Abstract
In order to obtain some information on the surface state of the reduced nickel powder in the case of the hydrogen adsorption, the change of magnetisation due to gas adsorption of the catalyst, the adsorption isotherms and heats of adsorption were measured before and after the sintering by the heat treatment at 500°C or the degassing at various temperatures. The change of magnetisation was determined by the low frequency a. c. permeameter method.
It is found that the distribution of nickel crystallites accommodated with the adsorbed gas is not homogeneous all over the surface of the catalyst and this distribution causes the occurrence of the first and the second stages in magnetisation isotherms. It seems that adsorption of the relatively finer particles on the surface occurs actively at the first stage, while that of the larger particles at the second stage. These phenomena can also be estimated by the modes of adsorption isotherm and adsorption heat.
Recently Selwood has reported that the magnetisation isotherm deviated from the straight line when the nickel was sintered. This finding is in line with my experimental result. My study indicates also that the transition point from the first to second stage in magnetisation isotherms shifts, when the catalyst was sintered, to smaller scale of abscissa, which represents the amount of adsorbed gas. The adsorption of the first stage in magnetisation isotherm was selectively inactivated by the heat treatment.
Diameter of nickel particles in the catalyst used in this study was determined by X-Ray diffraction pattern method, and these were 50-100A in diameter and in the super-para-magnetism range.
