D ielectrics having compositions in the system BaTi03-4 MgO:TiOz-Ti02 were matured (less th an 0.1 % of absorption) at 1,275 0 to 1,425 0 C. Data a re given for the dielectric constant K at a frequency of 1 mc/s and variou temperat ures from -60 0 to + 85 0 C, and fo r Q, t he reciprocal of t he power factor, at 25° C and frequencies of 50, 1,000, and 20,000 kc/s and 3,000 mc/s. Values of K (1 mc/s and 25 0 C) ranged from 12 to 1,550 and t hose of Q from 9 to 10,000. Values of K decreased, and those of Q increased for several weeks aftcr I'lpecimens were matured, when the content of BaO was greater than 30 percent and that of Ti02 less than 50 perccnt. P artial restoration of the original values of K and Q rcs ul tcd from heating these speci mcns at various temperatures for brief pcriods. Linear thermal expansion (25 0 to 700 0 C) ranged from 0.46 to 0.71 percent. A few specimen of bari umstrontium t itanate were tested for the effects of thermal history on the properties,
The glass phase in the bodies studied was more sensitive to variations in heat treatment than were the physical properties. Increased rates of heating caused less glass and mullite formation, less quartz corrosion, more pores and blebs, and increased heterogeneity of the glassy matrix. Microstructure and physical properties indicated an optimum heating rate between 50" and 90" per hour. Soaking increased the amount of glass, more so after slow than after rapid heating. Soaking after rapid heating did not reduce the number of blebs. Soaking too long and at too high temperatures made blebs more numerous.The optimum heating rate and minimum soaking time governed the shortest heating schedule productive of the best microstructure and physical properties.A minimum soaking time of one hour seemed desirable.
Dielectrics havin g co mpo itions in the system 3CaO:TiO,-BaTi03-TiO, were matured at 1,260° to 1,500° C. Data are given for the comp ositions, heat-treatme n ts, absorp tion, shrinkage, and for K, the die lectric constant, and Q, t he reciprocal of the power factor, at 25° C for fr equencies of 50, 1,000 and 20,000 kilocycles per second and for 3,000 megacycles per second when ]( is not g reater than 50. Values of K were a lso determin ed at 1 megacycle per second for variou tem peratures from -60° to + 85° C. Lowest valu e. of Q (and highest of K ) were associated wit h specim ens of high bari a co ntent. Linear t he rmal expansion (25° to 700° C) ra nged from 0.65 to 0.87 percent. The pecim ens of some compositions were un stable and cha nged in 1C and Q values with time.
This paper constitutes a preliminary report of an investigation to determine quantitatively the gases obtained by heating a feldspar in vacuo. Nineteen samples representative of the ground commercial material, such as is used in the ceramic industry, were tested. At 1,000°C. the gases consisted, by weight, of 32 to 96 per cent water vapor, to 59 per cent acid gases, and to 36 per cent unabsorbed gases. Calculated to volume relations a unit of feldspar when heated to 1,000°C. would evolve (extremes for the 19 samples) 16 to 140 volumes of water vapor and to 15 volumes of acid gases (assumed to be C0 2) measured at 1,000°C.
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