Three earlier determinations of the phase diagram of the sodium nitrite/sodium nitrate binary system resulted in considerably different conclusions, ranging from simple eutectic to continuous solid solution types, together with different sub-solidus lines. Recent melting enthalpy measurements have shown this binary system to be a simple eutectic. An isothermal solidus, ranging from 25 to 80 mole %, was indicated by differential scanning calorimetry (DSC) results together with a smaller endotherm feature at 150 oC. However the liquidus is probably that found early by the three sets of investigators, who, despite their other disparate conclusions, agreed on the liquidus position to be within ± 3 oC. New DSC and Raman mapping measurements of solidified mixtures of minimum melting point have provided support for a simple eutectic diagram with a solidus at 230 oC extending from 25 to 80 mole %. A sub-solidus transition was detected at 183 oC and a second at 159 oC by Raman spectroscopy measurements over a range of temperatures, showing an abrupt change of slope at around 150 oC when the wavenumber position of two bands (NO2- symmetric bending and stretching) is plotted versus temperature. The latter is considered to be related to the nitrite component and probably arising from the ferroelectric transition of sodium nitrite. The variation of the Raman lines with temperature also gave support to the latter transition.
|Title of host publication||EUCHEM 2004 Molten Salts Conference, June 20-25, 2004 : To appear in print|
|Place of Publication||Faculty of Chemistry, University of Wroclaw, Poland|
|Publication status||Published - 2004|
|Event||EUCHEM 2004 Molten Salts Conference, June 20-25 : Extended abstract Paper - Piechowice, Poland|
Duration: 1 Jan 2004 → …
|Conference||EUCHEM 2004 Molten Salts Conference, June 20-25 : Extended abstract Paper|
|Period||01/01/2004 → …|