Search

The atomic structure of a series of sodium iron phosphate glasses is studied using different experimental techniques: X‐ray and neutron diffraction (ND), infrared spectroscopy, extended X‐ray absorption fine structure (EXAFS), and X‐ray absorption near‐edge structure (XANES). Detailed information about the atomic pair correlations is obtained. The high resolution of ND in real space resolves two P–O distances at 1.48 Ǻ and 1.59 Ǻ as expected. All the glasses are found to consist of a phosphate tetrahedral network with metaphosphate chains and pyrophosphate units, and every phosphate unit is found to have two or three nonbridging oxygen (NBO) links available to coordinate with Na and Fe cations. The Fe–O coordination number in these glasses is found to decrease from 5.7 to 4.8 with increasing the Fe content, whereas the Na coordination number of approximately 5 is detected for all the samples.

We report a novel negative conversion electrode material, manganese (II) metaphosphate Mn(PO3)2. This compound can be synthesized by a facile solid-state method, and after carbon-coating delivers an attractively high reversible capacity of 477 mAh/g at 0.1C and 385 mAh/g at 1C. We investigated the reaction mechanism with a combination of ex situ X-ray absorption spectroscopy, in situ X-ray diffraction, and high-resolution transmission electron microscopy. We observed a direct conversion process by monitoring the first discharge in operando, in which Mn(PO3)2 reacts with Li to give fusiform Mn nanograins a few Ångstroms in width, embedded in a matrix of lithium conducting LiPO3 glass. Due to the fine nanostructures of the conversion products, this conversion reaction is completely reversible.

The effect of anisotropy on the mechanical properties was investigated for a chain-structured metaphosphate glass (12.5Li2O–12.5Na2O–12.5K2O–12.5Cs2O–50P2O5 mol%). Anisotropic glasses with different birefringence values were prepared with a fiber elongation method. The strength and Young's moduli of the glasses were measured with a three-point bending method. It was found that the strength and Young's modulus increased with increasing birefringence, reaching about 160% and 140%, respectively, compared with the values for the isotropic glass. The enhancement of the mechanical properties was attributed to the orientation of -P-O-P- chains in the glass.

A tetragonal modification of uranium polymetaphosphate U(PO3)(4), a mixed U4+/Nd3+ polymetaphosphate ''(U0.62Nd0.38)(PO3)(4)'', and two new tetraphosphates, Th(P4O12) and U(P4O12), were synthesized. The structures of the obtained materials were characterized by X-ray diffraction and Raman spectroscopy. The presence of Nd in (U0.62Nd0.38)(PO3)(4) was proven by energy-dispersive X-ray spectroscopy (EDX), and the measured degree of substitution for U agrees well with the X-ray crystallography results; however, the mechanism of the necessary charge compensation could not be identified. The cation arrangements in the crystal structures of thorium and uranium polymetaphosphates have been studied in terms of Voronoi-Dirichlet polyhedra. Different conformations of the tetraphosphate polyanions were observed in the crystal structures of Th(P4O12) and U(P4O12). The Raman spectrum of a single crystal of Th(P4O12) was recorded, and the bands were assigned.

[Mn4O4{O2P(OtBu)2}6] (1), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen-evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen-atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O-atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X-ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to Mn(II) species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin = pinacolate) is described.

Summary This paper presents the structural characterization of melt-quenched titanium metaphosphate glasses having compositions of 0.5P2O5–0.4CaO–(0.1–x)Na2O–xTiO2 (x = 0.00–0.07 mol fraction) by means of x-ray diffraction (XRD) techniques employed under both ambient and high-temperature conditions. Ambient XRD spectra of powdered glass samples revealed the amorphous nature of the glasses, while ambient XRD software analysis of crystallised glass powders provided information regarding the phase transitions in the glass compositions with an increase in the TiO2 content. High-temperature XRD (HT-XRD) contour plots showed good agreement with the results of both ambient XRD and differential thermal analysis, thereby demonstrating the correspondence between three distinct sets of experimental data and allowing us to correlate thermal events with the crystalline phases formed. Thus, the overall results offer interesting clues into the structure of these titanium metaphosphate glasses, which have emerged as major candidates in the biomedical field for use as substrates in the regeneration of hard and soft tissues.

