The effect of liquid gallium on the strengths of stainless steel and thermoplastics

We have investigated the effect of liquid gallium on type 316L stainless steel (as a candidate for the P-V-T pressure vessel), and four thermoplastics: two semicrystalline (high-density polyethylene and polypropylene) and two amorphous (polystyrene and poly(methyl methacrylate)). Specimens were coated with gallium and held at elevated temperatures and reduced pressure for extended periods. Measurements conducted on the plastics include weight change analyses, tensile tests and particle diffusion analysis using dispersion X-ray spectroscopy. For the stainless steel specimens, tensile and corrosion tests were conducted. Scanning electron microscopy was used to determine the level of corrosion. The results are compared with specimens heat treated identically but without gallium contact. After 3 months, the gallium corroded the surface of the steel to a depth of only 12 μm. No penetration path of the gallium into the steel has been observed. The gallium was also found to cause no change in the mechanical properties of the polymers tested, nor was it found to have caused any weight change in the specimens.