Mixture Of Cr Research Articles

Influence of substrate temperature and bias voltage on properties of chromium nitride thin films deposited by cylindrical cathodic arc deposition

Chromium nitride (CrN) thin films have been deposited on high speed steel (HSS) substrates using rotating cylindrical cathodic arc deposition technique and the influence of substrate temperature (TSub) and bias voltage (VSub) on the physical/mechanical and corrosion resistance properties of the films comprehensively investigated. An increase in TSub was found to significantly influence the phase composition of films, which changed from a mixture of Cr + CrxN + CrN to predominantly CrN. This was also accompanied by an increase in droplet formation and columnar grain size. With increase in TSub over the range investigated (230 °C to 500 °C), an increase in adhesion strength by nearly 30% was observed. In contrast, change in VSub from −50 to −150 V resulted in the growth of highly dense (111) oriented CrN thin films but with relatively little change in phase constitution, adhesion strength or microdroplet formation. A change in TSub from 230 °C to 500 °C was accompanied by a nearly 50% fall in corrosion resistance, plausibly due to the concomitant decrease in pure Cr phase content and increase in macroscopic defect concentration with increase in TSub. In view of the above, CrN thin films deposited using cylindrical cathodic arc deposition technique yield better corrosion resistance and mechanical properties when grown at low TSub.

Formation of Nanostructures in Ni-22Cr-11Fe-1<I>X</I> (<I>X</I> = Y<SUB>2</SUB>O<SUB>3</SUB>, TiO<SUB>2</SUB>) Alloys by High-Energy Ball-Milling

Powder mixtures of Ni, Cr, Fe and Y2O3 were high-energy ball-milled and subsequently sintered to fabricate Ni-based oxide-dispersion strengthened (ODS) alloys. Nano-sized Y2O3 and/or TiO2 seem to be dissolved in the Ni matrix forming a metastable solid solution during high-energy ball-milling or mechanical alloying (MA) process. The finely grained MA powders with high dislocation density facilitated the decomposition of oxides. The MA powders were consolidated to near-full density by spark plasma sintering at 1100 degrees C for 5 minutes in an Ar atmosphere. The Cr oxides as well as decomposed Y- and Ti-oxides thermally precipitated as oxide particles of several tens nanometers at this temperature, although sintering was carried out during a short time. The SPSed specimen showed a near full densification with almost pore-free microstructures. Examination of fractured surface showed a typical dimple rupture with fine and homogeneous distribution of dispersoids, indicating non-negligible room temperature ductility combined with high mechanical strength.

Immunological Effects of Gulf Oil Spill: Crude Oil, COREXIT® EC9500A Dispersant and Oil/Dispersant Mixtures

Workers involved in the gulf oil spill containment and cleanup efforts have reported health concerns including pulmonary distress, dermatological problems, and an increased incidence of infection. These concerns have prompted toxicological evaluation of samples recovered from the gulf oil spill including: COREXIT® EC9500A (CR), crude oil and crude oil/CR mixtures. Potential for hypersensitivity and immune suppression were evaluated in dermal exposure murine models. Dermal exposure to 50 μl of CR for 3 days induced irritation and significant increases in lymphocyte proliferation at concentrations of 10% and greater, while exposure to oil induced significant elevations in lymphocyte proliferation at concentrations of ≥50%. No alterations in serum IgE were observed after exposure to either test article. Exposure to crude oil was also found to be immunosuppressive. The spleen IgM response to sheep red blood cells was significantly inhibited when mice were exposed to 50 μl at concentrations of ≥25% crude oil for 14‐days. Increased liver and decreased spleen weights were also documented. Mixtures of crude oil and CR did not enhance either effect. Consistent with these results, CR did not enhance in vitro epidermal penetration of naphthalene. These studies suggest potential immunological effects from dermal exposure to crude oil and CR.

Amorphization of Co-base alloy by mechanical alloying

Structural transformations and the amorphization of cobalt base alloy particles are possible when a powder mixture of Co and Cr–Mo is subjected to the mechanical alloying (MA) process. Elemental powders mixed in adequate weight ratios were used as precursors. The process was carried out at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media, with a ball:powder weight ratio of 8:1. The characterization of the crystalline structure of milled powders was carried out by means of X-ray diffraction to analyze the phase transformations as a function of milling time. The aim of this work was to demonstrate that MA can induce the amorphization of Co–Cr–Mo alloy. The evolution of the phase transformation during milling time is reported. The results showed that it is possible to produce a partial solid solution at room temperature of elemental metallic powders Co 70Cr 30 and Co 90Mo 10 by mechanical alloying. Using specific experimental conditions, it is also possible to obtain an amorphous phase in a composition Co 60Cr 30Mo 10; first, Cr and Mo were mechanically prealloyed for 9 h to obtain a Cr 80Mo 20 solid solution, and Co was then added and milled in over 14 h.

Mechanical properties and microstructure of Al2O3/TiAl in situ composites doped with Cr

Cr-doped Al2O3/TiAl in situ composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al, TiO2 and Cr. The effect of the Cr addition on the microstructures and mechanical properties of the Al2O3/TiAl composites were investigated. The as-synthesized composites consisted of γ-TiAl, α2-Ti3Al, Al2O3, and a small amount of Laves phase Ti(Al,Cr)2. Microstructure analysis indicates that Al2O3 particles mainly distributed on grain boundaries of the TiAl matrix. As the Cr content increases, the Al2O3 particles are dispersed more fine and homogeneously in the TiAl matrix, which resultes in the increase of the hardness, flexural strength and fracture toughness of the composites gradually. When the Cr content was 3 wt.%, the flexural strength and fracture toughness of the Al2O3/TiAl composite reaches the top values of 820 MPa and 8.3 MPa·m1/2, respectively. The reinforcement mechanism of Cr addition to Al2O3/TiAl composites was also discussed.

Biosorption and growth inhibition of wetland plants in water contaminated with a mixture of arsenic and heavy metals

AbstractThe potential of wetland plants as an onsite biosorbent and a biomonitor for combined pollution of arsenic and four heavy metals from non‐point sources was investigated in this study. Ceratophyllum demersum, Hydrilla verticillata, Hydrocharis dubia, and Salvinia natans were exposed to a water containing mixture of As, Cr, Cu, Pb, and Zn. Growth inhibition and biosorption potential of the wetland plants in artificially contaminated conditions were studied. These contaminants significantly reduced the growth of the plants. The tested wetland plants accumulated appreciable amounts of the contaminants in the following order: Pb>Cr>Cu>Zn>As. H. verticillata showed distinct visual change and a high biosorption factor (BSF) rank for As and heavy metals among the plants used in the study. As an unspecific collector of contaminants, it might be useful as a biomonitor and biosorbent in the As and heavy metal‐contaminated aquatic system.

Influence of heat treatment on the structure and thermoelectric properties of CrSi2

Textured CrSi2 crystals obtained by heating finely dispersed constituents (Si, Cr) are studied. The use of a mixture of Cr and Si powders makes it possible to lower the CrSi2 synthesis temperature by 100 K. Crystallization conditions and post-crystallization annealing are found to influence the thermoelectric properties and composition of samples.

Role of 5-thio-(2-nitrobenzoic acid)-capped gold nanoparticles in the sensing of chromium(vi): remover and sensor

This study describes a simple, rapid method for sensing Cr(vi) using 5-thio-(2-nitrobenzoic acid) modified gold nanoparticles (TNBA-AuNPs) as a remover for Cr(iii) and as a sensor for Cr(vi). We discovered that TNBA-AuNPs were dispersed in the presence of Cr(vi), whereas Cr(iii) induced the aggregation of TNBA-AuNPs. Due to this phenomenon, TNBA-AuNPs can be used as a sorbent material for the removal of >90% Cr(iii), without removing Cr(vi). After centrifuging a solution containing Cr(iii), Cr(vi), and TNBA-AuNPs, Cr(iii) and Cr(vi) were separately present in the precipitate and supernatant. In other words, TNBA-AuNPs are capable of separating a mixture of Cr(iii) and Cr(vi). The addition of ascorbic acid to the supernatant resulted in a reduction of Cr(vi) to Cr(iii), driving the aggregation of TNBA-AuNPs. The selectivity of this approach is more than 1000-fold for Cr(vi) over other metal ions. The minimum detectable concentration of Cr(vi) was 1 μM using this approach. Inductively coupled plasma mass spectrometry provided an alternative for the quantification of Cr(iii) and Cr(vi) after a mixture of Cr(iii) and Cr(vi) had been separated by TNBA-AuNPs. The applicability of this approach was validated through the analysis of Cr(vi) in environmental water samples.

