The fracture stress of chemical vapour deposited diamond

The factors which control the fracture stress of chemical vapour deposited diamond have been studied using the 3-point bend geometry. Fracture stress values of 300–800 MPa for the growth side and 600–1200 MPa for the nucleation side were recorded for samples of thickness 0.4–2.4 mm. A Weibull modulus of 23 was calculated for the growth surface data, showing that the fracture stress variability was low for a brittle material. A theory based on these results demonstrates that the material behaviour is remarkably simple, depending only on the grain size and the sample thickness, regardless of wide variations in other parameters such as optical transmission and stress state. The paper also contains a possible explanation for this well-defined behaviour based on microstress variations resulting from differences in defect density in different growth sectors within a grain.     

Shear and extensional flow of a thermotropic liquid crystalline polymer

The flow of a thermotropic liquid crystalline polymer (unfilled and glass fiber filled) was studied using a capillary rheometer and an instrumented injection molding machine. Despite different thermal histories, the techniques gave similar results. From 330 to 350°C, viscosity was independent of temperature. At 340°C, where most measurements were carried out, pronounced shear-thinning occurred and the shear flow curves were nonlinear, the power law exponent decreasing from 0.51 at a shear rate of 10 s⁻¹ to 0.35 at 10⁴ s⁻¹. A previously reported model was used to derive elongational flow curves from die entry pressure data. Because of the nonlinearity of the flow curves, quadratic log-stress vs. log-strain rate plots were needed to model behavior over the strain rate region studied. The elongational flow curves were similar in shape to the shear flow curves, with an effective Trouton ratio of 30. Despite orientation and structure present in the melt, the extensional viscosities and Trouton ratios were within the range found with normal thermoplastic melts. The results suggest that extensional flow may be inhomogeneous, the flowing units possibly being partially ordered domains.     

A specification test for univariate and multivariate proportional hazards models

This paper applies White's (1982, Econometrica 50, 1-25) information matrix (IM) test for correct model specification to proportional hazards models of univariate and multivariate censored survival data. Several alternative estimators of the test statistic are presented and their size performance examined. White also suggested an estimator of the parameter covariance matrix that was robust to certain forms of model misspecification. This has been subsequently proposed by others (e.g., Royall, 1986, International Statistical Review 54, 221-226) and applied by Huster, Brookmeyer, and Self (1989, Biometrics 45, 145-156) as part of an independence working model (IWM) approach to multivariate censored survival data. We illustrate how the IM test can be used for both univariate data and as part of the IWM approach to multivariate data.     

Direct synthesis and characterization of the Fe3+ analogue of Naβ″-alumina

A new isomorphic analogue of-alumina, a potassium-free Na-ferrite (Na₂O · 5 (Al_0.10Fe_1.90)O₃, referred to as Na-ferrite), has been synthesized and is characterized using X-ray powder and single crystal diffraction, wet chemical analysis, and transmission electron microscopy (TEM). In addition, Na-aluminate-gallate-ferrate phases were also successfully synthesized, but were not characterized in detail. Na-ferrite grew in a slowly cooling melt or partial melt from 1250° C in air using Na₂CO₃ and Fe₃O₄ (magnetite) as starting materials. The compound was also synthesized using-Fe₂O₃ instead of Fe₃O₄ under the same conditions, but its abundance was much less and-Fe₂O₃ and NaFeO₂ were the dominant phases. The new material (cell dimensionsa = 0.5955,c = 3.5623 nm) is reversibly hygroscopic, andc increases 2% after hydration. TEM images dearly show the 1.19 nm lattice spacing corresponding to the ionic conduction planes, and these planes are observed to be both straight and curled. The origin of the curled lattice planes, the existence of which is also evident in the single crystal precession photographs, is not clear, although we believe it may involve a structural misfit between the ferric oxide spineI block and soda layer.     

A Kinetic study of the reaction of zinc oxide with iron powder

Electric arc furnace (EAF) dusts contain significant quantities of zinc, mostly in the form of zinc oxide. This dust has been classified as a hazardous waste due to the presence of lead, cadmium, and hexavalent chromium. It is important that environmentally acceptable processes be developed to treat this waste. One possible alternative process would involve reacting the zinc oxide in the dust with either solid or liquid iron. In addition, in the carbothermic reduction processes, which have been designed to treat the dust, metallic iron is formed, and this iron can participate in the reduction of zinc oxide. In the present research, the reduction of zinc oxide by iron according to the reaction $ZnO_{(s)} + Fe_{(s)} = Zn_{(g)} + FeO_{(s)} $ was studied using a thermogravimetric technique. Briquettes of zinc oxide powder and electrolytic iron were reacted in the temperature range of 1073 to 1423 K in an argon atmosphere. First, a thermodynamic analysis was performed using the Facility for the Analysis of Chemical Thermodynamics (F*A*C*T) computational system, and then the effect of experimental variables on the reaction kinetics was determined. These variables included argon gas flow rate, reaction temperature, reagent particle size, iron to zinc oxide ratio, aspect ratio of the briquette, briquetting pressure, and alkali and alkaline earth additions. It was found that, initially, the reaction was chemically controlled with an activation energy of 230 kJ/mol. Additions, such as sodium chloride and calcium fluoride, promoted the reaction, and the activation energies were 172.5 and 188.7 kJ/mol, respectively. Once a product layer had formed, the reaction was limited by the diffusion of zinc gas away from the reaction interface. The experimental data were fitted to a parabolic rate law, and the parabolic rate constant was found to be $k_p = - 2.47 + 0.0021 T(K)$      

Ultramicrotoming of Ceramic Powders for Electron Microscopy

Compacts of monosize TiO₂ particles and agglomerates of TiO₂ and γ-alumina were infiltrated with Spurr's epoxy resin, cured, and ultramicrotomed. Transmission electron microscopy of the thin sections revealed the packing of the TiO₂ spheres and the structure of the agglomerates.     

Design of a 5:1 bandwidth stripline notch array from FDTD analysis

A 5:1 bandwidth stripline notch array antenna is designed from parametric investigations of flare and feed dimensions. The finite-difference time-domain (FDTD) method is employed to perform the parametric studies. Both linear and planar single-polarization arrays are considered with half-wavelength element spacing at the highest frequency. The linear array elements depend upon E-plane element mutual coupling to achieve wideband behavior. Edge elements, which cannot benefit from full E-plane coupling, are shown to maintain good transmit performance with the application of amplitude tapering. The planar array is shown to have a scanability (active VSWR <2) averaging 51° off broadside in the E-plane and exceeding 60° in the H-plane. As an infinite planar array, the antenna is predicted to have a bandwidth exceeding 7:1 on broadside. Measurements are in good agreement with the computations     

Thermodynamic modelling of the multiphase pyrometallurgical processing of electric arc furnace dust

Electric arc furnace (EAF) dust is produced when automobile scrap is remelted in an electric arc furnace and about 10–20 kilograms are generated per ton of steel. The major elements present in the dust are usually zinc, iron and calcium with smaller amounts of numerous other elements such as lead, copper and nickel. Typically, in the pyrometallurgical EAF dust treatment processes, the lead and zinc are separated as a crude zinc oxide while the iron is generally not worth recovering. Copper and nickel are usually not recovered as they report either to the oxide residue or to any metallic iron that is produced. In the present research, the recovery of the non-ferrous metals in a multiphase system consisting of gas, slag, matte, metal and solid carbon phases was investigated. The equilibrium compositions of the various phases, resulting from the smelting of the dust, were calculated using the SOLGASMIX module of Outokumpu HSC Chemistry. The effects of the following operating variables were investigated; carbon additions, sulphur additions, nitrogen and oxygen additions, temperature and dust composition. The thermodynamic modelling results show that the majority of the non-ferrous metals can be recovered, with the zinc and lead concentrating in the gas phase and the nickel and copper concentrating in the matte phase.