OLIGOMERIZATION OF PBO-VAPOR

The oligomerization of PbO-vapor was determined by measuring partial p ressures using Knudsen effusion mass spectrometry in the temperature r ange 838 to 1018 K. The vapor of yellow lead oxide consists mainly of PbO, (PbO)2, (PbO)4. The partial pressures P(i) are lg (P(i)/bar) = -1 4480/T + 7.847\ -14734/T + 7.968\ -13446/T + 7.090, respectively. The standard enthalpies and entropies at 25-degrees-C are as follows: h298 infinity/kJ mol-1 = 72.370\ -137.137\ -591.234, and s298infinity/J K-1 mol-1 = 240.040\319.122\450.882. To differentiate between parent and fragment ions, the effusion mass spectrometry has been combined with a n electrochemical Knudsen cell containing liquid lead of varying oxyge n concentrations. - In addition, the electrochemical cell allows in si tu precipitation of red or yellow oxide, PbO(R) or PbO(y), in liquid l ead. Emf measurements correspond to normal enthalpies of h298(0)/kJ mo l-1 = -221.2 +/- 1.2 and -218.7 +/- 0.8, respectively.