THE STRUCTURE AND MAGNETIC PROPERTIES OF ZnCr2-xFexO4

ZnCr 1-x Fe x O 4 system (with x = 0, 0.5, 1, 1.5, and 2) at the nanoscale has been successfully synthesized by a simple combination of milling mixture of Zn , Cr , and Fe oxides precursors. X-ray diffraction and magnetic measurements were carried out on the as-milled powders. XRD pattern clearly shows that the mixed oxides are all nanosized. However, as Fe 2 O 3 increases the ZnCrFeO 4 phase becomes the main phase. However, magnetic measurements do not show any significance in saturation magnetization (Ms), only when the content of Fe becomes 50% and 0.75% the Ms increased drastically to 15.4 and 16.7 emu/g respectively. However, with Fe 75% He and Mr reduced abruptly to half of their values, showing a ferromagnetic behaviour with low He .

Synthesis and Crystal Structure of AgTl3(Cr2O7)2

Red single crystals of AgTl3(Cr2O7)2 were prepared via high oxygen pressure synthesis as well as by hydrothermal autoclave techniques. Initially, AgTl3(Cr2O7)2 was obtained from a reaction of stoichiometric mixtures of Ag2O, Cr and TlNO3 under elevated oxygen pressures. Following an optimized approach, the title compound can be synthesized at mild hydrothermal conditions, starting from AgNO3, TlNO3 and K2Cr2O7 in aqueous solution. AgTl3(Cr2O7)2 crystallizes in space group C2/c (no. 15) with a = 10.3638(3), b = 10.4817(3), c = 13.4717(4) Å , β = 106.55(1)°, V = 1402.80(5) Å3, and Z = 4. The structure refinement was based on 3554 independent reflections and resulted in R1 = 2.13 %, wR2 = 4.54 %. The crystal structure contains independent Cr2O7 2− anions, which are surrounded by silver and thallium cations forming layers that are stacked perpendicular to the bc plane.

Metal ion removal properties of crosslinked poly(acrylamide‐co‐2‐acrylamide‐2‐methyl‐1‐propane sulfonic acid)

AbstractPoly(acrylamide‐co‐2‐acrylamide‐2‐methyl‐1‐propane sulfonic acid) P(AAm‐co‐APSA) copolymers have been prepared to be used in the extraction of Pb(II), Hg(II), Cd(II), Zn(II), Al(III), and Cr(III) metal ions from aqueous solution by a batch and column equilibration procedures. The adsorption capacity was increased with pH for all metal ions studied. The contact time and the temperature did not affect the retention significantly. The resin did not show a preference in a mixture of Pb(II), Cd(II), Zn(II), and Cr(III). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Anelastic Behavior of Nanocrystalline Fe-Cr Alloy Obtained by Mechanical Alloying

Anelastic behavior of nanocrystalline Fe-17 wt.%Cr alloy obtained by mechanical alloying was investigated using a multifunctional internal friction apparatus. Internal friction (Q-1) and relative dynamic modulus (f2) have been measured as a function of temperature by free-decay method from room temperature to 400oC for the ball-milled Fe-17 wt.%Cr alloy The specimens with different milling time were examined by XRD to determine the solid solubility of Fe and Cr atoms and detect the lattice strain of the compacted specimen before and after annealing. TEM observation was employed to obtain further information about the morphology and microstructure, especially crystalline size, of the milled Fe and Cr mixture powders. It has been suggested that the anelastic behavior of ball-milled nanocrystalline Fe-17 wt.%Cr alloy origins from the viscoelastic sliding at the interfaces resulting from the thermally-activating process. The damping increasing of the specimen with smaller grain sizes is larger than that of the specimen with larger grain sizes with increasing temperature since the former contains more interfaces. The increase in the relative dynamic modulus is attributed to the structural reordering with the lowering of lattice micro-strain that is produced during milling when temperature is over 300oC.

