I. Order–disorder transitions and solid state reaction kinetics in Na₂SO₄–K₂SO₄ system

Abstract

M. SUNITHA KUMARI and ETALO A. SECCO. Can. J . Chcm. 61, 594 (1983) The physicochemical aspects of the order-disorder phase transitions occurring in the Na2SOI-K2S0, system were investigated by thermal analyses, infrared absorption, and X-ray diffraction methods.Kinetic and structural studies on the compounds KNaSO, and K,Na(S0,)2 are reported in more detail.M. SUNITHA KUMARI et ETALO A. SECCO. Can. J . Chcm. 61, 594 (1983).Faisant appel i I'analyse thermique, a I'absorption infrarougc et i la diffraction dc rayons-X, on a dtudid les aspects physicoch~n~iqucs dcs transitions dc phase ordrc-ddsordrc sc produisant dans le systtrne Na,SO,-K2S0,.On rapporte d'unc fason plus dCtaillCc lcs ttudcs dc structurc ct dc cindtiquc cffcctudcs sur Ic KNaSO, ct le K,Na(SO,),.[Traduit par le journal] Introduction Our study on phase transitions in Na2S04 ( I ) has revealed a number of interesting effects such as the dependence of the enthalpy of transition, the dependence of the transition temperature, and the dependence of the transition kinetics on the presence of K2S0,. Since Na2S04 and K2S04 are isostructural, orthorhombic at room temperature, our earlier work on phase transitions in K2S0, (2) could be extended to embrace the complete Na2S04-K2S04 composition range.The early papers of Nacken (3) and Janecke (4) recorded the Na2S04-K2S0, phase diagram showing the existence of solid-solid phase transitions over the whole range of composition. These early phase diagrams, however, leave a number of questions unanswered, e.g. the existence of compounds, the nature of the phase transitions, etc. Although the compounds KNaSO, and K,Na(S04)2 have been known for some time, it was only recently that Okada et u f . (5) have determined both structures to be trigonal at room temperature. This paper reports the results of a study on the condensed phase transitions in the Na2S04-K2S04 system and the kinetics of the solid state reactions between Na2S04 and K2S04 leading to the formation of KNaSO, and K,Na(SO& using thermal analyses, DSC, infrared spectroscopy, and X-ray diffractometry techniques.

Thermodynamic studies on the ferroelectric phase transition in neutron irradiated (LixK1−x)2SO4 crystals at high temperature

“…(4). As one can see [16], the further increase of x results in disappearance of the second high temperature phase besides the increase in the value of specific heat Cp at the first high temperature phase the same neutron fluence. …”

Thermodynamic evaluation and optimization of the (Na2SO4+ K2SO4+ Na2S2O7+ K2S2O7) system

“…A high-temperature solid solution with a hexagonal crystal structure also exists, and the intermediate phase, glaserite, K 3 Na(SO 4 ) 2 , shows considerable non-stoichiometry at temperatures above room temperature [27,28,[39][40][41][42]. Only the hexagonal phase shows solid solution over the whole compositional range of (Na 2 SO 4 + K 2 SO 4 ).…”

Inhomogeneous strain induced by fast neutron irradiation in NaKSO4 crystals

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A characteristic first-order phase transition of a solidsolid transformation in NaKSO4 crystals was observed using thermal analysis, infrared and X-ray diffraction techniques [1]. Previous studies of thermal properties of NaKSO4 crystals showed an anomaly in the temperature dependence of specific heat (Cp), linear thermal expansion coefficient, ~j, and heat transition, AQ, at 453 K [2].

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