24-02-1965 дата публикации
Номер: GB984446A
Автор:
A devitrified glass is formed by making a crystallizable glass, producing a frit from the amorphous mass formed by melting the glass, reducing the frit to a powder, heating the powder to a temperature sufficient to cause the particles of the powder to coalesce and maintaining the glass at a crystallizing temperature to partially crystallize it. Before maintaining the coalesced powder at a crystallizing temperature, the powder may be maintained at a nucleation temperature to cause the formation of crystal nuclei therein and subsequently maintained at a temperature sufficient to cause the particles in the powder to coalesce but insufficient to destroy the nuclei therein. The glass is particularly for use in coating metal surfaces, the coating being with the powder form so that an even coating is produced on heating to devitrification. Particular glasses are chosen to have a coefficient of expansion to give residual compressive stress of 8,000-30,000 p.s.i. in the coating surfaces. A number of examples are given comprising in weight percentages, SiO2 40-70; alkali metal oxides 10-25 and one or more of TiO2, Al2O3, CeO2, MnO2, ZrO2, B2O3, Fe2O3, Sb2O3, Cr2O3, CaO, ZnO and SrO. The crystal phases of these glasses may be b -spodumene, b -eucryptite, lithium titanium silicate, rutile, brookite, lithium disilicate, sphene, crystabolite, Mg2TiO4, Mg2TiO3 or Mg2TiO5. The glass coating may be applied over the usual ground enamel, a composition for which is given. Specification 829,447 is referred to.
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