DE1214971B - Process for the production of microporous membranes, especially for isotope separation - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C23f

German class: 48 dl-1/02

Number: . 1214 971

File number: C19522 VI b / 48 dl

Filing date: July 31, 1959

Opening day: April 21, 1966

With the means of powder metallurgy and ceramics it is not possible to produce thinner membranes, d. H. Membranes with a thickness of 0.1 mm and less, and to provide them with pores, whose mean radius is in the order of 0.01 μ. However, for isotope separation Membranes of such dimensions are required.

Attempts have already been made to produce an extremely fine-pored silver membrane by using Melting of a silver-zinc mixture went out, which was rolled out into foils of 0.2 mm thickness and from which the zinc was extracted using a hydrochloric acid solution to which cesium chloride was added. It did not succeed in ruling out an attack on the silver. Foils with a higher zinc content of for example 50% disintegrated when washed out, alloys below 30% zinc produced too coarse crystallized structure. Stable membranes were only obtained with a zinc content of about 33%, but their usefulness was limited.

The aim of the invention is to precisely define the working conditions under which from thin Sheets that consist of an alloy of several metals suitable for pore formation, the Base metal can be treated by means of an aqueous solution without affecting the structure of the noble metal is attacked. The definition of the working conditions then results in a general one Principle of selecting suitable millable alloys in which the less noble component removable and a porous membrane useful for isotope separation purposes as a result is available. The attack on the constituent to be extracted can not only be chemical, but can also be carried out electrolytically.

For explanation, it should be pointed out that the metals are arranged according to an electrolytic series of voltages. The noblest metals like gold, platinum, Silver, etc., have a high positive normal resolution potential, while the more variable ones Metals have strongly negative normal resolution potentials. Likewise, the oxidizing and reducing Solutions are classified according to their redox potential. The very strong oxidizing solutions, d. H. the solutions that hold electrons tightly have high positive redox potentials, while, the reducing solutions, d. H. the easily electron donating solutions, low redox potentials have (see in particular "Theory et method d'essai de la corrosion des metaux," by Latimer, at Prentice-Hall, New York).

According to the invention, the production of processes for the production of
microporous membranes, especially for
the isotope separation

Applicant:

Commissariat a l'Energie Atomique, Paris

Representative:

Dr. phil. W. P. Radt

and Dipl.-Ing. E. E. Finkener, patent attorneys,

Bochum, Heinrich-König-Str. 12th

Named as inventor:

Roger Lacroix, Suresnes, Seine (France)

Claimed priority:

France of August 30, 1958 (773 487)

microporous membranes, especially membranes for the separation of isotopes, from thin ones Sheets that consist of ■ an alloy of two metals, the less noble metal at least 40 atomic percent of the alloy by treatment with an aqueous solution of an acid or base, which attacks only the less noble of the two alloy metals, in such a way that the Immersion of the material to be treated in the solution resulting in redox potential to the dissolution potential The base metal of the alloy is adjusted by either adding an appropriate solution chemical substance added or the material to be treated in the solution with the application of a corresponding Potential is switched anodically.

In addition, it may be said that instead of a nobler metal and a less noble one Metal a group of nobler or less noble metals can occur, whereby the redox potential occurs the dissolution potential of the alloy of the group forming the less noble metals (second group) is set and care must be taken that the alloy of the metals of the noble group (first Group) shows no signs of dissolution.

609 559/397

3 4

The new method gives two alternatives while the other is negative. It means that

Ways to: those corresponding to the metal (zinc) to be dissolved

1. Pure chemically by the alloy is positive with a Arilösimgsstromstärke, while the electrolytic solution is brought into contact to be retained metal (Si BER) corresponding negawird which an oxidation and reduction ⁵ * f ü * · _e ^Ol J ^{smd the ideals} Conditions for the agent with a redox potential is added, practicing the process. ..

which is greater than the dissolution potential of the ^D .. ^{ie h} ? ^d ™ f ™ ^ven 9 ^{and C} * ^{must first}

Metals of the second group in alloyed enough be sufficiently different.

