The Thermal Decomposition of Sodium Nitrate and the Effects of Several Oxides on the Decomposition

Abstract The thermal decomposition of sodium nitrate and the effects of several oxides, such as silica, titania, zirconia, alumina, and magnesia, on the decomposition were studied up to 900 °C by means of the thermal analysis, gas analysis, and chemical analysis of the reaction products. The reaction of sodium nitrate and silica was especially investigated in some detail over a wide composition range. The thermal decomposition of sodium nitrate started at about 450 °C. The gases formed were O2, NO, and N2, the formation of N2 being detected above 680 °C The thermal decomposition of sodium nitrate was supposed to consist of the following three successive or concurrent reaction processes, according to the degree of the reaction: (I) the decomposition of sodium nitrate to nitrite and oxygen, (II) the first-order liquid-phase reaction, with some kind of quantitative relationship between nitrate and nitrite, and (III) the formation reaction of sodium oxide, expressed by the Avrami-Erofe’ef equation. The (II) and (III) reaction processes can be reasonably interpreted if the existence of the peroxide ion is assumed. Acidic oxides, such as silica and titania, were supposed to lower the activation energy of the (III) reaction process by forming stable salts with sodium nitrate and/or its intermediate reaction products. The effects of these oxides on the thermal decomposition of sodium nitrate could be interpreted by the relative scale of the acidity of oxides.