Electroformation

Nickel Sulfamate. Nickel sulfamate [13770-89-3] Ni(S02NH2)2 4H2O, commonly is used as an electrolyte ia nickel electroforming systems, where low stress deposits are required. As a crystalline entity for commercial purposes, nickel sulfamate never is isolated from its reaction mixture. It is prepared by the reaction of fine nickel powder or black nickel oxide with sulfamic acid ia hot water solution. Care must be exercised ia its preparation, and the reaction should be completed rapidly because sulfamic acid hydrolyzes readily to form sulfuric acid (57). 

Dissolution of Silver. Silver is dissolved by oxidising acids and alkaU metal cyanide solutions in the presence of oxygen. The latter method is the principal technique for dissolving silver from ore. Silver has extensive solubiUty in mercury (qv) and low melting metals such as sodium, potassium, and their mixtures. Cyanide solutions of silver are used for electroplating and electroforming. The silver is deposited at the cathode either as pure crystals or as layers on a mandrel. 

Nickel. Worldwide, nickel used in electroplating has averaged about 63,500 t annually from 1980—1990 (9). The United States uses about 18,000 t/yr, and Europe about the same quantity Japan consumes about 9,000 t, and another 9,000 t is used by the other Pacific rim countries. Canada and South America are reported to use about 4500 t aimuaHy. Electroforming apphcations consume another 4500 t of nickel worldwide. About half of this electroforming is done in the United States and Canada. Nickel deposited from autocatalytic solutions was estimated to account for 1600 t of nickel on a worldwide basis (10) in 1990. Nickel averaged 3.65/kg ia early 1993 (see Nickel and nickel alloys). 

Acid Copper. Bath compositions are shown in Table 8. The acid sulfate bath is by far the most widely used copper plating bath, both for plating and for electroforming and electrowinning. The fiuoborate baths have been Htde used in spite of the high current densities possible. Additional information can be found in the Hterature (98,99). 

Electroforrning is the production or reproduction of articles by electro deposition upon a mandrel or mold that is subsequendy separated from the deposit. The separated electro deposit becomes the manufactured article. Of all the metals, copper and nickel are most widely used in electroforming. Mandrels are of two types permanent or expendable. Permanent mandrels are treated in a variety of ways to passivate the surface so that the deposit has very Httie or no adhesion to the mandrel, and separation is easily accompHshed without damaging the mandrel. Expendable mandrels are used where the shape of the electroform would prohibit removal of the mandrel without damage. Low melting alloys, metals that can be chemically dissolved without attack on the electroform, plastics that can be dissolved in solvents, ate typical examples. 

Plating solutions used in nickel electroforming are primarily the Watts bath and the nickel sulfamate bath. Watts baths exhibit higher stress and require additives for stress control, which may affect other properties. Sulfamate baths produce much lower stress and are preferred where purer nickel or nickel—cobalt deposits ate needed. ASTM specifications are available that describe the mandrels and plating solutions (116,162). 

W. Blum and G. Hogaboom, Principles of Electroplating and Electroformings McGrawHiU Book Co., Inc., New York, 1924. 

A.STM. B503, Std. Practicefor Use of Copper and Hickel Electroplating Solutionsfor Electroforming, American Society for Testing and Materials, Philadelphia, Pa., 1984 Ref 57, Chapts. 13, 14, and 15. 

Sieves are often referred to by their mesh size, which is the number of wires per hnear unit. The U.S. Standard Sieve Series as described by the American Society of Testing and Materials (ASTM) document E-11-87 Standard Specification for Wire-cloth Sieves for Testing Purposes addresses sieve opening sizes from 20 [Lm (635 mesh) to 125 mm (5.00 in). Electroformed sieves with square or round apertures and tolerances of 2 [Lm, are also available. 

The second category was concerned with adhesion to porous or microfibrous surfaces on metals. Aluminium may be anodised to form an oxide surface comprising pores of diameter of tens of nanometers. Electroforming and chemical oxidation can be used to produce microfibrous or needle-like coatings on metals, including copper, steel and titanium. The substrate topography was demonstrated to play an vital part in adhesion to these surfaces [45-48]. 

Nickel is also widely used as an electrodeposited underlay to chromium on chromium-plated articles, reinforcing the protection against corrosion provided by the thin chromium surface layer. Additionally the production of articles of complex shape to close dimensional tolerances in nickel by electroforming —a high-speed electrodeposition process —has attracted considerable interest. Electrodeposition of nickel and the properties of electro-deposited coatings containing nickel are dealt with in greater detail in Section 14.7. 

Discs Discs of nickel electroformed on to mandrels bearing grooves modulated with recorded sound have been used for many years for stamping sound recording discs. This process has been adapted and refined for the manufacture of digital records, including video discs . Video disc stampers must be hard, stress-free, and flat to within 0.1 m results of a short investigation directed towards these requirements have been reported ". 

Other applications of nickel electroforms are reviewed in Reference 75. 

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