Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/0005—Other compounding ingredients characterised by their effect
  • C11D3/0073—Anticorrosion compositions
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/0005—Other compounding ingredients characterised by their effect
  • C11D3/0042—Reducing agents
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/02—Inorganic compounds ; Elemental compounds
  • C11D3/04—Water-soluble compounds
  • C11D3/042—Acids
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/16—Organic compounds
  • C11D3/34—Organic compounds containing sulfur
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
  • C11D7/02—Inorganic compounds
  • C11D7/04—Water-soluble compounds
  • C11D7/08—Acids
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
  • C11D7/22—Organic compounds
  • C11D7/34—Organic compounds containing sulfur
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/10—Other heavy metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D2111/00—Cleaning compositions characterised by the objects to be cleaned; Cleaning compositions characterised by non-standard cleaning or washing processes
  • C11D2111/10—Objects to be cleaned
  • C11D2111/14—Hard surfaces
  • C11D2111/16—Metals

Definitions

• a process has previously been developed for removing tarnish from silver articles in which tarnished silver articles are treated with an aqueous solution of an acid which is stronger than hydrosulphuric acid but is not such as will, in aqueous solution, attack silver to any material extent and a soluble compound capable of forming a soluble complex with silver ions, which complex gives rise to substantially no silver ions in aqueous solution, such as thiourea or thiosemicarbazide.
• the effect only occurs when the carrier metal is more electropositive than silver, and since copper and nickel silver (an alloy of copper, zinc and nickel) are commonly used as the basic metal, the phenomenon is quite frequent. Whilst we do not wish to be limited by a theoretical explanation, we believe that the effect is due to the formation of a cell with the exposed basic metal as one pole and the silver :as the other pole. As the exposed basic metal is more electropositive than the silver, in operation, negatively charged ions are discharged at the basic metal and thus bring about the discolouration above referred to, whilst hydrogen ions are discharged at the silver with evolution of hydrogen.
• the previously developed process has also another disadvantage, in that where the articles to be cleaned include other metals, as for example, silver-handled knives having steel blades or articles of 9-carat gold and silver, un desirable elfects may be obtained.
• the steel blade of a silver handled knife will be attacked by the process of the said prior application whilst with articles composed of silver and 9-carat gold, silvering of the gold may take place.
• disadvantages are likely to be met when the silver to be cleaned is associated with another metal which we shall call for convenience a secondary metal.
• a general object of the present invention is to provide a means whereby the above-mentioned disadvantages arising from the application of the previously developed detarnishing process can be reduced or removed.
• the presentinvention therefore comprises an agent for removing tarnish from silver, silver alloy and silver-plated articles comprising an aqueous solution of an acid which is stronger than hydrosulphuric acid but is not such as will in aqueous solution attack silver to any material extent and a soluble compound capable of forming a soluble complex with silver ions which complex gives rise to substantially no silver ions in aqueous solution, in combination with means for giving the silver and any secondary metal associated therewith negative electrochemical characteristics during the detarnishing operation.
• Suitable elements where copper is the secondarymetal are, forexample, aluminium, and nickel and where the-secondary metalis nickel, as in nickel silver, or iron, aluminum is satisfactory.
• Such metals may be present in the detarnishingv process in any convenient form; thus the container in which the detarnishing process is carried out may be formed wholly or partly from them, or they may be introduced into the detarnishing solution, before introduction of the silver articles to be cleaned, for example in the form of a plate, rod, turnings or filings; such metals in all cases being in electrical contact with the silver articles.
• the eifect of incorporating such metals is that being more electropositive than the basic metal, they attract the negatively charged ions and thus prevent discolouration of the basic metal.
• the detarnishing liquid is placed in a container of suitable material, for example polyvinyl chloride or polyethylene, the silver articles to be cleaned are placed ni an aluminium basket and the basket dipped in the solution. After removal from the detarnishing solution, the basket may be dipped in plain water in order to rinse the silver.
• suitable material for example polyvinyl chloride or polyethylene
• the detarnishing solution is electrolysed, the article being treated forming the cathode.
• the container of the detarnishing solution may, for example, be formed from an electrical conductor and be connected as the anode; alternatively the anode may simply be introduced into the solution as a plate, rod or the like.
• a deposit may form on thesilver, which is not however coherent and may be readily removed.
• one effect of the process according to the invention is to accelerate the detarnishing action of the said previously developed process and it is therefore advantageous to apply the process according to the invention to the detarnishing of silver of all kinds whether a secondary metal is present or not.
• silver articles associated with a secondary metal can be rapidly and effectively detarnished by the hereindescribed process without substantial discolouration of the secondary metal occurring even when such articles are left in the detarnishing solution for some length of time.
• the complex-forming compounds which may be used in the process according to the invention are, preferably, thiourea or thios'emicarbazide.
• the detarnishing solution contains at least 1% by weight of said complex-forming compound and preferably a solution containing about 5% of said complex-forming compound is employed.
