The coarsening of intergranular bubbles containing sparingly soluble monatomic gas

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Abstract
When gas bubbles of varying sizes exist in a material, the higher concentration of gas in solution around the smaller bubbles results in a net migration of gas atoms towards the larger bubbles which grow at the expense of the smaller ones. The driving force is derived from the consequent increase in ontropy of the system. When the bubbles are situated on grain boundaries and the gas is preferentially segregated at the boundaries, the gas migration may be confined mainly to the boundary planes. The bubble-coarsening process in such a situation is analysed in torms of gas atom diffusion along the grain boundaries and an equation is derived for the increase in mean bubble size. The possible significance of the coarsening mechanism in the development of intergranular porosity and life limitation of doped tungsten lamp filaments operating at high temperature is suggested.

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