Aluminium phosphates

Of the phosphorus-containing polymers the polyphosphates have been known for many years. Aluminium phosphate had been used in the manufacture of heat-resistant silica-fibre-reinforced laminates. 

Adsorption. The adsorption of the components of a vaccine on to a mineral adjuvant. The mineral adjuvants, or carriers, most often used are aluminium lydroxide, aluminium phosphate and calcium phosphate and their effect is to increase the immunogenieity and decrease the toxicity, local and systemic, of a vaccine. Diphtheria vaccine, tetanus vaccine, diphtheria/tetanus vaccine and diphtheriaAetanus/pertussis vaccine are generally prepared as adsorbed vaccines. 

Presence of aluminium and calcium. The quantity of aluminium in vaccines containing aluminium hydroxide or aluminium phosphate as an adjuvant is limited to 1.25 mg per dose and it is nsnally estimated compleximetrically. The qnantity of calcium is limited to 1.3 mg per dose and is usually estimated by flame photometry. 

A novel basic support and catalyst have been prepared by activation of aluminium phosphate with ammonia. Fine control of time and temperature allows to adjust the 0/N ratio of these oxynitride solids and thus to tune the acid-base properties. The aluminophosphate oxynitrides are active in Knoevenagel condensation, but a basicity range can not yet determined. Supporting Pt or Pt/Sn on AlPONs allows to prepare catalysts that are highly active and selective in dehydrogenation reactions. 

Wilson, Prosser Powis (1983) studied the adsorption of polyacrylate on hydroxyapatite using infrared and chemical methods. They observed an exchange of ions and concluded that polyacrylate displaced surface phosphate and calcium, and entered the hydroxyapatite structure itself (Figure 5.2). They postulated that an intermediate layer of calcium and aluminium phosphates and polyacrylates must be formed at the cement-... 

We have noted earlier that aluminium is unusual in forming alumino-phosphate complexes in phosphoric acid solution which may be of a polymeric nature. Bearing in mind the analogies between aluminium phosphate and silica structures, it may well be that during cement formation an aluminium phosphate hydrogel is formed. Its character may be analogous to that of silica gel, where a structure is built up by the... 

It is interesting that this cement has been known for over 100 years and yet certain features of its chemistry remain obscure. The exact nature of the matrix is still a matter for conjecture. It is known that the principal phase is amorphous, as a result of the presence of aluminium in the liquid. It is also known that after a lapse of time, crystallites sometimes form on the surface of the cement. A cement gel may be likened to a glass and this process of crystallization could be likened to the devitrification of a glass. Therefore, it is reasonable to suppose that the gel matrix is a zinc aluminophosphate and that entry of aluminium into the zinc phosphate matrix causes disorder and prevents crystallization. It is not so easy to accept the alternative explanation that there are two amorphous phases, one of aluminium phosphate and the other of zinc phosphate. This is because it is difficult to see how aluminium could act in this case to prevent zinc phosphate from crystallizing. 

As we have seen in Section 6.2, there is some evidence for supposing that zinc phosphate cements contain an amorphous aluminium phosphate or zinc aluminophosphate phase. Also, as we shall see in Section 6.5, amorphous aluminium phosphate is the binding matrix of dental silicate cement. 

The first period of development ended with the research of Wright (1919) who published the results of an extensive survey of cements prepared from experimental SiOj-AljOj-CaO glasses and orthophos-phoric acid solutions containing aluminium phosphate. By this time the main cement formulations had been established. Between 1919 and 1950 only minor improvements were attempted these were of a technological nature and unsuccessful. 

The setting reaction of dental silicate cement was not understood until 1970. An early opinion, that of Steenbock (quoted by Voelker, 1916a,b), was that setting was due to the formation of calcium and aluminium phosphates. Later, Ray (1934) attributed setting to the gelation of silicic acid, and this became the received opinion (Skinner Phillips, 1960). Wilson Batchelor (1968) disagreed and concluded from a study of the acid solubility that the dental silicate cement matrix could not be composed of silica gel but instead could be a silico-phosphate gel. However, infrared spectroscopy failed to detect the presence of P-O-Si and P-O-P bonds (Wilson Mesley, 1968). 

The nature of the setting reaction was finally elucidated by Wilson et al. (1970a), who established that formation of an aluminium phosphate gel was responsible although siliceous gel was also formed it merely coated the partly reacted glass particles. 

The following account is based mainly on the studies of Wilson and coworkers, with some re-interpretation of experimental data. The composition of the cement used is given in Table 6.9. In brief, the reaction takes place in several overlapping stages extraction of ions from the glass, migration of cations into the aqueous phase, precipitation of insoluble salts as pH increases, leading to formation of an aluminium phosphate gel. 

In the subsequent hardening phase, precipitation and hydration continue. The set cement consists, essentially, of partly-reacted glass particles embedded in an aluminium phosphate gel. The morphology of the filler particles is one where a glass core is sheathed by silica gel. 

Bjerrum, N. Dahm, C. R. (1931). Studies on aluminium phosphate. I. Complex formation in acid solution. Zeitschrift fur physikalische Chemie, Bodenstein Festband 627-37 Chemical Abstracts, 26, 666). 

Genge, J. A. R. Salmon, J. E. (1959). Aluminium phosphates. Part III. Complex formation between tervalent metals and orthophosphoric acid. Journal of the Chemical Society, 1459-63. 

The senior author first became interested in acid-base cements in 1964 when he undertook to examine the deficiencies of the dental silicate cement with a view to improving performance. At that time there was much concern by both dental surgeon and patient at the failure of this aesthetic material which was used to restore front teeth. Indeed, at the time, one correspondent commenting on this problem to a newspaper remarked that although mankind had solved the problem of nuclear energy the same could not be said of the restoration of front teeth. At the time it was supposed that the dental silicate cement was, as its name implied, a silicate cement which set by the formation of silica gel. Structural studies at the Laboratory of the Government Chemist (LGC) soon proved that this view was incorrect and that the cement set by formation of an amorphous aluminium phosphate salt. Thus we became aware of and intrigued by a class of materials that set by an acid-base reaction. It appeared that there was endless scope for the formulation of novel materials based on this concept. And so it proved. 

Aluminium borohydride Aluminium chloride Aluminium chlorate Ammonium tetrachloroaluminate Aluminium fluoride Aluminium trihydroxide Aluminium ammonium sulphate Aluminium potassium sulphate Aluminium nitride Aluminium nitrate Sodium aluminate Aluminium sodium aluminate Aluminium phosphate Aluminium phosphide Aluminium borate Aluminium oxychloride Aluminium fluorosilicate Aluminium magnesium silicate Aluminium sulphate... 

C. K. Jones, D. A. Williams, and C. C. Blair. Gelling agents comprising aluminium phosphate compounds. Patent GB 2326882, 1999. 

Although commonly formed from endogenous material, the occurrence of synovial crystals formed following environmental exposure to exogenous agents is indicated by the identification of both aluminium phosphate and aluminium silicate particulates (Netter etal., 1983, 1991). It is noteworthy in this context that arthritic symptoms have been reported following the... 

According to previous analyses of these paintings, the colour layers contain a high concentration of phosphorus (in the order of units of per cent) [40] this led restorers to the assumption that they contain casein which was ruled out by our detailed analysis. Thus, a high concentration of phosphorus coming from the proteinaceous binder is excluded because of the low concentration of phosphorus in the most phosphorylated binder (casein, max. 5% phosphoms) and the amount in the colour layer (up to 10%).The source of phosphorus was discovered by powder X-ray microdifffaction it comes from aluminium phosphate that was probably used as a substrate for the precipitation of red organic lake [40],... 

Uranium coprecipitated with aluminium phosphate, precipitate dissolved in nitric acid Adsorption onto colloidal ferric hydroxide... 

Monocalcium phosphate monohydrate reacts almost as quickly as cream of tartar (potassium acid tartrate). Anhydrous monocalcium phosphate has four-fifths of the reactivity. At ambient temperatures dicalcium phosphate dihydrate, sodium aluminium phosphate and some grades of sodium acid pyrophosphate are essentially unreactive. 

At baking temperatures the other acidulants start to dissolve so that sodium aluminium phosphate reacts midway through the baking cycle while dicalcium phosphate is insoluble until 80°C but then triggers a late release of carbon dioxide, which prevents dips in the middle of cakes or collapses. 

A number of mineral-based substances display an adjuvant effect. Although calcium phosphate, calcium chloride and salts of various metals (e.g. zinc sulfate and cerium nitrate) display some effect, aluminium-based substances are by far the most potent. Most commonly employed are aluminium hydroxide and aluminium phosphate (Table 13.13). Their adjuvanticity, coupled to their proven safety, render them particularly valuable in the preparation of vaccines for young children. They have been incorporated into millions of doses of such vaccine products so far. 

---