Alkali resistant protective coating for glass contg. lead - used esp. on glass solder in electron tube contg. alkali metal photocathode

摘要

The coating consists of a paste contg. SiO2 dissolved in lye, together with phosphates, borates, or inorganic oxide pigments. The inorganic oxide pigments pref. possess a spinel- or an inverse spinel-structure; and the grain size of the pigments in the paste is pref. below 1 m mu, esp. of size 0.1-0.5 m mu. A pref. pigment used in the paste is cobalt aluminate; and the coating is used esp. on glass surfaces inside an electron tube, partic. in an electron tube contg. a photocathode. The coating prevents the redn. by alkali metal vapour of lead constituents in the glass to elementary lead.