Cr Bond Research Articles

Bridging cyclobutadiene ligands with agostic hydrogen atoms in binuclear chromium carbonyl derivatives

The binuclear cyclobutadiene chromium carbonyls (C4H4)2Cr2(CO)n (n = 7, 6, 5, 4, 3), potentially accessible from the experimentally known (η4-C4H4)Cr(CO)4, have been examined by density functional theory. The low-energy structures for the heptacarbonyl (C4H4)2Cr2(CO)7 have terminal (η4-C4H4)2Cr2(CO)7 rings with a central Cr–Cr single bond bridged by one or three CO groups and the remaining CO groups as terminal ligands evenly distributed among the chromium atoms. The lowest energy structure for the hexacarbonyl (C4H4)2Cr2(CO)6 has a (η4-C4H4)2Cr(CO)2 complex functioning as a bidentate chelating ligand to a Cr(CO)4 fragment through the formation of two three-center C–H–Cr bonds with agostic hydrogen atoms exhibiting short Cr–H distances of ∼1.85 Å. The pentacarbonyl (η4-C4H4)2Cr2(CO)5 resembles the analogous experimentally known (η5-C5H5)2V2(CO)5 by having terminal η4-C4H4 rings, two bridging CO groups, and a central CrCr triple bond. The three lowest energy structures for the tetracarbonyl (η4-C4H4)2Cr2(CO)4 are singlet structures with two four-electron donor bridging η2-μ-CO groups, a terminal CO group on each chromium atom, and a central CrCr double bond. The lowest energy structure for the more highly unsaturated tricarbonyl (η4-C4H4)2Cr2(CO)3 by a margin of more than 12 kcal/mol is a triplet spin state structure with a terminal η4-C4H4 ring, a bridging η4,η1-C4H4 ring through an agostic C–H–Cr interaction, and a central CrCr triple bond. Thermochemistry suggests that the lowest energy structures for all of the (C4H4)2Cr2(CO)n (n = 7, 6, 5, 4) systems, especially the pentacarbonyl, are viable towards carbonyl dissociation.

Theoretical investigation of the crystallographic structure, anisotropic elastic response, and electronic properties of the major borides in Ni-based superalloys

ABSTRACT In Ni-based superalloys, it is usually found that borides can strengthen the grain boundaries, thereby resulting in an increase in mechanical strength and high-temperature creep properties. Due to their importance and prevalence in Ni-based superalloys, this study employs first-principles methods to investigate the crystallographic structure, anisotropic elastic response, and electronic properties of the major borides, such as M2B, M5B3 and M3B2 (M: Cr, Mo, W), respectively, which is necessary for the assessment of complex mechanical responses of Ni-based superalloys. The results demonstrate that the studied borides are all thermodynamically and mechanically stable. Among the M x B y binary borides analysed, Cr x B y exhibits the largest shear modulus, Young’s modulus, and Vicker hardness values, and these properties increase with the increase of B contents. The studied borides display nearly isotropic elastic properties except for W5B3 and W3B2. The electronic structure analysis of M x B y shows that the strong hybridisation between M-d and B-p orbitals leads to these borides exhibiting higher theoretical hardness, and the overlapping peaks of M-d and B-p orbitals move to a lower energy area with the increase of B contents, which leads to the increase of shear and Young’s moduli of M x B y . Furthermore, for M3B2 borides, the Cr-B bonds and Cr–Cr bonds are much stronger than the W-B & Mo-B bonds, and W-W & Mo-Mo bonds, respectively, which leads to Cr x B y yielding the largest values of elastic moduli.

