Effect of hypophosphite on electrodeposition of graphite@copper powders

The effect of sodium hypophosphite (NaH₂PO₂) on the electrodeposition of copper coated graphite powders (graphite@Cu) was investigated in this paper. The cathodic polarization curves were determined by potentiodynamic scanning method in the electrolyte containing various concentrations of NaH₂PO₂. Hypophosphite could reduce the overpotential of copper deposited on the graphite particles surface and accelerate electroless copper nuclei generated by the reduction reaction. The applied potential promoted the formation of copper nuclei on the surface of graphite powders. Uniform graphite@Cu powders were fabricated by optimizing the NaH₂PO₂ concentration in the range of 10–15 g dm⁻³. The residue of NaH₂PO₂ could be depleted to less than 0.25 g dm⁻³ by decomposition on the anode and chemical reduction in the bath during electrodeposition. The effect of hypophosphite on the electrodeposition of graphite@Cu is also discussed.     

Preparation of spherical silica in emulsion systems using the co-precipitation technique

Silica powders with particles of spherical shape and a low tendency to agglomeration of primary particles have been prepared by precipitation from sodium metasilicate and hydrochloric acid via the emulsion technique. The organic phase of the emulsion system was cyclohexane while a non-ionic surfactant was applied as an emulsifier. In the course of silica precipitation three alternative ways of dispersion induction were applied: the top stirrer, homogenization and ultrasounds. The precipitation was performed at three temperatures (25 °C, 40 °C and 60 °C), using different variants of dosing schemes of the emulsion and the aqueous solutions of substrates. Homogenization of the reactive system yielded silica of spherical particles of the lowest mean particle diameter and the most uniform character. The only appropriate mode of dosing the reagents to the emulsion was the introduction of alkaline emulsion to acidic emulsion. A decreased tendency for silica particles agglomeration could be achieved by increasing the volume of the organic phase in the emulsions prepared. The optimum temperature for the precipitation reaction was 25 °C. The procedure permitted obtaining in SiO₂ particles of the optimum diameter (<1 μm) and particles of spherical shape. Moreover, the silica adsorbents obtained manifested high activity. Their surface area reached values in the 340–390 m² g^?1 range.     

Preparation and electrochemical characterization of lithium cobalt oxide nanoparticles by modified sol–gel method

Uniformly distributed nanoparticles of LiCoO₂ have been synthesized through the simple sol–gel method in presence of neutral surfactant (Tween-80). The powders were characterized by X-ray diffractometry, transmission electron microscopy and electrochemical method including charge–discharge cycling performance. The powder calcined at a temperature of 900 °C for 5 h shows pure phase layered LiCoO₂. The results show that the particle size is reduced in presence of surfactant as compared to normal sol–gel method. Also, the sample prepared in presence of surfactant and calcined at 900 °C for 5 h shows the highest initial discharge capacity (106 mAh g^?1) with good cycling stability as compared to the sample prepared without surfactant which shows the specific discharge capacity of 50 mAh g^?1.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Influence of carbon precursors on thermal plasma assisted synthesis of SiC nanoparticles

Nanosized SiC was synthesized by solid state method using silicon and carbon powders followed by non-transferred arc thermal plasma processing. X-ray diffraction (XRD) analysis revealed that activated carbon has highest reactivity while graphite has lowest activity in the crystallization of SiC through solid state method. The reactivity was dependent on surface area of carbon source and activated carbon with highest surface area (590.18 m² g⁻¹) showed highest reactivity, whereas graphite with least surface area (15.69 m² g⁻¹) showed lowest reactivity. The free silicon content was decreased with increasing reaction time as well as carbon mole ratio. Scanning electron microscope (SEM) study showed that the shape and size of synthesized SiC depends on the shape and size of carbon source. SiC nanoparticles within 500 nm were formed for carbon black while bigger particles (∼5 μm) were formed for activated carbon and graphite. Plasma processing of these solid–solid synthesized SiC resulted into the formation of well dispersed, ultrafine SiC nanoparticles (30–40 nm) without any structural modification. Thermal plasma processing resulted into the increase in crystallite size of SiC.     

Unexpected effect of copper ions on electrochemical impedance behaviour of self-assembled alkylaminethiol monolayer

Effect of copper ions on the electrochemical behaviour of an alkylaminethiol monolayer has been studied by electrochemical impedance spectrosocpy. RAMAN experiment shows the effective adsorption of receptor onto the gold surfaces. The study of Nyquist plot shows that the gold/monolayer/electrolyte interface can be described by a serial combination of two R, CPE electrical circuits. In the presence of increasing amounts of copper, the Nyquist plots at low frequencies were modified showing an increase of the resistance of the second R, CPE electrical circuit. Moreover, this increase of resistance varies linearly with the amounts of copper ions added in solution from 10^? 8 mol·L^? 1 to 10^? 5 mol·L^? 1.     

