摘要:

The isotope effect for22Na/24Na diffusion was used to investigate the sodium ion transport mechanism in mixed Na‐K silicate glasses. A combined vacancy‐interstitialcy mechanism provided the best agreement with the experimental22Na/24Na isotope effect data. At low temperatures sodium diffusion occurs predominantly by 2‐atom interstitialcy jumps, but with increasing temperature an increasing fraction of the ions diffuse by a single‐atom vacancy me

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14085.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

This paper presents an analytical model of a float glass annealing lehr, considering radiation between the moving ribbon and its enclosure and the convection of gas in a flue system. Results illustrate the use of mathematical modeling to improve design and operation. A linear algorithm, verified by “computer experiments,” is proposed for on‐line temperature co

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14086.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Traditionally fictive temperature has been used to characterize the structural state of glasses. Since this concept has certain shortcomings, use of a second thermodynamic ordering parameter along with fictive temperature in a nonlinear model is proposed. This model is applied to refractive index relaxation data, from the literature, for B2O3glass. Data were considered as the refractive index relaxed to a new equilibrium temperature from both higher and lower fictive temperatures.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14087.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The Young's and shear moduli of polycrystalline monoclinic hafnium oxide were determined by the sonic resonance method at room temperature as a function of volume fraction porosity. The Spriggs equation empirically described the data and the zero porosity moduli as 283.6 GN/m2and 109.2 GN/m2for Young's and shear moduli, respectively. The Debye temperature calculated from the elastic constants was 484°K. Several specimens had anomalously low moduli values, attributed to microcracking. Grain size and internal friction measurements showed that the microcracking occurred in specimens with grain sizes>2 to 3 μm and was characterized by high internal frictio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14088.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Although high‐temperature strength loss in ceramics such as silicon nitride has been attributed to the presence of intergranular amorphous phases, until now no direct proof has been offered. The present paper describes high resolution electron microscopy lattice imaging studies of an MgO fluxed hot‐pressed silicon nitride. These studies indicate that intergranular second phases do indeed exist, but they are heterogeneously distributed, appearing especially at multiple grain junctions. These room temperature observations are compatible with the microstructures expected at elevated temperatu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14089.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The irreversible reaction between zircon and alumina to form mullite and zirconia was observed to proceed very slowly at 1480°C, confirming the existence of a stable join between mullite and zirconia in addition to the join between mullite and zircon. Attempts to determine equilibrium assemblages in powder samples of several combinations of the constituents at 1300° and 1400°C were unsuccessful. Metastable tetragonal ZrO2was observed in fired powder samples containing kaolinite, in fired zircon‐alumina samples, and in calcined gels prepared from zirconyl nitrate, aluminum nitrate, and colloidal silica in water. Tetragonal ZrO2was the dominant crystalline phase in gels fired for 24 h at 800°, 950°, and 1100°C; the thermal stability of the phase was enhanced by Al2O3and by SiO2, but most effectively by mixtures of the two. Line broadening measurements and electron microscope observation indicate that the tetragonal ZrO2, with apparent crystallite sizes between 0.009 and 0.1 μm, develops as an intergrowth with, and is stabilized by, the amorphous matrix of Al2O3

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14090.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The effective medium theory is developed for diffusion in random composite media. It is demonstrated that the theoretical diffusivity depends crucially on whether concentration or chemical potential is taken to be the field variable for describing transport.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14091.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The system HfO2‐EuzO3 was investigated at ∼5 mol% intervals over a temperature range of 960° to 1900°C, by X‐ray analysisof quenched specimens. Liquidus temperature measurements made over the entire system showed the lowest liquidus temperature of 1930°± 15°C to be located at ∼96 mol% Eu2O3A large fluorite solid solution region was also found to exist at higher Of HfO2concentrations over the entire tempe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14092.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The calcining temperature of the basic magnesium carbonate influences both the reactivity of the resultant MgO and the reaction products in the system MgO‐MgCl2‐H2O. The reaction products identified by X‐ray diffraction are: Mg3(OH)3Cl·4H2O (phase 5), Mg2(OH)3Cl·4H2O (phase 3) and Mg(OH)2. The present paper discusses the relationship between the properties of MgO and the observed reaction p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14093.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The coefficient of thermal expansion and the dynamic response to pulsed energy deposition were investigated in the 25 to 60 mol% TiO2region of the system HfO2‐TiO2. Thermal expansion results revealed very low coefficients (≅1 × 10−6/°C) for the 30 to 40% compositions and relatively high coefficients (≅3 × 10−6/°C) for the 45 to 60% TiO2compositions. The 25% TiO2composition fell between these two groups. Dynamic response measurements revealed considerably lower free surface velocities for the 30 to 40% TiO2compositions than for the 45 to 50% TiO2compositions. Calculation of Grueneisen parameters, using the thermal expansion and dynamic response data, revealed low values for the 30 to 40% TiO2compositions and an increase by a factor of 2 to 3 for the 45 and 50% TiO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb14094.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY