optimum parameters and concentrations of the bath, and introducing many important additives to speed up the deposition rate and prevent unwanted reactions, such as spontaneous deposition. They also studied the chemistry of the process. In 1969, Harold Edward Bellis from DuPont filed a patent for a general class of processes using sodium borohydride, dimethylamine borane, or sodium hypophosphite, in the presence of thallium salts, thus producing a metal-thallium-boron or metal-thalium-phosphorus; where the metal could be either nickel or cobalt. The boron or phosphorus contents was claimed to be variable from 0.1 to 12%, and that of thallium from 0.5 to 6%. The coatings were claimed to be "an intimate dispersion of hard trinickel boride () or nickel phosphide () in a soft matrix of nickel and thallium". Procedure Surface cleaning Before plating, the surface of the material must be thoroughly cleaned. Unwanted solids left on the surface cause poor plating. Cleaning is usually achieved by a series of chemical baths, including non-polar solvents to remove oils and greases, as well as acids and alkalis to remove oxides, insoluble organics, and other surface contaminants. After applying each bath, the surface must be thoroughly rinsed with water to remove any residue of the cleaning chemicals. Internal stresses in the substrate created by machining or welding can affect the plating. Plating bath The main ingredients of an electroless nickel plating bath are source of nickel cations , usually nickel sulfate and a suitable reducing agent, such as hypophosphite or borohydride . With hypophosphite, the main reaction that produces the nickel plating yields orthophosphite , elemental phosphorus, protons and molecular hydrogen : 2 + 8 + 2 → 2 (s) + 6 + 2 + 2 (s) + 3 (g) This reaction is catalyzed by some metals including cobalt, palladium, rhodium, and nickel itself. Because of the latter, the reaction is auto-catalytic, and proceeds spontaneously once an initial layer of nickel has formed on the surface. The plating bath also often includes: complexing agents, such as carboxylic acids or amines to increase phosphate solubility and to prevent the white-out phenomena by slowing the reaction. stabilizers, such as lead salts, sulfur compounds, or various organic compounds, to slow the reduction by co-depositing with the nickel. buffers, to maintain the acidity of the bath. Many complexing agents act as buffers. brighteners, such as cadmium salts or certain organic compounds, to improve the surface finish. They are