Vacuum microbalance investigations on heterogeneous surface reaction mechanisms

A vacuum apparatus including a microbalance and a gas-inlet system was designed. The microbalance had two symmetric reaction tubes which were heated with temperature-controlled furnaces. A cooling trap was built into the tubes above the furnaces to freeze out the reaction products. Thus, the thermodynamical equilibrium of the reaction and the reflection of the products from the tubewalls was avoided and the kinetics of the reaction could be studied. With the totally symmetric design, thermodiffusion of the reaction gas and other disturbances caused by thermal gasflow were minimized. Electrostatic effects were suppressed by a special grounding device inside the reaction tubes. The reduction of zinc oxide powder, pellets, and single crystals with carbon monoxide and hydrogen was studied in the temperature range of 450–950 °C and pressure range from 10−2 to 5 Torr