In order to improve our understanding of how the goethite crystal structure is affected by the incorporation of metals (and by variations in the amount of the incorporation), and to review any possible synergistic and antagonistic effects of co-metals, the present investigation focused on the incorporation of multiple (di-, tri-, and tetra-) metals, i.e. Cr, Zn, Cd, and Pb, in the goethite crystallographic structure. A series of single- and multi-metal M-Cr/Zn/Cd/Pb-substituted goethites with M/(M+Fe) molar ratios = 0.10 were prepared. The general sequence of metal entry in single-metal substituted goethites was Zn = Cr > Cd > Pb and in multi-metal-substituted goethites was Zn > Cr ⩾ Cd > Pb. Simultaneous incorporation of Cr, Zn, Cd, and Pb up to 10.5 mole % was achieved in goethite. Synchrotron X-ray diffraction and extended X-ray absorption fine structure (EXAFS) techniques were employed to assess the structural characteristics of the synthesis products. Rietveld refinement of XRD data showed small changes in unit-cell parameters and Fe/M-Fe/M distances due to M substitution(s). A typical goethite-like crystalline structure remained intact, however. The unit-cell parameters were mutually, linearly correlated, though Fe/M-Fe/M distances were not, indicating that complex changes occurred at the local scale. In single-metal substituted goethites, incorporation of Cr reduced the unit-cell volume by 0.13% while that of Zn, Cd, and Pb increased it by 1.09, 3.58, and 0.56%, respectively. The changes in multi-metal-substituted goethites appeared to be the complex combination of that of the individually incorporated metals. The X-ray absorption near edge structure study of Pb-substituted goethites showed that the majority of associated Pb was Pb2+, while Pb4+ was preferred over Pb2+ in the bulk structure. Measurements by EXAFS at the Fe K-edge indicated that the Fe polyhedra contracted in the presence of Cd2+ and Pb2+, providing room for the substitution of larger cations. Measurements by EXAFS at the Cr and Cd K-edges indicated symmetric Cr/Cd polyhedra with single Cr/Cd-O distances and, at Fe and Zn K-edges and the Pb LIII-edge, indicated asymmetric polyhedra with two sets of Fe/Zn/Pb-O distances. The Zn octahedra were possibly Zn(OH)4O2, which enlarged the metal-metal corner-sharing distance to 3.86 Å. This configuration of ligands around the Zn2+ cation might occur to balance local charges. Symmetric polyhedra appeared to reduce steric strains in the structure, compared to the asymmetric polyhedra. The result was that Cr enhanced the incorporation of Zn, Cd, and Pb, while the converse was true for Zn.

Co–Cr–B amorphous catalysts have been synthesized by the chemical reduction method. Catalyst powders were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunner-Emmet-Teller measurements (BET). Catalytic performance of the catalyst was measured by the hydrolysis rate of the sodium borohydride solution. Results showed that the particle size of the catalyst was reduced with the addition of a small amount of Cr. The specific surface area increased significantly, and the performance of the catalyst was improved. However, excess addition of Cr caused excess oxides and Cr3+, covering the surface active sites of the catalyst, which degraded the performance of the catalyst. When the ratio of Cr/Co is 0.005, the catalyst performance was optimal and showed nearly 2 times higher H2 generation rate than that of pure Co–B catalyst. In addition, the effect of catalyst content, NaBH4 concentration, reaction temperature, and NaOH concentration on the hydrogen generation of NaBH4 solution was also studied.

Nano/mesoporous carbon was prepared from pine wood sawdust via the pretreatment of acid and hydrothermal process, followed by potassium hydroxide (KOH) activation. This study proposed the enhancement of activated carbon (AC) adsorption capacity by utilizing the vacant sites and phenomena of opposite charge attraction via multilayer adsorption of Cr(VI) ions and dyes with positive and negative charges. On the first layer, the maximum adsorption capacities for Cr(VI) ions, methylene blue (MB) molecules, and acid red 18 (AR18) molecules onto AC were found to be 7.91 mg/g, 476.19 mg/g, and 434.78 mg/g, respectively. For multiple adsorption, after Cr(VI) ions uptake saturation, the sequential adsorption of MB and AR18 on the second layer, the maximum adsorption capacity, reached 322.58 mg/g and 333.33 mg/g. After MB and AR18 uptake saturation, the maximum Cr(VI) adsorption capacity reached 2.92 mg/g and 4.39 mg/g.

