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A computational approach has been undertaken to design and assess potential Fe--Cr--Ni--Al systems to produce stable nanostructured corrosion-resistant coatings that form a protective, continuous scale of alumina or chromia at elevated temperatures. The phase diagram computation was modeled using the THERMO-CALC[R] software and database (Thermo-Calc[R] Software, 2007, THERMO-CALC for Windows Version 4, Thermo-Calc Software AB, Stockhohn, Sweden; Thermo-Calc[R] Software, 2007, TCFE5, Version 5, ThermoCalc Software AB, Stockholm, Sweden) to generate pseudoternary, Fe--Cr--Ni--Al phase diagrams to help identity compositional ranges without the undesirable brittle phases. The computational modeling of the grain growth process, sintering of voids and interface toughness determination by indentation, assessed microstructural stability, and durability of the nanocoatings fabricated by a magnetron-sputtering process. Interdiffusion of Al, Cr, and Ni was performed using the DICTRA[R] diffusion code (Thermo-Calc Software[R], DICTRA, Version 24, 2007, Version 25, 2008, Thermo-Calc Software AB, Stockholm, Sweden) to maximize the long-term stability of the nanocoatings. The computational results identified a new series of Fe--Cr--Ni--Al coatings that maintain long-term stability and a fine-grained microstructure at elevated temperatures. The formation of brittle [sigma]-phase in Fe--Cr--Ni--Al alloys is suppressed for Al contents in excess of 4 wt %. The grain growth modeling indicated that the columnar-grained structure with a high percentage of low-angle grain boundaries is resistant to grain growth. Sintering modeling indicated that the initial relative density of as-processed magnetron-sputtered coatings could achieve full density after a short thermal exposure or heat-treatment. The interface toughness computation indicated that the Fe--Cr--Ni--Al nanocoatings exhibit high interface toughness in the range of 52-366 J/[m.sup.2]. The interdiffusion modeling using the DICTRA software package indicated that inward diffusion could result in substantial to moderate Al and Cr losses front the nanocoating to the substrate during long-term thermal exposures. [DOI: 10.1115/1.3204651]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2009.12.002 Byline: Monika Jain (a), Vinod Kumar Garg (a), Krishna Kadirvelu (b) Abstract: This paper reports the adsorption of Cr(VI) ions from aqueous solution by sulphuric acid treated sunflower waste. Two adsorbents, namely SHC and SSC, were prepared from sunflower plant head and stem waste. The adsorbents were characterized by FT-IR, SEM and EDX. The surface areas of SHC and SSC were 1.17 and 1.28m.sup.2 g.sup.-1, respectively. The effect of various process parameters namely pH, temperature, initial metal ion concentration, adsorbent dosage and contact time has been studied. The optimum conditions for removal of Cr (VI) were found to be pH=2, contact time=2h, adsorbent dosage=4.0g/L, concentration=250mg/L, temperature=25[+ or -]1[degrees]C, rpm=180. The percent removal at these optimum conditions was found to be 75.7% and 85.4% for SHC and SSC respectively. The Freundlich, Langmuir and D-R models were applied for mathematical description of adsorption equilibrium. Adsorption data were well described by the Langmuir isotherm with maximum adsorption capacities of 53.76mg/g and 56.49mg/g for SHC and SSC, respectively. Overall, the experimental results suggest that SHC and SSC could be used as low cost alternative adsorbents for the treatment of Cr(VI) containing wastewater. A comparison of different kinetic models showed that our data fitted well to the pseudo-second order model. Author Affiliation: (a) Department of Environmental Science and Engineering, Guru Jambheshwar University of Science and Technology, Hisar 125001, Haryana, India (b) Centre for Fire, Explosives and Environment Safety (CFEES), Defense Research and Development Organization, Timarpur, Delhi 110054, India Article History: Received 14 November 2008; Revised 16 September 2009; Accepted 5 December 2009

The influence of the presence of Cr (III) on the biosorption of Pb (II) by three olive wastes (olive stone, the two-phase olive mill solid, and olive tree pruning) was investigated in a batch system in terms of equilibrium isotherm and adsorption yield. The results show that the three olive wastes have greater affinity for lead than for chromium and the best results are achieved at pH=5. The presence of chromium in the solution reduces the percentage of lead removal suggesting that there is a competition between the two metals for the binding sites, and that the biosorbent retains both species presenting more affinity for lead. Simultaneous biosorption phenomena of Pb (II) and Cr (III) on the three solid wastes were expressed by multicomponent isotherms. The extended Freundlich-type and Sips-type models were found to exhibit good fit to the experimental data for olive stone and olive tree pruning, respectively. DOI: 10.1061/(ASCE)EE.1943-7870.0000096 CE Database subject headings: Adsorption; Abatement and removal; Heavy metals; Solid wastes; Water treatment; Chromium; Lead; Agricultural wastes.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2009.08.018 Byline: Yong-Chul Jang (a)(b), Pradeep Jain (a)(c), Thabet Tolaymat (a)(d), Brajesh Dubey (a)(e), Timothy Townsend (a) Abstract: Disposal and beneficial-use options for street sweeping residuals collected as part of routine roadway maintenance activities in Florida, USA, were assessed by characterizing approximately 200 samples collected from 20 municipalities. Total concentrations (mg/kg or [mu]g/kg) and leachable concentrations (mg/L or [mu]g/L) of 11 metals and a number of organic pollutant groups (volatile organics, semi-volatile organics, pesticides, herbicides, carbamates) in the samples were measured. The synthetic precipitation leaching procedure (SPLP) was performed to evaluate the leachability of the pollutants. From the total metal analysis, several metals (e.g., arsenic, barium, chromium, copper, nickel, lead, and zinc) were commonly found above their detection limits. Zinc was found to have the highest mean concentration of all metals measured (46.7mg/kg), followed by copper (10.7mg/kg) and barium (10.5mg/kg). The metal with the smallest mean concentration was arsenic (0.48mg/kg). A small fraction of the total arsenic, barium, lead, and zinc leached in some samples using the SPLP; leached concentrations were relatively low. A few organic compounds (e.g., 4,4'-DDT, endrin, and endosulfan II) were detected in a limited number of samples. When the total and leaching results were compared to risk-based Florida soil cleanup target levels and groundwater cleanup target levels, the street sweepings were not found to pose a significant human-health risk via direct exposure or groundwater contamination. Author Affiliation: (a) Department of Environmental Engineering and Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611-6450, USA (b) Department of Environmental Engineering, Chungnam National University, 220 Gung-dong, Yuseong-Gu, Daejeon 305-764, South Korea (c) Innovative Waste Consulting Services, LLC, 6628 NW 9th Blvd. Suite 3, Gainesville, FL 32605, USA (d) US Environmental Protection Agency, Office of Research and Development, National Risk Management Laboratory, Cincinnati, OH 45224, USA (e) Department of Environmental Health, 65 Lamb Hall, P.O. Box 70682, East Tennessee State University, Johnson City, TN 37614, USA Article History: Received 3 April 2008; Revised 2 June 2009; Accepted 31 August 2009

In this paper, the feasibility and efficacy of chromium (Cr(VI)) removal using three different kinds of tree leaves viz. Emblica officinalis, Azadirachta indica, Eucalyptus agglomerata, and the activated carbon is examined through batch and continuous flow experiments. Pretreatments were given to the selected tree leaf powders to remove the natural pigments and lignin present. Batch and continuous flow experiments have been conducted to study the kinetics of adsorption, effects of pH, adsorbent dose, contact time, bed depth, flow rate, and initial Cr(VI) concentration on Cr(VI) adsorption onto the selected adsorbents. The adsorption capacity is observed higher for Emblica officinalis followed by Eucalyptus agglomerata and Azadirachta indica. The adsorption equilibrium is reached in less than 30 min and the maximum Cr(VI) uptake occurred at pH 3.0 under the test conditions. The results are also compared with the commercially available activated carbon. A mathematical model incorporating diffusion, advection, and mass transfer mechanisms available in the literature has been simplified and is then tested to simulate the laboratory and literature data. A simple method for the determination of saturation Cr(VI) concentration along the length of column has been presented. The study reveals that the model incorporating the molecular diffusion and the mass transfer mechanisms simulates better the Cr(VI) adsorption onto tree leaf powders than the literature model and the advection term plays only a negligible role due to low flow rates applied during the experiments. The model parameters, i.e., axial dispersion coefficient, '[D.sub.L]' and the external mass transfer coefficient, '[k.sub.f]' are found in the order of [10.sup.-5]-[10.sup.-6] [m.sup.2]/s and [10.sup.-9]-[10.sup.-11] m/s, respectively. DOI: 10.1061/(ASCE)EE.1943-7870.0000050 CE Database subject headings: Adsorption; Chromium; Activated carbon; Mass transfer; Trees.

Quaternized poly(4-vinylpyridine) coated activated carbon has been proven to be successful in removal and recovery of Cr(VI) from aqueous solution. However, the key component of the mass transfer operations and the diffusion coefficient has not been determined. In this study, adsorption of Cr(VI) was investigated at different initial concentrations. A finite bath diffusion control model with changing bulk concentrations was derived analytically, and a constant related to radius of the absorbent particle and the fractional attainment of adsorption was first introduced into this model. Results indicated that the adsorbent provided fast adsorption kinetics and the modified diffusion-control model fitted the experimental data well. The observed sorption kinetics was consistent with the finite bath diffusion, with an average value of 4.10 x [10.sup.-6] [cm.sup.2]/s for the product of the distribution coefficient and the effective diffusivity in the adsorption of Cr(VI) on the quaternized poly(4-vinylpyridine) coated activated carbon. DOI: 10.1061/(ASCE)0733-9372(2007)133:8(834) CE Database subject headings: Chromium; Sorption; Activated carbon; Kinetics.

Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recorded on Cr:MgO periclase and Cr:(Mg,Fe)O ferropericlase synthesized at different pressures (4 and 12 GPa) and temperatures (1200 to 1400 [degrees]C) at reducing oxygen fugacity conditions (~iron-wustite buffer IW to IW -2), and on Cr:MgSi[O.sub.3] perovskite with 0.5 wt% [Cr.sub.2][O.sub.3]. [sup.57]Fe Mossbauer spectra were collected on the Fe-containing samples. The aim of the study was to determine the Cr oxidation state in phases found in the Earth's lower mantle, and to examine the possible relationship with the Fe oxidation state in the same materials. To calculate the amount of [Cr.sup.2+], the intensity of the shoulder at the low-energy side of the edge crest was quantified using the area of the corresponding peak in the derivative XANES spectra (Berry and O'Neill 2004). In Cr:(Mg,Fe)O the relative [Cr.sup.2+] content reached at most 12.5% but results from Mossbauer spectroscopy combined with chemical composition data suggest that some [Cr.sup.2+] oxidized during cooling through the reaction [Cr.sup.2+] + [Fe.sup.3+] [right arrow] [Cr.sup.3+] + [Fe.sup.2+]. In iron-free Cr-MgO, the [Cr.sup.2+] content is much higher and reaches ~40%. In Cr:MgSi[O.sub.3] perovskite with 0.006 Cr pfu (similar to estimated lower mantle abundance), chromium is mainly divalent. Keywords: XANES, Cr oxidation state, ferropericlase, periclase, Cr:MgSi[O.sub.3] perovskite

Phase relationships in the system MgO-[Al.sub.2][O.sub.3]-Si[O.sub.2]-[Cr.sub.2][O.sub.3] (MASCO were investigated experimentally from 1250 to 1560 [degrees]C using a 1-atm vertical quench furnace on 12 oxide mixtures covering a wide range of chemical compositions. Spinel, corundum, mullite, and sapphirine were found to display a wide range of solid solutions toward CR-rich end-members, whereas enstatite, cordierite, forsterite, and glasses were always Cr-poor. Glasses formed in relatively MgO-rich bulk compositions from 1250 [degrees]C, in assemblage with cordierite, enstatite, forsterite, and spinel, suggesting a lowering of the eutectic minimum in MASCr compared to available melting relationships in the model system MAS. Although unexpected, the relatively low-temperature melting of Cr-bearing mixtures is supported by topological constraints in the subsystems SACr and MSCr. The extent of Cr solubility in mullite has been found to reach ~14 wt% at 1560 [degrees]C, and 33 wt% in sapphirine at 1340 [degrees]C, which are the highest Cr values reported so far for these minerals. Liquidus surfaces are constrained by glass compositions that ate displaced systematically toward silica compared to corresponding liquids in the temary system MAS. As a consequence, the primary crystallization fields of Cr-spinel, Cr-sapphirine, and Cr-mullite are found to face the cristobalite/tridymite primary fields. A tentative liquidus diagram for the system MgO-[Al.sub.2][O.sub.3]-Si[O.sub.2]-[Cr.sub.2][O.sub.3] is proposed, which could serve as a basis for the interpretation of the high-temperature evolution of planetary materials as well as for the development of new ceramic materials. Keywords: Mullite, spinel, sapphirine, chromium, glass, liquidus phase diagram

The capabilities of ultraviolet femtosecond laser ablation inductively coupled plasma mass spectrometry (UV-fs-LA-ICPMS) for depth profile analysis of thin metal coatings were evaluated. A standard sample consisting of a single Cr thin layer of 500 nm [+ or -] 5% on a Ni substrate was used. A fast washout was obtained by a high-efficiency aerosol dispersion ablation cell (V ~1 [cm.sup.3]), which allowed single-shot analysis with increased depth resolution. Laser ablation was performed in helium at atmospheric pressure conditions. A laser repetition rate of 1 Hz and low laser fluence (

Steady-state and time resolved photoluminescence (PL) and PL excitation (PLE) measurements are used to investigate the red luminescence of chromium doped [beta]-[Ga.sub.2][O.sub.3] nanowires and submicron size crystals. The origin of the emission is assigned to [Cr.sup.3+] ions in the [beta]-[Ga.sub.2][O.sub.3] host and the values for the energy level separation and Huang-Rhys factor are estimated for the broad [super 4][T.sub.2]-[super 4][A.sub.2] emission.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.12.005 Byline: Biswajit Mukhopadhyay (a), Jon Sundquist (b), Rodney J. Schmitz (c) Keywords: Electrochemical process; Hexavalent chromium; Groundwater contamination; Groundwater remediation Abstract: The conventional chemical reduction-precipitation technique in the removal of Cr(VI) from contaminated groundwater involves a two-step process whereby Cr(VI) is first reduced to Cr(III) at an acidic pH by a reducing agent and in a subsequent step, Cr(III) is precipitated as insoluble hydroxide at an alkaline pH. In a variation of this method, Fe(II) is added electrochemically to the Cr(VI) containing water. From a pure iron electrode, Fe.sup.2+ ions are released into the solution and bring forth the reduction of Cr(VI). At the cathode, H.sub.2O is reduced whereby the OH.sup.- ions entering the solution keep the pH of the solution in the alkaline range. This latter fact greatly facilitates simultaneous reduction of Cr(VI) to Cr(III) and co-precipitation of hydroxides of trivalent Cr and Fe. On the basis of a set of experimental data, it is shown that this process is both thermodynamically and kinetically efficient, meaning, with the electrochemical method, rapid and nearly complete removal of Cr(VI) from a groundwater source with both high and low levels of Cr-contamination can be achieved. These factors make the electrochemical process superior to the conventional chemical process in remediation of Cr-contaminated groundwater. Author Affiliation: (a) Ecology and Environment, Inc. 1412 Main Street, Dallas, TX 75202, USA (b) Ecology and Environment, Inc. 368 Pleasantview Drive, Lancaster, NY 14086, USA (c) Andco Environmental Processes, Inc. 595 Commerce Drive, Buffalo, NY 14228, USA Article History: Received 18 January 2005; Revised 24 October 2005; Accepted 13 December 2005

