Dissolution in Ceramic Systems: III, Boundary Layer Concentration Gradients

By use of electron microbeam probe analysis on quenched samples, the concentration distribution of CaO, A1₂O₃, and SiO₂ was determined across the boundary layer between molten calcium aluminum silicates and dissolving or growing sapphire and fused silica. A definite shift in the concentration ratios of the solvent components was found near the interface. Analysis of diffusion flux equations for a ternary system successfully related the shift in concentration ratio to the intrinsic diffusion coefficient for each component. For alumina dissolution in a melt rich in CaO, evidence of incongruent dissolution was observed with the formation of new phases, CaO· 6Al₂O₃ and CaO· 2A1₂O₃.     

A Material Handling System Selection Model

A technique is presented which can be used to design, or assist in the design of, an integrated materials handling system for a manufacturing facility or a major department of the facility. The developed procedure selects the materials handling equipment to be used to perform a given set of moves in order to miriimize the system's costs associated with the handling, assuming the plant arrangement remains fixed. To demonstrate the selection procedure, an example problem is presented. Since the method is heuristic, no claim of optimality is made.     

DEFORMATION TESTING OF FOODS: III. Effect of Size and Shape on the Magnitude of Deformation

Slabs of uniform agar gels were cut into standard shapes of various sizes and their deformation under a small compressive force was measured in an Instron Universal Testing machine. The deformation of rectangular solids and regular cylinders with vertical axes was found to be directly proportional to the specimen height and inversely proportional to the cross-sectional area. The deformation of regular cylinders with horizontal axes was inversely proportional to the length and was a linear function of the diameter. Deformation of spheres first increased to a maximum, then decreased as the diameter increased giving an inverted V-shaped curve. The diameter at which the maximum deformation of spheres occurred depended on the agar concentration in the gel and the magnitude of the deforming force.     

Net Present Value from Complex Cash Flow Streams by Simulation

In models previously developed for the purpose of obtaining net present value from a stream of discounted cash flow increments, it is difficult to introduce complex economic, market and behavioral considerations without rendering the problem intractable computationally. Monte Carlo simulation with a digital computer, particularly in a simulation language, offers an attractive and feasible solution to the flexibility problem. This article illustrates the use of simulation techniques to find the net present value of a proposed project, together with its statistical distribution, when three types of phenomena are incorporated in the model: (1) long-term exponential market growth, (2) “non-instantaneous” response by the firm to price/elasticity fluctuations, and (3) imposition of arbitrary, yet reasonable, constraints on product output.     

Low-Temperature Sintering of Uranium Dioxide

Studies of the fabrication of uranium oxide fuel pellets by the low-temperature sintering of nonstoichiometric oxide are described. Completer reversion to stoichiometric UO₂ in the sintered pellets was attained by two methods: (1) Sintering in a nitrogen atmosphere which contained a small amount of hydrogen and (2) sintering in pure nitrogen and then exposing the pellets to hydrogen at the sintering temperature. Large variations in sinterability were found in commercially procured ceramic-grade UO₂ powder. In studying these variations, it was discovered that fluorine was a powerful inhibitor of low-temperature sintering. This impurity could be readily removed by oxidation in air at 500°C. The data strongly indicated that the primary mechanism responsible for the removel of residual fluorine was pyrohydrolysis. It was found that a preliminary oxidation-reduction cycle activated the less-sinterable oxides so that in every case densities of at least 95% of theoretical were obtained by sintering at 1200°C.     

Kinetics of Opacification of a TiO2-Opacified Cover Coat Enamel

Quantitative X-ray diffraction measurements were used to study the firing behavior of a typical TiO₂-opacified cover coat enamel. A model was developed for predicting the anatase and rutile concentrations as a function of time and temperature of firing. The model consists of three first order reactions: crystallization of anatase, crystallization of rutile, and inversion of anatase to rutile. It predicts successfully over a wide range of time-temperature conditions. Discrepancies are found, however, for short-time, low-temperature firings. The reflectance data do not correlate well with the crystalline concentration data. The correlation with color data is better, but is not perfect.     

Deformation and Fracture Processes in Calcium Fluoride Single Crystals

The plastic properties of calcium fluoride single crystals tested in compression were investigated in the temperature range 25° to 1000°C. Above 400° C., the crystals showed appreciable ductility. The critical resolved shear stress, t, decreased with absolute temperature, T , according to the equation t = t₀e^+K/T. The rate of work-hardening decreased rapidly as the temperature increased but retained a relatively high value even as the melting point was approached. Air-annealed crystals were harder than as-cleaved crystals. Crystals with a (111) plane normal to the applied stress hardened less rapidly than crystals with a (110) plane normal to the applied stress. The dislocation density increased linearly with strain. (100), (110), and (111) fractures were observed.