The work focuses on the analysis of electrochemical corrosion in synthetic salt medium of the TiC/Ni-20Cr composite through the polarization curve technique at four exposure times (0, 6, 12 and 24 h). The composite was prepared by liquid infiltration of the liquid alloy into a porous body of TiC. It was found a continuous and homogeneous distribution of the reinforcing material in the interconnected matrix, having a residual porosity of 6.49 vol.%. According to the electrochemical results, in both samples the highest corrosion rate (CR) was obtained at 12 h exposure due to the rupture of the film of the corrosion products, allowing the interaction of chloride ions with the metal surface. The CR of the composite was slightly higher than that of the alloy at all exposure times, so that the presence of the reinforcing particles and the residual porosity reduce the corrosion resistance of the matrix in the composite. The mechanism of corrosion observed in the alloy and the composite was by pitting, however, the composite also presents crevice corrosion by a differential aeration cell mechanism formed between the metal matrix and the ceramic reinforcement, affected by the residual porosity as confirmed by electron microscopy examination.

Developing functional, cleavable two-dimensional materials for use in next generation devices has recently become a topic of considerable interest due to their unique properties. Of particular interest, transition metal halides CrI3 and CrCl3 have shown to be good contenders for tunable and cleavable magnetic materials due to their unique magnetic properties in the monolayer. Here, electron spin resonance spectroscopy is used to pinpoint the atomic origins and underlying mechanisms of magnetic interactions as a function of temperature (5-500 K) and microwave frequency (9.43, 120 GHz) on CrI3 and CrCl3 bulk single crystals. ESR signals from CrI3 due to Cr3+ were observed to decay at 460 K, while ESR signals from CrCl3 remain up to 500 K. In the case of CrCl3, the temperature dependences of signal behavior, line width and g-value show characteristic signatures of ferromagnetic fluctuations at around 40 K, near to the antiferromagnetic phase transition at 17 K.

The crystal-chemical mechanisms by which transition metals are associated with goethite are fundamental to our understanding of the solubility and bioavailability of micronutrients and heavy metals in soils, and in the formation of laterite ore deposits. Transition metals such as Cr, Mn and Ni may sorb onto goethite by forming surface precipitates, surface complexes or by replacing Fe3+ in the goethite structure. In the work reported here, we investigated the local coordination environment of Cr, Mn and Ni in synthetic goethite using EXAFS spectroscopy. We demonstrate the isomorphous substitution for Fe3+ by Cr3+ (up to 8 mol.%), Mn3+ (up to 15 mol.%) and Ni2+ (up to 5 mol.%). We find, however, that the next-nearest-neighbour coordination environment changes with composition. The perturbations are likely to be responsible for limiting the accommodation of Cr3+, Mn3+ or Ni2+ in the FeOOH structure.

Back-scattered scanning electron microscopy (SEM) images of Cr-chlorite crystals from Erzerum (Turkey) reveal that the crystals are chemically inhomogeneous and display complex but well defined crystal zoning characterized by growth bands with contrasting chemical features. The chemical zoning has been investigated at the micron scale using an integrated approach, combining BSEM images, in situ chemical analysis by electron microprobe and Raman spectroscopy. Enrichment in Cr, due to octahedral Al substitution, reaches up to 0.7 atoms per half formula, especially in bands where the Mg content is depleted. These substitutions are also depicted at the micron scale on Raman spectra by changes in the v(OH) band intensities and positions that correlate with the Cr content. The Cr-enrichment occurs thus during specific stages of crystal growth, probably in response to changes in the fluid chemistry controlling the relative availability of Cr, Mg and Al in solution.

This work aims to develop simple and cost-effective methods in reduction of Cr(VI) from water to less toxic and easy separated Cr(III) using Titanium dioxide (TiO2).

TiO2 nanoparticles are prepared by a sol-gel method using titanium tetra-chloride and characterized using X-Ray Diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive X-ray Fluorescence spectrometer (EDX) and UV-visible spectroscopy. XRD shows Anatase structure of TiO2 after annealing at 600°C for four hours. The particles size is estimated to be 70 nm using SEM.UV-Visible spectroscopy indicated that TiO2 nanoparticles played important role in decreasing the concentration of Cr (VI) in water samples for different pH range of 1 to 4. The decrease in Cr(VI) concentration after the treatment is ascribed to the reduction caused by the photocatalyst effect that resulted from the presence of TiO2 nanoparticle in water samples under direct exposure to direct sunlight.

Estimates of seed viability using the imbibed seed crush test, a method performed by applying pressure to imbibed seeds, were compared with estimates obtained from using the imbibed seed crush test supplemented with tetrazolium staining. The seeds of three weed species, giant foxtail, green foxtail, and yellow foxtail, were collected from three different crops and tested by each method. The results from the two approaches were strongly and significantly correlated. The imbibed seed crush test requires considerably less skill and time to perform and is a reasonable alternative to tetrazolium staining to test the seed viability of newly produced foxtail seeds.