In addition, there must be such a work potential, i. H. the ",,, '. ,. ,. ,,,,. , ίο potential of the alloy used as anode in relation to

2. electrolytically by setting _{an anode potential in the electrolytic to the potential of a reference} s _an ode, so chosen solution, _{that it bd c between the points fl and b} which is above the resolution potentials of the Me- _{(pi 1}} ^ _{(preferably poss} very close to b parts of the second group in an alloyed state _to increase the rate of dissolution)

Λ ?? ^d "I" ¹⁶ "J ^{6 resolution} S ^s P ^otentiale ₁₅ or on the right side beyond point b of the metals of the first group. _{(z RM} ^ _F j _g ^ _{Jn this latter FaU came}

With the new process, the number of the metal to be retained is finally self-determined. in this case more noble - metals from which are drawn, so that the reactions become one porous membranes are to be produced, must be interrupted indefinitely at a certain point in time, expanded, and the conditions are established, 20 for the establishment of such an operating point among which others - in this case less noble ones - (at c or c ') one has in particular the Metals, for the production of such membranes, use both of the above-mentioned means, namely they can be stolen are by using the less noble metals either with either the addition or the choice of a solution be completely or only partially removed. a suitable redox potential or the application A previously closed path is thus opened, 25 of a certain potential to the anode to electromicroporous Membranes from the most varied of lytic routes.

To produce metals necessary for the separation of isotopes. In the first case, e.g. B. as follows

are suitable. proceeded:

The invention should first be based on the drawing a) The electrolytic solution is added

are explained in more detail. 30 once or gradually an oxidation and reduction

The invention is shown below with reference to some medium with a redox potential, which

concrete examples as well as with reference to the about the dissolution potentials of the metals

Drawing explained by way of example. second group is alloyed, but

F i g. 1 and 2 are two graphs of polar- less than the dissolution potentials of the metals of the

sation curves for silver-zinc alloys in two 35 first group, and waits for the end of the reac-

various reagents; tion.

F i g. 3 shows schematically a device for the reaction can also be interrupted after exercise of the process by electrolytic means. which only a certain amount of the metals of the second

The curves of FIG. 1 and 2 show quite all- group was solved.

in common the essentials of the inventive method 40 b) The electrolytic solution is set to a retraction, d. H. the curves from which one can at once or gradually determine oxidation and reduction of the parameters of the selective medium with a redox potential, which is about solution runs out. the dissolution potential of the material to be retained

The left curve C ₁ is the polarization curve of the talle of the first group (which is a relocation

Alloy, while the right curve C ₂ the polar 45 of the operating point to point c ' of FIG. 1

sation curve of the metal to be retained. This corresponds to). This potential is then obviously greater

curves previously established by experiments give as the dissolution potentials of the metals of the second

the current density i for the resolution as a function of the group. The reaction is interrupted when the

from the potentials E to which the metal ions desired amount of the metals of the second group

get abandoned. 5 ° has gone into solution.

Which depend on a component of the alloy If in this case the reaction is normal

The current strength of the dissolution current changes in which it would continue to run, if the reagent,

same way as the rate of dissolution whose redox potential is large enough to even the

of this component. A positive amperage will attack the noblest elements of the alloy, which

speaks of an actual attack (dissolution) of the 55 dissolution of the same begin when the metals

Component, while a negative current strength of the second group is almost completely attacked,

its precipitation on the alloy (if that is the reason for which to keep

Bath at this moment contains the constituent) of the metals of the first group, which are the micro-

is equivalent to. porous membrane should form the reaction in the

This shows e.g. B. Fi g. 1, in which the curve C ₁ 60 is interrupted at the desired moment,

and C ₂ the axis of abscissas at points α and b During the attack, the most precious metals can

cut which for a certain so-called the alloy temporarily back in solution

Normal solution escape the normal resolution potential and are reflected anew wherever

would speak. For a z. B. between the the element with low resolution potential free

Points α and b , point c, which is a 65 (pseudo-selective attack),

certain characteristic removal potential In the second case (electrolysis) one brings in

corresponds to the method according to the invention, the electrolytic solution sees the alloy on a

one that the ordinate of curve C _{1 is} positive, constant anode potential, which is greater than that

5 6

Dissolution potential of the metals of the second group after the complete removal of the silver

in the alloyed state and smaller than the dissolution rate, microporous membranes are obtained from pure

potentials of the metals of the first group. Gold, which are washed with water to

Practically the above results are obtained to remove any trace of silver salts, whereupon they

same results if one were to dry the same alloy 5.

the chemical attack of an oxidation and The parameters of these microporous membranes

The following are exposed to reducing agents with a redox potential:

which is equal to the anode potential. Mean pore diameter 0.01 to 0.06 μ.

After dissolving the desired amount of permeability to air under low pressure

soluble metals, the electrolysis is interrupted. io 1000 to 2500 · ΙΟ " ⁷ mol / cm ^a / minute / cm Hg.

In order to determine the course of the chemical attack of the ...

Components of the alloy by the oxidation example 11

and to monitor reducing agents if this is the manufacture of microporous membranes from silver

must be interrupted, periodically Wä- Man makes a silver-zinc alloy with 65%

of the alloy or determinations of the bath silver, which result in foils 0.1 mm thick.

composition made. is rolled, which at 50 ⁰ C with a hydrochloric acid

To monitor the course of the electrolytic solution treated, which is a Stannio-Stanni-

Attack of the components of the alloy is carried out with a normal oxidizing reducing agent

the redox potential of + 0.15 V given above for the chemical attack is added. the

Procedure the measurement of the electricity used - the choice of this reagent was carried out by means of the polar

quantities made. sation curves of the alloy and the silver, which

One can use microporous membranes made of gold those of the above already examined F i g. 1 are,

by dissolving the silver of a gold-silver after removal of an amount of zinc, which 30 to

Alloy or copper corresponds to a gold-copper 35% of the initial weight of the foils,

Make alloy. Microporous membranes can be obtained with the following

Burning out of silver through selective dissolution of the parameters:

Zinc of cadmium and aluminum with a mean pore diameter of 0.04 to Ο, ΙΟμ.

Silver-zinc, silver-cadmium or silver-aluminum permeability for air under low pressure

nium alloys and microporous membranes from _{1000 to 2500} . ₁₀ _ _{7 Md} j _cm , j _minute j _{cm Hg} copper by selective dissolution of the in a 3 °

Manufacture zinc containing brass. Example III

According to the invention, microporous mem- ""., .. ··. "- 1 ο ·"
branen, the pore diameter of which is smaller than 1μ Manufacture of microporous membranes made of silver and can be brought below 0.05μ. The through-man made a silver-zinc alloy with 65% permeability for gases is very large. You can get 35 silver for air. This alloy is to form films of membranes with a thickness of 0.1 mm is rolled at 0.1 mm thickness which is up to 2500 · 10 ^-7 moles air are each treated with a solution Salzsäuregeringem pressure 2000 which the Urano-Urani square centimeters per minute per centimeter of Hg oxidizing reducing agent with a normal pressure difference between the two sides of the redox potential of + 0.26 V was added.
Reach membrane. 40 The zinc is selectively dissolved.

These microporous membranes can have used the microporous membranes obtained

The following parameters can be used to create mixtures through diffusion:

to treat those gases in order to have them at certain of the mean pore diameter 0.04 to 0.12μ.

to enrich them whereby this process with its permeability for air 1000 to 2500 · 10 ~ '

Repetition of divorces taken very far 45 _mol / _cm 2 / minute / cm He
can lead.