The influence of preparation conditions on ZrO2 nanoparticles with different PEG–PPG–PEG surfactants by statistical experimental design

In this study mesoporous Zirconia powder with high surface area was prepared by using PEG–PPG–PEG new block copolymer as the non-ionic surfactant. The preparation conditions were optimized by Taguchi method of experimental design and Minitab Software to synthesize high surface area tetragonal-ZrO₂ nanoparticles. The BET surface area of powders was 114–175 m²/gr and the particles size calculated by Deby–Sherrer equation was 5–9 nm. pH = 11, aging time 38 h, Zr molarity 0.03, Surfactant/Zr mole ratio 0.04 and molecular weight 8400 were the best conditions to manufacture ZrO₂ with higher surface area. The sample prepared under optimized conditions was compared to that synthesized by PEG surfactant. XRD patterns of two ZrO₂ samples, hysteresis loop, pore size distribution, BET surface area and SEM results are similar.     

Precipitation strengthened high strength-conductivity copper alloys containing ZrC ceramics

Metal matrix composites (MMC) of copper and ZrC powders were prepared by the powder metallurgy route. Powders of both materials were introduced in stainless steel jag and mechanically mixed in a planetary mill under a protective atmosphere of argon during time ranging from 4 to 30 h. A characterization study of resulting powders indicated that a steady state particle distribution is developed after 12 h of milling. For this reason only these powders were consolidated by hot uniaxial pressing under 90 MPa at 923 K for 2 h. Residual porosity of these compacts was eliminated by rolling at 1073 K. Resulting materials present fine grained microstructure, tensile strength of 653 MPa and electrical conductivity up to 52% IACS. A detailed microstructural analysis by scanning and transmission electron microscopy showed not only ZrC particles but also the presence of very fine particles of carbides and oxides. WDX and EDX spectra of these particles revealed a high content of Fe and Cr for the carbides and Cu in the case of oxides.     

Influence of different parameters and their coupled effects on the stability of alumina nanofluids by a fractional factorial design approach

Nanofluids have been introduced as new-generation fluids able to improve energy efficiency in heat exchangers. However, stability problems related to both agglomeration and sedimentation of nanoparticles have limited industrial-level scaling. A fractional factorial experimental 2^k?1 design was applied in order to evaluate the effects of nanoparticle concentration, surfactant type and concentration, ultrasonic amplitude as well as ultrasonic time on the stability of alumina (Al₂O₃) nanofluids. Commercial alumina nanoparticles (particle diameter <50 nm) were dispersed in deionized water using ultrasonic probe dispersion equipment. Sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) were used as surfactants. The stability of the nanofluids in static mode was monitored by visual inspection and UV visible spectroscopy. The results of the experimental design showed that the coupled effects between surfactant type and surfactant concentration and between ultrasonication tip amplitude and ultrasonication time had the most pronounced effects on nanofluid stability. The experimental conditions providing the best stability were 0.5 wt% of Al₂O₃, CTAB, critical micelle surfactant concentration, 30% ultrasonic amplitude and 30 min of ultrasonication.     

Voltammetric behaviour of nitroxazepine in solubilized system and biological fluids

This study reports the development and validation of sensitive and selective assay method for the determination of the antidepressant drug in solubilized system and biological fluids. Solubilized system of different surfactants including cationic, anionic and non-ionic influences the electrochemical response of drug. Addition of cationic surfactant cetrimide to the solution containing drug enhances the peak current signal while anionic and non-ionic showed an opposite effect. The current signal due to reduction process was function of concentration of nitroxazepine, pH, type of surfactant and preconcentration time at the electrode surface. The reduction process is irreversible and adsorption controlled at HMDE. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for niroxazepine hydrochloride determination. The proposed SWCAdSV and DPCAdSV methods are linear over the concentration range 2.0 × 10^-7– 5.0 × 10^-9 mol/L and 6.1 × 10^-7– 1.0 × 10^-8 mol/L with detection limit of 1.62 × 10^-10 mo/L and 1.4 × 10^-9 mo/L respectively. The method shows good sensitivity, selectivity, accuracy and precision that makes it very suitable for determination of nitroxazepine in pharmaceutical formulation and biological fluids.     

Preparation and characterization of biocompatible carbon electrodes

Electron transfer in microbial fuel cell and biosensors could be facilitated through high conductive materials with enhanced active surface area and appropriate redox potential suited to microbial metabolism. In the first strategy based on bulk doping, graphite/epoxy composite electrode (GECE) bulk was modified with six types of metal ion which were prepared through a wet impregnation procedure. In the second strategy, immobilization of redox dye on carbon cloth and graphite sheet was carried out using N,N′-dicyclohexylcarbodiimide for surface modification. Crystallinity, morphology, surface chemistry and electrochemical properties of all modified electrodes were investigated. Influence of redox behavior of electrodes suited to microbial metabolism and conducive to biofilm formation have been examined. It was observed that the Fe³⁺ doped GECE surfaces exhibited significantly high biofilm formation of 1.10(±0.18) × 10⁷ CFU/cm² as compared to other dopants. The microbial growth on the carbon cloth electrode and carbon fiber reinforced plate were found to be less (2.6(±0.97) × 10⁴, 4.8(±1.8) × 10³ CFU/cm² respectively) compared to GECEs.     

Highly selective electrochemical biosensor for the determination of folic acid based on DNA modified-pencil graphite electrode using response surface methodology

An electrochemical DNA biosensor was proposed as a screening device for the rapid analysis of folic acid using a pencil graphite electrode modified with salmon sperm ds-DNA. At first, immobilization of the ds-DNA on pencil graphite electrode was optimized using response surface methodology. Solution pH, DNA concentration, time of DNA deposition and potential of deposition was optimized each at three levels. The optimum combinations for the reaction were pH 4.8, DNA concentration of 24 μg mL^? 1, deposition time of 304 s, and deposition potential of 0.60 V, by which the adenine signal was recorded as 3.04 μA. Secondly the binding of folic acid to DNA immobilized on a pencil graphite electrode was measured through the variation of the electrochemical signal of adenine. Folic acid could be measure in the range of 0.1–10.0 μmol L^? 1 with a detection limit of 1.06 × 10^? 8 μmol L^? 1. The relative standard deviations for ten replicate differential pulse voltammetric measurements of 2.0 and 5.0 μmol L^? 1 folic acid were 4.6% and 4.3%, respectively. The biosensor was successfully used to measure folic acid in different real samples.     

Magnetic and catalytic properties of cubic copper ferrite nanopowders synthesized from secondary resources

Cubic copper ferrite CuFe₂O₄ nanopowders have been synthesized via a hydrothermal route using industrial wastes. The synthesis conditions were systematically studied using statistical design (Box–Behnken Program) and the optimum conditions were determined. The results revealed that single phase of cubic copper ferrite powders can be obtained at different temperatures from 100 to 200 °C for times from 12 to 36 h with pH values 8–12. The crystallite size of the produced powders was in the range between 24.6 and 51.5 nm. The produced copper ferrite powders were appeared as a homogeneous pseudo-cubic-like structure. A high saturation magnetization (M_s 83.7 emu/g) was achieved at hydrothermal temperature 200 °C for 24 h and pH 8. Photocatalytic degradation of the methylene blue dye using copper ferrite powders produced at different conditions was investigated. A good catalytic efficiency was 95.9% at hydrothermal temperature 200 °C for hydrothermal time 24 h at pH 12 due to high surface area (118.4 m²/g).     

Electrochemical properties of all solid state Li/S battery

All-solid-state lithium/sulfur (Li/S) battery is prepared using siloxane cross-linked network solid electrolyte at room temperature. The solid electrolytes show high ionic conductivity and good electrochemical stability with lithium and sulfur. In the first discharge curve, all-solid-state Li/S battery shows three plateau potential regions of 2.4 V, 2.12 V and 2.00 V, respectively. The battery shows the first discharge capacity of 1044 mAh g^?1-sulfur at room temperature. This first discharge capacity rapidly decreases in 4th cycle and remains at 512 mAh g^?1-sulfur after 10 cycles.     

Surfactant-assisted synthesis of Sn nanoparticles via solution plasma technique

We have adopted a solution plasma synthesis for preparing Sn nanoparticles (Sn-NPs) directly from metallic Sn electrode. The Sn-NPs were synthesized in the presence of the surfactant, cetyltrimethylammonium bromide (CTAB), and the effect of the concentration of CTAB on the Sn-NPs was investigated. Without CTAB addition, SnO plates were precipitated. Sn-NPs with less than 200 nm were synthesized at a high concentration of 200 × 10⁻⁶ g ml⁻¹ of CTAB. Electrochemical properties of SnO plates and Sn-NPs were analyzed for use as an anode material in Li-ion batteries. A composite of Sn-NPs and graphite enhanced the cyclic stability owing to the buffer space provided by the graphite for volume expansion. In the case of the 30 wt% loaded Sn-NPs, the capacity was measured to be 414 mA h g⁻¹ after 20 cycles.     

Preparation of mesoporous silica by co-precipitation in the presence of non-ionic surfactant

Porous silica powders with high specific surface area were prepared by the chemical precipitation method from waterglass and hydrochloric acid. A non-ionic surfactant was used to induce precipitate and to form pore. The calcined products had uniform pores and high specific surface areas (>1000 m² g⁻¹). The specific surface area of the product was altered with the variation in the amount of the surfactant.     

Sodium gluconate-assisted hydrothermal synthesis,characterization and electrochemical performance of LiFePO4 powders

Nano- and micro-sized LiFePO₄ powders were synthesized by a sodium gluconate (C₆H₁₁NaO₇)-assisted hydrothermal synthesis method at 220 °C for 10 h with pH = 2–7. The resulting powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS). The obtained data showed that the pH of synthesis solution played a key role in the formation of the LiFePO₄ powders with different morphologies, such as ball-like microspheres, irregular microspheres with the agglomerated rods and particles, sphere-like nanoparticles and nano-ellipsoids. The results from electrochemical performance measurements revealed that the charge–discharge cycling characteristics of the samples were strongly dependent on their morphologies. In particular, the ellipsoidal LiFePO₄ nanoparticles with the average size of 70–90 nm showed the highest initial discharge capacity of 150 mA h g⁻¹ at 0.1 C rate, and cycling stability of the ellipsoidal LiFePO₄ nanoparticles was optimum among all the samples prepared due to their dual advantages of high tap density and good diffusion property. The present study offers a simple morphology-controllable route, without carbon coating or doping with supervalent cations, to synthesize and to design high performance cathode materials for lithium-ion batteries.     

Adsorption behavior of caffeine as a green corrosion inhibitor for copper

Electrochemical and impedance experiments were carried out to evaluate the corrosion behavior of copper in aerated 0.1 mol L^? 1 H₂SO₄ solutions in the presence of three xanthine derivatives with similar chemical structures. The corrosion rate of copper was found to increase in the presence of theophylline and theobromine and decrease in the presence of caffeine. The adsorption and inhibitory effect of caffeine on copper surfaces in aerated 0.1 mol L^? 1 H₂SO₄ solutions were then investigated in detail by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), contact angle measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and fluorescence experiments. The data obtained indicate that caffeine behaves as a cathodic-type inhibitor adsorbing onto the copper surface according to the Temkin isotherm, with the negative ?G°_ads value of ? 31.1 kJ mol^? 1 signifying a spontaneous adsorption process. The corrosion inhibition efficiency increased with caffeine concentration in the range of 1.0–10.0 mmol L^? 1. Furthermore, the EIS results obtained at the open-circuit potential and surface analysis (SEM, EDS and fluorescence) clearly demonstrated the adsorption of the organic compound onto the copper electrode. The contact angle measurements revealed the formation of a hydrophobic protective film. This film covers up to 72% of the total active surface, acts as a protective barrier and prevents interaction between the metal, water and oxygen molecules.     

Preparation of Nylon-6/flake graphite derivatives composites with antistatic property and thermal stability

Nylon-6/flake graphite (FG) composite, Nylon-6/graphene intercalation compounds (GIC) composite and Nylon-6/exfoliated graphite (EG) composite were prepared by FG, GIC, EG and caprolactam via in situ polymerization, and the volume resistivities of Nylon-6/flake graphite derivatives composites were also investigated. Meanwhile, the structure of Nylon-6/EG composite was characterized and the thermal stability of Nylon-6/EG composite was investigated as well. When the mass percents of FG, GIC and EG were 1%, 2–4% and 1%, the volume resistivities of flake graphite derivatives composites would reach 7.5 × 10⁶ Ω cm, 3.6 × 10⁸–1.4 × 10⁶ Ω cm and 2.3 × 10⁶ Ω cm. When the mass percent of EG increases from 0% to 9%, the thermal stability temperature of Nylon-6/EG composite would enhance from 70 to 196 °C. This shows that Nylon-6/flake graphite derivatives composites can have the antistatic property and thermal stability synchronously.     

Effect of cup and ball types on alumina–tungsten carbide nanocomposite powder synthesized by mechanical alloying

Alumina-based nanocomposite powders with tungsten carbides particulates were synthesized by ball milling WO₃, Al and graphite powders. X-ray Diffraction (XRD) was used to characterize the milled and annealed powders. Microstructures of milled powders were studied by Transmission Electron Microscopy (TEM). Results showed that Al₂O₃–W₂C composite formed after 5 h of milling with major amount of un-reacted W in stainless steel cup. The remained W was decreased to minor amount by increasing carbon content up to 10 wt.%. When milled with ZrO₂ cup and balls, Al₂O₃–W₂C composite was completely synthesized after 20 h of milling with the major impurity of ZrO₂. In the case of stainless steel cup and balls with 10 wt.% carbon, Fe impurity after 5 h of milling (maximum 0.09 wt.%) was removed from the powder by leaching in 3HCl·HNO₃ solution. The mean grain size of the powder milled for 5 h was less than 60 nm. The powder preserved its nanocrystalline nature after annealing at 800 °C.