Enthalpy of formation of selected mixed oxides in a CaO–SrO–Bi2O3–Nb2O5 system

Calorimetric Determination of Heat Capacity, Entropy and Enthalpy of Mixed Oxides in the System CaO–SrO–Bi2O3–Nb2O5–Ta2O5

“…[52], T = 973 K. Table 7. Enthalpies of drop-solution in 3Na2O + 4MoO3 melt (ΔdsH) and enthalpy of formation from constituent binary oxides (ΔoxH) [30] Our values for the calcium niobates are in good agreement with Raghavan's data [7,8], while the data from Dneprova et al [11] [12] are substantially more exothermic than our calorimetric data. These large differences in the ΔoxH values are not surprising in view of simultaneous differences in the ΔoxS values from the assessment [12] and those derived from low temperature dependences of the molar heat capacity of SrNb2O6 and Sr2Nb2O7 [24,26].…”

“…The above presented data derived from calorimetric measurements became the basis for thermodynamic database FS-FEROX [58] compatible with the FactSage software [59,60]. Missing data for other stoichiometric mixed oxides were estimated by the empirical methods described before: the Neumann-Kopp's rule for heat capacities, the entropyvolume correlation for molar entropies and electronegativity-differences method for enthalpies of formation.…”

“…This review brings a summary of our results [20][21][22][23][24][25][26][27][28][29][30] focused on calorimetric determination of heat capacity, entropy end enthalpy of mixed oxides in the system CaO-SrO-Bi2O3-Nb2O5-Ta2O5. Temperature dependences of molar heat capacity in a broad temperature range were evaluated from the experimental heat capacity and relative enthalpy data.…”

Recovery and Purification of Tin from Tailings from the Penouta Sn–Ta–Nb Deposit

“…The CaO formed in the decomposition of the carbonate reacts with the columbotantalite and ixiolite to form mixed oxides of Ca, Nb and Ta-the majority compounds in the slag (Equation (7)), plus acicular Ca(Fe,Mn)2O2 (Figure 7). However, these latter ferrites were not detected by XRD, suggesting they may actually have an amorphous nature [30]. …”

“…The enthalpy of formation (ΔHox) of Ca2Nb2O7, calculated from the binary oxides, is −208 kJ·mol −1 [30]. Thus, when the enthalpy of decomposition (ΔH) of CaCO3 is taken into account at 298 K (178.8 kJ·mol −1 ), the formation of the Ca2Nb2O7 becomes possible under the carbothermic reduction conditions employed.…”