摘要:

Heating experiments have been performed with titanosilicate glass melts to investigate possible losses of volatile radionuclides during preparation. The melts are precursors to sphene glass‐ceramics, the latter being candidate materials for immobilization of nuclear fuel recycle wastes. After the titanosilicate melts were heated for up to 24 h at 1300° and 1400°C, weight‐loss measurements and X‐ray fluorescence spectrometry analyses indicated that Cs, Mo, and, to a lesser extent, Na were the main contributors to the observed losses by volatilization. For comparison, similar experiments were performed with an AVM‐type borosilicate glass at temperatures of 1150° and 1250°C, when the viscosities are approximately equal to those of the titanosilicate melts at 1300° and 1400°C, respectively. The losses from the borosilicate glass were predominantly due to Na, B, Cs, and Mo volatilization and were generally higher than the corresponding losses from the titanosilicate glass, typically by factors of ∼4. Possible speciation of the volatile components in these glass

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05927.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Zinc oxide was deposited on the (111) face of an yttria‐stabilized zirconia single crystal using the chemical vapor phase method. Zinc vapor was obtained by reducing polycrystalline ZnO in hydrogen at 1200°C. The deposition of the ZnO was accomplished by the reoxidation of zinc vapor at temperatures of 1300° to 134

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05928.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A revised method to determine the transformation zone size in ceramics containing tetragonal ZrO2using X‐ray diffraction technique was described. The zone sizes of tetragonal ZrO2polycrystals (TZP) and partially stabilized ZrO2(PSZ) containing 2.0 to 5.0 mol% Y2O3were found to be larger than those determined by the method previously reported. The maximum zone size of TZP containing 2.0 mol% Y2O3was estimated to be 6.6 μm, whereas it had been determined to be 2.9 μm by the method previously repor

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05929.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Both silicon carbide and aluminum silicon carbide have simultaneously been obtained directly from naturally occurring aluminosilicate by carbothermal reduction for the first time. A precursor of a montmorillonite–polyacrylonitrile (PAN) intercalation compound was heated at 1700°C in Ar. For comparison, montmorillonite–carbon mixtures were similarly heated. α‐SiC, β‐SiC, and Al4Si2C5formed from the montmorillonite–PAN intercalation compound. Mainly α‐Al4SiC4was obtained with ternary carbides from the montmorillonite–carbon mixtures in addition to a large amount of β‐SiC. Hence, aluminum silicon carbide formation was affected by the mixing condition of th

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05930.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The rates of forming the superconducting YBa2Cu3Oxphase during the calcination of the Y2O3, BaCO3, and CuO powder mixture at 790° and 850°C are considerably enhanced when an inert atmosphere of N2or He is used instead of O2. Sintering in an inert atmosphere also produces higher density and larger grain size than in O2. These results are consistent with the possibility of rapid atomic diffusion in tetragonal YBa2Cu3Oxdue to either high oxygen vacancy concentration or expanded lattice in an inert atmospher

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05931.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Ball milling can be used for preparing large quantities of dense YBa2Cu3O7. Studies of superconducting properties show that while a medium of alumina in hexane can be used to mix and to reduce particle size of the starting materials, it contaminates the reacted ceramic. Copper slugs produce an excess of Cu through wear, while balls made of partially stabilized zirconia produce the best results.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05932.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Vickers and Knoop indentation tests have been used to study the fracture and deformation characteristics of 9.4‐mol%‐Y2O3‐stabilized ZrO2single crystals. Kcis anisotropic, with values of 1.9 and 1.1 MPa·m1/2for radial cracks propagating along (100) and (110), respectively. The toughness for these two orientations was also determined using the single‐edge notched‐beam geometry, and yielded values of 1.9 and 1.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05933.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The thermal diffusivity of AlN ceramics was significantly decreased by the addition of SiO2. The AlN ceramics with 4 wt% SiO2could not be densified by pressureless sintering in the temperature range 1400° to 1800°C. The thermal diffusivity of these samples was very low because of their porous structure. The AlN ceramics containing 2, 4, and 8 wt% SiO2were densified by hot‐pressing and also had low thermal diffusivity. In these samples, the grains of the 27R polytype that resulted from the reaction between AlN and SiO2were dispersed, obstructing the conduction of heat. The relation between the amount of 27R polytype and the thermal diffusivity of the AlN ceramics was determi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05934.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Mullite (3Al2O3·2SiO2) was prepared by a sol‐gel process and dried by supercritical extraction with CO2. The aerogel (<0.05 of the theoretical density of mullite) experienced a shrinkage of up to 0.6 and reached a density of only ∼0.5 of theoretical after 1 h at 1350°C Mechanically compacted aerogels, however, sintered to nearly theoretical density below 1200°C. This density is somewhat higher than those of gels prepared by conventional drying (i.e., exposure to the atmosphere) and is considerably higher than mullite prepared from mixed powders at higher temperatures. Although the X‐ray diffraction pattern of the sintered gels was almost identical to that of mullite, transmission electron microscopy and energy‐dispersive microanalysis showed two types of grain structure. Elongated grains with an Al/Si atomic ratio corresponding to that of stoichiometric mullite were surrounded by equiaxed grains with a lower A

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05935.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The luminescence spectra of Fe3+in alkali aluminosilicate glasses indicate that several species of Fe3+are present during early stages of melting. When the glass has been heat‐treated for periods of time on the order of 20 h at 1400°C, the luminescence spectra simplify to that of a single species which is interpreted as due to Fe3+in the glass‐forming frame

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05936.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY