Polyphosphates crystalline alkali

A comparative study of the products of dehydration of the dihydrogen monophosphates of polyvalent cations showed that the stable end-products for cations with ionic radii between 0.57 and 1.03 A. (Cu++, Mg++, Ni++, Co++, Fe++, Mn++, Zn"1-1", Cd++, A1+++) are tetrametaphosphates. When the cations are either larger or smaller the end-products of dehydration are crystalline high-molecular polyphosphates (Li+, Be++, K+, Rb+, Cs+, Ag+, Zn++, Cd++, Hg++, Ca++, Sr++, Ba++ Pb++, Cr+++, Fe+++, Bi+++). In the case of the alkali salts only sodium trimetaphosphate occurs as a condensed phosphate with a cyclic anion (304, 305). Up to the present, an alkali tctrametaphosphate has not been observed as the dehydration product of a dihydrogen monophosphate. Consequently, alkali tetrametaphosphates arc obtainable only indirectly. Reference is made later (Section IV,C,4) to the fact that the tetraphosphates of barium, lead, and bismuth are formed as crystalline phases from melts of the corresponding composition. There are also reports of various forms of several condensed phosphates of tervalent iron and aluminum (31, 242, 369). 

A range of high-molecular alkali polyphosphates occur in several crystalline forms. In the case of the sodium and potassium compounds the trivial names Maddrell s and Kurrol s salts have been adopted and these... 

Phosphorus has an even wider range of oxoacid chemistry, and a commensurately wide range of phosphates, phosphites, polyphosphates, hypophosphites, and so on of the alkali metals are preparable. Sodium and potassium are the most common cations used, largely because of their availability and low cost. The cation often has little effect on the properties and applications, which are covered in Phosphates Solid-state Chemistry. Most form a variety of crystalline hydrates, which have been well covered in previous treatments and need not be repeated here. Trae to form, lithium is the exception, forming no stable hydrates with phosphorus oxoanions. 

Alkali metal and alkaline earth polyphosphates crystallize as short chains, two to six phosphate groups per chain or very long chains with hundreds to thousands of PO3 per chain. All polyphosphates in the alkali metal and alkaline earth systems are amorphous in the intermediate chain lengths. Control of the short chain length polyphosphates, both crystalline or amorphous, is a function of R, the M2O-P2O5 ratio. The control of the chain lengths of very long crystalline polyphosphates as Maddrell s salt, Kurrol s salt, and calcium phosphate fibers is not well understood. 

Almost all metal cations will react with alkali metal polyphosphate solutions to form insoluble precipitates. Most of these are soluble in excess of polyphosphate as a result of complex ion formation. Polarographic and conductivity studies indicate the existence, in dilute solutions, of several complex pyrophosphate and triphosphate anions. These include (MP207) , where M = Cu, Co, Cd, Pb, Mg, Ni, Zn, and (MP2O7), where M = Al, Fe. Some crystalline double salts of type MM P207 which can be isolated are probably more correctly formulated as M+(M P207). ... 

Heating alkali metal or alkaline earth metal dihydrogen phosphates produces polymeric salts (cyclic metaphosphates and linear polyphosphates) and cross-linked polyphosphates (ultraphosphates), depending on temperature and the presence of other ingredients (11,12). This complex group of polymers includes materials with crystalline, glass-like, fibrous, or ceramic properties as well as some with thermoplastic and thermoset characteristics some are useful as binders for metals, ceramics, and dental restorations. Reviews are available on glasses (12,13), crystalline compounds (14), and polyphosphate fibers (15). 

From Example 1 above = 18/16 = 1.125, and when the crystallization was completed = 16/16 = 1.0. From equations (3.27), (3.28), and (3.29), y = 0.833, z = 1.667, and the percent amorphous phase is 94.3% of the weight of the sample or 5.7% of an enamel of this composition should be crystalline AIPO4. The glassy phase should be very long chain polyphosphates, with n approaching as high as 300 perhaps. This assumes that the system will behave similarly to amorphous alkali metal polyphosphates in this respect. 

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