metal crucibles, etc. When used as thermocouple protection sleeves, due to their poor airtightness and conductivity. Therefore, it must cooperate with the alumina inner sleeve to carry out effective temperature measurement. The thermocouple sleeve of this material can be used continuously for a long time in the molten molten iron and brass melt. ZrB2 ceramics can also be used as antioxidants for refractory materials.
② Electrode material
ZrB2 has low electrical resistivity and electronic conduction mechanism. It is suitable for electric shock materials and electrode materials. It can be used in electrodes and high-temperature heating elements of metal thermocouples. In 1994, a researcher developed a pair of ZrB2 and graphite paired thermocouple materials. Experiments have shown that they can work in an oxidizing atmosphere at 1200~1600℃. The thermocouple value is large, and it can reach about 70mV at 1600℃. , The thermoelectric potential rate is higher. It can play a role in continuous temperature measurement in some special occasions where metal thermocouples and radiation thermometers are not suitable. It is a very good thermocouple material.
③Other applications
Because of its extremely high hardness, ZrB2 is a good wear-resistant material and has good applications in cutting tools and cutting tools. Because ZrB2 has good corrosion resistance, foreign researches on ZrB2's anti-corrosion and anti-oxidation films are in-depth.
Zirconium diboride ceramics are valued and applied in the fields of high-temperature structural ceramic materials, composite materials, refractory materials, electrode materials, and nuclear control materials because of their high melting point and hardness, good electrical and thermal conductivity, and strong neutron control capabilities. ZrB2 ceramic is an excellent special refractory material, which can be used as a high temperature thermocouple protective sleeve…