Deposition throwing power

Most metals depositable Throwing power variable with, for example, metal, electrolyte and process conditions... 

The selection of a particular deposition process depends on the material to be deposited and its availabiUty rate of deposition limitations imposed by the substrate, eg, maximum deposition temperature adhesion of deposit to substrate throwing power apparatus required cost and ecological considerations. Criteria for CVD, electro deposition, and thermal spraying are given in Table 2 (13). 

The most common plafing bath uses fluoride to complex the fin. A typical solution contains 45 g/L staimous chloride, 300 g/L nickel chloride hexahydrate, and 55 g/L ammonium bifluofide. It is operated at pH 2.0—2.5 usiag ammonium hydroxide temperature is 65—75°C and current about 200 A/m. The bath has excellent throwing power. Air agitation is avoided. The deposit is bright without additives. Anodes are cast nickel, and the fin is replenished by additions of staimous chloride. AHoy anodes of 72% fin have been used to a much lesser extent. Tia-nickel deposits are covered by ASTM (136) and ISO (137) specifications. One other bath based on pyrophosphate has appeared ia the Hterature, but does not seem to be ia commercial use. 

Some electroplating solutions produce more uniform deposits than others, and the ability of a solution to deposit uniform coatings is measured by its throwing power (see Section 12.1). 

On this scale, zero represents the case when M = P, and electrolyte resistance is the main factor. Throwing power can be worse, down to a limit T = - 100% when A/ = oo, i.e. no deposit at all on the far cathode. Conversely, when M < P, T is positive. Were M to reach 1-0 despite the difference in position, 7" = -F 100%. At one time +100% was regarded as an unrealisable limit, but conditions have been found for which T = -f150% in a Haring-Blum cell. 

Deposit uniformity The uniformity of a deposit is an important factor in its overall corrosion resistance and is a function of geometrical factors and the throwing power of the plating solution. A distinction is made here between macro-throwing power, which refers to distribution over relatively large-scale profiles, and micro-throwing power, which relates to smaller irregularities... 

Concern over the health hazards of the hexavalent chromium solutions used to form the top coat of conventional nickel plus chromium coatings have encouraged research into trivalent chromium plating solutions. A process with better throwing power and improved covering power than those of hexavalent chromium has been described by Smart etal". A process for depositing a chromium-iron, or chromium-nickel-iron alloy, has been outlined by Law. ... 

Some bath compositions tend to have the property of decreasing the difference between the thinnest and thickest deposits. In other words, they give rise to uniform cathode coverage despite irregularities. Such solutions are referred to as having good throwing power. 

The ability to cover a surface and to reduce pinhole density in the film is affected by addition agents and deposition waveform. Throwing power, the ability of the depositing material to plate inside a deep, narrow recess, depends on a number of factors, including complexing of the ions, electrode polarization, current density, etc. Additives to increase throwing power are usually organic materials. 

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