Electrochemical determination of the Gibbs energy of formation of MgAl2O4

The standard Gibbs energy of formation of the spinel MgAl2O4 from component oxides, MgO and α-Al2O3, has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal CaF2 as the solid electrolyte. The cell can be represented as—Pt,O2,MgO+MgF2|CaF2|MgF2+MgAl2O4+α-Al2O3,O2,Pt—The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression—capdeltaG°f,ox=−23600 − 5.91T(±150) J/mol—The ‘second-law’ enthalpy of formation of MgAl2O4 obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature.

Gibbs energy of formation of CaCu3Ti4O12 and phase relations in the system CaO-CUO/CU2O-TiO2

he standard Gibbs energy of formation of CaCu3Ti4O12 (CCTO) from CaTiO3, CuO and TiO2 has been determined as a function of temperature from 925 to 1350 K using a solid-state electrochemical cell with yttria-stabilized zirconia as the solid electrolyte. Combining this result with information in the literature on CaTiO3, the standard Gibbs energy of formation of CCTO from its component binary oxides, CaO, CuO and TiO2, has been obtained: View the MathML source (CaCu3Ti4O12)/J mol−1 (±600) = −125231 + 6.57 (T/K). The oxygen chemical potential corresponding to the reduction of CCTO to CaTiO3, TiO2 and Cu2O has been calculated from the electrochemical measurements as a function of temperature and compared on an Ellingham diagram with those for the reduction of CuO to Cu2O and Cu2O to Cu. The oxygen partial pressures corresponding to the reduction reactions at any chosen temperature can be read using the nomograms provided on either side of the diagram. The effect of the oxygen partial pressure on phase relations in the pseudo-ternary system CaO–CuO/Cu2O–TiO2 at 1273 K has been evaluated. The phase diagrams allow identification of secondary phases that may form during the synthesis of the CCTO under equilibrium conditions. The secondary phases may have a significant effect on the extrinsic component of the colossal dielectric response of CCTO.

Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10

An isothermal section of the system Al2O3-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca3CoAl4O10, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca3CoAl4O10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: ( - )\textPt,\textCaAl 2 \textO 4 + \textCa 1 2 \textAl 1 4 \textO 3 3 + \textCa 3 \textCoAl 4 \textO 10 + \textCo//(CaO)ZrO 2 \text// \textCoO + \textCo,\text Pt ( + ). (−)PtCaAl2O4+Ca12Al14O33+Ca3CoAl4O10+Co//(CaO)ZrO2//CoO+Co Pt (+) From the emf of the cell, the standard Gibbs energy change for the Ca3CoAl4O10 formation reaction, CoO + 3/5CaAl2O4 + 1/5Ca12Al14O33 → Ca3CoAl4O10, is obtained as a function of temperature: \Updelta Gr\texto Unknown control sequence '\Updelta'/J mol−1 (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca3CoAl4O10 from its component binary oxides, Al2O3, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca3CoAl4O10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al2O3-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.

Gibbs Energy of Formation of Ca3Ti8Al12O37 and Phase Relations and Chemical Potentials in the System Al2O3-TiO2-CaO

The quaternary oxide in the system Al2O3-CaO-TiO2 is found to have the composition Ca3Ti8Al12O37 rather than CaTi3Al8O19 as reported in the literature. The standard Gibbs energy of formation of Ca3Ti8Al12O37 from component binary oxides is measured in the temperature range from 900 to 1250 K using a solid-state electrochemical cell incorporating single crystal CaF2 as the solid electrolyte. The results can be represented by the equation: delta G(f(0x))(0) (+/- 70)/J mol(-1) = -248474 - 15.706(T/K). Combining this information with thermodynamic data on calcium aluminates and titanates available in the literature, subsolidus phase relations in the pseudo-ternary system Al2O3-CaO-TiO2 are computed and presented as isothermal sections. The evolution of phase relations with temperature is highlighted. Chemical potential diagrams are computed at 1200 K, showing the stability domains of the various phases in the chemical potential-composition space. In each chemical potential diagram, chemical potential of one component is plotted against the cationic fraction of the other two components. The diagrams are valid at relatively high oxygen potentials where Ti is present in its four-valent state in all the oxide phases.

System Ho-Rh-O: Phase Equilibria, Chemical Potentials and Gibbs Energy of Formation of HoRhO3

The thermodynamic properties of the HoRhO3 were determined in the temperature range from 900 to 1300 K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of orthorhombic perovskite HoRhO3, from Ho2O3 with C-rare earth structure and Rh2O3 with orthorhombic structure, can be expressed by the equation; Delta G(f)degrees((ox)) (+/- 78)/(J/mol) = -50535 + 3.85(T/K) Using the thermodynamic data of HoRhO3 and auxiliary data for binary oxides from the literature, the phase relations in the Ho-Rh-O system were computed at 1273 K. Thermodynamic data for intermetallic phases in the binary Ho-Rh were estimated from experimental enthalpy of formation for three compositions from the literature and Miedema's model, consistent with the phase diagram. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1273 K, and temperature-composition diagrams at constant oxygen partial pressures were computed for the system Ho-Rh-O. The decomposition temperature of HoRhO3 is 1717(+/- 2) K in pure O-2 and 1610(+/- 2) K in air at a total pressure p(o) = 0.1 MPa.

Electrochemical Determination of Gibbs Energy of Formation of LaCrO3 Using a Composition-Graded Bielectrolyte

Presented are new measurements of the standard Gibbs free energy of formation of rhombohedral LaCrO3 from component oxides La2O3 and Cr2O3 in the temperature range from 875 to 1175K, using a bielectrolyte solid-state cell incorporating single crystal CaF2 and composition-graded solid electrolyte (LaF3)(y)(CaF2)(1-y) (y=0-0.32). The results can be represented analytically as Delta G(f(ox))(o) (+/- 2270)/Jmol(-1)=-72329+4.932 (T/K). The measurements were undertaken to resolve serious discrepancies in the data reported in the literature. A critical analysis of previous electrochemical measurements indicates several deficiencies that have been rectified in this study. The enthalpy of formation obtained in this study is consistent with calorimetric data. The standard enthalpy of formation of orthorhombic LaCrO3 from elements at 298.15K computed from the results of this study is Delta H-f(298.15)(o)/kJmol(-1)=-1536.2 (+/- 7). The standard entropy of orthorhombic LaCrO3 at 298.15K is estimated as 99.0 (+/- 4.5)J(molK)(-1).

Do carboximide-carboxylic acid combinations form co-crystals? The role of hydroxyl substitution on the formation of co-crystals and eutectics

Carboxylic acids, amides and imides are key organic systems which provide understanding of molecular recognition and binding phenomena important in biological and pharmaceutical settings. In this context, studies of their mutual interactions and compatibility through co-crystallization may pave the way for greater understanding and new applications of their combinations. Extensive co-crystallization studies are available for carboxylic acid/amide combinations, but only a few examples of carboxylic acid/imide co-crystals are currently observed in the literature. The non-formation of co-crystals for carboxylic acid/imide combinations has previously been rationalized, based on steric and computed stability factors. In the light of the growing awareness of eutectic mixtures as an alternative outcome in co-crystallization experiments, the nature of various benzoic acid/cyclic imide combinations is established in this paper. Since an additional functional group can provide sites for new intermolecular interactions and, potentially, promote supramolecular growth into a co-crystal, benzoic acids decorated with one or more hydroxyl groups have been systematically screened for co-crystallization with one unsaturated and two saturated cyclic imides. The facile formation of an abundant number of hydroxybenzoic acid/cyclic carboximide co-crystals is reported, including polymorphic and variable stoichiometry co-crystals. In the cases where co-crystals did not form, the combinations are shown invariably to result in eutectics. The presence or absence and geometric disposition of hydroxyl functionality on benzoic acid is thus found to drive the formation of co- crystals or eutectics for the studied carboxylic acid/imide combinations.

Approaches to crystallization from ionic liquids: complex solvents-complex results, or, a strategy for controlled formation of new supramolecular architectures?

There are now more than 1200 papers a year describing research results using the 'neoteric' solvents, known as ionic liquids (ILs). If ILs are such highly studied solvents, why has there been so comparatively little research in their use in crystallization? Here we explore this question and discuss possible strategies for utilization of the mundane and the unique aspects of ILs for novel crystallization strategies including crystallization of high and low melting solids using thermal shifts; ''solvothermal'' techniques; slow diffusion; electrocrystallization; and use of a co-solvent. The results presented here and those appearing in the literature indicate both the complex nature of these solvents and their promise in delivering unique solvation, metal ion coordination numbers, coordination polymer motifs, and metal-anion interactions, to name but a few. These complex, but fascinating, results and the promise of much more intimate control over crystallization processes will drive a growing interest in using ILs as crystallization solvents.

The European Union’s Role in the Formation of India’s Climate Change Policy. Bruges Regional Integration & Global Governance Papers 2/2012, September 2012

This paper focuses on the role of the European Union (EU) in the formation of India’s climate change policy; an increasingly high profile issue area. It is based on an extensive study of relevant literature, EU-India policy documents and the execution of thirteen semi-structured interviews with experts; many of whom have experienced EU-India cooperation on climate change first-hand. A three-point typology will be used to assess the extent of the EU’s leadership role, supporting role or equal partnership role in India, with several sub-roles within these categories. Further, for clarity and chronology purposes, three time periods will be distinguished to assess how India’s climate policy has evolved over time, alongside the EU’s role within that. The findings of the paper confirm that the EU has demonstrated signs of all three roles to some degree, although the EU-India relationship in climate policy is increasingly an equal partnership. It offers explanations for previous shortcomings in EU-India climate policy as well as policy recommendations to help ensure more effective cooperation and implementation of policies.

Response surface analysis of extract yield and flavour intensity of Brazilian cherry (Eugenia uniflora L.) obtained by supercritical carbon dioxide extraction

This work evaluated the effect of pressure and temperature on yield and characteristic flavour intensity of Brazilian cherry (Eugenia uniflora L) extracts obtained by supercritical CO(2) using response surface analysis, which is a simple and efficient method for first inquiries. A complete central composite 2(2) factorial experimental design was applied using temperature (ranging from 40 to 60 degrees C) and pressure (from 150 to 250 bar) as independent variables. A second order model proved to be predictive (p <= 0.05) for the extract yield as affected by pressure and temperature, with better results being achieved at the central point (200 bar and 50 degrees C). For the flavour intensity, a first order model proved to be predictive (p <= 0.05) showing the influence of temperature. Greater characteristic flavour intensity in extracts was obtained for relatively high temperature (> 50 degrees C), Therefore, as far as Brazilian cherry is concerned, optimum conditions for achieving higher extract yield do not necessarily coincide to those for obtaining richer flavour intensity. Industrial relevance: Supercritical fluid extraction (SFE) is an emerging clean technology through which one may obtain extracts free from organic solvents. Extract yields from natural products for applications in food, pharmaceutical and cosmetic industries have been widely disseminated in the literature. Accordingly, two lines of research have industrial relevance, namely, (i) operational optimization studies for high SFE yields and (ii) investigation on important properties extracts are expected to present (so as to define their prospective industrial application). Specifically, this work studied the optimization of SFE process to obtain extracts from a tropical fruit showing high intensity of its characteristic flavour, aiming at promoting its application in natural aroma enrichment of processed foods. (C) 2008 Elsevier Ltd. All rights reserved.

A mechanism for the formation of oxygen and iron bimodal radial distribution in the disc of our Galaxy

Recently, it has been proposed that there are two type Ia supernova progenitors: short-lived and long-lived. On the basis of this idea, we develop a theory of a unified mechanism for the formation of the bimodal radial distribution of iron and oxygen in the Galactic disc. The underlying cause for the formation of the fine structure of the radial abundance pattern is the influence of the spiral arms, specifically the combined effect of the corotation resonance and turbulent diffusion. From our modelling, we conclude that in order to explain the bimodal radial distributions simultaneously for oxygen and iron and to obtain approximately equal total iron output from different types of supernovae, the mean ejected iron mass per supernova event should be the same as quoted in the literature if the maximum mass of stars, which eject heavy elements, is 50 M(circle dot). For the upper mass limit of 70 M(circle dot), the production of iron by a type II supernova explosion should increase by about 1.5 times.

TEM, XRD and AFM study of poly(o-ethoxyaniline) films: new evidence for the formation of conducting islands

The existence of conducting islands in polyaniline films has long been proposed in the literature, which would be consistent with conducting mechanisms based on hopping. Obtaining direct evidence of conducting islands, however, is not straightforward. In this paper, conducting islands were visualized in poly(o-ethoxyaniline) (POEA) films prepared at low pH, using Transmission Electron Microscopy (TEM) and atomic force spectroscopy (AFS). The size of the islands varied between 67 and 470 angstrom for a pH=3.0, with a larger average being obtained with AFS, probably due to the finite size effect of the atomic force microscopy tip. In AFS, the conducting islands were denoted by regions with repulsive forces due to the double-layer forces. On the basis of X-ray diffraction (XRD) patterns for POEA in the powder form, we infer that the conducting islands are crystalline, and therefore a POEA film is believed to consist of conducting islands dispersed in an insulating, amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasi-one dimensional variable range hopping (VRH) mechanism.

Singlet oxygen reacts with 2 `,7 `-dichlorodihydrofluorescein and contributes to the formation of 2 `,7 `-dichlorofluorescein

There are controversial reports in the literature concerning the reactivity of singlet oxygen ((1)O(2)) with the redox probe 2`,7`-dichlorodihydrofluorescein (DCFH). By carefully preparing solutions in which (1)O(2) is quantitatively generated in the presence of DCFH, we were able to show that the formation rate of the fluorescent molecule derived from DCFH oxidation, which is 2`,7`-dichlorofluorescein (DCF), increases in D(2)O and decreases in sodium azide, proving the direct role of (1)O(2) in this process. We have also prepared solutions in which either (1)O(2) or dication (MB(center dot 2+)) and semi-reduced (MB(center dot)) radicals of the sensitizer and subsequently super-oxide radical (O(2)(center dot-)) are generated. The absence of any effect of SOD and catalase ruled out the DCFH oxidation by O(2)(center dot-), indicating that both (1)O(2) and MB(center dot 2+) react with DCFH. Although the formation of DCF was 1 order of magnitude larger in the presence of MB(center dot 2+) than in the presence of (1)O(2), considering the rate of spontaneous decays of these species in aqueous solution, we were able to conclude that the reactivity of (1)O(2) with DCFH is actually larger than that of MB(center dot 2+). We conclude that DCFH can continue to be used as a probe to monitor general redox misbalance induced in biologic systems by oxidizing radicals and (1)O(2).

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint

In the present work. the resonance Raman. UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about similar to 300 rim in diameter) and nanofibers (about similar to 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of hands at 578, 1400 and 1632cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609cm(-1) of PANI fibers is correlated with the extended PANI chain coil formation. (C) 2008 Elsevier B.V. All rights reserved.

SSM samba: a survey of brazilian approaches to soft systems methodology (1999-2005)

This paper reports the results of a survey intended to discover the manner in which Soft Systems Methodology (SSM) is understood and used in Brazil. The focus is upon SSM papers published in national and international journals, and conferences, incorporating a refereeing procedure. To be included in the survey, publications had to meet at least one of the following criteria: (a) authorship is clearly of Brazilian nationality; or, (b) authorship is affiliated to a Brazilian institution; or (c) application is set in Brazil. Similar surveys reporting on the United Kingdom, Australia and, to a lesser extent, Spain have been published previously in the literature. This paper, therefore, contributes to the growing international understanding and usage of SSM. Ultimately the paper serves as an initial map of the developing context in Brazilian SSM theory and practice.