On the Formation and the Properties of the Sb Coating by a Special Cementation Method

Abstract

It was found that the metallic coating of Sb was formed of Sb powder by a special cementation method. This method is to pack the iron in the powder composed, on the volume percentage, of 30%Sb, 30%ZnO, 30%C and 10%Na₂CO₃, and heat it at 550∼650° for 30∼60 minutes. The author postulates that the coating is formed by the solid diffusion and the gaseous penetration of Sb into iron. The effects on the nature of coating produced by a sort of powder, Sb contents in the powder (from 10% to 90%Sb), heating temperature (from 400° to 800°) and heating time (from 0.5 to 4 hr) were sutdied. The coating consists of two layers. The outer layer, that forms the greater part of the coating, consists of Sb containing, in the state of solid solution, a small amount of iron and the inner layer consists of Fe-Sb metallic compounds. But the inner layer was not formed by heating below 630°. The total thickness of the coating was about 0.02 mm, when heated at 600° for 30 minutes. The cohesion of the coating was tested by measuring the difference of weight after striking the specimens with iron plate or rubbing them with carborundom powder. The stability of coating depends upon the thickness of inner layer. It was largest when heated at 650°,and the thickness of inner layer at the time was very small. The corrosion of the coating in the 10%HCl, 10%H₂SO₄, 10%HNO₃ and 2%NaCl aq.solution and that in the air were also examined.
Merits of this method are as follows: (1) Apparatus and technique for it are very simple. (2) The coating has a beautiful silver lustre. (3) The cohesion of coating is superior to that by electro-plating. But a grave defect is that the coating is relatively brittle.