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doi: 10.1111/j.1151-2916.1972.tb13411.xpmid: N/A
Calcium carbonate‐silica mixtures produced by carbonation of wollastonite and pseudowollastonite and by intergrinding precipitated CaCO3 with SiO2 flour were calcined. At calcination temperatures of <850°C, mixtures of β‐Ca2SiO4 and CaO were formed. The quantities of these products were determined by X‐ray diffraction, and their dependence on calcination time, temperature, and the degree of homogeneity of the starting material was determined. Kinetic data were also obtained. Calcined materials mixed with water and compacted under pressure hardened slowly at room temperature and more rapidly under atmospheric steam or autoclave conditions. The relation between compressive strength, porosity, curing time, and temperature was determined.
HIGGINS, T. J.; MACEDO, P. B.; VOLTERRA, V.
doi: 10.1111/j.1151-2916.1972.tb13412.xpmid: N/A
Mechanical relaxation in Na2O·3SiO2 glass was measured. The data are compared with dielectric relaxation results for the same glass. The mechanical and electrical relaxation processes have not only the same activation energy but also (within experimental error) the same average relaxation time and distribution of relaxation times. From this result, it may be concluded that the mechanical loss in single‐alkali silicate glass arises from the same ionic process that is associated with long‐range ionic diffusion.
PROVENZANO, V.; BOESCH, L. P.; VOLTERRA, V.; MOYNIHAN, C. T.; MACEDO, P. B.
doi: 10.1111/j.1151-2916.1972.tb13413.xpmid: N/A
The electrical relaxation associated with alkali diffusion in Na2O·3SiO2 glass was studied from 0.2 Hz to 700 kHz at –1° to 163°C. A formalism for analysis of electrical relaxation in conducting dielectrics which associates the nonexponential decay of the electric field to zero and the dispersions in the dielectric constant and the conductivity with a distribution of relaxation times for the electric field was developed and is shown to be in qualitative accord with current molecular theories of electrical relaxation in alkali silicate glasses. A relation between the dc conductivity, the limiting high‐frequency dielectric constant, and the average electric field or conductivity relaxation time was derived and is verified experimentally for the Na2O·3SiO2 glass. The distribution of electric‐field relaxation times for the glass is broad, asymmetric on a logarithmic scale, and weighted in favor of the shorter relaxation times; the distribution narrows with increasing temperature. A reduced electrical relaxation curve which can be used to compare electrical and mechanical relaxations in Na2O·3SiO2 glass was generated.
doi: 10.1111/j.1151-2916.1972.tb13414.xpmid: N/A
Lanthanum‐doped lead zirconate‐titanate ferroelectric ceramics (PLZT) were tested acoustically using the pulse‐echo technique at 20 MHz. Phase transitions occurring within the range –269° to 300°C were detected in poled and unpoled Pb1.02‐xLax(Zr0.65Ti0.35)O3 with x=0.00 to 0.15. For x=0.00 to 0.08 a phase transition observed between 0° and 100°C was defined by changes in the longitudinal sound velocity as great as 5% accompanied by pronounced absorption peaks. Measurements of resonance and electromechanical coupling in poled samples indicate that this transition involves 2 ferroelectric phases. The acoustic techniques reported made possible the detection of the subtler phase transitions in PLZT ceramics with a degree of sensitivity much higher than that available from the more conventional techniques. Both poled and unpoled samples may be tested by this technique, so that the influence of domain orientation on the transitions observed can be demonstrated.
doi: 10.1111/j.1151-2916.1972.tb13415.xpmid: N/A
Phase equilibria in the system SrO‐CdO‐V2O5 in air were established from data obtained by DTA, quenching, and high‐temperature solid‐state reaction experiments. The SrO‐V2O5 boundary system contains 4 compounds at SrO to V2O5 molar ratios of 4:1, 3:1, 2:1, and 1:1. A fifth compound with a molar composition of ∼10:3 with the apatite crystal structure was also found; it may, however, be a hydroxyapatite phase. The CdO‐V2O5 system contains the compounds 3CdO·V2O5, 2CdO·V2O5, and CdO·V2O5. The latter compound exhibits a rapid reversible polymorphic transition at 180°C. Complete solid solubility exists in the SrO‐CdO system. The most probable compatibility relations were determined from the data available for the SrO‐CdO‐V2O5 ternary system. Limited solid solubility exists between SrO·V2O5 and CdO·V2O5, and the high‐temperature CdO·V2O5 polymorph is stabilized to room temperature by solid solution of SrO·V2O5. Evidence for the existence of 2 ternary compounds with limited local solid solubility is also presented.
