Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10

Abstract

An isothermal section of the system Al 2 O 3 -CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca 3 CoAl 4 O 10 , was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca 3 CoAl 4 O 10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: ð-ÞPt; CaAl 2 O 4 + Ca 12 Al 14 O 33 + Ca 3 CoAl 4 O 10 + Co//(CaO)ZrO 2 //CoO + Co; Pt ð + Þ: From the emf of the cell, the standard Gibbs energy change for the Ca 3 CoAl 4 O 10 formation reaction, CoO + 3/5CaAl 2 O 4 + 1/5Ca 12 Al 14 O 33 fi Ca 3 CoAl 4 O 10 , is obtained as a function of temperature: DG o r /J mol 21 (±50) = 22673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca 3 CoAl 4 O 10 from its component binary oxides, Al 2 O 3 , CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca 3 CoAl 4 O 10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al 2 O 3 -CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.

Ru Ti1−O2 as the support for Pt nanoparticles: Electrocatalysis of methanol oxidation

“…In Ru 0.7 Ti 0.3 O 2 the intensity of the anatase peaks is relatively low, so TiO 2 is likely to be distributed within anatase and solid solution of TiO 2 in RuO 2 . According to the phase diagram of RuO 2 -TiO 2 system in air [35], at temperatures below 1400 K the solubility of TiO 2 in RuO 2 , as well as solubility of RuO 2 in TiO 2 is less than 10 at%, which means that in Ru 0.7 Ti 0.3 O 2 single Here, it should be considered that phase diagrams relate to bulk phases, while the oxide samples examined are nano-sized particles.…”

Phase equilibria in Ca–Co–O system

“…The thermodynamic behavior of high temperature rock-salt type Ca 1 À x Co x O solid solution has been studied by several authors by direct determination of miscibility limits by phase equilibration studies [12,16,17] and by measuring the respective component activities in solid electrolyte galvanic cells [23,24]. Although only the data reported by Jakob et al [16] and Mukhopadhyay and Jakob [17] were used to evaluate the temperature dependent R-K parameters for excess Gibbs energy (Eq.…”

“…Although only the data reported by Jakob et al [16] and Mukhopadhyay and Jakob [17] were used to evaluate the temperature dependent R-K parameters for excess Gibbs energy (Eq. (2), Table 3), the agreement between the other experiments and the miscibility gap calculated using the optimized parameter values shown in Fig.…”

“…In this study we thus focus on the assessment of the Ca-Co-O phase diagram based on both our and literature experimental data [12][13][14][15][16][17]. Since the system under study should be considered as closed for Ca and Co while open for oxygen which is exchanged with the surrounding atmosphere and whose content is determined and controlled by the oxygen activity in surroundings, the phase diagram is represented by means of three experimentally adjustable predictors -temperature, cation composition and oxygen activity (partial pressure).…”

Thermodynamic properties of Pb2PtO4 and PbPt2O4 and phase equilibria in the system Pb–Pt–O

“…Phase equilibria in the systems Pb-Ru-O [9], PbO-RuO 2 -TiO 2 [11] and RuO 2 -TiO 2 in air [12] have been delineated. Also available is a thermodynamic analysis of the interaction between Pb(Zr,Ti)O 3 solid solutions and RuO 2 electrodes as a function of PZT composition, temperature and oxygen partial pressure [13].…”