ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06493.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Colloidal processing has been shown to produce low defect and uniform ceramic microstructures from submicrometer ceramic powders. These concepts were applied to colloidal pressing to determine critical design relationships for uniaxial consolidation of dense and uniform green bodies from colloidal suspensions. Carefully controlled constant rate of strain consolidation experiments were carried out using alumina in water. The compression index decreased from 0.143 for a poorly dispersed alumina system to 0.077 for a well‐dispersed alumina suspension compression curve, indicating that the well‐dispersed system is stiffer in consolidation. The compression curves showed that, as the degree of dispersion decreases, increased consolidation stresses are required to achieve a given particle packing density. The compression index increased with increasing strain rate for well‐dispersed alumina suspensions. Permeability through the sample ranged from 3 × 10–8to 4 × 10−7cm/s, decreasing with decreasing void ratio during consolidation. Well‐dispersed samples gave lower permeabilities than did poorly dispersed samples over a given consolidation increment. Coefficients of consolidation were nonconstant over the experimental effective stress range, invalidating the general solution to the linear consolidation equation. An approximate incremental solution was applied which indicated rapid pressing cycles are possible by starting with a suspension having a high solids concentration. Application of this consolidation data to nonlinear consolidation models is recommended for more exact prediction of conso

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06494.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Glasses in three alkaline‐earth (Ca, Sr, and Ba) galliosilicate systems were prepared, and the density, viscosity, thermal expansion coefficient, and glass transformation temperature were measured. All glasses contain 30 mol% alkaline‐earth oxide. It is suggested that alkaline‐earth ions can play a role in the glass structure which is similar to that of an intermediat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06495.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The tolerance of titanate nuclear waste ceramics to fluctuations in the concentrations of processing contaminants was monitored using X‐ray diffraction, electron microscopy, secondary ion mass spectrometry, and analysis of dissolution liquors. Several waste forms were fabricated, all of which contained idealized Purex waste simulant and, in addition, varying quantities of the common waste stream impurities P2O5, MgO, Fe2O3, Na2O, and SiO2. Incorporation of the oxides individually stabilized new phases including monazite (P2O5), pseudobrookite (MgO), loveringite (Fe2O3), freudenbergite (Na2O), and pollucite (SiO2)—only the latter phase deleteriously affected waste form performance by promoting cesium dissolution. However, when the processing contaminants were added simultaneously, a number of synergetic effects, particularly the stabilization of a soluble glassy phase, resulted in elemental losses which were an order of magnitude greater for some matrix and radwaste species. It was found that up to 25 wt% of the idealized Purex waste could be incorporated in the waste without diminution of its propert

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06496.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Reaction‐controlled binder burnout of ceramic multilayer capacitors (CMCs) is conducted in a series of small‐scale experiments. the burnout process is followed by monitoring the weight of the CMCs. The observed maximum weight loss rate, obtained with a conventional linear heating process, is used to design a weight‐time program for a reaction‐controlled process. In this process the actual CMC weight is controlled to closely follow the weight program by means of continuous control with the batch temperature. The advantages of this procedure are discussed. The results of the present study, although being restricted to oxidative burnout of a special product, are thought to be of some use for other ceramic burnout situations. The relevant parts of controller design are discussed together with some comments on s

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06497.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The polymorphic phase transformation of PbO from massicot to litharge phase is easily produced by mechanical force. The transformation is relatively quick by wet ball‐milling. The additions of TiO2and ZrO2tend to retard it. A second‐order exponential relation is observed between the fractional conversion and the milling time for pure PbO, PbO‐TiO2, and PbO‐ZrO2‐TiO2systems with a rutile constituent. This exponential relation is changed into a first‐order logarithmic relation when anatase instead of rutile is used. Although the PbOssphase is observed irrespective of the phase of the PbO in the raw materials, this PbOsspeak is more obvious when massicot PbO or anatase TiO2is used. The formation of PbOssphase is also dependent on the reactivity of the ZrO2, and its presence can affect the formation and piezoelectric properties of P

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06498.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A systematic study of the role of the composition of polysilane homo‐, co‐, and terpolymers on their pyrolysis yield to silicon carbide (SiC) was performed. The ceramic yield was found to increase as the poly(dimethylsilane) structure was substituted with hexyl and, especially, phenyl groups. the best improvement in SiC yield came from the copolymerization of low levels of silane monomers containing unsaturated groups (vinyl or allyl). For a given composition, ceramic yield increased with increasing heating rate under argon. Infrared spectroscopy and thermogravimetry were used to identify the chemical changes accompanying the pyrolysis process up to 1200°C. These changes included the formation of carbosilane linkages and Si‐H

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06499.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Two germania gels were synthesized by hydrolytic condensation of germanium ethoxide and by dissolution of germanium dioxide powder in ammonium hydroxide solution. The two gels were characterized using differential scanning calorimetry, X‐ray powder diffraction, surface area and weight loss data, and infrared spectroscopy. The results indicate that, in gels, germanium is capable of tetragonal as well as hexagonal coordination, resulting in different crystallization behavior

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06500.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Colloidal sols of ZnS were prepared by thermal decomposition of thioacetamide in acidic zinc solutions. Precipitation was carried out in the presence of nitrate, acetate, chloride, and sulfate ions. Particle morphology was influenced by the chemical nature of the anions present in the solution as well as the rate of sulfide ion generation. Spherical, monodisperse particles having a specific type of particle size distribution, i.e., monosized, bimodal, or continuous distribution, with mean sizes in the range of 0.15 to 3 μm, were formed depending on the anion type and sulfide ion generation rate. Individual particles always consisted of clusters of sphalerite crystallites except when sulfide ions were generated at low rates and sulfate ions were present. In such cases a mixture of α‐ and β‐ZnS was

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06501.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Results of shrinkage measurements on constrained and corresponding unconstrained films of materials that densify by viscous flow or solid‐state diffusion mechanisms have been presented. Constrained‐film shrinkage was measured in situ during sintering using laser reflectance; unconstrained‐film shrinkage was measured using scanning electron microscopy (SEM). Data for unconstrained films were fitted to densification kinetics expressions for the operative densification mechanism. Constrained‐film shrinkage behavior predicted by the Scherer‐Garino model,1using expressions that fit data for the unconstrained case, was compared to actual data for the constrained films. Data for the viscous sintering case fit the predictions made by the model well, but data for densification by solid‐state diffusion deviated from predicted behavior even when grain growth was accounted for, possibly because of pore growth caused by local de

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06502.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY