Identification of nickel hydride phase in nickel matrix by optical microscope observation

Abstract

It is well known that nickel transforms into nickel hydride under high hydrogen fugacity. However, distribution of the hydride formation is not necessarily uniform. It is proposed that the nickel hydride phase in the nickel matrix can be identified by the difference in contrast by optical microscope observation. That is to say that, the hydride phase is observed as a dark region in the matrix. The ratio of the observed dark regions, compared to the light regions, corelated with the ratio of the integrated intensity of the X-ray diffraction profile of hydride to nickel during the decomposition process of hydride formed by electrochemical cathode charging of hydrogen in pure nickel. Such agreement was also confirmed for the hydride distribution below the surface of the sample. The identification of nickel hydride in the present work concludes that the depth of hydride formation is different between crystal grains.