Calcium aluminate glasses containing alkali oxides and iron oxide will transmit infrared radiation to about 6 p and still have satisfactory working properties. Their refractive index, density, expansion, Young's modulus, modulus of rupture, fracture velocity, Knoop hardness, and some electrical and chemical properties are evaluated.

499Figure 6(A) illustrates the structure of pyrolytic TiB2 as deposited. The (1 10) plane, which includes both boron atoms as well as the four titanium atoms a t the extreme corners of the hexagonal unit cell, was parallel to the plane of deposition. The atomic arrangement of alternating layers of titanium and boron atoms perpendicular to the plane of dcposition as well as the TiBz unit cell are indicated. The interatomic distances were based on the data of Kiessling.2(0) Figure 6(B) illustrates the array of atoms in the plane parallel to the plane of deposition and indicates the anisotropy within this plane. Since two electrical paths, one involving Ti-B bonds only and the other involving B-B bonds, are possible, a determination of the electrical resistivity in each of the anisotropic directions should indicate the strength and importance of boron-to-boron bonding in such compounds.A number of phosphate glasses with unusually high vanadium content were studied with respect to some of their electrical properties.It was found that 75 to 85 wt% V205 could be reacted with various metaphosphates (Ba, Pb, Li, Na, Cd, V, and K) resulting in good-quality reproducible glasses in 500-g melts. The electrical resistance of these glasses appeared to be particularly dependent on their thermal history below the liquidus but above the transformation range. A large change in specific resistance resulted when vitreous specimens were heattreated to produce varying amounts of devitrification. For a specimen containing potassium metaphosphate, resistivity was reduced from about lo3 to 10 ohm-cm.

The density of a 517 : 645 optical borosilicate glass increased by more than 1% when samples quenched from the highest temperature at which no further decreases in density were observed were annealed at the lowest temperature at which increases were observed within reasonable time. Conversely, stabilization times increased with decrease of stabilization temperature. This behavior was in agreement with that exhibited by this and other glasses in respect to other properties. The increase in density caused a much smaller increase in refractive index than expected from conventional refraction-density relations. This was interpreted to mean that in glasses packed to a high density, the specific refraction decreased in relation to the tightening of the electronic structure. It may then be said that the refractive index of a fine annealed glass was the result of two opposing trends-the increasing density tended to increase it, the decreasing specific refraction indicative of a tight and less responsive electronic system tended to decrease it. The net result is the moderate increase observed in previous studies.

The partial dispersion ratios of phosphate and borate glasses are defined and found significantly different from those of silicate glasses; thus, they are useful for secondary spectrum correction. Refractive index measurement accuracy necessary to ensure significant partial dispersion ratios is analyzed. Measurement techniques and corrections are described.

A number of calcium aluminate glasses have been developed for use as infrared-transmitting window materials. These glasses have been stabilized with respect to devitrification by introducing alkali and iron into the batch composition. The iron reduced visible transmission of these glasses and at the same time to a lesser extent tends to decrease infrared transmission as the iron concentration increases. In a study of the influence of transition elements, Mn and particularly Cu are found to increase significantly the infrared transmission of these iron-alkali stabilized calcium aluminate glasses.