Calcium orthophosphates,

Phospha.tes. Many phosphates cl aim unique material advantages over siUcates that make them worth the higher material costs for certain apphcations. Glass-ceramics containing the calcium orthophosphate apatite, for example, have demonstrated good biocompatibiUty and, in some cases even bioactivity (the abiUty to bond with bone) (25). Recent combinations of fluorapatite with phlogopite mica provide bioactivity as well as machinability and show promise as surgical implants (26). 

Fig. 12. Phase diagram of the CaO—H2O—P20 (calcium orthophosphate) system where the circle represents the variable hydroxylapatite composition and...

Precipita.tingInhibitors. As discussed earlier, the localized pH at the cathode of the corrosion cell is elevated due to the generation of hydroxide ions. Precipitating inhibitors form complexes that are insoluble at this high pH (1—2 pH units above bulk water), but whose deposition can be controlled at the bulk water pH (typically 7—9 pH). A good example is zinc, which can precipitate as hydroxide, carbonate, or phosphate. Calcium carbonate and calcium orthophosphate are also precipitating inhibitors. Orthophosphate thus exhibits a dual mechanism, acting as both an anodic passivator and a cathodic precipitator. 

Phosphate is sometimes present in MU water sources (say, 1-2 ppm or more) usually as a result of field and factory run-off or from the deliberate addition as a city water threshold agent to prevent corrosion and deposition in the mains. The steady growth in the reuse of secondary water sources such as municipal and industrial waste waters means that phosphate is increasingly likely to be present in MU. If the phosphate remains undetected, it likely will scale and foul FW lines by forming amorphous calcium orthophosphate [tricalcium phosphate Caj(P04)2] sludge before it reaches the boiler section. 

Oxide glasses have been reported by Crisp Wilson (1978a,b, 1979), Wilson et al. (1980), and Hill Wilson (1988a). The fusion mixtures contain silica, alumina and calcium carbonate to which sodium carbonate or calcium orthophosphate may be added. They may be represented thus, with fusion temperature given in parentheses ... 

In fluoride glasses, calcium fluoride is an essential constituent, but generally cryolite, NajAlFg, is also added as a flux to lower the temperature of fusion. Aluminium orthophosphate is also generally added to the fusion mixture for various reasons. Of course, the various elements may be added in different ways. Thus, calcium orthophosphate, aluminium fluoride and sodium carbonate are often used in the preparation of fluoride glasses. 

The disadvantage of the polyphosphates is that at the temperatures (100 °C or higher) used in many textile processes they can be hydrolysed into simpler phosphates that cannot retain the metal atom in the sequestered form. For example, dicalcium disodium hexametaphosphate hydrolyses on prolonged boiling to yield the insoluble calcium orthophosphate. This is one of the main reasons why polyphosphate sequestrants are used much less extensively than the more versatile and stable aminopolycarboxylates. 

Elliott, J. C. "Structure and Chemistry of the Apatites and Other Calcium Orthophosphates Elsevier Amsterdam, 1994. 

Synonyms calcium orthophosphate calcium phosphate tricalcium phosphate tertiary calcium phosphate precipitated calcium phosphate bone ash (technical product). 

J.C. Elliott, Stmcture and chemistry of the apatites and other calcium orthophosphates, in Studies in Inorganic Chemistry, Vol. 18. Elsevier, Amsterdam, 1994. 

BAKERY PROCESSES AND LEAVENING AGENTS - YEAST-RAISED PRODUCTS] (Vol 3) -calcium orthophosphates m [PHOSPHORIC ACID AND PHOSPHATES] (Vol 18)... 

J. T. Meckstroth 22 showed that the largest use for phosphoric acid is in sugar defecation. It is also used in the manufacture of jellies, preserves, and soft drinks in pharmaceutical preparations and in the rust-proofing of iron. The chief phosphates in industry are the calcium hydrophosphates used in making baking-powder, and self-rising flour sodium phosphates used in making boiler compounds, in laundry work, etc. The superphosphates are used in fertilizers. Calcium orthophosphate is the form of bone ash extensively used in the manufacture of bone china. 

Calcium phosphate will ordinarily precipitate at concentrations typically exceeding 5 ppm PO4 or less, forming amorphous calcium orthophosphate (tricalcium phosphate) sludge, Ca3(P04>2, in the bulk water and crystalline hydroxyapatite, Caio(OH)2(P04)2, at heat-transfer surfaces. 

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