Chain polyphosphates tripolyphosphates

Sodium tripolyphosphate is produced by calcination of an intimate mixture of orthophosphate salts containing the correct overall Na/P mole ratio of 1.67. The proportions of the two anhydrous STP phases are controlled by the calcination conditions. Commercial STP typically contain a few percent of tetrasodium pyrophosphate and some trimetaphosphate. A small amount of unconverted orthophosphates and long-chain polyphosphates also may be present. 

A rather different structure-motif is observed in the chain polyphosphates these feature comer-shared PO4 tetrahedra as in the polyphosphoric acids (p. 522). The general formula for such anions is [Pn03 4.i] + , of which the diphosphates, P2O7 ", and tripolyphosphates, PsOjo , constitute the first two members. Chain polyphosphates have been isolated with n up to 10 and with n infinite , but those of intermediate chain length (10 < n < 50) can only be obtained as glassy or amorphous mixtures. As the chain length increases, the ratio (3n + l)/n approaches 3.00 and the formula approaches that of the polymetaphosphates [P03 ]oo-... 

The stoichiometry of the tin(II) and tin(IV) phosphates is controlled by the particular phosphate ion which is complexing to the tin(II) or the tin(IV) ion thus a whole range of pyrophosphates and tripolyphosphates of tin have been detected, and there is a trend for tin(II) to complex long-chain polyphosphates, with average chain lengths up to fourteen". ... 

Sodium hexametaphosphate is one of a series of chain polymers termed polyphosphates, and threshold treatment using various members of the series has found extensive use in controlling calcium carbonate scale formation. Veale [1984] states that typically 5 mg/l of polyphosphate will inhibit the precipitation of 500 mg/l of CaCOy To control scale in sea water evaporation an additive mixture could include sodium tripolyphosphate, lignin sulphonates and an antifoaming agent. 

It should be noted that calcium polyphosphates are often called metaphosphates in the literature and patents, if they have M2O-P2O5 ratios near unity. Throughout this work, the word metaphosphate will be reserved for ring phosphates while chain phosphates will be named polyphosphates. In most modern usage the prefix poly- has unfortunately been dropped from a name. Calcium tripolyphosphate, Ca5(P30io)2, is named calcium triphosphate, which can easily be confused with tricalcium phosphate, Ca3(P04)2, an orthophosphate, by those who only occasionally engage in phosphate chemistry. In this work polyphosphates shall be named polyphosphates, unless reference is made to work where polyphosphates are named without the prefix. Here, they will be named as in the cited literature. 

The condensed phosphates contain more than one phosphorus atom in a molecule but with the structure always built up by PO4 tetrahedra. Whereas in orthophosphates the phosphate tetrahedra are isolated, in condensed phosphates they share corners (but never edges or faces). The larger the O/P ratio in the formula is, the more broken the tetrahedra chains are and the smaller the O/P ratio is, the more cross-linked the chains are (Hong, 1974b). The condensed phosphates can be divided into three groups branched or ultraphosphates cyclic or metaphosphates [P 03 ]" , and chain or polyphosphates [P 03 4i] ". In addition, there is a group of oligophosphates which contain separate anions pyrophosphate, tripolyphosphate, etc., but compounds of the rare earths with these anions have been little studied (Palkina, 1978). The... 

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