Thermodynamic properties of Na2MgSiO4: DFT calculation and experimental validation

Abstract

Magnesium disodium silicate Na2MgSiO4 (N2MS) was synthesized by the sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The synthesized N2MS is a single-phase material with an orthorhombic crystal structure, and the Rietveld refined parameters are a = 10.7976 Å; b = 5.2736 Å; c = 7.0349 Å; V = 400.585 (1) Å3, Z = 4, Mr = 162.367 g mol−1, Dx = 2.692 g cm−3. The thermodynamic properties of N2MS including heat capacity (C), entropy (S), Helmholtz free energy (F), thermal expansion coefficient and bulk modulus, were computed from the first principles using the density functional theory (DFT). The heat capacity (230-800 K) was measured and fitted as Cp = 138.41053 + 173.93 × 10−3T - 19.4389 × 105 T−2-11.5876 × 10−5T2 by the Differential Scanning Calorimetry (DSC) sapphire method. The heat capacity experimentally measured shows a good agreement with that computed heat capacity by DFT, and the thermodynamic functions ΔHT-300, ΔST-300 and ΔGT-300 were calculated and fitted into polynomials.