exposed to highly corrosive acidic environments such as oil drilling and coal mining. Their hardness mat score up to 600 on Vickers test. Surface finish Electroless nickel plating can have a matte, semi-bright, or bright finish. Structure Electroless nickel-phosphorus coatings with less than 7% phosphorus are solid solutions with a microcrystalline structure, with each grain 2–6 nm across. Coatings with more than 10% phosphorus are amorphous. Between these two limits, the coating is a mixture of amorphous and microcrystalline materials. Physical properties The melting point of the nickel-phosphorus alloy deposited by the EN process is significantly lower than that of pure nickel (1445 °C), and decreases as the phosphorus content increases, down to 890 °C at about 14% P. The magnetic properties of the coatings decrease with increasing phosphorus contents. Coatings with more than 11.2% P are non-magnetic. Solderability of low-phosphorus coatings is good, but decreases with increasing P contents. Porosity decreases as the phosphorus contents increases, while hardness, wear resistance, and resistance to corrosion increase. Applications Electroless nickel-phosphorus is used when wear resistance, hardness and corrosion protection are required. Applications include oilfield valves, rotors, drive shafts, paper handling equipment, fuel rails, optical surfaces for diamond turning, door knobs, kitchen utensils, bathroom fixtures, electrical/mechanical tools and office equipment. Due to the high hardness of the coating, it can be used to salvage worn parts. Coatings of 25 to 100 micrometers can be applied and machined back to the final dimensions. Its uniform deposition profile means it can be applied to complex components not readily suited to other hard-wearing coatings like hard chromium. It is also used extensively in the manufacture of hard disk drives, as a way of providing an atomically smooth coating to the aluminium disks. The magnetic layers are then deposited on top of this film, usually by sputtering and finishing with protective carbon and lubrication layers. Its use in the automotive industry for wear resistance has increased significantly. However, it is important to recognize that only End of Life Vehicles Directive or RoHS compliant process types (free from heavy metal stabilizers) may be used for these applications. Printed circuit boards Electroless nickel plating, covered by a thin layer of gold, is used in the manufacture of printed circuit boards (PCBs), to avoid oxidation and improving the solderability of copper contacts and plated through holes and vias. The gold is typically applied by quick immersion in a solution