Israel J. Lin

Review of the Phase Transformation and Synthesis of Inorganic Solids Obtained by Mechanical Treatment (Mechanochemical Reactions)

Abstract The theoretical background, based on thermodynamical concepts, of experimentally observed polymorphic transformations occurring during comminution processes (e.g. dry grinding of minerals) is discussed. It is shown that both the specific surface energy and volumetric elastic strain energy terms in the overall Gibbs free energy equation for the system in question play a major role in these transformations. Phenomenological kinetic equations are also discussed. Solid state reactions induced by the reactivity of newly exposed surfaces and by stress relaxation are described with the main emphasis on the synthesis of new compounds during the grinding or milling of powdered mixtures (e.g. production of ferrite from a mixture of oxides, mechanical alloying of metals etc.). The similarity between a shock-induced mechanochemical reaction (including its fundamental background) and a comminution process is pointed out. The paper concludes with a review of the applications of mechanochemistry and a list of fields of technology where it can be used to advantage.

More about the dielectrophoretic force

Using the theory of Molinari and Viviani, we show that it is possible to calculate the dielectrophoretic force on a sphere, in almost all the interesting cases. In particular, in an ac field we find that it is necessary to take into account the transient regime.

Production of zinc ferrite in a mechano-chemical reaction by grinding in a ball mill

Abstract Zinc ferrite was obtained by prolonged dry grinding of stoichiometric powder mixtures of ZnO + α-Fe 2 O 3 or ZnCO 3 + α-Fe 2 O 3 . The kinetics of transformation was studied by X-ray diffraction, Mossbauer spectroscopy and DTA. Crystallite size reduction followed the process, and defect structures resulted. The carbonate decomposed as a necessary step in the process. In the mixture of NiO + α-Fe 2 O 3 , nickel ferrite was not obtainable, although considerable grain size reduction was observed. This was attributed to the inverse spinel configuration of the nickel ferrite, differing from the normal spinel configuration of the zinc ferrite. In the α-Fe 2 O 3 and the zinc ferrite, iron ions occupy octahedral sites, while in ZnO and the ferrite, zinc ions occupy tetrahedral sites, and metal ion—oxygen distance is almost identical. These facilitate the transformation. In the nickel ferrite, iron ions occupy both sites, which calls for high strains of α-Fe 2 O 3 before it can undergo transformation. Further implications of the processes are discussed.

General conditions for dielectrophoretic and magnetohydrostatic levitation

Abstract Contactless separation of particles, droplets, or bubbles in solid-liquid, solid-solid, liquid-liquid, and gas-liquid systems can be achieved using electric and magnetic fields. Dielectric levitation and magnetohydrostatic separation techniques exemplify such separation processes. In this paper, the analogy between dielectric and magnetic levitation in non-uniform fields is exploited to provide general conditions for stable, contactless suspension of particles, droplets, or bubbles. Certain general properties of axisymmetric (cusped) electric and magnetic fields are used to obtain general equations of motion for levitated objects.

Phenomenological aspect of particle trapping by dielectrophoresis

We studied experimentally the trapping of particles by action of the dielectrophoretic force, in a matrix of glass beads in an inhomogeneous electric field. A phenomenological analysis of the trapping process is presented.

High-intensity, high-gradient electric separation and dielectric filtration of particulate and granular materials

Abstract High-gradient electric separation (HGES) and dielectric filtration (DF) are new techniques based on the use of the polarization force exerted by a non-uniform electric field (dielectrophoretic effect). Matrices of finely divided filamentary dielectric material and other types (glass fabric, titanates in the form of beads, balls or rods, perovskite-type ferroelectric bodies, ceramic wool, glass beads, etc.) containing 50–95% void space are used. The system requires an electric cell capable of generating high-intensity fields in large volumes. Dielectric separation is discussed under the following aspects: (i) intensity of the electric field and its gradient; (ii) size, density and dielectric constant of the particles; (iii) dielectric constant of the fluids serving as separation media; and (iv) flow regime in the separator system. The enormous potential of this technology is still to be realized. The most promising areas of application for the unique processes are identified.

Implications of Fine Grinding in Mineral Processing Mechanochemical approach

Fine grinding of minerals may change physical and chemical properties of the material to the extent that has to be considered in laboratory verification work or processing work in the industrial plant. The ground material is mechanically activated by increase of both: specific surface energy and elastic strain energy. The activation energy can then be dissipated through different mechanisms, such as: polymorphic transformation, mechanochemical decomposition or synthesis. The thermodynamical principles and kinetics mechanisms responsible for the relaxation modifications are thoroughly discussed. Important factors such as: Reaction triggering dimension, action of shear stresses, surface groups activity, product reactivity, etc. are described. A short survey on comminution by fine grinding is also presented.

Dielectrophoretic Filtration of Nonconductive Liquids

Abstract The filtration of liquids using highly nonhomogenous electric field was investigated. Very good results were achieved in removing metallic, ceramic, and plastic particles from practically nonconductive liquids.

Experimental analysis of dielectrophoretic forces

We performed a direct measurement of dielectrophoretic forces on particles immersed in a fluid, in a given electrode configuration which permits particle levitation. We show that the force on several neighboring particles is much larger than that acting on an isolated particle in the same field distribution. We discuss the consequences of the measurements on the use of dielectrophoresis for material separation.

The Effect of Irrigation With MagneticallyTreated Water on The Translocation ofMinerals in The Soil

Magnetically treated water (MTW) is water passed through a magnetic field before being used. Applications of MTW are abundant in industry where it is used to prevent scaling on inner walls of pipes conveying fluids, especially water. In recent years scientists investigating the subject have concluded that the magnetic field interacts with the surface charges of particles in the fluid solutions affecting the crystallisation and precipitation of the solids in them. These processes are of significant effect on the translocation of minerals in irrigated soil.