Partial Pressures of Strontium and Strontium Oxide over Strontium Oxide Heated on Platinum

A quadrupole mass filter was used to determine the partial pressures of Sr(g) and SrO(g) over strontium oxide heated on a platinum-ribbon filament. The ion currents of 88Sr+and 88Sr16O+were measured while the filament temperature was continuously increasing at a heating rate of about 14°C/min; the calculations of the partial pressures were carried out by the integral method for Sr(g) and by the sensitivity-calibration method for SrO(g). The data are represented by:logPSr(g)(atm)=6.633−\frac2.536×104Tin the temperature range of 1643–1851°K, and by:logPSrO(g)(atm)=6.707−\frac2.793×104Tin the 1747–1850°K range. From the values of the partial pressures, the dissociation energy of strontium oxide was determined to be D0°(SrO)=96.2±0.9 kcal/mol by the third-law treatment and D0°(SrO)=102±5 kcal/mol by the second-law treatment.