A bakeable vacuum microbalance for determining metal oxidation kinetics

Abstract

Details are given of a vacuum microbalance used to study the oxidation of metals at high temperatures over a pressure range of 10−6–760 Torr. The balance is a modified Cahn RG Electrobalance housed inside a stainless steel chamber, which forms part of a bakeable all-metal UHV system. All possible electrical components were taken outside the vacuum system and all internal electrical connections were replaced by spot-welded platinum wire. After bakeout at 100 °C pressures of <5×10−8 Torr were obtained, the outgassing rate from the balance, walls, etc., being ∼8×10−8 Torr·liter·sec−1. Low oxygen pressures were maintained by a Granville-Phillips automatic pressure controller and either a conventional wire-wound resistance furnace or a radiant heating furnace using quartz-iodine lamps was employed to heat the samples. The performance of the balance is illustrated by some results on the oxidation kinetics of iron and nickel at 500 and 700 °C. The total noise level during an experiment was typically about 3 μg.