Breviary Technical Ceramics


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 Sintered fused silica

Silicon oxide ceramics (SiO2) (also known as fused silica ceramics or quarzware5) are sintered from (amorphous) silicon dioxide powders. The goal is to obtain the typical properties of silicon dioxide, with its thermal expansion coefficient very close to zero, in ceramic components where those properties can be exploited. If the process is appropriately controlled, it is possible to retain the (amorphous) silicon dioxide phase in the sintered ceramic. The result is a ceramic with relatively low strength compared to the high strength oxide and non-oxide ceramics, but which has an extremely high thermal shock resistance as a direct result of the extremely low thermal expansion of the amorphous silicon dioxide phase.

Figure 29: Microstructure of sintered fused silica

The maximum application temperature of 1,050° C should not be exceeded. Correspondingly, the application of these ceramics lies in areas where extreme thermal shocks are experienced and in the

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5) The term ‘Quartzware’ originates from the manufacture of quartz glass. Due to the wide variety of methods used to manufacture more or less pure SiO2 glasses, they are grouped nowadays from the scientific point of view under the general heading of silica glass. Chemically, transparent silica (quartz) glass, which is manufactured from a quartz sand or rock crystal, is practically identical to non-transparent quartzware ceramics. The primary difference between silica glass and quartzware is therefore just the different transparencies. From a scientific point of view, the term ceramic quartzware is wrong, since it does not contain crystalline phase SiO2, but just particles of quartz glass.