*Article* **Experimental Determination of Phase Equilibria in the Na2O-SiO2-WO<sup>3</sup> System**

**Baojun Zhao 1,2, Kun Su 2,\* and Xiaodong Ma 2,\***


**Abstract:** The present study investigated phase equilibria in the Na2O-SiO<sup>2</sup> -WO<sup>3</sup> system experimentally using high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA). New thermodynamic information on the Na2O-SiO<sup>2</sup> -WO<sup>3</sup> system was derived based on the newly obtained experimental results and data from the literature. The primary phase fields of sodium metasilicate, sodium disilicate, and tridymite were determined along with the isotherms at 1073, 1173, and 1273 K. The solubilities of WO<sup>3</sup> in SiO<sup>2</sup> , Na2Si2O<sup>5</sup> , and Na2SiO<sup>3</sup> , and the solubility of SiO<sup>2</sup> in Na2WO<sup>4</sup> were accurately measured using EPMA. Comparisons between the existing and newly constructed phase diagram were carried out and the differences are discussed. The phase equilibrium data will be beneficial to the future development of sustainable tungsten industries and thermodynamic modelling in WO<sup>3</sup> related systems.

**Keywords:** phase equilibria; thermodynamics; Na2O-SiO<sup>2</sup> -WO<sup>3</sup> system; liquidus temperature; pyrometallurgy
