Phosphate coatings spray

Paint-base phosphate coatings could be appHed in two to five minutes. In 1934, this time constraint was shortened even further when phosphate solutions were sprayed onto the metal surface. Processing times as short as 60 seconds became possible. 

Product Utilization. The principal appHcation for chromium phosphate coatings is as a paint base for painted aluminum extmsions and aluminum beverage can stock. In these appHcations, extremely demanding performance criteria are met by the chromium phosphate conversion coatings. As an example, the Architectural Aluminum Manufacturer s Association Voluntary Specification 605.2-92 requires humidity and salt spray testing for 3000 hours and allows only minimal incidence of paint failure after testing (26). 

Jaudon tested phosphate coatings with and without paint and found the salt-spray resistance, as judged by the first appearance of rust, to be as follows ... 

The most widely used accelerated tests are based on salt spray, and are covered by several Government Specifications. BS 1391 1952 (recently withdrawn) gives details of a hand-atomiser salt-spray test which employs synthetic sea-water and also of a sulphur-dioxide corrosion test. A continuous salt-spray test is described in ASTM B 117-61 and BS AU 148 Part 2(1969). Phosphate coatings are occasionally tested by continuous salt spray without a sealing oil film and are expected to withstand one or two hours spray without showing signs of rust the value of such a test in cases where sealing is normally undertaken is extremely doubtful. 

The main value of salt-spray tests is in the evaluation of the effectiveness of phosphate coatings in restricting the spread of rust from scratches or other points of damage in a paint film. This feature is of particular interest to the motorcar industry, as vehicles are often exposed to marine atmospheres and to moisture and salt when the latter is used to disperse ice and frost from road surfaces. Great care is needed in the interpretation of a salt-spray test, as it has been found to favour thin iron phosphate coatings more than is justified by experience with natural weathering. In the motorcar industry the present custom is to use zinc phosphate coatings on the car bodies and all other parts exposed to the outside atmosphere. 

Table 15.14 Salt-spray resistance of phosphate coatings under various finishes...

Table 15.13. This specification follows good industrial practice, with additional safeguards in rinsing to remove residues to treatment solutions. Nonaccelerated treatments must be followed by a single rinse which may contain chromate accelerated treatments must be followed by three rinses—cold water, hot water and a final chromate rinse. Table 15.14 shows the salt-spray test requirements for phosphate coatings with various finishes without formation of rust the paints and lacquer have the additional requirement that no rust shall be visible beyond 0-2 in (5 mm) from the deliberate scratches and no blistering, lifting or flaking beyond 0-05 in (1-27 mm) from the original boundaries of the scratches.

The American Aeronautical Material Specification AMS 2480 A calls for 150h salt-spray test without rusting extending more than 0-125 in (3-175 mm) on either side of scratch marks, using a black enamel finish for the phosphate coating. 

In general, paint adhesion and salt spray corrosion inhibition of iron phosphate coatings post-treated with polyvinylphenol derivatives have been equal to or superior to that obtained with chromate based systems. This has been the case particularly with many high solids paints. 

C.P.A.T. Klein, J.G.C. Wolke, J.M.A. de Blieck-Hogervorst, K. de Groot, Calcium phosphate plasma-sprayed coatings and their stability An in vivo study, J. Biomed. Mater. Res. 28 (1994) 909-917. 

Figure 9.43 Raman spectra of plasma sprayed calcium phosphate coating shows the difference in hydroxyapatite content by comparing intensity of the OH stretching band at (a) near substrate (b) in the middle and (c) near the surface of the coating layer.

Leeuwenburgh, S.C.G., Wolke, J.G.C., Schoonman, J., and Jansen, J.A. (2006) Deposition of calcium phosphate coatings with defined chemical properties using the electrostatic spray deposition technique. /. Fur Ceram. Soc., 26 (4-5), 487 —493. 

A review on calcium phosphate coatings produced using a sputter process - an alternative to plasma spraying. Biomaterials, 26 (3), 327-337. 

Table 6.5 Phase contents of as-sprayed calcium phosphate coatings (in mass%) (Figure 6.2a-c).

Figure 7.64 Electron diffraction pattern of amorphous calcium phosphate (ACP) of a plasma-sprayed calcium phosphate coating adjacent to the interface with the Ti6AI4V substrate (Heimann and Wirth, 2006).

Dey, A., Nandi, S.K., Kundu, B., Kumar, C., Mukherjee, P., Roy, S., Mukhapadhyay, A.K., Sinha, M.K., and Basu, P. (2011) Evaluation of hydroxyapatite and B-tricalcium phosphate microplasma spray coated pin intra-medullary for bone repair in a rabbit model. Ceram. Int.,... 

Klein CP AT, Wolke JGC, de Blieck-Hogervorst JMA, de Groot K (1994) Features of calcium phosphate plasma-sprayed coatings An in vitro study. J Biomed Mater Res 28 961-967 Knepper M, Milthorpe BK, Moricca S (1998) Interdiffusion in short-fibre reinforced hydroxylapatite ceramics. J Mater Sci Mater in Med 9 589-596... 

Fig. 1 Photograph of (a) femoral hip stem with (b) inset of the microbeaded surface, (c) Photomicrograph of a plasma-deposited calcium phosphate coating on a hip stem (image kindly provided by Smith Nephew, Memphis, TN, USA), (d) Dental implant with (e) inset showing a titanium plasma-sprayed surface coating...

This process is applied mainly to steel components which are sprayed or dipped in a phosphoric acid solution containing iron, zinc or manganese phosphate. The most common processes use zinc or manganese phosphate and are employed in the treatment of car bodies and domestic appliances before painting. Where long-term corrosion protection is required, the phosphate coating must be sealed with oil lacquer or paint... 

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