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.

Densification studies on amorphous ZrO2-Al2O3 powders

Densification characteristics of amorphous ZrO2-40 mol% Al2O3 powder with 3 to 15 mu m nominal particle size range, produced by spray pyrolysis, have been studied by conducting hot pressing experiments at 573, 723 and 873 K with uniaxial pressures of 250, 500 and 750 MPa. Most of the increase in relative density from the starting value of similar to 40% occurred during loading up to the desired pressure. The increments in density during 1 hour constant pressure dwells were less than 4% at all temperatures and pressure. Inter-particle bonding was not observed at 573 K. Correlation between the results with a viscous sintering model for hot pressing is not satisfactory for describing the behavior as normal viscous sintering.

Generalized method for assessment of compressibility of rockfill material

Examination of experimental data of the modelled rockfill materials using parallel gradation technique has revealed that the plots of logarithm of strain at failure against logarithm of confining pressure are linear. Also, a trend of increase in failure strain with increase in confining pressure and maximum size of the particle have been observed. The approach presented in this paper highlights the prediction of volume change properties of rockfill materials over a range of confining pressures and particle sizes based on the results of only two tests carried out at two different confining pressures for a maximum particle size of modelled material with the use of parallel gradation technique. Two test approach and its application in modelling of rockfill materials to estimate its volume change behaviour is illustrated by means of a selected experimental data available in the literature.

Experimental Studies on High-Pressure Spray Structure of Biofuels

The high-pressure spray characteristics of biofuels, specifically, Pongamia oil and its blends with diesel are studied for various gas pressures. Two single-hole solenoid injectors with nozzle diameters of 200 and 260 mu m are used along with a high-pressure common-rail direct-injection system to inject fuel into a high-pressure spray visualization chamber. The spray structure is characterized using a high-speed laser-based shadowgraphy technique. The spray structure of Pongamia oil revealed the presence of an intact liquid core at low gas pressure. At high gas pressures, the spray atomization of the Pongamia oil showed marked improvement. The spray tip penetration of Pongamia oil and its blends with diesel is higher compared to that of diesel for all test conditions. The spray cone angle of Pongamia oil and 50% Pongamia oil blend with diesel is lower as compared to that of diesel. Both these observations are attributed to the presence of large droplets carrying higher momentum in oil and blend. The droplet size is measured at an injection pressure of 1000 bar and gas pressure of 30 bar at 25 mm below the nozzle tip using the particle/droplet image.analysis (PDIA) method. The droplet size measurements have shown that the Sauter mean diameter (SMD) in the spray core of Pongamia oil is more than twice that of diesel. The spray tip penetration of the 20% blend of Pongamia with diesel (P20) is similar to that of diesel but the SMD is 50% higher. Based on experimental data, appropriate spray tip penetration correlation is proposed for the vegetable oil fuels such as Pongamia.

Janus Hybramers: Self-Adapting Amphiphilic Hyperbranched Polymers

Janus structures have attracted a great deal of interest because of their fascinating properties and potential for applications. In this study, we demonstrate that hyperbranched polymers, bearing randomly placed docosyl (C22 alkyl segment) and PEG segments on their periphery, can readily reconfigure so as to segregate the alkyl and PEG segments, thereby generating Janus-type structures that we have termed Janus hybramers. DSC studies clearly reveal an endothermic transition that corresponds to the melting of the docosyl domains, while Langmuir isotherms demonstrate that these polymers form stable monolayers that appear to undergo a slight densification beyond a critical surface pressure; this suggested possible crystallization of the docosyl segments at the air-water interface. AFM studies of the transferred monolayers reveal various interesting aggregate morphologies at different surface pressures suggestive of island formation at the air-water interface; at the same time they also provided an estimate of the monolayer thickness. These Janus HBPs also form vesicles as evident from TEM and AFM studies; the AFM height of the deposited vesicles, as expected, was roughly 4 times that of the monolayer. SAXS studies revealed the formation of lamellar structures; the interlamellar spacing was largest when the relative mole fractions of docosyl and PEG segments were similar, but the spacing decreased when the mole fraction of either of these peripheral segments is substantially smaller; this suggested the possible presence of interdigitation within the domains of the minor component.

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 degrees C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance. AC conductivity and activation energy were determined and the results are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Studies on Field Dependent Domain Structures in Multi-Grained 0.85PbMg(1/3)Nb(2/3)O3-0.15PbTiO(3) Thin Films by Scanning Force Microscopy

0.85PbMg(1/3)Nb(2/3)O(3)-0.15PbTiO(3) (0.85PMN-0.15PT) ferroelectric relaxor thin films have been deposited on La0.5Sr0.5CoO3/(111) Pt/TiO2/SiO2/Si by pulsed laser ablation by varying the oxygen partial pressures from 50 mTorr to 400 mTorr. The X-ray diffraction pattern reveals a pyrochlore free polycrystalline film. The grain morphology of the deposited films was studied using scanning electron microscopy and was found to be affected by oxygen pressure. By employing dynamic contact-electrostatic force microscopy we found that the distribution of polar nanoregions is majorly affected by oxygen pressure. Finally, the electric field induced switching in these films is discussed in terms of domain wall pinning.

Estimation of vapour pressure and partial pressure of subliming compounds by low-pressure thermogravimetry

A method for the estimation of vapour pressure and partial pressure of subliming compounds under reduced pressure, using rising temperature thermogravimetry, is described in this paper. The method is based on our recently developed procedure to estimate the vapour pressure from ambient pressure thermogravimetric data using Langmuir equation. Using benzoic acid as the calibration standard, vapour pressure temperature curves are calculated at 80, 160 and 1000 mbar for salicylic acid and vanadyl bis-2,4-pentanedionate, a precursor used for chemical vapour deposition of vanadium oxides. Using a modification of the Langmuir equation, the partial pressure of these materials at different total pressures is also determined as a function of temperature. Such data can be useful for the deposition of multi-metal oxide thin films or doped thin films by chemical vapour deposition (CVD).

Experiments on and thermodynamic analysis of a turbocharged engine with producer gas as fuel

This article presents the studies conducted on turbocharged producer gas engines designed originally for natural gas (NG) as the fuel. Producer gas, whose properties like stoichiometric ratio, calorific value, laminar flame speed, adiabatic flame temperature, and related parameters that differ from those of NG, is used as the fuel. Two engines having similar turbochargers are evaluated for performance. Detailed measurements on the mass flowrates of fuel and air, pressures and temperatures at various locations on the turbocharger were carried out. On both the engines, the pressure ratio across the compressor was measured to be 1.40 +/- 0.05 and the density ratio to be 1.35 +/- 0.05 across the turbocharger with after-cooler. Thermodynamic analysis of the data on both the engines suggests a compressor efficiency of 70 per cent. The specific energy consumption at the peak load is found to be 13.1 MJ/kWh with producer gas as the fuel. Compared with the naturally aspirated mode, the mass flow and the peak load in the turbocharged after-cooled condition increased by 35 per cent and 30 per cent, respectively. The pressure ratios obtained with the use of NG and producer gas are compared with corrected mass flow on the compressor map.

Infrared Spectra of Dimethylphenanthrenes in the Gas phase

Infrared spectra of atmospherically and astronomically important dimethylphenanthrenes (DMPs), namely 1,9-DMP, 2,4-DMP, and 3,9-DMP, were recorded in the gas phase from 400 to 4000 cm(-1) with a resolution of 0.5 cm(-1) at 110 degrees C using a 7.2 m gas cell. DFT calculations at the B3LYP/6-311G** level were carried out to get the harmonic and anharmonic frequencies and their corresponding intensities for the assignment of the observed bands. However, spectral assignments could not be made unambiguously using anharmonic or selectively scaled harmonic frequencies. Therefore, the scaled quantum mechanical (SQM) force field analysis method was adopted to achieve more accurate assignments. In this method force fields instead of frequencies were scaled. The Cartesian force field matrix obtained from the Gaussian calculations was converted to a nonredundant local coordinate force field matrix and then the force fields were scaled to match experimental frequencies in a consistent manner using a modified version of the UMAT program of the QCPE package. Potential energy distributions (PEDs) of the normal modes in terms of nonredundant local coordinates obtained from these calculations helped us derive the nature of the vibration at each frequency. The intensity of observed bands in the experimental spectra was calculated using estimated vapor pressures of the DMPs. An error analysis of the mean deviation between experimental and calculated intensities reveal that the observed methyl C-H stretching intensity deviates more compared to the aromatic C-H and non C-H stretching bands.

Phonon anomalies and structural transition in spin ice Dy2Ti2O7: a simultaneous pressure-dependent and temperature-dependent Raman study

We revisit the assignment of Raman phonons of rare-earth titanates by performing Raman measurements on single crystals of O18 isotope-rich spin ice Dy2Ti2O718 and nonmagnetic Lu2Ti2O718 pyrochlores and compare the results with their O16 counterparts. We show that the low-wavenumber Raman modes below 250 cm-1 are not due to oxygen vibrations. A mode near 200 cm-1, commonly assigned as F2g phonon, which shows highly anomalous temperature dependence, is now assigned to a disorder-induced Raman active mode involving Ti4+ vibrations. Moreover, we address here the origin of the new Raman mode, observed below TC similar to 110 K in Dy2Ti2O7, through a simultaneous pressure-dependent and temperature-dependent Raman study. Our study confirms the new mode to be a phonon mode. We find that dTC/dP = + 5.9 K/GPa. Temperature dependence of other phonons has also been studied at various pressures up to similar to 8 GPa. We find that pressure suppresses the anomalous temperature dependence. The role of the inherent vacant sites present in the pyrochlore structure in the anomalous temperature dependence is also discussed. Copyright (c) 2012 John Wiley & Sons, Ltd.

