Special Ceramics Now in an Important Position:
Special ceramics have a variety of molding methods such as hot die casting, hot pressing, static pressure and vapor deposition. These ceramics are called special ceramics or high-tech ceramics because their chemical composition, microstructure and properties are different from ordinary ceramics. It is called fine ceramics in Japan.
New Development Trend of Special Ceramics:
A. new developments in technology of special ceramics:
(1) In terms of powder preparation of special ceramics, the most noticeable technology is ultra-high temperature technology. Using ultra-high temperature technology can not only develop special ceramics cheaply, but also develop new types of glass cheaply, such as optical fiber, magnetic glass, hybrid integrated circuit board, zero expansion crystalline glass, high strength glass, artificial bone and tooth stick. In addition, special ceramics can also use ultra-high temperature technology to develop materials such as tantalum, molybdenum, tungsten, ferrovanadium alloy and titanium that can be used in cutting-edge fields such as space flight, ocean, and nuclear fusion. For example, Japan produces diamond at 4000-15000 ℃ and below one atmosphere, and its efficiency is 120 times higher than the commonly used low-temperature and low-pressure plasma technology.
(2) Special ceramics in the molding: special ceramic molding methods are generally divided into dry molding and wet molding two categories, dry molding including steel mold pressing molding, isostatic pressing molding, ultra-high pressure molding, powder electromagnetic molding, etc.; wet molding can be roughly divided into plastic molding and colloidal casting molding two categories. In recent years, colloidal molding and solid molding technology have also made rapid development in the molding research of special ceramics.
Special ceramic colloidal forming is a wet forming of highly dispersed ceramic slurry. Compared with dry forming, it can effectively control agglomeration and reduce defects. Die-free forming is actually the application of Rapid prototyping manufacturing technology (RP & M) in the preparation of ceramic materials. The colloidal non-mold forming process of special ceramic materials is a process of directly converting ceramic slurry with or without binder from liquid to solid under certain conditions, and then manufacturing special ceramic green bodies layer by layer according to the principle of RP & M. The green bodies of special ceramics after forming generally have good rheological properties, which can ensure no deformation during the post-treatment process.
(3) Sintering of special ceramics: Due to its special performance requirements, special ceramic products need to use different firing processes and sintering technologies from traditional ceramic products. With the development of the special ceramic industry, breakthroughs have been made in the research of its firing mechanism, sintering technology and special kiln facilities. The main sintering methods of special ceramics are: atmospheric sintering method, hot pressing sintering/hot isostatic sintering method, reaction sintering method, liquid phase sintering method, microwave sintering method, arc plasma sintering method, self-propagating sintering method, vapor deposition method, etc.
(4) In the precision processing of special ceramics: special ceramics are brittle materials with high hardness and brittleness. Their physical and mechanical properties (especially toughness and strength) are quite different from those of metal materials, with poor processing performance and difficult processing. Therefore, studying the grinding mechanism of special ceramic materials and choosing the best grinding method are the main problems to be solved at present.
B. new developments in the application of special ceramics:
(1) Special ceramics with excellent heat resistance are expected to be used as ultra-high temperature materials for high temperature structural materials related to atomic energy, high temperature electrode materials, etc;
(2) Special ceramics with excellent heat insulation can be used as new high-temperature heat insulation materials for high-temperature heating furnaces, heat treatment furnaces, high-temperature reaction vessels, nuclear reactors, etc;
(3) Special ceramics with excellent thermal conductivity are highly expected to be used as heat sinks with large-scale integrated circuits and ultra-large-scale integrated circuit electronic devices inside;
(4) Hard special ceramics with excellent wear resistance are widely used, and today's work is mainly focused on bearings and cutting tools;
(5) High-strength special ceramics can be used for combustors, blades, turbines, bushings, etc. of gas turbines; in processing machinery, it can be used for machine tools, bearings, combustion nozzles, etc. Many countries, such as the United States, Japan and Germany, have invested a lot of manpower and material resources in an attempt to gain a leading position. These ceramics include silicon nitride, silicon carbide, cylon, aluminum nitride, zirconia, etc;
(6) The lubricity of special ceramics, such as hexagonal boron nitride, is extremely noticeable and is being studied abroad;
(7) Research on the use of alumina, phosphorus and carboniferous as artificial teeth, artificial bones, artificial joints, etc. in bioceramics in special ceramics is being carried out, and the application in this area has attracted great attention;
(8) Some new functional ceramics with other special purposes in special ceramics (such as far infrared ceramics, etc.) have also begun to play their unique role in industrial and civil fields.
Research and development priorities;
The production of special ceramic products has a long history in China. After long-term development, the manufacturing process has been continuously developed. Especially in the past two decades, the reasonable adjustment of the structure of special ceramic products has catered to the consumption needs of consumers at home and abroad, and with the development of society and the improvement of living standards, it will be more and more widely used in life.
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