ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15385.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Grain growth and densification were studied in a hot‐pressed ferroelectric composition of 65/35 (Zr/Ti molar ratio) lead zirconate‐lead titanate containing 2 at.% bismuth. The grain growth and densification rate processes were measurable from 1050° to 1300°C and from 700° to 1100°C, respectively. Grain growth as a function of time followed a ⅓ power law (D(grain size) =kt⅓). An activation energy of 95 kcal/mole was calculated. Densification was a two‐stage process as a function of time: a rapid initial stage and a slower final stage. The initial stage of densification behaved viscously with an activation energy of 36.7 kcal/mole. Grain boundary sliding and the Nabarro‐Herring mechanism of stress‐directed movement of vacancies are suggested as the densification mechanisms. Results indicated that densification is sensitive to stoichiometry

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15386.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Crystallization rates were measured in vacuum, dry nitrogen, and water‐saturated nitrogen atmospheres from 1300° to 1540°C. In all cases the observed rates were linear. Three reactions appeared to contribute to crystallization: the intrinsic crystallization, the impurity effect of H2O vapor, and furnace contamination. Enhancement of crystallization by both water vapor and furnace contamination is attributed to the breaking of silicon—oxygen bonds of the glass structure. Competitive adsorption mechanisms were proposed to characterize the adsorption of water and impurity species. The activation energy for apparent intrinsic crystallization was 134 kcal/mole; the activation energy for crystallization in H2O vapor was 77 kcal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15387.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

It has been shown previously that alumina (sapphire) whiskers grown on single‐crystal alumina grow coherently with and in the directions of screw dislocations in the substrate. A possible explanation is that the whiskers grow by the screw‐dislocation mechanism at the site of emergent screw dislocations on the substrate surface. The present study was undertaken to determine if the whiskers grow at the sites of substrate dislocations as revealed by etching techniques. To do this, whisker growth sites were compared with the positions of dislocation etch pits. This was done for the prismatic [{112¯0},] and basal [(0001), (112¯0)]slip systems on (112¯0), (11¯01), and (0001) crystal surfaces. The whiskers and etch pits did not form at the same places on the crystal surfaces. The reason may be that (1) the etch pits form at pure edge dislocations only, (2) surface nucleation generates screw dislocations at which the whiskers grow, or (3) screw dislocations play no part in the growth of these

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15388.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

The five elastic constants of single‐crystal BeO were measured to determine their magnitude relative to those of other hexagonal materials and to enable a correlation with related properties. The pulse‐echo method was used. The stiffness constants arec114.70,c121.68,c131.19,c334.94, andc441.53 × 1012dynes/cm2. These were related to the Young's, shear, and bulk moduli of polycrystalline BeO, the Debye temperature, and the repulsion term for the crystal en

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15389.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

A Knudsen study of the reaction SnO2(c) = SnO(g) +½O2(g) yielded for the enthalpy of dissociation of SnO(g), D°0= 5.44 × 0.1 ev/molecule, which is in agreement with literature values (average 5.5 × 0.1 ev/molecule) obtained by various methods. Langmuir studies indicated an evaporation coefficient upper limit of 0.1 for the measured reaction. The Langmuir enthalpy of activation (ΔH*298= 134 × 2.9 kcal/mole), as calculated by the second‐law method, is less than that measured for the equilibrium reaction (ΔH*298= 143.4 × 1.1 kcal/mole), but probably should be considered to agree within experimental error. Electron micrographs showed evidence of stepwise evaporation that depends on the crystallographic orientation of the polycrystalli

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15390.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Oxygen diffusion was measured by the sectioning technique on single‐crystal and polycrystalline specimens of Zr0.858Ca0.142CO1.858. The diffusion coefficient, which may be represented by the equationD= 0.01818+0.068‐0.015exp ‐ (31, 200 × 4300)/RTcm2/secagrees with that calculated from the electrical conductivity and an oxygen transport number of 1. The oxygen surface exchange coefficient may be represented byα= 0.078+0.443‐0.066exp ‐ (22,800 × 4400/RTcm/secThe quantitative influence of ignoring the exchange rate on the apparent diffusion coefficient

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15391.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

The scatter usually seen in strength data for virgin E‐glass fibers can be reduced to a very low level by controlling the thermal history of the glass melt from which the fibers are formed. Provided the glass melt is heated substantially above the drawing temperature, strengths of subsequently produced groups of 10 specimens will have a coefficient of variation of ∽1%. Unless glass is prevented from stagnating in the nozzle of the fiber‐forming apparatus during a pause in the drawing operation, a secondary effect, associated with the spontaneous creation of defects in the glass in the nozzle, causes fibers produced immediately after such a pause to exhibit low strengths and high sc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15392.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

A preliminary examination of the crystallization sequences in some alkali aluminogermanate glasses is described. The glasses investigated are represented by the following chemical formulas: [Li3AlGeO4], [LiAlGe2O6], [NaAl‐GeO4], [Li3AlGe3O9], [Li2NaAlGe3O9], and [Li2‐KAlGe3O9]. Three new compounds, KAlGeO4, RbAlGeO4, and CsAlGeO4, were synthesized in the solid state. A simple, arithmetical approach is presented for determining the statistical existence of six‐coordinated germanium (IV) in a given glass. The experimental results, particularly in [LiAlGeO4], [LiAlGe2O6], and [Li3AlGe3O9], indicate that the potential existence of six‐coordinated germanium (IV) has a substantial effect on the mechanism as well as on the energetics of the respective glass crystalli

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15393.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Lattice parameters were measured on MgO specimens prepared in air between 450° and 1200°C. The lattice parameter,a, decreases with increase in preparation temperature,Tp, and with increase in crystallite size. A hydroxide layer is present on the MgO particles. If MgO is prepared in vacuum,aincreases asTpincreases and as crystallite size,D, increases. It is concluded that a dilatant volume stress is imposed by the hydroxide layer. It is also shown that the oxide surface reactivity toward water is linked to the deviation from perfect order ensuing from low preparation temperature

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb15394.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY