Abstract
In the previous report, a new method of precipitation of hydrated iron oxide by interfacial reaction between concentrated ferric-ferrous salt solution and sodium hydroxide solution was described. The fact that the addition of small amounts of CuCl2 to FeCl3- FeCl2 solution depresses the growth of spinell type oxide in the reaction product called ‘artificial rust’ was also reported.
In the present paper, the change of specific surface area and a related change of the property of the artificial rust by the addition of CuCl2 is described.
Specific surface area determined by the BET method is larger for the artificial rust formed from the solution containing CuCl2. This effect becomes remarkable when the amount of CuCl2 added exceeds 1mol%.
The amount of water adsorbed on the artificial rust at 30°C and 100% relative humidity is also larger for the rust made from the solution containing Cu (II).
Determination of specific surface area of natural rusts was carried out with steel samples exposed in urban and industrial atmospheres. The result showed that the specific surface area of the rusts produced on low alloy steels was somewhat larger than those on ordinary steels.
On the basis of these experimental findings and other known facts, the protective nature of rust layers is discussed.
