A gas-inlet system coupled with a Knudsen cell mass spectrometer for high-temperature studies

gas-inlet system coupled with a Knudsen effusion mass spectrometer has been developed to study at high temperature the interaction of solids and vapors with reactive permanent gases, such as H2 and O2, directly introduced into the cell from external low-pressure reservoirs (pressure range: 10-4 < p < 1 bar). By selecting the gas flow from the external reservoir the pressures of the gases inside the Knudsen cell can be quantitatively controlled over three orders of magnitude, approximately from 10-8 to 5.10-5 bar. Mixtures of two different gases can be introduced into the cell, controlling their partial pressures independently. The capabilities of the device have been tested with four gas-solid systems: PbO(s) + O2(g), GeO2(s) + O 2(g), Ga(s) + H2(g) and Au(s) + H2(g), by studying the relevant high-temperature equilibria. The results obtained for the dissociation energies of the diatomic molecules PbO(g), GeO(g), GaH(g), and AuH(g) compare well with the literature data giving confidence in the reliability and versatility of the method. Preliminary experiments on the in situ formation of H2O(g) in the Knudsen cell by the introduction of controlled gaseous H2/O2 mixtures are also presented.