Physical and Metallurgical Characteristics of Fiber Reinforced Ceramic Matrix Composites
Advances in Ceramics - Characterization, Raw Materials, Processing, Properties, Degradation and Healing
Introduction Ceramics represent a very wide range of materials, which differ from each other by their chemical composition, structure and properties. These materials can be defined as predominantly crystalline materials, formed mainly by inorganic compounds of nonmetallic character, which are bound particularly by ionic and ion-covalent bonds. Ceramics are most frequently divided by the purpose of its use into traditional and structural ceramics. Traditional ceramics are produced entirely from
... uced entirely from natural raw materials (such as kaolin, clays, quartz, feldspar), which are formed and fired. These ceramic materials can also be designated as vitreous or porous due to the fact that they contain a considerable portion of vitreous phase, pores and crystals of various compositions. Traditional ceramics can be further divided into constructional, artistic, utility and refractory. Structural ceramics are produced only from synthetic raw materials. It is a newer type of ceramic, which has a considerable development from the seventies of the 20th century. It is used in numerous technical applications, especially under extreme conditions where, thanks to its properties, completely replaces the traditional ceramics. These ceramic materials include also functional and bio-ceramic materials. Structural ceramics represent a fine-grained, poly-crystalline material, usually with grains smaller than 1 µm. It contains random technological defects and micro-structural heterogeneities. The structure of ceramic materials can be characterized as heterogeneous, poly-crystalline and poly-phased. Classification of structural ceramics Oxidic ceramics The ceramics based on aluminium oxide (Al 2 O 3 ) called also sintered alumina (Al 2 O 3 with addition of ZrO 2 ) has the biggest significance for structural applications. Thanks to the zirconium oxide this ceramics has better mechanical properties. Increasing the Al 2 O 3 content increases its mechanical strength and hardness, as well as thermal expansion coefficient. Oxidic ceramics have high strength, hardness, corrosion resistance, and they are very good electric insulators. They are used mainly at the machining of cast iron, as a structural material for components of high-temperature devices, melting crucibles, cutting plates for metals machining, spark plug insulators for engines, etc.