US2475186A - Method of protecting metallic surfaces against tarnishing and corrosion - Google Patents

Description

Patented July 5, 1949 METHOD OF PROTECTING METALLIC SUB- FACES AGAINST TARNISHING AND COR- ROSION Jonas Kamlet, New York, N. Y., assignor to Boyle- Midway Inc., New York, N. Y., a corporation of Delaware No Drawing. Application August 8, 1945,

- Serial No. 609,717

1 Claim. 1

This invention relates to solid compositions of matter adapted to prevent the tarnishing of metallic surfaces, especially silver surfaces, during storage.

One purpose of this invention is to provide solid compositions which may be placed in a cabinet, chest or other container together with the metal to be protected and which will by their presence retard or prevent the tarnishing of the surfaces of such metal, especially the surfaces of silver.

Another purpose is to provide solid compositions which will retard or prevent by their presence in the neighborhood of the metal to be protected the discoloration, oxidation, rusting, etching or similar attack on such metal by acidic components of the atmosphere.

A further purpose of this invention is to provide compositions of matter in solid form which will obviate the drawbacks and disadvantages of liquid and waxy preparations heretofore employed for the prevention of tarnishing of silverware. I

A further purpose of this invention is to pro- -vide a method and material for protecting metals,

especially silverware, against corrosion, which obviates the necesssity of mechanically applying coating material to the metal surfaces as by brushing, spraying or dipping.

As is well known, silver surfaces are subject to discoloration upon exposure to hydrogen sulfide, sulfur dioxide and other acidic gases present in the atmosphere, especially in urban and industrial areas. This discoloration, or tarnishing, is

changes in the nature of metallic surfaces are often initiated or accelerated by the presence of acid-reacting compounds in the neighboring atmosphere, especially when conditions of high humidity prevail. Metallic or metal-coated objects on storage or in transit are thus often etched so badly that they may no longer be used for the purpose originally intended.

Although the Accordingly, it is an additional purpose of this invention to provide solid compositions of matter which ma be contained in molds, boxes, cans or like containers, which may be tabletted, compressed, or otherwise dispensed in a unitary form, which may be stored, or transported in conjunction with metallic or metal-coated objects, and which will, by virtue of their chemical action on the circumambient atmosphere, retard or inhibit the surface tarnishing. or corrosion of such objects.

' Other and additional objects of the present irivention will become obvious in the course of the following description.

Numerous products and methods of widely varying nature have been proposed for preventing the tarnishing and corrosion of silver and other metallic surfaces. Thus, by way of example, Gangloff and Hieronymus (U. S. Patent 2,117,657 of 1938) wash silverware in a hydrochloric acid solution of stannous chloride; Stoughton and Davis (U. S. Patent 2,144,642 of 1939) coat silver surfaces with a triethanolamine soap emulsion of a hard wax, such as carnauba or candelilla; Sowa (U. S. Patent 2,339,200 of 1944) applies over the surface of a metal an aqueoussolution of a film-forming hydrophilic colloid and evaporates the solvent to deposit on the surface a thin continuous film of the colloid. Many other products based on widely divergent chemical and physical principles have likewise been described.

Briggmann (U. S. Patent 2,323,369 of 1943) has described an interesting process based on the exposure of silverware in' a confined space to the vapor of a dilute aqueous solution of a volatile amine, such as morpholine, butylamine, ethylene diamine, propylene diamine, etc. The presence of the vapors of the volatile organic amine in the surrounding atmosphere exerts an excellent protective action and efiectively retards or prevents the tarnishing of the metallic surface.