Structural, Magnetic, and Magnetocaloric Properties in Rare Earth Orthochromite (Sm, Nd, and La)CrO3 for Cooling Product

Polycrystalline phase of SmCrO3, NdCrO3, and LaCrO3 orthochromites was synthetized with solid-state reaction method. The pure orthorhombic phases with space group Pnma have been confirmed by X-ray diffraction. In addition, the FTIR spectroscopy proved the formation Sm–O, Nd–O, and La–O bonds in SmCrO3, NdCrO3, and LaCrO3 respectively, and Cr–O and Cr–O–Cr bonds in all our samples. The particles morphology and composition results were obtained using the scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The Quantum Design XL-SQUID magnetometer is used in order to determine the magnetic transition type and transition temperature for each sample. We found that our samples exhibit a transition at 195 K, 65 K, and 35 K for SmCrO3, NdCrO3, and LaCrO3 respectively. The magnetic entropy change (∆Sm), as the key parameter to evaluate the magnetocaloric effect, is calculated. Our samples present a ∆Sm in the range of 0.11 and 0.25 J kg−1 K−1 for an external magnetic field of 5 T.

Experimental research on reconditioning transmission axles by MAG robotic welding

The current paper presents the experimental program conducted in order to determine the welding technology for shaft bond wheels, of Cr and Ni low alloyed steel, in enhanced condition. The material that makes up the shaft bond wheel is in laminated state, with a diameter of 70 mm and a high tendency to cracks when subjected to welding. During exploitation, these axles are subjected to stress and fatigue which imposes developing materials with equal resistance as well as avoiding concentrators in the joint design. The steel transmission shafts, butt welded together, contain Fe-1.7%Cr-2%Ni type with a 0.4%C, respectively Fe-0.7%Mn-1%Cr type with 0.3%C, with hardness approx. 250HB on the shaft and 350HB on the axle. The preheating and inter-pass temperature, combined with mechanical characteristics of welded joints, that have similar resistance, was performed according to SR EN 1011-2-2004, using the help of equivalent carbon computational relations. Fractometric analysis of deficiency areas extracted from parts used in exploitation, at the beneficiary exploitation site, due to defects, highlighted “fish eye” defects, fatigue cracks, that determined choosing this welding technology, namely robotic, in protective gas environment, Corgon 18 – 82%Ar and 18%CO2, using EN ISO 16834-A G694MMn3Ni1CrMo wire with a diameter of Φ1.6 mm. Welding was performed by maintaining 150°C temperature between layers, at a welding speed of 280 mm/min, power 200±10A, wire feed speed 3.7 m/min, in protective gas, Corgon 18 with a 18.22 l/min flow. The joint was designed so it will have minimum concentration areas and assure cooling of welded zones, after the joint was completely filled. After the repair we extracted samples from the joint, in order to test the weld quality and assimilate the technology. Metallographic and compositional analysis performed on specific areas highlighted improved structures in the center of the weld – zone 2, which ensures a proper tenacity of the joint and a hard coat, at the exterior, that favors the good operation of the assembly under critical fatigue conditions. Results obtained confirm and recommend implementing the developed welding technology into industrial environment.

Trapping of CO2 by Cr–Cr quintuple bonds. A theoretical approach

The reaction of CO2 with quintuple Cr–Cr bond organometallic compounds is investigated using Density Functional Theory calculations. In these organometallic compounds, the electronic density is localized at the multiple Cr–Cr bonds. As expected, there is an electron transfer from this multiple bond to the Lowest Unoccupied Molecular Orbital (LUMO) of CO2, yielding a reaction with the carbon atom of the CO2 molecule. A posterior reaction of NH2− with the captured CO2 is also investigated and it is possible to see that CO2 interacts with the amine anion generating carbamate ion, which is one of the main products of the natural photosynthesis process. The whole reaction is considered a homogenous catalysis procedure since this ion is released allowing the complex to return to its initial geometry.

