Gibbs Energy of Formation of MnO: Measurement and Assessment

Based on the measurements of Alcock and Zador, Grundy et al. estimated an uncertainty of the order of +/- 5 kJ mol(-1) for the standard Gibbs energy of formation of MnO in a recent assessment. Since the evaluation of thermodynamic data for the higher oxides Mn3O4, Mn2O3, and MnO2 depends on values for MnO, a redetermination of its Gibbs energy of formation was undertaken in the temperature range from 875 to 1300 K using a solid-state electrochemical cell incorporating yttria-doped thoria (YDT) as the solid electrolyte and Fe + Fe1-delta O as the reference electrode. The cell can be presented as Pt, Mn + MnO/YDT/Fe + Fe1+delta O, Pt Since the metals Fe and Mn undergo phase transitions in the temperature range of measurement, the reversible emf of the cell is represented by the three linear segments. Combining the emf with the oxygen potential for the reference electrode, the standard Gibbs energy of formation of MnO from alpha-Mn and gaseous diatomic oxygen in the temperature range from 875 to 980 K is obtained as: Delta G(f)(o)/Jmol(-1)(+/- 250) = -385624 + 73.071T From 980 to 1300 K the Gibbs energy of formation of MnO from beta-Mn and oxygen gas is given by: Delta G(f)(o)/Jmol(-1)(+/- 250) = -387850 + 75.36T The new data are in excellent agreement with the earlier measurements of Alcock and Zador. Grundy et al. incorrectly analyzed the data of Alcock and Zador showing relatively large difference (+/- 5 kJ mol(-1)) in Gibbs energies of MnO from their two cells with Fe + Fe1-delta O and Ni + NiO as reference electrodes. Thermodynamic data for MnO is reassessed in the light of the new measurements. A table of refined thermodynamic data for MnO from 298.15 to 2000 K is presented.

'Wet N2O oxidation' process and interface state density characterization of nanoscale nitrided SiO2 for flash memory application

In this paper we first present the 'wet N2O' furnace oxidation process to grow nitrided tunnel oxides in the thickness range 6 to 8 nm on silicon at a temperature of 800 degrees C. Electrical characteristics of MOS capacitors and MOSFETs fabricated using this oxide as gate oxide have been evaluated and the superior features of this oxide are ascertained The frequency response of the interface states, before and after subjecting the MOSFET gate oxide to constant current stress, is studied using a simple analytical model developed in this work.

Phase diagram of the system Ca-Ti-O at 1200 K

Phase relations in the system Ca-Ti-O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti-O, and of Ti in CaO. Four ternary oxides were identified: CaTiO3, Ca4Ti3O10 and Ca3Ti2O7 containing tetravalent titanium, and CaTi2O4 containing trivalent titanium. Tie-lines link calcium titanite (CaTi2O4) with the three calcium titanates (CaTiO3, Ca4Ti3O10 and Ca3Ti2O7), CaO, oxygen excess TiO1+delta and stoichiometric TiO. Tie-lines connect CaTiO3 with TiO2-x, Magneli phases TinO2n-1 (28 >= n >= 4), Ti3O5, Ti2O3 and TiO1+delta. CaO was found to coexist with TiO, and Ti-O solid solutions alpha and beta. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO2 to metal and electrochemical reduction of TiO2 using graphite anode and molten CaCl2 electrolyte.

Towards a green synthesis of isoquinoline: Beckmann rearrangement of E,-cinnamaldoxime over H-zeolites

Isoquinoline was prepared through the Beckmann rearrangement of cinnamaldoxime over different H-zeolites, K-10 montmorillonite clay, amorphous SiO2–Al2O3 and γ-alumina under well-optimized conditions of temperature, weight hourly space velocity and catalyst loading. Cinnamaldoxime under ambient reaction conditions over the catalysts underwent migration of the anti-styryl moiety to electron deficient nitrogen (Beckmann rearrangement) followed by an intramolecular cyclization to yield isoquinoline. Cinnamo-nitrile (dehydration product) and cinnamaldehyde were formed as by-products. Isoquinoline formation was high on zeolite catalysts (ca. >86.5%) and mordenite (ca. 92.3%) was the most efficient in the series. Catalysts were susceptible for deactivation and the decrease in the percentage conversion of oxime with time is associated with a corresponding increase in the acid hydrolysis producing salicylaldehyde at later stages of the reaction. However, these catalysts retain activity considerably and can be recycled without loss of activity and change of product distribution.

Activity of Ferric Oxide in Steelmaking Slag

Refining reactions in steelmaking primarily involve oxidation of impurity element(s). The oxidation potential of the slag and the activity of oxygen in the metal (h(O)) are the major factors controlling these chemical reactions. In turn, the oxidation potential of the slag is influenced strongly by the equilibrium distribution of oxygen between ferrous and ferric oxides. We recently investigated the activity coefficient of FeO in steelmaking slag and the effect of chemical composition thereon. This work is focused on estimation of theactivity coefficient of Fe2O3.

Gasifier stoves - science, technology and field outreach

Development of a new class of single pan high efficiency, low emission stoves, named gasifier stoves, that promise constant power that can be controlled using any solid biomass fuel in the form of pellets is reported here. These stoves use battery-run fan-based air supply for gasification (primary air) and for combustion (secondary air).Design with the correct secondary air flow ensures near-stoichiometric combustion that allows attainment of peak combustion temperatures with accompanying high water boiling efficiencies (up to 50% for vessels of practical relevance) and very low emissions (of carbon monoxide, particulate matter and oxides of nitrogen). The use of high density agro-residue based pellets or coconut shell pieces ensures operational duration of about an hour or more at power levels of 3 kWth (similar to 12 g/min). The principles involved and the optimization aspects of the design are outlined. The dependence of efficiency and emissions on the design parameters are described. The field imperatives that drive the choice of the rechargeable battery source and the fan are brought out. The implications of developments of Oorja-Plus and OorjaSuper stoves to the domestic cooking scenario of India are briefly discussed. The process development, testing and internal qualification tasks were undertaken by Indian Institute of Science. Product development and the fuel pellet production were dealt with by First Energy Private Ltd.Close interaction at several times during this period has helped progress the project from the laboratory to large scale commercial operation. At this time, over four hundred thousand stoves and 30 kilotonnes fuel have been sold in four states in India.

A novel fibre-coated sorbent for rapid removal of heavy metals from wastewater. Sorption of Zinc(II) from dilute aqueous solutions in the presence of high concentrations of common salts

The commercial acrylic fibre "Cashmilon" was partially hydrolyzed to convert a fraction of its nitrile (-CN) groups to carboxylic acid (-COOH) groups and then coated with polyethylenimine (PEI) resin and cross-linked with glutaraldehyde to produce a novel gel-coated fibrous sorbent with multiple functionalities of cationic, anionic and chelating types, and significantly faster sorption kinetics than bead-form sorbents. The sorption properties of the fibrous sorbent were measured using Zn(II) in aqueous solution as the sorbate to determine the effects of pH and the presence of common ions in the solution on the sorption capacity. The rate of sorption on the gel-coated fibre was measured in comparison with that on Amberlite IRA-68 weak-base resin beads, to demonstrate the marked difference between fibre and bead-form sorbents in their kinetic behaviour.

Suppression of spinel formation to induce reversible thermal behavior in the layered double hydroxides (LDHs) of Co with Al, Fe, Ga, and In

The layered double hydroxides (LDHs) of Co with trivalent cations decompose irreversibly to yield oxides with the spinel structure. Spinel formation is aided by the oxidation of Co(II) to Co(III) in the ambient atmosphere. When the decomposition is carried out under N-2, the oxidation of Co(II) is suppressed, and the resulting oxide has the rock salt structure. Thus, the Co-Al-CO32-/Cl- LDHs yield oxides of the type Co1- Al-x(2x/3)rectangle O-x/3, which are highly metastable, given the large defect concentration. This defect oxide rapidly reverts back to the original hydroxide on soaking in a Na2CO3 solution. Interlayer NO3- anions, on the other hand, decompose generating a highly oxidizing atmosphere, whereby the Co-Al-NO3- LDH decomposes to form the spinel phase even in a N-2 atmosphere. The oxide with the defect rock salt structure formed by the thermal decomposition of the Co-Fe-CO32- LDH under N2, on soaking in a Na2CO3 solution, follows a different kinetic pathway and undergoes a solution transformation into the inverse spinel Co(Co, Fe)(2)O-4. Fe3+ has a low octahedral crystal field stabilization energy and therefore prefers the tetrahedral coordination offered by the structure of the inverse spinel rather than the octahedral coordination of the parent LDH. Similar considerations do not hold in the case of Ga- and In-containing LDHs, given the considerable barriers to the diffusion of M3+ (M=Ga, In) from octahedral to tetrahedral sites owing to their large size. Consequently, the In-containing oxide residue reverts back to the parent hydroxide, whereas this reconstruction is partial in the case of the Ga-containing oxide. These studies show that the reversible thermal behavior offers a competing kinetic pathway to spinel formation. Suppression of the latter induces the reversible behavior in an LDH that otherwise decomposes irreversibly to the spinel.

A novel fibre-coated sorbent for rapid removal of heavy metals from wastewater. Sorption of Zinc(II) from dilute aqueous solutions in the presence of high concentrations of common salts

The commercial acrylic fibre "Cashmilon" was partially hydrolyzed to convert a fraction of its nitrile (-CN) groups to carboxylic acid (-COOH) groups and then coated with polyethylenimine (PEI) resin and cross-linked with glutaraldehyde to produce a novel gel-coated fibrous sorbent with multiple functionalities of cationic, anionic and chelating types, and significantly faster sorption kinetics than bead-form sorbents. The sorption properties of the fibrous sorbent were measured using Zn(II) in aqueous solution as the sorbate to determine the effects of pH and the presence of common ions in the solution on the sorption capacity. The rate of sorption on the gel-coated fibre was measured in comparison with that on Amberlite IRA-68 weak-base resin beads, to demonstrate the marked difference between fibre and bead-form sorbents in their kinetic behaviour.

Preparation, characterization and thermal decomposition of praseodymium, terbium and neodymium carbonates

The preparation of three different types of carbonates of praseodymium, neodymium and terbium has been described. The carbonates have been characterized by potentiometry, chemical analysis, X-ray crystallography, infra-red spectroscopy and by their thermal behaviour. The thermal decomposition of several carbonates has been studied exhaustively under a variety of conditions and the stoicheiometry, thermodynamics and energetics of the reactions at various stages of decomposition have been examined. The stoicheiometry of the oxides obtained as final products of decomposition has been examined.

The elastic properties of a group of optical glasses by the pulse echo set-up

The pulse-echo apparatus, designed and constructed by the author, has been used to reinvestigate the elastic properties of the eighteen optical glasses. The elastic constants are correct to 0·5%. The results are compared with the earlier investigation which utilised the optical method. The possible causes for large discrepancies observed are critically and briefly discussed. A qualitative interpretation of the results has been successfully attempted. The acoustic velocity increases with the decrease in lead and barium oxides and with increase in calcium oxide and boron trioxide components.

Role of entropy in the stability of cobalt titanates

The standard molar Gibbs free energy of formation of Co2TiO4, CoTiO3,and CoTi2O5 as a function of temperature over an extended range (900 to 1675) K was measured using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte, with CoO as reference electrode and appropriate working electrodes. For the formation of the three compounds from their component oxides CoO with rock-salt and TiO2 with rutile structure, the Gibbs free energy changes are given by:Delta(f)G degrees((ox))(Co2TiO4) +/- 104/(J . mol(-1)) = -18865 - 4.108 (T/K)Delta(f)G degrees((ox))(CoTiO3) +/- 56/(J . mol(-1)) = -19627 + 2.542 (T/K) Delta(f)G degrees((ox))(CoTi2O5) +/- 52/(J . mol(-1)) = -6223 - 6.933 (T/K) Accurate values for enthalpy and entropy of formation were derived. The compounds Co2TiO4 with spinel structure and CoTi2O5 with pseudo-brookite structure were found to be entropy stabilized. The relatively high entropy of these compounds arises from the mixing of cations on specific crystallographic sites. The stoichiometry of CoTiO3 was confirmed by inert gas fusion analysis for oxygen. Because of partial oxidation of cobalt in air, the composition corresponding to the compound Co2TiO4 falls inside a two-phase field containing the spinet solid solution Co2TiO4-Co3O4 and CoTiO3. The spinel solid solution becomes progressively enriched in Co3O4 with decreasing temperature. (c) 2010 Elsevier Ltd. All rights reserved.

Investigation of activated transport in hole doped rare earth manganites in the high temperature paramagnetic regime

Electronic transport in the high temperature paramagnetic regime of the colossal magnetoresistive oxides, La(1-x)A(x)MnO(3), A=Ca, Sr, Ba, x similar or equal to 0.1-0.3, has been investigated using resistivity measurements. The main motivation for this work is to relook into the actual magnitude of the activation energy for transport in a number of manganites and study its variation as a function of hole doping (x), average A-site cation radius (< r(A)>), cationic disorder (sigma(2)) and strain (epsilon(zz)). We show that contrary to current practice, the description of a single activation energy in this phase is not entirely accurate. Our results clearly reveal a strong dependence of the activation energy on the hole doping as well as disorder. Comparing the results across different substituent species with different < r(A)> reveals the importance of sigma(2) as a metric to qualify any analysis based on (r(A)). (c) 2006 Elsevier Ltd. All rights reserved.

X-ray photoelectron spectroscopy of superconducting RuSr2Eu1.5Ce0.5Cu2O10 and nonsuperconducting RuSr2EuCeCu2O10

We report x-ray photoelectron spectroscopic investigation of RuSr2Eu1.5Ce0.5Cu2O10 with ferromagnetic T-C similar to 100 K and a superconducting transition temperature of similar to 30 K compared with RuSr2EuCeCu2O10, which is a ferromagnetic (T-C similar to 150 K) insulator. Our results show that the rare earths, Eu and Ce, are in 3+ and 4+ states, respectively. Comparing the Ru core level spectra from these compounds to those from two Ru reference oxides, we also show that Ru in these ruthenocuprates is always in 5+ state, suggesting that the doped holes in the superconducting compound arising from the substitution of Ce4+ by Eu3+ are primarily in the Cu-O plane, in close analogy to all other doped high-T-C cuprates. Analysis of Cu 2p spectra in terms of a configuration interaction model provides a quantitative description of the gross electronic structures of these ruthenocuprates.

Thermodynamics of GdMnO3 and GdMn2O5 phases determined by the EMF method

Using solid oxide galvanic cells of the type: MnO + Gd2O3 + GdMnO3/O-2/Ni + NiO and Mn3O4 + GdMnO3 + GdMn2O5/O-2/air the equilibrium oxygen pressure for the following reactions :MnO + 1/2Gd(2)O(3) + 1/4O(2) = GdMnO3 1/3Mn(3)O(4) + GdMnO3 + 1/3O(2) = GdMn2O5 was determined in the temperature range from 1073 to 1450 K. From the determined equilibrium oxygen partial pressure the corresponding G i b b s free energy change for these reactions was derived: Delta G(f,GdMnO3)(0) (+/- 425J) 132721(+/ - 2240) +51.91(+/ - 0.81)T Delta G(f,GdMn2O5)(0)(+/- 670J) 121858(+/ - 6176) + 79.52(+/ - 4.83)T From these data, standard G i b b s energies, enthalpies and entropies of formation of GdMnO3 and GdMn2O5 from component oxides and from the elements are derived. Thermodynamic data tables for the two ternary phases are compiled from 298.15 to 1400 K.