ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12110.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The reduction by hydrogen of Fe3+, Ce4+, and Sn4+in soda‐lime‐silica glass was found to be diffusion‐limited in the glass transition temperature range (500°C). The reduction was studied in fibers by chemical analysis and in bulk samples by optical absorption. Reduction to Fe2+, Ce3+, and Sn2+proceeds by a reaction of the type H2+2(ɛSi‐O)‐+2Fe3+→2Fe2++2(ɛSi–OH). Since the rate of reduction by hydrogen is quite similar for these systems and since reduction cannot be accomplished with CO, it is concluded that hydrogen is the diffusing species. A mechanism is developed in which hydrogen diffuses through the glass until it is trapped by

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12111.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Free‐surface and equilibrium sublimation pressure measurements indicate that the sublimation coefficient of tin selenide is essentially 1 from 726° to 975°K. Torsion‐Langmuir measurements from 726° to 879°K gave the following expression for the free‐surface pressure: logP(atm) = (7.021°0.161)‐(1.036°0.013)104/T.The third‐law heat of sublimation calculated from these results was 51.5±0.3 kcal/mol SnSe. Similar treatment of the equilibrium pressures obtained by the torsion‐effusion method from 789° to 975°K gave the following least‐squares expression: logP(atm) = (7.473±0.133)‐(1.069±0.012) 104/T.The third‐la

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12112.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The effects of sintering temperature and cooling rate on the magnetic and crystallographic properties of lithium ferrite were studied. The magnetic moments and lattice parameters increased with increasing sintering temperature; these increases result from correlated oxygen and lithium oxide losses. Either annealing at lower temperatures or slow cooling under O2causes reoxidation of the Fe2+formed at higher temperatures with attendant decreases in moment and lattice parameter and gradual precipitation of α‐Fe2O3as a second phase. The products formed on rapid cooling are equivalent to solid solutions of spinel lithium ferrite with Fe3O4, and those formed on slow cooling, to solid solutions of lithium ferrite and γ‐Fe2O3with precipitation of α‐Fe2O3. Lithium losses and α‐Fe2O3precipitate amounts are calculated. The magnetic moment of stoichiometric lithium ferrite at 25°C is 3736±20 G; the lattice parameter at 28°C is 8

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12113.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

An exploratory study of the effects of compositional variation on glass formation in low‐silica aluminate compositions revealed that CaO is essential for glass formation at ordinary quenching rates. Other oxides, such as Li2O, MgO, BaO, ZnO, Na2O, K2O, BeO, B2O3, and PbO, can be present in the glass in limited amounts (in some cases up to 30 mol%). A necessary, but insufficient, condition for easy glass formation is that the ratio of oxygen ions to network‐forming cations (assumed to be Si4+and Al3+) be ∼2.5. The glass‐forming compositions were also characterized by liquidus temperatures below ∼1500°C (2732°F). Young's modulus ranged from 13.0 to 17.8×106psi. Glasses containing network‐modifying cations with high field strengths generally had the higher moduli. Strength (420,000 to 650,000 psi in 0.3‐mil fibers), static fatigue, viscosity, annealing, and surface tension were studied to a limited extent for the composition (in mol%) 30Al2O3

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12114.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Spectra of divalent transition metal ions in ZnCl2, KOAc‐Ca(OAc)2, KNO3‐Ca(NO3)2, and K2SO4‐ZnSO4glasses are presented. Ions with low octahedral site preference energies (e.g. CO2+) can be used as “probes” for divalent cations in glass and can indicate the presence or absence of network structures. Thus ZnCl2glass has a tetrahedral network structure, analogous to vitreous BeF2, but KOAc‐Ca(OAc)2and KNO3‐Ca(NO3)2glasses contain potassium ions and discrete acetatocalcate(II) and nitratocalcate(II) “complex ions.” The structure of acetate and nitrate glasses is discussed in terms of the id

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12115.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Silicon and aluminumKβ band X‐ray emission spectra of a series of lithia‐aluminosilica (LAS) glasses were determined using the X‐ray spectrometric systems of commercially available electron microprobes. Comparison with spectra of reference materials, including glassy and crystalline forms of silica, high‐quartz‐phase crystals of the L:A:S‐1:1:2 (mol ratio) composition (high‐eucryptite), and 6‐ and 4‐coordinated aluminum oxides, led to tentative assignment of spectral peaks to specific electronic transitions. Molecular orbital theory and crystallographic structural data were used to assign bands in crystalline materials. The LAS glass spectra indicated progressive bond weakening with decreasing silica content; theKβ peak shifts permitted approximate calculation of the decreases in Si–O and Al–O bond energies, which were as great as 30 kcal/mol relative to SiO2(for

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12116.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Ceramic and piezoelectric properties of the Pb(Co1/3Nb2/3)O3‐PbTiO3‐PbZrO3system were investigated. The system contains rhombohedral, tetragonal, and pseudocubic phases at room temperature. The triple point is at 0.07Pb(Co1/3Nb2/3)O3‐0.43PbTiO3‐0.50PbZrO3. High dielectric constants (750 to 1500) and radial coupling coefficients (40 to 45%) and low average temperature coefficients of resonant frequency (of the order of 10‐6°C) were obtained for compositions near the morphotropic phas

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12117.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Glasses activated with Mn2+exhibit green to red luminescence. A widely accepted model proposes that these colors denote 4‐ and 6‐coordination, respectively, for Mn2+. The luminescence and absorption of Mn2+‐activated silicate glasses were studied; the luminescence changed from green to red with increasing Mn2+concentration. The difference in the intensities of emission bands with peaks near 520 and 620 nm accounts for the luminescent color. No experimental evidence for a change in coordination from 4 to 6 was found. Exchange‐coupled groupings are proposed to explain red emission in these glasses and possibly in borate and phosphate glasses studied by other workers. Improved resolution of bands and theoretical calculations demonstrate that a covalent‐octahedral Mn2+species can account for the spectral data for the silicat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12118.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Several predominantly single‐phase uranium oxycarbide compositions were examined to determine the effect of oxygen content on the hot hardness, thermal diffusivity, thermal conductivity, and electrical resistivity. Little difference was noted in hot hardness over the low‐temperature range; however, increased oxygen content appears to reduce the hardness above 700°C. Thermal diffusivity and thermal conductivity are reduced by increased oxygen content. This decrease is most pronounced at lower temperatures, and the temperature dependence varies significantly with oxygen content. The thermal diffusivity of oxycarbides having small percentages of oxygen decreases with increasing temperature, whereas that of oxycarbides with greater oxygen content increases, very slightly. The thermal conductivity data are in fair agreement with those reported for the monocarbide. Electrical resistivity is increased by increased oxygen content and shows a positive temperature dependence. The data indicate that electronic conductivity at 1500°C accounts for approximately 85% of the total thermal conduction at the 2‐at.%‐oxygen level and approximately 95% of the total at the 16‐at.%

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb12119.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY