Untitled record

The invention relates to corrosion-resistant diaphragms and filters aux Oxydker.amik-coated metal network fittings, in particular for the operation of electrolysis and material separation and filtration operations at temperatures above 373 ° K in acidic, neutral or alkaline solutions, and methods for the production of these diaphragms and filters.

It has already been proposed to manufacture diaphragms and filters for the stated application from a coated metal mesh fitting. Ceramic-coated networks have also been mentioned occasionally in this context, but have so far only been used to a limited extent. This is due to the fact that the well-known ceramic-coated diaphragm and filter materials in the work area mentioned above 373 ° K only insufficiently meet the requirements for corrosion resistance, resistance to solution, adhesive strength, hardness and porosity.

The invention has for its object to produce corrosion-resistant or solution-stable diaphragm and filter materials with an oxide-ceramic coating on a metal mesh fitting for acidic, neutral and alkaline solutions, both in their adhesive strength and in their mechanical properties, such as hardness and porosity, a significantly improved behavior show at temperatures above 373 ° K.

The object is achieved according to the invention in that the oxide-ceramic coating is at least partially and preferably entirely composed of interoxidic compounds of, on the one hand, oxides of bivalent and trivalent transition metals, and oxides of the heavy metals of alkaline earths and, on the other hand, amphoteric oxides of the metals of the fourth, fifth or sixth subgroup of the periodic system. Suitable transition metals are, for example, manganese, iron, cobalt or nickel. Typical alkaline earth metals are calcium, strontium and barium. The metals of the fourth, fifth or sixth subgroup can be selected, for example, from the following group: titanium IV, zirconium IV, hafnium IV, vanadium V, niobium V, tantalum V, molybdenum VI or tungsten VI.

I

In the coating method according to the invention, the oxidic starting materials, each consisting of at least one representative of each of the three groups mentioned, can consist of oxides or compounds such as cafbonates, which release oxides when heated. The oxidic starting materials can also contain or consist of separately prepared interoxidic compounds, for example titanates or zirconates.

The oxidic starting materials are mixed in finely divided form, the metal oxides of the first two groups and the amphoteric oxides being metered in advantageously in a molar ratio of 1: 1.

A suspension of this mixture in distilled water is applied, for example, by spraying, brushing on or dipping onto a net which is advantageously made from pure iron or pure nickel or alloys of these metals with a low carbon content, and at temperatures just below the melting point of the metals mentioned ( in the case of iron typically at 1800 ° K) solidified by sintering in an oxidizing atmosphere. The sintering time differs depending on the selected oxidic starting materials and is typically between five minutes and three hours. For the production of coated. Diaphragms and filters to be used in acidic solutions are made of stainless steel mesh fittings.

The optimal weight ratio of coating / coated dried diaphragm can be empirically determined from case to case. Good results have generally been achieved with a ratio of 25-40¾.

EXAMPLE

A mixture of 50% by weight barium titanate and 50% by weight nickel titanate, which in turn was obtained by sintering stoichiometric amounts of BaCO ^ and TiÛ2 or NiO and T1O2, is placed on a nickel mesh (0.3 mm diameter, 0.52 mm mesh size) aqueous suspension so that around 35% by weight of the coated and dried nickel mesh is given by the oxide-ceramic substances. The coated mesh is in an oxidizing bang for 30 minutes

-3 gas flame sintered at about 1700 ° K. The product can be bent with a radius of curvature of 3 cm without the oxide-ceramic coating breaking. The mechanical permeability is measured on aqueous solutions and is around 0.3 (cm poise / bar.cm). The area-specific electrical resistance measured in 30% KOH at 300 ° K is around 0.05 cnZ. The mean pore radius measured by electron microscopy is around 5 / im. The mass loss of the oxide ceramic in 70% by weight KOH at 493 ° K after 200h is less than 4h.

These properties make the oxide ceramic-coated metal nets suitable according to the invention

J for use as diaphragms in high-temperature electrolysis j (especially for alkaline high-temperature water electrolysis). They can also be used advantageously as filters: for high-temperature filtrations, for example for cleaning the circuit electrolyte in high-temperature water electrolysis.