GB776954A - Process for the production of protective layers on surfaces of metals - Google Patents

Abstract

Silicate layers are formed on metal surfaces by applying thereto an aqueous solution comprising an alkali metal silicate, having a ratio of alkali metal oxide to silicon dioxide within the range 1:2.5 to 1:5, and at least one alkali-resistant water-soluble compound of a "heavy metal" (defined as a metal which has a density greater than 4 g/cc.), the weight of the heavy metal in this compound being not more than 2 per cent, preferably not more than 1 per cen, of the weight of the total solids in the solution, and heating the coated surface to a temperature of 100 DEG -400 DEG C. so as to form an adherent non-crystalline silicate layer in which at least a part of the heavy metal is present in the form of a silicate. The layer may be subjected to an after-treatment by heating to a temperature higher than 400C DEG . The heavy metal is preferably a metal which exhibits variable valency, e.g. As, Ri, Co, Cr. Cu, Fe, Mn, Mo, Ni, Pb, Sb, Sn and V; other metals which may be used include Ag and Zn. Water-glass is used as the alkali metal silicate. The water in the treating solution may be partially replaced by one or more organic substances soluble in water, e.g. alcohols, aldehydes and ketones. Water-repelling layers may be obtained (a) from solutions which contain substances capable of polymerizing when the layer is heated, or (b) by after-treatment of the layers with compounds such as silicones or isosolid metals or their metal coatings procyanates. The layers may be formed on solid metals or their metal coatings produced, for example, by vaporization. Eight specific examples of the treatment are disclosed.