Compositions having negative linear thermal expansions ranging from 0 to -0.38~0 have been obtained in two areas of the system lithia-alumina-silica.Petrographic and X-ray examinations indicate the presence of three principal crystalline phases, each of which is a solid solution: 0-eucryptite, 0-spodumene, and a n unidentified quartzlike phase. All compositions were prepared from lithium carbonate, clay, flint, a n d alumina. Some compositions have been prepared which, for all piactical purposes, exhibit no change in length when heated from room temperature to as high as 600°C. Some of these compositions have excellent thermal endurance, withstanding repeated quenchings from a temperature of 1100°C. into water at room temperature.Temp. ("C.1 Fig. 1. linear thermal expansion, Q series.

Thermal endurance in the field zircon‐calcium zirconium silicate‐clay was evaluated together with those physical properties that should contribute most to this characteristic. The coefficient of thermal expansion was similar throughout the field, resulting in an area of high thermal endurance which coincided quite closely with that of high transverse strength. The best compositions did not fail until the 500 °F. quenching cycle (one cycle at each temperature) and withstood 30 cycles from 400°F. Petrographic analysis revealed that good thermal endurance could be attained over a wide range of compositions.

The findings allow the prediction of densities achievable in an aggregate of angular particles by purely mathematical methods. The predicted densities show agreement within *0.015 with densities achieved in practice. Prediction of achievable densities of aggregates of angular particles by this method reduces the time and inaccuracies involved in graphical solutions or extrapolations from similar systems. Pure barium titanate was made into a glass by flamespraying and after sufficient comminutionwas processed into specimens and fired. During this firing the glass devitrified to tetragonal barium titanate and contained crystals of sizes from 0.5 to below 0 . 2~. The small crystals exhibit Curie temperatures from 120° to above 185OC. The dielectric Curie temperature of the devitrified ceramic is 150° to 155OC.

The objective of this program is to ;mprove the structura of cerainics by 0 processing. The over-all. temperature range of interesnt is IR-00 to above 3000 F.:n the high portion of the range, 3000 F and above, com,-sitions 0oft pure aluina, plus 0 to 2% additions of HgO were studied between 2822 and 31L80 F, at 1 to 7 hour soaking periods and in atmospheres of hydrogen, helium and vacuunm, This work was reported in the previous Final Report; however, the analysis of remalts is reported herein. Petrogiaphic, x-ray, d.c. cinductivity, electron tranamisgion and elb,.tron probe methods wsre used and the results are reporved, The second tMperature range, 2600-3000 F, was studied utilizing the presintered approach to the prereacted raw materials technique and the results were reported -i n earlier reports. The low range, 1800 to 2600 0 F, was studied usi 1 ng the devitrification approach to the prereacted materials technique. The are a of crystallizationi of cordierite in the I'g0'Al~,0 -SiO system was evaluated as a single glass system. A two-glass system, in wfii~h ong glass devitrifies cordierite and the second supplies the bonding system, was studied. Bonding glass compositions were evaluated in the RO'Al 0 *SiO system, in which the RO members are alkaline earth oxides., Composites WUr madi at 10,'-20 and 30% bonding glass. Processing, structures and properties are reported.

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