Improvements in the preparation of ferrous surfaces to receive a vitreous enamel

摘要

A ferrous surface is prepared to receive one or more coats of vitreous enamel by forming a coating of one or more As compounds, Sb compounds and Bi compounds on the surface, and then heating the coated surface in an oxydizing atmosphere to form an iron oxide coating containing As, Sb or Bi or a mixture of two or more of these. The coatings can be formed on enamelling iron and on low-carbon and alloy steels. Preferably, an acidic (acidified by a strong inorganic acid e.g. HCl, H2SO4HNO3) aqueous solution of As, Sb and Bi compounds is used: suitable compounds are As2O5, As2O3, Na3AsO3, NaH2 AsOz, Na2HAsO4, Sb2O3, Sb2O4, Sb2O5 and (BiO)2 CO3. The compounds are preferably in their highest valency states and it is thus preferred to add to the solution an oxidizing agent such as sodium chlorate, hydrogen peroxide. sodium nitrate, sodium nitrate, sodium nitrobenzene sulphonate, sodium bromate, sodium dichromate, potassium permanganate or potassium persulphate. The iron oxide may be formed by rinsing the coating in cold water and immediately introducing the wet oxide into a furnace with an oxidizing atmosphere at a temperature above 1100 DEG F.