摘要:

TiO2above 4 mol% is an effective nucleating agent for CaO–P2O5glass which also contains substantial SiO2and Al2O3additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β‐Ca2P2O7, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca‐P‐Ti‐Si‐Al oxide phase surrounded by impure AlPO4dendrites. Metastable calcium phosphate grows on the AlPO4dendrites and later transforms

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04237.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composites were fabricated by a novel technique referred to as “relic” processing. Basically, this involved impregnating a woven carbon‐fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon‐fiber fabric twice in an intermediate concentration (405‐mg PZT/(1‐g solution)) alkoxide PZT solution and sintering at 1285°C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT‐fiber orientation and polymer‐matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes,K= 75,d33= 145 pC/N,dh= 45 ± 5 pC/N, anddhgh= 3150 × 10−15m2/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces,K= 190,d33= 250 pC/N,dh= 65 ± 2 pC/N, andd

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04238.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The density of Ga2O3liquid in equilibrium with air has been measured at 18000to 19000C using an Ir double‐bob Archimedean method. The data yield the following description of the density of Ga2O3liquid: ρ= 4.8374(84)–0.00065(12)(T −18500C). This density‐temperature relationship is compared with the partial molar volume of Ga2O3in glasses in the systems CaO–Ga2O3–SiO2and Na2O–Ga2O3–SiO2, corrected to the glass transition temperature using thermal expansivities. The comparison illustrates that a positive excess volume term is required in these systems at low temperature. This observation is similar to those deduced from studies of the partial molar volumes of Fe2O3and Al2O3i

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04239.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

It was found that the IR absorption bands appearing at 600 to 1600 cm−1, which had been previously assigned to the fundamental vibrations of [BiO3] or [BiO6] polyhedra, are due to residual carbonate ions (CO2−3) dissolved in Bi‐Sr‐Ca‐Cu‐O glasses. The concentrations of the remaining CO2−3in the Bi2.2Sr2Ca1Cu2Oxglasses that melted at 1100° and 1400°C are 170 × 10−5mol/cm3(3.3 mol%) and 3.2 × 10−5mol/cm3(0.25 mol%), respectively. The apparent activation energy for the dissociation of the carbonates was approximately 220 kJ/mol. The CO2−3content in the precursor glasses did not significantly affect the superconducting properties of the r

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04240.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Processing and nitridation of MgO/CeO2‐doped silicon containing SiC whiskers was studied. The reaction time was dramatically reduced by incorporating MgO/CeO2dopants and SiC whiskers in silicon powders prior to nitridation. The decomposition of SiC whiskers depends on the nitriding temperature, sintering aids, and whisker surface compositio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04241.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The oxidation reaction equilibrium constant and the holes mobility inp‐type‐semiconducting SrTiO3single crystals were determined directly by simultaneous Hall and conductivity measurements between 500° and 1000°C. This information and the SrTiO3defect model were used to interpret the electrical measurements taken on this substance which represents a model substance for semiconducting perovskites. Measurements with varying oxygen partial pressures showed that shifts of the crystal defect equilibrium give rise to changes in the carrier concentration with unchanged carrier mob

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04242.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The mechanism for the slow rate of reaction between portland cement and water during the early stage is not well understood, but it probably is controlled by either the rate that the reactants diffuse through a barrier that surrounds the unreacted cement grains or by the rate that nuclei of the stable product form and grow or by both rates. New evidence using environmental scanning electron microscopy is presented about the structure of a layer that forms around the particles of cement. Preliminary observations that relate mixing to the structure of the layer are also presented.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04243.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

BaTiO3ceramics were fabricated by sintering a mixture of fibrous and commercial powders, and the effects of crystal‐axis orientation on the resonance characteristics of the poled specimens was investigated. Resonance in the radial direction was observed only for the fibrous BaTiO3ceramic disk. The degree ofc‐axis orientation of the sintered compact decreased with an increase in the initial amount of the commercial powder, and the decrease in the degree of orientation caused the appearance of the resonance in the thickness direct

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04244.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Ductile toughening of niobium aluminide (Nb2Al) has been accomplished in situ while combustion synthesizing the compound from a mixture of Nb, Al, and 3 wt% B powders. An enhancement of the fracture toughness of the resulting Nb2Al has been shown to be primarily caused by the interaction of propagating cracks and cores of ductile Nb phases inside the partly combusted Nb powders.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04245.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The room‐temperature fracture behavior of polycrystalline MoSi2was characterized using Vickers indentation fracture. Fracture analysis was aided by the optically active grain structure of MoSi2revealed under polarized light. Radial crack propagation from indentations was found to be predominantly transgranular. The approximate indentation fracture toughness of MoSi2was 3 MPa.m1/2, while the measured hardness was 8.7 GPa. Fracture behavior is believed to be controlled by anisotropy and cleavage energy of the tetragonal MoSi2crystal structur

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04246.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY