Phosphate crystallization

The Zinc Phosphating Process. The zinc phosphating reaction involves acid attack on the substrate metal at microanodes and deposition of phosphate crystals at microcathodes (8). Liberation of hydrogen and the formation of phosphate sludge also occur. The equation for the dissolution of iron together with precipitation of dissolved iron as sludge in a nitrite accelerated system is as foUows ... 

As with chemical etches, developing optimum conversion coatings requires assessment of the microstructure of the steel. Correlations have been found between the microstructure of the substrate material and the nature of the phosphate films formed. Aloru et al. demonstrated that the type of phosphate crystal formed varies with the orientation of the underlying steel crystal lattice [154]. Fig. 32 illustrates the different phosphate crystal morphologies that formed on two heat-treated surfaces. The fine flake structure formed on the tempered martensite surface promotes adhesion more effectively than the knobby protrusions formed on the cold-rolled steel. 

Chitosan scaffolds were reinforced with beta-tricalciiun phosphate and calcium phosphate invert glass [177]. Along the same line, composites of Loligo beta-chitin with octacalcium phosphate or hydroxyapatite were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The octacalciiun phosphate crystals with the usual form of 001 blades grew inside chitin layers preferentially oriented with the 100 faces parallel to the surface of the squid pen and were more stable to hy-... 

Monitor for hypernatremia or hyperkalemia, hypocalcemia, and metastatic soft tissue deposition of calcium-phosphate crystals... 

Following ternary phosphorus oxynitrides, which involve only phosphorus as a cationic element, quaternary and higher oxynitrides will be described. A number of other solid-state PON compounds are under study and, when considering the richness of the phosphate crystal chemistry and the additional degree of freedom given by the presence of nitrogen, it is very probable that many new nitridooxophosphate compositions will be found in the near future. 

Some signs and symptoms of hyperphosphatemia are a result of the low solubility of the calcium-phosphate complexation product. Calcium-phosphate crystals are likely to form when the product of the serum calcium and phosphate concentrations exceeds 50 to 60 mg2/dL2. 

O Sodium phosphate, Na3P04, is sold at hardware stores as TSP (trisodium phosphate). Crystals of Na3P04 are dissolved in water to make an effective cleaning solution. TSP can be used, for example, to prepare a surface before painting. 

In arrested enamel lesions, increased contents of iron (Torell, 1957a) and iron phosphate crystals (Torell, 1957b) have been observed. In pigmented dentin from carious teeth, however, no increase of iron or heavy metals has been found (Malone ef al., 1966). 

In Region IV, performance again increases. Crystallographic transformations in phosphate conversion coatings at 180 C are known to adversely affect phosphate crystal adhesion (26). However, nitrile cyclization may be important at these higHer temperatures. Cyclization is believed to enhance barrier properties of high nitrile polymers (27,28.29). 

While a non-phosphated topcoat/adhesive interface provided an excellent, moisture resistant, occlusive seal even under the most severe cycle testing, phosphated ZM adherends did not prove to be as durable in comparison (Figure 11). The reason for this lies in the fact that phosphate coverage on Zincrometal is incomplete. Partially crystalline phosphates are non-uniformly interspersed on randomly exposed zinc dust spheres at the surface. Consequently, the moisture resistance normally provided at the adhesive/topcoat interface was reduced due to the incomplete sealing between the topcoat/ adhesive surfaces. This became apparent as most of the failures examined after aging in these environments were concentrated at the adhesive/phosphate/paint interface. Results obtained on these samples were similar to those obtained for phosphated CRS joints, indicating that the locus of failure occurred at phosphate crystal sites. Note, however, that the durability of these joints was still considered to be very good in comparison to other metallic oxide/ adhesive interfaces. 

Although chromate is the best aqueous corrosion inhibitor available, its use has been severely curtailed due to toxicity and environmental concerns ( ). One of the more successful non-chromate treatments involves the use of phosphate/phosphonate combinations. This treatment employs high levels of orthophosphate to promote passivation of the metal surfaces. Therefore, it is important to control calcium phosphate crystallization so that high levels of orthophosphate may be maintained in the system without fouling or impeding heat-transfer functions. 

This subcategory involves sodium tripolyphosphate and calcium phosphates. Sodium tripolyphosphate is manufactured by the neutralization of phosphoric acid by soda ash or caustic soda and soda ash, with the subsequent calcining of the dried mono- and disodium phosphate crystals. This product is then slowly cooled or tempered to produce the condensed form of the phosphates. 

Fluidized-Bed Process for Phosphate Removal by Calcium Phosphate Crystallization... 

Calcium phosphate crystallizes on the surface of the seeds by the following equation. 

Lu Taijing, R. B. YaUee, C. K Ong, and 1. Sunagawa, Formation mechanism of tapering of crystals A comparative study between potassium dihydrogen phosphate crystals and natural quartz crystals,/. Crystal Growth, 151,1995,342-7... 

Watson, M. L., Robinson, R. A. Collagen-crystal relationships in bone. II. Electron microscope study of basic calcium phosphate crystals. Amer. J. Anat. 93, 25 (1953)... 

Fleisch, H., Russell, R. G. G., Bisaz, S., Muhlbauer, R. C., Williams, D. A. The inhibitory effect of phosphonates on the formation of calcium phosphate crystals in vitro and on aortic and kidney calcification in vivo. Europ. J. Clin. Invest. 7,12 (1970)... 

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