Mercury(II) selective membrane electrode based on 1,3-bis(2-methoxybenzene)triazene

A plasticized poly (vinyl chloride) membrane electrode based on 1,3-bis(2-methoxybenzene)triazene (MBT) for highly selective determination of mercury(II) has been developed. The electrode showed a good Nernstian response (30.2 ± 0.3 mV decade^− 1) over a wide concentration range (1.0 × 10^− 7−1.0 × 10^− 2 mol L^− 1). The limit of detection was 5.0 × 10^− 8 mol L^− 1. The electrode has a response time about 15 s and can be used for at least 1 month without observing any deviation from Nernstain response. The proposed electrode revealed an excellent selectivity toward mercury(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions and could be used in the pH range 2.6–4.2. The electrode was used in the determination of Hg²⁺ in aqueous samples and as an indicator electrode in potentiometric titration of Hg(II) ions.     

Electrochemical determination of cadmium(II) at platinum electrode modified with kaolin by square wave voltammetry

In this work, determination of cadmium(II) using square wave voltammetry (SWV) was described. The method is based on accumulation of these metal ions on kaolin platinum electrode (K/Pt). The K/Pt performance was optimized with respect to the surface modification and operating conditions. The optimized conditions were obtained in pH of 5.0 and accumulation time of 25 min. Under the optimal conditions, the relationship between the peak current versus concentration was linear over the range of 9 × 10⁻⁸ to 8.3 × 10⁻⁶ mol L⁻¹. The detection limit (DL, 3σ) was 5.4 × 10⁻⁹ mol L⁻¹. The analytical methodology was successfully applied to monitor the Cd(II) content in natural water. Interferences were also evaluated.     

Electrochemical behaviour of Cu24Zn5Al alloy in alkaline medium in the presence of chloride ions and benzotriazole

This paper deals with electrochemical behaviour of Cu24Zn5Al alloy in a sodium tetraborate solution (borax), in the presence of chloride ions and benzotriazole. It was found that during anodic polarization of the investigated alloy, in a sodium tetraborate solution, at lower potentials, copper (I)-oxide formed on the alloy surface. The voltammograms show peak potential shifts corresponding to the formation of Cu₂O towards more positive values with longer immersion time. It was found that chloride ions had an activating effect in a sodium tetraborate solution containing various concentrations of chloride ions (0.001, 0.005, 0.010, 0.050 and 0.100 mol dm⁻³ Cl⁻). It was observed that Cu24Zn5Al alloy corroded more intensely in more concentrated solutions and with longer exposure to Cl⁻. Investigations of the effect of inhibitor concentrations (8.4 × 10⁻⁶, 8.4 × 10⁻⁵, 8.4 × 10⁻⁴ and 8.4 × 10⁻³ mol dm⁻³ BTA in 0.1 mol dm⁻³ borax solution) showed that BTA had a good protective effect. The inhibiting effect of BTA was also confirmed with various times of immersion of this alloy in a 1.7 × 10⁻² mol dm⁻³ solution of this inhibitor.     

Europium (III) PVC membrane sensor based on N-pyridine-2-carboxamido-8-aminoquinoline as a sensing material

Conductometric study in acetonitrile solution shows the selectivity of PCQ toward europium ion. Therefore, a new europium PVC membrane electrode was prepared based on N-pyridine-2-carboxamido-8-aminoquinoline (PCQ) as an ion carrier. The electrode has a wide concentration range from 1.0 × 10^− 2 and 1.0 × 10^− 6 mol L^− 1, Nernstian slope of 19.8 ± 0.3 mV per decade and a detection limit of 6.4 × 10^− 7 mol L^− 1. The potentiometric response is pH independent in the range of 2.4-7.4. The proposed sensor has a relatively fast response time less than 10 s and it can be used for at least 2 months without any considerable divergence in its potentials. The proposed electrode revealed good selectivity toward europium ion in comparison with variety of other metal ions. The practical utility of the electrodes has been demonstrated by their use as indicator electrodes in the potentiometric titration of Eu^3 + ions with EDTA and for determination of Eu^3 + ion concentration in mixtures of two and three different ions.     

