摘要:

Beta‐type CVD‐Si3N4plates (up to 1.1 mm thick) have been prepared by adding TiCl4vapor to the system SiCl4‐NH3‐H2at deposition temperatures of 1350° to 1450°C, while α‐type or amorphous CVD‐Si3N4was obtained without TiCl4vapor at the same deposition temperature. Three to four wt % 777V was included in the β‐type CVD‐Si3N4matrix. The density, preferred orientation, and lattice parameters of β‐type

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10307.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

A leaching experiment is conducted on thin transmission electron microscope samples of a tailored polyphase nuclear waste ceramic. The results demonstrate that the intergranular noncrystalline phase is preferentially dissolved, which calls attention to the possibly detrimental role of any intergranular glass in ceramics designed to immobilize nuclear waste.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10308.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

A simple method to determine the liquid‐in‐liquid immiscibility boundary is applied to a BaO‐B2O3glass. The method is based on the scanning electron microscope observation of the heat‐treated and quenched specimens and differentiation of the microst

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10310.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

EPR spectra of lead silicate glasses doped with small amounts of V2O5were studied at −150°C to room temperature. Only the glasses with the higher SiO2contents produced EPR signals. The spin Hamiltonian parameters are characteristic of the V(IV) species in axial symmetry. The values of g, g ⊥, A, and B indicate that V(IV) is present as VO2plus;in a tetragonally distorted octahedral site. This ion probably does not enter the SiO2network but rather behaves as a modifier ca

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10311.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10312.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Analyses of 131 particles of C‐S‐H in several mature tricalcium silicate pastes hydrated for 1 to 30 years gave a mean Ca/Si ratio of 1.46 with a range of 1.2 to 1.8. Similar analyses of 152 particles in mature cement pastes hydrated for 2 to 3 years gave a mean Ca/ Si ratio of 1.53 with a range of 1.0 to 2.8. Taken together with similar, previously published data for younger pastes, these findings indicate that the mean Ca/Si ratio does not change significantly after 1 day in tricalcium silicate pastes but decreases significantly with time in cement pastes; after several years, the mean Ca/Si ratios are similar in the two cases, despite the presence of other components in the C‐S‐H formed from cement. For the C‐S‐H of cement pastes, the mean Al/(Ca plus; Mg) and Fe/(Caplus;Mg) ratios increase with time but the mean S/(Caplus;Mg) ratio decreases. The composition of the AFm phase does not change greatly af

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10294.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Residual contact stresses about indentation flaws are demonstrated to have a strong deleterious effect on specimen lifetime in static fatigue. The underlying basis of conventional fatigue analysis is first examined critically and is argued to be deficient in the way the stress intensity factor for the flaws is related to the characteristic parameters of crack geometry and applied loading. In general, it is necessary to incorporate a residual term into the stress intensity formulation. A modified theory of static fatigue is accordingly developed, in which the residual contact stresses play a far from secondary role in the micromechanics of flaw evolution to failure. Strength tests on Vickers‐indented soda‐lime glass disks in water environment provide clear experimental confirmation of the major theoretical predictions. Implications of the residual stress effect concerning fracture mechanics predictions of lifetimes for “real” ceramic components under service conditions are di

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10295.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

In the modified chemical vapor deposition (MCVD) process for making glass fibers, most of the hydrogen coming into the reaction from hydrogen‐bearing impurities in the starting materials is not incorporated in the glass. It is instead mostly converted to HCl, which is not absorbed by the newly formed silica particles, and passes out the exhaust stack. The residual partial pressure of H2O formed in equilibrium with HCl in the presence of O2and Cl2accounts quantitatively for the OH appearing in the glass when the known solubility of H2O in silica is considered. The H2O/HCl equilibrium is quenched at a temperature below that of the reaction zone at a value for which the rate of reaction approximates the transit time across the deposition zone. Quantitative agreement is obtained for published OH concentrations produced by SiHCl3dopin

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10296.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The oxidation kinetics of sintered α‐ and hot‐pressed SiC were investigated over the temperature range 1200° to 1500°C. Oxide thicknesses were measured by ellipsometry, interferometry, and profilometry. The two materials behaved similarly, exhibiting parabolic behavior for short times (up to 100 min) followed by decreasing rates for longer times. The oxidation rates for the sintered material were lower than for the hot‐pressed material at all temperatures studied. Apparent activation energies varied with temperature, from 134 to 389 kJ/mol for the sintered alpha material and from 155 to 498 kJ/mol for the hot‐pressed variety. Platinum‐marker experiments indicated that new oxide is formed at the silicon carbide/ oxide interface. It is proposed that the diffusion of oxidant through the growing oxide film is the rate‐controlling process. The details of the oxidation kinetics were complicated by the partial crystallization of the oxide film at higher temperatures, leading to complex paths for transport of oxidant through the film so that the apparent activation energies are difficul

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10297.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The redistribution of the boron impurity in sintered α‐SiC during thermal oxidation was investigated over the temperature range 1200· to 1400,°C using sputter‐induced photon spectrometry (SIPS). The process was modeled with the Stanford University Processing Engineering Models Program (SUPREM) which permitted the estimation of diffusivities of boron in the growing oxide and the substrate. The process is characterized by segregation of the boron in the oxide near the interface and a corresponding depletion of boron in the substrate. The apparent diffusivities in the oxide were about three orders of magnitude higher than the published values for boron in pure SiO2, presumably because the film is much less pure than pure SiO2. The apparent diffusivities of the boron in the polycrystalline silicon carbide were almost five orders of magnitude higher than the published values for boron in single‐crystal silicon carbide. The diffusivities in the silicon carbide represent boron transport via the grain boundaries which were partially oxidized during the thermal t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb10298.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY