摘要:

“The grain‐boundary diffusivity of U in UC was measured between 1200” and 2200°C in pure carbides with a wide range of C/U ratios (0.93 to 2.00) and in material doped with up to 2.4 wt% W, V, or Ta. Grain‐boundary diffusion is ∼ 103to 105times faster than volume diffusion, and, for UC1,0, has an activation enthalpy of 75.9 ± 9.1 kcal/mol, ∼ 55% of that for volume diffusion. In the monocarbide region, grain‐boundary mobility increases as the C/U ratio decreases and is impeded by the additio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19561.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Measurements of the elastic moduli for Na2O‐TiO2‐SiO2, glasses located in 2 adjacent primary phase fields are quantitatively represented by equations in terms of linear mole fractions. Evaluation of the data showed that these linear relations are unique for each group of glasses stud

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19562.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The rate of paste hydration of 3CaO·SiO2(C3S) and the effects of additions of CaCl2, CdI2, and CrCl3, were studied by differential thermal analysis and thermogravimetry. X‐ray analyses were used to identify the synthesized C3S. The salts CaCl2, CdI2, and CrCl3, accelerated the hydration of C3S. The degree of hydration was estimated by the amount of Ca(OH)2, formed, as determined by

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19563.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The crystal structure of α‐Si3N4was reinvestigated by an X‐ray method using a single‐crystal specimen prepared by chemical vapor deposition. The oxygen content of the specimen (0.05 ± 0.03%) was determined by 14 MeV neutron activation analysis. The α form crystallizes in the space group P31c with uniteell dimensionsa=7.818 ± 0.003 Å andc= 5.591 ± 0.004 Å. The structure was refined by the full‐matrix least‐squares method using 1143 observed structure factors. The Si‐N distances determind ranged from 1.715 to 1.759 Å, and the final value ofRwas 0.041. Structural evidences indicated that the α form is es

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19564.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The magnitude of grain‐boundary sliding in 6 specimens of polycrystalline MgO of 2 grain sizes (33 and 52 μm) was measured by interferometry after compressive creep at 1200°C uner stresses from 34.4 to 103.3 MN m‐2. Grain‐boundary sliding increases in importance with decreasing stress and/or grain size, although the largest strain contributed by sliding under these experimental conditions was only 20% of the total

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19565.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Scientific publications fall, traditionally, into two general categories: reports of original research and state‐of‐the‐art reviews of areas of research. In both types, scientists communicate with other scientists. If science is to Serve technology, however, there must be effective communication or transfer of information between the scientist and the technologist. At present, many believe that such transfer is not very effective and that this ineffectiveness contributes to the difficulty the technologist experiences in predicting the performance of materials. The authors plan a series of papers that will provide a critical assessment of what will be required if research is to improve predictability in the technology of cements. Part I discusses problems involved in the characterization of hydraulic cements in terms of reactivity, role of admixtures, surface area, crystal modification, and chemical compos

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19566.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The Fe2+‐Fe3+equilibrium in binary Na2O‐P2O5, glasses was studied by equilibrating glass melts at different temperatures in air. The enthalpy change (δH) of the reaction 1/2Fe2O3⇌FeO+1/4O2was calculated for 4 glasses. The results indicate that (1) the equilibrium shifts toward the oxidized state as the Na2O content of the glass increases (plots of log ([Fe2+]/[Fe3+]) vs mol% alkali were linear) and (2) ΔHvalues for glasses of different composition are nearly equal but differ from the standard (calculated) value for the reaction. The experimental ΔH values were nearly equal to that for the reaction FePO4→1/3 Fe3(PO4)2+ 1/6P2O5+1/4O2, indicating that Fe forms phosphate or polyphosphate configurations in the Na2O‐P2O5glasses. In certain of the glasses studied a faint‐pink solid precipitated; its X‐ray diffraction pattern indicated that its principal component is crystalli

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19567.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

An instrument for measuring spectral transmittance at wavelengths from 0.25 to 7 μm of samples at temperatures between ambient and 1300°C is described. Data showing the effect of temperature on the fundamental, Fe, and water absorption bands in glass are given and discusse

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19568.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The kinetics of the K+⇌ Na+exchange in Na2O·3SiO2glass at 350°C were studied. The distribution of K in the glass specimens after exchange in molten KNO3was determined with an electron microprobe. The calculated interdiffusion coefficients, which varied with the local composition in the glass, were compared with those obtained using the Nernst‐Planck equation and Fleming and Day's self‐diffusion data for xNa2O. (1‐x)K2O·3SiO2glasses. Deviations of the observed interdiffusion coefficient from the Nernst‐Planck formula were noted. These deviations are explained on the basis of changes in the average size of the alkali ion sites and in the strain energy that occur during

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19569.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Magnesium aluminate powders, both pure and doped with 0.5 wt% LiF, were hot‐pressed under vacuum at 1050°, 1170°, and 1290°C and 2500 and 5000 psi. Densification data were analyzed according to the classical hot‐pressing equation,In P/P0= ‐Kt; deviations are discussed in terms of the Occurrence of primary recrystallization. Examination of fracture surfaces and thermally etched polished surfaces by SEM corroborated this approach, indicating that strain‐induced primary recrystallization Occurred during hot‐pressing. Increased hydrostatic components of stress resulting from the presence of a liquid phase associated with LiF are proposed as the cause of plastic flow in the LiF‐doped spinel at low temperatures. Analogies are suggested between densification during primary recrystallization and reactiv

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19570.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY