Thermodynamic Considerations of Chemical Reaction Phenomena in HID Lamps

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This paper presents considerations on thermodynamic calculations for four lamp phenomena of HID lamps. The first phenomenon is the reactions of Sc or Sc iodide with silica, The standard free energy changes of the reactions associated with Sc_2O_3 and Sc_2Si_2O_7 formations were calculated. Using these calculation results, the Sc analysis result of the experimental lamp was considered. The second phenomenon is Na reactions with alumina in a high-pressure sodium lamp. The standard free energy changes of the reactions associated with NaAlO_2 and β-alumina formations were calculated. The reacting areas for gaseous Na reactions with alumina were defined. The third phenomenon is tungsten transport from the electrodes to the lamp wall in an Fe iodide lamp. By comparing the calculated gaseous Fe pressure with Fe vapor pressure at the electrode temperature region, the formation of the W-Fe allay which has a low melting point can be explained. The last phenomenon is the chemical reactivity of metal elements with silica. Using the standard free energy formation data for fifty metal oxides, the standard free energy changes of the reactions of fifty metal elements with silica were calculated. From these results fifty metal elements were classified according to the probability of their reaction with silica.
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