Bulk cementite samples with chromium (Cr) concentrations of 0, 3.01, 6.03, 8.22, and 9.76 wt% were prepared by mechanical alloying and spark plasma sintering. The elastic modulus, elastic recovery, and hardness increased with increasing chromium content. The maximum microhardness was 1070.74 HV (Vickers hardness) and the maximum elastic modulus was 199.32 GPa using a nanoindentation device. The effect of different concentrations of Cr on the wear behavior of the cementite plowing depth, roughness, debris from the worn surfaces, and weight loss due to wear were measured using pin-on-disk tribometric equipment. It was found that both the morphology and the abrasion resistance of a surface worn by microcutting and microplowing increased markedly with increasing Cr content.

Equipment wear is caused by the disintegration of material due to the contact between the machines components and the ore, resulting in stress to the surface of the material. Wear causes loss of efficiency, vibration, misalignment and, in severe cases, cracks that may lead to fracture and damage to the equipment. In mining, wear is caused by operational problems in which generate high costs. Some researchers studied white cast iron alloys with high chromium and the addition of niobium for wear plates manufacturing and therefore, plates to protect structural parts of the equipment have been developed. This study presents the characterization of the microstructure of two alloys of white cast iron with high chromium containing 3.8 wt.% C and 27.1 wt.% Cr and the addition of 0.9 wt.% Nb (alloy 1) and 1.6 wt.% Nb (alloy 2), respectively. Samples of the two alloys were subjected to metallographic tests, microhardness and abrasion type rubber wheel tests, according to the ASTM: G65-91 standard. Complexes carbides have been identified in both alloys. The results of microhardness and wear resistance tests were correlated and identified the effect of niobium addition. The findings suggest that the addition of niobium in these alloys contributes to the formation of NbC and increase of Cr in the matrix; consequently increase in the hardenability of the material. The wear resistance of alloy 2 was 47.95% higher than alloy 1 in abrasion type rubber wheel tests. It demonstrates that the increase of niobium in the alloy has contributed to improve wear resistance due to the substantial change in the microstructure and distribution of NbC carbides.

Ultra thin films of chromia (Cr2O3), less than 3 nm thick, grown epitaxial on α-Al2O3 (sapphire), and are thus compressively strained in-plane. The resulting films show evidence of some magnetic ordering above the Néel temperature of chromia (307 K). The observed higher temperature hysteresis effect observed are very likely a strain effect, and not associated with the typical antiferromagnetic ordering expected of chromia.

Tungsten carbide (WC) particle–reinforced iron matrix surface composites with different content of Cr were fabricated using vacuum evaporative pattern casting technique. It was found that the morphology of carbides changed from continuous net-shape to isolated block-shape patterns. The amount of carbides increase with the increasing Cr content in the matrices. Composites with different Cr content show better abrasive wear resistance than those without Cr. With the increase of Cr content in the matrices, the three-body abrasive wear resistance of the composites increased, while the impact abrasive wear resistance of the composites increased under 1 J impact load, but first increased and then decreased under 3 J impact load. The influences of the addition of Cr in the matrices on the abrasive wear resistance were the synergistic effects of two protecting effects and two supporting effects. The results might provide significant references for the design and practical application of WC particle–reinforced iron matrix surface composites.

Imprinting is a well-established technique to induce recognition features in both organic and inorganic materials for a variety of target analytes. In this study, ion imprinted polysiloxanes with varying percentage of coupling agent i.e. 3-chloro propyl trimethoxy silane (CPTM) were synthesized by sol-gel method for imprinting of Cr3+. The imprinting of Cr3+ in cross-linked siloxane network was investigated by FT-IR which indicates the metal ion is coordinated with oxygen atoms of polysiloxanes. SEM images revealed that imprinted polysiloxanes possess uniform particles of submicron size. It was experienced that by increasing the concentration of CPTM up to 10% (v/v) substantially improves the binding capacity of polysiloxanes which allows us to recognized Cr3+ down to 50µg/L. Furthermore, the selectivity of Cr3+-imprinted polysiloxanes was evaluated by treating them with other competing metal ions of same concentration i.e. Cr6+, Pb2+ and Ni2+. In this regard, polysiloxanes showed much higher binding for imprint ion i.e. Cr3+ in comparison to above mentioned metal ions. Finally, the regenerated polysiloxanes were studied in order to reuse them thus, developing cost effective biomimetic sensor coatings.

Precipitates of Cr at Σ3 <110> {112} GB in α-Fe have been studied using molecular dynamics with a two-band embedded atomic model potential. The accumulation and segregation of Cr atoms and the evolution of the GB depend on local Cr concentration and temperature. At the early stage, with the existence of vacancies, the strong attraction of Cr with the GB core provides a pathway for Cr atoms to quickly accumulate within the GB core. With the increase of Cr concentration, the size of Cr dilute precipitates increases dramatically. And the strong segregation of Cr at the GB is observed, when Cr concentration reach 20%. Also, the size of Cr precipitates increases with increasing the temperatures from 300 K to 1000 K. The accumulation and segregation of Cr atoms at the GB lead to significant deformation of the GB structure and the formation of GB steps, causing the displacement and broadening of the GB.

Magnetite nanoparticles were produced by the chemical co-precipitation of iron sulfates at alkaline conditions and were tested as a Cr(VI) adsorbent from water. Batch adsorption experiments showed a high removal efficiency, which is maximized at pH values below 6. This behavior was also verified in a continuous flow reactor, where nanoparticles were in contact with the polluted water. In particular, using a particle concentration of 1 g/L in water containing 100 μg Cr(VI)/L, a contact time of at least 2 h was required to achieve complete removal of Cr(VI). The recovery of nanoparticles after their use was accomplished using their magnetic nature. Application of an external magnetic field at the sides of the tube in which the suspension was flowing was sufficient to completely collect the nanoparticles in the outflow of the contact reactor, thus, providing water free of Cr(VI) and a solid phase.

Traumatic brain injury (TBI) is the most common cause of brain damage, resulting in long-term disability. The “reserve” construct has been proposed to account for the reported mismatch between brain damage and its clinical expression. Although numerous studies have used various measures thought to reflect this construct, few studies have examined its underlying structure in clinical populations, and no studies have systematically studied this construct in TBI. In the present study, structural equation modeling technique was used to evaluate several models hypothesized to represent cognitive reserve (CR) in TBI. A broad range of data typically reported in the literature as representing CR was collected from 89 individuals who sustained moderate-to-severe TBI. Analyses revealed a best fitting model that consisted of three separate factors representing premorbid intelligence, socioeconomic status and leisure activity, with distinct pattern of associations among the three factors. Findings provide empirical support for the notion of a multi-factorial CR and suggest a coherent framework for further investigation. (JINS, 2013, 19, 1–8)

The state of Phillips Cr/silica catalyst technology is discussed in this article, including recent advances in the science and also economic and environmental challenges to its continued viability. Although these catalysts have often been described as “mature,” many new innovations have been introduced in the past decade that reduce cost, improve quality, and expand the range of products that can be made. Polymers having unusually high, and low, levels of long-chain branching have been introduced. Several advances in the control of the short-chain branch distribution have also been made. Ways to lower the catalyst costs have been successfully implemented, such that Phillips-type catalysts are still the least expensive in the industry. Finally, new chromium-containing hybrid catalysts have been made that marry attributes from single-site and conventional Cr oxide catalysts.

Six alloys based on Cr-10Ta-7Si (by at.%) with quaternary additions of 0.5Ag, 5Ti, 1Hf, 3Mo, 3Al, or 3Re (by at.%) substituted for Cr were produced by vacuum arc-melting. The microstructures of the alloys were found to predominantly consist of a eutectic mixture of an A2 Cr-based solid solution and a C14 Cr2Ta Laves phase along with proeutectic Cr2Ta dendrites. Microstructural macro- and micro-scale inhomogeneities were observed in all alloy ingots, which were attributed to the non-equilibrium arc-melting process. The measured lattice parameters of the constituent phases and the elemental partitioning behaviour between the phases have been correlated with the respective covalent atomic radii. The bulk hardnesses of the alloys, along with the hardness of individual phases, have also been reported.

The present study was carried out to evaluate the microstructures and mechanical properties of severely deformed Ni-30Cr alloy. Cross-roll rolling (CRR) as severe plastic deformation (SPD) process was introduced and Ni-30Cr alloy sheets were cold rolled to a 90% thickness reduction and subsequently annealed at 700 °C for 30 min so as to obtain the recrystallized microstructure. For the analysis of grain boundary character distributions (GBCDs), electron back-scattered diffraction (EBSD) technique was introduced. CRR on Ni-30Cr alloy was effective to enhance the grain refinement through heat treatment; consequently, average grain size was significantly reduced from 33 μm in initial material to 0.6 μm in CRR processed material. This grain refinement directly affected the mechanical properties improvement, in which yield and tensile strengths were significantly increased than those of initial material. In this study, we systematically discussed the grain refinement, accompanying with increase in mechanical properties, in terms of the effective strain imposed by CRR, comparing with conventional rolling (CR).