This paper briefly summarizes studies related to the oxidation of Fe-Al alloys. Emphasis is placed on oxide phase composition, morphology, and the development of protective α-Al2O3 scales on oxidation-resistant Fe-Al alloys both with and without ternary additions.

The oxidation of iron-aluminum alloys

Solid solutions of hematite (α-Fe2O3) and corundum (α-Al2O3) have been synthesized by coprecipitation. The resulting particles have been used as oxygen carriers for the production of hydrogen by chemical looping and characterized using X-ray diffraction (XRD), temperature programmed reduction (TPR), specific surface area measurements (BET), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDXS). The particles were repeatedly (i) reduced with, e.g., CO to, nominally, Fe, (ii) then oxidized with steam to Fe3O4 to produce hydrogen, (iii) then returned to Fe2O3 by oxidizing with air. The optimum loading of Al2O3 in the composite particles was found to be 25 wt % for the production of hydrogen over 50 cycles, resulting in an average yield (mole H2 formed/theoretical amount possible on reduction to Fe and oxidation to Fe3O4) of hydrogen of ∼48%. It was found that although Al2O3 is often thought of as inert, it participates in the oxidation and reduction reactions by forming FeAl2O4 ...

Interaction of Iron Oxide with Alumina in a Composite Oxygen Carrier during the Production of Hydrogen by Chemical Looping

The Fe-O (Iron-Oxygen) System

The use of solid electrolytes for the measurement of the thermodynamic properties of materials is reviewed. A concise history of the development of solid electrolyte galvanic cell techniques is presented, and their advantages and the essential criteria for the satisfactory application of the method are discussed. The principal electrolytes in contemporary use and investigations for which they have been employed are surveyed. Special variations of the cell technique used in thermodynamic and phase equilibria studies are described. A bibliographic review of major investigations up until 1988 is included.

Applications of solid electrolytes in thermodynamic studies of materials: A review

Composites of an intermetallic alloy matrix (such as iron aluminide) and ceramic particle reinforcement (such as alumina) have potential for high-temperature structural applications requiring excellent oxidation resistance. In contrast to conventional processing methods (e.g. mechanical alloying), in situ processing techniques can be inexpensive and can also lead to unique microstructures, such as very fine dispersions of the reinforcements or interconnecting phases. The feasibility of processing Fe–Al alloy/Al2O3 composites by an in situ displacement reaction between Fe–40at.%Al and the iron oxide Fe2O3 was investigated and the results are presented in this paper. Specimens were prepared by hot pressing of the powder mixtures at 1300°C. The final volume fractions of Al2O3 were determined by the initial ratio of Fe–40%Al to Fe2O3 and composites with 7 and 20 vol.% Al2O3 were investigated in this study. Compression creep tests performed at 700°C showed that composites with 7 and 20 vol.% Al2O3 had higher compressive strengths than monolithic iron aluminide (Fe–28at.%Al). In particular, the compressive strength of the composite with 20 vol.% Al2O3 was three times that of the monolithic iron aluminide. Further increases in compressive strength, as well as significant improvements in bend and fracture strength, were obtained when the particle size of the starting Fe–40%Al powders was less than 10 μm. Improved fracture toughness with the smaller Fe–40%Al powders could be attributed to the ductile failure of fine iron aluminide ligaments. The effect of Cr and Ti additions of up to 8 at.% on the strength of the interface between the iron aluminide and alumina phases was also investigated. The compressive strength of a composite processed with

Iron aluminide–Al2O3 composites by in situ displacement reactions: processing and mechanical properties

Equilibrium oxygen pressures of the univariant ternary coexistences hematite + spinel + alumina, alloy + wustite + spinel, and alloy + spinel + alumina were determined at temperatures in the range 1123 to 1423 K using solid state electrochemical cells. The compositions of alloys and oxide phases of this Fe-Al-0 system that equilibrated with one another at 1273, 1423, and 1573 K were determined. These results and those from the literature are used to determine stabilities of the ternary oxide phases as a function of oxygen pressure and composition by constructing equilibrium oxygen pressure diagrams at 1073, 1173, and 1273 K.

F. A. Elrefaie

Papers

Thermodynamics of the system iron-aluminum-oxygen between 1073 K and 1573 K