Increasing Na2O Content Research Articles

Heats of Solution of Sodium Phosphate Glasses

Heats of formation for some glassy and crystalline sodium phosphates were investigated by measuring their heats of solution in distilled water and in 3N-HNO3 aq. using a microcalorimeter.The glass samples used in this study were prepared from reagent grade NaOH and H3PO4 through dehydrating condensation, that is, these reagents were mixed in such proportions that the resulting glasses possessed given chemical compositions and heated in a platinum crucible at 700° to 800°C for 2 hours to drive off water. The samples thus obtained were chemically analyzed for a constituent P2O5 and “residual water” which reached a maximum content of 2.5wt%.In this study the solution calorimetry was made with a twin type differential microcalorimeter in which the quantity of heat is measured as difference of the electromotive force produced with the thermomodules. The detecting sensitivity is 6.5mV/°C, and the thermostat is regulated within ±1μV. Both the time and the temperture difference were successively plotted in a recorder and the quantity of heat was measured as an area enclosed between the temperature curve and the time-axis, which was later compared with a standard heater for correction.It was confirmed by paper chromatography that both the glassy and crystalline samples were decomposed into orthophosphate molecules with 3N-HNO3 aq.. The heats of solution for water and 3N-HNO3 aq. at 25°C were found to be exothermic and the dependence of the chemical composition is shown in Figs. 9 and 10 where a minimum is seen near the meta composition on the curve of the phosphate glasses.At the stoichiometric meta composition the enthalpy difference between the glassy and crystalline samples was estimated to be about 21cal/g and the heat of formation of NaPO3 glass from Na(s), P(s) and O2(g) states was of about 277kcal/mole. The increase of ΔH in the ultra phosphate region may be attributed to hydrolysis of branching points in chain structure but the increase in the polyphosphate region can be explained by increase of P-ONa→P-OH ion-exchange reaction because the long chain structure is more easily cut by Na+ ions with increasing Na2O content in the glass. The enthalpy change associated with annealing of the glass was thought to be negligible small.

Isomorphic sodium admixture in garnets formed at high pressures

Na2O contents were determined by electron microprobe analysis in 124 garnets from diamonds, xenoliths of peridotites, eclogites from kimberlitic pipes and metamorphic complexes. Na2O content ranges between 0.01 and 0.22% with the limit of detection at about 0.01%. In the garnets of diamond-bearing eclogites and orange garnets from diamonds a regular increase in the Na2O content has been established, varying from 0.09 to 0.22, as compared to garnets from eclogites of metamorphic complexes (range 0.01 to 0.06). It is assumed that the increased Na2O content in the garnets of eclogites is mainly connected with higher pressure, whereas isomorphism of sodium is connected with the initial stages of the transition from Si4 to Si6 in the garnet structure: CaAl⇄NaSi.

DIELECTRIC LOSS OF GLASS AT HIGH FREQUENCIES*

Power factor measurements at frequencies of 100, 500, 1500, and 5000 kilocycles were made on a series of soda-lime-silica glasses and on another series of glasses, starting with a base glass of the composition of 17.4% Na2O, 10.1% CaO, 72.5% SiO2 (or 1.4 Na2O to 0.9 CaO to 6.0 SiO2), to which 0.030 gram-atom of various elements in the form of their oxides were added. In the first series, the power factor for all glasses measured decreased with increasing frequency and increased markedly with increase in Na2O content. In the second series, the power factor decreased with increasing frequency as in the case of the first series. An increase in power factor was produced by additions of Zr, Na, and Al oxides, and a decrease was produced by additions of the oxides of Si, V, Zn, Mg, B, Ti, Co, Ca, Ce, Ni, Mn, Fe, Ba, Pb, Li, and K.