Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing bipolar membrane
Patent
1996-01-25
1997-08-26
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing bipolar membrane
205508, 205509, C25B 100
Patent
active
056607091
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns an electrochemical process for the production of metallic hydroxides and/or metallic-oxide hydroxides from metal ions and hydroxide ions, as well as a device for implementation of the process.
BACKGROUND OF THE INVENTION
Metallic hydroxides and metallic-oxide hydroxides find the broadest application in the most diverse industrial fields, for example, as intermediate products of the production of metals themselves or of the corresponding metallic oxides, which are then in turn processed further, for example, into ceramics, etc.
Zinc hydroxides, for example, can be applied as preliminary stages for pigments, photoconductors (for example, in electrophotography), catalyst components (for example, in methanol synthesis), fluorescent substances, absorptive agents (for example, for the removal of H.sub.2 S from gases), etc. Zinc-oxide hydrates are suitable, for example, as a catalyst component for the oxidation of aromatics, iron(III) hydroxide is employed, for example, in water purification, for pharmaceutical purposes or for the manufacture of iron colorants, and cobalt(II) hydroxide can, for example, serve as a starting material for the production of siccatives. Many applications of the metallic hydroxides and metallic-oxide hydroxides concern especially their particulate form, the particle size of the same and their particle-size distribution.
Thus, in the chemical industry for example, Ni(II) hydroxide is utilized as a base chemical in the ceramic-products sector and especially in the construction of batteries. In addition to use as the positive electrode in commercial secondary cells, such as nickel-cadmium and nickel-iron battery systems, nickel hydroxide is being applied to an increasing degree in environmentally friendly nickel-metallic hydroxide batteries which contain no heavy metals. The active components of the batteries are the anode, consisting of a hydratable metal alloy which is free of heavy metals, and the cathode which consists of nickel hydroxide. The mass electrodes are installed in a gastight steel housing and separated by a plastic fleece. Determined by the mechanical structure of the battery, various requirements are imposed upon the product nickel hydroxide relative to morphology and appearance. The most uniform product possible with a spherical morphology and narrow particle-size distribution should be obtained to achieve good flowing behavior during the filling of the porous nickel-foam electrodes.
STATE OF THE TECHNOLOGY
Various methods involving precipitation out of metallic-salt solutions in an alkaline medium are described for the production of metallic hydroxides and metallic-oxide hydroxides. Nickel chloride, for example, is the most common starting material for the precipitation of nickel hydroxide. Precipitation from nickel sulfate, nickel carbonate and nickel nitrate solutions is likewise known. Employed as precipitating agents are alkali hydroxides, alkaline-earth hydroxides, alkali carbonates and aqueous ammoniac solutions.
The production of nickel hydroxide from a nickel(II)-chloride solution combined with caustic soda at an elevated temperature (T=70.degree.-80.degree. C.) corresponds to the following gross equation:
Nickel(II) hydroxide thereby precipitates as a voluminous, gel-like, green precipitate, which is then dehydrated during standing to form an amorphous product. The hydroxide precipitated in this way is also in a colloidal form after drying and, with regard to its physical-chemical and morphological properties, does not correspond to the desired characteristics for use in batteries.
In very general terms, the precipitation of metallic hydroxides from metallic chlorides with caustic soda solution corresponds to the following gross equation:
A focused influencing of the physical-chemical and morphological properties of nickel hydroxide can result by the addition of ammoniac during product formation. The ammoniac serves as a complexing agent and prevents a spontaneous precipitation of the hydroxide. Ammoniac incr
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patent: 5135622 (1992-08-01), Abys et al.
patent: 5282935 (1994-02-01), Cawlfield
patent: 5384017 (1995-01-01), Lumbroso
patent: 5391265 (1995-02-01), Krynitz
Bauer Bernd
Menzel Thomas
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Mee Brendan
Niebling John
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