Jean Marie Quets

Kinetics of the Oxygen—Tungsten Reaction at High Temperatures

The rate of reaction of molecular oxygen with tungsten was measured from 2000° to 3300°K at pressures from 0.11 to 11.5 torr. High gas‐phase mass transfer coefficients were obtained by impinging a high‐velocity gas jet on the sample. A maximum reaction rate was observed at each O2 pressure, the temperature of maximum rate increasing with pressure. Below the temperatures of the maxima, an apparent activation energy near 23 kcal mole−1 was observed. These results are well described by the empirical equations of Perkins, Price, and Crooks, except that no transition to a regime of higher activation energy at lower temperatures was observed here and the maxima were found at slightly higher rates and temperatures than previously reported. Appreciable diffusion effects were found only near the observed maxima. These data and the 10−4 torr data of Schissel and Trulson were correlated in terms of the two‐layer oxygen‐atom adsorption model for tungsten oxidation kinetics proposed by the latter authors. Kinetic cons...

Density separation of solids in ferrofluids with magnetic grids

Abstract Nonmagnetic solids in a superparamagnetic ferrofluid are subjected to body forces proportional to the intensity of magnetization of the fluid and the gradient of the magnetic field. An apparent density of the fluid can be defined from the force equations, and since the apparent density can be much larger than the true density, it is possible to levitate or float dense objects. Mixtures of solids with a density greater than the apparent density sink while lower density solids float. In practice it is difficult to create a uniform gradient over a large volume and “single gap” magnetic separators require very large magnets or have a limited throughput. To overcome that problem, “multiple gap” magnetic grids have been designed. Such grids consist of planar arrays of parallel bars of alternating polarity, driven by permanent magnets. When immersed in ferrofluid, magnetic grids create nonuniform field gradients and apparent densities in the fluid. However, both analysis and experimental measurements sh...