Averting biodiversity collapse in tropical forest protected areas

The rapid disruption of tropical forests probably imperils global biodiversity more than any other contemporary phenomenon(1-3). With deforestation advancing quickly, protected areas are increasingly becoming final refuges for threatened species and natural ecosystem processes. However, many protected areas in the tropics are themselves vulnerable to human encroachment and other environmental stresses(4-9). As pressures mount, it is vital to know whether existing reserves can sustain their biodiversity. A critical constraint in addressing this question has been that data describing a broad array of biodiversity groups have been unavailable for a sufficiently large and representative sample of reserves. Here we present a uniquely comprehensive data set on changes over the past 20 to 30 years in 31 functional groups of species and 21 potential drivers of environmental change, for 60 protected areas stratified across the world's major tropical regions. Our analysis reveals great variation in reserve `health': about half of all reserves have been effective or performed passably, but the rest are experiencing an erosion of biodiversity that is often alarmingly widespread taxonomically and functionally. Habitat disruption, hunting and forest-product exploitation were the strongest predictors of declining reserve health. Crucially, environmental changes immediately outside reserves seemed nearly as important as those inside in determining their ecological fate, with changes inside reserves strongly mirroring those occurring around them. These findings suggest that tropical protected areas are often intimately linked ecologically to their surrounding habitats, and that a failure to stem broad-scale loss and degradation of such habitats could sharply increase the likelihood of serious biodiversity declines.

Spray characterization of gasoline-ethanol blends from a multi-hole port fuel injector

This work reports the measured spray structure and droplet size distributions of ethanol-gasoline blends for a low-pressure, multi-hole, port fuel injector (PFI). This study presents previously unavailable data for this class of injectors which are widely used in automotive applications. Specifically, gasoline, ethanol, and gasoline-ethanol blends containing 10%, 20% and 50% ethanol were studied using laser backlight imaging, and particle/droplet image analysis (PDIA) techniques. The fuel mass injected, spray structure and tip penetrations, droplet size distributions, and Sauter mean diameter were determined for the blends, at two different injection pressures. Results indicate that the gasoline and ethanol sprays have similar characteristics in terms of spray progression and droplet sizes in spite of the large difference in viscosity. It appears that the complex mode of atomization utilized in these injectors involving interaction of multiple fuel jets is fairly insensitive to the fuel viscosity over a range of values. This result has interesting ramifications for existing gasoline fuel systems which need to handle blends and even pure ethanol, which is one of the renewable fuels of the future. (C) 2012 Elsevier Ltd. All rights reserved.

Mixture solubilities of nitrobenzoic acid isomers in supercritical carbon dioxide

The ternary solubilities of solid isomers of nitrobenzoic acid (NBA) were experimentally determined at 308, 318 and 328K over a pressure range of 12-18 MPa in supercritical carbon dioxide (SCCO2). Compared to its binary solubility, the ternary solubilities of m-NBA increased at 308 K while it decreased at 328 K. However, the ternary solubilities of p-NBA increased at all temperatures and pressures except at 13 MPa and 328K. A new model was developed by applying solution model and activity coefficient model for the ternary solubilities of pharmaceutical and non-pharmaceutical solid mixtures in terms of temperature, density and cosolute composition. The model equation involves four temperature independent constraint-free parameters. The model equation correlates the ternary solubilities of seven pharmaceutical solid mixtures along with current data with an average AARD around 9.5% and sixteen non-pharmaceutical solid mixtures with 9% AARD. (C) 2012 Elsevier B.V. All rights reserved.

Peraluminous sapphirine-cordierite pods in Mg-rich orthopyroxene granulite from southern India: Implications for lower crustal processes

Sapphirine-cordierite intergrowths occur as pods within garnet-absent, high-Mg orthopyroxene-granulite xenoliths in the Kambam valley, Madurai Block, southern India. Whereas the cores of the pods are composed of sapphirine (X-Mg = 0.871-0.897) - cordierite (X-Mg = 0.892-0.931) intergrowth along with rutile, zircon and monazite, the rims are characterized by cordierite, apatite, plagioclase, K-feldspar, quartz and minor calcite. The surrounding matrix comprises orthopyroxene (maximum Al2O3 4.1 wt.%, X-Mg 0.848-0.850), plagioclase, biotite and quartz, similar to the assemblage in the surrounding charnockites. Sapphirine in the Kambam rocks is characterized by high Al contents with an end-member composition in the range of 7:9:3 and 3:5:1. The occurrence of peraluminous sapphirine in association with cordierite and in the absence of phases such as sillimanite and garnet is distinct from ultrahigh-temperature assemblages in other localities within the Madurai Block. The peraluminous composition of the pods suggests that these domains could represent cryptic pathways through which aluminous melts migrated. The reaction of such peraluminous melts with Mg-rich orthopyroxene in the host granulite at temperatures of 1025 degrees C and pressures around 8 kbar as computed from phase equilibria modeling followed by an isobaric cooling is inferred to have generated the sapphirine-cordierite pods. The unusual high-Mg orthopyroxene granulite suggests interaction of supracrustal rocks with mafic magmas, which probably acted as the heat source for the partial melting of lower crust and UHT metamorphism.