This is the peer-reviewed version of the following article: Prado, V., Lence, E., Vallejo, J., Beceiro, A., Thompson, P., Hawkins, A., & González-Bello, C. (2016). Study of the Phosphoryl-Transfer Mechanism of Shikimate Kinase by NMR Spectroscopy. Chemistry - A European Journal, 22(8), 2758-2768, which has been published in final form at https://doi.org/10.1002/chem.201504438. This article may be used for non-commercial purposes in accordance with Wiley-VCH Terms and Conditions for Self-Archiving The phosphoryl‐transfer mechanism of shikimate kinase from Mycobacterium tuberculosis and Helicobacter pylori, which is an attractive target for antibiotic drug discovery, has been studied by 1D 1H and 31P NMR spectroscopy. Metaphosphoric acid proved to be a good mimetic of the metaphosphate intermediate and facilitated the ready and rapid evaluation by NMR spectroscopic analysis of a dissociative mechanism. The required closed form of the active site for catalysis was achieved by the use of ADP (product) or two synthetic ADP analogues (AMPNP, AMPCP). Molecular dynamics simulation studies reported here also revealed that the essential arginine (Arg116/Arg117 in H. pylori and M. tuberculosis, respectively), which activates the γ‐phosphate group of ATP for catalysis and triggers the release of the product for turnover, would also be involved in the stabilisation of the metaphosphate intermediate during catalysis. We believe that the studies reported here will be helpful for future structure‐based design of inhibitors of this attractive target. The approach is also expected be useful for studies on the possible dissociative mechanism of other kinase enzymes Spanish Ministry of Economy and Competiveness. Grant Number: SAF2013-42899-R Xunta de Galicia. Grant Number: GRC2013-041 European Regional Development Fund Sara Borrell Programme. Grant Number: CD13/00373 ISCIII General Subdirection of Assesment and Promotion of the Research. Grant Number: PI14/00059 SI

Cobalt metaphosphate Co(PO3)2 nanoparticles are prepared via the thermolytic molecular precursor (TMP) method. A Ni form electrode decorated with Co(PO3)2 nanoparticles is evaluated as an anode for water oxidation electrocatalysis in pH 6.4 phosphate-buffered water. Catalytic onset occurs at an overpotential of ca. 310 mV, which is 100 mV lower than that observed for Co3O4 nanoparticles, with a comparable surface area under identical conditions. A per-metal turnover frequency (TOF) of 0.10–0.21 s−1 is observed at an overpotential, η, of 440 mV, which is comparable to the highest rate reported for a first-row metal heterogeneous catalyst. Post-catalytic characterization of the catalyst resting state by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy reveals that surface rearrangement occurs, resulting in an oxide-like surface overlayer.

Ferrous and ferric phosphate crystalline compounds and glasses were studied using Raman spectroscopy. A comparison of the spectra from crystalline and glassy ortho-, pyro-, and metaphosphates indicates that similar phosphate anions constitute the structures of the respective materials, and some information about the compositional dependence of the phosphate-site distributions in the glasses can be gleaned from relative peak intensities. A correlation exists between the average P–O bond distance and the Raman peak frequencies in the crystalline compounds, and this correlation is used to provide information about the structures of the iron phosphate glasses. For example, the average P–O bond distance is estimated to decrease from about 1.57 A for iron metaphosphate glasses (O/P∼3.0) to 1.54 A for iron orthophosphate glasses (O/P∼4.0). These bond distances are in good agreement with those reported from diffraction studies of similar glasses.

The rate of solvolysis of p-nitrophenyl phosphate (PNPP) dianion in DMSO/water strongly decreases by increasing water concentration. Addition of linear alcohols (methanol, propanol, butanol, pentanol, and hexanol) at constant DMSO/water molar ratio produced an even sharper rate decrease. Alkyl phosphate formation, resulting from PNPP solvolysis in ternary DMSO/water/alcohol mixtures, increased with alcohol concentration and was essentially temperature independent. Methanol and hexanol were the poorest nucleophiles under all conditions. Activation energies and enthalpies for solvolysis in ternary mixtures were similar and entropies varied with alcohol concentration. Taken together these results can be best interpreted in terms of a dissociative mechanism with the intervention of metaphosphate. Copyright © 2011 John Wiley & Sons, Ltd.

The chemical mode of action as a flame retardant of calcium carbonate nanoparticles combined with ammonium polyphosphate in polypropylene was investigated. Reduction in burning rates for 0.5 mm thick samples were observed without appreciable char formation up to 30 wt % loading of additives. Thermogravimetric analysis (TGA) of the mixture of CaCO3 and ammonium polyphosphate (APP) showed that calcium carbonate nanoparticles react with ammonium polyphosphate before the degradation of the phosphate chains. TGA–FTIR studies of the polymer composite samples and powder mixtures of the additives confirmed the evolution of ammonia and carbon dioxide due to interaction between the additives. X-ray diffraction (XRD) analysis of chars, obtained after burning the films, showed definite diffraction peaks corresponding to that of calcium metaphosphate. The inert gasses produced by the interaction of the additives hindered the advancing flame and, thus, reduces the burning rates, at times even without char formation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The reduction of silver phosphate with graphite under vacuum conditions was studied at final reaction temperatures varying from 430 to 915°C to determine: (i) the CO2 extraction yield, and (ii) the oxygen isotopic composition of CO2. The CO2 yield and oxygen isotopic composition were determined on a calibrated dual inlet and triple collector isotope ratio mass spectrometer. We observed the following three stages of the reduction process. (1) At temperatures below 590°C only CO2 is formed, while silver orthophosphate decays to pyrophosphate. (2) At higher temperatures, 590–830°C, predominantly CO is formed from silver pyrophosphate which decays to metaphosphate; this CO was always converted into CO2 by the glow discharge method. (3) At temperatures above 830°C the noticeable sublimation of silver orthophosphate occurs. This observation was accompanied by the oxygen isotope analysis of the obtained CO2. The measured δ18O value varied from −11.93‰ (at the lowest temperature) to −20.32‰ (at the highest temperature). The optimum reduction temperature range was found to be 780–830°C. In this temperature range the oxygen isotopic composition of CO2 is nearly constant and the reaction efficiency is relatively high. The determined difference between the δ18O value of oxygen in silver phosphate and that in CO2 extracted from this phosphate is +0.70‰. Copyright © 2010 John Wiley & Sons, Ltd.

Solid-state (23)Na and (31)P magic-angle spinning nuclear magnetic resonance spectroscopy and X-ray crystallography have been used to study the structures of the chain metaphosphates NaCa(PO(3))(3) and NaSr(PO(3))(3). The compounds are isostructural and crystallise in space group P(-1) with the following parameters: NaCa(PO(3))(3), a = 6.711 A, b = 6.934 A, c = 7.619 A, alpha = 83.44 degrees , beta = 81.41 degrees , gamma = 82.80 degrees ; NaSr(PO(3))(3)a = 6.805 A, b = 7.133 A, c = 7.720 A and alpha = 83.71 degrees , beta = 80.48 degrees , gamma = 82.87 degrees . Both structures contain anionic metaphosphate chains of (PO(3))(n) (n) with ionic contacts to Na(+) ions in distorted octahedral sites and Ca(2+) (or Sr(2+)) in distorted dodecahedral sites. (31)P and (23)Na NMR are entirely consistent with the crystallographic data and an empirical method for assigning (31)P resonances to particular crystallographically unique P atoms is described.

The glass transition temperature increases and the thermal expansion coefficient and density decrease with increasing B2O3 concentration in a series of (100−x)(50BaO–50P2O5)−xB2O3 where x=0–10 mol% for bulk samples. According to Raman spectroscopy, the bulk BaO–P2O5–B2O3 (BaP–B) glasses consist of metaphosphate Q2 units with ring-type metaborate, diborate, and PO4–BO4 groups. X-ray photoelectron spectroscopy results reveal qualitatively that P–O–B bonds are formed at the surface of BaP–B glass samples ground in laboratory air over 6 mol% B2O3 only. The P–O–B bonds are related to the suppression of the crystallization of powdered BaP–B glasses with >6 mol% B2O3 during differential thermal analysis.

Aluminum phosphate products formed by the reactions of alumina and alumina-gel systems with acidic phosphates were analyzed. Drying of alumina-gel to form microcrystalline boehmite and conversion to γ-alumina by thermal treatment was indicated by the appearance of octahedral, pentacoordinate, or tetrahedral sites, which were established using 27Al magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Crystalline aluminum phosphate products and amorphous material were identified using this technique. α-alumina and heat-treated alumina-gel that were reacted with phosphate in an Al:P ratio of 1:1 yielded dramatically different aluminum orthophosphate:aluminum metaphosphate product ratios of 8.2:1 and 1:1.1, respectively. When alumina-gel was heat-treated with phosphate, an abundance of aluminum orthophosphate, aluminum metaphosphate, and hydrated aluminum phosphate products were affected by varying conditions of temperature and time of heat treatment and by the amount of phosphate present. An α-alumina/alumina-gel composite sol–gel phase that was reacted with phosphoric acid (H3PO4) in a Al:P ratio of 1:1 exhibited an increased quantity of aluminum metaphosphate products compared with an α-alumina:H3PO4 ratio of 1:1 and a higher percentage of reaction (79%) compared with the reactions of an α-alumina:H3PO4 ratio of 1:1 or an alumina-gel:H3PO4 ratio of 1:1. The morphologies of aluminum triphosphate hydrate and aluminum metaphosphate product phases were observed using scanning electron microscopy.

A novel method for preparing calcium hydroxyapatite (Ca10(PO4)6(OH)2: HAp) fibers has been developed. HAp fibers can be prepared successfully by heating a compact consisting of calcium metaphosphate (s-Ca(PO3)2) fibers with Ca(OH)2 particles in air at 1000°C and subsequently treating the resultant compact with dilute aqueous HCl solution. The s-Ca(PO3)2 fibers and the Ca(OH)2 in the compact were converted into fibrous HAp and CaO phases by the heating, and the CaO phase was removed by acid-leaching. HAp fibers obtained in the present work were 40-150 µm in length and 2-10 µm in diameter. The fibers had almost the same dimensions as those of the s-Ca(PO3)2 fibers.

The reactions of two series of benzoyl derivatives of nucleophiles were investigated and the results were compared with those for N-benzoylimidazole. The general structure is ArCO-Nu, where Ar = X-C 6 H 4 - and/or X 2 -C 6 H 3 -; X=4-Me, H, 4-Cl, 4-CN, 4-NO 2 and X 2 =3,5-dinitro; Nu=iodosobenzoate, ArCO-Iba, and phosphate dianion, ArCO-Phos. Catalytic rate constants, kinetic solvent isotope effects, kinetic substituent effects (Hammett equation) and the dependence of ΔH ≠ and ΔS ≠ on σ x were determined. For ArCO-Iba, the hydrolysis occurs via two pathways, uncatalyzed (k H 2 O ) and specific base-catalyzed (k O H ) water attack on the iodine atom of the iodosobenzoate ring. This conclusion is based on theoretical calculations of the partial charges on ArCO-Iba, and the small /) values calculated at 25 °C, -0.22 and 0.92 for k H 2 O and k O H , respectively. The data for the reaction of ArCO-Phos are consistent with a dissociative transition state, leading to elimination of the metaphosphate monoanion (PO - 3 ). The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions of ArCO-Iba: (i) moderate to large substituent effects on the activation entropies suggest that solvation of the leaving benzoate anion and desolvation of the entering nucleophile contribute to the OH - -mediated reaction; (ii) the negative and positive signs of ΔS ≠ indicate large differences in solvation of the transition states of the k H 2 O and k O H pathways. For the spontaneous decomposition of ArCO-Phos, sizeable substituent effects on both ΔH ≠ and ΔS ≠ were observed. This shows the contribution of solvation of the leaving benzoate and substituent-induced shift of the structure of the transition state.

Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P 2 O 5 -WO 3 -A 2 O (A = Li, Na). Structural approach of the highly modified glasses P 2 O 5 -A 2 MoO 4 -A 2 O (M = Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO 6 octahedra, MO 4 tetrahedra, M 2 O 7 dimers, PO 4 tetrahedra, and also P 2 O 7 or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A 2 O increases. ESR experiments were conducted on both X-ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W 5+ and Mo 5+ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus-oxygen-hole-center and peroxy radicals. The M 5+ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted for vitreous materials.

Many chromite-rich rocks contain relatively high concentrations of the platinum-group elements (PGE). In many cases, the phases carrying PGE occur as either platinum-group minerals (PGM) or as base metal sulfides in solid solution in sulfides. In some cases, such as the UG-2 unit of the Bushveld Complex, the PGM are occluded inside chromite grains. Chromites are notably difficult to dissolve in most fluxes and if the chromite contains some PGM the possibility exists that not all the PGE will be recovered during fusion. In this work, shortcomings in published methods of analysis based on the nickel sulfide fire assay procedure were investigated and a new procedure developed based on the addition of sodium metaphosphate to the fusion mixture. Optimum composition of the fusion mixture was found to be 10 g sodium metaphosphate and 9 g silica to 10 g sample, 15 g sodium carbonate, 30 g lithium tetraborate, 7.5 g nickel and 4.5 g sulfur to achieve complete dissolution of chromite grains. The new flux mixture was evaluated by the analysis of reference material CHR-Pt+ (which is known to contain PGM inside chromite grains) and no undissolved chromite grains were found in the glassy slag. Analysis of the nickel sulfide beads from this fire assay using neutron activation analysis showed similar results for Rh and Ru when compared with published conventional true (or accepted) values, while Au, Ir, Os, Pd and Pt values determined here were 10 to 30% higher than the corresponding published conventional true values. It was concluded that the addition of sodium metaphosphate improved chromite dissolution in the flux and appears to improve PGE recovery. De nombreuses roches riches en chromites ont des teneurs relativement elevees en elements de la mine du Platine (PGE). En general, les phases porteuses des PGE sont soit des mineraux du groupe du Platine (PGM) ou des sulfures de metaux de base en solution solide dans les sulfures. Dans certains cas, tels que l’unite UG-2 du complexe du Bushweld, les PGM sont inclus dans les grains de chromite. Les chromites sont tres difficiles a dissoudre quel que soit le fondant utilise, et si les chromites contiennent des PGM, il existe un risque que l’ensemble des PGE ne soit pas recupere durant la fusion. Dans ce travail, les differentes methodes publiees basees sur l’essai pyrognostique, ont ete testees et une nouvelle procedure a ete developpee, basee sur l’addition de metaphosphate de sodium dans le melange de fondant. La composition optimale de ce melange a ete determinee comme etant : 10 g de metaphosphate de sodium et 9 g de silice pour 10 g d’echantillon, 15 g de carbonate de sodium, 30 g de tetraborate de lithium, 7.5 g de nickel et 4.5 g de sulfure pour permettre d’achever la dissolution complete des grains de chromite. L’efficacite de ce nouveau melange de fondant a ete controlee a travers l’analyse du materiau de reference CHR-Pt+ (que l’on sait contenir des PGM a l’interieur des chromites) et aucun grain de chromite non dissous n’a ete trouve dans le verre de fusion. L’analyse par activation neutronique des perles de sulfure de nickel issues de cet essai pyrognostique, donne des resultats similaires aux valeurs vraies (ou acceptees) publiees pour Rh et Ru, tandis que les donnees pour Au, Ir, Os, Pd, et Pt determinees ici sont de 10 a 30% superieures aux valeurs publiees "vraies" obtenues de facon conventionnelle. On en conclut que l’addition de metaphosphate de sodium ameliore la dissolution de la chromite dans le fondant et se revele ameliorer la recuperation des PGE.

Styrene-butyl acrylate copolymer (St-BA)/graphite oxide (GO) nanocomposites and St-BA/GO/MPP [melamine poly(metaphosphate)] composites were prepared via an intercalation process by the ball-milling method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microanalyzer (SEM). Cone calorimetry experiments were carried out to evaluate their flammability. The cone calorimetry data suggested that the addition of GO can decrease the heat release rate of St-BA copolymers significantly. Furthermore, there was also a synergistic effect on the fire retardant property by the combination of GO and MPP. However, no prominent effect of the GO content on the reduction of peak heat release rate (HRR) in nanocomposites could be found.

Changes in the thermal properties of sodium phosphate glasses during melt production have been investigated using Pt/Au and fused alumina crucibles. Glasses were produced from NaH2PO4 as a starting material, providing an intrinsic Na2O:P2O5 ratio of 1:1 and giving an O/P = 3, that is, a metaphosphate. In Pt/Au crucibles, glass transition temperatures rose to a plateau value of 295°C at a rate determined by melt temperature. No contamination of the glass by platinum or gold was detected or indicated in the results. Ea for the reaction was found to be 66.4 kJ mol−1. In fused alumina crucibles, glass transition temperatures rose to over 450°C, with these values showing some convergence at higher furnace temperatures. Extensive erosion of the alumina crucibles was observed. The amount of alumina incorporation within the glasses correlated well with the rise in glass transition temperature up to a maximum of 15.5 mol % Al2O3 content. Al2O3 incorporation above this value caused a reduction in the value of the Tg. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 71B: 22–29, 2004

The thermal behavior of amorphous cerium phosphate has been characterized by X-ray powder diffraction, thermal gravimetric and differential thermal analysis, Fourier transform infrared and Raman spectroscopy. Crystallization from amorphous phase occurred at around 773K to form crystalline cerium pyrophosphate, CeP 2 O 7 . Further heating induced a phase transition from CeP 2 O 7 to CePO 4 at 923K via coexistence of a small amount of metaphosphate phase.

Reversion of sodium metaphosphate was studied in two types of experiments. The beaker experiments used stoppered glass containers, pH-buffered solutions, variable calcium (Ca) concentrations, and either 2 or 4 mg/L total phosphorus. The rate of orthophosphate [(PO 4 ) -3 ] production increased as the Ca concentration increased. There was 70% reversion for systems with 120 mg/L Ca. (PO 4 ) -3 production was first-order with respect to total polyphosphate. The rate constants were an approximately linear function of the logarithm of the Ca concentration. The pipe-rig experiments used sections of copper and lead pipe that had been exposed to modified Boulder, Colo., tap water. Metaphosphate reversion was much more rapid in the pipe-rig experiments than in the beaker experiments, and the rate of reversion increased substantially as the pipes aged over a period of years.

High-resolution solid-state 31 P, 27 Al, and 23 Na nuclear magnetic resonance (NMR), Raman spectroscopy, differential scanning calorimetry, and density measurements were used to characterize the local structure of the glasses (1-x)(NaPO 3 ) 3 xAl(PO 3 ) 3 . A systematic increase in density, glass transition temperature (T g ), and frequencies of P-O stretching vibrations for terminal nonbridging oxygens (NBOs) was observed as the Al content was increased. A change of slope in the behavior of T g as a function of was clearly detected around x = 0.25 ± 0.03. Also, changes of behavior in the 23 Na NMR line shape and in the Raman band of the PO 2 symmetric vibration are detected for concentrations higher than x = 0.17. According to these facts, a reorganization of the network affecting the degree of connectivity between phosphate chains is proposed to explain the observed behaviors of T g and P-NBO vibrations in these glasses.

High-performance electrocatalysts are desired for electrochemical energy conversion, especially in the field of water splitting. Here, a new member of phosphate electrocatalysts, nickel metaphosphate (Ni2 P4 O12 ) nanocrystals, is reported, exhibiting low overpotential of 270 mV to generate the current density of 10 mA cm-2 and a superior catalytic durability of 100 h. It is worth noting that Ni2 P4 O12 electrocatalyst has remarkable oxygen evolution performance operating in basic media. Further experimental and theoretical analyses demonstrate that N dopant boosts the catalytic performance of Ni2 P4 O12 due to optimizing the surface electronic structure for better charge transfer and decreasing the adsorption energy for the oxygenic intermediates.

Alkali aluminophosphate glasses, including those in the system xAl2O3·(1−x)CsPO3 (0 ≤x≤ 0.25), were examined by high-performance liquid chromatography (HPLC), infrared (IR), and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Phosphate anions become progressively shorter with the addition of alumina to a metaphosphate glass. Al3+ ions are initially incorporated into the structure in octahedral sites, but the average Al coordination number (CN) decreases with increasing alumina content and tetrahedral species are the preferred moiety when [O]/[P] > 3.5. Al[4] sites appear to be associated with monophosphate (Q0) anions. The role of modifier size on aluminophosphate structure is investigated. At low alumina content (

A series of R(PO3)3 (R = Ga, In, Y, Sm, Gd, Dy) metaphosphate crystals representing four different structural types were prepared and their vibrational spectra recorded. The distribution of internal and external chain modes was obtained taking into account the configuration (site symmetry) of the polyphosphate anions in the corresponding structures. The spectra presented reveal that the P—O− force constants are very sensitive to both the coordination of oxygen atoms and POP bond angles. The spectra of crystalline R(PO3)3 were compared with data for glassy metaphosphates. It was found that decreasing the size of R(III) cation leads to different structural effects in glasses and crystals of the same composition. Copyright © 2001 John Wiley & Sons, Ltd.

Single crystals of Ga(PO3)3 were grown in polyphosphoric acid melts by heating a mixture of Ga2O3 and H3PO4 (350 °C, 7 d). The compound belongs to the series of metaphosphates MIII(PO3)3 forming the C-type structure (monclinic, Cc, Z = 12, a = 13.0058(21), b = 18.915(3), c = 9.3105(15) A, β = 126.900(11), 5348 independent reflections (I > 0); 354 variables; 39 atoms in asymetric unit; R1 = 0.048, wR2 = 0.1034). The structure is characterized by a superstructure with tripled monoclinic b-axis. Three crystallographically independent GaIIIO6 octahedra (d¯(Ga–O) = 1.950 A) are linked by 1∞(PO3)– chains. Verfeinerung der Uberstruktur von C-Typ Gallium-tris(metaphosphat) Einkristalle von Ga(PO3)3 wurden in Polyphosphorsaureschmelzen aus Ga2O3 und H3PO4 gezuchtet (620 K, 7 d). Die Verbindung gehort zu einer Serie von Metaphosphaten MIII(PO3)3, welche den sogenannten C-Strukturtyp (z. B.: C–Al(PO3)3) ausbilden. Charakteristisches Strukturmerkmal ist eine Uberstruktur mit Verdreifachung der monoklinen b-Achse. Drei kristallographisch unabhangige GaIIIO6 Oktaeder (d¯(Ga–O) = 1.950 A) werden durch 1∞(PO3)– verknupft.

High-strength calcium metaphosphate fibers, which are expected to show good biocompatibility, are extracted from crystallized products of ultraphosphate glasses by aqueous leaching. Porous ceramics with skeletons of β-Ca(PO3)2 fibers for biomedical use are prepared by the sintering of the fibers. In the present work, porous ceramics having a large porosity of −70% were obtained. The compressive test of these porous ceramics showed that large strains of 0.2–0.3 are requisite for their fracture; the calcium phosphate porous ceramics in this work show much higher flexibility than conventional ceramics. The present work discusses the influence of the preparation conditions of the porous ceramics on their compressive strength behavior.

The first prominent peak observed at s 1 in the total X-ray structure factors, S(s), of metaphosphate glasses containing the metal ions Li, Na, K, Ag, Ba, Sr, Cd, Pb, and of barium phosphate glasses with BaO mol% concentrations ranging from 2.5 to 56.5 has been studied to extract information on the intermediate range structure. The period, 2π/s 1 , of the quasi-periodic real-space electron density fluctuations is shown to be correlated with the ionic volume fractions of the glasses.

Influence of surface treatment of calcium metaphosphate ceramic was analyzed in detail to achieve high adhesion in an aqueous environment with N-(vinylbenzyl)iminodiacetic acid as a novel dental adhesive monomer. The adhesion strength was enhanced greatly by alkali etching of the ceramic surface, although the adhesion profile varied with etching conditions. Scanning electron microscopy, electron probe microanalysis, and roughness evaluation indicated that high adhesion was closely associated with the formation of fine irregularity on the surface that was rich in Ca. N-(Vinylbenzyl)iminodiacetic acid was thus confirmed to be a suitable adhesive monomer for the ceramic in dentistry in terms of strength and durability when the ceramic surface was properly etched. © 1996 John Wiley & Sons, Inc.

Kinetic isotope effects of deuterium and oxygen-18 were measured on fragmentation of syn-3-ethoxy (1a) and syn-3-(N,N-diethylamino) (1b) 2,3-oxaphosphabicyclo[2.2.2]octene derivatives in 1,2-dichloroethane at 100°C. The secondary deuterium isotope effect on hydrogen adjacent to the P(SINGLE BOND)C bond was found to be 1.060 ± 0.008 for 1a and 1.081 ± 0.009 for 1b. The kinetic oxygen isotope effect on the bridge P(SINGLE BOND)O(SINGLE BOND)C is 0.9901 ± 0.0016 for 1a. The data indicate an unsymmetrical transition state for retrocycloaddition extrusion of the metaphosphate moiety, with the breakage of the C(SINGLE BOND)P bond and formation of the P (DOUBLE BOND) O bond more advanced than the C(SINGLE BOND)O breakage. A synthesis of 1a and 1b labeled with deuterium is described. © 1996 John Wiley & Sons, Inc.

Calcium phosphate invert glasses, which contain P2O72− and PO43− ions, have been prepared via the addition of a small amount of TiO2. The formation of bonelike calcium phosphate apatite on the surface of the phosphate invert glasses was examined in simulated body fluid (SBF) at a temperature of 37°C. Soaking for 20 d resulted in the deposition of leaflike apatite particles on 6CaO·3P2O5·TiO2 invert glass (based on molar ratio). The glass had much-greater chemical durability against SBF, in comparison with a metaphosphate glass; P ions were not dissolved excessively from the 6CaO·3P2O5·TiO2 glass, so the apatite formation was not suppressed.

31P MAS and 11B NMR are used for structural investigations on glass samples with chemical composition (1 − X) [NaPO3−R Na2B4O7]−X Ca5(PO4)3OH. For the sodocalciphosphate glasses (R = 0), the 31 P MAS NMR spectra show a shortening of the length of metaphosphate chains together with the formation of chain ends, when X increases. The Ca2+ cations probably “cross-link” the short phosphate chains. From 11 B NMR spectra of the sodocalcicborophosphate glasses (R > 0), the boron atom fraction in four-fold coordination is determined. In the phosphate rich glasses, the borate groups, mainly under the BO form are used as branching between short phosphate chains. For R > 0.2 borate groups including boron atoms in three- and four-fold coordination such as those found in pure vitreous Na2B4O7 are considered. The phosphate units are located out of the borate network. The extent of the vitreous domain and the physical and chemical properties are correlated with these different structures.

Twelve methacrylamide derivatives containing carboxyl and phenyl groups have been evaluated as adhesives for calcium metaphosphate ceramic, a promising but hard-to-adhere cast ceramic restoration material. Although methacrylamide monomers having a carboxyl group showed low adhesive tensile strength for the ceramic, contrary to the glycidyl methacrylate derivatives, the monomer having neighboring two carboxyl groups at the phenyl ring exhibited quite high adhesion. Moreover, the monomer proved to retain high adhesion strength for the surface-etched ceramic for a long period of time even in water and would thus be suitable for practical clinical applications. © 1994 John Wiley & Sons, Inc.

The title compound, a new cyclodecaphosphate, was prepared by precipitation from an aqueous solution of K10P10O30. The sparingly soluble salt crystallizes monoclinic in the space group P21/a, with Z = 2, and the unit-cell dimensions a = 14.546(10), b = 15.211(10), c = 9.860(6) A, β = 105.12(4)°. The crystal structure was solved using 6501 unique reflections with a final R-value of 0.044. The centrosymmetrical ring anions rather distant from each other and arranged in a pseudo-tetragonal way create, parallel to the c direction, large channels containing the water molecules. Darstellung und Kristallstruktur von Kaliummangancyclodecaphosphat-octadecahydrat: K2Mn4P10O30 · 18 H2O Die Titelverbindung, ein neues Cyclodecaphosphat, wurde durch Fallung aus wasriger K10P10O30-Losung hergestellt. Das in Wasser wenig losliche Salz kristalliert monoklin in der Raumgruppe P21/a mit den Gitterkonstanten a = 14,546(10), b = 15,211(10), c = 9,860(6) A, β = 105,12(4)°. Die Kristallstruktur wurde unter Verwendung von 6501 unabhangigen Reflexen gelost, der R-Wert betragt 0,044. Die zentrosymmetrischen Ringanionen sind relativ weit voneinander entfernt und in einer pseudotetragonalen Weise angeordnet, so das parallel zur c-Achse grose, die Wassermolekule enthaltende Kanale gebildet werden.

Synthetic methods which provide alternatives to the oxide melting method for the preparation of inorganic glasses are described. These methods were monitored by Raman spectroscopy. The transformation products involved in two main synthetic methods, the ‘sol–gel’ method illustrated here for obtaining glassy SiO2 and the ‘polymeric’ route used for the first time in the preparation of calcium phosphate glasses (CaO.P2O5, calcium metaphosphate; xCaO.P2O5, calcium oligophosphates, where x ≤ 1.6) are characterized and discussed using their Raman spectra. These alternative methods allow vitreous materials to be prepared at moderate temperatures. They can therefore be important in the field of biomaterials for coating metal implants with bioactive glasses and ceramics. The melting method (for glasses) and the plasma spray technique (for ceramics) frequently induce changes of stoichiometry in the coating and also activation of the support material, metal or alloy, resulting in a lack of biocompatibility.

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3),independent of the (Cu sup 2+)/(Cu(total)). However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the (Cu sup 2+)/(Cu (total)) ratio in the glass. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, but small at high temperature. The glass transition temperature of the glass increases as the (Cu sup 2+)/(Cu(total)) ratio is raised. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.

Based on attempts to generate methyl metaphophate in solution by thermal fragmentation of a cyclic pyrocarbonate phosphate, it has emerged that reaction of methyl dichlorophosphate with anhydrous potassium hydrogen carbonate serves as an alternative approach as proven by trapping with styrene oxide to form a 1,3,2-dioxaphospholane.

Single crystals of potassium dihydrogen phosphate (KDP) were grown by slow evaporation from supersaturated aqueous solution. The crystal structure of KDP was identified by X-ray diffraction analysis. Simultaneous TG, DTG and DTA thermal analysis of KDP crystals over the temperature range 25–600° C showed that the potassium orthophosphate decomposed to potassium pyrophosphate and then to metaphosphate as end product. DTA studies at the higher heating rates of 50 and 100° C min−1 showed a clear resolution of the first peak into two peaks; the first was attributed to a phase transition at 200 °C and the second was due to the decomposition of the sample. It is interesting to note that the high-temperature phase transition for KDP was also obtained at 175° C by DSC studies at 2° C min−1. The activation energies for the thermal processes of KDP occurring at 230, 265 and 310°C were calculated as 155.56, 286.56 and 81.46 kJ mol−1 by the Kissinger method, and 164.01, 294.97 and 91.34 kJ mol−1 by the Ozawa method. X-ray diffraction and infrared absorption spectra confirmed the high-temperature phase transition obtained by DTA and DSC as well as the thermal decomposition of the KDP samples.

Phosphonopyruvate (1) is prepared in 56% yield from triethyl phosphonopyruvate (3) and pKa values of 1.63, 2.40 and 7.41 determined. The stability of phosphonopyruvate is monitored at 75 °C in aqueous buffers over the pH range 0.6 to 8.3. The only products detected are pyruvate and inorganic phosphate. The pH–rate profile shows that the C–P bond is hydrolysed fastest in the monoanion and dianion of phosphonopyruvate, with rate constants of 1.94 × 10–4 s–1 for the monoanion and 1.05 × 10–4 s–1 for the dianion. For the reaction at pH 4.75, where the dianion predominates, ΔH‡ is 114.0 kJ mor–1 and ΔS‡ is 5.4 J mol–1 K–1, the deuterium isotope effect, kH/kD is 1.08 ± 0.04, and there is non-selective phosphorylation of methanol and H2O in an equimolar solution of these solvents. These results are consistent with a mechanism of hydrolysis of both the monoanion and dianion that involves a very largely dissociative transition state with monomeric metaphosphate character.