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doi: 10.1111/j.1151-2916.1965.tb14755.xpmid: N/A
Simple silicate glasses of high purity and melted under strong reducing conditions develop a characteristic visible color center on absorbing ionizing radiation. This center peaks at 570 mμ in soda‐silica glasses but changes position depending on the specific modifier ions. The center grows to relatively large concentrations in glass irradiated by long wavelength ultraviolet light but also decays rapidly at room temperature, imparting phototropic response to the glass. The 570 mμ center probably does not require specific ion impurities; however, minor additions of Ce, Eu, and Zr enhance its formation in certain base compositions. Transition series elements, even in small concentrations, inhibit the center. Sustained irradiation by ultraviolet light leads to lower equilibrium concentrations of the center and hence to fatigue of phototropic response.
doi: 10.1111/j.1151-2916.1965.tb14756.xpmid: N/A
The influence of proof‐testing on the behavior of CFW graphite is described and the improvements in the strength associated with a given probability of failure are established. Damage induced in the graphite by the proof‐test process was examined in more detail by conducting low‐cycle fatigue tests. Fatigue deterioration of the strength of the graphite is cumulative and the number of cycles of load significantly influences the probability of failure. A modified Gaussian distribution function accounts for the influence of both the stress and the number of load cycles on the probability of failure.
doi: 10.1111/j.1151-2916.1965.tb14757.xpmid: N/A
The piezoelectric, dielectric, and optical proper ties of hydrothermally grown ZnO were exam ined. Although the material was strained it was not electrically twinned and the values of the electromechanical coupling factors, k33 (= 0.47) measured by static loading and k31 (= 0.188) measured by the resonance‐antiresonance tech nique, compared favorably with those measured in vapor‐grown crystals. The concentration of Li + substituted on a Zn site which was necessary to compensate the crystals was about 5 × 1018atoms/cm3. This concentration could be ob tained easily by growth from hydrothermal solu tions containing 2.0 molal LiOH. It was neces sary to heat‐treat hydrothermally grown crystals at 800° for about 50 hours, to diffuse out inter stitial zinc, to obtain high‐resistivity material. Typical dc resistivities of 1010 ohm‐cm were ob tained by such treatment. There was a pro nounced anisotropy in the dielectric constant with K33 varying between 9.9 and 11.7 and K11 varying between 8.1 and 9.0 at 100 kc. The size and properties of Li +‐doped hydrothermal ZnO make it of interest for transducers.
SCHWARTZ, E. G.; WEINSTEIN, A. S.
doi: 10.1111/j.1151-2916.1965.tb14758.xpmid: N/A
The use of the Coulomb yield criterion to describe the compaction of granular material is proposed. Its use is demonstrated by the numerical solu tion of the stress and displacement equations de scribing the axisymmetric pressing of a cylindrical compact. The model is applied to the pressing of uranium dioxide pellets; to do so, the shear strength of the pellets is measured as a function of normal stress. These measurements showed an increase of shear strength with normal load and permitted assignment of values of cohesion and angle of internal friction to be used in the Coulomb failure condition. The computed re sults of die wall friction, normal force at the die wall, and stress distribution in the compact are compared with measured results.
doi: 10.1111/j.1151-2916.1965.tb14759.xpmid: N/A
The mechanical behavior of pyrolytic graphite was investigated: (1) to develop an understand ing of the phenomena of failure and to apply it to the interpretation of mechanical properties data, and (2) to explore techniques for increasing room temperature strength. Pyrolytic graphite is ex ceedingly anisotropic and brittle. The condi tions of deposition determine the degree of ani sotropy and this, in turn, has a marked effect on the relations among specimen‐test configuration, nominal strength, and fracture mode. Further more, the “notch sensitivity” is orientation de pendent and thus related to the degree of ani sotropy. The mechanical test results and studies of the fracture modes suggest that results from testing conventional laboratory specimens are not necessarily representative of those which would be obtained by testing free‐standing structures.
doi: 10.1111/j.1151-2916.1965.tb14760.xpmid: N/A
The vaporization rates in vacuum of hot‐pressed HfC, TaC, and solid solutions of these carbides in the range 2225° to 2725°C were determined by a Langmuir‐type method. A composition near 80TaC.ZOHfC (mole %) exhibited the lowest vaporization rate of the compositions within this pseudobinary system. Variations in initial sample bulk density and vapor‐specie condensa tion on the furnace wall have negligible effects on the measured vaporization rates.
doi: 10.1111/j.1151-2916.1965.tb14761.xpmid: N/A
Phase relations in the system CaO‐MgO‐iron oxide were determined at 1500°C at two levels of oxygen pressure, 10–9 atm and 0.2 atm (air). Particular attention was directed toward de termining the maximum amount of iron oxide which may be tolerated in CaO‐MgO‐iron oxide bodies before a liquid phase forms under equilib rium conditions at the two chosen oxygen pres sures. Inferences are made regarding the possible bearing of the results on the perform ance of tar‐bonded dolomite brick used in steel making furnaces.
CARNAHAN, R. D.; BRITTAIN, J. O.
doi: 10.1111/j.1151-2916.1965.tb14762.xpmid: N/A
The early stages of the reduction kinetics of single‐crystal rutile, TiO2, were studied by optical absorption techniques for specimens re duced in the range 550° to 760°C at a constant vacuum level of 10−3 mm Hg. When reduced to a room‐temperature resistivity value of ∼103 ohm‐cm, rutile shows a blue coloration as a re sult of a broad infrared absorption band centered at a wavelength of 1.2μ. The kinetics of growth of the optical absorption coefficient at 1.2μ fit a parabolic relation of the form (Δα)2=K′t. The Arrhenius rate constant, K′, exhibited an activation energy of 111 ± 9 kcal/mole which is ∼50% too high for the diffusion of oxygen in rutile. It is postulated that the defect center is likely to be a Ti interstitial and that the kinetics reflect the self‐diffusion of Ti as the rate‐con trolling mechanism.
doi: 10.1111/j.1151-2916.1965.tb14763.xpmid: N/A
Polycrystalline garnets with the general composition Gd3‐xYxFe5‐yInuO12 were investigated. Ferrimagnetic resonance line widths at S‐ and X‐bands and saturation induction are reported. The temperature dependence of the magnetization was determined on materials in which x= 0 to 3 and y = 0 to 1. Special emphasis is given to compositions having relatively stable magnetizations over the range 20° to 100°C.
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