Spinel deoxidation equilibria in the Fe Mn Al O system - experiments and computation

The concentration and chemical potential of oxygen in liquid Fe--Mn alloys equilibrated with the spinel solution, (Fe, Mn)Al sub 2+2x O sub 4+3x , and alpha -Al sub 2 O sub 3 have been determined at 1873K as a function of manganese concentration. The composition of the spinel phase has been determined using electron probe microanalysis. The results are compared with data reported in the literature. The deoxidation equilibrium has been computed using data on free energy of solution of oxygen in liquid iron, free energies of formation of hercynite and galaxite, and interaction parameters reported in the literature. The activity--composition relationship in spinel solution was derived from a cation distribution model. The model is in excellent agreement with the experimental data on oxygen concentration and potential and the composition of the spinel phase. 23 ref.--AA

Measurement and modeling of Alloy-Spinel-Corundum equilibrium in the Ni-Mn-Al-0 system at 1873 K

The oxygen content of liquid Ni-Mn alloy equilibrated with spinel solid solution, (Ni,Mn)O. (1 +x)A12O3, and α-Al2O3 has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential of the three-phase system has been determined with a solid state cell incorporating (Y2O3)ThO2 as the solid electrolyte and Cr + Cr2O3 as the reference electrode. The equilibrium composition of the spinel phase formed at the interface of the alloy and alumina crucible was obtained using EPMA. The experimental data are compared with a thermodynamic model based on the free energies of formation of end-member spinels, free energy of solution of oxygen in liquid nickel, interaction parameters, and the activities in liquid Ni-Mn alloy and spinel solid solution. Mixing properties of the spinel solid solution are derived from a cation distribution model. The computational results agree with the experimental data on oxygen concentration, potential, and composition of the spinel phase.

Alloy oxide equilibria in the system Ca Al O at 1373 K

The tie lines delineating equilibria between different oxides of the Ca-Al-O system and liquid Ca-Al alloy has been determined at 1373 K. Equilibration of the alloy with two adjacent oxide phases in the CaO-Al2O3 pseudo-binary system was established in a closed cell made of iron. Equilibrium oxide phases were confirmed by x-ray analysis and alloy compositions were determined by chemical analysis. The compound 12CaO.7Al2O3 Ca12Al14O33 was found to be a stable phase in equilibrium with calcium alloys. The experimental diagram is consistent with that calculated from the free energies of formation of the oxide phases and activities in liquid Ca-Al alloys at 1373 K reported in the literature.

System Cu-Rh-O: Phase diagram and thermodynamic properties of ternary oxides CuRhO2 and CuRh204

An isothermal section of the phase diagram for the system Cu-Rh-O at 1273 K has been established by equilibration of samples representing eighteen different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). In addition to the binary oxides Cu2O, CuO, and Rh2O3, two ternary oxides CuRhO2 and CuRh2O4 were identified. Both the ternary oxides were in equilibrium with metallic Rh. There was no evidence of the oxide Cu2Rh2O5 reported in the literature. Solid alloys were found to be in equilibrium with Cu2O. Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. Yttria-stabilized zirconia was used as the solid electrolyte, and an equimolar mixture of Rh+Rh2O3 as the reference electrode. The reference electrode was selected to generate a small electromotive force (emf), and thus minimize polarization of the three-phase electrode. When the driving force for oxygen transport through the solid electrolyte is small, electrochemical flux of oxygen from the high oxygen potential electrode to the low potential electrode is negligible. The measurements were conducted in the temperature range from 900 to 1300 K. The thermodynamic data can be represented by the following equations: {fx741-1} where Δf(ox) G o is the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides. Based on the thermodynamic information, chemical potential diagrams for the system Cu-Rh-O were developed.

Stress Evolution With Temperature in Titanium-Rich NiTi Shape Memory Alloy Films

The effect of deposition temperature on residual stress evolution with temperature in Ti-rich NiTi films deposited on silicon substrates was studied. Ti-rich NiTi films were deposited on 3? Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 degrees C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 degrees C and the lowest for the film deposited and annealed at 300 degrees C. All the three films were found to be amorphous in the as-deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 degrees C) was similar for all three films although the spike in tensile stress, which occurs at similar to 330 degrees C, was significantly higher in the film deposited and annealed at 300 degrees C. All the films were also found to undergo partial crystallisation on heating up to 450 degrees C and this resulted in decrease in the stress values around 5560 degrees C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 degrees C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.

A Generalized Enthalpy Update Scheme for Solidification of a Binary Alloy with Solid Phase Movement

A generalized enthalpy update scheme is presented for evaluating solid and liquid fractions during the solidification of binary alloys, taking solid movement into consideration. A fixed-grid, enthalpy-based method is developed such that the scheme accounts for equilibrium as well as for nonequilibrium solidification phenomena, along with solid phase movement. The effect of solid movement on the solidification interface shape and macrosegregation is highlighted.

Evolution of sub-micron grain size and weak texture in magnesium alloy Mg-3Al-0.4Mn by a modified multi-axial forging process

This is the first successful attempt to produce simultaneously ultrafine grain size and weak texture in a single-phase magnesium alloy Mg-3Al-0.4Mn through an optimal choice of processing parameters in a modified multi-axial forging (MAF) process. An average grain size of similar to 0.4 mu m and a weak texture could be achieved. This has led to an increase in the strength as well as room-temperature ductility (55%). The plot of the yield loci shows a decrease in anisotropy after MAF. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Influence of Tempered Microstructures on the Transformation Behaviour of Cold Deformed and Intercritically Annealed Medium Carbon Low Alloy Steel

This research is focused on understanding the role of microstructural variables and processing parameters in obtaining optimised dual phase structures in medium carbon low alloy steels. Tempered Martensite structures produced at 300, 500, and 650 degrees C, were cold rolled to varied degrees ranging from 20 to 80% deformation. Intercritical annealing was then performed at 740, 760, and 780 degrees C for various time duration ranging from 60 seconds to 60 minutes before quenching in water. The transformation behaviour was studied with the aid of optical microscopy and hardness curves. From the results, it is observed that microstructural condition, deformation, and intercritical temperatures influenced the chronological order of the competing stress relaxation and decomposition phase reactions which interfered with the rate of the expected alpha -> gamma transformation. The three unique transformation trends observed are systematically analyzed. It was also observed that the 300 and 500 degrees C tempered initial microstructures were unsuitable for the production of dual structures with optimized strength characteristics.

Phase relations and Gibbs energies of spinel phases and solid solutions in the system Mg-Rh-O

Pure stoichiometric MgRh(2)O(4) could not be prepared by solid state reaction from an equimolar mixture of MgO and Rh(2)O(3) in air. The spinel phase formed always contained excess of Mg and traces of Rh or Rh(2)O(3). The spinel phase can be considered as a solid solution of Mg(2)RhO(4) in MgRh(2)O(4). The compositions of the spinel solid solution in equilibrium with different phases in the ternary system Mg-Rh-O were determined by electron probe microanalysis. The oxygen potential established by the equilibrium between Rh + MgO + Mg(1+x)Rh(2-x)O(4) was measured as a function of temperature using a solid-state cell incorporating yttria-stabilized zirconia as an electrolyte and pure oxygen at 0.1 MPa as the reference electrode. To avoid polarization of the working electrode during the measurements, an improved design of the cell with a buffer electrode was used. The standard Gibbs energies of formation of MgRh(2)O(4) and Mg(2)RhO(4) were deduced from the measured electromotive force (e.m.f.) by invoking a model for the spinel solid solution. The parameters of the model were optimized using the measured composition of the spinel solid solution in different phase fields and imposed oxygen partial pressures. The results can be summarized by the equations: MgO + beta -Rh(2)O(3) -> MgRh(2)O(4); Delta G degrees (+ 1010)/J mol(-1) = -32239 + 7.534T; 2MgO + RhO(2) -> Mg(2)RhO(4); Delta G degrees(+/- 1270)/J mol(-1) = 36427 -4.163T; Delta G(M)/J mol(-1) = 2RT(xInx + (1-x)In(1-x)) + 4650x(1-x), where Delta G degrees is the standard Gibbs free energy change for the reaction and G(M) is the free energy of mixing of the spinel solid solution Mg(1+x)Rh(2-x)O(4). (C) 2011 Elsevier B. V. All rights reserved.

Kinetics of carbon monoxide oxidation with Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts

Base metal substituted Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts were synthesized by the solution combustion method and characterized by XRD, XPS, TEM and BET surface area analysis. The catalytic activities of these materials were investigated by performing CO oxidation. The rates and the apparent activation energies of the reaction for CO oxidation were determined for each catalyst. All the substituted catalysts showed high rates and lower activation energies for the oxidation of CO as compared to unsubstituted SnO(2). The rate was found to be much higher over copper substituted SnO(2) as compared to other studied catalysts. 100% CO conversion was obtained below 225 degrees C over this catalyst. A bifunctional reaction mechanism was developed that accounts for CO adsorption on base metal and support ions and O(2) dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. The high rates of the CO oxidation reactions at low temperatures were rationalized by the high dissociative chemisorption of adsorbed O(2) over these catalysts.

Structure and Photocatalytic Activity of Ti 1- x M x O 2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements. The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions. The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1-xMxO2±δ. The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation. However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25. The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2.

Synthesis, structure and photocatalytic activity of nano TiO2 and nano Ti1-xMxO2-delta (M = Cu, Fe, Pt, Pd, V, W, Ce, Zr)

We have synthesized 5-7 nm size, highly crystalline TiO2 which absorbs radiation in the visible region of solar spectrum. The material shows higher photocatalytic activity both in UV and visible region of the solar radiation compared to commercial Degussa P25 TiO2. Transition metal ion substitution for Ti4+ creates mid-gap, states which act as recombination centers for electron-hole induced by photons thus reducing photocatalytic activity. However, Pt, Pd and Cu ion substituted TiO2 are excellent CO oxidation and NO reduction catalysts at temperatures less than 100 degrees C.

Creep behaviour of short fibre reinforced QE22 magnesium alloy using impression creep test

Creep properties of QE22 magnesium based alloy and composites reinforced with 20 volume percent of short-fibers - Maftech (R), Saffil (R) or Supertech (R), were evaluated using the impression creep test. In the impression creep test, a load is applied with the help of a cylindrical tungsten carbide indenter of 1 mm diameter. This has advantages over conventional creep testing in terms of small specimen size requirement and simple machining. Depth of impression is recorded with time and steady state strain rate is obtained from the slope of the secondary strain (depth of impression divided by indenter diameter) vs. time plot. The results are compared with the creep obtained from conventional creep performed in tension on the same materials earlier. Microstructural examination of the plastically deformed regions is carried out to explain creep behaviour of these composites.