Superplastic behavior of a fine-grained ZK60 magnesium alloy processed by high-ratio differential speed rolling

Grain size of the ZK60 alloy was effectively reduced to 12 μm through high-ratio differential speed rolling (HRDSR) for a thickness reduction of 70% in a single pass. Due to the strengthening effects of grain boundaries and particles, the HRDSR processed ZK60 exhibited a high tensile strength of 340 MPa. Low temperature superplasticity was attained at 473–493 K at low strain rates (5 × 10⁻⁴ s⁻¹) and high strain rate superplasticity was attained at 523–553 K at high strain rates (10⁻² s⁻¹). The optimum superplastic temperature was found to be 553 K where a maximum tensile elongation of 1000% was obtained at 1 × 10⁻³ s⁻¹. The deformation behavior of the HRDSR processed ZK60 at elevated temperatures could be depicted by considering contribution of grain boundary sliding and slip creep to total plastic flow. Difference in superplastic deformation behavior between the HRDSR processed and equal channel angular press processed ZK60 alloys was examined and discussed.     

Compressive and wear behaviors of bulk nanostructured Al2024 alloy

Compressive and wear properties of bulk nanostructured Al2024 alloy prepared by mechanical milling and hot pressing methods were investigated. Al2024 powders were subjected to high-energy milling for 30 h to produce nanostructured alloy. As-milled powders were compacted at 500 °C under 250 MPa in a uniaxial die. Consolidated sample had an average hardness and relative density values of 207.6 HV and 98%, respectively. Uniaxial compression tests at strain rates in the range of 1.67 × 10⁻⁴–1.67 × 10⁻² s⁻¹ were performed using an Instron-type machine. The wear behavior of nanostructured sample was investigated using a pin-on-disk technique under an applied load of 20 N. The compression and wear experiments were also executed on samples of commercial coarse-grained Al2024-O (annealed) and Al2024-T6 (artificially-aged) alloys, for comparison. The structure of consolidated Al2024 was characterized by X-ray diffraction (XRD). The yield strength and compressive strength of nanostructured Al2024 reached a value of 698 MPa and 712 MPa at strain rate of 1.67 × 10⁻⁴ s⁻¹, respectively, which was considerably higher than those for coarse-grained Al2024-O and Al2024-T6 counterparts. Worn surfaces and the wear debris were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and XRD. Nanostructured Al2024 revealed a low friction coefficient of 0.3 and a wear rate of 12 × 10⁻³ mg/m, which are significantly lower than those obtained for Al2024-O and Al2024-T6 alloys. This enhanced wear resistance was mainly caused by nanocrystalline structure with high hardness value. The dominating wear mechanism of nanostructured Al2024 appeared to be delamination mechanism.     

Optimization and kinetics of electroless Ni–P–B plating of quartz optical fiber

The preparation of Ni–P–B coatings on surface of quartz optical fibers was carried out using electroless plating method. The effects of the concentrations of nickel chloride, sodium hypophosphite, potassium borohydride, ethylenediamine, cadmium sulfate and temperature on the quality of Ni–P–B coatings were investigated by orthogonal experiment and their optimal values were determined to be: 0.1 mol L⁻¹, 0.094 mol L⁻¹, 0.185 mol L⁻¹, 0.36 mol L⁻¹, 5.68 × 10⁻⁴ mol L⁻¹ and 90 °C, respectively. The effect of coarsening time of the naked fiber on the quality of Ni–P–B coatings was also researched and the optimal coarsening time was determined to be 15 min. Stereomicroscope, Scanning Electron Microscope and X-ray diffractometer were used to characterize the apparentness, morphology and structure of the prepared Ni–P–B coatings. Inductively Coupled Plasma-Atomic Emission Spectroscopy, Thermal Shock Method and Gravimetric Analysis Method were employed to analyze the composition, force of adhesion and solderability of the coatings, respectively. The results showed that a Ni–P–B coating with low surface roughness, good strength of adhesion, low resistivity and good solderability was successfully prepared. The kinetic models (Ni–P–B deposition rate equations) of the process were established as . The theoretical values calculated by the models were proved to be basically consistent with the practical measurements through experimental verification.     

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 1. Equilibrium parameters

This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (5 μg L⁻¹ to 500 μg L⁻¹ at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L⁻¹ for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1–5 mg L⁻¹) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites (K_L  10³ L mg⁻¹) which are 10–20 less present in a carbon surface than lower reactivity sites (K_L  10 L mg⁻¹), according to the q_m values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g⁻¹ and 190 mg g⁻¹. This theoretical value is very close to the experimental q_m values obtained when using linearized forms of Langmuir, Tóth and Fritz–Schluender models.     

