摘要:

One of the important steps in the manufacture of glass by the float process is the control of glass thickness by stretching the ribbon. The first step in a program to model the stretching of float glass is discussed. A simple, 1‐dimensional analysis is presented for the mechanics of stretching a free ribbon, i.e. one without edge constraints in the stretching region. For the case of a stiff (“cold”) ribbon, the present analysis yields closed‐form solutions which are generally valid but do not encompass all phenomena of interest. The stretching of a “hot” ribbon is, therefore, treated quantitatively by computer simulation. This approach is used to illustrate the differential attenuation of the width and thickness of hot ribbons. In another numerical example, the caculated width attenuation is compared with the results of in‐plant

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16081.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Nuclear fuels for the high‐temperature gas‐cooled reactor (HTGR) consist of spherical kernels of actinide compounds contained in gaslight pyrolytic carbon and SiC. The fuel kernels migrate up the temperature gradient and into the coating layers. A theoretical analysis of in‐reactor migration data indicates that a solid‐state diffusion process controls the migration rate in fissioned Th0.84U0.16C2, UO2, ThO2, PuO2‐x, and Th0.8U0.2O2particles. The theoretically based kernel migration coefficient (KMC) measured in units (cm/s) °K2(oK/cm)‐1, is thus used to correlate the laboratory and in‐reactor data. The KMC values for Pu‐containing particles may be dependent on the initial and in‐reactor O/Pu values. The other in‐reactor KMC values were apparently not dependent on the extent of fission, the fission of either233U or235U, or the presence of an SiC coating layer. Laboratory KMC values were obtained for unirradiated ThO2, UO1.65N0.25,UC2ThC2, and Th0.84U0.16C2particles and generally appeared to be consistent

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16082.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Permittivity, dielectric loss tangent, radial coupling coefficient, and radial frequency constant have been measured as a function of composition for pressure‐sintered Li.rNa1‐xNbO3in the range 0.015≤x≤0.15. An anomaly in each of these properties when plotted as a function of composition is associated with a structural transition between 2 ferroelectric phases; this transition lies near room temperature for compositions where x∼0.12. Compositions near this phase boundary exhibit room‐temperature properties which are of interest for high‐frequency filter

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16083.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Previous explanations of strengthening of glass‐ceramics after heat treatment to produce crystallization are discussed. Explanations relating strength enhancement in brittle material systems either to flaw size limitation by interparticle spacing or to the increase in the system modulus as a result of the presence of a higher modulus dispersed phase were found to be inadequate. The measured loss of strength in glass‐ceramics with increasing temperature indicated strength enhancement as a result of thermomechanically induced stresses in the sys

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16084.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The theory of structural stability of ceramics in severe thermal environments was explored via the use of precracking. It was shown that structural stability should be possible when an array of precracks is used, but that the precracks required for this purpose are relatively large. The approach is thus limited to systems which are not required to sustain a significant mechanical stress. Preliminary quenching experiments on short cylinders confirmed that stabilization can be achieved by precracking.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16085.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Samples of LaMn1‐xCuxO3‐yin the range 0≤x≤0.8 were prepared from freeze‐dried solutions of the nitrates. Samples with x≤0.6 were single‐phase perovskites. At higher values ofx, the samples contained La2CuO4and CuO as well as the perovskite phase. Samples of LaMn1−x,Cux,O3−ysupported on ceramic monoliths or when mixed with powdered A12O3exhibit catalytic activity for the oxidation of CO. Greatest activity is shown for 0.4≤x≤0.7. Although the catalysts are severely poisoned by SO2, 2% H2O in the gas stream causes only slight deactivation. Activities of other oxide catalysts were also measured and compared. Rate constants per unit surface area at 200° to 400°C follow the order Co3O4>Pt>LaMn1−xCuxO3−y(0.4≤x≤0.7)>copper chromite>La1−xSrx,MnO3≤ other substituted LaMnO3materials, CuO, or La2CuO4. The perovskite catalyst is more stable than Co3O4or copper chr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16086.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Thermogravimetry in reducing atmospheres was used to study the oxygen Stoichiometry of several Cu‐substituted lanthanum manganates. The oxygen content of the samples at various levels of reduction (to La2O3, MnO, and Cu) was calculated from the gravimetric data. Freeze‐dried samples prepared by firing at 1100°C in O2and cooling in O2had the following composition: LaMnO3.13, LaMn0.7Cuo.3O2.96, LaMn0.5Cu0.5O2.93, and LaMn0.3Cu0.762.71. Single‐phase perovskite structure was obtained in all but the last. The lanthanum manganate LaMnO3.13was reduced to LaMnO3.00, which shows considerable stability. A 50% substitution of Cu for Mn gave LaMn0.5Cu0.5O2.93, indicating that the ions involved were mostly Mn4+and Cu2+. This compound could be reduced to LaMng0.5Cu0.5O2.26(largely Mn2+and Cu1+) without destroying the perovskite structure. This reduced phase could be reoxidized to the original oxygen level but subsequent reduction required considerably higher temperatures and was accompanied by the precipitation of Cu‐rich phases. Samples with a Cu:Mn ratio 30:70 and 70:30 were O‐deficient. The compound LaMn0.7Cuo.3O2.96reduced to LaMn0.7Cu0.3O2.54, a relatively stable composition. The highly Cu‐rich sample LaMn0.3Cu0.7O2.71was ea

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16087.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Mobilities and zeta potentials ofβ‐alumina particles have been measured in 1‐pentanol, nitromethane, and dichloromethane media. The effects of grinding, aging, water content, and acid solute content were observed; all of these variables were critical. The charge on theβ‐alumina particles could be either positive or negative, depending on the suspension con

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16088.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Dehydroxylation phases of a kaolinite from Zettlitz, Czechoslovakia, were investigated by radial electron density distribution (RED) and X‐ray spectroscopy. Special emphasis was placed on the 2 amorphous or poorly crystallized transition phases, i.e. metakaolinite (600° to 800°C) and the spinel structure (900°C). The RED diffraction method, which is particularly suited to the study of such materials, indicated (1) a particularly expanded tetrahedral configuration for the Al atoms in metakaolinite and (2) a pure Al2O3spinel structure. The first result confirms earlier observations; the second eliminates, for the experimental conditions and kaolinite studied, the possibility of the formation of an Al‐Si spinel structure with the AI and Si occupying the octahedral and tetrahedral interstices, respectively. Complementary measurements on theAlKαline shifts for the same samples support the present interpretation. Determination of the apparent Si coordination number by the same spectroscopy procedure revealed a regular 4 coordination for all phases except the end‐membe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16089.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The creep properties of polycrystalline A12O3(grain size 14 to 65 μm) were examined under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C. Two distinct types of behavior were observed. The creep rate of medium‐grained specimens (14 to 30 μm) could be described by ασ1.2/d2where σ is the applied stress anddis the grain size. These results are consistent with the Nabarro‐Herring creep mechanism. For the coarse‐grained (65 μm) specimens, the creep rate was related to the stress by ασ2.6. This behavior was not related to cracking; instead, a dislocation mechanism was thought to be rate‐controlling. Considerable evidence for grain‐boundary sliding was seen, and measurements showed that grain‐boundary sliding contributed between 46 and 77% of the total strain in the 3 medium‐grained specimens examined and between 38 and 50% in the 3 coarsegra

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1977.tb16090.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY