High-temperature borate liquids: physical properties of glass-forming compositions

Several experimental routes can be used to develop a better understanding of the polymeric constitution (polyanionic and/or polyhedral distribution) of borate, germanate, and silicate glasses. Spectral, chemical, physical-chemical, and mechanical property information can be determined directly for the glass compositions of interest. Generally, only physical-chemical information is readily accessible for the corresponding high temperature liquids. It will be shown that information on each state of matter has its own particular merits. Most of the evidence thus far published suggests an excellent agreement between polyhedral distributions in an oxide glass and its corresponding high temperature liquid state. There is no well known oxide glass forming system for which such a state of affairs does not exist. In spite of this, occasional efforts are put forth which ignore some of what is known for oxide liquids, glasses, and crystals. Such attempts therefore invariably imply, if only indirectly, that significant changes occur in the polyhedral distributions close to the glass transition temperature region. Specific examples to be discussed will include efforts that avoid well known coordination change equilibria such as BO/sub 3/ reversible BO/sub 4/ and GeO/sub 4/ reversible GeO/sub 6/

Quasi-chemical viscosity model for fully liquid slag in the Al2O3-CaO-MgO-SiO2 system. Part II: evaluation of slag viscosities

A model is presented that enables viscosities to be predicted reliably over the whole range of compositions and temperatures in the AlO -CaO-MgO-SiO slag system above liquidus in the temperature range from 1543 K to 2643 K (1270°C to 2370°C). Experimental procedures and data from the studies reported in the literature have been collected and critically reviewed with particular attention to the viscometry methods and possible contamination of slag samples to select reliable data points for further model development. Relevant revised formalism to describe the complex viscosity trends including charge-compensation effect of the Ca and Mg cations on the formation of tetrahedrally coordinated Al was introduced. Parameters of the quasi-chemical viscosity model have been optimized to reproduce within experimental uncertainties most of the selected experimental data in the AlO -CaO-MgO-SiO system and all subsystems. This study is part of the overall development of the self-consistent viscosity model of the AlO-CaO-FeO-FeO- MgO-Na O-SiO multicomponent slag system

Structure-properties changes in ZnO-PbO-GeO 2 glasses

We have studied the structure of ZnO-PbO-GeO2 glasses by Fourier transform infrared spectroscopy and showed that the analysis of the vibrational spectra can lead to a quantitative description of the network structure in terms of the fraction of the local germanate polyhedra. The presence of GeO4, GeO6 and GeO4 with NBOs units was evidenced in the studied glass network. The initial additions of ZnO would introduce modifier Zn2+ ions at the expense of the former PbO4 units. With increasing ZnO content, ZnO4 tetrahedra would mainly replace modifier PbO. The decrease in density when introducing ZnO at the expense of PbO content is not only due to the vast difference in molecular mass between PbO and ZnO, but also due to the formation of Q2 and Q3 units. The glass network of the investigated glasses posseses a more covalent character upon replacing ZnO for PbO. This is the reason for increasing the microhardness and the glass transformation temperature of the glasses investigated with increasing zinc oxide content. The change in the conductivity at certain temperature not only attributed to the change in the covalency of the glass matrix upon replacing PbO by ZnO but also due to a change in the strain energy because of the change in Vm