Cobalt Peak Research Articles

Physical, mechanical and magnetic properties of cobalt-chromium alloys prepared by conventional processing

In this work, the cobalt-chromium alloys (Co-xCr) with various compositions, x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 wt.%, were prepared by conventional powder metallurgical processing cooperated with cold isostatic press technique (CIP) followed by traditional sintering in argon media. The effects of chemical compositions on phase formation, microstructure and properties of cobalt-chromium alloys were studied. Phase evolution, densification, microstructure, mechanical and magnetic properties of this system were investigated. X-ray diffraction patterns show the existence of cobalt peak along with chromium peak and the intensity of Cr peaks increase with increasing of x. SEM micrographs reveal high dense of very large irregular-shaped-grains and the average grain size of this alloy decreases with increase of x. Physical, mechanical and magnetic properties strongly depend on chemical composition.

Lithium-Cobalt Glass for Sapphire

Sapphire was improved by filling lithium-cobalt glass. Cobalt concentration in lithium glass is 0.1-2 wt%. The sapphires with glass were heated by an electric furnace at 1100 °C for 1-5 hours. Physical properties of the stone before and after treatment were investigated by measuring refractive index and specific gravity. Stones were investigated the inclusion and fissure by a gem microscope. Reflectance spectrum was analyzed by UV-visible spectrophotometer and color changes were referenced by CIEL*a*b* system. Fluorescence was examined with a UV Lamp. Experimental results of heated sapphire treatment with lithium-cobalt glass found that the refractive index (RI) decreased from 1.76 - 1.77 to 1.53 - 1.55 and the specific gravity (SG) decreased from 3.95 - 4.00 to 3.37 – 3.40. Cause of these results is that the refractive index and specific gravity of lithium-cobalt glass are lower than of sapphires. The cobalt in glass filled in fissure of sapphires is cause of blue color appeared in crack. The orange-red fluorescence appeared in both short wave and long wave of UV. For analysis of trace elements by the UV-visible spectrophotometer range 300-800 nm, cobalt peak appeared at wavelength 530 nm while iron peak and another peak of improved sapphire in all conditions were found at wavelength 488 nm and 750 nm, respectively. The height of peak at 750 nm depended on the amount of cobalt. The color of improved sapphire was closed to blue color when compared with sapphire before improvement.

Experimental investigation and simulation of the effect of Ti and N contents on the formation of fcc-free surface layers in WC–Ti(C,N)–Co cemented carbides

The effect of Ti and N contents on the formation of fcc-free surface layers in WC–Ti(C,N)–Co cemented carbides is systematically studied by experimental investigations and DICTRA simulations. The cemented carbides with different Ti and N contents have been sintered in a nitrogen free atmosphere. The microstructure, concentration distributions and concentration profiles have been analyzed via SEM, EPMA and EDX, respectively. The thermodynamic database for multi-component cemented carbides has been developed through a combination of experimental, theoretical and assessment work. Ti and N activity profiles between the surface and bulk are thermodynamically calculated to show the influence to the gradient zone. The modified Sutherland equation is employed to construct the diffusion database. Based on the databases, the gradient zone formation of the cemented carbides is simulated by DICTRA software. The simulation results are compared with the experimental results to demonstrate the application of the established databases. Besides, the growth rate of the fcc-free surface layers and the maximum value of cobalt peak in cemented carbides as a function of nitrogen or titanium content are predicted.

Analysis of molecular monolayers adsorbed on metal surfaces by glow discharge optical emission spectrometry

The pioneering study of Shimizu et al. (J. Anal. At. Spectrom., 2004, 19, 692) on the examination of adsorbed organic molecules on a copper substrate by radio frequency glow discharge optical emission spectrometry (rf-GDOES) displayed the potential of GDOES for determination of the orientations of molecular monolayers. Here, the study has been extended to the examination of thiourea adsorbed on silver, gold and copper surfaces and metal-centred molecular wires (MCMWs) of 4–6 nm length, with cobalt atoms in the middle of the chain adsorbed on a gold surface. According to established data, these molecules are adsorbed onto a metal surface through a sulphur atom. Depth profiling of thiourea adsorbed on the copper surface confirmed the results of Shimizu et al., with a nitrogen peak followed by a sulphur peak in the depth profile revealed with sputtering time. However, in the case of silver and gold substrates, the positions of the sulphur and nitrogen peaks in the depth profiles were not as predicted from the orientation of the thiourea molecule, i.e. the nitrogen peak followed the sulphur peak with sputtering time or the peaks overlapped. In the depth profiles of the adsorbed MCMWs, the sulphur peak appeared prior to the cobalt peak with sputtering time. Further, the time required for sputtering of thiourea and the wires are comparable, whereas the lengths of thiourea and the wire molecules differ by more than one order of magnitude. Thus, in this case, no correlation between the orientation of the molecules and the peak sequence in the depth profiles has been observed.

Determination of Trace of Cobalt in Complex Matrices by Adsorptive Stripping Voltammetry at a Lead Film Electrode

AbstractAn adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10−10 to 2×10−8 mol L−1 and from 1×10−10 to 1×10−9 mol L−1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10−11 mol L−1. The interference of high concentrations of foreign ions and surfactants was studied.

Determination of Traces of Cobalt in Zinc Matrix by Catalytic Adsorptive Stripping Voltammetry at Bismuth Film Electrode

AbstractAn catalytic adsorptive stripping voltammetric procedure for the determination of cobalt in a zinc matrix at an in situ plated bismuth film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–dimethylglyoxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. Using optimized conditions, in a solution containing 0.01 mol L−1 Zn(II) the calibration plot for Co(II) following accumulation time of 120 s was linear from 2×10−10 to 5×10−8 mol L−1. The detection limit (based on 3σ criterion) for Co(II) of 6×10−11 mol L−1 was achieved. The proposed procedure was applied for Co(II) determination in zinc reagent for analysis and in tap water.

Determination of subnanomolar concentrations of cobalt by adsorptive stripping voltammetry at a bismuth film electrode

Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)-dimethylglyoxime-cetyltrimethylammonium bromide-piperazine-N,N'-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 x 10(-10) to 2 x 10(-8) mol L(-1). The relative standard deviation from five determinations of cobalt at a concentration of 5 x 10(-9) mol L(-1) was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 x 10(-11) mol L(-1). The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples.

Determination of traces of cobalt in the presence of nioxime and cetyltrimethylammonium bromide by adsorptive stripping voltammetry

A sensitive method of Co(II) determination by adsorptive stripping voltammetry is presented. The method exploits the enhancement of cobalt peak current observed in the system Co(II)-nioxime-cetyltrimethylammonium bromide-piperazine- N, N′-bis(2-ethanesulfonic acid). The calibration plot for an accumulation time of 60 s is linear from 5 × 10 −11 to 3 × 10 −9 mol L −1. The relative standard deviation is 3.8% for Co(II) determination at concentration 1 × 10 −9 mol L −1. The detection limit is 1.7 × 10 −11 mol L −1. The validation of the method is performed by the analyses of certified reference materials and comparing the result of Co(II) determination in river water sample by the proposed method with those obtained by ET AAS. The main advantage of this new system is the micro-trace Co(II) determination by adsorptive stripping voltammetry, as compared to those described before, a low concentration of the supporting electrolyte used, and so commercially available reagents without additional purification can be used.

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide.

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)-dimethylglyoxime-piperazine-1,4-bis(2-ethanesulfonic acid)-cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 sigma criterion) for Co(II) of 1.2 x 10(-11) mol L(-1) (0.7 ng L(-1)) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5 x 10(-11) to 4 x 10(-9) mol L(-1). The procedure was validated by analysis of certified reference materials and natural water samples.

Chemical modifiers for direct determination of cobalt in coal combustion residues by ultrasonic slurry-sampling-ETAAS.

Five modifiers were tested for the direct determination of cobalt in coal fly ash and slag by ultrasonic slurry-sampling electrothermal atomic absorption spectrometry (USS-ETAAS). The furnace temperature programs and the appropriate amount for each modifier were optimized to get the highest signal and the best separation between the atomic and background signals. Nitric acid (0.5% v/v) was the most adequate chemical modifier for cobalt determination, selecting 1,450 degrees C and 2,100 degrees C as pyrolysis and atomization temperatures, respectively. This modifier also acts as liquid medium for the slurry simplifying the procedure. The remaining modifiers enhanced the background signal, totally overlapped with cobalt peak. The method optimized gave a limit of detection of 0.36 microg g(-1), a characteristic mass of 13 +/- 1 pg and an overall-method precision which is highly satisfactory (<7%, RSD). The method was validated by analyzing two certified coal fly ash materials, and satisfactory recoveries were obtained (83-90%) and no statistical differences were observed between the experimental and the certified cobalt concentrations. Additionally, certified sediment, soil and urban particulate matter were assayed; again good results were obtained. The developed methodology was used to determine cobalt in several coal combustion residues from five Spanish power plants.

Cathodic stripping voltammetric determination of 2-mercaptobenzothiazole using the catalytic cobalt peak

Previously, thiols have been determined indirectly by cathodic stripping voltammetry (CSV) after accumulation as their mercury and copper(I) salts. Following a previous report of the first use of the catalytic nickel peak (for the determination of cysteine), this paper reports the first use of the catalytic cobalt peak in CSV (for the determination of 2-mercaptobenzothiazole (MBT)): only a very ill-defined catalytic cobalt peak had been observed previously with cysteine, and was unreported. MBT is accumulated at pH 4 (Britton-Robinson buffer) as its cobalt(II) complex at −0.1 V, and is then determined indirectly by observing the reduction of the cobalt(II) in the complex at −0.95 V, i.e., with a much lowered overpotential: hydrated cobalt(II) is reduced at −1.2 V. The peak is catalytic because the thiol released on reduction of the complex complexes further cobalt ions and causes their reduction. The detection limit for the determination of MBT was calculated to be 2.5 × 10 −9 M (3σ) using an accumulation time of 1 min. The sensitivity is about three times that obtained with the corresponding catalytic nickel peak.

High‐Performance adsorptive cathodic stripping voltammetry of nickel and cobalt in seawater

AbstractThe voltammetric determination of trace metals in seawater suffers from the interference of dissolved oxygen and engine vibrations onboard ship. It is here attempted to overcome these interferences using a high‐frequency (1 to 20 kHz) staircase modulation during the voltammetric scan (high‐performance adsorptive cathodic stripping voltammetry, HPACSV). Comparative experiments using the square‐wave modulation showed that this modulation was not effective at such a high frequency. A comparison between various complexing agents (DMG and nioxime) and pH buffers (HEPES/NH4OH, borate/NaOH, and TEA/NH4OH) showed that the determination of nickel and cobalt was similarly improved by the high‐speed potential scan in all conditions. Fast potential scans cause a large increase of the peak area and peak heights using staircase modulation. The peaks are wider, and the peak potentials are shifted toward negative values due to the ohmic drop, but the analytical determination is not disturbed. Optimal sensitivity for the determination of cobalt and nickel in seawater was obtained using TEA buffer and DMG as the adsorptive ligand. The nioxime wave was found to interfere in the cobalt peak at high scan rates so that this ligand is not recommended for HPACSV. Comparative tests showed that the sensitivity for nickel and cobalt determinations was highly improved by the fast scan rates. Furthermore, the reduction current of dissolved oxygen was partially masked so that measurements could be taken without a previous purge of the sample. Finally, the scans were insensitive to the solution turbulence so measurements could be readily carried out onboard of an oceanographic vessel or without switching off the stirrer. Low levels of nickel (2 nM) could be determined in seawater by using a deposition time of 20 seconds and of 120 seconds for 0.05 nM cobalt from turbulent and unpurged solutions. A fast determination method for labile nickel and cobalt is proposed.

Ultrastructural localization and X-ray analysis of calcium-induced electron-dense deposits in the skate retina

The technique of Oschman & Wall (1972) was used to visualize the sites at which electron-dense deposits accumulate in neural layers of the skate retina. The method, which involves the addition of calcium to the primary fixative, resulted in the formation of electron-dense deposits along the plasma membranes of horizontal cells, within the outer segments, mitochondria and synaptic vesicles of the visual cells, and at pre- and postsynaptic membranes of the synaptic elements of the outer plexiform layer. Energy dispersive X-ray spectrometry of the electron-dense deposits yielded prominent peaks for calcium and phosphorus. In the dark-adapted retina, the electron-dense deposits were seen more frequently in association with the receptor terminal than with the processes of second-order neurons; after light adaptation, the reverse situation was observed. A light-induced translocation of electron-dense deposits was not found at any other retinal location. The addition of cobalt to the fixative in lieu of calcium produced results equivalent to those obtained with calcium; i.e. electron-dense deposits were formed at simular loci within the retina. The emergence in the X-ray spectrum of a small calcium signal in the presence of a large cobalt peak suggests that the two ions compete for similar membrane sites. On the other hand, the formation of electron-dense deposits was suppressed completely by exposing the retinas to Ca 2+-free solutions, with or without the addition of Mg 2+. These findings are consistent with physiological observations that suggest that Mg 2+ and Co 2+ act at different sites in modifying the actions of Ca 2+ at synapses.

An x-ray photoelectron spectroscopy study of the activated cobalt-molybdenum-alumina hydrodesulfurization catalysts

Abstract ESCA was used to monitor the chemical modification of a series of commercial cobalt-molybdenum-alumina hydrodesulfurization catalysts subjected to different reaction conditions. In the oxide form, the surface phase resembles MoO 3 and CoAl 2 O 4 . Reduction and sulfiding using a 15:85 H 2 S/H 2 mixture shifts the molybdenum peaks to the region of MoS 2 . Part of the cobalt is apparently reduced and sulfided, but this species is susceptible to re-oxidation by moist air. The supported cobalt which is not changed by this treatment is interpreted as actually being CoAl 2 O 4 formed by interaction of the dispersed material with the support during calcination. The presence of this aluminate phase seems to be important for the stability of the catalyst under the harsh conditions of industrial usage. Reduction of the oxide form by pure hydrogen leaves the molybdenum binding energy unchanged and shifts the cobalt peak to higher binding energy. This is interpreted as arising from a shift in reference level and it is concluded that the actual transformation