The Imino Stannylene SnNH Incorporated in a Molecular Tin‐Nitrogen Cage and other Tin(II)‐Nitrogen Derivatives

The iminostannylene HNSn was successfully incorporated in a molecular cage of composition (Me2RSi–NSn)3(HNSn) with group R either being a methyl (1) or vinyl (2) substituent. An X‐ray structure analysis reveals that 2 consists of a distorted Sn4N4 cube. The Sn–N(H) bond lengths [2.189(2) Å] are in the range for Sn4N4 hetero cubanes. When stored in a toluene solution the clusters 1 and 2 decompose slowly into the symmetric cubanes (Me2RSi–NSn)4 [R = Me (3), CHCH2 (4)] and an amorphous and insoluble powder of composition HNSn. The decomposition follows a first order rate law as established for 2 with a half life time t1/2 = 320 d at 20 °C. The compounds 1 and 2 can thus be regarded as a result of interaction between three entities {Me2RSi–NSn} and one entity {HNSn}. We also isolated the twistane‐like Me2Si(NtBu)2Sn2NtBu (5) in a crystalline form. The central structure of this molecule, which has almost C2v symmetry, has a trigonal bipyramid Sn2N3 unit with the nitrogen atoms occupying the equatorial plane. Each nitrogen atom has a tert‐butyl ligand and two of the N atoms are further connected by the dimethylsilyl group. There is one nitrogen atom in an almost planar environment (only bonding to tert‐butyl and two tin atoms) with a remarkable short Sn–N bond length of 2.048(5) Å. Both tin atoms in cage 5 can bond to Cr(CO)5 to form [Me2Si(NtBu)2Sn2NtBu][Cr(CO)5]2 (6) with an almost linear Cr–Sn···Sn–Cr arrangement and Sn–Cr bond lengths of 2.581(1) Å (X‐ray diffraction).

Plasma-sprayed alumina coating on Inconel 600 for fast reactor neutron detector application

ABSTRACTAlumina coating, with high electrical resistivity, has been proposed over Inconel 600 rings for application in fission chamber neutron detectors, operating at 923 K in fast breeder reactor. For improving the thermal cycling life and adhesion strength of alumina coating, selection of the suitable coating technique and bond coat, with appropriate spray parameters was pursued. In the present study, Ni–50%Cr bond coat was deposited over Inconel 600 by the high velocity oxygen fuel technique, while the top alumina coat was deposited using air plasma spray process. A dense coating with minimum porosity and a stable insulation resistance (600 V DC) of ∼1011 ohm at room temperature and ∼108 ohm at 923 K was achieved. Thermal cycling studies on coated samples and rings showed good thermal cycle life tested up to 100 cycles. The coating exhibited good bond strength and only marginal decrease in bond strength was observed with increase in thermal cycling.

The Crystal Structure, Raman Spectra, and Magnetic Properties of HoCrO3 Annealed in Different Atmospheres

The crystal structure, phonon Raman scattering, and magnetic properties of HoCrO3 were studied in a way of impacting the oxygen site by annealing treatment in argon and oxygen atmospheres. Although there are no dramatic changes in magnetic properties, a negative magnetization phenomenon below TN was observed in all prepared HoCrO3 samples and a certain of lattice distortion was affected due to the variation of Ho–O bond length and Cr–O–Cr bond angle and bond lengths. The Raman spectra exhibit an obvious shift of mode-related Ho ion instead of modes involved with Cr, which unconsciously leads to the variation of effective paramagnetic moments. The magnetic properties were systematically analyzed by Curie-Weiss and modified Curie-Weiss laws. The effective magnetic moment and symmetric and antisymmetric exchange interactions of Je and D were discussed. The reduced effective magnetic moments in HoCrO3 and annealed ones demonstrate possible vacancies of Ho and Cr, which was verified by elemental composition tested by energy-dispersive X-ray spectroscopy.

Structural evolution and magnetic properties of anionic clusters Cr2Gen (n = 3–14): photoelectron spectroscopy and density functional theory computation

The structural, electronic and magnetic properties of dual Cr atoms doped germanium anionic clusters, (n = 3–14), have been investigated by using photoelectron spectroscopy in combination with density-functional theory calculations. The low-lying structures of are determined by DFT based genetic algorithm optimization. For with n ⩽ 8, the structures are bipyramid-based geometries, while cluster has an opening cage-like structure, and the half-encapsulated structure is gradually covered by the additional Ge atoms to form closed-cage configuration with one Cr atom interior for n = 10 to 14. Meanwhile, the two Cr atoms in clusters tend to form a Cr–Cr bond rather than be separated. Interestingly, the magnetic moment of all the anionic clusters considered is 1 μB. Almost all clusters exhibit antiferromagnetic Cr–Cr coupling, except for two clusters, and . To our knowledge, the cluster is the first kind of transition-metal doped semiconductor clusters that exhibit relatively stable antiferromagnetism within a wide size range. The experimental/theoretical results suggest high potential to modify the magnetic behavior of semiconductor clusters through introducing different transition-metal dopant atoms.

