Formation of gradient palladium-hydrogen alloy and the change in the form of a palladium plate during one-sided hydrogen saturation

Abstract

Forming of a palladium plate (60 × 5.5 × 0.27 mm) saturated one-sidedly with hydrogen at 240°C at various hydrogen pressures from 0.03 to 0.43 MPa has been investigated experimentally. It has been established that forming of a palladium plate during its saturation with hydrogen is time-dependent and occurs in two functionally different stages. At the first stage, the plate becomes bent and its bending quickly reaches the maximum value. At the second, much longer stage, the plate straightens back almost completely. An increase in pressure of gaseous hydrogen leads to a sharp rise in the maximum possible bending of the plate. The degree of reversibility of hydrogen-induced bending of the plate also grows with an increase in hydrogen pressure. The experimental research and an analysis within the framework of the elasticity theory has shown that the palladium plate investigated demonstrates during mechanical loading the elastic reversible bending at deflections approximately three times smaller than those observed upon hydrogen loading. It is concluded that the mechanism of bending of the palladium plate upon saturation with hydrogen is fundamentally different from that under mechanical loading. A fundamental feature of the process of hydrogen-induced shape change is in that it is always implemented through the formation and development of the temporary gradient material of a metal-hydrogen type. Under experimental conditions of this work, the hydrogen-induced reversible bending of the palladium plate results from the “work” of the temporal gradient elastically stressed coherent alloy α-PdHn.