摘要:

calcium silicates such as C3S, βT‐C2S, and γgM‐C2S†were carbonated under saturated humidity at room temperature. Carbonation products were examined by DT‐TGA, gasphase mass spectroscopy, and XRD. Two types of carbonate were produced: one type, which was rather poorly crystallized, was decarbonated at a very low temperature, below 600°C; the other type was a crystalline phase such as calcite, aragonite, and/or vaterite which was decarbonated above 600°C. The data were compared to existing data for calcium carbonates and basic calcium carbonates. The results suggest that an amorphous calcium silicate hydrocarbonate was one of the carbonation products which formed during the hydration/carbonati

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09057.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The structure of pure zirconia powders prepared by homogeneous precipitation was examined by electron microscopy. Some of these powders consisted of metastable tetragonal zirconia in the form of spherical aggregates up to 1 μm in diameter. The size of single crystals within these particles exceeded 100 nm, which is much larger than usually reported for metastable zirconia. We conclude that the existence of these large teragonal monocrystals is due principally to the very fine internal porosity within the domains, which gave rise to a surface area/volume ratio sufficient to stabilize tetragonal zirconia by the same mechanism as in nanocrystalline powders

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09058.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Novel microcomposite powders, consisting of inert cores (αAL‐Al2O3) surrounded by reactive cement‐based coatings (CaAl2O4), were synthesized by a modified Pechini process. The evolution of the crystalline CaAl2O4phase during calcination was studied using multiple analytical techniques, including DRIFTS,13C and27AlMAS FT‐NMR, and XRD, for both pure CaAl2O4and CaAl2O4‐coated Al2O3precursor powders. In both powders, decomposition proceeded via hydrocarbon chain scission and removal of ester groups at low temperatures (T450°C). These decomposition processes were accelerated by the underlying Al2O3cores. Transmission electron microscopy (TEM) of the fully calcined powders showed that the inert αAL‐Al2O3particles were surrounded by relatively uniform CaAl2O4coatings ranging in thickness from approximately

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09059.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Scanning acoustic microscopy (SAM) has been applied to investigate Vickers indentation‐induced damage in Y2O3‐stabilized tetragonal zirconia polycrystal (Y‐TZP). The leaky Rayleigh wave velocity,vR, around the indentation is determined from the V(Z) curve technique. A considerable anisotropy invRis observed within the elastic/plastic zone which results from the indentation‐induced residual stresses. In contreast, an isotropic reduction invRis found within the indentation core, implying the presence of microcracks. Furthermore, the SAM observations reveal that the elasic/plastic boundary is axisymmetric with respect to the loading axis and that its radius is 1.2 times as large as the indentation half‐diagonal. These results are discussed in terms of an analysis based on the pressurized‐sphericalc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09060.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

An investigation was carried out concerning the effect of mullite seed particles on phase development, densification behavior, and microstructure evolution in powder compacts prepared with silica/alumina microcomposite particles. The incorporation of ∼2 wt% seed particles in the microcomposite powder compacts had relatively little effect on densification, but resulted in significant decreases in the temperature for mullite formation and the grain sizes in mullitized samples. Samples could be sintered to almost full density and subsequently converted to mullite with average grain sizes ≤0.4 μm at temperatures in the range of 1300°‐1400°C. The available evidence indicated that mullite formation occurred primarily by nucleaton and growth in the siliceous matr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09061.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effect of oxygen nonstoichometry on physical and magnetic properties of a Mn‐Zn ferrite has been studied by using annealed samples under various oxygen pressures and temperaure. The dependence of oxygen nonstoichiometry7 on disaccommodation and Fe2+content changed at the stoichiometric composition, and the lattice parameter became maximum at the stoichiometric composition. These results suggest that Mn‐Zn ferrites have two different defect structures: cation vacancies in cation‐deficient regons and oxygen vacancies in anion‐deficient regions. Initial permeability was maximum and power loss was minimum at the stoichiometric composition, suggesting he importance of the number of point defects for the magnetic pro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09062.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Piezoelectric ceramic/polymer composites with 1‐3 connectivity were made by weaving sized lead zirconate titanate (PZT) fiber bundles through a honeycomb support. Bundles comprised of fine‐scale, 20‐50 μm green fibers, made using the viscous suspension spinning process, were sized to increase their manageability. The sizing step comprised of soaking the green PZT fiber bundles in an aqueous solution of poly(vinyl alcohol), then pulling the wet fibers through a steel sizing die. Sizing resulted in dense and flexible fiber bundles, which facilitated composite construction and led to composites with increased volume fractons. Sintering, polymer embedding, and machining produced a composite exhibiting 1‐3 connectivity. Composites with 10 vol% PZT yildedd33values of 230 pC/N and a dielectric constan

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09063.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Dysprosium‐doped glasses were prepared in the system of gallium‐based sulfide, tellurite, zirconium‐baed and indium‐based fluorides and their optical properties were studied. From the absorption cross sections of fivef‐fbands, three Judd‐Ofelt parameters, ωt(t= 2, 4, 6), of Dy3+ion were determined. The compositional variaton of the ω2value showed the order sulfide>tellurite>fluorozirconate>fluoroindate, whereas the ω6value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (4F9/26H13/2)/(4F9/2)→6H15/2) is explained by the ratio of ω2/ω6of doped Dy3+. The emission probabilitiesAand the branching ratio β from6H9/2and6F11/2levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω2against the glass composition. In the sulfide glass,Awas 2.6 × 103S‐1and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr3+:1G4leve

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09064.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The wetting of polycrystalline alumina by a colored, calciamagnesia aluminosilicae glass was found to be dependent on temperatutre between 1300° and 1500°C, but independent of gas atmosphere effects. Neither the oxygen partial pressure, oveer the range of 10‐6to 10‐10Pa, the gas buffer system (Co/CO2or H2/H2O), nor pre‐equilibration of the substrate surface with the atmosphere at tge exoperimental temperature before solid‐liuid interface formation affected the stable contact angle. An initial drop in contact angle the stable contact angle. An initial drop in contact angle occurring within the first hour is attributed to repaid dissolution of alumina and the formation of a stable glass/alumina interface. The contact angle after an 8‐h isothermal hold decreased from 1300° to 1500°C. The solid‐liquid interfacial energy, μMS1, controls the wetting behavior. Changes in μMs1are attributed to he breakup of the silica network as temp

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09065.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1995.tb09066.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY