Phosphate Glass Structure

Present structural knowledge of phosphate glasses largely confirms theories put forward by Van Wazer over 50 years ago [7,8]. 

Sodium phosphates generally form glassy phases much more easily than potassium phosphates. Melts of the latter with / = 1 are difficult to quench to glasses. 

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Eirst systematic study of phosphate bonding and phosphate cements Kirsanov reaction discovered Identification of UDP glucose Formulated rules for base composition of DNA Advanced theories of phosphate glass structure First NMR spectra of P compounds published Showed (with P) that viruses work by injecting their DNA or RNA into cells under attack... 

Prabakar, S., Wenslow, R.M., and Mueller, K.T. (2000) Structural properties of sodium phosphate glasses from Na -> cross-polarization NMR./. Non-Cryst. Solids, 263, 82-93. 

Meadoweroft T. R. and Richardson F. D. (1965). Structural and thermodynamic aspects of phosphate glasses. Trans. Faraday Soc., 61 54-70. 

Badyal, Y., Karabulut, M. et al. 1999. The effect of uranium on the structure of iron phosphate glasses. Materials Research Society Symposium Proceedings, 556, 297—304. 

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). 

Figure 39 Illustration of a possible lanthanum phosphate-calcium aluminate glass structure for lower LaP04 content in calcium aluminate, derived from Raman and NMR data. For clarity, only a segment of the network is portrayed, with some oxygen atoms removed from the diagram. Taken from Ref. [168].

Very recently, Brown and co-workers65 published a concise paper in which they presented short review of the possibilities and limitations of the refocused INADEQUATE and refocused INADEQUATE spin-echo (REINE) NMR spectroscopy. The authors discussed how these experiments can be used for obtaining various structural parameters, for example identification phosphate units, phosphate chain length, 2/p p couplings and correlation with chemical shift. It is worthy of note that the approach presented there can be applied not for phosphate glasses alone. 

Solid phosphates show a huge variety of crystal structures, and it is not practical to classify them in terms of structural types as is done with simple oxides, halides, etc. However, some general classes of metal phosphate structures will be considered three-dimensional frameworks of linked phosphate tetrahedra and tetrahedrally or octahedrally coordinated cations, layered phosphates, and phosphate glasses. In all of these materials the size and topology of pores within the structure are of importance, as these determine the ability of ions and molecules to move within the structure, giving rise to useful ion exchange, ionic condnction, or catalytic properties. Ion exchange can also be nsed to modify the properties of the host network, for example, the nonlinear optical behavior of potassium titanyl phosphate (KTP) derivatives. 

Phosphate glasses have also been investigated as nuclear waste forms. These are typically made with nonvolatile, high-valent metals such as Fe, Zr, lanthanides, or Th, sometimes with additions of lead to promote glass formation, for example, Fe-Pb-phosphate glasses. Crystalline waste forms based on the NaZr2(P04)3 NASICON structure (see Section 5.2.1) have also been studied as these can exchange Na for Cs, which is difficult to immobilize. 

Bruckner, R., H. U. Chan, H. Goretzki, and M. Sammet (1980). XPS measurements and structural aspects of silicate and phosphate glasses. J. Noncryst. Solids 42, 49. 

A Al MAS NMR study of a series of lanthanum aluminium phosphate glasses has shown the presence of Al in 4-fold, 5-foId and 6-fold coordination. The average Al coordination number increases with increasing Al/La ratio and decreases with increasing 0/P ratio, as can be understood in terms of the tendency of the structure to avoid forming Al-O-Al bonds (Karabulut et al. 2001). 

One-dimensional - P NMR is only able to probe the the local structure of phosphate glasses. To gain information about the manner in which the different Q" units or domains in phosphate glasses are connected, two-dimensional MAS exchange experiments have been used in which radio-frequency dipolar recoupling (RFDR) techniques allow the reintroduction of the through-space dipolar-dipolar interaction even... 

R467 P. Mustarelli, The NMR Information on Phosphate Glasses A Review , Phosphorus Res. Bull., 1999,10, 25 R468 K. Nagashima and F. D. Blum, Adsorption and Dynamics of Sodium Alkylbenzenesulfonates on Alumina , Colloids Surf, A, 2001,176, 17 R469 M. Nakahara, N. Matubayasi, C. Wakai and Y. Tsujino, Structure and Dynamics of Water From Ambient to Supercritical , J. Mol. Liq., 2001,90, 75... 

An X-ray diffraction and P MAS NMR study of rare-earth phosphate glasses of composition (R203)(x)P205)(l — x) where x = 0.175-0.263 and R = La-Er (except for Pm), is presented. The structures of these materials were investigated as a function of (a) rare-earth atomic number and (b) glass composition. The results show an increase in rare-earth coordination number from six to seven as the rare-earth ion increases in size. ... 

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