MECHANISM OF THE PACK PROCESS OF CHROMISING BY THERMAL DIFFUSION - 1.

Equilibrium gas phase composition of the chromizing box has been found out by considering the following gases, namely, H//2, N//2, H//1, CrI//3, FeI//2, FeI//3, Fe//2I//4, FeI//5, dissociated iodine at various temperatures, pressure and activity of iron specimen surfaces by computer techniques and it has been shown that out of the above gases only H//2, N//2, CrI//2 and its dimer Cr//2I//4, FeI//2, HI and dissociated iodine constitute more than 99% of the gas phase constituents and only chromium iodides iron iodide and dissociated iodine changes with variables studied. It is shown that initially the reaction Fe plus I//2 equals FeI is predominant and corrodes the specimen surface and subsequently chromium iodide reactions give the coatings. Surface diffusion of chromium plays an important role in determining the nature of this coating obtained.