Jewelry coating

Sputtering is an important thin-film process used extensively in the semiconductor and hard-coating industries and for decorative and jewelry coatings. PlP] Excellent coatings of refractory compounds and metals can be readily produced with good adhesion and composition control without the high temperature requirements of CVD. 

It is used in coinage and is a standard for monetary systems in many countries. It is also extensively used for jewelry, decoration, dental work, and for plating. It is used for coating certain space satellites, as it is a good reflector of infrared and is inert. 

Skiving is a variant in which the base metal surface oxides are mechanically removed foUowed immediately by pressure rolling of a precious metal or alloy strip. This is commonly used for inlays for electrical contacts and for jewelry fabrication. The common inlay materials include gold, silver, copper, brass, and solder. No heat is needed, and the coating is appHed only to designated areas so there is Htde waste (3,50). 

Calcined aluminas are also used for polishing appHcations by mixing into polishing compounds in the form of paste or suspensions. Polishing aluminas are used to alter the surfaces of metals, plastics, glass, and stones in the manufacture of cutlery, automobiles, computers, furniture, eyewear, semiconductors, and jewelry. Polishing aluminas are also used to coat surfaces, such as video tapes (1). 

Coatings of refractory carbides and nitrides and more recently carbon and DLC are used extensively in decorative applications on jewelry, eyeglasses, and similar products in attractive colors such as gold (TiN) and metallic grey, or charcoal (DLC, CrN, and TaN). They provide a surface which is hard and wear resistant, sweat resistant and, in the case of gold, less costly. They are usually applied by cathode sputtering and less frequently by CVD. 

Evaporation is used extensively for the deposition of aluminum and other low melting-point metals as well as hard coatings such as TiN for cutting tools, decorative coatings (jewelry), and for the metallization of paper and fibers. It is also a major coating... 

The bluish white, hard, yet ductile, metal is inert to all acids and highly non-abrasive. Used for heavy-duty parts in electrical contacts and spinning jets. Reflectors are prepared from the mirror-smooth surfaces (e.g. head mirrors in medicine). Thin coatings provide a corrosion-resistant protective layer, for example, for jewelry, watches, and spectacle frames. The metal is a constituent of three-way catalysts. Rhodium complexes are used with great success in carbonylations (reactions with CO) and oxidations (nitric acid) in industry. Platinum-rhodium alloys are suitable thermocouples. 

Because of its beauty and rarity, gold bullion is still used as the international standard for money, accepted as such by all nations. It is also used in jewelry, in dentistry, and as a protective or decorative coating on the surface of other metals. Gold has even been used in space vehicles. Though men have fought and died for gold down through the centuries, the element has comparatively few uses. 

Palladium is used in the manufacture of surgical instruments, electrical contacts, springs for watches and clocks, high-quality spark plugs, and special wires and as white gold in jewelry. Because it is noncorrosive, it is used as a coating for other metals and to make dental fillings and crowns. 

Platinum metal and its alloys have numerous applications. As a precious metal it is used extensively in jewelry. Other important applications include construction of laboratory crucibles and high temperature electric furnaces in instruments as thermocouple elements as wire for electrical contacts as electrodes in dentistry in cigarette lighters and for coating missile and jet engine parts. 

Students will discuss the pros and cons of coating a piece of jewelry in an electrochemical cell. 

The plating of jewelry in an electrochemical cell is not very satisfactory. Because the reaction is spontaneous, there is not much control over the rate of plating. Metal is deposited unevenly. Also, often the metal does not adhere to the jewelry being coated and will flake off, leaving a mottled appearance. A better way to coat jewelry is in an electrolytic cell. 

Except for its source of outside current, the electrolytic cell has the same elements as the electrochemical cell an anode and a cathode placed in an electrolyte in which cations (positive ions) move toward the cathode, and anions (negative ions) move toward the anode. The oxidation half reaction at the anode and the reduction half reaction at the cathode can be added together to find the overall redox reaction for the cell. The process is called electrolysis. If a coating of silver metal is desired on a piece of silver jewelry, electrolysis can be performed to coat or plate the silver jewelry in an electrolytic cell. The electrolyte silver nitrate (AgN03) solution supplies a source of silver ions (Ag+). The cathode is the silver jewelry, from which silver ions are reduced to silver metal. The anode... 

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