However, this method has the serious draw-' back of requiring the use of an aqueous solution in an open container. Obviously, it can therefore not be employed in silver chests, cabinets, drawers, etc., subject to frequent jarring and motion. The aqueous solutions of the volatile amines are strongly alkaline and, when spilled, may stain or otherwise harm the'appearance ofwood and other adjacent materials. 'The acrid odor of the split solution may permeate and spoil foodstuffs and otherwise damage valuable materials stored in the same container.

container is similarly unsuitable for use in con- The open obviously not suitable for the housewife who wishes to keep free of tarnish a small chest of silver cutlery, which may be jarred and moved about constantly. Nor is it suitable, for example,

for the protection of delicate precision instruments from corrosion by acidic gases during a prolonged shipment. By the present invention 1 provide products which will be suitable for use by the housewife, which will not be subject to spillage or deposition of an undesirable residue, which will be transportable without loss of efil- I cacy and which will require no further attention or manipulation after being exposed near the silverware or other metallic object to be protected. The basis of the present invention is the finding that excellent protection against tarnishing and corrosion of silver and other metallic surfaces can be obtained with the use of a solid composition containing from 0.1% to 20% of an organic amine important. Excessively volatile amines, such as ammonia, ethylamine, methylamine, dimethylamine, etc., are unsuitable because they evaporate too rapidly and at a rate much greater than the sublimation rate of the remainder of the compositions. They are also excessively ammoniacal in odor and may impregnate or be absorbed by porous materials or other odor-sensitive matter in the vicinity. On the other hand, all of the aromatic amines and most of the aliphatic amines containing polar groups (e. g., mono-, diand triethanolamines, mono-, diand tri-propanolamines, 2-amino-2-methylpropandiol-1,3, etc.) are not volatile enough and do not liberate sufiicient amine into the circumambient atmosphere to produce the desired efiect.

I have found that the group of organic amines suitable for use in the present invention may be characterized by vapor pressures between about 7.5 millimeters and about 60 millimeters of mercury at 20 C. Among the commercially available amines falling within this category and therefore suitable for use are: morpholine, N-methylmorpholine, ethylene diamine, and propylene diamine. Unlike Briggmann, I find butylamine to be excessively volatile and therefore unsuitable for use in the present invention (U. S. Patent 2,323,369, page 1, column 1, line 37).

The group of subliming compounds to be associated with the amines of my new compositions must also meet certain specific requirements. Sublimation is the process whereby a solid passes directly into the gaseous or vapor state without liquefying. In the strictest sense, all solids sublime to some extent, but in most cases the rate i 4 of sublimation is infinitesimal and imperceptible over prolonged periods of time.

Such compoimds or mixtures of compounds as will sublime at normal temperatures and pressures at rates suitable for the present invention are those having vapor pressures above 0.15 millimeter of mercury at reference temperature of 35 C. However, compounds or mixtures of compounds which are excessively volatile are quite unsuitable since they will sublime too rapidly for effective use in commercial preparations. Thus, I'have found that such compounds are excluded by limiting my subliming compounds to those having a melting point above about 50 C.

I at atmospheric pressure.

Among the subliming compounds eminently suitable for use in the present invention, two general groups may be indicated herewith:

(a) Compounds which sublime quite rapidly, such as paradichlorbenzene (M. Pt. 53 0.; vapor pressure-37.5 mm. at 30.3 C., 52.2 mm. at 35.3 C., 100.0 mm. at 45.3 C. (Speranskl, 'Zeitschrift fur physikalische Chemie, 51, 4'! (1905)), and sym-trioxane (M..Pt. 6162 C.; vapor pressure 13 mm; at 25 C., 31 mm. at 3'7.5 C. (Walker and Carlisle, Chemical and Engineering News, 21, 1250, August 10, 1943) (b) Compounds which sublime rather slowly, such as naphthalene (M. Pt. 80.2 C.; vapor pressure-0.21 mm. at 35 C., 0.32 mm. at 40 C. (Allen, Journ. Chem. Soc. (London) 77.400 (1900)), and camphor (M. Pt. 174-l7'7 0.; vapor pressure 0.38 mm. at 35 C. (Allen, Journ. Chem. Soc. (London) 7'7, 413 (1900)).

