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Structural Studies on Ag2O-P2O5Glasses

New Journal of Glass and Ceramics 2017年第3期7卷 77-89页

作者： Gomaa El-Damrawi Abdelmajued Hassan Hamdy Doweidar Ahamed Shaboub Glass Research Group Physics Department Faculty of Science Mansoura University Mansoura Egypt

Silver phosphate glasses of general formula xAg2O·(100 - x)P2O5 have been investigated over compositional range from x = 40 to 62.5 mol%. The local structure around phosphorus atom has been studied via 31P nuclear magnetic resonance. The distribution of [PO4]Qn species as a function of composition has been shown to slightly deviate from the simple binary alkali phosphate model. An anomalous behavior has been recorded and interpreted in terms of mixed ring-chain effect in metaphosphate composition. The splitting of NMR spectra into sub resonances is assigned to different binding sites characterizing Q1 ring and Q1 chain structure. Higher Ag2O concentration (≥50 mol%) leads to formation of phosphate groups with specific resonance peaks which are mainly related to pyro and orthophosphate species. The rate of change of the chemical shift of the 31P NMR depends on the bond type, which in turn reflects the extent of double bonding between phosphorus and oxygen atoms. Increasing concentration of Q0 with increasing Ag2O content leads to decreasing quantities of bridging and double bonds. As a consequence, specific symmetric resonance peak of higher intensity and chemical shift (Q0) is a feature of silver rich glasses (orthophosphate). The latter species is therefore proposed to compose of separated membered rings,?which cause deshielding of phosphate units.?XRD and EDP studies have shown that, amorphous phosphate network is the dominant structure of glasses containing ≤ 55 mol% Ag2O. Some ordered and well crystallized phases are formed at higher Ag2O concentration. Increasing non-bridging oxygen atoms is shown to have the main effect on crystallization behavior. Orthophosphate composition is the most crystalline one among the other compositions (ultra, meta- and pyrophosphate). Presence of orthophosphate species which typically contains highest concentration from isolated Q0 units is the main reason for building up crystalline Ag3PO4phosphate phase.

关键词： Nuclear Magnetic Resonance Chemical Shift Phosphate Species orthophosphates

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Acknowledgments to reviewers of World Journal of Methodology

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World Journal of Methodology 2012年第1期2卷 18-18页

Many reviewers have contributed their expertise and time to the peer review,a critical process to ensure the quality of World Journal of *** editors and authors of the articles submitted to the journal are grateful to the following reviewers for evaluating the articles(including those published in this issue and those rejected for this issue)during the last editing time period.

关键词： Calcium orthophosphates Fluorapatite Hydroxyapatite Dissolution Model Mechanism

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