Silicon Carbide Research Paper

SILICON CARBIDE CERAMICS AND SINTERING PROCESS

1.1 SILICON CARBIDE CERAMICS

Silicon carbide is a member of the group of materials known as the non-oxide ceramics. They are generally compounds of metals and semi-metals with non-metallic elements other than oxygen. This group of ceramic materials include carbides, nitrides and borides and silicon carbide is one of the most widely used. Silicon carbide is known for its hardness, very high melting point and also for other extremely useful properties. It is widely used in industrial applications as refractory material, as abrasives and recently as a structural ceramic of high grade with very good wear resistance.

Silicon carbide does not occur

Almost all ceramic bodies must be sintered to produce a microstructure with the required properties. From the view of processing of ceramic powders the word sintering defines a high temperature heat treatment bringing about the bonding of powder particles and the development of the grain boundaries with the elimination of much of the inter particle pores or void spaces. The temperatures used are high, but not high enough to melt the major phase of the material. Sometimes liquid may be produced from impurities, or from specially added ingredients during sintering. At high temperatures, atoms develop sufficient mobility and the powder particles reshape themselves to develop interparticle bonding with formation of grain boundaries. This reshaping process occurs as the system tries to minimise its energy, specifically the interfacial or surface energy. During sintering in addition to the bonding of the powder particles some chemical reactions may occur, with the result that the sintered product may contain crystalline phases or glasses, which were not present in the original starting powder mixture. The sintering operation is therefore a very complex series of processes and

Fig 3.1 Archimedes density measurement apparatus

3.2.2 MICROSTRUCTURE

Microstructure is defined as the structure of a material revealed by microscopy. The microstructure of a material can strongly influence the physical properties such as strength, toughness, hardness, high/low temperature behaviour, wear resistance and so on, which in turn govern the application of these materials.

3.2.2.1 OPTICAL MICROSCOPY

Optical or light microscopy is the primary means for scientists and engineers to examine the microstructure of materials. A light microscope use either transmitted or reflected light for illumination. Reflected light microscopes are most commonly used for metallography studies, while transmitted light microscopes are used to examine transparent or semi-transparent materials mainly in biological studies. The main components of light microscope are illumination system, objective lens, eyepiece and movable specimen stage. The differences in properties of the light waves which are reflected from microscopic objects enable one to observe these objects by light microscopy. The light wave changes either in amplitude or phase when it interacts with an object.