First-principles investigation of Cr-doped Fe2B: Structural, mechanical, electronic and magnetic properties

The structural, mechanical, electronic and magnetic properties of Fe8−xCrxB4 (x = 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7 and 8) have been investigated by first-principles calculation. It was found that the calculated structural parameters are well consistent with available experimental data. Moreover, all studied compounds are thermodynamically stable phases. On the whole, the moduli of the compounds firstly increase and then decrease with the increase of Cr concentration, whereas the variation of hardness exhibits more fluctuations. All Cr-doped Fe2B have better ductility than Fe2B except Fe2Cr6B4 and Fe5Cr3B4. Interestingly, Fe4Cr4B4 is of not only the slightly larger hardness, but also much better ductility than Fe2B. As the Cr concentration is lower than 20 wt%, the hardness of Cr-doped Fe2B slightly decreases with increasing Cr, whereas the sharply increased hardness of (Fe, Cr)2B in Fe-B alloys or boriding layer should be attributed to the multiple alloying effects resulting from Cr and the other alloying elements. The electronic structures revealed that the Fe-B and/or Cr-B bonds are mainly responsible for their mechanical properties, and the M-N (M = Fe or Cr, N = Fe or Cr) bonds in 〈2 2 0〉 and 〈1 1 3〉 orientations show covalent character. Additionally, the magnetic moments (Ms) of the compounds do not monotonically decrease with increasing Cr.

Raman and EPR spectroscopic studies of chromium-doped diamond-like carbon films

The diamond-like carbon (Cr-free DLC) and chromium-doped DLC (Cr doped-DLC) films prepared by a hybrid technology using a combination of pulsed laser deposition and magnetron sputtering were studied by Raman and electron paramagnetic resonance (EPR) spectroscopy. Raman spectra are dominated by the well-known carbon (D/G) band. The intensity ratio of the D/G bands was found to increase with the increase of the Cr content. Careful elimination of the substrate-related (SiO2) peaks enabled us to identify new weak features attributable to the presence of the CCr bonds. Two EPR signals were observed in Cr-free and Cr-doped DLC films. The EPR signal at g = 2.0025(3) was attributed to the sp2 coordinated carbon-related defect (CRD) and the second EPR signal at g = 2.0064 was assigned to the Pb0 interface defect which may appear due to the formation of the oxidized Si on the interface of the DLC film and SiO2 substrate. The observed temperature behavior of the CRD EPR signal g-factor in Cr free DLC films was described by the model of exchange coupled two spin systems (localized defects and conduction electrons) in the bottleneck regime. From the temperature dependence of the linewidth and integral intensity of the CRD EPR signal it was concluded that ferromagnetic ordering occurs in the spin system with exchange constant of J = 0.069 meV. The spin density of the CRD was found to be significantly decreased in Cr-doped DLC films, possibly due to the formation of the CCr bonds. The observed change of the CRD lineshape from Lorentzian in Cr free DLC films to Gaussian in Cr-doped DLC films indicates that there is a superhyperfine coupling between unpaired spins of the CRD and surrounding Cr nuclei.

An XPS study on oxidation of exposed-to-air Cr1−xZrxN film surfaces

Chromium zirconium nitride (CrZrN) thin films were prepared on Si (100) substrates with various Zr contents by using co-sputtering technique. The Zr content was varied by variation of the Zr sputtering current from 0.2 to 0.8 A while the Cr current and the N2 flow rate were kept at 0.8 A and 6.0 sccm, respectively, to fix the concentration of Cr and N atoms. An oxidation caused by exposure to air of the Cr1−xZrxN thin films were studied by using X-ray photoelectron spectroscopy (XPS). Chemical composition analysis of XPS spectra revealed that oxygen detected on the film surfaces was increased with the rise in the Zr content. Deconvolutions of O 1s photoemission lines revealed bonding separately of O atoms to Cr and Zr atoms. Moreover, the fraction of the O–Cr bond was increased with the increasing Zr content.

Reactions of [rad]Sn(Si(tBu)2Me)3 with HM(CO)3C5R5 (M = Cr or Mo, R = H or CH3) and Hg. Ionic, covalent, and μ-CO bonding patterns between transition metals and tin

Hydrogen atom transfer (HAT) reactions to the planar triorganotin radical Sn(Si(tBu)2Me)3 from HMo(CO)3C5H5 and HCr(CO)3C5R5 (R=H, Me) have been investigated at room temperature in toluene or pentane solution. Sn(Si(tBu)2Me)3 and HMo(CO)3C5H5 react rapidly to yield the previously unreported tin hydride HSn(Si(tBu)2Me)3 and [Sn(Si(tBu)2Me)3]+[Mo(CO)3C5H5]−. Similarly, Sn(Si(tBu)2Me)3 and HCr(CO)3C5H5 react at a slower rate to produce HSn(Si(tBu)2Me)3 and a complex formulated as Cp(CO)2CrCOSn(Si(tBu)2Me)3 based on its solubility in toluene, infrared spectrum, and computational studies. A product with identical spectroscopic properties to the proposed Cp(CO)2CrCOSn(Si(tBu)2Me)3 is obtained rapidly in the reaction of Sn(Si(tBu)2Me)3 and [Cr(CO)3C5H5]2. Reaction of Sn(Si(tBu)2Me)3 and HCr(CO)3C5Me5 does not occur at a significant rate at room temperature nor does reaction of Cr(CO)3C5Me5 and HSn(Si(tBu)2Me)3. Fast exchange between HCr(CO)3C5H5 and [Cr(CO)3C5H5]2 results in a single broad peak in the cyclopentadienyl area for mixtures of these two complexes in toluene-d8 at room temperature implying that Cr–Cr bond cleavage and also hydrogen atom transfer (HAT) are faster than the NMR time scale. Computational studies accurately reflect experimental observations. The computed Sn–H bond dissociation enthalpy (BDE) of only 66.7kcal/mol in HSn(Si(tBu)2Me)3 places it near the values for M-H BDE in HM(CO)3C5H5 (M=Cr, Mo) leading to a near equilibrium situation with respect to HAT. Reaction of Sn(Si(tBu)2Me)3 and elemental Hg forms the linear trinuclear HgSn2 cluster Hg[Sn(Si(tBu)2Me)3]2. The crystal structures of Hg[Sn(Si(tBu)2Me)3]2 and BrSn(Si(tBu)2Me)3 are reported.

Binuclear chromium carbonyl complexes of the highly basic small bite bidentate diphosphine bis(dimethylphosphino)methane

The structure and thermochemistry of the triads of binuclear chromium carbonyl complexes [(Me2P)2CH2]Cr2(CO)n (n=10, 9, 8), [(Me2P)2CH2]2Cr2(CO)n (n=8, 7, 6) and [(Me2P)2CH2]3Cr2(CO)n (n=6, 5, 4) have been investigated using density functional theory. The lowest-energy structures of the carbonyl-richest triad members [(Me2P)2CH2]Cr2(CO)10, [(Me2P)2CH2]2Cr2(CO)8, and [(Me2P)2CH2]3Cr2(CO)6 have long Cr⋯Cr distances indicating the absence of direct chromium bonds. The lowest energy structures of the intermediate triad members [(Me2P)2CH2]2Cr2(CO)7 and [(Me2P)2CH2]3Cr2(CO)5 systems have Cr–Cr single bonds of lengths of 3.13 and 3.39Å, respectively, and intact diphosphine ligands. However, in the lowest energy [(Me2P)2CH2]Cr2(CO)9 structure, one of the terminal CO groups is converted into a four-electron donor bridging η2-μ-CO group, retaining a long non-bonding Cr⋯Cr distance of 4.80Å. The lowest energy structure of the carbonyl-poorest [(Me2P)2CH2]Cr2(CO)8, [(Me2P)2CH2]2Cr2(CO)6, and [(Me2P)2CH2]3Cr2(CO)4 members of each triad show different features. In the lowest energy [(Me2P)2CH2]Cr2(CO)8 structure the ligand splits into separate Me2P and Me2PCH2 units, both of which bridge a Cr–Cr bond of length 3.06Å. The lowest energy [(Me2P)2CH2]2Cr2(CO)6 structure has a four-electron donor bridging η2-μ-CO group and a Cr–Cr single bond of length 2.91Å. The lowest energy [(Me2P)2CH2]3Cr2(CO)4 structure is a triplet structure with a Cr–Cr single bond of length 3.03Å.

