Surface treatment metals

In 1864, De Bussey [9a] obtained a patent for the treatment of red-hot iron with a mixture of coal dust and Ca(H2P04)2, in order to secure a degree of corrosion resistance. The earliest patent relating to the phosphoric acid treatment of metal surfaces is that due to Ross [9] in 1869. This British patent refers to the rustprooflng of corset stays by plunging them, red hot, into the acid. In 1906, Cosslett 

Another purpose of phosphate treatment of pipes is to guard against lead poisoning. The use of lead pipes to convey drinking water is now banned in many countries. However, if such lead piping is treated over several months with phosphoric acid (or NaH2P04), a protective buildup of insoluble Pb3(P04)2 is achieved on the inside surface of the pipe. 

Present processes are variously referred to as phosphating, phosphorising or phosphatising, and all involve the formation of relatively insoluble, electrically non-conducting thin films of metallic phosphates on the surface of the metal being treated. A very large and continually growing number of patents now exist in this field. 

Present-day application is mostly to steel and zinc (galvanised steel) products although iron, aluminium, tin and cadmium may also be successfully treated. Principal advantages obtainable from phosphating treatments are 

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Metals treatments Metal sulfides Metal surface cleaners Metal surface treatment Metal surface treatments... 

Corrosion. Ammonium bifluoride dissolves in aqueous solutions to yield the acidic bifluoride ion the pH of a 5% solution is 3.5. In most cases, NH4HF2 solutions react readily with surface oxide coatings on metals thus NH4HF2 is used in pickling solutions (see Metal surface treatments). Many plastics, such as polyethylene, polypropylene, unplasticized PVC, and carbon brick, are resistant to attack by ammonium bifluoride. 

Uses. Alkah metal and ammonium fluoroborates are used mainly for the high temperature fluxing action required by the metals processing industries (see Metal surface treatments Welding). The tendency toward BF dissociation at elevated temperatures inhibits oxidation in magnesium casting and aluminum alloy heat treatment. 

They readily dissolve metal oxides and are effective metal surface cleaners and fluxes (see Metal surface treatments). They also have bactericidal and fungicidal properties (74). However, the main commercial appHcation among monofluorophosphates is of sodium monofluorophosphate ia dentifrices. 

Fluorotitanic acid is used as a metal surface cleaning agent, as a catalyst, and as an aluminum finishing solvent (see Metal surface treatments). Fluorotitanates are used in abrasive grinding wheels and for incorporating titanium into aluminum aHoys (see Abrasives Aluminumand aluminum alloys). 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

Sa.lts Salting out metal chlorides from aqueous solutions by the common ion effect upon addition of HCl is utilized in many practical apphcations. Typical data for ferrous chloride [13478-10-9] FeCl2, potassium chloride [7447-40-7] KCl, and NaCl are shown in Table 9. The properties of the FeCl2-HCL-H2 0 system are important to the steel-pickling industry (see Metal SURFACE TREATMENTS Steel). Other metal chlorides that are salted out by the addition of hydrogen chloride to aqueous solutions include those of magnesium, strontium, and barium. 

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