Double pyrovanadates CaMgV₂O₇: Formation mechanism, phase structure, and thermodynamic properties

Abstract

A double pyrovanadate CaMgV 2 O 7 sample was synthesized via a facile solidstate route under an air atmosphere. The nonequilibrium formation pathways of the CaMgV 2 O 7 were investigated via powder X-ray diffraction. A multistep reactions path (metavanadates-pyrovanadates-double pyrovanadate CaMgV 2 O 7 ) was proposed to describe the formation of the CaMgV 2 O 7 considering the thermodynamic and kinetic factors. The cell unit parameters of the CaMgV 2 O 7 sample indicated the crystallization according to a monoclinic system with space group P12/c1( 14), and the lattice parameters of a = 6.756 Å, b = 14.495 Å, c = 11.253 Å, β = 99.12, and V = 108.806 Å 3 . X-ray photoelectron spectroscopy also confirmed the +5 oxidation state vanadium in CaMgV 2 O 7 . The endothermic effects at 1033 and 1143 K were related to the incongruent melting and liquidus temperatures of CaMgV 2 O 7 , respectively. The comprehensive thermodynamic properties of CaMgV 2 O 7 were established in both low-and high-temperature regions, utilizing a physical property measurement system and multi-hightemperature calorimetry (96 lines). The heat capacity (200 J mol K −1 ) and entropy (198 J mol K −1 ) at 298.15 K were computed based on the low-temperature heat capacity values, and the enthalpy of formation at 298.15 K was also estimated. The fitted high-temperature capacity can be used to obtain the changes in the enthalpy, entropy, and Gibbs free energy. This study is part of building a reliable thermodynamic database of the CaO-MgO-V 2 O 5 system.

The phase structure, thermodynamic properties, and dissolution behavior of Ca5Mg4V6O24

“…The molar C p of the Ca 5 Mg 4 V 6 O 24 at 298.15 K is equal to 374 J mol K −1 based on present measurements, and the entropy at 298.15 K is calculated to be 687.5 J mol K −1 . It should be noted that the temperature range of measurement in this study is 10–300 K, and the contribution to entropy below 10 K was calculated using Debye model, Debye temperature θ D can be obtained using the B 3 term in Equation () according to the relation θ D = (12 R π 4 /5 B 3 ) 1/3 43,44 . The entropy contribution using Debye model below 10 K is 0.1323 J mol −1 K −1 .…”

“…Vanadium is widely utilized in high‐temperature alloys, advanced energy materials, and catalysts, owing to its special physical and chemical properties 1–4 . Most of the vanadium in the world is extracted from the vanadium titanomagnetite ore 5 .…”

“…Vanadium is widely utilized in high-temperature alloys, advanced energy materials, and catalysts, owing to its special physical and chemical properties. [1][2][3][4] Most of the vanadium in the world is extracted from the vanadium titanomagnetite ore. 5 One of the traditional and common processes for extracting vanadium from vanadium slag, which is obtained by oxidizing the hot metal bearing vanadium, is sodium salt roasting followed by water leaching. However, this traditional vanadium extraction process is not favorable anymore due to the harmful gas emission, fusion agglomeration by the liquid phase at high roasting temperatures, and high content of alkali metal in tailings and wastewater.…”

High‐temperature phase transformation and thermodynamic properties of Ca3(VO4)2

“…For the Rietveld refinement, the pseudo‐Voigt and the spherical harmonics functions were applied to describe the Bragg reflection profile and measure the preferred orientation, respectively. More information and parameters about the Rietveld refinement are described elsewhere 18,19 . An inductively coupled plasma optical emission spectroscopy (ICP–OES) analysis, using an Optima 8000 Instrument (PerkinElmer), was carried out to quantitatively determine the vanadium content of the as‐prepared sample.…”

“…More information and parameters about the Rietveld refinement are described elsewhere. 18,19 An inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, using an Optima 8000 Instrument (PerkinElmer), was carried out to quantitatively determine the vanadium content of the as-prepared sample.…”