Investigation of hot ductility in Al-killed boron steels

The influence of boron to nitrogen ratio, strain rate and cooling rate on hot ductility of aluminium-killed, low carbon, boron microalloyed steel was investigated. Hot tensile testing was performed on steel samples reheated in argon to 1300 °C, cooled at rates of 0.3, 1.2 and 3.0 °C s⁻¹ to temperatures in the range 750–1050 °C, and then strained to failure at initial strain rates of 1 × 10⁻⁴ or 1 × 10⁻³ s⁻¹. It was found that the steel with a B:N ratio of 0.19 showed deep hot ductility troughs for all tested conditions; the steel with a B:N ratio of 0.47 showed a deep ductility trough for a high cooling rate of 3.0 °C s⁻¹ and the steel with a near-stoichiometric B:N ratio of 0.75 showed no ductility troughs for the tested conditions. The ductility troughs extended from 900 °C (near the Ae₃ temperature) to 1000 or 1050 °C in the single-phase austenite region. The proposed mechanism of hot ductility improvement with increase in B:N ratio in these steels is that the B removes N from solution, thus reducing the strain-induced precipitation of AlN. Additionally, BN co-precipitates with sulphides, preventing precipitation of fine MnS, CuS and FeS, and forming large, complex precipitates that have no effect on hot ductility.     

Radioactivity contents in dicalcium phosphate and the potential radiological risk to human populations

Potentially harmful phosphate-based products derived from the wet acid digestion of phosphate rock represent one of the most serious problems facing the phosphate industry. This is particularly true for dicalcium phosphate (DCP), a food additive produced from either sulphuric acid or hydrochloric acid digestion of raw rock material. This study determined the natural occurring radionuclide concentrations of 12 DCP samples and 4 tricalcium phosphate (TCP) samples used for animal and human consumption, respectively. Metal concentrations (Al, Fe, Zn, Cd, Cr, As, Hg, Pb and Mg) were also determined. Samples were grouped into three different clusters (A, B, C) based on their radionuclide content. Whereas group A is characterized by high activities of ²³⁸U, ²³⁴U (10³ Bq kg⁻¹), ²¹⁰Pb (2 × 10³ Bq kg⁻¹) and ²¹⁰Po (800 Bq kg⁻¹); group B presents high activities of ²³⁸U, ²³⁴U and ²³⁰Th (10³ Bq kg⁻¹). Group C was characterized by very low activities of all radionuclides (<50 Bq kg⁻¹). Differences between the two groups of DCP samples for animal consumption (groups A and B) were related to the wet acid digestion method used, with group A samples produced from hydrochloric acid digestion, and group B samples produced using sulphuric acid. Group C includes more purified samples required for human consumption. High radionuclide concentrations in some DCP samples (reaching 2 × 10³ and 10³ Bq kg⁻¹ of ²¹⁰Pb and ²¹⁰Po, respectively) may be of concern due to direct or indirect radiological exposure via ingestion. Our experimental results based on ²¹⁰Pb and ²¹⁰Po within poultry consumed by humans, suggest that the maximum radiological doses are 11 ± 2 μSv y⁻¹. While these results suggest that human health risks are small, additional testing should be conducted.     

Di-tert-butylazodicarboxylate based PVC membrane sensor for Fe(III) ion measurement in pharmaceutical formulation

Preliminary solution study shows the selectivity of di-tert-butylazodicarboxylate (TBADC) toward Fe(III) ions. Due to this selectivity, it was applied as an ionophore for construction of a Fe(III) sensor. The proposed sensor exhibits a wide linear response range with a Nerstian slope of 19.4 ± 0.4 mV decade^− 1 and detection limit of 4.8 × 10^− 8 mol L^− 1. The sensor response is pH independent in the range of 2.3-3.4 and has a fast response time of < 10 s. It also shows very good selectivity to Fe(III) ion over many mono-,di- and trivalent transition and heavy metal ions. The life time of the electrode was at least 10 weeks. The application of the TBADC-based sensor to analysis of Fe(III) ion in a pharmaceutical formulation, and also to the monitoring of Fe(III) ion in mixtures of two, three and four different ions showed satisfactory results.     

Superplastic flow in a nanostructured aluminum alloy produced using high-pressure torsion

Samples of a spray-cast Al-7034 alloy were processed by high-pressure torsion (HPT) at temperatures of 293 or 473 K using an imposed pressure of 4 GPa and torsional straining through five revolutions. Processing by HPT produced significant grain refinement with grain sizes of 60 and 85 nm at the edges of the disks for the two processing temperatures. In tensile testing at room temperature, the alloy processed by HPT exhibited higher strength and lower ductility than the unprocessed material. Good superplastic properties were achieved in tensile testing at elevated temperatures with a maximum elongation of 750% for the sample processed at 473 K and tested in tension at 703 K under an initial strain rate of 1.0 × 10⁻² s⁻¹. The measured superplastic elongations are lower than in samples prepared by equal-channel angular pressing because of the use of very thin disks in the HPT processing.     

Heptadentate Schiff-base based PVC membrane sensor for Fe(III) ion determination in water samples

Tests performed using heptadentate Schiff's base ((tris(3-(thiophenal)propyl)amine (TTA)) toward Fe(III) ions indicated that it could be used as an Fe(III) selective ionophore to be used in a plasticized polymeric membrane sensor. The resulting sensors were found to produce a linear response range of five orders of magnitude with a slope of 19.8 ± 0.3 mV decade^− 1 with a detection limit is 8.3 × 10^− 9 mol L^− 1. The sensor could be used in a pH window of 2.4-4.3 and the response time of the sensor was below 10 s, in addition to its very good Fe(III) selectivity over many mono-,di- and trivalent transition and heavy metal ions. The life time of the electrode was found to be at least 10 weeks.     

Biosensor enhanced by glucose oxidase biomimetic membrane containing the platinum and silica nanoparticles

In this paper, glucose biosensor is fabricated with immobilization of glucose oxidase (GOx) in platinum and silica sol. The glucose biosensor combined with Pt and SiO₂ nanoparticles could make full use of the properties of nanoparticles. A set of experimental results indicates that the current response for the enzyme electrode containing platinum and silica nanoparticles increases from 0.32 µA cm^− 2 to 33 µA cm^− 2 in the solution of 10 mM β-D-glucose. The linear range is 3 × 10^− 5 to 3.8 × 10^− 3 M with a detection limit of 2 × 10^− 5 M at 3σ. The effects of the various volume ratios of Pt and SiO₂ sols with respect to the current response and the stability of the enzyme electrodes are studied.     

Determination of cadmium at ultra-trace levels by CPE–molecular fluorescence combined methodology

A highly sensitive micelle-mediated extraction methodology for the preconcentration and determination of trace levels of cadmium by molecular fluorescence has been developed. Metal was complexed with o-phenanthroline (o-phen) and eosin (eo) at pH 7.6 in buffer Tris medium and quantitatively extracted into a small volume of surfactant-rich phase of PONPE 7.5 after centrifugating. The chemical variables affecting cloud point extraction (CPE) were evaluated and optimized. The RSD for six replicates of cadmium determinations at 0.84 μg L⁻¹ level was 1.17%. The linearity range using the preconcentration system was between 2.79 × 10⁻³ μg L⁻¹ and 2.81 μg L⁻¹ with a correlation coefficient of 0.99. Under the optimal conditions, it obtained a LOD of 8.38 × 10⁻⁴ μg L⁻¹ and LOQ of 2.79 × 10⁻³ μg L⁻¹. The method presented good sensitivity and selectivity and was applied to the determination of trace amounts of cadmium in commercially bottled mineral water, tap water and water well samples with satisfactory results. The proposed method is an innovative application of CPE-luminescence to metal analysis comparable in sensitivity and accuracy with atomic spectroscopies.     

The bromination kinetics of phenolic compounds in aqueous solution

The purpose of this study was to investigate the bromination kinetics of selected phenolic compounds in aqueous solutions over the pH range of 5–11. The experiment results indicated that the reaction of hypobromous acid with the phenoxide ions controlled the overall reaction rate, whereas the reaction between hypobromite ion and the phenoxide ions and the reaction between hypobromous acid and the undissociated phenolic species were considered to be negligible respectively in the pH range of 7–9. The apparent second-order rate constants of the reaction of hypobromous acid with the phenoxide ions ranged from 7.9 × 10⁶ M⁻¹ s⁻¹ for 3-chlorophenol to 6.5 × 10⁸ M⁻¹ s⁻¹ for 3-methoxyphenol, respectively. The Hammett correlation could be successfully used to estimate the reactivity of bromine with substituted phenols and the linear regression was log(k₂) = −2.85б + 8.00. The rate constants of the reaction of bromine with phenol-like organic compounds were about three orders of magnitude higher than with chlorine and two to three orders of magnitude lower than with ozone.     

