摘要:

A foaming‐agent‐free aluminate glass of the composition 59CaO·7MgO·27Al2O3·7SiO2(mol%) exhibited marked effervescence on heating the as quenched glass to near its softening temperature. Numerous bubbles evolve over the entire glass. Their radii are nearly constant (50 μm) and depend on heat‐treatment conditions. Their maximum volume goes up to ∼ 10 vol%. The bubbles consist solely of oxygen gas and pressure is ∼ 130 kPa (1.3 atm) at the softenin

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04958.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The sintering behavior and microstructural development of dielectric ceramics based on Pb(Mg1/3Nb2/3)O3‐PbTiO3solid solutions are greatly affected by the formation of a liquid phase at ∼ 1290°C. Prolonged sintering at and above this temperature gives rise to an excessive PbO loss and the resultant variation in composition leads to an inhomogeneous microstructure. The inhomogeneity is characterized by the formation of a dense, localized region containing a PbO‐rich liquid near the surface with a porous interior region in the bulk of the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04959.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A novel procedure is outlined whereby fracture toughness values for ceramics can be measured under uniaxial tension (mode I) in specimens containing a fatigue crack. Circumferentially notched rods of rapolycrystalline aluminum oxide were precracked in cyclic compression to introduce a fatigue crack at room temperature, following the technique proposed by Suresh and co‐workers.7,10,11Subsequently, the precracked rods were fractured in pure tension. Highly reproducible values of fracture toughness were obtained using this metho

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04960.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Sample disks prepared from Al2O3(61 wt%), SiO2(28 wt%), and Fe2O3(II wt%) powders were sintered at 1270° and 1440°C and then annealed between 1300° and 1670°C. The annealed samples consisted of mullite as the main compound with minor amounts of glass and sometimes magnetite. The iron content of the mullites decreases strongly from ∼ 10.5 wt% Fe2O3at 1300°C to ∼ 2.5 wt% Fe2O3at 1670°C. A complex temperature‐controlled exsolution mechanism of iron from mullite is

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04961.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The independent crystallization sequence of an Al2O3component is modified in the presence of SiO2and vice versa. Mixed SiO2‐Al2O3, gel (28 wt% SiO2and 72 wt% Al2O3) forms neither cristobalite nor γ‐Al2O3and corundum at 1000°C but forms Si‐Al spinel; an amorphous aluminosilicate phase invariably also forms after the gel is heated. However, the composition of this amorphous aluminosilicate phase is not as ye

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04962.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The sodium titanates Na4TiO4, α, β‐, and γ‐Na2TiO3, Na8Ti5O14, Na2Ti3O7, and Na2Ti6O13, all of which can be synthesized in the temperature range 800° to 1200°C, have been characterized by X‐ray diffraction (XRD) and Raman spectroscopy. The existing XRD data have been critically reviewed and several inconsistencies and errors have been

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04963.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Submicrometer silicon powder synthesized by thermally induced, vapor‐phase reaction in an aerosol reactor was densified by reaction sintering to form Si3N4. The densification behavior of these spherical, nonagglomerated particles in the 0.1 to 0.2 μm size range is described. Competition between densification by silicon sintering and reaction product infilling was observed at typical reaction sintering temperatures. In addition, pore growth during the early stages of silicon presintering adversely affected nitrogen permeability and nitriding rates. The factors influencing the nitridation of ultrafine silicon powders are discuss

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04964.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The dissolution of Al2O3, MgAl2O4. Y3Al5O12, MgO, and other refractory oxides in molten Ca‐Al silicates is heterogeneous over significant temperature and silicate composition ranges with the formation of at least one solid reaction product at the oxide‐silicate interf

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04965.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Transmission lectron microscopy using bright‐field and darkfield imaging and selected area electron diffraction was used to study ceramics pyrolyzed from a variety of organometallic polymer precursors. Determination of whether the pyrolyzed products were truly amorphous or microcrystalline was made and correlated to previous scanning electron microscopy or powder X‐ray diffraction observations. Results indicated that most of the resultant as‐pyrolyzed microstructures were amorphous, and that polymer pyrolysis presents significant opportunities for fabricating unique amorphous mate

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04966.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

For a one‐component crystalline solid, the driving force for diffusion in a temperature gradient by any path is the gradient in the equilibrium vapor pressure. A When transport is limited by a surface step, the driving force is the difference in vapor pressures at the extremes of the temperature gradients. Sample calculations suggest that temperature gradients are important in driving densification during fast firing and probably are important during conventional firin

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04967.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY