Hot deformation and microstructural evolution in an alpha(2)/O titanium aluminide alloy Ti-25Al-15Nb

Deformation processing and microstructural development of an alpha(2)/O aluminide alloy Ti-25Al-15Nb (at.%) was studied in the temperature range of 950 to 1200 degrees C and strain rate range of 10(-3) to 100 s(-1). Regions of processing and instability were identified using dynamic materials model. Dynamic recrystallization (DRX) of alpha(2)/O phase and p phase were seen to occur in the region of 950 to 1050 degrees C/0.001 to 0.05 s(-1) and 1125 to 1175 degrees C/0.001 to 0.1 s(-1), respectively. Unstable flow was seen to occur in the region of 1050 to 1190 degrees C/10 to 100 s(-1). Thermal activation analysis showed that DRX of alpha(2)/O and beta was controlled by cross-slip.

Deformation behaviour of commercially pure titanium at extreme strain rates

The evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions. At a low strain rate (epsilon)over dot = 3 x 10(-4) s(-1) the different initial textures yielded the same end texture, despite different microstructural evolution in terms of twin boundaries. High strain rate deformation at (epsilon)over dot = 1.5 x 10(3) s(-1) was characterized by extensive twinning and evolution of a texture that was similar to that at low strain rate with minor differences. However, there was a significant difference in the strength of the texture for different orientations that was absent for low strain rate deformed samples at high strain rate. A viscoplastic self-consistent model with a secant approach was used to corroborate the experimental results by simulation. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Processing map for the hot working of near-alpha titanium alloy 685

Using a dynamic materials model, processing and instability maps have been developed for near-alpha titanium alloy 685 in the temperature range 775-1025 degrees C and strain-rate range of 0.001-10 s(-1) to optimise its hot workability. The alloy's beta-transus temperature lies at about 1020 degrees C. The material undergoes superplasticity with a peak efficiency of 80% at 975 degrees C and 0.001 s(-1), which are the optimum parameters for alpha-beta working. The occurrence of superplasticity is attributed to two-phase microduplex structure, higher strain-rate sensitivity, low flow stress and sigmoidal variation between log flow stress and log strain rate. The material also exhibits how localisation due to adiabatic shear-band formation up to its beta-transus temperature with strain rates greater than 0.02 s(-1) and thus cracking along these regions. (C) 1997 Published by Elsevier Science S.A.

Synthesis of nanostructured titanium alloys

The synthesis of nanostructured materials is a critical step in the development elf these novel materials. The basic principles involved in the production of nanocrystals and nanocomposites by rapid solidification are dealt with. An analysis of the various factors influencing the final grain size of the nanocrystals achieved during mechanical alloying has been presented. The devitrification of amorphous phase formed during rapid solidification processing and mechanical alloying provides an alternative and attractive route. Examples of the synthesis of nanostructured materials using these three different routes are drawn from our work on titanium alloys.

Investigation of valence states in the perovskite oxides, LaAFeNbO(6) (A = Ca, Sr)

Compounds of the type, LaAFeNbO(6) (A = Ca Sr) have been synthesized to study the electrical and magnetic properties and to examine valence degeneracy. The results show that valence degeneracy is not operative and the compounds are insulating. Magnetic susceptibility data show that part of the Fe is in Fs(2+) state, thus oxidizing part of Nb4+ to Nb5+ by an internal redox mechanism. The presence of mixed valent Fe is confirmed by Mossbauer spectra. (C) 1999 Elsevier Science B.V. All rights reserved.

Thermodynamic modeling to analyse composition of carbonaceous coatings of MnO and other oxides of manganese grown by MOCVD

Equilibrium thermodynamic analysis has been applied to the low-pressure MOCVD process using manganese acetylacetonate as the precursor. ``CVD phase stability diagrams'' have been constructed separately for the processes carried out in argon and oxygen ambient, depicting the compositions of the resulting films as functions of CVD parameters. For the process conduced in argon ambient, the analysis predicts the simultaneous deposition of MnO and elemental carbon in 1: 3 molar proportion, over a range of temperatures. The analysis predicts also that, if CVD is carried out in oxygen ambient, even a very low flow of oxygen leads to the complete absence of carbon in the film deposited oxygen, with greater oxygen flow resulting in the simultaneous deposition of two different manganese oxides under certain conditions. The results of thermodynamic modeling have been verified quantitatively for low-pressure CVD conducted in argon ambient. Indeed, the large excess of carbon in the deposit is found to constitute a MnO/C nanocomposite, the associated cauliflower-like morphology making it a promising candidate for electrode material in supercapacitors. CVD carried out in oxygen flow, under specific conditions, leads to the deposition of more than one manganese oxide, as expected from thermodynamic analysis ( and forming an oxide-oxide nanocomposite). These results together demonstrate that thermodynamic analysis of the MOCVD process can be employed to synthesize thin films in a predictive manner, thus avoiding the inefficient trial-and-error method usually associated with MOCVD process development. The prospect of developing thin films of novel compositions and characteristics in a predictive manner, through the appropriate choice of CVD precursors and process conditions, emerges from the present work.

