JPS60235609A - Preparation of ion permselective membrane - Google Patents

Abstract

PURPOSE:To prepare a membrane capable of permeating cation selectively by a simple method by stripping off an anodized film from an anodized aluminium and heat-treating the film. CONSTITUTION:A cation permselective membrane is prepd. by a process consisting of a stage for anodizing aluminium in an electrolytic bath contg. aq. phosphoric acid added with an org. acid such as citric acid, a stage for stripping off the anodized film by dipping the anodized aluminium in a stripping bath contg. bromomethanol, a stage for heat treating the stripped anodized film by heating it at >=850 deg.C after it is dried, and a stage for diffusing alkali metal by dipping the heat-treated film in aq. caustic alkali and heat-treating again at >=900 deg.C, successively.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application) The present invention relates to a method for producing an ion-selective membrane that selectively transmits only cations.

(Prior art) In recent years, the development of solid electrolytes, which are substances that can selectively transmit only specific ions, has been progressing, and β-alumina is known as a solid electrolyte that selectively transmits sodium ions. ing. However,
In attempting to put β-alumina into practical use, forming it into a thin film is a major challenge, but no suitable method for manufacturing such an ion-selective membrane has yet been proposed.

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to produce an ion-selective membrane that can selectively permeate cations by a simple method of heat-treating the anodic oxide film of aluminum. It's about trying.

(Structure of the Invention) The method of the present invention includes an anodic oxidation process in which aluminum is anodized using an electrolytic bath prepared by adding a citric acid organic acid to a phosphoric acid water bath, and The oxide film is peeled off by immersing it in a stripping bath consisting of a bromine methanol solution;
By sequentially carrying out a heat treatment step in which heat treatment is carried out at a temperature of 0.degree. It is characterized by manufacturing an ion-selective membrane that selectively permeates.

(Function) In the method of the present invention, a thick oxide film with a thickness of 100 μm or more is formed on the aluminum surface by using a phosphoric acid bath in the anodizing process, and after this oxide film is peeled off from the aluminum base metal in the peeling process. An ion-selective membrane that selectively permeates l ions can be obtained by imparting alkali resistance in the heat treatment step and by an alkali metal diffusion step in which the alkali metal is diffused into the oxide film.

($ Example) (1) RAMM T3 20 (g/l)') acid water mfei 0.3 (g/l)
l) Pure aluminum plate (vertical 3011A1 width 70cm, thickness 0.3cm) using an electrolytic bath made by adding acid
A so-called anodic oxidation treatment is performed in which direct current electrolysis is performed for 60 minutes using as an anode. The liquid temperature at this time was controlled so that it was 10℃ at the start of electrolysis and 0℃ at the end of electrolysis, and the applied voltage was 20V at the start of electrolysis, and # and OV between IIo and 60 minutes after the start. Control it as you see fit. Then, an oxide film having a thickness of about 720 μl is formed on the aluminum surface. In this step, the thickness of the oxide film produced is increased by using a phosphoric acid bath, and the pore size of the oxide film is expanded by the presence of citric acid, contributing to the increase in film thickness. Note that, of course, other suitable organic acids may be used in place of citric acid.

(1) Stripping process The aluminum on which the oxide film was formed in the anodizing process was immersed in a stripping bath consisting of a 30 W/v 96 prom methanol solution for about 3 days to dissolve the aluminum base metal and remove the oxide film (At203 ) is obtained.

(1) Heat treatment step The oxide film peeled off in the above peeling step is once dried and heated at a temperature of rso° C. or higher for 7 hours to impart alkali resistance.

(W) Alkali metal diffusion step The oxide film after the heat treatment step is immersed in a 20 W/V% caustic soda aqueous solution for several minutes, and then heat treated at qoo°C or higher for 7 hours to diffuse sodium into the oxide film.

The ion-selective membrane obtained through the above steps has the property of selectively allowing only cations to pass therethrough.

By using the ion-selective membrane obtained in this example, an electrolyte as shown in the diagram can be constructed. That is, two M2, 3 and 0. Contain IN caustic soda water bath solution and 0.7N hydrochloric acid aqueous solution, 1lllll
Graphite electrode 1. on heather 2.3. Place j. Then, sodium ions (%cx”
) permeates to the hydrochloric acid aqueous solution side and generates sodium chloride, and as a result, the hydrochloric acid aqueous solution side becomes a positive potential, while the caustic soda aqueous solution side becomes a negative potential, and an electromotive force is generated between the Ii+1 and 5 electrodes. According to experiments, the electromotive force of this ll pond is 0.3
/2V. However, intentional 110 (at), water temperature 3
0′″C.

(Effects of the Invention) Like soft soil, according to the present invention, cations can be removed by a simple manufacturing method of peeling off the anodic oxide film obtained in a Liele acid bath, followed by heat treatment, and then an alkali metal diffusion treatment. This has the excellent effect of being able to manufacture an ion-selective membrane that selectively permeates only ions.

Moreover, the obtained ion-selective membrane has a sufficient membrane thickness to maintain mechanical strength, and is sufficiently durable for practical use.

[Brief explanation of drawings]

The drawing is a schematic diagram of a gIi pond, which is an application example of the ion-selective membrane produced by the method of the present invention. l...Ion selective membrane

Claims (1)

[Claims] /, Aluminum was anodized using an electrolytic bath made by adding an organic acid such as citric acid to a phosphoric acid water bath, and the oxide film was removed by immersing it in a stripping bath made of bromine methanol solution. After that, the oxide film is dried and then heat-treated at a temperature of 50° C. or higher, then immersed in a caustic alkali aqueous solution, and further heat-treated at a temperature of 900° C. or higher. Method.