Stress Corrosion of Ionic and Mixed Ionic/Covalent Solids

Slow crack growth data, surface reaction studies, and solubility results for sapphire and magnesium fluoride crystals are used to identify stress corrosion mechanisms for each material. Results suggest that stress corrosion in sapphire proceeds by the dissociative chemisorption of environmental species on strained crack tip bonds. Crack growth rates measured in nonaqueous environments and isotopically labeled water suggest that ion solvation rather than dissociative chemisorption dominates the crack tip interaction in magnesium fluoride.     

Mass Transport and Sintering in Impure Ionic Solids

The chemical potentials of the constituents in an impure ionic solid are derived as a function of the pressure and the impurity concentration. After consideration of the diffusion fluxes caused by gradients of these chemical potentials, the theory is applied to a sintering model which illustrates a possible effect of impurity additions on sintering rates. The results indicate that caution must be exercised to distinguish between a phenomenological vacancy diffusion coefficient and the intrinsic vacancy diffusion coefficient in ionic solids.     

Space Charge Signature and Its Effects on Ionic Transport in Heterogeneous Solids

The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LATP) glass–ceramic, Al₂O₃, and Ba_0.6Sr_0.4TiO₃ (0.6 BST) exhibit an inflection or peak around 27°C, which is interpreted as a signature of space charge. The space charge is formed by the adsorption of lithium ions onto the dielectric phases below 27°C. The space charge is also a source of an electric field, which influences the transport of conducting ions. The adsorbed ions are desorbed above 27°C, resulting in a reduction or elimination of the space charge effect. A high dielectric constant phase, 0.6 BST, retains the space charge effect even at temperatures greater than 27°C.     

Bouncing Bubbles

We discuss here soap bubbles hitting a bath of water and bouncing off the surface. We first describe the characteristics of this event, that is, the bubble deformation during impact and the contact time associated with the rebound. Then we propose a tentative scenario for understanding this behavior, which stresses the importance of the transient film of air between the bubble and the bath, preventing the coalescence from taking place.     

Bouncing Bubbles

We discuss here soap bubbles hitting a bath of water and bouncing off the surface. We first describe the characteristics of this event, that is, the bubble deformation during impact and the contact time associated with the rebound. Then we propose a tentative scenario for understanding this behavior, which stresses the importance of the transient film of air between the bubble and the bath, preventing the coalescence from taking place.     

Gas-Filled polymers. II. Mechanical behavior of polyethylene

The mechanical properties of gas-filled polyethylene have been studied for material with density greater than about 0.85 g/cm³. The effect of gasification on the tensile properties of both high and low density polyethylene beyond a certain critical density reduction is to cause a general weakening of the material. The yield stress falls by about 25% over the range of density investigated, while the elongation to fracture decreases by an order of magnitude. A mechanism is proposed to this weakening and for the yielding and fracture phenomena observed for gasified polyethylene.     

Dissolution of Multicomponent Bubbles

The behavior of an isolated, stationary, multicomponent gas bubble in a glassmelt containing several dissolved gases is considered. The relevant mass-transport equations are formulated and calculations are performed for the case of two diffusing gases using a quasi-stationary model and a numerical solution of the exact mass-transfer equations. The results obtained from these two approaches are compared. The factors which govern the dissolution or growth of a bubble are thermodynamic and kinetic in origin. The tendency of a bubble to grow or shrink at long times is controlled by departure from overall equilibrium, whereas the short-time bubble dynamics may be dominated by kinetic effects. As a result of the existence of these dual influences, maxima and/or minima occur in the functional dependence of the bubble radius on time.     

非牛顿流体中的气泡行为

非牛顿流体广泛存在于各学科领域（如化工、食品和生物医学等）,也与许多工业过程及人类的生命过程密切相关。非牛顿流体中的气泡行为直接影响流体传质、传热及化学过程的快慢。因此,了解和研究非牛顿流体中的气泡行为具有重要意义。本文分别从气泡生成、聚并和破裂3个方面对非牛顿流体中气泡行为的研究进展进行评述。     

Migration of Large Gas-Filled Pores in Potassium Chloride Due to a Temperature Gradient

The migration of gas-filled pores in KCl subjected to a temperature gradient occurs by a vaporization-condensation mechanism. In many cases the vaporization step, rather than gas-phase diffusion, can limit the rate of migration. Movement of large (>100 μ m ), argon-filled pores in pure and Ba-doped KCl was observed using hot-stage microscopy. Velocities of large pores in pure KCl were limited by the diffusion rates of KCl monomers and dimers in argon. This observation is consistent with a model in which the vaporization rate is moderately reduced due to widely spaced surface ledges, but is still rapid with respect to gas-phase diffusion. The velocities of large pores in 10 and 40 ppm Ba-doped samples were significantly lower than those in pure samples. A model was developed which explains these decreased migration rates in terms of impurity poisoning of surface kink sites. The model couples detailed expressions for vaporization kinetics with those for gas-phase diffusion rates.     

Solids transport in mixed-flow dryers

Mixed-flow dryers are broadly used in worldwide agriculture for the drying of grain, corn and rice but are also applied in industry. Although this drying process is well established, there is still a need to optimize the dryer apparatus. Unfavorable design can cause uneven mass flow and air flow distributions, broad residence time distributions and, hence, inhomogeneous drying histories of the particles resulting in non-uniform drying. The transport of solids in mixed-flow dryers has not yet been sufficiently considered and investigated. Therefore, the objective of this study is to derive basic equations on particle flow in mixed-flow dryers which are practically operated in the interrupted flow regime and equipped with discharge gates. The function of the discharge gate, the discharge characteristic and the solids mass flow rate were studied by varying the discharge and standstill times, respectively. The experiments were conducted at a semi-technical dryer test station with a transparent acrylic glass front wall using wheat as bed material. The fundamentals developed serve as a basis for further theoretical and experimental investigations. The future goal is to improve apparatus design and process control so as to homogenize the drying process, to increase energy efficiency and to save product quality.     

Solids motion in flowing froths

Flotation is a widely used process within the minerals processing industry, as well as being used for water treatment and de-inking of recycled paper. The froth phase and its role in the separation achieved is as yet ill understood. A fundamentally based model of the behaviour of solids within a flowing froth allows for a fuller understanding of the froth phase of flotation vessels and process optimisation.This paper outlines a model for the motion of solids within a flowing froth. It builds on earlier work on the modelling of bubble and liquid motion within a flowing froth and includes all the effects of same phenomena that effect liquid motion, as well as including the effect of solids concentrations on liquid motion.The solids are divided into two classes for the purposes of modelling, namely the attached material, which follows the bubbles, and the unattached material, which mainly follows the liquid, but can move relative to the water by means of hindered settling and geometric and Plateau border dispersion. The attached material consists of hydrophobic particles, while the unattached material can consist of both hydrophobic and hydrophilic particles. Attached particles can become unattached due to coalescence or bursting.Results from simulations are shown to illustrate the movement and concentration of the solids from the pulp-froth interface to the upper, bursting surface and overflowing the weir.     

Thermal-Gradient-Induced Migration of Bubbles in Molten Glass

Buoyant fining of molten glasses does not occur in a weightless environment. One method suggested for fining is to apply a temperature gradient to cause bubbles to move because of the surface tension temperature dependency. Ground-based experiments were conducted to demonstrate that thermal migration actually occurred in glassmelts and to estimate the magnitude of the effect. Thermal migration, consistent with theory, was found in borax melts, evidencing an approximately linear relation between bubble diameter and bubble velocity for a given temperature and gradient. Other effects, such as near-bubble interaction, were also observed.     

Mass Spectrometric Analysis of Bubbles in Glass

Procedures have been developed for analyzing, by quadrupole mass spectrometry, gases contained in bubbles within glass. Commonly sought-for species are detected individually at minimum levels of 3 to 70x10⁻⁴ nL (STP) in bubbles 0.1 to 1 mm in diameter. Calibration is obtained by analyzing certified gas mixtures contained in glass capillaries at known pressures and volumes.