Fluidity of glass

SiOj A substance that forms the network structures of glass. It has a high melting point and hi viscosity. If the silica content in glass is high, the glass has a high transition temperature, low thermal expansion, and excellent chemical durability. 

BjOi A substance that forms network structures. Added to the network structure of quartz glass, it reduces viscosity without any negative impact on thermal expansion and chemical durability. If is one of the ingredients of heat-resisting glass and chemical glassware. 

PbO Although it does not form network structures, it can connect Si04 tetrahedrons. It is used for glass with a large dielectric constant, refractive index and specific resistance. As it is easily deoxidized, heat treatment in an atmosphere containing oxygen is necessary. 

NE20 A modifier oxide. It lowers the sofiening point markedly. Furthermore, it increases the thermal expansion coefficient and ionic conductance. It also reduces chemical durability. 

K20 A modifier oxide. Although it has the same effect as NajO, its K. ion is comparatively large and therefore immobile. 

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