By a proper admixture of rapidly-subliming and slowly-subliming compounds, the solid composition may be made so as to sublime at any desired rate. Compounds and mixtures which sublime slowly require more of the amines than do those that sublime rapidly. Preferably the pri mary amines, like ethylene diamine and propylene diamine, are used in concentrations between 0.1% and 10.0%; the secondary and tertiary amines, like morpholine and N-methylmorpholine are used in concentrations between 2.0% and 20.0%. These proportions are subjectto considerable variation and extension without departing from the scope of my invention, but the solidified mixture should be homogeneous and should not separate out undissolved amine upon cooling.

In preparing these compositions the organic amine may be dissolved in the subliming compound or mixture of compounds while the latter is kept in a molten state, the solution being stirred until homogeneous and then poured into molds, cans or other containers, where it is cooled.

The compositions may be colored or, perfumed in any desired manner, although the subliming compounds themselves often possess quite pleasant odors (e. g. camphor, trioxane). Additional or ancillary agents may be added without changing the nature of the present invention.

In choosing a dye for these compositions their alkaline nature must be considered. Basic or neutral oil-soluble dyestuffs are most suitable. Thus, 0.01% to 0.02% of dry indigo powder dissolved in the molten compositions prior to cooling, imparts a pleasant stable indigo blue coloration thereto.

The compositions, while still in the molten state, may be poured into their ultimate containers or they may be poured into molds or frames, cooled, solidified, comminuted and compressed into tablets or pellets of a unitary size. The cooled solid may also be cut into blocks, shaped or otherwise changed in physical form to suit the marketing requirements of a product of this'gena h eral nature.

Y The tins, boxes or cans containing these products may be stored indefinitely if kept tightly closed. when ready for use,' the cover of the receptacle is removed, or orifices opened therein (e. g. by punching holes) and the composition 7 commences to sublime. Blocks, tablets or pellets of these compositions may be wrapped in impervious plastic or metallic films and stored indefinitely in this state. Removing the wrapper activates the block or tablet for use.

Tins or blocks of these compositions may be placed in silver chests. in bureau drawers, in

display cases, in cabinets and receptacles of any nature, stationary or mobile, without fear of spillage. They will evaporatewithout trace and without saturating the surrounding atmosphere with water vapor. They may be wrapped with metallic or metal coated instruments, tools, equipment, etc., to keep them free of corrosion Example ilgrams-oftrioxane are heated on the waterbath until moltenfand 100 grams of morpholine are dissolved therein. The solution is colored by the addition of 0.1% of dry indigotin powder.

then poured into cans, where it is cooled and permitted to crystallize. The containers are sealed as soon as possible after pouring. An opened upon prolonged storage or transportation and (in a powdered or comminuted form) they may be scattered into inaccessible crevices and corners without fear of clogging, corroding, or otherwise injuring moving parts.

My compositions appear to afford a' three-fold protection to silver surfaces. The presence of 'the volatile organic amine in the circumambient atmosphere serves to neutralize any acidic gases which may be present and will continue to do so until the composition has dissipated completely.

It-also' appears that silver objects adsorb on their surface a thin layer (perhaps no more than one or two molecules thick) of the volatile organic amine and possibly form a complex cation (such as silver morpholinium,

etc.) in which the ionization of the silver atom is repressed below that of the silver atom in silver sulfide. Thus the silver will no longer tend to react with hydrogen sulfide in the atmosphere to form a tarnish (which is usually silver sulfide).

Finally may be mentioned the contribution of the subliming compounds to the protection of the surface. Metallic and metal-coated objects almost invariably have a lower specific heat or better thermal conductivity than the surrounding atmosphere. Thus, in a receptacle or container where convection currents are set up by the sublimation of a volatile compound, some condensation of the subliming compound will usually occur on the colder metallic surface. This condensation is imperceptible in extent and in no way dims the luster of the polished metal, but sensitive reagents will invariably show the presence of the subliming compound on the metallic surface it the composition has been exposed within its vicinity.