• acids may be employed, examples of which are hydrochloric 'acid, sulphuric acid, citric acid, chloracetic acid, aminosulphonic acid, and malic acid.
• hydrochloric 'acid sulphuric acid
• citric acid citric acid
• chloracetic acid aminosulphonic acid
• malic acid a metal which is more electropositive than the secondary metal
• the acid employed must be capable of dissolving said other metal.
• hydrochloric acid is conveniently used but sulphuric acid by itself is unsuitable; the rate of reaction of hydrochloric acid with aluminium is however inconveniently fast so that mixtures of sulphuric acid or aminosulphonic acid with hydrochloric acid or chloracetic acid are conveniently used, the respective proportions of each acid in which are balanced to provide a satisfactory rate of reaction.
• a suitable acid mixture contains sulphuric acid and hydrochloric acid in the ratio of 9:1 by weight.
• the actual acid concentration of the detarnishing solution will depend on the strength of the acid employed and the rate of detarnishing desired; in the case of strong acids a suitable concentration is from 0.03% to 6.0%. Preferably the acid concentration is at least 0.15%.
• a further advantage of this invention is that the loss in weight (by dissolution of the silver) of silver articles treated according to the said prior process is reduced and thus for example in tests we have carried out, a number of silver-plated forks have been allowed to remain in the detarnishing solution in contact with aluminium for several months without harmful effect on the silver; were the aluminium not present etching of the silver would have taken place after a day or two.
• Example 1 A detarnishing solution was made up containing:
• Example 2 The detarnishing solution used in Example 1 was placed in a glass container, together with a carbon electrode connected to a 4.5 volt D. C. supply as the anode. A heavily tarnished electroplated nickel silver fork, the prongs of which were so badly worn that some of the nickel silver was exposed, was then connected to the same supply, as the cathode. The fork was placed in the detarnishing solution and the current switched on. Detarnishing was very rapid and no discolouration of the exposed nickel silver took place. If the application of black deposit may be formed which is not however coherent and may be readily removed by simple polishing.
• Example 3 A detarnishing solution was made up containing:
• Example 4 A detarnishing solution was made up as follows:
• Example 5 A two gallon batch of detarnishing solution made up as in Example 4 was poured into a specially designed container which was fabricated from rigid polyvinyl chloride.
• a batch of tarnished cutlery comprising:
• Example 6 A detarnishing solution was made up having the following composition:
• Example 7 A detarnishing solution was made up having the following composition:
• Example 8 A detarnishing solution was made up having the following composition:
• a method of detarnishing articles comprising silver and a secondary metal in which the surfaces of said articles have exposed thereon both silver and secondary metal, without tarnishing the exposed secondary metal, comprising: immersing said articles in an aqueous solution which will not materially attack silver, said solution having dissolved therein an acid stronger than hydrosulphuric acid and at least 1% by weight of a compound selected from the group consisting of thiourea and thiosemicarbazide capable of forming a soluble complex with silver ions in aqueous solution; and imparting to said articles negative electrochemical characteristics during the de-tarnishing operation.
• a method of detarnishing articles comprising silver and a secondary metal in which the surfaces of said articles have exposed thereon both silver and secondary metal, without tarnishing the exposed secondary metal, comprising: immersing said articles in an aqueous solution which will not materially attack silver, said solution having dissolved therein an acid stronger than hydrosulphuric acid and at least 1% by weight of a compound selected from the group consisting of thiourea and thiosemicarbazide capable of forming a soluble complex with silver ions in aqueous solution; and imparting to said articles negative electrochemical characteristics during the de-tarnishing operation by placing in said aqueous solution in contact with said articles another metal more electropositive than any metal in said articles, said acid being capable of dissolving said other metal.
• said acid stronger than hydrosulphuric acid is selected from the group consisting of hydrochloric acid, sulphuric acid, citric acid, chloracetic acid, aminosulphonic acid and malic acid.
• said acid stronger than hydrosulphuric acid is a mixture of an acid selected from the group consisting of sulphuric acid and aminosulphonic acid with an acid selected from the group consisting of hydrochloric acid and chloracetic acid.
• a method of detarnishing articles comprising silver and a secondary metal in which the surfaces of said articles have exposed thereon both silver and secondary metal, without tarnishing the exposed secondary metal, comprising: immersing said articles in an aqueous solution which will not materially attack silver, said soluton having dissolved therein an acid stronger than hydrosulphuric acid and at least 1% by weight of a compound selected from the group consisting of thiourea and thiosemicarbazide capable of forming a soluble complex with silver ions in aqueous solution; and imparting to said articles negative electrochemical characteristics during the de-tarnishing operation by making said articles the cathode of an electrolysis carried out in said aqueous solution as electrolyte.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Wood Science & Technology (AREA)
• Metallurgy (AREA)
• Inorganic Chemistry (AREA)
• Materials Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Electrochemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Printing Plates And Materials Therefor (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10288056

Family Applications (1)

Country Status (5)

Cited By (1)

Citations (3)

• 0
  • BE BE532709D patent/BE532709A/xx unknown
• 1953
  • 1953-10-22 GB GB29220/53A patent/GB762961A/en not_active Expired
• 1954
  • 1954-10-19 US US463315A patent/US2801961A/en not_active Expired - Lifetime
  • 1954-10-21 CH CH331865D patent/CH331865A/de unknown
  • 1954-10-22 FR FR1114948D patent/FR1114948A/fr not_active Expired

Patent Citations (3)

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