STUDY OF THE HETEROCOMPLEXES IN THE VAPOR OF THE NA-SN-BR-1 SYSTEM AND THEIR RELEVANCE FOR METAL HALIDE LAMPS

The vapor of the Na-Sn-Br-I system was investigated under equilibrium conditions in the temperature range between 623 and 913 K by the use o f Knudsen effusion mass spectrometry with a two-compartment Knudsen ce ll. The gaseous species NaBr, NaI, (NaBr)2, Na2BrI, (NaI)2, SnBr2, SnB rI, SnI2, NaSnBr3, NaSnBr2I, NaSnBrI2, and NaSnI3 were detected in the vapor. The enthalpy and entropy changes of the reactions NaSnBr2I(g) = NaI(g) + SnBr2(g) [1], NaSnBrI2(g) = NaBr(g)+ SnI2(g) [2], and SnI2( g) + 2NaBr(g) = SnBr2(g) + 2NaI(g) [3] resulted as DELTAH-degrees-298 = 172.9 + 6.4 kJ mol-1, DELTAS-degrees-298 = 140.5 +/- 9.9 J mol-1 K-1 for reaction Eq. 1, DELTAH-degree-298 = 181.6 + 5.8 kJ mol-1, DELTAS- degrees-298 = 143.1 +/- 9.3 J mol-1 K-1 for reaction Eq. 2, and DELTAH -degrees-298 = -12.9 +/- 1.7 kJ mol-1, DELTAS-degrees-298 = 3.9 +/- 3. 5 J mol-1 K-1 for reaction Eq. 3. Gas-phase equilibria important for t he development of metal halide lamps were computed using the results o f this work and ancillary data.