Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1990-06-28
1994-03-29
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
2041812, C25D 1300
Patent
active
052981339
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of recycling organic liquids and method of manufacturing articles by electrophoretic deposition.
DESCRIPTION OF THE PRIOR ART
In electrophoretic deposition a suspension of electrically charged particles in a carrier liquid, hereinafter referred to as a slurry, is passed between a pair of electrodes. One of the electrodes serves as a mandrel to which the particles are attracted and pressed to form an article.
Electrophoretic deposition processes are well known for use for a variety of purposes, one such purpose being the manufacture of the beta alumina electrolyte cup as used in sodium-sulphur electrochemical cells. In such a process a liquid medium is used for suspending the particles, that is the beta alumina particles, to be deposited, and it is desirable for such liquid medium to be either cheap so that re-use is not necessary, or reclaimable for re-use to save expenditure.
Water has been proposed as a cheap liquid medium but is not generally satisfactory since electrolysis of the water occurs during the electrophoretic deposition process, this resulting in the production of gaseous products which result in void-like defects in the article built-up from the deposited particles. This is clearly undesirable for the strength of the article.
Thus, organic liquids are preferred as the liquid medium since gassing is considerably reduced with such liquids. Reclamation of the liquid medium is, however, essential for economic and environmental reasons.
In principle an organic liquid medium can be reclaimed after use in an electrophoretic deposition process simply by allowing or causing the used suspension to separate into solid and liquid phases and then decanting off the supernatant liquid.
Drying of the supernatent liquid can then be effected by passage through a molecular sieve. Reference to this method may be found in the article by Robert W. Powers in the Am. Ceram. Soc. Bull., 65[9]1270-77 (1986) entitled "Ceramic Aspects of Forming Beta Alumina by Electrophoretic Deposition". Drying is required since the presence of water in the reclaimed organic liquid beyond about 0.03% will seriously affect any electrophoretic deposition process carried out using the reclaimed liquid by reversing the charge on the particles suspended therein. One of the particular problems faced when using beta alumina is that the particles require negative charging. The prescence of even very small quantities of water is therefore a problem since the beta alumina is extremely hydroscopic and any hydrogen ions will of course disrupt the charge status.
However, attempts to reuse an organic liquid reclaimed in such a way have proved to be unsuccessful, and it is thought that this is due to chemical changes which occur in the organic liquid in the electrophoretic deposition process. In an electrophoretic deposition process the suspension of the particles to be deposited in the organic liquid may be vibro-milled to charge the particles as necessary, and during such operation the conductivity of the organic liquid rises, possibly due to ionic dissociation from the particles. This rise in conductivity is not removed if the organic liquid is reclaimed by the method mentioned above, and thus if such a reclaimed organic liquid is reused, the new particles added thereto will not become adequately charged during the vibro-milling operation, and the suspension produced will not be suitable for an electrophoretic deposition process.
STATEMENT OF THE INVENTION
Thus, in accordance with the present invention, a method of reclaiming an organic liquid used as the suspending medium in an electrophoretic deposition process, comprises the steps of separately de-ionising the used liquid and then removing water from the de-ionised liquid.
Consequently, the invention is predicated on the appreciation of the deficiencies in previous approaches to recycling organic liquids. Preferably, de-ionising is effected by distillation, which can be carried out using a conventional single-stage Liebig conden
REFERENCES:
patent: 3067120 (1962-12-01), Pearlstein
patent: 4366049 (1982-12-01), Knorre
patent: 4542114 (1985-09-01), Hegarty
Amer. Ceram. Soc. Bull. 65[9] 1270-77 (1986) "Ceramic Aspects of Forming Beta Alumina by Electrophoretic Deposition" by Robert Powers.
Chloride Silent Power Limited
Niebling John
Phasge Arun S,.
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