High temperature vaporization studies by mass spectrometry I: The coinage metals-a discussion of the method and errors

Abstract

The vaporization of the coinage metals was studied using a mass spectrometer equipped with a high temperature furnace and molecular beam system. The Knudsen equation, the measured sensitivity of the mass spectrometer and the molecular beam geometry were used to calibrate the instrument for absolute values of the pressures in the Knudsen cell. Random errors within an experiment were found to be 2-3% in the second law heats of vaporization and 0.3-0.7% in the third law heat of vaporization at standard temperature. Unknown changes in instrumental conditions between experiments may introduce additional errors of up to 3% in the third law values; the calibration procedure is therefore shown to be as satisfactory as other conventional methods. Heats of vaporization determined for the coinage metals (Cu, 82.4; Ag, 67.1; Au, 85.5; ±3 kcal per gramme atom) agree well with the accepted values quoted in the literature.