Electrolysis: processes – compositions used therein – and methods – Electroforming or composition therefor – Powder – flakes – or colloidal particles
Reexamination Certificate
2001-12-04
2004-01-13
Phasge, Arun (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electroforming or composition therefor
Powder, flakes, or colloidal particles
C205S538000
Reexamination Certificate
active
06676821
ABSTRACT:
This invention relates to a process for the production of amorphous and/or crystalline oxides of metals of the third to fifth main group or the secondary groups which have mean particle diameters in the nanometer range. In the context of the invention, this is the range from about 1 to about 500 nanometers. More particularly, the amorphous or crystalline metal oxides obtainable by the process according to the invention have particle diameters in the range from about 5 to about 100 nanometers. Metal oxides such as these may be used for various industrial applications: as dielectrics for miniaturized multilayer capacitors, as catalysts, as additives in paints and cosmetics, as additives in plastics to stabilize them against thermal or photochemical decomposition and/or to modify their dielectric and/or magnetic properties and as polishes.
Metal oxides with particle diameters in the nanometer range may be obtained, for example, by dissolving alkoxides of the metals in a water-immiscible solvent, preparing an emulsion of the resulting solution in water using suitable surfactants, the emulsified droplets of the solvent having diameters in the nanometer range, and hydrolyzing the metal alkoxides to the oxides. The disadvantages of this process lie in particular in the fact that the metal alkoxides are expensive starting materials, in the fact that emulsifiers also have to be used and in the fact that the preparation of the emulsion with droplet sizes in the nanometer range is a complicated process step.
It is also known that metal particles (not metal oxide particles!) with a particle size below 30 nm can be produced by cathodically reducing suitable metal salts in organic solvents or mixtures thereof with water in the presence of a stabilizer and optionally in the presence of a supporting electrolyte. Instead of dissolving metal salts in the electrolyte, the metal ions to be cathodically reduced can also be dissolved by using anodes of the corresponding metals which dissolve during the electrolysis. One such process is described in DE-A-44 43 392.
In addition, DE-A44 08 512 describes a process for the electrolytic production of metal colloids in which one or more metals belonging to groups IV, VII, VII and I.b of the periodic system are anodically dissolved in aprotic organic solvents in the presence of a supporting electrolyte and cathodically reduced in the presence of stabilizers to colloidal metal solutions or redispersible metal colloid powders with a particle size below 30 nm. The supporting electrolyte and the stabilizer may be identical. If the cathodic reduction is carried out in the presence of suitable supports, the metal colloids are precipitated onto those supports.
In addition, according to Chemical Abstracts Report 110:65662, fine-particle zirconium oxide powder can be obtained by electrochemically producing a base in a solution of zirconyl nitrate, the zirconyl nitrate being hydrolyzed by the base with precipitation of hydrated zirconium oxide. Crystalline zirconium oxide can be obtained from the hydrated zirconium oxide by calcination. According to Chemical Abstracts Report 20 114:31881, mixed oxides of iron, nickel and zinc can be produced by electrochemically precipitating a hydroxide mixture of those metals from metal salt solutions and calcining the isolated hydroxides to the mixed oxides.
The problem addressed by the present invention was to provide a new process for the production of amorphous and/or crystalline oxides of metals or mixed oxides of several metals which have mean particle diameters of about 1 to about 500 nm.
Accordingly, the present invention relates to a process for the production of amorphous and/or crystalline oxides of metals of the third to fifth main group or the secondary groups of the periodic system which have mean particle diameters in the range from 1 to 500 nm, characterized in that, using a cathode and an anode, ions of those metals dissolved in an organic electrolyte are electrochemically reduced at the cathode in the presence of an oxidizing agent.
FIGS. 1
to
3
are X-ray diffractograms of certain metal oxide samples produced in the working examples of the present invention.
In this process, the mean particle diameter can be adjusted by varying the temperature of the electrolyte or the electrical voltage or current intensity or through the nature of the supporting electrolyte optionally used. The process is preferably carried out in such a way that the metal oxides obtained have mean particle diameters in the range from 5 to about 100 nm.
Using this process, it is only possible to produce metal oxides which do not react with moisture to form hydroxides at a temperature below about 100° C. Accordingly, the process is not suitable for the production of oxides of alkali or alkaline earth metals. It is particularly suitable for the production of oxides of metals which are oxidized by atmospheric oxygen at temperatures below about 100° C. Where metals such as these are used, the process according to the invention may be carried out at temperatures below 100° C. using air as the oxidizing agent. This enables the process to be carried out in an uncomplicated manner. The process is particularly suitable for the production of amorphous and/or crystalline oxides of Ti, Zr, Cr, Mo, Fe, Co, Ni and Al.
The organic electrolyte used is preferably a substance which is liquid at temperatures in the range from about −78° C. to about +120° C. at normal pressure. In one particularly preferred embodiment, a substance which is liquid at temperatures in the range from about 0 to about 60° C. at normal pressure is used. The organic electrolyte is preferably selected from alcohols, ketones, ethers, nitrites and aromatic compounds, those which are liquid at temperatures in the ranges mentioned being preferred. Particularly suitable electrolytes are tetrahydrofuran, acetone, acetonitrile, toluene and mixtures thereof with alcohols.
Depending on the metal oxide to be produced, it can be favorable if the electrolyte contains small quantities of water. For example, the water content of the organic electrolyte may be in the range from about 0.01 to about 2% by weight and, more particularly, is in the range from about 0.05 to about 1% by weight, the percentages by weight being based on the total quantity of organic electrolyte and water.
Should the electrolyte not of itself have an adequate electrical conductivity or acquire an adequate electrical conductivity by dissolution in salts of the metals whose oxides are to be produced, it is advisable to dissolve a supporting electrolyte in the electrolyte. The usual supporting electrolytes which are normally used to give the electrolytes mentioned an electrical conductivity sufficient for electrochemical processes may be employed. Suitable supporting electrolytes are, for example, electrolyte-soluble hexafluorophosphates, sulfonates, acetyl acetonates, carboxylates and in particular quaternary phosphonium and/or ammonium salts with organic groups at the phosphorus or at the nitrogen. Preferred supporting electrolytes are quaternary ammonium compounds which bear aryl and/or alkyl groups at the nitrogen and which are preferably present as halides. A particularly suitable example is tetrabutyl ammonium bromide.
The process according to the invention is preferably carried out in a temperature range in which the supporting electrolyte is sufficiently soluble in the organic electrolyte. The process is preferably carried out in such a way that the organic electrolyte has a temperature in the range from about 30 to about 50° C. If tetrahydrofuran is used as the electrolyte and tetrabutyl ammonium bromide as the supporting electrolyte, the process is preferably carried out at temperatures above 35° C. for example in the range from 35° C. to 40° C.
The supporting electrolytes have the additional effect that they protect the oxide particles formed against agglomeration. A very narrow particle size distribution can be obtained in this way. As described in a following Example, zirconium dioxide with a volume-
Hempelmann Rolf
Natter Harald
Henkel Kommanditgesellschaft Auf
Phasge Arun
Woodcock & Washburn LLP
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