US2136496A - Tinning compound - Google Patents

Description

Patented Nov. 15, 1933 PATENT GFFICE 1 TINNING COMPOUND Newell M. Epperson, Chattanooga, Tenn., assigner, by mesne assignments, to Taywal Ltd.,

Chattanooga, Tenn., it

limited partnership composed of Carl Neidhardt as generalpartner and Blanche Neidhardt, limited partner No Drawing. Application March '29, 1937, Serial No. 133,663

8 Claims.

This invention relates to a composition of matter especially for use in metallically coating aluminum and alloys which are largely aluminum, particularly as a bonding treatment incident to applying metal, such as solder, pure tin, zinc, and other metals over the aluminous metal, as

by spraying. The class of coating indicated has.

become generally known as cold tinningfl such being characterized in that no specific use is made of electrolysis or heat. The invention also relates to a method of preparinga cold tinning compound, particularly for use on aluminum or aluminous metal. The above indicates the principal objects.

Aluminum and most alloys containing a high percentage oi aluminum are dimcult to coat with other metals, principally because of the lemmacoating and the aluminum is much greater than tion thereon of'a thin oxide immediately upon exposure of the cleaned metal to the air; making itv virtually necessary to clean and coat as one operation. The diiiiculties are greatly increased by the characteristic porosity of aluminum and most of its alloys. A superficial film or coating, i. e. a film which bridges the pores but does not reach into them, is unlikely to adhere for any great length of time. This is principally because when air or other foreign material becomes pocketed in the pores beneath such superficial metallic coating, such matter eventually destroys the bond between the surfaces of the two metals which do become united. When such metallic film coating is used to form a bond, between the aluminous metal, and a super-coating of metal,

such as solder, sprayed on or otherwise deposited 35 to a considerable depth, as in making repairs in event of dents or cavities in the metal, the importance of firm bonding between the initial will form a sufilciently tenacious film or coating to serveas an effective bonding base for a heavily built-up metallic coating, as of solder, zinc, etc., effected as by spraying.

Aiurther object is to provide an improved cold tinning compound which may be used effectively to "tin" aluminum or aluminous metal, both in A roasting and sheet form.

Other objects and Ieatures of the invention will become apparent from the following description.

(Cl. l48-24) It is already known that aluminum can be tinned, i. e. coated with a tin-like film, by compounds containing a preponderance of mercury and relatively smaller percentages of mercuric chloride, copper sulphate, and silver niu trate, (e. g. together with abrasive powder for cleaning; and suspending and /or binding means such as glycerine for the various ingredients). Such compound can be used as a paste for both cleaning aluminum or aluminous metal, and depositing a coating of other metal thereon. The present invention distinguishes in part from such prior knowledge by the use of ammonium chloride, and in part in the manner of making the compound,-reierring particularly to the order of procedure, etc, in mixing the ingredients.

A highly satisfactory composition for cold tinning aluminum and aluminous metals, may be made as follows:

Assuming that a batch of approximately eight and one-half pounds is to be prepared, ll proceed, as a first step, to mix together thoroughly, as in a mortar or triturating apparatusoi suitable type, the following ingredients:

2 pounds mercury 12 ounces corrosive sublimate .12 ounces copper sulphate lit ounces of copper nitrate may be substituted for the copper-sulphate) when the above ingredients are thoroughly mixed, or triturated, the mixture is heated to ap-- proximately 210 degrees-F. and glycerine is added 35 in small amounts until the compound is crystallized. From 8 to 32 ounces of glycerlne is usually sufllcient, and complete v crystallization takes place in from '7 to 10 hours at the temperature given. The mercuric chloride, glycerine and mercury crystallizes to form a compound (may be a. complex or mixed salt) having several'mole- 'cules of water, (from the glycerine or aqueous solution of it as may be used). The appearance of the mixture at completion of the first step resembles small grains of wheat separated from each other.

After the first step is complete, the following ingredients are added, in the order mentioned, one at a time:

4 ounces corrosive sublimate 4 ounces ammonium chloride 4 pounds powdered glass 'When the additional 4 ounces of corrosive 55 sublimate is added, this is mixed in very thoroughly in order to prevent the mercury from precipitating.

The importance of observing the above described order of procedure will be better comprehended from a discussion of what, apparently, takes place. When the materials which are mixed during the first step, are heated, as described, the mercuric chloride (HgClz) is reduced to mercurous chloride (HgZClz) in the presence of metallic mercury. The excess chlorine gas is driven oif during the initial heating.

Part of the corrosive sublimate of the first IIliX.

ture becomes lost (gases off) and the additional four ounces replenishes the same. The resulting composition, in which there is little or no free mercury, is then apparently stabilized by the ammonium chloride, since it is found that if the corrosive sublimate is replenished first (thoroughly mixed in), then the ammonium chloride will keep the mercury from precipitating to any substantial extent. The ammonium chloride is stirred in thoroughly as a fourth step.

If there is any appreciable quantity of free mercury present after the additional four ounces of corrosive sublimate has been added, it is best to warm the batch and if necessary to increase the amount of corrosive sublimate. A small amount of free mercury will not render the compound ine'iiective to tin aluminum or aluminous metals.

