摘要:

This review examines the stages of drying, with the emphasis on the constant rate period (CRP), when the pores are full of liquid. It is during the CRP that most of the shrinkage occurs and the drying stresses rise to a maximum. We examine the forces that produce shrinkage and the mechanisms responsible for transport of liquid. By analyzing the interplay of fluid flow and shrinkage of the solid network, it is possible to calculate the pressure distribution in the liquid in the pores. The tension in the liquid is found to be greatest near the drying surface, resulting in greater compressive stresses on the network in that region. This produces differential shrinkage of the solid, which is the cause of cracking during drying. The probability of fracture is related to the size of the body, the rate of evaporation, and the strength of the network. A variety of strategies for avoiding fracture during drying are discussed.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05082.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A thermodynamic assessment of the quasi‐binary system CaO‐Al2O3has been made using a computerized CALPHAD (calculation of phase diagrams) technique. The actual optimization was carried out with a computer program for the optimization of parameters in thermodynamic models called PARROT. The liquid phase is described by a simple two‐sublattice subregular solution model with Ca2+and Al3+as cationic species and O2‐as anionic species. All solid phases are treated as stoichiometric compounds. A consistent set of parameters describing the system is presented, and numerous comparisons with experimental data are made. There is a lack of accurate data in the high‐alumina part of the system, and the importance of a better knowledge of the CaO·6Al2O3phase i

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05083.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Research has been conducted on the effects of the particle size distribution of a glass batch on the reaction path leading up to the first glassy phase. The research has involved DTA/TGA, X‐ray diffraction, and SEM/EDS studies of particle size effects on the reaction path. The results of the studies were compiled to give a description of the reaction path for three soda‐lime‐silica batches, each with a different silica particle size distribution. The purpose of this work was to determine the effect of the silica particle size distribution on the reaction path and to determine the feasibility of building a predictive computer model consistent with these re

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05084.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Fine, homogeneous lead lanthanum zirconate titanate (PLZT) powder prepared by the hydrolysis of an aqueous nitrate solution with ammonia gas exhibits high reactivity when calcined. The minimum temperature for crystal formation in PLZT is 400°C. The kinetics of crystallization between 400° and 600°C are studied isothermally by XRD. The isothermal crystallization process is best fitted to a first‐order equation derived for a random, nucleation‐controlled system on a large number of small particles with an activation energy of 297 kJ/mol. Characterization of the powder by XRD line‐broadening and BET surface‐area examination in the range 400° to 500°C shows a microstructure consisting of ∼20‐nm subunits agglomerated into ∼60‐nm particles. Each subunit evidently generates a single nucleus, which grows

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05085.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A new ceramic dental mold can cast excellent Ti restoratives by controlling expansion due to the oxidation of additive metal particles. The packing structure of the metal and aggregate particles in the mold can be considered a function of the size distribution of the aggregate grains. An investigation of the expansion mechanism reveals three different relationships of void fraction versus linear thermal expansion for the molds at the high temperature under which oxidation of the metal particles occurs. Room‐temperature casting, favorable for making high‐quality Ti restoratives, can also be achieved by precisely controlling both the amount of additive metal powder and the compositional distribution of aggregate grain sizes in the m

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05086.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Rare‐earth aluminosilicate glasses of the general formula 20R2O3· 20Al2O3· 60SiO2have been formed for 10 of the 14 possible rare‐earth oxides. Two series of “mixed‐rare‐earth” glasses were also formed (Nd/Er and Nd/Y). These glasses exhibit exceptionally high glass transformation temperatures, moderate thermal expansion coefficients, and refractive indices of approximately 1.65. The glass transformation temperature and thermal expansion coefficients vary linearly with the field strength of the rare‐earth ion. No evidence of a “mixed‐rare‐earth effect” was observed. MAS‐NMR indicates that the aluminum ions are tetrahedrally coordinated in at le

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05087.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Electrical de fields applied through electrodes on either side of a slow‐running crack in soda‐lime‐silica glass resulted in a deviation of the crack plane and in delayed deceleration, arrest, and healing. In some cases crack closure occurred while still under load. Resumption of propagation resumed gradually upon removal of the field. It is suggested that the effects involve displacement of the dilated negatively charged zone at the crack tip, while healing is effected by reformation of bonds between the crack sur

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05088.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effect of shock treatment on the kinetics of transformation of transition‐phase alumina has been examined. Alumina powder, consisting of spherical particles produced by melting and quenching, was shock‐treated at 13‐ to 26‐GPa maximum pressure and subsequently heat‐treated at 1000° and 1050°C for various times. At 1050°C, the transformation of unshocked powder was typical of other aluminas with an incubation period of 60 min before significant conversion occurred. In contrast, in the shock‐treated material, no incubation period was observed and the α‐phase content increased exponentially with time. The growth kinetics of the shocked powder corresponded to a linear growth process with an activation energy of 482 kJ/mol. TEM examination revealed α‐phase morphologies consisten

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05089.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The interaction between two spherical, rigid inclusions in an infinite, linearly viscous, densifying medium has been studied. The stresses in the vicinity of the two spheres are highly anisotropic, with significantly enhanced rates of densification in the gap between these particles. A pairwise‐additive approximation for the densification rate of the composite is presented and compared with the composite‐sphere and self‐consistent models described by Sc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05090.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A model is used to predict solid particle formation during spray pyrolysis by correlating droplet shrinkage before salt precipitation with its relative solution saturation. For the rapid drying conditions and droplet size of ∼ 10 μm, which are characteristic of conventional spray pyrolysis, solid salt particles are formed when a droplet's initial relative solution saturation is ∼ 10−2and the precipitated salt is sufficiently permeable to permit evolution of the remaining solvent after precipitation. It is proposed that this concentration allows the drying droplet more time and a shorter diffusion distance in which to maintain chemical homogeneity before precipitation. Using these concepts it is demonstrated that zirconyl chloride (ZrOCI2· 8H2O) and zirconyl hydroxychloride (ZrO(OH)CI) are excellent zirconium salts for solid zirconia particle synthesis by spray py

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb05091.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY