Differential thermal and thermogravimetric analyses of CdO 9 1 .65H20 showed that four processes were involved in the thermal decomposition. Isothermal weight loss determinations showed that, a t 300' and above, the decomposition to CdOo.80 was continuous. The composition of intermediates is uncertain because of the rapid and continuous reaction.The decomposition was accompanied by marked textural changes of the solid. Surface areas of pure hydroxide as well as samples containing 1 atom yo Li+, Znf2, Mgf2, or Alfa were measured after heating in vacuo for various times at temperatures from 150 to 500'. Alf3-addition inhibited and Lif-addition enhanced oxide sintering up to 400', through the destruction or creation of oxygen vacancies. At 450 and ZOOo both Alfa and Lif additions increased sintering, suggesting that a cation vacancy mechanism became dominant.Some oxide was formed as low as 265'.During a study of the surface properties of CdO, it became necessary to prepare well-defined CdO samples by various means, including the thermal decomposition of the hydroxide. Although some work has been reported on the isobaric and isothermal dehydration of cadmium hydroxide,1s2 the information available was incomplete. Additional work was required and, consequently, the thermal decomposition of doped and undoped cadmium hydroxides was studied.
Experimental DetailsCadmium hydroxide was precipitated from the nitrate with a m m~n i a ,~ thoroughly washed and dried a t 100' in air. A portion of the powder was mixed with enough LiOH, Zn(NO&, Mg(N0&, or Al(N03)a solution to yield a stiff paste, which was dried a t 110'. The amounts of solutions and their concentrations were sufficient to result in hydroxide samples that, when converted to CdO, would contain 1 atom % of foreign cations. Differential thermal analyses (d.t.a.) were made a t linear heating rates of 10°/min., using Pt-10% Pt.Rh thermocouples. A slowly moving stream of purified nitrogen passed over the nickel detector block. Thermogravimetric analysis (t.g.a.) was made in air with a modified Ainsworth automatic recording balance, a t linear rates of 4.6'/min. from room temperature to 500°. Isothermal weight loss (i.w.1.) was measured in air with a modified analytical balance. Sitrogen adsorption isotherms and B.E.T. surface areas4 were obtained with an apparatus of conventional desigm6 The initial degassing of each sample was carried out overnight a t room temperature because of the instability of the hydroxide. Surface areas were then measured for a sequence of heat treatments of various durations in vacuo {at each temperature. The surface areas, 'each calculated from data a t six relative pressures, are given in m.2/g. of starting material.
Experiments and ResultsD.t.a. Experiments. These experiments are described in somewhat greater detail than would normally be warranted, because electrical disturbances of the instrument brought about by CdO can be used to deduce information about the extent of the decomposition. In studying the hydroxide-oxide transformation, it ...
