Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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the chloride-fluoride bath, a pyrophosphate bath came into existence. The bath is stated to operate at lower temperature (~50O C, ~120° F) and near neutral (7.5- 8.5) pH. Unlike the chloride-fluoride bath, the composition of the plated tin-nick- el alloy varies with the contents of individual metals, tin and nickel, in the bath and very little affected with the changes in the pH or the pyrophosphate concentration. The bath composition and the control limits are provided in Table V. The color of the tin-nickel alloy varies with the tin and nickel contents in the pyrophosphate bath. An excellent application of this bath falls in obtaining gun color from tin-nickel alloy plating. The gun color is accomplished by varying and adjusting the tin and nickel contents of the bath till the desired color is achieved. 260

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