On the origin of magnetic anisotropy in two dimensional CrI3

The observation of ferromagnetic order in a monolayer of CrI3 has been recently reported, with a Curie temperature of 45 K and off-plane easy axis. Here we study the origin of magnetic anisotropy, a necessary ingredient to have magnetic order in two dimensions, combining two levels of modeling, density functional calculations and spin model Hamiltonians. We find two different contributions to the magnetic anisotropy of the material, favoring off-plane magnetization and opening a gap in the spin wave spectrum. First, ferromagnetic super-exchange across the ≃90 degree Cr–I–Cr bonds, are anisotropic, due to the spin–orbit interaction of the ligand I atoms. Second, a much smaller contribution that comes from the single ion anisotropy of the S = 3/2 Cr atom. Our results permit to establish the XXZ Hamiltonian, with a very small single ion anisotropy, as the adequate spin model for this system. Using spin wave theory we estimate the Curie temperature and we highlight the essential role played by the gap that magnetic anisotropy induces on the magnon spectrum.

Study of the influence of functionalization on the reorganization energy of naphthalene using DFT

In this work, a number of naphthalene derivatives have been constructing by including various functional groups, i.e., F, Cl, or N atoms or NO2 or CN groups, and investigated theoretically by using the B3LYP/6-31G∗∗ method with the aim of studying their electronic and charge transport properties. Special attention is paid to the reorganization energy of the charge transport process, as well as the adiabatic electron affinities (EA), the 1st ionization potential (IP), the HOMO and LUMO orbital energies, and the HOMO-LUMO energy gap. We find that the reorganization energies (λ+ and λ−) in some cases are higher compared to those of the unsubstituted system, whereas the calculated λ values for Cl-functionalized naphthalene are significantly smaller than those of the F-functionalized system. The enhancement of λ is attributed to additional contributions from the CR bonds (R=F, Cl, CN, NO2, and/or N). On the other hand, functionalization of naphthalene tends to increase the electron affinity and the ionization potential. The electron-withdrawing groups were found to increase the reorganization energy and decrease the HOMO-LUMO gap. Based on our findings, we suggest that functionalization can be used as valuable techniques to control the electronic properties of these n-type and p-type semiconductor materials.

Silane-modified halloysite/Fe3O4 nanocomposites: Simultaneous removal of Cr(VI) and Sb(V) and positive effects of Cr(VI) on Sb(V) adsorption

New adsorbents were successfully prepared by in-situ growing Fe3O4 nanoparticles on halloysite nanotubes (HNTs) followed by subsequent modification with silane coupling agents. The as-prepared composites were characterized by TEM, XRD, TGA, ATR-FTIR, BET, and Zeta potential. The results confirm that Fe3O4 nanoparticles were successfully decorated on internal nanotube surfaces and silane coupling agents were grafted onto the external surfaces. Among the four types of silane coupling agents modified HNTs/Fe3O4, anilino-methyl-triethoxysilane (KH-42) modified HNTs/Fe3O4 composite exhibits the highest capacity for single adsorption of Cr(VI) and simultaneously adsorption of Cr(VI) and Sb(V). Moreover, the maximum Sb(V) removal efficiency increases from 67.0% in the single-solute system to 98.9% in the bi-solute system, suggesting that the presence of Cr(VI) enhances the Sb(V) removal by m-HNTs/Fe3O4. ATR-FTIR and XPS results reveal the existence of N–O–Cr bonds on adsorbent surfaces in the corresponding single-solute system, while Cr–O–Sb binding forms in the bi-solute system, which is responsible for the synergistic promoting effect on simultaneous adsorption of Cr(VI) and Sb(V) by m-HNTs/Fe3O4. The present work evinces that m-HNTs/Fe3O4 holds the potential in treating industrial wastewater and natrual surface water with coexisting heavy metals such as Cr(VI) and Sb(V).

Probing structural distortions in rare earth chromites using Indian synchrotron radiation source

Effect of R site ionic radius on the structural distortions in RCrO3 (R: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y) rare earth perovskite chromites is investigated through synchrotron based X-ray diffraction technique. The said structural distortions are measured in the terms of CrO bond lengths, CrO6 octahedral tilt, tolerance factor (t) and RO12 polyhedral distortion. It is observed that the lattice parameters (b and c), RO bond length, tolerance factor and Cr–O–Cr bond angle increases with increase in the radius of R site ion; whereas octahedral tilts (along [010] and [101]) and RO12 polyhedral distortion decreases with increase in the radius of R site ion. Further it is observed that the radius of R site cation does not have significant effect on lattice parameter ‘a’ and CrO bond length (hence on the distortion of CrO6 octahedra). A comparison of the crystal structure parameters obtained using refinement of synchrotron powder X-ray data and that estimated theoretically using modern bond valence parameters (SPuDS) has been carried out. A one to one correlation between the experimental and theoretical results has been observed.

Efficient Removal of Cr(VI) from Aqueous Solution onto Palm Trunk Charcoal: Kinetic and Equilibrium Studies

In the present study, carbonization method using mineral acids at elevated temperature. The potential of chemically carbonized palm trunk charcoal (PTC) for the effective removal of Cr(VI) ions from aqueous solution has been investigated in batch experiments. The sorption kinetics at pH=1.5 and the sorption isotherms at different pHs were studied. Chromium concentration was analyzed spectrophotometrically using 1,5-diphenylcarbazide. In order to the maximal adsorption at pH 1.5 was 24.7 mg g-1. The equilibrium adsorption capacity of PTC increases (4.99 to 24.7 mg g-1) as the initial Cr(VI) concentration increases (10-50 mg L-1). The adsorption behavior of Cr(VI) is best described by the pseudo-second order model and the calculated equilibrium capacity (15.6 mg g-1) agree with the experimental value (14.75 mg g-1). The equilibrium data were well fitted by the Langmuir isotherm model by revealing the maximum sorption capacity of PTC (24.7 mg g-1). The mechanism of adsorption was also studied using Fourier transform infrared (FTIR) spectroscopy. The bond of Cr(VI) to the functional groups of charcoal seems to be irreversible in the case of dried Cr(VI) saturated charcoals.

Bonding and Spectral Character of Cr Doped Cdte, Cdse and Cds Nano-Clusters

The geometrical structures, bonding characteristics, Raman spectra, and molecular orbitals of hexagonal and tetrahedral Cr-doped CdX molecules have been investigated using density functional theory calculations at the B3LYP/LANL2DZ level. The structures of Cr-doped CdX molecules had obvious distortions compared with pure CdX clusters, especially CdCr2Se3 and CdCr2S3 clusters. The Mulliken charges of Cr atoms were negative and were lower than those of Cd atoms in the corresponding structures. Raman spectra showed that there was the vibration of the Cr–Cr bond in Cr-doped CdX molecules. Wiberg bond indices (WBI) values show that there were Cr–Cr bonds in some clusters. WBI values have also revealed that bonds between Cr and Te, Se, S were stronger than those between Cd and X atoms. Finally, molecular orbital observations indicate that the transitions in doped structures were from d orbital to d orbital, which is different from undoped structures.