According to the development history of Chinese special ceramics, the preparation technology of Chinese special ceramics has developed rapidly in just a few decades, and special ceramics have become one of the indispensable new materials in today's society. However, the industrialization of special ceramics in our country is still restricted by many factors. Rao Pinggen, professor of the School of Materials, South China University of Technology, believes that raw materials, technology and equipment are the bottlenecks in the development of domestic special ceramics. Special ceramics require high purity and sintering activity of raw materials, and at present all kinds of high-end raw materials are in Japan; In technology, our special ceramics production technology level and overall strength compared with the United States, Japan, especially in the practical application, production level and degree of industrialization is still far from the developed countries; For sintering equipment, because the non-oxide materials such as carbide, boron ide and silicide require very high sintering equipment, while the equipment used in our country mostly relied on foreign imports, and sintering equipment is very expensive.

It is understood that special ceramics using artificial refined chemical raw materials and synthetic raw materials as the main raw materials, because the raw materials are pure compounds, so its composition is determined by the artificial ratio, and traditional ceramics using natural mineral raw materials as the main raw materials, the composition is determined by the origin of clay, feldspar, quartz. Therefore, it is very important to effectively control the preparation process of special ceramic and make it reach the predetermined structure for improving the performance of special ceramic materials, further exploring its new functions and improving the use efficiency. At present, the preparation technology of special ceramic materials is not mature enough, and many mechanisms are not very clear, so it is difficult to achieve the required properties and use efficiency. The firing of special ceramics is mainly carried out in various electric kilns or furnaces, such as tunnel kiln, tube furnace, bell jar furnace, box furnace, vertical lifting furnace and other kilns. Generally, air atmosphere is used for firing, and some functional ceramic products are fired in reducing atmosphere, oxidation atmosphere, neutral atmosphere or vacuum atmosphere.

Special ceramics corrosion resistance, high hardness, wear resistance, thermal shock resistance and other characteristics make its application scope further expanded, however, as ceramic materials, special ceramics have its fatal weakness -- brittleness. The direct manifestation of the brittleness of ceramics is: the fracture under the action of external load is without warning, explosive; Indirect performance is: no mechanical impact and temperature variability. Brittleness is determined by the chemical bond properties and crystal structure of ceramic materials. In addition, there are a large number of microcracks in ceramic materials, which are easy to cause a high concentration of stress, resulting in brittle fracture of ceramic materials.

Therefore, how to improve the brittleness and toughness of ceramic materials has become one of the long-term concerns of ceramic workers. Through the research in recent decades, it has been confirmed that the main ways to improve the brittleness of ceramics and strengthen ceramics are: 1. 2. Microcrack toughening and surface toughening; Three, particle dispersion strengthening and toughening; 4. Fiber (whisker) reinforcement and toughening; 5. Nanometer ceramics are strengthened and toughened.

At the same time, the heterogeneity and complexity of the microstructure of ceramic materials directly determine the special mechanical and physical properties of special ceramic materials. These structural characteristics make the ceramic materials have the advantages of high melting point, wear resistance, high strength, corrosion resistance and so on, but also have the fatal weaknesses of high brittleness, difficult processing, poor reliability and reproducibility.

The development direction of special ceramics

As a new material, special ceramics are highly valued by people because of their excellent performance. So, what are the development directions of special ceramics in the future?

In the preparation of nano-powders, the gas phase condensation method will become the focus of the research and development of special ceramic powders. With the improvement of the performance of special ceramic products, the performance of the powder used will be more demanding. The traditional powder preparation method can not be used, only the gas phase condensation method can achieve this goal. The gas phase condensation method is to directly use the gas phase or through various means to change the substance into a gas, so that it can undergo biochemical reaction or physical change under the gas state, and then form nano ceramic powder in the rapid cooling process. The main methods include gas evaporation method, chemical gas phase reaction method, arc plasma method, high frequency plasma method, electron beam method and laser method.

Second, in terms of raw materials, the application of nanomaterials will bring new vitality to special ceramic materials. Nanomaterials refer to particles or structures, crystals or nano-composite materials in the range of nanometer length (1~100nm). Nanomaterials can fundamentally improve the brittleness of special ceramic materials, which is the fatal weakness, and realize the plastic deformation and even superplastic deformation processing of ceramics. In terms of function, the electrical, optical, thermal and magnetic properties of nano-functional ceramics have mutations, which opens up a wide range of application prospects for micro-coating, super filtration, adsorption, deodorization, catalyst, heat transfer, optical functional components, electromagnetic components, as well as life comfort and environment improvement.

Thirdly, in terms of molding technology, rapid prototyping (RPM) and colloidal molding will challenge traditional molding technology. Traditional forming technology mainly includes extrusion forming, dry pressing forming, hot die casting forming, rolling film forming, rolling process forming, printing forming, isostatic pressing forming, grouting forming, car blank forming and so on. Different from traditional molding methods, RPM technology uses integral method to manufacture 3D entity. In the molding process, 3D modeling software is first transformed into 3D solid model of components in the computer, and then the 3D solid model is "cut" out several micron thick layers by software. Then the data information of these layers is transmitted to the molding machine and manufactured by adding material layer by layer. It can form complex special ceramic parts without mold.

The colloidal forming technology of special ceramics combines the ordinary ceramic grouting molding process and polymer chemistry. The technology uses organic monomer polymerization to form a network of macromolecules to solidify the ceramic paste into a blank in situ.

Fourth, in terms of sintering methods, microwave sintering and spark plasma sintering (SPS) are effective methods to obtain nano bulk ceramic materials. Microwave heating uniform, high speed (can reach 500℃/min above), energy saving and can achieve high temperature above 2000℃ and many other advantages, but also can be used for ceramic welding, for the production of complex special-shaped ceramics or ceramic parts repair conditions. Discharge plasma sintering is a process in which the local high temperature of several thousand degrees to ten thousand degrees is generated instantaneously to condense the contact points of the grains, accelerate the evaporation and condensation of the matter transfer, and obtain high quality nano-bulk ceramic sintered in a relatively short time.