After the ammonium chloride has been added and mixed in thoroughly, the powdered glass is similarly mixed in. Other abrasive material may be used in place of powdered glass. Thereupon there is dissolved one-half ounce of silver nitrate in distilled water, and the solution added to the batch, stirring in slowly, as in a batter.

The mixture is then placed in an oven at approximately degrees F. for a period of about hours, during which time the product gasses off. When gassing ceases the attendant is informed that chemical action has terminated.

All active ingredients in the above compound may be varied in proportion as much as twentyfive percent above and below the amounts given.

The powdered glass or other abrasive may be varied as much as desired, since this is only useful as an abrasive in cleaning the metallic surface to be coated, during the coating process.

The compound may then be placed in small non-metallic containers, such as glass jars, which are preferably allowed to stand (covered as with paper) for a short period, to make sure that if further chemical action tends to take place in the smaller spaces this will occur before sealing. The jars may be sealed by threaded caps, leaving sufiicient space for a small amount of expansion, in the event that the heat of the storagespaces for the containers should start further chemical action.

Referring to the action of the various ingredients when the compound is applied to an aluminum or aluminous surface, it is sufficient to note, as to the abrasive, that this merely assists in cleaning foreign matter off the metal to be coated. The ammonium'chlcride acts both as a cleaner and a filler for the pores of the metal. The use of ammonium chloride alone, as a means for removing oxide from metal, as a flux for soldering, is well known. However, I believe, it is not known that ammonium chloride can be used in a cold tinning compound for aluminum without interfering with simultaneous coating or deposition of metals on alum.num or alloys of aluminum. The ammonium chloride in the compound also appears of benefit in that it prevents excessive oxidation on the deposited metallic coating (mercury and copper). The method of incorporation of ingredients, above described, substantially stops the chloride and sulphuric radical from throwing off loose crystalline deposits having the appearance of feathers growing on the surface, such as previously experienced when attempts were made to coat sheet-aluminum with a compound similar to that described.

One or two applications of the paste, rubbed on as with a rough cloth, are usually suflicient to secure a complete and permanent film. The metal of such film apparently enters all the pores of the aluminum and seals them, preventing oxidation from the depths of the cavities. A subsequently sprayed on coating of solder, tin and other metals adheres indefinitely. No kerfing or puncturing of the metal base is ever necessary to assist in bonding the sprayed-on metal thereto. Spraying should be effected promptly after tinning the aluminum or aluminous surface but it need not be done immediately for the tinning stays untarnished for some time.

I claim:

l. A cold tinning compound made from a mixture of metallic mercury,- a salt containing murcury and chlorine, another salt selected from the group consisting of copper sulphate and copper nitrate and a stabilizer for the first mentioned salt selected from the group consisting of mercurous or mercuric chloride and ammonium chloride.

2. A cold tinning compound according to claim 1 which also contains silver nitrate.

3. A cold tinning compound composed of a mixture of mercury, corrosive sublimate, copper sulphate, a recrystallizing agent such as glycerine, and silver nitrate.

4. A cold tinning compound made from approximately thirty-two parts metallic mercury, sixteen par'ts corrosive sublimate, twelve parts copper sulphate, a recrystallizing agent such as glycerine in from eight to thirty-two parts, and one and one-half parts of ammonium chloride.

5. The method of making a cold tinning com-' pound comprising tr'iturating together mercury, corrosive sublimate and copper sulphate, heating the mixture and adding glycerine until recrystallization takes place and then mixing in the following ingredients, one at a time; corrosive sublimate, suflicient substantially to prevent precipitation of metallic mercury from the 1..ixture, ammonium chloride further to stabilize the mixture, and silver nitrate; and then gassing off the final mixture.

6. The method of making a cold tinning compound comprising mixing mercury, corrosive sublimate and copper sulphate, heating the mixture, then adding a recrystallizing agent, and then, after crystallization, mixing in sufficient additional corrosive sublimate substantially to prevent precipitation of metallic mercury from the mixture.

'7. The method of making a cold tinning compound comprising mixing mercury, corrosive sublimate and a metal salt selected from the group consisting of copper sulphate and copper nitrate, heating and adding a crystallizing agent to form new crystals which substantially incorporate all the, mercury, and then adding separately, one after the other, an agent which tends to prevent precipitation of free mercury from said new crystals, and also silver nitrate:

anaemic 3 8. The method of making a cold tinning com- (a) About 4 parts corrosive sublimate, pound for aluminous metals comprising mixing (b) About 4 parts ammonium chloride, the following ingredients: i (c) Abrasive material;

About 32 parts mercury; v 5 then adding, while stirring slowly, about /2 5 About 12 parts corroslve subhmate' part silver nitrate dissolved in water, and finally About 12 parts copper sulphate,

letting the mixture stand until all chemical action Working off at around 210 F., while adding has ceased.

glycerine until the compound crystallizes; then 10 mixing with the above separately, one after the NEWELL M. EPPERSON.

10 other I