Dry sliding wear behaviour of Al–12Si–4Mg alloy with cerium addition

The purpose of this work is to understand the effect of cerium addition on wear resistance behaviour of as-cast alloys. Al–12Si–4 Mg alloys with 1–5 wt% cerium addition were prepared using the casting technique. A sliding wear test was carried out under applied loads of 10 N, 30 N and 50 N at a fixed sliding speed of 1 m/s using a pin-on-disc configuration. The wear test was conducted in dry conditions at room temperature of 25 °C. Detailed analysis of the microstructure, worn surface, collected debris and microhardness was undertaken in order to investigate the differences between the as-cast alloys with different levels of cerium addition. The addition of 1–5 wt% cerium was found to lead to the precipitation of intermetallic phases (Al–Ce), resulting a needle-like structures. Increasing cerium content up to 2 wt% improved both wear resistance and microhardness of as-cast alloys. Addition of more than 2 wt% cerium, however, led to a decrease in microhardness, resulting in lower wear resistance of the alloys. Moderate wear was observed at all loads, with specific wear rates (K′) ranging from 6.82 × 10⁻⁵ with 2 wt% Ce at applied load of 50 N to 21.48 × 10⁻⁵ mm³/N m without added Ce at an applied load of 10 N. Based on K′ ranges, the as-cast alloys exhibited moderate wear regimes, and the mechanism of wear is a combination of abrasion and adhesion. Alloy containing 2 wt% Ce, with the highest hardness and lowest K′ value, showed the greatest wear resistance.     

Deposition of low-resistivity gallium-doped zinc oxide films by low-temperature radio-frequency magnetron sputtering

The transparent and conductive gallium-doped zinc oxide (GZO) film was deposited on 1737F Corning glass using the radio-frequency (RF) magnetron sputtering system with a GZO ceramic target. (The Ga₂O₃ contents are approximately 5 wt. %). In this study, the effect of the sputtering pressure on the structural, optical and electrical properties of GZO films upon the glass or polyester film (PET) substrate was investigated and discussed in detail. The GZO film was grown under a steady RF power of 400 W and a lower substrate temperature from room temperature up to 200 °C. The crystal structure and orientation of GZO thin films were examined by X-ray diffraction. All of the GZO films under various sputtering pressures had strong c-axis (002)-preferred orientation. Optical transparency was high (> 80%) over a wide spectral range from 380 nm to 900 nm. According to the experimental data, the resistivity of a single-layered GZO film was optimized at  8.3 × 10^− 4 Ω cm and significantly influenced by the sputtering pressure. In further research, the sandwich structure of the GZO film/Au metal/GZO film was demonstrated to improve the electrical properties of the single-layered GZO film. The resistivity of the sandwich-structured GZO film was around 2.8 × 10^− 4 Ω cm.     

Thin films deposition with ECR planar plasma source

The results of film deposition of pure tungsten as well as intermetallic compound of NdFeB type on various substrates using planar ECR plasma source (with multipole magnetic field) developed in our laboratory are presented. The frequency of 2.45 GHz was generated within the magnetic system by two-slot antenna. The ions of ECR argon plasma are used for target sputtering. The main plasma parameters are density 10¹⁰ cm⁻³, T_e15 eV, ions energy 20 eV, ion current density 3.5 mA/cm² at the ultimate magnetron power. Under sputtering of Nd₈Fe₈₆B₆ target the amorphous films with high adherence and thickness of 5 μm were formed on the substrate. The deposition rate of tungsten films (target biasing 900 V) was 0.59 nm/s. The fine-grained films with high adhesion were obtained. They were tested against heat loads up to 100 J/cm² produced under irradiation of coatings with plasma streams.     

BL Lacs bright in rays

In this preview we consider implications from the recent AGILE γ-ray detection of the BL Lac 0716+714 in September–October 2007, marked by two intense flaring episodes reaching peak fluxes of 200×10⁻⁸ photons cm⁻² s⁻¹ in the energy range 0.1–10 GeV. The source shows no evidence of emission lines or disk radiation, related to any surrounding gas; its pure non-thermal radiation is effectively represented in terms of the synchrotron-self Compton radiation in the Thomson regime, also supported by the observed quadratic relation of the γ-ray to the X-ray flux variations. With source parameters so derived, we find a total jet power of about 4×10⁴⁵ erg s⁻¹, that makes 0716+714 one of the brightest gas-poor BL Lacs so far detected at γ-ray energies. Thus it provides an ideal benchmark to compare its intrinsic luminosity with the top power extractable from a maximally rotating black-hole via the Blandford–Znajek mechanism. With a mass close to 5×10⁸M for the associated BH, we find the source to remain close to the Blandford–Znajek threshold during the flare. Other gas-poor but weaker BL Lacs remain well below the threshold. These findings and those expected from FERMI will provide a powerful test of GR at work.