The diffusion of gases through metals

Abstract

Since the original discovery by Graham in 1866 that hydrogen could diffuse through platinum, the phenomena of diffusion of gases through metals have been the subject of many investigations. Various empirical equations have been proposed to represent the effect of temperature and pressure on the rate of diffusion, and in 1904 Richardson, Nicol, and Parnell arrived at an equation from theoretical considerations which was in good agreement with their own measurements of the diffusion of hydrogen through platinum. This equation, generally known as Richard­ son’s equation, may be written D = k / d . P ½ T ½ e ─ b /T , (1) where D is the rate of diffusion per unit area of surface, P is the gas pressure, T the temperature, d the thickness of the metal, and b a constant for the gas-metal system. The equation applies to conditions in which gas is maintained at a pressure P on one side of the metal, whilst a vacuum is maintained on the other side. If instead of a vacuum a pressure P 1 , where P 1 < P, exists, the term √P in the equation is replaced by (√P ─ √P 1 ).