摘要:

The effects of Dy doping and sintering parameters on the properties of BaTiO3ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5μm by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is<3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3ceramics. Lattice constantcdecreases with increasing Dy concentration whereasaincreases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3ceramics are cooled belowTc, strongly influences the effects of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15479.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The distribution of hydrogen between substitutional sites and Mg(OH)2precipitates in MgO single crystals depends on the thermal treatment of the crystal. Isochronal annealing studies of quenched and slow‐cooled crystals indicate that the substitutional H, as monitored by the O–H stretching frequency at 3296 cm‐1, is not mobile at<800 K. However, under the influence of electron irradiation, H is mobile below room temperature. The net result of the irradiations is the appearance of the paramagnetic vacancy left behind by the H and an enhancement of the amplitude of the Mg(OH)2absorption band. The mobility of the substitutional H, which was found to be a strong function of the irradiation temperature, was greater at 290 K than at 85 K. A mechanism for the displacement of the substitutional H is pro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15480.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Surface, grain‐boundary, and volume inter diffusion coefficients for the NiO‐Al2O3system were measured concurrently by using a diffusion couple consisting of an A12O3bicrystal and an NiO single crystal. The A12O3bicrystals having various tilt angles were fabricated by firing 2 single crystals to be joined in an H2atmosphere at 1800°C for 30 h. Diffusion profiles over the surface, along the grain boundary, and in the bulk of the bicrystal were determined with an electron probe microanalyzer. Mathematical analysis of the diffusion profiles gives Ds= 7.41×10‐2exp (‐35,200/RT), Dgb= 2.14×10‐1exp (‐63,100/RT) (tilt angle =30°), and Dv= 1.26×104exp (‐104,000/RT). The grain‐boundary diffusion coefficient increases with the mism

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15481.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Flexural strength was measured on high‐purity selenium glass over a wide range of temperatures and strain rates. This glass exhibited wide variations in strength and other properties as temperature and strain rate varied. The strength of glassy Se increased significantly with temperature over 2 temperature ranges, and the highest strength occurred at temperatures just below the glass transition region. The flexural strength also increased with strain rate at all temperatures investigated. Substantial evidence of crack blunting was found in tests at 25

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15482.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Adsorption of N2and water vapor was studied in completely hydrated tricalcium silicate and in fully hydrated tricalcium silicate from which Ca(OH)2had been extracted. Compared with results obtained using N2, water vapor adsorption led to increased values for small‐pore volume, peak shifts to smaller sizes, and decreased values for large‐pore volume. Marked hysteresis was observed in the case of water vapor adsorption; the resorption branch apparently represents the true pore structure. Extraction of Ca(OH)2from the paste increased the calculated volume of small pores strikingly, suggesting that adsorption is hindered by Ca(OH)2; this tendency is more obvious in water vapor adsorption. The adsorption measurements indicate the existence of two kinds of pores, i.e. a wider intergel‐particle pore and a smaller pore existing within the gel particle. The latter pore was further classified into intercrystallite and intracrystallite

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15483.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Fracture mechanics is combined with fracture surface analysis to analyze brittle failure of glass bars which were tested relative to the direction of grinding. Grinding essentially produces two sets of flaws from which failure occurs. In the most severe set, formed basically parallel to the grinding direction, the ratio of the average depth (a) to the half‐width (b) is 0.5. In the less severe set, formed perpendicular to the grinding direction, the averagea/bratio is 1.6. In both sets the most severe flaws are generally associated with a particularly deep grinding groove or gouge. The strength reduction resulting from testing perpendicular to the grinding direction results from the larger flaw size and slightly higher stress‐intensity factor resulting from the greater ellipticity of the flaws formed parallel to the grinding grooves and perpendicular to the tensile axis. Detailed analysis of these 2 sets of flaws causing failure of appropriately oriented specimens shows that (1) the fracture mirror radius,r, occurs at a constant stress‐intensity level independent of flaw geometry; (2) unsymmetric fracture mirrors result from unsymmetric, irregular flaws leading to unsymmetric stress‐intensity distributions; (3)is constant for semielliptical flaws; and (4) fracture energy calculated from an expression including mirror constants, the flaw‐to‐mirror size ratio, and the flaw geometry agrees with measured values over a wide range

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15484.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Reproducible “complexed” Hertzian cones were formed in glass as a result of thermally induced tensile stresses. These cones differ from normal cones by having wavy profile patterns, indicating two modes of fracture operating alternately. One mode is shallow and the other steep, together averaging a crack angle of 18.9 ± 1°. The thermal technique offers new test conditions for studying Hertzian fra

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15485.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The contributions of the space‐charge cloud to impurity and self‐diffusion in the grain‐boundary region of ionic materials are shown by calculations for doped KC1. The magnitude of these effects is modest (<103Dl) and limited in dimension (10 to 200 Å). Both enhancement and reduction in the charge cloud contribution to boundary diffusivities are predicted. In the charge cloud, appreciable diffusivity enhancement is indicated only for the ion on the sublattice opposite that of the principal impurity. The large boundary‐diffusion enhancements and boundary widths often reported in “pure” and doped samples cannot be explained by the space‐charg

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15486.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The transition‐metal‐based ferromagnetic amorphous alloys made by the continuous splat‐quenching method are excellent soft magnetic materials with low coercivity. Furthermore, their low‐field magnetic properties are sensitive to heat treatments and can be greatly improved by such treatments. A review of low‐field properties of these alloys such as anisotropy, remanence, and coercivity (as‐received and after heat treatments) is presented together with data on the Fe80B20amorphous alloy and the effect of fast‐neutro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15487.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The evolution of enthalpy of As2Se3glass during structural relaxation in the glass transition region was measured via differential scanning calorimetry for two types of time‐temperature programs: rate‐heating at 10 K/min following a cool at a constant rate (‐20 to ‐0.31 K/min) and isothermal annealing following a temperature step from an equilibrium state. The rate‐heating data yield kinetic parameters for the structural relaxation which predict accurately the evolution of the enthalpy during isothermal annealing. The glass heat capacities were independent of cooling rate within experimental precision (≤0.2%). In this respect, As2Se3is unlike previously studied glasses whose heat capacities are more dependent on ther

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb15488.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY