ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11836.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Dispersions of (UTh)O2in beryllia containing 1.7 to 25 vole%, (UTh)02in coarse (150 to 200P), medium (33 to 35P), and fine (<10 and<5μ) fuel particle sizes were irradiated to burnups of 3 to 10% of heavy metal atoms between 300’and 900°C, in both fast and thermal fluxes. Changes in volume, lattice parameter, line breadth, and modulus of rupture were measured; volume changes in the fine dispersions were ascribed wholly to fission fragment damage and were about 50% greater than those caused by fast neutrons alone; they increased with increasing fission fragment flux, and decreased as irradiation temperature increased. Volume changes in medium and coarse dispersions were about 25% greater than those caused by fast neutrons alone; the increased damage is attributed to the additional β‐flux. As fuel particle size increased, deterioration in strength under irradiation was more marked. This was attributed to more intense fission fragment damage in the recoil zone around larger particles causing volume increases which exceeded those of the remainder of the matrix. For maximum initial strength and retention of strength under irradiation, the fuel particle size should not exceed 5β, and the interparticle spacing should not exc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11837.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Creep extension without dislocation movement across grains may be obtained in polycrystalline aggregates by diffusion through the grains (Nabarro‐Herring) or through grain boundaries (Coble). These mechanisms are compared with a suggestion that creep can occur by grain‐boundary sliding controlled by diffusion which can lead to movement along the boundary of grain‐boundary protrusions and can be accommodated by diffusion around triple p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11838.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

A new compound with the composition PbCrO3, with Cr in the valence state of 4, was synthesized at high pressures above a pressure‐temperature line extending from about 50 kbars at 750°C to 60 kbars at 1450°C. PbCrO3can be quenched and retained at 1 atm but decomposes on heating above 275° C at the same pressure. PbCrO3is considered to be an equilibrium phase at high pressures because it was synthesized from mixtures of PbO: CrO2as well as from several other mixtures of compounds in the Pb‐Cr‐0 system. The new phase has the cubic perovskite structure and is the only known compound with Cr4+in an octahedral site. PbCrO3crystallizes primarily as black cubes which are often twinned

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11839.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The fracture of thermally tempered glass is discussed in terms Of both the stored elastic strain energy in the glass due to tempering and the elastic energy release rate Of crack extension, 9. The latter is used to obtain an analytical correlation between the maximum tensile stress and the average particle size at time of fracture. The theoretical predictions are supported by experimental data obtained for various glass thicknesses and temper levels.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11840.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Dimensional and weight changes on refiring of clay mineral mixtures were used as a measure of moisture expansion and moisture uptake, respectively. Pore‐size distributions were measured by the mercury penetration method. With specimens containing more than 15% muscovite, the moisture expansion had a peak value when fired between 1000° and 1050°C. At 1050° the magnitude of moisture expansion and moisture uptake was approximately linear with the muscovite content. For specimens with less than 15% muscovite, the variation of moisture expansion with mica content was complex and this was ascribed to the fact that muscovite particles coated with kaolinite behaved differently from bulk mica in the original firing treatment and on subsequent exposure to moisture. The volume percentage of pores greater than 0.2μ in diameter increase as the muscovite content and firing temperature increased and reached a maximum when moisture expansion was at a maximum. The volume percentage of pores less than 0.2μ in diameter decreased under the same conditions but increased slightly in specimens of low muscovite content because the kaolinite reacted on firing with the mica which it

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11841.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

A major difference is demonstrated in the mechanisms whereby silicon and titanium carbides are deposited at high temperatures from gas mixtures containing the appropriate tetrachloride, hydrogen, and methane. For silicon carbide, reduction of the halide by hydrogen to elemental silicon is involved, whereas for titanium carbide the process does not involve elemental titanium. It is proposed that initial formation of pyrocarbon is required for the deposition of titanium carbide near 1200°C or that gas phase reactions involving subhalides are important

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11842.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Slip line and transmission electron microscopy observations on the plastic deformation of cuprous oxide were made on large‐grained polycrystalline specimens. The specimens were prepared by the complete oxidation of OFHC copper strips in air followed by a high‐temperature anneal. Plastic deformation occurred by motion of α(100) dislocations on (100) glide planes. Some dislocation segments of a(110) Burgers vector were present but were probably formed by recombination reactions between α(100) dislocations. The unusual structure of Cu20, which can be described as two interpenetrating and identical frameworks of copper and oxygen which are not cross‐connected by any primary copper–oxygen bonds, did not result in any unusual behavior of dislocations. The effect of temperature on plasticity was explained in the same way as for other materials of less complex structure, su

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11843.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Isostatic hot‐pressing was used to fabricate solid MgO bodies of high purity (with respect to metallic impurities) to 90 to 95y0 density with high translucency and a grain size of approximately 0.2μ. The densified material contained significant amounts of brucite as a result of water in the starting material which was not removed during vacuum baking. The fabricated pieces showed many cracks which were apparently introduced into the compacts before densification. When the hot‐pressed pieces were reheated, the brucite decomposed, the density increased, and the porosity coalesced while grain growth occurred. The general technique appears to be usable for fabricating finely divided powders if powder degassing and predensification procedures are impr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11844.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Glasses in the Na2O–Ba0–A12O3‐Si02system, nucleated with TiO2, were heat‐treated to effect controlled crystallization. Resulting materials consisted of a dense, micro‐crystalline mixture of nepheline (Na20–A12O3‐2SiO2) and barium feldspar (BaO‐A12O3‐2Si02) in a glassy matrix. Thermal expansion coefficients (O° to 300° C) of these bodies ranged from 75 to 125 × 10 –7/°C. Glazes in the Na2O‐CaO‐PbO‐B2O2‐A1203‐SiO2system having expansion coefficients of about 40 to 80 × 10‐7/0°C were applied to the glass‐ceramics. On firing, the glazes matured well and reacted with the bodies to form interlocking crystals at the interface. This interfacial region was investigated using several instrumental techniques, and the crystals were identified as plagioclase feldspar. Applying these compressive glazes resulted in modular of rupture up to five times that of the initial glass‐ceramic. Calculated strengths

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11845.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY