Thermodynamics of CuAlO₂ and CuAl₂O₄ and Phase Equilibria in the System Cu₂O‐CuO‐Al₂O₃

Abstract

I , 0 3 / Ca0-Zr0,/02,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock-salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rocksalt and corundum structures. The temperatures corresponding to 3-phase equilibria in the system Cu20-Cu0-AI2O3 at specified 0, pressures calculated from the present results are discussed in reference to available phase diagrams. I. IntroductionHERMODYNAMIC data for CuAIO, and CuAI,O, are of interest T in determining the conditions under which Cu melts will react with refractories containing AI,O,. Rigby and Hamilton' identified CuA10, during petrological examination of high-AI20, bricks used in a Cu refining furnace. Von Wartenberg and Reusch, presented a phase diagram for the system Cu,O-AI,O,, and Misra and Chaklader? studied phase relations in the systems CuO-AI,O, and Cu,O-AI2O3 in air. Gadalla and White,4 who provided the most extensive information available for the system CU,O-CUO-A~~O,, used a thermobalance to measure the dissociation temperatures of prefired CuO+ Al2O3 mixtures underp,,'s from 0.21 to 1 atm. The thermodynamic information derived from these measurements is valid for only a limited temperature range (= 50°C) and cannot be used to derive accurate free energies of formation for the aluminates of Cu. There are significant discrepancies in the results of the phase diagram studies2-l; e.g. at 1 100"C, Von Wartenberg and Reusch identified no compounds in the system Cu20-A120, in air, whereas Misra and Chaklader reported CuA10, and Gadalla and White both CuA10, and CUAI,~,. The crystal structure of CuAIO, beloBgs to the rhoTbohedral system (D2d-R%n),l*5*6 with a = 3.489 A andc= 16.98 A. Cupric aluminate has a spinel structure similar to the structures of the aluminates and chromites of Mn, Fe, Co, Ni, and Zn. When spinel phases are formed from component oxides having rock-salt and corundum structures, the entropy of formation can be expressed as -1.75+AS"cal "C-' mol-I, wherehS" represents theentropyof cation mixing in the interstitial sites of the spinel structure, if the spinel phases do not exhibit tetragonal distortion at low temperat~res.~ Therefore, the entropy of the formation of spinel CuAI,O, from CuO and AlzO,, which have the tenorite and corundum structures, respectively, is of interest.Navrotsky and Kleppa8 measured the heat of formation of CuA1,0, as 5.17k0.2 kcal mol-l at 723°C by high-temperature oxide-melt-solution calorimetry. The free energy of formation of CuA10, was measured by Schmalzried9 at 1000°C using an emf method and by Zalazinskii et a1.I" from 700" to 1000°C using an HZ/H20 gas equilibrium method. The oxygen potential corresponding to the CU~O-CUO equilibrium has been firmly established by the direct dissociation temperature measurements of Foote and Smith," Roberts and Srnyth,l2 Gadalla et al., Hochgeschwender and Ingraham,', and Schmahl and Mueller'j and...

Catalytic combustion of methane on novel catalysts derived from Cu-Mg/Al-hydrotalcites

“…According to Severino et al [27] the reducibility of surface copper aluminate was lower than that of copper oxide, and the reduction of copper aluminates takes place in the range of 230-270°C. Thus, the last peak at 270°C may be attributed to the reduction of the bulk CuO in the mixed oxides [26]. Although the extent of reduction of 15CMAO-800 was lower than that of 20-40CMAO-800, its H 2 consumption peak was steeper, implying the rapid reduction of copper ions.…”

“…There was only one diffuse H 2 consumption peak centered at 350°C for 5CMAO-800, initialed at 230°C and ended around 390°C, which is higher than that of the bulk CuO reduction. This peak could be ascribed to the highly dispersed Cu 2þ in bulk periclase or copper aluminate structure, because the strong affinity of CuO and supports resulted in higher reduction temperature [26]. For the sample 10CMAO-800, the two peaks centered at 255 and 315°C corresponded to highly dispersed copper ions in the supported catalysts and in the bulk copper aluminates, respectively [21].…”

Thermal-Chemical Characteristics of Al–Cu Alloy Nanoparticles

“…In the Cu-Al system, the formation of complex aluminum copper oxide at atmospheric pressure conditions, i.e., PO2=0.21 atm, are generally observed at temperature above 1000 o C [40]. Here we showed the existence of CuAl2O4 phase at ~900 o C, which should be associated with the increased reactivity at the nanoscale and the early ignition phenomenon ~560 o C. As the diffusion of metallic ions at 900 o C was slow hence its formation was not favorable, which resulted in weak peaks observed (Eq.…”

Dellafossite CuAlO2 film growth and conversion to Cu–Al2O3 metal ceramic composite via control of annealing atmospheres

“…20 Normally it is considered essential to ensure that the Cu and Al are intimately 40 mixed in order to achieve a phase pure material and this requirement necessitates remixing and multiple anneals when preparing powders using solid state methods. In contrast, by complexing the Cu 2+ during sol-gel preparation methods phase separation can be inhibited leading to phase pure material, which 45 can be obtained in a single anneal.…”

“…There is a growing interest in transparent wide bandgap p-type 20 semiconductor oxides as they may become an essential component in the development of next generation devices in areas such as transparent electronics and solid state UV optoelectronics. [1][2][3] The discovery of intrinsic wide bandgap p-type conduction in the dellafossite material CuAlO 2 represents an 25 important step towards realising these technologies.…”