You can also use Example IV for isotopic enrichments

and divorces are used. They allow ins- _TT ,, ...,. _r , _. _1f

special the enrichment of the natural uranium production of microporous membranes made of silver

at its isotope with the mass number 235 and the 5 ° One represents a silver-zinc alloy with 67%

Deposition of this isotope by diffusion of the silver, which in a caustic soda solution a

gaseous uranium hexafluoride. anodic attack below a between - 0.07

Below are four concrete examples of constant potential at and + 0.13V

^{the Mem- 50 0} C produced by the method according to the invention is exposed,

branes described. 55 The polarization curves of silver and this

In the various examples the specified alloys in caustic soda show that the dissolution

Percentages are percentages by weight and correspond to all of the zinc being selectively made. These curves are in

a variable metal content which is shown in FIG. 2 shown,

is over 40 atomic percent. The attack takes place z. B. in the schematic in

. 60 F i g. 3 arrangement shown.

Example I _{This figure shows the} electrolysis trough 1,

Manufacture of microporous membranes from gold the anode 2 formed by the silver-zinc alloy,

It is a gold alloy with 40 percent by weight the cathodes 3, the reference electrode 4, which through

Gold and 60 percent silver by weight. a very slim siphon 5 with the electrolysis

This is then rolled in such a way that foils from 65 trough 1 are connected and the measurement of the anode

40 μ thickness result. These foils are allowed at 100 ⁰ C potentials, the measuring potentiometer 6, the

treated with an acidic and oxidizing agent, direct current source 7 with the as a voltage divider

which is formed by nitric acid with 36 ⁰ Be. switched rheostat 8 and the counter 9,

IO

which constantly the amount of electricity consumed and thus the amount of zinc withdrawn from the alloy indicates.

The microporous membranes obtained in this way starting from foils with a thickness of 0.1 mm have the following parameters:

Mean pore diameter 0.01 to 0.02 μ.
Permeability to air under very low pressure 100 to 200 · ΙΟ " ⁷ mol / cm ² / minute / cm Hg.

When using silver-zinc alloys with more than 33% zinc, the permeability can still be considerable can be enlarged without the mean pore diameter is noticeably changed.

Claims (5)

Patent claims: 1. Process for the production of microporous membranes, in particular membranes for the separation of isotopes, made of thin sheets made of an alloy of two metals, ao wherein the less noble metal constitutes at least 40 atomic percent of the alloy, by treatment with an aqueous solution of an acid or base, which is only the less noble of the two alloy metals attacks, characterized in that it occurs when the item to be treated is immersed redox potential resulting in the solution to the dissolution potential of the less noble Metal of the alloy is adjusted by adding either an appropriate solution chemical substance added or the material to be treated in the solution with the creation of a corresponding Potential is switched anodically. 2. The method according to claim 1 for the production of a microporous silver membrane, characterized in that one starts from a silver-zinc alloy with about 65% silver, which is rolled into flakes of 0.1 mm thickness, and this at a temperature of 50 ⁰ C treated in a hydrochloric acid solution to which a Stanno-Stanni compound with a redox potential of 0.15V is added. 3. The method according to claim 1 for the production of a microporous silver membrane, characterized in that one starts from a silver-zinc alloy with 65% silver, which is rolled into flakes of 0.1 mm thickness and ^{treated at 50 0} C with a hydrochloric acid solution, to which a Stanno-Stanni compound with a redox potential of 0.26 V is added. 4. The method according to claim 1 for the production of a microporous silver membrane, characterized in that a present in flake form silver-zinc alloy with a silver content of 65 ° / qi ^{Q of} a caustic soda solution at 50 ⁰ C anodically at a constant potential between - 0.07 and + 0.13V switches. 5. The method according to claim 1 for the production of a microporous gold membrane, characterized in that an alloy with 40% gold, which is rolled on flakes of 40 μ thickness, is subjected to a treatment in nitric acid of 36 ° Be ^{at 100 0 C.} Considered publications:
German Patent No. 86 459;
U.S. Patent No. 2,837,424;
Reports magazine, October 1956, Vol. 3, pp. 135 and 136. 1 sheet of drawings 609 559/397 4.66 © Bundesdruckerei Berlin