Cesium Silicate Research Articles

Studies of NiO dissolved in alkali silicate melts based on redox potential and visible absorption spectra

The redox behavior of Ni 2+ ions in alkali silicate melts, xR 2O · (1 - x)SiO 2, (R = Na, K and Cs and x in the range 0.175 – 0.45), was investigated using linear sweep voltammetry and differential pulse polarography. The half-wave potential of Ni 2+ Ni 0 depends on the alkali species and contents. It shifted to the positive side when the alkali species changed from sodium through potassium and cesium at a fixed ratio of alkali oxide to silica, indicating that NiO loses its thermodynamic stability in this order. Based on visible absorption spectra, it is shown that the Ni 2+ ion exists in tetrahedral and octahedral coordinations in the alkali silicate glasses. The relative ratio of tetrahedral to octahedral species of Ni 2+ also depends on the alkali species, and the content of the tetrahedral species of Ni 2+ in potassium or cesium silicate is greater than that in sodium silicate. From these two results, it is assumed that, while NiO dissolves in the silicate melts as a weak base, some Ni 2+ ions change into a tetrahedral coordination in a strongly basic solvent such as cesium silicate.

Compositional and temperature effects on five-coordinated silicon in ambient pressure silicate glasses

Using 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, silicon coordinated by five oxygens has recently been found in a number of alkali silicate glasses quenched from liquids both at high and ambient pressure. In this report, both the presence of this species in other ambient-pressure samples and the increase in its concentration with fictive temperature are confirmed. However, it has not been possible to detect this species in a hydrated cesium silicate glass sample or in a silica gel, the latter at a detection limit of about 0.02%. Also as previously noted for high-pressure samples, it is found that five-coordinated Si is more abundant in K 2Si 4O 9 than in Na 2Si 4O 9 glass. Given the effects of alkali size on the coordination and bonding to oxygen known from crystalline silicates, this finding supports a mechanism for the formation of the high-coordinate species that involves the consumption of non-bridging oxygens.

Acidity and ionic structure of molten alkali silicates

An attempt has been made to identify the structural elements in binary lithium, sodium, potassium and cesium silicate melts by voltammetry. In the lithium melts g-SiO 2 or quartz-like clusters are proposed, although other interpretations are possible. Further, a second voltammetric wave may be an indication of peroxo bonds in lithium melts. In sodium melts, anions derived from cristobalite have been confirmed by comparison with information from Raman spectra, as have the tridymite derivatives in potassium melts. The structural elements in cesium silicate melts resemble those of potassium. The influence of the alkali ion on the acidity of the melt is calculated and is found to increase in the order Cs < K < Na < Li.

Vaporisation of Cesium from Cesium Metaborate, Cesium Silicate, Cesium Borosilicate and Mixtures of Cesium Nitrate, Boric Oxide and Silica

Volatilisation loss of cesium from glass melts and from glass batches containing cesium nitrate has been reported. Transpiration vapour pressure measurement of stoichiometric CsBO2 in the temperature range 898–1361° K and pseudo-vapour pressure of cesium over cesium silicate and cesium borosilicate in the temperature range 1323–1423° K have been determined. Cesium metaborate has a vapour pressure of the order of 10−2 atmosphere at 1361° K whereas cesium vapour pressures over cesium tetrasilicate and cesium borosilicate are of the order of 10−5 atmosphere. Cesium vapour pressure over cesium borosilicate is about 3 times higher at 1150° C than the corresponding pressure of cesium silicate. Heat and entropy of evaporation for the reaction CsBO2 (l) ⇌ CsBO2 (v) have been found to be 41.38 ± 4 Kcal/mole and 23.5 e.u. respectively.The reaction between CsNO3 and SiO2 or B2O3 is rapid and is accompanied with evolution of NO2 fumes. Rapid reaction between CsNO3 starts at about 680° C and is complete within 15 minu...

Ionic Conduction and Structure in Cesium and Thallium Silicate Glasses

Density, NMR absorption, and ionic conductivity were measured for cesium and thallium silicate glasses. Results indicate that the cesium ions change their environment between 20 and 35 mole % Cs2O, possibly by means of a phase separation. These observations are consistent with the composition independence of the activation energy for conduction above 25 mole % Cs2O but do not reflect the rapid change in activation energy below 25 mole %. The extreme breadth of the 205Tl NMR Une varied with Tl2O content in the same manner as the activation energy for conduction. This result indicates that the distribution of ionic environments may provide a similar distribution of energy barriers to ionic motion. The relation between ionic conduction and structure appears to be different in cesium and thallium silicate glasses.