A new method for pretreating blood samples for trace Cr analysis is described. The advanced oxidation process (AOP with [H.sub.2][O.sub.2] and 5.5-W UV irradiation for 60 min) is used to remove biological/organic species for subsequent analysis. Prior to the AOP pretreatment, acid (HN[O.sub.3]) is used at pH 3.0 to inhibit the enzyme catalase in the blood samples. Catalytic adsorptive stripping voltammetry at a bismuth film electrode gives a Cr concentration of 6.0 [+ or -] 0.3 ppb in the blood samples. This concentration was confirmed by dry-ashing the blood samples and subsequent analysis by atomic absorption spectroscopy. This current method may be used to monitor chromium, a trace metal in humans, and the efficacy and safety of chromium supplements as adjuvant therapy for diabetes.

The reaction process of the production of CrOH(C2H4)2(super +) is studied in connection with the ethylene polymerization on a silica-supported chromium oxide catalyst. The calculation shows that the dimerization proceeds through CrOH(C2H4)(super +) (ethylene complex) and CrOH-(C2H4)2(super +) (ethylene complex), in which the ethylene molecules bind with CrOH(super +) through a pi-bonding.

The acceleration of the arene ligand exchange in the (eta(super 6)-arene)Cr(CO)(sub 2)L series can be done if the ligand L is an electronically unsymmetrical bidentate ligand. A series of 2-L'-subsituted pyrroles are proposed to provide temporary coordination to the Cr and to lower the barrier to arene exchange.

A novel D-pi-A system in which tetrathiafulvalene (TTF) and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl [eta(super 6)-arene]chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units are synthesized by Wittig-Horner olefination reaction.

A detailed mechnaistic study into the copolymerization of CO2 and cyclohexene oxide utilizing Cr(super III) x complexes and N-methylimidazoile is conducted. By studying salen ligands with various groups on the diimine backbone, it is observed that bulky groups oriented perpendicular to the salen plane reduce the activity of the catalyst significantly, it is further stated that while such groups oriented parallel to the salen plane do not retard copolymer formation.

The chromium addition has less influence on the denitrification bacteria than on the nitrification bacteria. Various measures to determine the removal efficiency of carbon and nitrogen substance using lab scale sequencing batch reactors (SBR) reactor fed with untreated tannery wastewater containing a relevant amount of chromium are discussed.

The preparation, properties and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds are reported. Complexes with strongly donating axial or equatorial ligands give rise to symmetrical molecular structure, while more weakly donating ligands give rise to unsymmetrical structures.

The movement of transition-metal ions was observed in an inhomogeneous magnetic field. The solution containing Cr(super 3+), Mn(super 2+), Co(super 2+), Ni(super 2+), and Cu(super 2+) ions was spotted on a silica gel support and exposed to a magnetic field of 410 kOe(super 2) cm(super -1) intensity x gradient.

The porous rotating disk electrode technique in pure and methanol containing electrolyte is used to study the oxygen reduction reaction (ORR) on carbon supported nanosized Pt-Cr alloy. The tolerance of methanol during ORR on the Pt-Cr alloy is reported to be higher than for the Pt/C catalyst.

Complexation by M(super +1)(M=Li, Be, Na, Mg, Al, K, Ca) of the highly unsaturated linear molecules NC(sub 2n) X (X=N, CH; n=0, 1, 2, 3) occurs exclusively by coordination to the terminal N atom. The results report that the M(super +1) - NC(sub 2n)X series featuring an alkali metal ion exhibits a remarkably close adherence to the r(super -12) dependence of the empirically assigned repulsive potential energy term.

The catalysis of the reaction of carbon dioxide with epoxides using the (salen)Cr(super III)Cl complex as catalyst, where H2salen = N,N'-bis(3,5-di-tert-butysalicylidene)-1,2-cyclohexenediimine (1), to provide copolymer and cyclic carbonate has been investigated by in situ infrared spectroscopy.

The rotational orientation of cyclopentadienyl rings, their effect on d-orbital energy levels and splitting in transition metal complexes are described. The possibility of using sterically imposed ligand rotation as a means of spin-state manipulation makes indenyl compounds a potentially rich source of magnetically adjustable molecules.

The kinetics and mechanism of the reaction of a superoxochromium(III) ion with nitrogen monoxide is detailed. The kinetics of the rapid reaction between Cr(sub aq)OO(super +2) and NO are determined by laser flash photolysis of CrNO(sub aq)(super +2) in oxide saturated acidic aqueous solutions.

The preparative transformations of three strained , 4-phenyl-3,6-dehydrohomoadamantane, 3,6-dehydrohomoadamantane and 1,3-dehydroadamantane, which allows to study the competition between the C-H and the C-C bond activations in the reactions with dimethyldioxirane (DMD) and CrO2Cl2 and verify the differences in their reactivities, are reported. The results show the important mechanistic aspects of the reactions of aliphatics with uncharged closed-shell electrophiles, like DMD.

The cyclopropanation reaction of chromium Fischer carbene complexes with alkenyl oxazolines are studied in both racemic and enantioselective methods. The results show that alkenyl oxazolines are excellent electron-poor alkene surrogates for the cyclopropanation reaction with many Fischer carbene complexes.

A series of organoarsenic and antimony chromium carbonyl complexes are synthesized and structurally characterized and the role of the main group on the formation of the resultant complexes is discussed.

A combined experimental and theoretical study on the bond characterization of Cr-L (L = O, N, C) multiple bonds is applied to a series of Cr-complexes. The findings indicate that all four Cr-L multiple bonds display essentially a triple bond character consisting of one sigma and two pi bonds.

A study of (chloro)(pyridine)(5, 10, 15, 20-tetraphenylporphyrinato)chromium(III), [Cr(TTP)(Cl)(Py)], in both dichloromethane and toluene containing water using laser photolysis is presented. The results show that the direct ligand exchange reaction of the axial HO-H...Py in [Cr(TTP)(Cl)(HO-H...PY)] with exogenous Py does not occur as the hydrogen bond, HO-H...Py, increases the basicity of H2O.

Water exchange reactions on various aqua amine complexes of chromium(III) were studied with ab initio quantum chemical calculations on the hydrated ions, whereby the solvent was treated as a dielectric continuum. It is concluded that all thermally activated substitution reactions on Cr(super III), Ru(super III) and Rh(super III) proceeded with retention of the configuration.

The gas-phase depletion kinetics of chromium atoms by sulfur dioxide is reported. The depletion rate constants of chromium when compared to depletion rate constants of the other group, it was found that the s(super 1) are generally more reactive than s(super 2) states.

Incorporation of the triangular mu(super 3) )[(C(CN)(sub 3)](sub -) ligand into polymeric arrays has led to a new class of spin-frustrated molecule-based magnets of the type M(super II)[(C(CN)(sub 3)](sub 2) (M = V, Cr). The crystal structure of Cr(super II)[(C(CN)(sub 3)](sub 2) (M = V, Cr) was determined from neutron powder diffraction at low temperature and was seen that it adopts an interpenetrating rutile-like topology.

We investigated the effects of Cr element substitution on thermal stability of magnetic flux and oxidation resistance of SmFeN compounds by X-ray diffraction (XRD), thermogravimetry analysis (TG), and flux aging loss measurement methods. We found that with increases in Cr substitution, the irreversible flux losses of bonded magnets made from these alloys decrease remarkably. When Cr substitution reaches 2 at %, the beneficial effect reaches a maximum; the irreversible flux loss of such bonded magnets exposed to a temperature 170 [degrees]C for 2 h is only 4.97 %. The oxidation resistance of SmFeN magnetic powders is also notably improved with the increased Cr substitution. Index Terms--HDDR, metal materials, nitride, rare earth.

Appropriate modification of the salphen ligand has allowed an easy modular design of flexibly linked dimeric salphen species and their complexes, which has acted as bifunctional catalysts. The results have shown an enhancement in activity upon dimerization, thus highlighting the role of bifunctional catalysis in the processes and extending the strategies for improvement of catalysts in these reactions.