The system PbO-B20 3, of interest to investigators and manufacturers of ceramic glazes and glasses, was studied by well-known methods involving quenching and petrographic examination. In addition, limits of liquid immiscibility were obtained by direct observation. Seven crystalline forms of binary compounds were found and the chemical compositions of six of these established. A number of compositions were studied also as glasses to obtain data on thermal expansion, softening behavior, and relative solubility.

The oxides of cerium, yttrium, silicon, magnesium, and calcium were added in various proportions to zirconia of 99-percent purity, and the effects of these additions, combined with preheating at various temperatures ranging from 1,450° to 1,950° C, on thermal length changes of the zirconia during heating and cooling between room temperature and a maximum of 1,700° C were observed. The results are compared with similar observations on zirconia of 96-, of 98-, and of 99-percent purity without oxide additions.The results show that the irregular thermal lcngth changes accompanying phase transformations in zirconia may be prevented by changing the crystal to the stable cubic form. This was accomplished by (a) 11.5-and IS-percent additions of Y20a and heating at 1,700 0 C or higher; (b) 8-and 15-percent additions of MgO and heating at 1,550 0 C or higher, but only for the range from room temperature to 1,200° C; and (c) 5-, 6-, 8-, and IS-percent additions of CaO and heating at 1,550° C or higher, but additions of more than 6 percent caused the specimens to be very porous and proportionately weak. In a ll cases, however, the expansion during heating and contraction during cooling was relatively high. The coefficients of linear thermal expa nsion of the specimens that were all, or nearly all, cubic ranged from 8.8 to 11.8 X 10-6 • Also, zirconia has a low thermal conductivity relative to such materials of high thermal expansion as alumina, magnesia, and beryllia (unpublished data).

Phase relations were studied for those portions of the binary and the ternary systems containing over 50 p ercent of PbO. It is reasonably certain that the binary syst em contains the compound PbO.AlzOa. In the t ernary syst em 3 compounds (8PbO.AI20 a.4Si02, 4PbO.AI20 a.2Si02, and 6PbO.AhOa.6Si02) were identified, 4 others were indicated by optical and X-ray properties, and 10 quintuple points, which include 6 eutectics, were established. Also, Al20 a (99.9 plus purity) was observed to m elt at 2,035 °C. .

A nearly pure talc was investigated both unheated and after heating at numerous temperatures ranging up to 1,435° C. The studies in cluded the measurement of heat effects, weight losses, and cha nges in true specific gravity occurring on heating talc. X-ray and microscopical examinations were made of the heat ed. samples.There was no change in the crystal structure of the talc up to 800° C. At 800 to 840 0 C the t alc decomposed to enstatite, amorphous silica, and wat er' vapor. The enstatite graduall y changed to clinoenstatite around 1,200° C, and the amorphous silica changed to cristobalite around 1,300° C, giving clinoenstatite and cristobalite as final products. CONTE NTS

Results are given of seven melting-point determinations on alpha-alumina of high purity in an oxidizing atmosphere and under atmospheric pressure. There was detectable contamination of the specimens by vapors of other elements in the furnace atmosphere, but the results are believed to show that the melting point of alpha-alumina is within the range 2,000° to 2,030° C.