Synthesis and structure of a novel terminal imido complex of titanium

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis of mesoporous materials based on titanium(IV)oxide and titanium nitride

Nanoparticles of titania were obtained by the controlled hydrolysis of Ti(i-OC3H7)(4) in the reverse micelles of dodecylamine derived from dodecylamine-isopropanol-water solution (water/oil microemulsion). The mesolamellar phase based on titanium nitride (TiN) was obtained by first decomposing TiN atleast partially using the 1:1 solution of acid mixture (HF and HNO3 in the ratio of 9:1) in water and then templating onto the cationic surfactant namely, cetyltrimethylammaniumbromide (abbreviated as CTAB) at 80 degrees C. The synthesis of mesolamellar phase based on TiN involves the charge matched templating approach following the counter-ion mediated pathway. The samples thus obtained were characterized by small angle x-ray diffraction using Cuk(a) radiation, scanning electron microscopy and transmission electron microscopy, which indicated some satisfactory results. (C) 1999 Acta Metallurgica Inc.

Reaction of La2CuO4 with binary metal oxides in the solid state: Metathesis, addition, and redox metathesis pathways

Investigation of the reaction of La2CuO4 with several binary metal oxides in the solid state at elevated temperatures has revealed three different reaction pathways. Reaction of La2CuO4 with strongly acidic oxides such as Re2O7, MoO3, and V2O5 follows a metathesis route, yielding a mixture of products: La3ReO8/La2MoO6/LaVO4 and CuO. Oxides such as TiO2, MnO2, and RuO2 which are not so acidic yield addition products: La2CuMO6 (M = Ti, Mn, Ru). SnO2 is a special case which appears to follow a metathesis route, giving La2Sn2O7 pyrochlore and CuO, which on prolonged reaction transform to the layered perovskite La2CuSnO6. The reaction of La2CuO4 with lower valence oxides VO2 and MoO2, on the other hand, follows a novel redox metathesis route, yielding a mixture of LaVO4/LaCuO2 and La2MoO6/Cu, respectively. This result indicates that it is the redox reactivity involving V-IV + Cu-II --> V-V + Cu-I and Mo-IV + Cu-II --> Mo-VI + Cu-0, and not the acidity of the binary oxide, that controls the nature of the products formed in these cases. The general significance of these results toward the synthesis of complex metal oxides containing several metal atoms is discussed.

Removal of As(V) by adsorption onto mixed rare earth oxides

Arsenic pollution of water is a major problem faced worldwide. Arsenic is a suspected carcinogen in human beings and is harmful to other living beings. In the present study, a novel adsorbent was used to remove arsenate [As(V)] from synthetic solutions. The adsorbent, which is a mixture of rare earth oxides, was found to adsorb As(V) rapidly and effectively. The effect of various parameters such as contact time, initial concentration, pH, and adsorbent dose on adsorption efficiency was investigated. More than 90% of the adsorption occurred within the first 10 min and the kinetic rate constant was found to be about 3.5 mg min(-1). Adsorption efficiency was found to be dependent on the initial As(V) concentration, and the adsorption behavior followed the Langmuir adsorption model. The optimum pH was found to be 6.5. The presence of other ions such as nitrate, phosphate, sulphate, and silicate decreased the adsorption of As(V) by about 20-30%. The adsorbed As(V) could be desorbed easily by washing the adsorbent with pH 12 solution. This study demonstrates the applicability of naturally occurring rare earth oxides as selective adsorbents for As(V) from solutions.

Simultaneous reduction of oxides and dissolution of alumina in stainless steelmaking slag

During stainless steelmaking, reductions of oxides, dissolution of oxides in the slag, and foam formation take place simultaneously. Each of these phenomena independently has been studied by a number of investigators, but little information is available for these phenomena acting simultaneously. Experiments have been conducted to study the simultaneous reduction of oxides of chromium, vanadium, and iron from stainless steelmaking slag by carbon along with the dissolution of alumina in the slag. The overall phenomena and the effect on the chromium oxide reduction have been studied..

Systematic trends in structural and thermodynamic properties of ternary oxides in the systems Ln-Pd-O (Ln = lanthanide element)

Isothermal sections of the phase diagrams for the systems Ln-Pd-O (Ln = lanthanide element) at 1223 K indicate the presence of two inter-oxide compounds Ln(4)PdO(7) and Ln(2)Pd(2)O(5) for Ln = La, Pr, Nd, Sm, three compounds Ln(4)PdO(7), Ln(2)PdO(4) and Ln(2)Pd(2)O(5) for Ln = Eu, Gd and only one compound of Ln(2)Pd(2)O(5) for Ln = Tb to Ho. The lattice parameters of the compounds Ln(4)PdO(7), Ln(2)PdO(4) and Ln(2)Pd(2)O(5) show systematic nonlinear variation with atomic number. The unit cell volumes decrease with increasing atomic number. The standard Gibbs energies, enthalpies and entropies of formation of the ternary oxides from their component binary oxides (Ln(2)O(3) and PdO) have been measured recently using an advanced version of the solid-state electrochemical cell. The Gibbs energies and enthalpies of formation become less negative with increasing atomic number of Ln. For all the three compounds, the variation in Gibbs energy and enthalpy of formation with atomic number is markedly non-linear. The decrease in stability with atomic number is most pronounced for Ln(2)Pd(2)O(5), followed by Ln(4)PdO(7) and Ln(2)PdO(4). This is probably related to the repulsion between Pd2+ ions on the opposite phases Of O-8 cubes in Ln(2)Pd(2)O(5), and the presence of Ln-filled O-8 cubes that share three faces with each other in Ln4PdO7. The values for entropy of formation of all the ternary oxides from their component binary oxides are relatively small. Although the entropies of formation show some scatter, the average value for Ln = La, Pr, Nd is more negative than the average value for the other lanthanide elements. From this difference, an average value for the structure transformation entropy of Ln(2)O(3) from C-type to A-type is estimated as 0.87 J.mol(-1).K-1. The standard Gibbs energies of formation of these ternary oxides from elements at 1223 K are presented as a function of lanthanide atomic number. By invoking the Neumann-Kopp rule for heat capacity, thermodynamic properties of the inter-oxide compounds at 298.15 K are estimated. (C) 2002 Elsevier Science Ltd. All rights reserved.

System Dy-Fe-O: thermodynamic properties of ternary oxides using Calvet calorimetry and solid-state electrochemical cell

The enthalpy increments and the standard molar Gibbs energies of formation-of DyFeO3(s) and Dy3Fe5O12(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A co-operative phase transition, related to anti-ferromagnetic to paramagnetic transformation, is apparent. from the heat capacity data for DyFeO3 at similar to 648 K. A similar type of phase transition has been observed for Dy3Fe5O12 at similar to 560 K which is related to ferrimagnetic to paramagnetic transformation. Enthalpy increment data for DyFeO3(s) and Dy3Fe5O12(s), except in the vicinity of the second-order transition, can be represented by the following polynomial expressions:{H(0)m(T) - H(0)m(298.15 K)) (Jmol(-1)) (+/-1.1%) = -52754 + 142.9 x (T (K)) + 2.48 x 10(-3) x (T (K))(2) + 2.951 x 10(6) x (T (K))(-1); (298.15 less than or equal to T (K) less than or equal to 1000) for DyFeO3(s), and {H(0)m(T) - H(0)m(298.15 K)} (Jmol(-1)) (+/-1.2%) = -191048 + 545.0 x (T - (K)) + 2.0 x 10(-5) x (T (K))(2) + 8.513 x 10(6) x (T (K))(-1); (208.15 less than or equal to T (K) less than or equal to 1000)for Dy3Fe5O12(s). The reversible emfs of the solid-state electrochemical cells: (-)Pt/{DyFeO3(s) + Dy2O3(s) + Fe(s)}/YDT/CSZ//{Fe(s) + Fe0.95O(s)}/Pt(+) and (-)Pt/{Fe(s) + Fe0.95O(s)}//CSZ//{DyFeO3(s) + Dy3Fe5O12(s) + Fe3O4(s)}/Pt(+), were measured in the temperature range from 1021 to 1250 K and 1035 to 1250 K, respectively. The standard Gibbs energies of formation of solid DyFeO3 and Dy3Fe5O12 calculated by the least squares regression analysis of the data obtained in the present study, and data for Fe0.95O and Dy2O3 from the literature, are given by Delta(f)G(0)m(DyFeO3,s)(kJmol(-1))(+/-3.2)= -1339.9 + 0.2473 x (T(K)); (1021 less than or equal to T (K) less than or equal to 1548)and D(f)G(0)m(Dy3Fe5O12,s) (kJmol(-1)) (+/-3.5) = -4850.4 + 0.9846 x (T (K)); (1035 less than or equal to T (K) less than or equal to 1250) The uncertainty estimates for Delta(f)G(0)m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams for the system Dy-Fe-O were developed at 1250 K. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Evolution of crystallographic texture during deformation of submicron grain size titanium

Evolution of deformation texture in commercially pure titanium with submicron grain size (SMG) was studied using x-ray diffraction (XRD) and electron back scatter diffraction (EBSD) methods. The material was deformed by rolling at room temperature. The deformation mechanism was found to be slip dominated with a pyramidal slip system facilitating plastic deformation. No evidence of tensile or compressive twinning was detected, as generally seen in the case of titanium with conventional microcrystalline grain size. The absence of twinning and the propensity of the pyramidal slip system in the SMG Ti is attributed to the lack of coordinated motion of zonal partial dislocations that leads to twinning.

Novel metal oxides prepared by ingenious synthetic routes

Several novel oxides have been prepared by the decomposition of carbonate precursors of calcite structure of the general formulas Mn1−xMxCO3 (M = Mg,Co,Cd), Ca1−xMx'CO3, and Ca1−x−yMxMy”CO3.