MEITZLER, A. H.; O'BRYAN, H. M.
doi: 10.1111/j.1151-2916.1972.tb13416.xpmid: N/A
The elastic and piezoelectric properties of PLZT ceramics with a 65/35 Zr/Ti ratio undergo pronounced changes as La is added to the structure. At the rhombohedral‐tetragonal phase boundary, material constants plotted as functions of La concentration show strong discontinuities in slope; these discontinuities provide a precise means of locating the boundary. The radial‐mode coupling factor, kp, compliance coefficient, S11E, and piezoelectric coefficient, d31, attain peak values at the boundary, whereas Poisson's ratio, σE, and the resonance‐frequency constant exhibit pronounced minima. This behavior is evidence of the increasing ferroelastic sensitivity of the material as the distortion angle of the rhombohedral phase approaches a minimum.
doi: 10.1111/j.1151-2916.1972.tb13417.xpmid: N/A
Cracks introduced into single‐crystal sapphire broke up after annealing, first into channels of cylindrical voids and ultimately into rows of spherical pores, with the thicker gap spacings in the original crack remaining open. Breakup of the cylindrical voids on subsequent annealing conformed to the models for surface‐diffusion‐controlled material transport. At the temperatures of measurement, the magnitudes of the calculated surface diffusivities agree well with values reported previously.
DiMARCELLO, F. V.; KEY, P. L.; WILLIAMS, J. C.
doi: 10.1111/j.1151-2916.1972.tb13418.xpmid: N/A
The degree of preferred orientation (texture) of doctor‐bladed polycrystalline 99.5% Al2O3 substrates from 3 sources was evaluated by qualitative optical and quantitative X‐ray analyses. The substrates exhibit a fiber texture in which the basal planes lie preferentially in the plane of the substrate. The same texture is weakly evident in the unfired materials. The strength of the texture in fired substrates varies from lot to lot and among suppliers, but its character remains essentially the same. Measurements of dielectric constant, flexural strength, and thermal expansivity are consistent with the observed texture. The possible origins of the texture and its importance in substrate applications are discussed.
doi: 10.1111/j.1151-2916.1972.tb13419.xpmid: N/A
The 1200°C isothermal section of the system CaO‐BaO‐WO3 was studied in detail. The system contains one ternary compound, Ba2CaWO6, which can exist in binary equilibrium with BaO, CaO, Ba3WO6, Ba2WO5, BaWO4, and Ca3WO6. The composition range of solid solutions based on the ternary compound extends from Ba2CaWO6 to Ba1.86Ca1.14WO6 at 1200°C. Solid solubility along the binary join BaWO4‐CaWO4 was studied in the interval 1000° to 1340°C. Maximum solid solubilities occur at the eutectic temperature (1340°±10°C) and are 18 mol% CaWO4 in BaWO4 and 3.5 mol% BaWO4 in CaWO4. A phase diagram is given for the BaWO4‐CaWO4 system. Evidence is presented which shows that Ba2WO5 is a stable phase, and the BaO‐WO2 phase diagram is revised accordingly. There are 3 polymorphs of Ba2WO5 related by rapid reversible inversions at 1385°±5° and 1490°±10°C. The low‐temperature form of Ba3WO6. is tetragonal (α=8.65(2) Å and c=16.43(4) Å), not cubic as previously reported. The compounds Ca6WO9, BaW2O7, BaCa2WO6, Ba5CaW2O12, and Ba1.5Ca1.5WO6 reported in earlier studies were not confirmed.
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