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Preparation of Water Base Magnetic Fluids Containing Small Magnetic Particles by the Use of Ultrafiltration

IP.com Disclosure Number: IPCOM000083467D
Original Publication Date: 1975-May-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 4 page(s) / 24K

Publishing Venue

IBM

Related People

Ronay, M: AUTHOR

Abstract

Magnetic particles are formed by chemical precipitation, for example Fe(3)O(4) is formed by the reaction (Image Omitted)

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Preparation of Water Base Magnetic Fluids Containing Small Magnetic Particles by the Use of Ultrafiltration

Magnetic particles are formed by chemical precipitation, for example Fe(3)O(4) is formed by the reaction

(Image Omitted)

The desalting of this suspension takes place by dialysis combined with ultrafiltration. In this process, continuous addition of fresh solvent washes out the membrane permeating salt through the membrane while the magnetite particles are retained. During this desalting process the volume of the dilute suspension is kept constant. In addition to this, the fluid is exposed to high-shear rate during its flow along the membrane surface. These two factors prevent the growth and agglomeration of the uncoated magnetic particles during the desalting process.

The membrane to be used in the process is an anisotropic membrane. Such membrane consists of very thin (0.1 to 1.5 Mu m) dense "skin" of extremely fine controlled fore texture upon a much thicker (50 to 250 Mu m) spongy layer of the same polymer with increasingly larger openings. This structure produces a unique combination of selectivity and high throughput at modest pressure. It also provides resistance to clogging, because retained substances are rejected at the surface. By selecting a membrane with about 20-30A pore diameter in the skin, only salt permeates and even the smallest magnetic particles are retained.

In order to prevent particle interaction and clogging of the membrane surface, the suspension is kept in turbulent flow or high shear rate laminar flow at the membrane surface. The latter may be achieved by tubular systems, capillary systems or thin channel systems. By flowing the fluid across the membrane with high velocity through channels of very small depth, the shear rate is sufficient to reduce the accumulation of the retained species on the membrane surface in a gel-like boundary layer. The result is increased transmembrane flow and high- ultrafiltration rates.

The volume of the wash solution may be computed from

(Image Omitted)

where c(o) is the initial salt concentration in the suspension, c(f) is the salt concentration after volume v wash solution has passed through the cell, and v(o) is the volume of the initial preparation added to the By this technique 99% effective wash out of salt occurs with a 5 volume turnover.

After desalting, the suspension is concentrated to the desired extent in the same high shear rate flow ultrafiltration process, but without introducing fresh solvent.

If surfactants or other additives are wanted, they may be introduced at any stage of the process, such as: 1. During or after the chemical precipitation of particles.

2. Dissolved in the wash solution.

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3. After desalting.

4. After concentration.

Surfactants bound to the particles will not permeate a properly chosen membrane, while free surfactants with lower molecular weight than the membrane cutoff level will be washed out. This gives a possibility...