Orthophosphates stabilization

Orthophosphates. Expls characterized by the evolution of N on heating may be effectively stabilized by the addition of approx 1% of a neutral mixt of alkali metal dihydrogen orthophosphate (ie, NaH2PC>4) and dialkali metal hydrogen orthophosphate (ie, Na2 HPO4)... 

Fixation in 6-12 hours with a mixture of sodium hydroxide and trisodium orthophosphate, a metering device being necessary. This method is recommended for regenerated cellulosic fibres. This formulation contains the same total amount of alkali as method (1) with the same bath stability, but may be preferred where some buffering capacity is required and sodium silicate is undesirable. 

The stabilization reaction for essentially all ash systems likely involves solubilization of the available fraction, contact between the orthophosphate and the element to be stabilized via either (1) solution phase precipitation by... 

Low-temperature treatment of low-level mixed wastes has also been accomplished by solidification/stabilization with chemically bonded phosphate ceramics (CBPC). These are made by hydrothermal chemical reaction rather than by sintering. Chemical bonding develops when acid phosphates react with oxides to form crystalline orthophosphate (Singh et al. 1997). The ceramic matrix stabilizes the wastes by microencapsulation. The low temperature of the reaction allows volatile radionuclides to be treated (Singh et al. 1997). 

Nriagu, J. O. 1973a. Lead orthophosphates. II stability of chloropyromorphite at 25 °C. Geochimica Cosmochimica Acta, 37, 367-377. 

Additives. Orthophosphates, and less frequently citrates, have long been used commercially to increase the stability of concentrated milk. The mechanism was believed to involve Ca-chelation but pH adjustments may be the principal mechanism. 

Indium orthophosphate is essentially insoluble in water, but salts of [In(P04)2]3- and [In2(P04)4]6- have been prepared,163 and a solution phase complex with the H2POj anion has been identified.164 The coordination chemistry of In3+ with the higher phosphates is at present ill defined. Stability constant measurements,9 and preparative and spectroscopic studies7 suggest that In06 is the central core of the compounds in the solid state. The same appears to be true for the complexes reported for L = fluorophosphate,165 methylphosphonate,166 dichlorophosphate,167 dimethylthiophosphate,168 diethylthiophosphinate169,170 and diisopropyl-methylphosphonate.171... 

These reactions are reversible, and removal of the caustic alkali by addition of acids effects the immediate conversion of ortho- or pyro-salts into the meta-salts. On the other hand, the presence of a large excess of caustic alkali favours the formation of the ortho- and pyro-salts. The order of stability is the reverse of that which applies to the ortho-, pyro-, and meta-phosphates. Orthophosphates are prepared from the other two classes either by boiling or by addition of weak acids. 

E.Whitworth Sc J.C.Hornel, USP 2470733(1949) CA 43,5594(1949) (Blasting expls are stabilized by addn of approx 1% of a neutral mixt of alk metal dihydrogen orthophosphate dialkali metal hydrogen orthophosphate)... 

In many hard-working cooling systems where orthophosphate is present without adequate stabilizing dispersant, tricalcium phosphate initially forms, often with variable water of crystallization and together with other calcium phosphate salts. These salts gradually change, under high alkalinity and temperature conditions, into the even more insoluble hydroxyapatite. 

In the studies of mechanochemical synthesis of hydroxylapatite from the mixtures of calcium orthophosphates and oxides, Chaikina demonstrated that the synthesis rate is changed depending on the type of phosphate complex the more protons in the complex, the higher the reaction rate. It was demonstrated that water molecules, being one of the structural components of the intermediate phase, stabilize it, that makes the rate of the formation of this phase dependent on the amount of bound water in the mixture [39 ]. 

A variety of other plots have been found useful for predicting unknown data and appraising published data. Figure 8 shows stability constants for metal orthophosphate complexes as a function of decreasing valence of the H P0 ligand (n = 0-3). ... 

Fig. 9. Thermal stability of some aluminum orthophosphates. The phases are numbered in the different circles according to Table IV, and the other numbers are temperatures (in °C) [reprinted with permission from Kniep (i4) copyright 1986 Wiley-VCH].

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