Vitreous silica melting point

Air or water cooled mercury discharge lamps find many uses, one of the more obvious of which is the study of photochemical reactions. These lamps are usually made of vitreous silica because of its low thermal expansion, high melting point and its transparency to ultraviolet radiation. Their operating pressure has a profound effect on the spectral distribution of the radiation produced and therefore it is important to consider the requirements in the design of such lamps. 

Glazes are thin, transparent coatings (colored or colorless) fused on ceramic materials. Vitreous enamels are thin, normally opaque or semiopaque, colored coatings fused on metals, glasses, or ceramic materials. Both are special glasses but can contain little silica. They have typically low melting points and are often not easily mixed in with more traditional glasses. 

Metals do not generally react with vitreous silica below 1000°C or their melting point, whichever is lower. Exceptions are aluminum, magnesium, and alkali metals. Aluminum readily reduces silica at 700—800°C. Alkali metal vapors attack at temperatures as low as 200°C. Sodium vapor attack involves a diffusion of sodium into the glass, followed by a reduction of the silica. 

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