Zinc phosphate glasses

In the hydraulic transport of solids through steel pipelines, inhibitors of the sodium-zinc-phosphate glass type have been shown" to be effective. In the case of coal slurries the polyphosphate type was rejected because the de-oxygenating action of the coal lowered the inhibitor effectiveness. Hexavalent chromium compounds at 20 p.p.m. were more effective". ... 

Both zinc and iron sulfides have to be present in a mixed Fe/Zn polyphosphate matrix and iron sulfide is present in the more severe tribological conditions. The XANES analytical technique is considerably more chemically sensitive than XPS, and the degree of phosphate polymerization was quantified for sodium phosphate glasses (Fuller et al., 2002 Yin et al., 1995), zinc phosphate glasses (Kasrai et al., 1995), and the antiwear tribofilms. 

Fig. 7. Absorption spectrum of trivalent chromium in an aluminium zinc phosphate glass...

Some zinc phosphate glasses have low transition temperatures and excellent water resistance [19], Fluorophosphate glasses based on AlfPOjlj and LiF possess special optical properties in addition to having good water resistance. Glasses of this kind, based on combinations of other cation metaphosphates and fluorides, have been patented [20]. 

Liquid silicone rubber Low-temperature zinc phosphate glasses Maleic anhydride (mtMiomer)... 

Onyiriuka, E.C. Zinc phosphate-glass surfaces studied by XPS. J. Non-Cryst. Solids 163, 268-273 (1993)... 

Figure 12. Comparison of the experimental and computer-simulated spectra for zinc-phosphate glass (ZnO-PrOs). The upper trace represents the experimental spectrum after subtracting the broad underlying resonance. The lower trace is the computed best-fit spectrum (for the central fine-structure transition) with g = 2.0, Alg = -93 G, Do/gitB = 220 G, = 70 G, AD/gpB = 80 G, A /gpB = 30 G, v = 8.9 GHz and A5pp = 6 G (Lorentzian lineshape). Adapted with permission from Kliava and Purans (1980).

B.C. Tischendorf, T.M. Alam, R.T. Cygan, J.U. Otaigbe, The structure and properties of binary zinc phosphate glasses studied by molecular dynamics simulations. J. Non-Cryst. Solids 316(2-3), 261-272 (2003)... 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

Unlike other aqueous dental cements, the zinc polycarboxylate retains plastic characteristics even when aged and shows significant stress relaxation after four weeks (Paddon Wilson, 1976). It creeps under static load. Wilson Lewis (1980) found that the 24-hour creep value for one cement, under a load of 4-6 MPa, was 0-7 % in 24 hours, which was more than that of a zinc phosphate cement (0-13 %) and a glass-ionomer cement (0-32%), but far less than that of the zinc oxide eugenol cement (2-2%). 

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. 

Zinc phosphate cement is prepared by introducing small incremental amounts of powder into the liquid and mixing the paste over a large area on a glass slab in order to dissipate heat because of the excessive exotherm... 

In vivo studies have indicated that zinc phosphate cements erode under oral conditions. Also, cements based on zinc oxide, including the zinc phosphate cement, are less durable in the mouth than those based on aluminosilicate glasses, the dental silicate and glass-ionomer (Norman et al., 1969 Ritcher Ueno, 1975 Mitchem Gronas, 1978,1981 Osborne et al., 1978 Pluim Arends, 1981, 1987 Sidler Strub, 1983 Mesu Reedijk, 1983 Theuniers, 1984 Pluim et al., 1984, Arends Havinga, 1985). However, there is some disagreement on whether the zinc phosphate cement is more durable than the zinc polycarboxylate cement. 

Laswell et al., 1971 Arato, 1974). All were prone to excessive dissolution and only one had adequate strength and film thickness. Their working characteristics were found to be unduly sensitive to changes in temperature and humidity (Simmons, D Anton Hudson, 1968). All were inferior to conventional zinc phosphate cements. No further development of these cements has taken place, nor is it likely that interest in them will be revived. The modem water-activated glass-ionomer cement has filled this niche and has vastly superior properties including adhesion to tooth material. 

The thermal film made of long-chain zinc polyphosphates is formed on the surface. When friction increases, the process of transformation of phosphorus compounds into short-chain phosphate glasses is observed and iron sulfide abrasive particles are eliminated by tribochemical acid-base reactions. Under very severe wear conditions (nascent metal surface creation), an iron sulfide is formed, which will be mixed with the phosphate glasses tribofilm. 

A Cameron-Plint friction machine generated tribofilms with two-layer structure a zinc polyphosphate thermal film overlying a mixed short-chain phosphate glass, containing iron sulfide precipitates. A tribochemical reaction between the zinc polyphosphate and the iron oxides species is proposed on the basis of the hard and soft acid and base HSAB principle (Martin, 1999 Martin et al., 2001). 

The tribochemical film produces two major bands, one centered between 1130 cm"1 and 1185 cm"1 and one centered at 620 cm"1. Amorphous ortho- and pyrophosphate were prepared and their spectra seem to be consistent with the spectra of the tribochemical films. The films had two broad major bands consistent with the phosphorus-oxygen bonds. This indicates that the tribochemical film was not composed of phosphate glasses as expected, but rather predominantly amorphous orthophosphate or pyrophosphate formed by thermooxidative decomposition of zinc dialkyldithiophosphate. These groups may be connected by the metal cations. 

In parallel to the work on zinc phosphate cements, porcelain dental cements also were developed. Steenbock [23] was the first to produce silicophosphate dental cement using 50 wt% concentrated phosphoric acid solution and an aluminosilicate glass. Schoenbeck [24] introduced fluoride fluxes in these glasses and vastly improved the dental cements. Fluorides lower the temperature of fusion of the glasses used in forming these cements. The same fluorides impart better translucency to the cement, and have some therapeutic effects. As a result, fluorides have become a part of modern dental cements. 

Fig. 13. Emission of divalent manganese at five different concentrations (x mole percent) in a glass of magnesium zinc phosphate...

Not unexpectedly in view of the related functions of luting and lining materials, most of the materials discussed in Section n.B as luting agents are more or less equally useful as cavity base and liner cements. Cements classified as cavity liners include the calcium hydroxide materials, the zinc phosphates, zinc chelating agents, polycarboxylates, and glass ionomers. 

Within clinical dentistry, there are several types of cement available, including the zinc phosphate and the zinc polycarboxylate. They share with glass-ionomers the feature of being acid-base cements and setting as the result of a neutralization reaction, and consequently they are hydrophilic by nature [7]. These cements differ from each other in that they have different acid and base components, but they resemble each other in that the acid is always an aqueous solution and the base is a water-insoluble soUd metal oxide powder. The setting reaction, which begins immediately when the components are mixed, involves acid attack on the solid powdered base, and leads to the release of metal ions into the aqueous phase. In this phase, the metal ions interact with the acid (or its anion) to form metal salts, and these are rigid and insoluble. As these salts form, so the overall cement hardens and becomes insoluble in saliva and other aqueous media [7]. 

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