Patent GB-989469-A (GB)
Title: Formation of corrosion resistant silicide coatings on metal compositions
Inventor: COOK NEWELL CHOICE
IPC: C01B33/06
Filed: 1962-02-15
Abstract: A corrosion resistant silicide coating is formed on a metal composition of melting-point above 600 DEG  C., in which at least 50 mol. per cent of the composition is at least one of the metals with atomic numbers 23-29, 41-47 and 73-79, by the method comprising (1) forming an electric cell containing the metal composition and silicon as electrodes joined together through an external circuit and a fused salt electrolyte composed of at least one alkali metal fluoride and from 0.5 to 50 mol. per cent of at least one alkali metal fluosilicate, which may prepared in situ by dissolving SiF4 vapour in a fused bath of the alkali metal fluoride, the electrolyte being maintained at a temperature of at least 600 DEG  C. but below the melting-point of the metal composition in the absence of oxygen such as by using a vacuum, (2) controlling the current flowing in the cell, e.g. increasing the resistance in the circuit for a slower deposition rate or applying a voltage of up to 0.5 volt for a faster deposition rate, during the formation of the silicide coating, so that the current density does not exceed 5 amp/sq. dm., and (3) interrupting the flow of electric current after the desired thickness of silicide coating is formed.  Preferably a porous graphite basket containing pieces of silicon is used instead of a single piece of silicon for the anode.  Examples of silicide coated products disclosed are strips, wires or panels of pure Fe with coating of Fe3Si, Mo with coating of MoSi2 with some Mo3Si and Mo3Si2, V with coating of VSi2 and V5Si3, Nb with NbSi2 coating, W with WSi2 coating; other specified metal compositions are Cr, Co, Cu, Rh, Pd, Ag, Ta, Re, Ir, Pt, Au, Mo-W alloy (50-50%), 3.5% Si-Fe alloy, "Inconel" and "Hastelloy" (Registered Trade Marks), 17% Cr-Fe alloy and alloy composed of 38% Co, 20% Ni, 20% Cr, 6% Fe, 5% W, 4% Mo, 4% Ta/Nb, 2% Mn, 1% Si.ALSO:A corrosion resistant silicide coating is formed on a metal composition of melting point above 600  DEG C., in which at least 50 mol per cent of the composition is at least one of the metals with atomic numbers 23-29, 41-47 and 73-79, by the method comprising (1) forming an electric cell containing the metal composition and silicon as electrodes joined together through an external circuit and a fused salt electrolyte composed of at least one alkali metal fluoride and from 0.5-50 mol per cent of at least one alkali metal fluosilicate, which may be prepared in situ by dissolving SiF4 vapour in a fused bath of the alkali metal fluoride, the electrolyte being maintained at a temperature of at least 600 DEG C. but below the melting point of the metal composition in the absence of oxygen such as by using a vacuum, (2) controlling the current flowing in the cell, e.g. increasing the resistance in the circuit for a slower deposition rate or applying a voltage of up to 0.5 volt for a faster deposition rate, during the formation of the silicide coating so that the current density does not exceed 5 amp/sq.dm., and (3) interrupting the flow of electric current after the desired thickness of silicide coating is formed. Preferably a porous graphite basket containing pieces of silicon is used instead of a single piece of silicon for the anode. Examples of silicide coated products disclosed are strips, wires or panels of pure Fe with coating of Fe3Si, Mo with coating of MoSi2 with some Mo3Si and Mo3Si2, V with coating of VSi2 and V5Si3, Nb with NbSi2 coating, with WSi2 coating; other specified metal compositions are Cr, Co, Cu, Rh, Pd, Ag, Ta, Re, Ir, Pt, Au, Mo-W alloy (50-50%), 3.5% Si-Fe alloy, "Inconel" and "Hastelloy" (Registered Trade Marks), 17% Cr-Fe alloy, and alloy composed of 38% Co, 20% Ni, 20% Cr, 6% Fe, 5% W, 4% Mo, 4% Ta,/Nb, 2% Mn, 1% Si.