摘要:

Isothermal crack healing and strength recovery were investigated in UO2pellets subjected to varying degrees of thermal shock by water quenching. It is shown, as was speculated in an earlier paper, that crack density and/or crack width in the specimen strongly influence the subsequent healing behavior. Experimental data were used to demonstrate that, under the present thermal shock conditions, the time required for complete healing increased exponentially with the number of cracks/unit length of the specimen.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16091.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The effects of porosity and grain size on the magnetic properties of NiZn ferrites were examined on groups of specimens with controlled porosity and grain size; both the permeability and theB‐Hloop were measured. The demagnetizing factor, which is proportional to porosity, was estimated on the basis of the permeability‐porosity relation determined. The discussion of the permeability‐grain size relation takes into consideration the dependence of domain wall spacing on grain size. The experimental results for theB‐Hloops indicate that the remanent magnetic flux density is independent of grain size and the coercive field is independent of porosity. Both the remanent magnetic flux density‐porosity and the coercive field‐grain size relations are explained via the formul

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16092.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The problem of unidirectional diffusion with 2 moving boundaries is pertinent to the study of reactions between condensed phases. The solution for binary diffusion is presented, and an eigenvector approach is outlined for the solution of the problem in a ternary diffusion system. The complete solution is given for some specific situations. Typically, the diffusion path deviates from the series of simple mixtures and tends to follow the direction of the minor eigenvector. This behavior is also true for cases where linear approximations are applicable.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16093.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The critical stress‐intensity factor,K1C, and the fracture strength, σf, have been investigated on both hot‐pressed and sintered lithia‐stabilizedβ”‐alumina. The hot‐pressed material possessed a strong preferred orientation with many of the basal planes aligned perpendicular to the direction of hot‐pressing. BothK1Cand σfwere found to be orientation‐dependent. Two regimes of fracture were identified. In fine‐grained material (<120 μm), the strength was slightly dependent on grain size.For larger grain sizes, the strength decreased rapidly with increasing grain size and the fracture mode was almost entirely transgranular. TheK1Cvalues for sinteredβ”‐alumina were in the same range as those obtained o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16094.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

An arc fusion technique was used to grow single crystals of MgO with an aliovalent impurity level of ∼ 250 ppm. Diffusion coefficients for Cr3+in single‐crystal MgO were measured from 1353° to 1553°C using a high‐specific‐activity isotope,51Cr. The diffusion coefficient of51Cr for both arc‐grown and vapor‐deposited MgO crystals can be characterized by an activation energy of 70.0±2.1 kcal/mol. These results are comparable with the interdiffusion coefficients in Cr2O3‐MgO when the interdif‐fusionDis extrapolated to low

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16095.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

A factorial design experiment was conducted to determine the major parameters affecting the densification of mixtures having the composition (in mol%) 50 Si3N4, 25 A12O3, and 25 A1N. Improved densities of the resulting sialon were achieved using a longer milling time and SN‐502 Si3N4powder. However, sialon samples prepared from the SN‐502 powder contained some of the X‐phase, whereas those fabricated from AME Si3N4powder did not. This difference is considered to be due to the higher SiO2content of the SN‐502 powder and its greater susceptibility to partial hydrolysis during the milling process. Reaction‐sintered sialon (97.2% theoretical density) fabricated using AME powder had a room‐temperature bend strength of 352MN/m2(51,000 psi) and exhibited slow crack growth at 1300° and 1400°C. It is suggested that this is not an inherent property of sialon but is due to the presence of a calcium‐containing grain‐boundary phase, as in

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16096.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Cobalt tracer self‐diffusion coefficients were determined in single crystals of Co1‐xO at 1037° to 1350°C and for x=0.002 to 0.00s. In crystals with x fixed at 0.005, the results wereThe activation energy in this constant‐stoichiometry case was identified as the enthalpy of motion for Co ions moving via a vacancy jump mechanism. Based on known stoichiometry rela‐ tions, a published activation energy for Co self‐diffusion mea‐ surements in air was corrected to yield an enthalpy of motion in excellent agreement with the number given above. At a constant temperature of 115O0°±2°C, the Po2dependence of Co self‐ diffusion wasThe Po2expynent suggests that the predominant mobile ion defects are singly ionized Co vacancies. Simple defect reactions with no modifications for defect clustering were adequate to explain al

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16097.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Differential scanning calorimetry studies of As40SexTe60‐xglasses with 0≤x≤60 show a 2‐stage crystallization when 5≤x≤35, followed by a double‐peaked melting endotherm. The enthalpy of crystallization for the low‐temperature species is independent of composition and equals 11.6±0.9 cal/g for x≤25, whereas that for the high‐temperature species decreases from 2.2±0.2 cal/g forx =5 to 1.1±0.3 cal/g for x =15. The total enthalpy of melting also is independent of composition and equals 18.8±1.2 cal/g forx≤25. No crystallization was observed for xe40. The high‐temperature phase has the mono‐clinic As2Te3structure; that of the low‐temperature phase was not identified. Annealing experiments for compositions withx =15 or 20 gave time‐temperature transformation maps. A kinetic anal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16098.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16099.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16100.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY