Defect Structure of NiO-CoO Solid Solutions

Measurements at high temperature of integrated intensities of Bragg peaks were used to examine the defect structure in two NiO-CoO solid solutions. The results indicate that the concentrations of vacant cation sites at 1100° to 1500°C are 4 to 10% and the tetrahedral occupations 2 to 5%. The concentration of these defects increases with temperature and partial pressure of O₂. The mean-square displacements of oxygen ions and cations increase with temperature and CoO concentration.     

Interdiffusion in CoO-NiO Solid Solutions

Interdiffusion coefficients were measured in CoO-NiO solid solutions over the range 1000° to 1600°C in air and at po₂=5×10⁻⁸ atm. Isothermal values of the interdiffusion coefficients in this system increased exponentially with the CoO concentration. Comparison of the present results with cation-tracer diffusion coefficients for this system measured under similar conditions by Chen and Peterson shows that a Darken-type equation relating the interdiffusion coefficient to the cation-tracer diffusivities is valid for these data.     

Control Requirements for Control Systems: Matching Surety To Risk

Abstract

Auditing Software Development: A Manual With Case Studies, by S. Rao Vallabhaneni. John Wiley and Sons (605 Third Avenue, New York, 10158-0012), 1990, 439 pp. Includes a glossary and bibliography. Price: $75.00, plus shipping and handling charges.

Computer Crime: Techniques For Preventing And Detecting Crime In Financial Institutions, by Gregory Wold and Robert Shriver. Bankers Publishing (60 Gould Center, Rolling Meadows IL 60008), 1989, 255 pp. Includes a glossary. Price: $49, with a discount for BAI members.     

ADSORPTION ISOTHERMS AND CATALYST SELECTIVITY FOR A UNIFORM SURFACE: THE ROLE OF MULTIPLE LANDING AREAS

In general a gas phase species can be present simultaneously in more than one adsorbed form on a uniform solid surface. The different adsorbed forms tie up different combinations of surface sites. Each such combination is termed a landing area. The different adsorbed forms present on the surface of a catalyst may form different products. (In the more general case, each different adsorbed form yields a different distribution of a set of products.) Hence the relative amount of each adsorbed form and landing area present on the surface determines the selectivity of the solid catalyst. The variation of the landing area distribution with temperature and partial pressure of the gas phase species is examined in the first part of this work. In general, increasing the pressure or decreasing the temperature leads to the relative decrease of molecules adsorbed on landing areas consisting of larger number of sites and the relative increase of molecules adsorbed on smaller landing areas. The kinetics of metal catalyzed skeletal isomerization and hydrogenoly-sis of hydrocarbons on supported metal catalysts is examined in the framework of the landing area in the second part of this work. A simple model for the variation of reaction order with pressure agrees with experimental data from other laboratories.     

Measurement of the Lattice Parameter of Wustite at High Temperatures

The lattice parameter of wustite (Fe₂O) single crystals was measured at high temperatures. Plots of both lattice parameter vs composition and lattice parameter vs temperature were linear, and no appreciable changes in slope were detected at the boundaries of the subphases suggested by Vallet and Raccah.     

Diffraction from a Natural Grain Boundary in a Magnetite Bicrystal

The structure of a natural small-angle boundary in a magnetite bicrystal was investigated by X-ray diffraction. This boundary was a "general" type with a mixed twist and tilt character. The grain-boundary reflections observed around an 040 matrix reflection were in good agreement with those predicted by Boll-mann's O-lattice theory. These extra reflections appear to arise from a predominantly planar dislocation network. The structural width of the boundary, determined from the length of the relrods of the grain-boundary reflections, was of the order of four unit cells, close to the average spacing of the expected dislocation network.     

Differential Thermal Analysis Investigation of the High-Low Cristobalite Inversion Under Hydrostatic Pressure to 7 Kbar

The high-low inversion in polycrystalline cristobalite, synthesized from quartz at 1500°C, was investigated by differential thermal analysis to 7 kbar in hydrostatic apparatus. A region of anomalous curvature ( d²T/dp² >0) exists to ∼1 kbar; at higher pressure, the low→high and high→low transition temperatures vary linearly with pressure, with slopes of ∼51.₁ and 53. ₆ deg kbar⁻¹, respectively. Extrapolated 1-bar intercepts are ∼232° and ∼209°C, respectively. It is concluded that high cristobalite is less compressible than low cristobalite near the inversion. The hysteresis between the high→low and low→high transition temperatures decreases with increasing pressure.