摘要:

The interactions of very pure and practically 100% dense α‐SiC with nickel and iron at 850°C were investigated. Large reaction zones, consisting of carbon and silicides of Ni and Fe, were examined by microprobe analysis. By means of marker experiments, the diffusion mechanisms were investigated: only Ni and Fe migrate through the reaction layer. Isothermal sections of the ternary phase diagrams Ni‐Si‐C and Fe‐Si‐C at 850°C a

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05903.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Subsolidus‐phase studies in the calcium‐silicon‐oxygen‐nitrogen system have been conducted using the reactive precursors calcium nitride, calcium oxide, and silicon nitride. A new structure has been isolated with a large, face‐centered cubic lattice, a=1.4864 nm, which coexists with several new CaSiON phases as well as Ca3Si2O4N2and the unknown “D’ phase, reported previously by other workers. The new structure is not isotypic with any known mineral oxide. The highest degree of phase purity has been obtained using a 1.1 calcium nitride:silicon nitride starting mixture. Structural and approximate compositional analyses were conducted by X‐ray diffraction and TEM energy dispersi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05904.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Tape‐cast slurries of Ba2YCu3O7powders offer a convenient means of preparing sintered ceramic samples for critical current density (Jc) measurements where the transport cross section is small and the current electrode areas are large. Samples were sintered from 900° to 1000°C and characterized for bulk density, grain size, phase composition, Tc, and Jc. Bulk density and grain size both increase with sintering temperature while all samples were single‐phase perovskite except for those sintered at 900°C. The onset temperature for superconductivity is constant at about 93 K while the transition sharpens to R=0 at about 92 K for the densest samples. Jcrises with sintering temperature to a maximum of ∼103A/cm2. A linear relationship between Jcand bulk density is predicted from microstructural consid

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05905.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Li2O and LiAlO2are two candidates for solid breeder materials in the United States' Fusion Power Program. Critical to breeder design efforts are thermophysical data, the bulk of which have only recently become available, for un‐irradiated lithium ceramics. This paper expands the current limited data base by presenting thermal conductivity data between 373 and 1173 K for both materials following fast neutron irradiation. Samples were irradiated at 773 to 1173 K to lithium burnups ≤11.5 × 1020captures/cm3. Comparisons are made between these data and those from unirradiated archive samples of these same mater

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05906.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Microstructures of Y‐Ba‐Cu‐O superconductor were observed using a polarized microscope. Orthorhombic and tetragonal phases were easily distinguished by the optical etching with cross‐polarized light. In the specimen cooled rapidly in oxygen, it was possible to see the path of oxygen diffusion by observing the variation of the twin concentration. At the boundary between transformed and untransformed materials, evidence for diffusion‐driven transformation could be cle

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05907.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In alumina, R‐curve behavior is frequently attributed to “wake” effects which partially shield the crack tip from the applied stress. A novel method is introduced to prove the existence of crack‐bridging wake effects and to examine their influence on toughness. Short double‐cantilever‐beam (DCB) specimens were modified to contain a machined notch at the back face of the specimen. As the growing crack enters this rear notch, the load‐bearing capacity of the specimen, and thus the effectiveness of the wake to withstand fracture, is determined. This paper describes the use of such a specimen to evaluate the magnitude of the bridging stresses developed and the contribution of the wake to toughness in polycrysta

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05908.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The electric‐field‐induced strain in single‐crystal BaTiO3was investigated. For crystals relatively free of twinning, a longitudinal strain of 0.35% can be induced just above the ferroelectric‐paraelectric phase transition temperature (Tc1) primarily by field‐forced paraelectric‐ferroelectric phase transition. For heavily twinned crystals, 90° domain reorientation under the applied electric field plays an important role in the induced strain below Tc1, and an induced strain of 0.6% is observed a few degrees below Tc1. Above Tc1, the electrostrictive property measured by a weak excitation field is purely intrinsic. When the excitation field is large, so that a field‐forced paraelectric‐ferroelectric phase transition is involved, the x33/P23value (where x33and P3are the induced strain and polarization along the z axis, respectively) is intrinsic at higher temperature, but may be modified at temperatures just at and slightly above Tc1by residual 90

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05909.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The presence of intergranular Cu2O has been identified in polycrystalline YBa2Cu3O7‐xsuperconducting samples (Tc∼90 K) which are prepared by dry‐powder processing techniques. Transmission electron microscopy was employed to determine the crystal structure of the phase while energy‐dispersive analysis provided the composition. The intergranular Cu2O, as indicated by XRD and shown by optical microscopy, is concentrated around pores and extends back along grain boundaries adjacent to these pores. Analysis performed on samples sintered in a furnace atmosphere at 950°C, with and without a post‐oxygen anneal at 450°C, gave simi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05910.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Fracture toughness of several different materials was measured using chevronnotched short bar and four‐point bend specimens For glass‐ceramic and ceramic samples both specimens gave valid results. Fracture toughness values measured with bend specimens are 5% to 10% higher compared to those of the short bar. Consistent results for glass could be obtained only with short bar specimens. The notch width of the bend specimen affected the stability of crack growth in glass samples. Fracture toughness values measured in the present study are in good agreement with those of the previous stud

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05911.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05912.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY