Phosphates, crystalline

A large number of crystalline phosphates contain two or more cations, and many phosphate minerals are mixed metal salts. 

Analysis. Excellent reviews of phosphate analysis are available (28). SoHds characterization methods such as x-ray powder diffraction (xrd) and thermal gravimetric analysis (tga) are used for the identification of individual crystalline phosphates, either alone or in mixtures. These techniques, along with elemental analysis and phosphate species deterrnination, are used to identify unknown phosphates and their mixtures. Particle size analysis, surface area, microscopy, and other standard soHds characterizations are useful in relating soHds properties to performance. SoHd-state nmr is used with increasing frequency. 

Phosphorus is the eleventh element in order of abundance in crustal rocks of the earth and it occurs there to the extent of 1120 ppm (cf. H 1520 ppm, Mn 1060 ppm). All its known terrestrial minerals are orthophosphates though the reduced phosphide mineral schrieber-site (Fe,Ni)3P occurs in most iron meteorites. Some 200 crystalline phosphate minerals have been described, but by far the major amount of P occurs in a single mineral family, the apatites, and these are the only ones of industrial importance, the others being rare curiosities. Apatites (p. 523) have the idealized general formula 3Ca3(P04)2.CaX2, that is Caio(P04)6X2, and common members are fluorapatite Ca5(P04)3p, chloroapatite Ca5(P04)3Cl, and hydroxyapatite Ca5(P04)3(0H). In addition, there are vast deposits of amorphous phosphate rock, phosphorite, which approximates in composition to fluoroapatite. " These deposits are widely... 

Table 6.5. Crystalline phosphate species found in magnesium phosphate cements...

While a non-phosphated topcoat/adhesive interface provided an excellent, moisture resistant, occlusive seal even under the most severe cycle testing, phosphated ZM adherends did not prove to be as durable in comparison (Figure 11). The reason for this lies in the fact that phosphate coverage on Zincrometal is incomplete. Partially crystalline phosphates are non-uniformly interspersed on randomly exposed zinc dust spheres at the surface. Consequently, the moisture resistance normally provided at the adhesive/topcoat interface was reduced due to the incomplete sealing between the topcoat/ adhesive surfaces. This became apparent as most of the failures examined after aging in these environments were concentrated at the adhesive/phosphate/paint interface. Results obtained on these samples were similar to those obtained for phosphated CRS joints, indicating that the locus of failure occurred at phosphate crystal sites. Note, however, that the durability of these joints was still considered to be very good in comparison to other metallic oxide/ adhesive interfaces. 

Solubility of Crystalline Phosphates as Poly-energetical Conjugation Property... 

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. 

In forming CBPCs, this dissociation is essential. The cations formed by dissociation react with phosphate anions that are present in the aqueous solution and form phosphate salt molecules. These salt molecules connect to each other and form a network and consolidate into a crystalline phosphate ceramic. Thus, success in forming CBPCs lies mainly in successfully dissociating sparsely soluble oxides in acidic solutions and precipitating salt in crystalline form. We wiU discuss the fundamentals of this dissociation in the next several chapters and present methods of dissociating various oxides in phosphate solutions to form ceramics. 

Biogenic polyamines are long linear chains composed of 3 or more amino groups interconnected by methylene bridges (CH2)n where n typically is 3-5. Spermine is a quintessential example, isolated as its crystalline phosphate salt from human sperm by Anton van Leeuwenhoek in 1678. Spermine, and its bio-genetic precursor spermidine, occur in almost all tissues and they play a major role in the modulation of calcium-dependent immune processes and in cell differentiation and proliferation. The discovery that polyamines are structural components of potent spider neurotoxins has lent a certain frisson to their synthesis and it has elevated one of the dullest groups of natural compounds an aura of interest. 

The chemical shifts for the crystalline phosphates follow the broad trends shown schematically in Figure 7.20, but the overlaps in such a diagram make it suitable for determining only the broader aspects of phosphate structure rather than the structural details. 

Figure 7.20. Schematic diagram of the range of P chemical shifts in crystalline phosphate and aluminophosphate phases. The Q° range refers to the alkali and alkaline earth orthophosphates, Q denotes the end groups, the middle and ring groups and the branching groups in these compounds. The upper three bands refer to aluminophosphates, including those of the alkali and alkaline earth metals. From data of Turner et al. (1986a).

A method is being developed to transform actinide ions in the near surface environment to less soluble, less reactive, thermodynamically stable phosphate minerals phases through application of organophosphorus complexants. These complexants decompose slowly, releasing phosphate to promote the formation of stable phosphate mineral phases, particularly with the more soluble trivalent, pentavalent, and hexavalent actinide ions. The complexant of choice, myo-inositol(hexakisphosphoric acid) or phytic acid, is a natural product widely used as a nutritional supplement. We have determined that phytic acid decomposes slowly in the absence of microbiological effects, that crystalline phosphate minerals are formed as a consequence of its decomposition, and that the formation of actinide (lanthanide) phosphates reduces the solubility of trivalent and hexavalent metal ions under environmental conditions. 

Parallel experiments with uranyl-phytate mixtures produced a uranyl phosphate solid identified as (U02)3(P04)2 H20 by X-ray powder diffraction (2i), not U02HP04 nH20 as expected. Neither crystalline phosphates nor phytates, were observed in the thorium-phytate mixtures, although amorphous thorium phytates were likely present initially. Hydroxide or oxide species seem to control thorium solubility. 

Surface treatment of a filler may also affect crystallinity. Phosphate coating on talc increased the crystallinity at a low concentration of coating (up to 0.5%). But there was a decrease in crystallinity when the talc was coated with higher concentrations of phosphate. ... 

Broensted and Lewis acid sites in crystalline phosphates, silicates and in gels with moleculeu sieve properties were studied by IR-spectroscopy. Two types of bridged hydroxyls were fovmd in SAPO-5 which were accessible to adsorbed molecules and were able to interact with ethylene. Lewis sites in metallophosphates, zirconosilicate and in Ti-containing silica gel were observed which did not interact with weak bases (CO, hydrogen) but formed strong complexes with acetonitrile. They were supposed to be framework metal ions in tetrahedral coordination. 

LEWIS ACID SITES IN CRYSTALLINE PHOSPHATES, ZIRCONOSILICATE AND IN Ti-CONTAINING SILICA GELS. 

In vertebrates, 99% of the total body calcium (1.0-1.3 kg in adult humans see Hlu-chan and Pomerantz 2002) is confined to bone, where it exists predominantly as crystalline phosphate salt in the form of hydroxyapatite [Caio(P04)6(OH)2]. To a minor extent, calcium in bone is bound to carbonate and citrate. The remaining 1% of total body calcium is unevenly distributed between the extra- and intracellular fluids. The total extracellular calcium is in the mil-limolar range thus, the mean plasma Ca " concentration in healthy individuals is 2.5 x 10 M, of which approximately 50% exists as free Ca " ", 40% is bound to plasma proteins (mainly albumin), and 10% is com-plexed by citrate and phosphate ions. Although the total intracellular Ca " "... 

The early work on phosphate glasses led to the idea that crystalline phosphates might make extremely durable waste forms, particularly for actinides. The earliest suggestion was for the use of monazite (Boatner 1978, Boatner et al. 1980, McCarthy et al. 1978, 1980). The attractive qualities of monazite as a nuclear waste form are (1) a high solubility for actinides and rare earths (10 to 20 wt %) (2) evidence from natural occurrences of good chemical durability (3) an apparent resistance to radiation damage, as natural monazites are seldom found in the metamict state, despite very high alpha-decay event doses (Boatner and Sales 1988). There have been extensive studies of monazite and apatite as potential waste form phases, and a considerable amount of work on a number of synthetic phosphate phases has been completed. 

Crystalline phosphates and phosphate glasses continue to receive attention as potential hosts for the immobilization and disposal of radionuclides, particularly actinides and waste streams with a high phosphorous content. The principal crystalline phases considered are apatite, silicates with the apatite-structure, and monazite. As has been discussed by Lutze and Ewing (1988a), there are a number of factors that have to be considered in selecting a nuclear waste form. The most important are ... 

Koul, SL (1979) On the fission track dating and annealing behavior of accessory minerals of eastern Ghats (Andlua Pradesh, India). Radiation Effects 40 187-192 Kryii ova AI, Kulikov lA, Artem eva GY (1992) Crystalline phosphates of the NaZr2(P04)3 family radiation stability. Radiochem 34 82-89. 

Crystalline phosphates exhibit greater activity and selectivity than their amorphous counterparts in phenol hydroxylation. 

The major use of crystalline phosphating today is as a pretreatment before cat-aphoretic painting for the automotive industry. The metal is formed and assembled... 

Crystalline phosphate layers of natural origin are rare. Vivianite (Fe2 (P04)2-4H20) layers have been observed on steel artifacts dating from around the third century AD, and not withstanding speculation that the Romans had... 

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