摘要:

Barium titanate shows discontinuous grain growth in the presence of small amounts of the liquid eutectic Ba6Ti17O40‐BaTiO3atT>1312°C. The exaggerated grain growth in the presence of the liquid phase can be explained in terms of a solution‐segregation process. The grain size distribution of sintered BaTiO3ceramics and the average grain size are strongly modified by addition of “seed grains” to BaTiO3powder. The addition of seed grains seems to be a general method of controlling the discontinuous grain growth of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04847.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The gelation of aluminum hydroxide sols obtained from aluminumsec‐butoxide has been studied as a function of the conditions of preparation, including pH, temperature, and time of aging. The preceding studies of Yoldas have been extended in more acidic conditions, up to a molar proportion of 1.12 HNO3per Al(OC4H9)3. It has been found that stable sols can easily be obtained by processing at any temperature between 20° and 90°C beyond a molar proportion of 0.28 HNO3. The corresponding gels are suggested to have a boehmite‐like structure in which there is a metastable folding of the (020) layers at 20°C, and a stable unfolding at 80°C, the two structures coexisting at intermediate processing tempe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04848.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The formation of Al2TiO5has been studied in equimolar Al2O3‐TiO2powder mixtures of ∼1μm particle sizes and moderate purity (∼99.8 wt%) at temperatures around 1300°C, where the free energy of formation is very small. Micro‐structural development and reaction kinetics indicate that different mechanisms operate depending on the advancement of the reaction. The rapid initial reaction stage is interpreted as the nucleation‐growth of Al2TiO5cells in a virtually non‐reacting matrix. The final reaction stage corresponds to the slow diffusion‐controlled elimination of Al2O3and TiO2dispersoids trapped during the growth of the initi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04849.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The phases existing in the system CaO‐SiO2‐CaF2were synthesized and their hydraulicity was determined. Out of these only the phase which corresponds to the formula Ca6–0.5xSi2O10‐xFxexhibited distinct hydraulic properties. The hydration rate of tricalcium silicate doped with CaF2declined with increasing degree of doping, while its compressive strength—found at a given degree of hydration—increased. The stoichiometry and specific surface area of the formed hydrates were altered because of the presence of fluorine in the crystall

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04850.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

When abraded or indented glasses are annealed, a strength increase of 20% to 30% is observed. Crack tip blunting and removal of tensile residual stress near the crack tip have both been proposed to explain this phenomenon. In order to resolve which is the more likely mechanism, the kinetics of strength increase of soda‐lime, borosilicate, and high‐silica glasses were measured as a function of heat‐treatment temperature and atmosphere. The sinusoidal profile decay of corrugated glass surfaces of the soda‐lime glass was also investigated at similar temperatures and atmospheres. From these two complementary measurements, it was concluded that the observed strength increase of glasses upon annealing is caused by crack tip blunting, most likely due to viscous flow assisted by water diffused from the atm

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04851.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Crystal growth of 4K2O·CaO·10SiO2from its own melt occurred with a faceted interface, while crystal growth from a melt ∼4 wt% richer in silica than the crystal showed dendritic morphology and growth from a melt ∼5 wt% leaner in silica showed dendritic growth at undercoolings30°C. The crystal growth velocities in all cases were independent of time and fit well the empirical relation In [U/(Tl‐T)1.6] =A – Q/T, whereUis velocity,AandQare constants, andTl, is the liquidus temperature of the melt. The crystal growth data for the three melt compositions lie together in a narrow swath when plotted using the above equation. An explanation for this behavior is proposed which suggests that the phase boundary reaction aided by nucleation at surface sites provided by screw dislocations determines the growth kinetics even when the melt and crystal have different c

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04852.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Y‐TZP ceramics with various amounts of glassy intergranular phase were fabricated in order to investigate the effect of this amorphous phase on the properties of TZP. The presence of a liquid silicate phase not only enhanced sintering but also controlled the evolution of distinctly different grain morphologies, dependent on the amount of liquid phase present. The influence of the glass phase on the transformability of grains is discussed with respect to the room‐temperature fracture toughness and surface degradation at 25

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04853.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Photoproduction of interstitial atomic hydrogen centers (H0i), apparently at the expense of boron electron centers (BEC) in barium aluminoborate glasses X‐irradiated at 77 K, is reported. Electron paramagnetic resonance studies of isothermal and isochronal annealing of BEC and correlated decay of BEC with corresponding growth of H0iunder exposure of light were carried out. Some possible interactions between chemical states induced by irradiation are discusse

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04854.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY