The kinetics of the tungsten-bromine system.
thesisposted on 19.11.2015, 08:45 by V. W. Goddard
A comprehensive study has been made of the tungsten-bromine system, the thermal stability of the important bromides has been established and the reaction between the elements has been studied. The experimental results have been applied to the tungsten-bromine lamp in an effort to elucidate the reaction path of the regenerative cycle which contributes to the high efficiency of these lamps. The important species involved in the regenerative cycle was shown to be WBr5; this compound was stable up to 1300°C which was in excess of the temperature required to operate an efficient cycle. Decomposition of WBr5 was according to the equation: WBr5 ? W + 5Br Tungsten dibromide was shown to decompose to the elements at temperatures between 700 and 860°C; the evidence suggested that the decomposition took place in the gas phase. Tungsten tetrabromide, for many years thought to be the important species in the bromine lamp, was shown to decompose in the solid state at temperatures in excess of 280°C according to the equation:- 3WBr4 ? 2WBr5 + WBr2 This reaction was studied by the Differential Scanning Calorimetry technique and the equation for the rate constant for the decomposition was given as :- k = 1 x 1013.75 +/- 1.15 e -45,000 +/- 3,500/RT sec-1 It was shown that WBr5 reacted with quartz glass at temperatures in excess of 700°C according to the equation:- 2WBr5 + Si02 ? SiBr4 + 2WOBr3 The reaction products were complex due to the thermal decomposition of WOBr3. The reaction between tungsten metal and bromine was studied; the reaction was shown to be zero order with respect to tungsten and 3/2 order with respect to bromine. The equation for the rate constant was given as:- k = (7.8 +/- 1.8 x 10-8) PBr2 e -14,750 +/- 650/RTmols/(cm2sec). It was shown that when the bromine was diluted with argon and nitrogen a corresponding reduction in the rate was produced.