Interrelation between transport properties in phosphate glasses through their atomic structure

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Inorgánica. Fecha de lectura: 01-04-2016Esta tesis tiene embargado el acceso al texto completo hasta el 01-10-201

Structure–properties relationships in fibre drawing of bioactive phosphate glasses

New bioactive phosphate glasses suitable for continuous fibre production are investigated in this work. The structure of both bulk and fibres from Na2O–CaO–MgO–P2O5 glasses has been studied by means of Raman and 31P and 23Na nuclear magnetic resonance spectroscopies, and the structural results have been correlated with the mechanical properties of the fibres and the dissolution rate of the bulk glasses. It has been observed that the mechanical properties of the phosphate glass fibres are influenced by the glass network connectivity, while the dissolution rates are governed by the Qi speciation of the PO4 units. As seen in previous studies, molar volume seems to play an important role in the fragility behaviour of phosphate glasses. Here, a lower molar volume resulting from the increase in the oxygen packing density hinders the cooperative flow of the PO4 units throughout the glass network and, therefore, causes a reduction in the kinetic fragility

A model for the construction of the network in phosphate glasses through viscosity-structure relationships

We have established a relationship between the viscosity activation energy of metaphosphate melts and the NMR chemical shift anisotropy of phosphorus that is measured in their corresponding glasses, and proposed a model by which the fragility of the glasses can be explained as dependent on the particular modified random network that is originated upon cooling. The increase of the modifier field strength gives rise to higher viscosity activation energy during the glass formation upon cooling, with a maximum at the calcium metaphosphate composition. The lower rates of increase of viscosity would produce network structures characterized by higher anisotropicity and be the responsible for the higher fragility of the glasses, which can be defined as a measure of the degree of difference between the structures of the glassy state and the melt from which this is obtained.Funding from project MAT2013-48246-C2-1-P from MINECO of Spain is acknowledged

Kinetic fragility and structure of lithium borophosphate glasses analysed by solid state NMR

The macroscopic and high temperature properties of lithium borophosphate glasses were determined in this contribution. Our data, obtained on 50Li2O–xB2O3–(50−x)P2O5 glasses, confirm a continuous and linear increase of the glass transition temperature with the B/P substitution but show a two-domain evolution of the kinetic fragility with a steep decrease in the low B2O3 region (0 ≤ x ≤ 10) followed by a moderate increase for higher B2O3 contents. In order to understand this different behaviour, the glass structure was investigated in detail using 1D and 2D 11B/31P correlation solid state nuclear magnetic resonance. The local and medium orders of borate units were determined by 1D MAS-NMR, 2D 11B DQSQ- and 11B(31P) D-HMQC NMR experiments. The latter NMR technique was also used to deeply interpret the 1D 31P MAS-NMR spectra. Altogether the data allow (i) highlighting of the presence of four borate and seven phosphate units, (ii) evaluation of the number of homopolar POP and mixed POB linkages, and (iii) contribute to a better understanding of the Tg and kinetic fragility evolution.Funding from projects MAT2010-20459 and MAT2013-48246-C2-1-P from Ministerio de Economía y Competitividad (MINECO) of Spain is acknowledged. L. Muñoz-Senovilla also thanks the MINECO for her PhD scholarship (BES-2011-044130). G. Tricot would like to thank Region Nord Pas de Calais, Europe (FEDER), CNRS, University of Lille and TGIR-RMN-THC FR3050 CNRS for funding

Investigation of the relationships between acoustic attenuation and ionic conduction of metaphosphate glasses

[EN] This paper deals with phosphate-based glasses and summarizes the results obtained from acoustic attenuation and ionic conduction investigations. Several relaxation processes have been found to be connected with different activation energies, for which Double Power Law and Gaussian functions have been used for their modelling. The activation energy of the acoustic relaxations in the metaphosphate glasses increases with the increasing cationic potential of the modifier elements, following a direct relationship between the cationic potential of the modifier in the glasses and their influence on the short and medium range structural arrangements of the PO tetrahedra. On the other hand, the variation of the activation energy for the ionic conduction shows a similar trend than those observed in the acoustic attenuation processes, which indicates that both phenomena are closely influenced by the short and medium range structure of the glasses, particularly through the strength of the modifier-oxygen bonds and the glass network reticulation.This study was supported by projects KEGA No. 003TU Z-4/2015 and ITMS: 26210120021 co-funded from EU sources and European Regional Development Fund. F. Muñoz and L. Muñoz-Senovilla are thankful to the projects MAT2010-20459 and MAT2013-48246-C2-1-P from MINECO of Spain and L. Muñoz-Senovilla also thanks the MINECO for her PhD scholarship (BES-2011-044130)