This surface layer of condensed subliming compound is not static. It resublimes and is continually replaced by freshly condensing layers. Thus, it provides a third barrier between the metallic surface and the corosive gases of the surrounding atmosphere."

It is to be understood that the explanations advanced above are not intended to limit my invention, but to offer a. possible explanation of the mechanism of the observed protective action.

can of this material is placed in a closed chest containing domestic fiat silver.

Example II 950 grams of para-dichlorbenzene are heated on the waterbath until molten, and grams of morpholine are dissolved therein. '8 grams of coumarin and 2.0 grams of vanillin are added to the melt, and when a clear solution is obtained it is poured into its ultimate containers. These are sealed and cooled as rapidly as possible to solidify the composition.

Example III 475 grams of para-dichlorbenzene, 4'15 grams of trioxane, and 50 grams 'of morpholine are heated together on the waterbath until a homogeneous solution is obtained. 5 .grams of ethyl vanillin and 0.1 gram of fiuore'scein are added and dissolved with stirring. The solution is then poured into its ultimate containers, capped an allowed to solidify by cooling.

Example IV 125.0 grams of morpholine and 875.0 grams of camphor in powder or comminuted form are re-- fiuxed together for a few minutes until completely dissolved. The solution is immediately poured into its ultimate containers; these are sealed and permitted to cool.

Example V 950 grams of trioxane are heated on the waterbath until molten, and 50 grams of ethylene diamine are dissolved therein. To this solution are now added 0.25 gram of tetracl'ilorfluorescein The following examples will illustrate specific embodiments of my invention, but it is not in tended to limit the invention otherwise than as defined in the appended claims.

5.0 grams of vanillin and 5.0 grams of coumarin.

When a homogeneous solution is obtained it is poured into containers, sealed, and permitted to solidify by cooling.

Example VI 475 grams of naphthalene, 4'75 grams of paradichlorbenzene, 50 grams of propylene diamine, 10 grams of vanillin and 5 grams of coumarin are heated together on the boiling waterbath until a uniform solution is obtained.' This-is poured into its ultimate containers, covered an allowed to cool, whereupon it solidifies.

Example VII 950 grams of camphor and 50 grams of N- methylmorpholine are heated together on the oiibath until completelydissolved. The solution is poured into a mold, solidified by rapid chilling,-

and then cut into blocks of convenient size. Several blocks are placed in open trays in a show case containing scientific instruments having exposed metal parts, such as sextants, goniometers;microscopes, etc. The remaining blocks are individually wrapped in glassine paper and stored in a tightly covered tin box.

Example VIII 950 grams of camphor, 25 grams of morpholine and 25 grams of N methylmorpholine are heated together on the oiibath until completely dissolved,

r 1 0.2 gram oi indisotin powder is added, and when a iuniiorm solution is obtained it is chilled until it crystallizes. The crystalline material is com- 'minuted and the eomminuted material is then compressed into tablets of convenient size and shape.

I claim:

The method of protecting metallic surfaces against tarnishing and corrosion which comprises confining the metal surfaces together with cir-' SJIIJOB file of this patent:

8 at least 50' C. and a vapor pressureof at least 0.15 millimeter of mercury at 35 0., whereby the vapors from the corrosion inhibitor difluse through the circumambient atmosphere and con- 5 tact the metallic surfaces to be protected.

JONAS KAMLET.

REFERENCES CITED The jollowing rei'erenlces are of record in the UNITED STATES PATENTS Number Name Date 1,851,493 'Calcott et a1. Mar. 29, 1932 16 1,903,287 Cox Apr. 4, 1933 1,941,014 Lucas Dec. 26, 1933 2,195,689 Bash Apr. 2, 1940 2,323,369 Briggmann July 6, 1943