The total chromium oxide (Cr2O3) solubility is measured in Na2O–xSiO2 melts as a function of temperature (1125°

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Chromium oxide solubility was measured in soda-lime-silicate melts using a thermochemical reactor allowing an independent control of temperature, glass composition, and oxygen fugacity in a closed system. This investigation performed in the ternary Na 2 O-CaO-xSiO 2 (NCS) system showed that the physicochemical and thermochemical models used for chromium chemistry description in binary melts are applicable in the ternary system. The presence of Cr(II), Cr(III), and Cr(VI) has been evidenced and their respective contributions in the total chromium content dissolved in the melt were determined. A new approach based on optical basicity allowed the quantification of the basicity of the melt and consequently the free oxygen ions activity (aO 2À ). The treatment of the obtained results led to the determination of thermodynamical properties of the system. The standard enthalpies and entropies corresponding to the oxidation and reduction reactions were determined. J. Smialek-contributing editorThis work was financially supported by the ANR through the Actimelt project.