Ceramic materials

Modern ceramic materials are a new type of ceramics that are developed from traditional ceramics based on special ceramics and have distinctive characteristics that are different from traditional ceramics. It has long gone beyond the concept and scope of traditional ceramics. It is a product of high and new technology. Therefore, ceramic materials are an ancient and young subject.

The so-called modern ceramic materials are inorganic non-metallic materials. It is one of the three major categories of modern materials alongside metals and organic materials. It is also the general recognition of all materials except metal materials and organic materials. The object of discussion in this chapter is modern ceramic materials or modern inorganic non-metallic materials.

Modern ceramic materials have high-tech connotations. Compared with traditional materials. It mainly has the following three characteristics:

(1) Based on the requirements of modern scientific and technological develoPment. It is the product of the development of modern science and technology and is a high-tech product.

(2) The manufacturing process is complex and requires the guidance of modern scientific and technological achievements. Therefore, it is a technical knowledge-intensive product.

(3) It has excellent and special properties and can meet the requirements of commercial and new technology industries.

Classification of ceramic materials

With the development of production and science and technology. The types of ceramic materials and products are increasing day by day. In order to facilitate the understanding of the characteristics of various materials or products, they are usually classified from different angles.

1. Classification by chemical composition

(1) Oxide ceramics. There are many types of oxide ceramics, which occupy a very important position in the ceramic family. The most commonly used oxide ceramics are Al2O3, SiO2, MgO, ZrO3, CeO2, CaO. Cr2O3, mullite (3Al2O3.2SiO4) and spinel (MgAl2O3), etc. Al2O3 and SiO2 in ceramics are as widely used as steel and aluminum alloys in metallic materials. Some oxide ceramics are listed in Table 11.1. Silicates also belong to the oxide series. Such as ZrsiO4. Call has waited. There are also composite oxides such as BaT, CgyiO; etc. also fall into this category.

Ceramic materials are classified by chemical composition

(2) Carbide ceramics. Carbide ceramics generally have a higher melting point than oxides. The most commonly used ones are SIC, SC, Phoenix C. TIC etc. Carbide ceramics should have atmosphere protection during the preparation process.

(3) Amide ceramics. The most widely used chloride is a-ji, which has excellent comprehensive mechanical properties and high temperature resistance. In addition, the applications of TZN, BN, and AI nitride ceramics are becoming increasingly widespread. C3N4, which has just appeared recently, is expected to have better performance than Si3O4.

(4) Four chemical ceramics. The applications of boride ceramics are not very wide. They are mainly used as deep additives or second phases to be added to other ceramic matrices to improve performance. Commonly used ones include Ti, Zr&, etc.

2. Classification by performance and use

(1) Structural ceramics. Structural ceramics are used as structural materials to manufacture structural parts. Mainly use its mechanical properties. Enhanced strength, toughness, hardness, modulus, wear resistance, high temperature resistance (high temperature strength, thermal shock resistance, ablation resistance), etc. Most of the four ceramics classified by nuclear chemical composition mentioned above are structural ceramics. Such as AjZQ stone. 3N4 and ZX are representative structural ceramic materials with superior mechanical properties.

(2) Functional ceramics. Functional ceramics are used as functional materials to manufacture functional devices, mainly using their physical properties such as electromagnetic properties, thermal properties, optical properties, biological properties, etc. For example ferrite. Ferroelectric ceramics are mainly used for their electromagnetic properties. It is used to make electromagnetic components, dielectric ceramics are used to make capacitors, and piezoelectric ceramics are used to make displacement or pressure sensors. Solid electrolyte ceramics can be used to make oxygen detectors using their ion transfer properties. Bioceramics are used to make artificial bones and artificial teeth. Superconducting materials and optical fibers also belong to the category of functional ceramics.

It is worth mentioning that the above classification is also relative. Rather than being absolute, there is sometimes no strict boundary between structural ceramics and functional ceramics. For some ceramic materials, there is both. Piezoelectric ceramics. Although it can be classified as functional ceramics, it also has certain requirements for its mechanical properties, such as strength, toughness, hardness, and elastic modulus. First of all, it must have sufficient strength to prevent damage when withstanding E force, so that common piezoelectric characteristics can be achieved. In addition, such as high-temperature structural ceramics or thermal shock-resistant and fire-resistant ceramics for spacecraft heat-proof parts, although they belong to the category of structural ceramics. However, the thermal expansion resistance is not only determined by its own strength, toughness, and modulus, but the thermal conductivity and thermal expansion coefficient are also the same as the mechanical properties, which have a very important impact on the thermal shock resistance. Corrosion resistance is an important performance of chemical ceramics (such as acid-resistant pumps), but it must have certain mechanical properties to meet the requirements of the industry. Superconducting materials are difficult to make into wires because they are highly fatty. Therefore, it cannot yet enter the practical application stage. To sum up, whether it is structural ceramics or functional ceramics, mechanical properties are the most basic properties of ceramic materials. It's just that different uses have different requirements for mechanical properties.

This chapter discusses mainly structural ceramics.

Advantages of ceramics

1. Performance characteristics of ceramic materials

As we all know, the chemical bonds of metallic materials (pure gold or alloys) are mostly metals. They are composed of metal positive atoms and electron clouds filling them. Metal bonds have no directionality. Therefore, the metal has good plastic deformation properties. As for ceramics that ignore non-metallic compounds, their chemical properties are higher than health and covalent bonds. This chemistry has strong directionality and high binding energy. Therefore, it is difficult for ceramic materials to undergo plastic deformation. High brittleness and strong crack sensitivity. This is the Achilles heel of ceramic materials. But it is precisely because of this chemical bond type that structural ceramics have a series of special properties that are superior to metallic materials.

①High hardness determines its excellent wear resistance;

②High flame point. Determined that it has outstanding heat resistance;

③High chemical stability. It determines that it has good corrosion resistance.

Although ceramic materials have such excellent advantages. However, its fatal disadvantage—brittleness—limits its performance and practical applications. Therefore, the toughening of ceramics has become a core topic in the field of ceramic materials research that attracts worldwide attention (see the toughening of ceramics section for details).

2. Comparison between modern (advanced) ceramics and traditional ceramics

Modern ceramics compared with traditional ceramics. There are significant differences in raw material composition, preparation process, organizational structure and performance.

Contrast between traditional ceramics and modern ceramics