ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15993.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The reaction of nitrogen with arc‐melted UC was studied from 1475° to 1700°C at an N2pressure of about 400 torr. The reaction appeared to proceed toward equilibrium in distinct stages: (1) UC and N2reacted to form UC2and UC0.8N0.2; (2) UC2reacted with N2to produce more UC0.3N0.2and free C; and (3) this U(C,N) reacted with N2to produce more free C and the equilibrium product, a high‐N U(C,N). These results are consistent with known thermodynamic and phase behavior in the U‐C

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15994.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The linear growth rate of a BaO.2B2O3crystal in its melt was measured as a function of temperature; a growth mechanism was proposed which involves the folding of chains of boroxol rings back and forth on the crystal surface. At small undercoolings, the growth rate appeared to be limited by the number of suitable nucleation sites for a chain to attach to the crystal; at large undercoolings, it appeared to be limited by the rate of orientation of the chains at the crystal‐melt interfac

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15995.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Cracks in soda‐lime‐silica glass specimens closed spontaneously; the recovery in strength was determined by fracture mechanics techniques. Approximately 80% strength was recovered in cracks formed by mechanical shock, whereas approximately 20% was recovered in cracks that closed after being held open to the atmosphere for several minutes. The high strength recovery in the mechanically shocked specimens is attributed to the very active surface formed during fracture. If the surface is allowed to adsorb O2or H2O vapor, the activity is reduced, and healing is less complete. Crack healing can introduce surface flaws into glass that cannot be detected by current methods of nondestructive test

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15996.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Theoretical predictions of crack propagation behavior in brittle solids under conditions of thermal shock were verified by water quenching of cylindrical polycrystalline alumina rods followed by strength testing. The calculated quenching temperature difference (ΔTO) required to initiate thermal‐stress fracture agreed fairly well with experiment. When fracture was initiated, strength decreased catastrophically, in agreement with theory. An expression for the strength remaining after thermal stress fracture was derived in terms of the pertinent physical parameters. Values of surface fracture energy similar to those reported in the literature agreed with experiment. Strength after thermal shock was predicted to be inversely proportional to the 1/4 power of the rod diameter; this prediction was supported by experimental data for two rod sizes. Over a range of quenching temperature differences ΔTΔT0strength remained constant, in agreement with the theoretical expectation that the newly formed cracks were subcritical. Only at the highest quenching temperature differences could further decreases in strength be observed; the quantitative changes, however, were masked by nonlinear deformation (evidenced by permanent crack opening). It was concluded that, although thermal shock behavior of brittle ceramics can be approximated fairly well, reliable quantitative estimates require considerably more information about strength and surface fracture energies as a function of environment, stress distribution, strain rate, and temperature and specimen size eff

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15997.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The effects of thermal treatment, crystalline phases, and crystal size on thermolumineseence in the system ZrO2−H2O were studied. The results suggest that thermolumineseence is not affected by the water content and that it is strongly dependent on the degree of crystallinity and on crystal size. An interpretation of the changes in the glow curves is suggested on the basis of the dat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15998.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The reaction kinetics for NiCr2O4formation and the diffusion of Cr3+ions into single‐crystal NiO were studied between 1300° and 1600°C in air. The experimental activation energy for NiCr2O4formation was about 83 kcal/mol. After incubation, NiCr2O4formed by a diffusion‐controlled process. The origin of pores at the NiO/NiCr2O4interface is discussed. The concentration profiles of Cr3+in NiO were linear because the interdiffusion coefficient was directly proportional to the mol fraction Cr3+. Theoretical considerations indicate that the interdiffusion coefficient equals 3/2 the self‐diffusion coefficient of Cr3+, which is rate‐determining. The interdiffusion coefficient at 1 mol% Cr2O3can be expressed as D̄=4×10−3exp (−55

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15999.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Methods for determining the parameters of the Weibull distribution function from the results of brittle fracture tests are considered. Linearization, direct (least‐squares) curve fitting, and maximum likelihood techniques are applied to a set of data for the fracture of glass specimens in cross‐bending and the results compared. It is suggested that the maximum likelihood method is to be preferred since it is completely objective and involves no arbitrary assumptions. However, none of the methods yields reliable results for functions involving three parameters for small sets of d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb16000.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The axial stress in clad glass fibers was measured by photoelastic techniques and compared with calculated values. In general, there was good agreement when the hydrostatic stress development was included in the calculation. The systems studied were primarily those which would produce a surface compression. Fibers of a soda‐lime‐silica glass clad with a high‐silica glass gave the largest surface compression, 46,00

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb16001.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The internal friction and self‐diffusion coefficients of sodium and rubidium ions for (l‐X)Na2O‐XRb2O‐3SiO2glasses were measured. Diffusion was measured by radioactive isotopes and a thin‐sectioning technique at 350° to 500°C. Internal friction was measured at −140° to 500°C and 0.05 to 6000 Hz. The maximum height for the mixed‐alkali internal friction peak occurs at the composition at which the Na and Rb diffusion coefficients are equal. It is concluded that the mechanism responsible for the mixed‐alkali peak is a coupled, cooperative rearrangement of sodium and rubidium ions, with the slower moving ion controlling the rate of rearrangement. This mechanism should also apply to other mixed‐alkali silicate glasses since the internal friction for the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb16002.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY