DE1254932B - Bath for the galvanic deposition of tin-bismuth alloys - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4057 * W PATENT OFFICE

EDITORIAL

1η / if

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C 23 b

German class: 48 a-5/38

M65165VIb / 48a

May 7, 1965

November 23, 1967

C2SQ 3-60

The invention relates to a bath for the galvanic deposition of tin-bismuth alloys.

It is known that metallic tin is electroplated onto the surface of various base metals can be, e.g. B. on steel, brass, bronze, copper etc. Typical tin-plated products due to their superior properties due to the excellent resistance of Tin against oxidation and / or the ability of tin as a lubricant, e.g. B. on threads used will.

Items such as pipe couplings that are tinned have proven their worth under normal operating and / or storage conditions. If temperatures above 18 ^° C. are maintained, the electrodeposited tin retains its excellent properties, including its lubricity, for an unlimited period of time.

It has been found that tin-plated objects at ambient temperatures below 18 ^° C., especially if these conditions persist for a long time, lead to the so-called tin plague becoming noticeable on the tin.

Tin plague can form on tin recognize by the development of a dull gloss on a previously shiny surface. Particularly after long exposure to temperatures below 18 ° C, this occurs in and on the tin deposit Formed tin pest appears as a fine, non-sticking powder. That loose tin powder separates from the surface of the base metal during its formation and therefore loses the Ability to protect this. As the tin plague progresses, the loose, fine powder can form flakes, which in turn can fall off the base metal, exposing it to corrosion, whereby at the same time the tin layer is removed, which has a lubricating effect on a coupling connection should. When this phenomenon occurs, the affected part looks less noticeable, can be connected less easily with another coupling part because of the sliding and lubricating ability has decreased and is not as resistant to corrosion before and after use.

The invention is based on the object of a bath for the galvanic deposition of tin-containing layers to create that have a high resistance to tin plague.

Thus, according to the invention, there is provided a bath for the electrodeposition of tin-bismuth alloy coatings proposed, which is characterized in that the bath is an alkali metal stannate,

Electroplating bath
of tin-bismuth alloys

Applicant:

M&T Chemicals Inc.,

New York, N.Y. (V. St. A.)

Representative:

Dr.-Ing. H. Fincke, Dipl.-Ing. H. Bohr
and Dipl.-Ing. S. Staeger, patent attorneys,
Munich 5, Müllerstr. 31

Named as inventor:
Jan Cornell's Jongkind,
Roseville, me. (V. St. A.)

Claimed priority:

V. St. v. America May 8, 1964 (366 193)

free alkali metal hydroxide and hydroxyalkyl bismuthate contains.

Any metal can be used as the base metal. Typical base metals with The baths of the invention that can be galvanized are steel, iron, brass, bronze, copper, etc. The The invention is particularly useful for the electrodeposition of a tin-containing layer on the Threads of pipes or couplings od. The like. Or on the surfaces of copper wires. As a preferred one The base metal for treatment in the baths of the invention can be soft iron. The aqueous baths according to the invention can be used as alkali metal stannate, sodium stannate or, preferably Potassium stannate in amounts of 10 to 300 g / l, preferably 50 to 100 g / l and in particular 90 g / l Contains tin as an alkali metal stannate. The bath preferably contains 285 g / l potassium stannate.

The aqueous baths also contain free alkali metal hydroxide, e.g. B. Potassium Hydroxide or Sodium Hydroxide, especially potassium hydroxide. The baths can contain 5 to 35 g / l, preferably 15 to 25 g / l and in particular 20 g / l alkali metal hydroxide are added.

709 689/384

It is emphasized that when preparing the aqueous bath with potassium stannate or a content on potassium stannate the alkali metal hydroxide used is preferably potassium hydroxide. When preparing of the bath using sodium stannate is preferred as the alkali metal hydroxide Sodium hydroxide used.

Another essential feature of the baths according to the invention is their content of a hydroxyalkyl bismuthate and preferably on a polyhydroxyalkyl bismuthate. Those useful for the invention Bismuth esters can be prepared by reacting a polyhydric alcohol with an alkali metal bismuth, are preferably made with sodium bismuth.

The following typical polyhydric alcohols can be used: ethylene glycol, propylene glycol, Glycerine, erythritol, arabitol, sorbitol, dulcitol, mannitol, α-cyclohexanetriol, cyclohexanediol, cyclohexanpentol (Quercitol), Cyclohexanhexol (Inositol).

The reaction between the alcohol and the bismuth can, for. B. be carried out as follows: There are equimolacular parts of sodium bismuth and z. B. erythritol, mannitol or inositol are mixed together in a suitable container, adding sufficient water if necessary to make a solution, then adding sodium bismuthate slowly and with constant stirring. When using ethylene glycol, propylene glycol or glycerine, the use of water as a solvent is unnecessary. The resulting reaction temperature must be carefully monitored (using ice or a cold water bath) and kept at 55 to 80 ^° C., since decomposition begins ^{above 80 ° C.} The reaction begins at about 55 ^° C. and can be carried out up to 80 ^° C. Above 80 ° C, in addition to decomposition, charring also occurs.

When the reaction is complete, the mixture is allowed to cool to room temperature and it results a slightly amber colored translucent liquid. This mixture is alkaline, and one aqueous solution of the same (1:10) has a pH value from about 12 on. In order to avoid decomposition, one can immediately use the free sodium hydroxide neutralize. An organic acid is preferably used for this.

The acids used are preferably soluble organic acids, such as acetic acid, tartaric acid, citric acid, Malic acid and lactic acid. The strong mineral acids, such as hydrochloric acid, nitric acid and sulfuric acid, are not favorable, as a slight excess of them reduces the bismuth compound produced can destroy.

If the neutralization is carried out by adding an organic acid to a pH of about 7 is carried out, the product is poured into about five times the volume of ethyl alcohol. This will the bismuth compound is precipitated and a solution of the corresponding sodium salt remains, i.e. H. of Acetats, tartrates, etc. are left over from the acid used to neutralize. The precipitate can be flaky and dense, and it may therefore be necessary, after filtering, about three times as much To dissolve water, based on its own weight, and again, as mentioned above, in ethyl alcohol felling. It is preferable that the second precipitate thus formed redissolve in water and one

ίο to carry out the third precipitation with ethyl alcohol.

The thus purified compound may getroknet in an oven at 100 ⁰ C and are ground to a fine powder. In powder form, the compounds are typically pale yellow or brown and heavy and, after tumble drying, may consist of thin, transparent amber-yellow to brown flakes. These are relatively stable in air and have a characteristic odor.

Examples of compounds obtained by reacting a polyhydric alcohol and bismuth have the following composition given in percent by weight:

Dihydroxypropyl bismuthate, C ₃ H ₅ (OH) ₂ BiO ₃

Bismuth 62.8%

Carbon 10.8%

Oxygen 24.1%

Hydrogen 2.1 ° / ₀

Trihydroxybutyl bismuthate, C ₄ H ₆ (OH) ₃ BiO ₃

Bismuth 57.7 ° / ₀

Carbon 13.2 ° / ₀

Oxygen 26.5%

Hydrogen 2.4 ° / "

Pentahydroxyhexyl bismuthate, C ₆ H ₅ (OH) ₅ BiO ₃

Bismuth 49.5 ° / ₀

Carbon 17.1 ° / ₀

Oxygen 30.3%

Hydrogen 3.0 ° / ₀

Pentahydroxycyclohexyl bismuthate, C ₆ H ₆ (OH ₅ ) ₅ BiO ₃

Bismuth 49.7% / ₀

Carbon 17.1 ° / ₀

Oxygen 30.3 ° / ₀

Hydrogen 2.6 ° / ₀

These compounds are very soluble in water and glycerin, but insoluble in alcohol, or acetone

Ether. The preferred compound is pentahydroxyhexyl bismuthate, which is made up of sorbitol and sodium bismuthate can be produced. For the production of the bismuth ester is not used within the scope of the present invention Protection claimed.

The aqueous baths according to the invention contain 0.05 to 1.5 g / l, preferably 0.4 to 1 g / l and in particular 0.5 g / l bismuth as a bismuth tester.

The baths according to the invention can therefore contain the following components in solution:

link

far concentration in S / l j 100 preferably up to 300 25th 90 10 up to 35 0.5 20th 5 to 1.5 0.3 0.05 closely 50 to 15 to 0.1 to

Tin as an alkali metal stannate
free alkali metal hydroxide.
Bismuth as a bismuth tester ..

The deposition of tin-bismuth alloys from the baths produced in this way can take place under Use a soluble or an insoluble anode. As an insoluble anode, in typically steel and preferably stainless steel can be used. As a soluble anode system is suitable e.g. B. typically tin and preferably commercially available tin metal or a rapidly soluble one Tin alloy, which can contain small amounts of metals such as aluminum.

The deposition of the tin layer on the cathode is carried out in such a system preferably at temperatures of 60 to 105 ° C., preferably at about 95 ° C. The deposition can be carried out using a cathode current density of 1 to 40 A / dm ² , preferably 8 A / dm ² .

The elimination of the risk of tin plague formation with coatings according to the invention can be best achieved by the formation of a tin layer with a content of 0.1 to 0.3, in particular 0.2 weight percent bismuth in the tin precipitate. It has been found that the formation of a Tin-bismuth alloy coating with a bismuth content in this area is characterized by a special low incidence of tin plague.

The deposition is carried out for 1 to 60 minutes, preferably for 20 minutes. Using the equilibrium baths of the invention; H. such baths that have been in operation long enough to have overcome their break-in period, it is this one Time easily possible to produce a coating containing bismuth in the desired proportion. It is particularly characteristic of the baths according to the invention that they are after their original running-in period can be used essentially indefinitely; d. H. for times above 1 to 125 ampere hours per liter. During this time the precipitates obtained are essentially uniform.

A special property of the baths according to the invention is their short running-in time. It is typical for the baths that they get the desired alloy deposit after a running-in time of less than 5 ampere hours per liter and often after only 4 ampere hours per liter. Thereafter, the method enables the production of precipitates for an essentially unlimited period long time.

During the electrodeposition process, the bismuth and tin content of the bath can slightly affect the desired level, normally at a bismuth concentration in the bath of 50 to 150 mg / 1, preferably 100 mg / 1, whereby a ratio of bismuth to tin of 0.001 to 0.006, preferably 0.003 arises in the precipitate. Such ratios of bismuth to tin in that Bath produce precipitates containing bismuth and tin, the former in the amount of 0.1 to 0.6 ° / o> normally 0.3 ° / o-

The break-in period, which normally is 4 to 5 ampere-hours per liter can be reduced to substantially zero by using a ratio of bismuth to tin during the running-in period of from about 50 ° / ₀ of the above-mentioned values for the normal operation., During the running-in period, the bismuth content of the bath should be 0.025 to 0.75 g / l, preferably 0.05 to 2 g / l and in particular 0.10 g / l.

It is evident that when the bath is operated, deposits of a bismuth-tin alloy are produced the bath is depleted of tin and bismuth. If a soluble tin anode is used, it is done Substantially no depletion of tin except for drag on extraction of the objects. The required refilling of tin can be achieved by adding appropriate amounts of a Alkali metal stannate done to the bath. the

ίο Depletion of the bath in bismuth can be caused by constant Adding a bismuth ester to the bath as described above, preferably eliminated Pentahydroxyhexyl bismuthate at a rate of from 0.0005 to 0.005 g, preferably 0.003 g Bismuth per ampere-hour. The addition can be done at suitable intervals, e.g. B. every 2 hours. If the bath system is used with an insoluble anode, the tin can be made more suitable by adding Quantities of an alkali metal stannate are made up, approximately in the amount of 1.107 grams of tin per ampere hour. In this case, 1.04 g of potassium hydroxide per ampere hour must be carried out by methods known per se neutralized or an equivalent amount of sodium hydroxide if the bath contains sodium.

Maintaining the bismuth level in bath systems with an insoluble anode can be achieved by adding of a bismuth ester can be effected in the same way as in systems with a soluble anode.

It is a particular feature of the bath according to the invention that when electrolytic deposition a bismuth-tin alloy in a bath system (especially if this is based on potassium stannate is) using an insoluble or inert anode to increase the tin content of the bath Its value can be maintained or adjusted by adding a water-containing tin oxide sol to the bath admits. These alkyl tin oxide sols are characterized by their essentially complete convertibility in stannate when they come into contact with solutions containing 5 to 100 g / l potassium hydroxide at temperatures of 50 to 100 ° C, can be prepared that at a temperature below 75 ° C an alkali metal stannate in an aqueous solution to a final pH of about 6 is implemented, wherein hydrous tin oxide is precipitated that this hydrous tin oxide separated from the aqueous medium and then washed to remove water-soluble ions, and that it finally comes with a peptizer consisting of potassium hydroxide and potassium stannate Group is peptized to an alkaline tin oxide sol, the molar ratio of potassium to tin in the final sol is maintained at 0.5 to 1.5 and the hydrous tin oxide prior to peptization is brought to a temperature below 75 ° C.

Such a convertible tin sol can be

prepare about by heating a solution of 1000 g of potassium stannate in 2 l of water to 49 ° C. During of heating, 700 g of sodium bicarbonate are added in small amounts. During this encore the solution is stirred and the temperature is kept at 49 ± 3 ° C. The precipitate formed will filtered off and washed with 500 ml of cold water. The precipitate is then suspended in 1.5 liters of water and added 120 ml of glacial acetic acid to adjust the pH to about 5. The precipitate will then filtered off again and washed with water. It is then mixed with 200 g of solid potassium stannate,

whereupon an easily mobile, clear, slightly amber colored alkaline tin oxide sol is obtained. That The finished sol weighs 1465 g, has a density of 1.63 and contains 28.6 percent by weight tin.

It should be emphasized that the baths according to the invention by using a solution of a Hydroxyalkyl bismuthate esters and alkaline tin oxide sol and made at the correct concentration can be held. A typical set up for making baths includes an alkaline tin oxide sol in an amount of 100 to 700 g / l, preferably 300 g / l tin metal per liter and a hydroxyalkyl bismuthate ester in an amount of 0.1 to 3.5 g / l, preferably 0.9 g / l of bismuth metal per liter. These mixtures containing bismuth and tin can be used in aqueous form by Mixing the reaction product of a polyhydric alcohol and bismuth directly with the das aqueous phase containing alkaline tin oxide sol. A typical composition for the bathroom approach and to maintain proper concentrations comprises 0.1-3.5 parts, preferably 0.9 parts Pentahydroxyhexyl bismuthate (expressed in parts of bismuth metal) and an alkaline tin oxide sol with 100 to 700 parts, preferably 300 parts of tin metal. This composition can be maintained the bath concentration can be used if the bath contains an insoluble anode.

When using the invention, over extended operating times, electrolytic deposition of a bismuth-tin alloy can be achieved consistently, which is 0.1 to 0.6%> preferably 0.1 to 0.3% and in particular 0.2% ₀ bismuth and from 99.4 to 99.9 ° / _0, preferably from 99.7 to 99.9% ^{un <3,} in particular 99.8 ° / o tin contained. These electrolytically deposited layers are particularly notable for their high resistance to the formation of tin pest if they were exposed to ^{temperatures below 18 ° C. for a long time.}

The invention is additionally described below with the aid of examples, the Parts represent parts by weight.

example 1

45

Two identical electrolytic baths were set up, each containing 283 g / l potassium stannate and Contained 20 g / l potassium hydroxide. Dihydroxypropyl bismuthate was added to the first bath so that a bismuth to tin ratio of 0.002 resulted. The second bath was sorbitol bismuth ester added, so that the ratio of bismuth to tin was also 0.002.

18 steel cathodes, each 0.1 × 2.5 × 15 cm in size, were galvanized ^{in succession in each bath at a current density of 6 A / dm 2} for 30 minutes and at 77 ^{° C.}

After the initial break-in period of about 4.4 ampere-hours per liter that produced the dihydroxypropyl bismuthate Manufactured bath resistant deposits with a uniform bismuth content of 0.25 to 0.3%. After the bath during about 6.3 ampere hours per liter had been in operation, the layers formed contained 0.25% bismuth, and this value was held essentially constant until the test at 12.5 ampere hours per liter was canceled.

Example 2

A life test was carried out to ensure the excellent results when using the bath to illustrate according to the invention. For this purpose, a bath was prepared similar to that of Example 1 corresponded. The bismuth content of the solution was adjusted by adding a solution of pentahydroxyhexyl bismuth at intervals during electrodeposition. The bismuth and tin levels were maintained by adding an aqueous solution with 500 g / l tin as alkaline tin oxide sol and with 1 g / l bismuth as pentahydroxyhexyl bismuth. These additions were made in accordance with the degree of use expressed in ampere-hours per liter, being 1.107 g Tin was added per amp hour. This addition was made at approximately 2 hour intervals executed.

The same steel plates as in Example 1 were used successively in this bath throughout Electrolytic treated duration of the test. It turned out that after the initial break-in period the percentage bismuth in the tin precipitate was essentially 0.2% by the end of the month Tests sustained at 119 ampere-hours per liter became.

Claims (5)

Patent claims: 1. Bath for the galvanic deposition of tin-bismuth alloy coatings, thereby characterized as being an alkali metal stannate, free alkali metal hydroxide and hydroxyalkyl bismuthate contains. 2. Bath according to claim 1, characterized in that it contains potassium as the alkali metal. 3. Bath according to claim 1 or 2, characterized in that it is a hydroxyalkyl bismuth contains a polyhydroxyalkyl bismuthate. 4. Bath according to one of claims 1 to 3, characterized in that it is a hydroxyalkyl bismuth Contains pentahydroxyhexyl bismuthate. 5. Bath according to one of claims 1 to 4, characterized in that it is 0.05 to 1.5 g / l Contains bismuth as a hydroxyalkyl bismuth.