Nickel coatings application

The application of the tin-nickel coating for out of doors service has been restricted by fear of pore corrosion and of physical damage, and by... 

Resistance to abrasion The resistance to abrasion of electroless nickel-phosphorus hardened to 600 Hy, assessed by Taber abrasion tests, has been found to be double that of electroplated nickel However, electroless nickel coatings are not suitable for applications where two electroless nickel surfaces rub together without lubrication unless the values of hardness are made to differ by over 200 Hy units. Galling of aluminium, titanium or stainless steel may be overcome by applying electroless nickel to one of the two mating surfaces. 

Decorative coatings It is impossible to give a comprehensive list of the uses of nickel coatings but applications of decorative nickel coatings, usually with a chromium top-coat, are given below ... 

For new components, the nickel coating is usually 25-250 im thick. Normally, the deposits are not machined. Applications include pump bodies, laundry plates, heat exchanger plates, evaporator tubes, alkaline battery cases and food-handling equipment of various sorts. 

When the direct-on process is utilized, surface preparation requirements are more critical to ensure effective enamel adhesion. The acid etch is often deeper and the nickel deposition is always thicker. Typically, the nickel coating is 0.01 to 0.02 g/m2 for direct-on coating as compared to 0.002 to 0.007 g/m2 for two-coat applications. A few porcelain enamelers prefer to omit the nickel deposition step. Although the nickel enhances enamel bonding, product quality requirements may not require nickel deposition. The omission of the nickel step necessitates the utilization of a heavy acid etch to ensure a clean, properly conditioned surface for enamel bonding.3-6... 

Water rinses are used in surface preparation operations such as acid pickling, alkaline cleaning, and nickel deposition to remove any process solution film left from the previous bath. A water rinse may also follow the neutralization step. Another common water use is in the ball milling process, which uses water as the vehicle for the enamel ingredients, as a cooling medium, and for cleaning the equipment. Coating application processes normally use wet spray booths to capture oversprayed enamel particles. Water wash spray booths use a water curtain into which the enamel particles are blown and captured. 

Watts bath — The Watts bath is the classical electrolyte for the -> electrodeposition of functional nickel coatings. It contains nickel sulfate (240-450 gL-1 of the hexahy-drate), nickel chloride (45-90 gL-1 of the hexahydrate), and boric acid (30-50 g L-1) and is usually operated between pH 2 and 4.5 and at 40-70 °C. The chloride content of the bath is crucial to ensure the dissolution of the nickel anode. In combination with - leveling agents and brighteners the Watts bath is also used for decorative nickel coatings. Its applicability for -> electroforming is limited due to tensile stresses in the deposits. 

An interesting coatings application for lecithin is in producing nonpyrophoric Raney nickel (339). The lecithin in this application creates a lipophilic surface on the metal, along with a wax, fat, or organic polymer. 

VaporFab - nickel coated carbon fiber by a chemical vapor deposition process for EMI shielding applications... 

X-ray radiography of nickel-coated fibers, surface atoms of hydroxyapatite, coating analysis of silane treated hydroxyapatite, and composition of the failure area of an adhesive joint between rubber and metal. This review of applications shows that carbon fibers are the most frequently tested material by XPS. 

For industrial use, nickel coatings are applied without chromium on top, and the coatings are most often thicker, usually 25-250 pm, and up to 500 pm for some applications. Such coatings are most suitable for environments that tend to cause general corrosion with reaction products of low solubility (environments without chlorides). However, it is also stated that nickel performs well in seawater provided that the flow rate is high. Furthermore, the experience with nickel in various alkalis, neutral and alkaline salts and organic chemicals is good. 

Electrochemical deposition (electroplating) has traditionally been, and is still, the dominating technique for application of nickel coatings. In recent years, the number of applications of chemical (electroless) deposits of nickel has been growing (parts in pumps, valves, compressors, storage vessels for chemicals etc). 

The overall scheme employed to pretreat unfilled polyetherimide substrates utilizing nitric acid as the impiegnator is given in Table IV. Unfilled polyetherimide substrates could be plated on all sides without delamination when this pretreatment scheme was employed. Furthermore, excellent adhesion was obtained for either an initial copper or nickel coating. Table V. Application of cathodic charging techniques to impregnator-pretreated polyetherimide... 

Similar studies on nickel-coated polyetherimide indicated that only the first two regions were present. Thermal deterioration of the nickel/polymer bond, region C, was not observed after 3000 hrs at 175 C. This indicates that nickel is superior to copper for prolonged high temperature applications. 

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