Sodium metaphosphates NaPOj

The rate-determining step for the sodium salt has been identified [73] as a surface process below 470 K ( , = 158 kJ mol" ) and, above 470 K, the diffiision of H2O becomes controlling. Sodium metaphosphate, NaPOj, is formed only above 510 K. 

Other abrasives include dicalcium phosphate dihydrate (CaHP04 2H2O), which is not stable in toothpaste formulations and converts into CaHP04 which is much harder. Nevertheless, CaHP04 2H2O can be stabilized by addition of tetrasodium pyrophosphate. Insoluble sodium metaphosphate ((NaPOj) ), calcium pyrophosphate (Ca2P207), and sodium bicarbonate may also be encountered in toothpaste formulations. 

Chemical Designations - Synonyms Sodium phosphate is generic term and includes the following (1) monosodium phosphate (MSP sodium phospWe, monobasic), (2) disodium phosphate (DSP sodium phosphate dibasic), (3) trisodium phosphate (TSP sodium phosphate, tribasic), (4) sodium acid pyrophosphate (ASPP SAPP disodium pyrophosphate (TSPP), (6) sodium metaphosphate (insoluble sodium metaphosphate), (7) sodium trimetaphosphate, and (9) sodium tripolyphosphate (STPP TPP) Chemical Formula (1) NaHjPO (2) Na HPO (3) NajPO (4) Na H P O, (5) Na P O, (6) (NaPOj) (7) (NaP03)3 (8) (NaP03) NaO (9) Na,P30,o. 

Individual Lux acids derived from B2O3 (borax) and P2O5 (sodium metaphosphate) are interesting since they are often used as acidic components of different fluxes. Delimarsky and Andreeva determined PbO solubility in molten NaPOj at 720 C by isothermal saturation method with the potentiometric control of saturation. The concentration cell with oxygen electrodes Pt(02) was used. PbO solubility was estimated as 31.6 mol%. 

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