NAA for studying detoxification of Cr and Hg by Arthrobacter globiformis 151B

Instrumental neutron activation analysis was used to study accumulation of Hg(II) and Cr(VI) ions in Arthrobacter globiformis 151B, a gram-positive, Cr(VI)-reducer aerobic bacterium isolated from basalt sample taken from the most polluted region in the Republic of Georgia (Kazreti). Experiments were focused on (1) accumulation of Hg(II) in bacterial cells; (2) accumulation of Cr(VI) in A. globiformis 151B in the presence of Hg(II) and (3) effects of Hg(II) and mixture of Cr(VI)–Hg(II) on the elemental composition of bacteria. It was shown that this bacterial strain possesses uptake mechanisms by which mercury toxicity can be reduced in environment and that accumulation of Cr(VI) in A. globiformis 151B is much higher in the presence of Hg(II) ions. Accumulation of Hg(II), similar to the Cr(VI) accumulation, follows well the Lengmuir–Freundlich model. NAA measurements showed increased content of Fe in bacteria under Hg and Cr action, suggesting that Fe-containing biomolecules play a decisive role in detoxifying of heavy metals by A. globiformis 151B. A concentration of 5000 μg/L of Hg(II) was found to be critical for A. globiformis 151B. At this concentration of Hg(II) the concentrations of both essential (Na, Mg, Al, Cl, K, Mn, Zn) and some non-essential elements (Rb, Sb, Sc, As) changed drastically along with a decrease of the biomass of bacteria by a factor of two. One may assume that under this high exposure to Hg(II) the structure of the bacterial cell wall was destroyed.

Combined effects of water quality parameters on mixture toxicity of copper and chromium toward Daphnia magna

In this study, a central composite design (CCD) was employed to evaluate the combined effects of pH, hardness and dissolved organic carbon (DOC) on the toxicity of a mixture of Cu(II) and Cr(VI) toward Daphnia magna. Overall, the results showed that increases in pH, hardness and DOC concentration led to decreased mixture toxicity of Cu(II) and Cr(VI) by reducing the concentrations of toxic species such as Cu 2+ and HCrO 4 - . In addition, empirical models for the prediction of 24-h and 48-h mortalities of D. magna were developed and validated by using three different sources of dissolved organic matter (DOM). Because the DOMs had different Cu(II)-binding capacities, the empirical models were revised using the ligand concentration of DOMs instead of the DOC concentration; however, the prediction capability of these models did not differ significantly. These results suggest that it is not likely that the chemical property of DOM is important for prediction of the mixture toxicity of Cu(II) and Cr(VI) toward D. magna when the ligand concentration of DOMs greatly exceed the Cu(II) concentration.

Mechanical properties of low temperature synthesized dense and fine-grained Cr 2AlC ceramics

Mechanically activated hot-pressing technology was used to synthesize a fine-crystalline Cr 2AlC ceramic at relatively low temperatures. A mixture of Cr, Al and C powders with a molar ratio of 2:1.2:1 was mechanically alloyed for 3 h, and then subjected to hot pressing at 30 MPa and different temperatures for 1 h in Ar atmosphere. The results show that a dense Cr 2AlC ceramic with a grain size of about 2 μm can be synthesized at a relatively low temperature of 1100 °C. The synthesized fine-grained Cr 2AlC has a high density of 99%, which is higher than the 95% density for the coarse-grained Cr 2AlC (grain size of about 35 μm) as synthesized by hot pressing unmilled Cr, Al and C. The flexural strength, fracture toughness and Vickers hardness of the fine-grained Cr 2AlC were determined and compared with the values for the coarse-grained Cr 2AlC.

Microstructure and mechanical properties of a Cr 2Al(Si)C solid solution

A new Cr 2Al(Si)C solid solution has been synthesized by hot pressing a mixture of Cr, Al, Si and C powders with a molar ratio of 2:1.1:0.2:1 at 1450 °C with 30 MPa for 1 h in Ar atmosphere. The phase composition and microstructure was investigated with X-ray diffraction analysis and scanning electron microscopy. The Cr 2Al(Si)C solid solution exhibits a layered structure. The flexural strength, fracture toughness and Vickers hardness of the Cr 2Al(Si)C solid solution was determined and compared with the values for synthesized Cr 2AlC. Buckling and kinking of the layered structure as well as grain delamination crack deflection were extensively observed around indentations and on the fracture surfaces. These multiple energy-absorbing mechanisms endow the sold solution with damage tolerance and micro-scale plasticity at room temperature.

Reactions of “in‐Situ” Generated Cr(CO)5CN–C(Cl)–PR3 (R = Ph, NMe2) with Potential Dipolarophiles. New Examples of [3+2] Cycloadditions with Concomitant Interligand CC Bond Formation [1

AbstractThe highly functional chromio nitrile ylides Cr(CO)5C≡N–C(Cl)–PR3 (R = Ph, NMe2) (2a, b) form readily in mixtures of Cr(CO)5CNCCl3 (1) with the respective phosphanes. Their reactions without isolation with the acylating agent Cr(CO)5CN(C=O)Ar (Ar = C6H4‐p‐NO2), MeO2CC≡CCO2Me, ketones (R2C=O, R = Me, Et; 2R = 9‐fluorenediyl) and phenyl isocyanate to give the Cl/COAr‐substitution‐ (6a), alkyne insertion‐ (10) and [3+2] cycloaddition products (13, 14) are described. Formation of the latter is accompanied by an interligand CC coupling with loss of P(NMe2)3 and OP(NMe2)3 (after hydrolysis). Their reactions are compared with those of the parent compounds LnMCN–C(H)–PPh3.

Metal/semiconductor hybrids consisting of self-assembled CdS nanoparticles on Cd nanowires

We report on the synthesis and the characterisation of metal/semiconductor hybrids consisting of self-assembled CdS nanoparticles on Cd nanowires, which are grown by thermal evaporation of the mixture of CdS and Cr. The growth of the hybrids is attributed to the decomposition of CdS at high temperature and the strain relieving that arises mainly from the lattice mismatch between Cd and CdS. Temperature dependence of zero-field resistance of single nanohybrid indicates that the as-produced Cd/CdS nanohybrid undergoes a metal-semiconductor transition as a natural consequence of hybrid from metallic Cd and semiconducting CdS. The metal/semiconductor hybrid property provides a promising basis for the development of novel nanoelectronic devices.

Differential effect of metals/metalloids on the growth and element uptake of mesquite plants obtained from plants grown at a copper mine tailing and commercial seeds

The selection of appropriate seeds is essential for the success of phytoremediation/restoration projects. In this research, the growth and elements uptake by the offspring of mesquite plants ( Prosopis sp.) grown in a copper mine tailing (site seeds, SS) and plants derived from vendor seeds (VS) was investigated. Plants were grown in a modified Hoagland solution containing a mixture of Cu, Mo, Zn, As(III) and Cr(VI) at 0, 1, 5 and 10 mg L −1 each. After one week, plants were harvested and the concentration of elements was determined by using ICP-OES. At 1 mg L −1, plants originated from SS grew faster and longer than control plants (0 mg L −1); whereas plants grown from VS had opposite response. At 5 mg L −1, 50% of the plants grown from VS did not survive, while plants grown from SS had no toxicity effects on growth. Finally, plants grown from VS did not survive at 10 mg L −1 treatment, whilst 50% of the plants grown from SS survived. The ICP-OES data demonstrated that at 1 mg L −1 the concentration of all elements in SS plants was significantly higher compared to control plants and VS plants. While at 5 mg L −1, the shoots of SS plants had significantly more Cu, Mo, As, and Cr. The results suggest that SS could be a better source of plants intended to be used for phytoremediation of soil impacted with Cu, Mo, Zn, As and Cr.

Chromium nitride films on stainless steel as bipolar plate for proton exchange membrane fuel cell

Abstract A series of chromium nitride films are prepared on stainless steel substrates by pulsed bias arc ion plating (PBAIP) at different N 2 flow rate as bipolar plates for proton exchange membrane fuel cell (PEMFC). The film chemical composition and phase structure are characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). The characterization results indicate that the nitrogen content of deposited films varies from 0.28 to 0.50, and the phase structure changes from mixtures of Cr + Cr 2 N, pure Cr 2 N through Cr 2 N + CrN, to pure CrN. The interfacial contact resistance between samples and carbon paper is measured by Wang's method, and a minimum value of 5.8 mΩ cm 2 is obtained under 1.2 MPa compaction force. The anticorrosion property is examined by potentiodynamic test in the simulated corrosive circumstance of the PEMFC under 25 °C, and the lowest corrosive current density of 5.9 × 10 −7 A cm −2 is obtained at 0.6 V (vs. SCE). Stainless steel substrates coated by the film with lowest contact resistance are chosen as the bipolar plates to assemble cells. An average voltage value of 0.62 V is achieved at 500 mA cm −2 , which is close to that of the cell with Ag-plated bipolar plates.