DE1903580A1 - Process for the surface treatment of uranium and uranium alloys - Google Patents

Description

PATENT ADVOCATE
DR. HANS ULRICH MAY 1903580

B MUNICH 2, OTTOSTRASSE 1a TELEPHONE COSVO 00 38 82

Bο2555-3 J? Munich, January 24, 1069

Br.lL / Bh

CP 258/685

Commissariat ä 1 »Energie Atomique in Paria / France Process atur surface treatment of uranium and Uranium alloys

The invention relates to a method for the surface treatment of workpieces made of non-alloyed uranium or alloys based on uranium, for example those with a content of V, Zr. Pu, Ho, Cr, etc., dleae surface treatment with regard to the Heratellung metallic coatings and, in particular electrodeposited Ubersüge is performed.

Eb iat known to produce electrolytic (galvanic) coatings on at least on their surface conductive pieces, which immersed in electrolyte baths of a precisely defined concentration and connected to the negative pole of a direct current source. The positive pole of the source is in turn with conductors immersed in the bath, the anodes.

So that the Abscheidimg takes place correctly and leads to a high-quality coating, ie adhesive, with dimensions within narrow limits and without interruptions, the surface must

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of the workpiece must be pretreated. This measure is generally used as a surface pretreatment of the "base metal" to be coated. Of course, the workpiece either massive or simply already with a leading örand · » be metal coated.

The surface pretreatment is intended to pickle the workpiece and remove any foreign layer «that is normally on the surface of the base metal! Fat, oxides, tinder new » In the case of the usual metals, such as iron, copper or their Ie « Alloys provide satisfactory results for various common pretreatments! In particular, a process can be used which begins with chemical degreasing using an organic solvent such as trichlorethylene, followed by an electrolyte degreasing at the cathode of an alkaline soda bath, a washing and stripping. In the case of ferrous metals, for example, Ban uses anodic pickling in an aqueous sulfuric acid solution and in the case of copper-containing metals, chemical pickling in a solution containing nitric acid and possibly other components of alkali salts, to carry out «After the pickling process, which exposes the surface of the metal to be treated, the workpiece washed and the metal coating applied. If it is ia

If an electrolytically applied layer is involved, the workpiece coming from the washing bath is immediately transferred to the brought a bath of the desired metal »

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The basic terfabrics that have been observed are not exactly the same Easily applicable when the material related to the cover is borrowed oxidizable or corrodible · metal is «da Schienten τοη" Products resulting from the removal of the iron remain on the surface after the brine, as do ions, which later unite the faster the attack, the higher the concentration de Belsbades 1st. This is especially the case with alloyed or unalloyed uranium "

To address the downsides of the earlier procedures are already in place suggesting different ways. One has in particular chemical treatments applied. Such a treatment "which gives satisfactory results overall," 1st in the French see patent specification 1,523,216. it consists of the following work item Degreasing using Trlohlorethylene;

Cathodic electrolytic degreasing in an alkali solution containing 40 g / l sodium hydroxide for 3 minutes. IwI a current density of 5 to 10 λ / An ² ι

To wash; ·,.,

Cast off with 10 B * nitric acid at room temperature} Washing again;

Pickling with IO S Ohlorwasserstoffefture at room temperature, after which the workpiece is taken out of the hydrochloric acid '

will allow the airborne attack to evolve;

Washing again; Renewed stripping with 10 H nitric acid at room temperature; Final washing.

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This stripping process enables the production of on <Ã ¼fer The surface of the pickled uranium has an electrolyte that adheres very well! «See deposits, but has some disadvantages the pickling obtained surface of the base metal has no metallic appearance but remains covered with a greyish film, which can be assumed to have the quality of the Adhesion of the coating to the uranium is impaired, even if this adhesion appears good. ”In addition, this layer can occasionally Yfäsaer or traces of the baths in which the workpiece is ™ acts, withhold and thereby subsequently attacks on the uranium underneath the coating, causing these attacks to result in loss of adhesion or destruction of the Overlay can lead to «The attack of the various attacks« · Benen baths on the pure or alloyed uranium is changeable, in particular the sensitivity to different depends Reagents from the alloy being treated, which makes it necessary to determine the concentrations and treatment times for each alloy adapt ^ and often violent, occasionally irregular Leads to attacks which dissolve the base metal to a variable depth, resulting in a Uncertainty about the remaining dimensions and the uranium weight of the treated pieces and thus a fluctuation of the results obtained. It is therefore a very precise one Control of the treated pieces required «,

In addition, the surface of the round metal after attack, especially in the case of alloys, is rough and irregular, which affects the quality of the electrolyte coatings deposited thereon and, above all, their tightness and thus their value as protection against corrosion " 909834/1260

BADOHfGtNAL

The invention aims to eliminate or at least essential "=" lent reduction of these disadvantages »

For this purpose, according to the invention, a method for f laolia treatment of pieces of uranium or uranium alloys proposed, in addition to the usual treatment stages of degreasing, rinsing and, if necessary, chemical stripping, an anodi « 3Ches pickling in an aqueous solution containing an organic salt or sulfate of lithium and / or magnesium is provided ο

This method brings a decisive improvement over the methods given above, since not only, as before, only the Anions become effective during anodic electrolytic stripping, but at the same time the cation of the salt used. the Results are fundamentally different from those obtained using the salts of other cations, such as the acetates of Sodium? Potassium, ammonium, zinc, cadmium, etc. This The difference is probably due to the special properties of the cations lithium and magnesium and to that the salts formed at the moment of stripping easily go into solution, in contrast to the salts formed with other cations which adhere to the surfaces of the treated pieces or remain suspended in the solution.

It has been found that of the various solutions of lithium " and magnesium salts, especially the acetates, lead to very good stripping results

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In the majority of cases, satisfactory results will be obtained with uranium and uranium alloys if the anodic stripping is carried out in a 2 to 3 N lithium acetate solution at pH 6 and 3 to 7 A / dm between 10 and 50 ° C, preferably 25 ° C a selected depending on the current density time of the order of 35 min ₀ at 3 a / dm ² and 15 minutes' at 7 a / dm is performed. ² This current density must practically be between 2 and 10 A / dm *

The following operations can be carried out before this stripping process:
Chemical degreasing using trichlorethylene or perchlorethylene; Electrolytic cathodic degreasing in a solution containing 40 g / l sodium hydroxide in the cold at 10 A / dm for 3 minutes,

To wash;

Chemical stripping in 7N nitric acid at 25 ° C for 1 min .; To wash"

The last two steps are only required if the workpiece is heavily oxidized so that the anodic stripping only has to remove a relatively thin layer « If the surface of the piece to be treated is only very weakly oxidized, you can do without it »

The anodic stripping can be followed by the following operations: a chemical stripping in 7 N nitric acid at 25 ° C for a few seconds to 1 minute *;
To wash,

Finally the piece taken from the last wash bath has to be

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BATH

Immediately electrified in the electrolyte bath for deposition v / ground c.

This procedure seems to be generally applicable and is suitable for processed, natural or enriched uranium « metal v / ie for most of its alloys «

It is found that at the end of the anodic pickling on the uranium mar a thin skin remains instead of remaining after the previously known Beliandlungsdchritten thick layer _o This skin is more easily eliminated or reduced in the course of the following operations and makes the structure of the base metal erschei "neiio As As can be seen from the above, currents can be used in anodic stripping, the strength and corresponding voltage of which are considerably smaller than the values previously considered necessary so that the final dimensions of the pieces can be anticipated before the treatment and the surface properties of the piece obtained during the previous metallurgical treatments (especially cold working) are preserved larger number l used by operations and eliminates much less Ün "soluble from, especially when using lithium salts," This last point is important .fall's dee the risk criticality is _a

One can see the nitric acid attacks that had to precede and follow the anoeic stripping in the previously known methods,

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weaken and omit in certain exceptional cases., _Λ:

The surface condition of the base metal and that of the electrodeposited layer obtained on this metal are significantly improved, the structure of the deposit obtained is much more regular and this deposit has the same thickness a much improved continuity and tightness, which makes its value as a corrosion protection layer much higher than that of previously obtained electrolytically deposited coats

The adhesion of the coating to the uranium is at least comparable to « bar of the coatings obtained by the other processes, although the roughness is considerably reduced, which is also leads to an improvement in the protective properties of the separation »

In the following the treatment dishing are described as examples, which cylindrical pieces made of alloyed uranium before W nickel plating and tin plating after the French in the above mentioned patent 1,523,216 t-described methods were subjected "

Example 1 (Hagneslum Acetate Bath)

It was made from a uranium alloy with a ^ ylhdrical piece $ 1.5 molybdenum length of 40 mm in diameter, 299 mm in length, one

2 ·

Treated surface of 400 cm and a hasse of 6905 g. That The piece had a threaded hole 10 mm in diameter and 15 mm deep at one of its ends and in the direction of the cylinder axis, into which a threaded rod was screwed to hold the piece and to supply electricity; on these catfish could the ge «=»

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entire surface of the uranium alloy can be submerged. she Edges of the piece were rounded to a radius of 2 mm »

The piece prepared in this way was 2 mim long with trichlorethylene degreased o Then it was used as a cathode in an electrolyte! " A degreasing bath consisting of a sodium hydroxide solution, given for 3 minutes under 40 A, i.e. 10 A / dm. The appearance of the surface remains unchanged and that of it The mass loss caused by the operation is insignificant, on the order of 10 mg.

After washing with water, the piece is in a 1 min '' fN saltpeter oil solution chemically stripped at 21 ° C. Not at all visible reaction was observed and the bar lost about 20 mg in the process.

After washing, pickling is done anodically while stirring in a reference »

2+
Borrowed tyg 2 N magnesium acetate solution for 13 hours, below 7 A / dm at 21 C, the initial pH of the solution was 6.00 and the final pH was 6.01.,

Observe the workpiece during this treatment stage Very little gas development and the formation of a black layer that dissolves in the yellowing solution. The Span « The voltage and amperage remain during the entire treatment period stable. At the end of the treatment, the piece is coated with a black • layer, which becomes underneath during the subsequent washing running water and see the surface of the metal! · » nen, which is then colored gray. The piece loses at

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this stripping was 10.43 g, and the beading of the metal layer peeled from the surface was 14 microns.

The piece is then chemically in a 7 ff nitric acid solution Stripped for 1 min. At room temperature «, in advance At this stage of treatment there were some remaining traces of the black layer dissolved, and the piece lost about 40 mg »

The piece was then carefully washed with cold running ™ water and placed in a nickel plating * as quickly as possible. Electrolyte bath energized »

Example 2 (lithium tartrate bath)

The same treatment steps were used to treat a piece of the same alloy with the same properties from the start the treatment up to the nitric acid stripping preceding the anodic stripping.

The anodic stripping was then carried out in a related manner

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^w lithium 2 N lithium tartrate solution at 7 A / dm for 15 minutes at 21 ° C. The solution was stirred. Its initial pH was 6.00, the final pH 6.01,

The same phenomena as in Example 1 were observed. The black layer was lifted off in the course of the subsequent wash, and more easily than in the case of stripping with Magnesium acetate, and the pickled metal underneath then showed a gray color. The piece lost with dies® !? Se «= · action level 10.18 g.

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After washing, the piece was immersed in a 7N nitric acid solution for 1 min., Washed thoroughly and as indicated in Example 1, broken into the electrodeposition bath.

Example 3 (lithium acetate bath)

A treatment process corresponding to the preceding was carried out on a cylindrical piece 35 mm in diameter and 4 mm in length with a mass of 72.13 g made of uranium with 0.2 weight vanadium. The piece degreased with trichlorethylene for 2 minutes was at the cathode in a ^ N Natriumhydroxidbad at 2.4 a (d _o h. 10 a / dm ²⁾ was added for 3 minutes. "

The appearance of the surface remains unchanged, and the treatment leads to only an insignificant loss of mass, (less than 1 mg),

The piece is then chemically stripped for 1 minute in a 7N nitric acid solution at 21.5 ° C. One does not observe any lei reaction, and the piece loses 4.8 mg in the process.

After washing, the anodic stripping is carried out at 3 A / dm in a Li ⁺ 3 N lithium acetate solution with stirring for 35 minutes, at a temperature of 2 initial pH is 6.00 and the final pH is 6.03.

for 35 minutes at a temperature of 21.5 ° C. The An «

Observed during the first few minutes of this treatment level there is a slight evolution of gas. No visible layer is formed on the surface. The lithium acetate solution becomes light yellowish. The piece loses 615 mg in the course of this treatment; the depth of attack was 14 microns, and the macrostructure of the

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Alloy was exposed

The piece was washed for 1 minute in a 7N nitric acid solution immersed (which led to the dissolution of 21.6 ng), carefully washed again and finally in the electrolyte is before Brought coating bath, as indicated in Example 1 *.

Example 4 (Ltthiumeulfatbad)

A piece of uranium containing $ 1.5 molybdenum, 35 mm in diameter a length of 4 mm with a mass of 70.16 g was a corresponding Subject to severe treatment. The electrical current was supplied through a rod screwed into the piece.

The piece was degreased in toluene for 2 min and cathodic degreasing in a sodium hydroxide solution for 3 min

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at a current density of 10 A / dm, washed, chemically for 1 min. in a 7N nitric acid solution at 23 ° C stripped with no apparent reaction observed and the piece lost 1.8 mg,

"After washing, the anodic stripping was carried out. The piece, which was subjected to vertical vibrations, was immersed in a lithium 4N lithium sulfate solution which had been _{brought to pH 0 by adding B 2} SO. The stripping was carried out below 6 A / dm ² at 23 ° C for 20 minutes «

At the beginning of this treatment, a considerable amount of gas was observed. The piece covered itself with a slight black layer that was almost completely removed during the subsequent washing. The solution turned yellow and its final pH was 0.2o In the course of this stripping process, the piece lost 718 mg, '909834/1260

i.e. a 16 micron deep layer «After washing this became Piece immersed in a 7 N nitric acid solution for 1 minute « This treatment step resulted in a weight loss of 3.8 mg. The piece coming out of the nitric acid solution was light » gray and revealed its macrostructure.

The carefully washed piece was instantly rolled into one Electrolytic nickel-plating bath energized.

Instead of the acetates (Examples 1 and 3), which however have the advantage of being readily available, or the tartrates (Example 2), numerous other salts of lithium can also be used or magnesium, especially those whose anions form soluble salts or complexes with uranium. Good results are obtained when using organic acid salts, such as Citrates, oxalates, lactates, formates, malonates, pyrogallates and Succlnate. The values of the various treatment parameters are hardly changed with respect to those given above for lithium acetate. Magnesium sulfate or lithium sulfate can also be used (Example 4). In contrast, the use delivers lithium nitrate or magnesium nitrate results in completely different results of the same kind as those obtained by attack by nitric acids (which can form part of the chemical felling preceding the anodic pickling): one obtains a irregular attack »

Of course, the invention can be implemented in various ways can be modified, with one or more anodic stripping treatments provided in lithium or magnesium salt solutions

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could be. One can see the composition of the baths and those Modify the concentration of the ingredients or add different products, such as surface-active agents » Anodic degreasing and / or stripping (or alternating anodic and cathodic stripping) can be provided Length of treatment times, current densities, temperatures and pH values change to the composition of the pieces and their volume? «u take into account ,,

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Claims (1)

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Claims 1,) Method of surface treatment of pieces of uranium or uranium alloys, the preliminary stages chemical degreasing, electrolytic degreasing and, if necessary, chemical stripping comprises, characterized by an anodic stripping at a current strength between 2 and 10 A / dm in a containing an organic salt or sulfate of lithium and / or magnesium aqueous solution. 2o) Method according to claim 1, characterized in that dae anodic stripping is carried out in a solution that contains an acetate, citrate, tartrate, oxalate, Contains malate, lactate, formate, majonate, pyrogallate or succinate, 3o) Method according to claim 2, characterized in that lithium or magnesium acetate in a concentration of 2 to 3 W in the solution is used as the salt * 4o) Method according to claim 2 or 3 »characterized in that anodic pickling at a temperature between 10 and 50 ^ 0 while 10 to 35 mim is performed « 5o) Method according to claim 3, characterized in that the current intensity between 3 and 7 A / dm, the temperature in the order of magnitude of 25 ° C and the duration of the anodic stripping between 15 and 35 minutes can be »selected« 90983 4/1260