Voltammetric determination of ibuprofen using a carbon paste – multiwalled carbon nanotube composite electrode

An optimized voltammetric method is reported for the quantification of ibuprofen in aqueous solution using a carbon paste–multiwalled carbon nanotube composite as the working electrode. The electrode preparation and the experimental conditions were optimized; a sensitivity of 228.08 mA mol^?1 L was obtained. The limits of detection and quantification were 9.1 µM and 25.5 µM, respectively, and the linear dynamic range extended from 2.36–242 µM. The repeatability was 5.35% expressed as the relative standard deviation. Using statistical analysis for the lower concentrations, the detection limit was reduced to 4.13 µM. The method was employed for the analysis of ibuprofen tablets.     

Wear study of carbon–silicon carbide couples

This experimental study concerns the tribological properties of different carbon/porous silicon carbide couples. The aim of this is to characterize the optimum friction couple (carbon/silicon carbide) for dynamic sealing elements in automotive water pumps. A tribometer was used to determine the wear of these material couples. The parameters able to influence the wear, namely the surface finish of the porous silicon carbide material, the quality of the carbon material, the normal load, the surroundings and the speed (in the case of dynamic friction), have been studied. It is evident from this study that the estimated average wear calculated by an empirical mathematical model is reliable except under conditions of extreme friction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radial-mode abrasive waterjet turning of short carbon–fiber-reinforced plastics

An experimental study is carried out for single-pass radial-mode abrasive waterjet (AWJ) turning of a short carbon–fiber-reinforced polyetheretherketone (PEEK) specimen to understand the machining process and the effects of major process variables (feed speed, water pressure, abrasive mass flow rate, nozzle tilt angle, and rotational surface speed) on the major machining performance measures, that is, the depth of cut, material removal rate (MRR) and surface roughness. It is found that high water pressure, normal nozzle impact angle and high rotational speed with suitably selected feed speed and abrasive flow rate may be selected to achieve a high MRR without significantly compromising the surface roughness. Mathematical models for the three cutting performance measures are then developed for use in process control.     

Plasma–powder application of antifrictional babbitt coatings modified by carbon nanotubes

Modification of Babbitt coatings by carbon nanotubes in plasma–powder application is considered. A model is proposed for the interaction of a graphene-like surface and atoms from the Babbitt alloy. The influence of carbon nanotubes obtained by different means on the performance of antifrictional coatings is studied.     

Microstructural and abrasive characteristics of high carbon Fe–Cr–C hardfacing alloy

A series of high carbon Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit hardfacing alloys on ASTM A36 steel substrates. Depending on the four different graphite additions in these alloy fillers, this research produced hypereutectic microstructures of Fe–Cr phase and (Cr,Fe)₇C₃ carbides on hard-facing alloys. The microstructural results indicated that primary (Cr,Fe)₇C₃ carbides and eutectic colonies of [Cr–Fe+(Cr,Fe)₇C₃] existed in hardfacing alloys. With increasing the C contents of the hardfacing alloys, the fraction of primary (Cr,Fe)₇C₃ carbides increased and their size decreased. The hardness of hardfacing alloys increased with fraction of primary (Cr.Fe)₇C₃ carbides. Regarding the abrasive characteristics, the wear resistance of hardfacing alloys were related to the fraction of primary (Cr,Fe)₇C₃ carbides. The wear mechanism was also dominated by the fraction of primary (Cr,Fe)₇C₃ carbides. Fewer primary carbides resulted in continuous scratches worn on the surface of hardfacing alloy. In addition, the formation of craters resulted from the fracture of carbides. However, the scratches became discontinuous with increasing fraction of the carbides. More primary carbides can effectively prevent the eutectic colonies from the damage of abrasive particles.     

Influence of fiber orientation on abrasive wear of unidirectionally reinforced carbon fiber–polyetherimide composites

A composite with continuous carbon fibers (CF) (80% by vol.) and high performance thermoplastic polyetherimide (PEI) matrix was developed and evaluated for various mechanical properties as a function of fiber orientation angle (0°, 30°, 45°, 60° and 90°). It was observed that Young's modulus, Poisson's ratio, toughness and % strain decreased with the increase of fiber orientation angle with respect to loading direction. In-plane shear modulus was highest for fibers with 45°. Overall, unidirectional (UD) CF reinforcement enhanced all strength properties of PEI significantly. Composites with fibers in 0° (parallel to loading direction) proved best in almost all the properties. Tribological evaluation in abrasive wear mode under different loads and fiber orientations indicated that coefficient of friction (μ) and specific wear rate (K₀) decreased with load, in general. Comparatively low specific wear rate (K₀), (in the order of 0.7 1×10^?9 m³/Nm) was observed for 0° fiber orientation, while fibers in 90° showed almost three times higher wear rate. Overall fiber reinforcement in 0° orientations proved beneficial from both strength and tribological performance point of view. SEM proved useful to correlate wear rate with surface topography.     

Electrochemical determination of hydrogen peroxide on a gold nanoparticle–nitrogen-doped graphene glassy carbon electrode

A novel nonenzymatic sensor based on gold nanoparticle–nitrogen-doped graphene was synthesized by electrochemical sequential deposition on the surface of a glassy carbon electrode. Nitrogen-doped graphene was synthesized by a hydrothermal method using graphene oxide and carbamide as the raw materials mixed in specific proportions. The gold nanoparticles were used in the electrochemical sensor to provide unique electronic and electrochemical properties. Under the optimized conditions, hydrogen peroxide was determined by differential pulse voltammetry with a linear relationship for concentrations from 1.0?×?10^?7 to 1.0?×?10^?5?mol?L^?1. The detection limit was 4.9?×?10^?8?mol?·?L^?1 (according to the 3σ rule) and the recoveries were 95.0–98.0%. This sensor is simple, reproducible, and demonstrates that nitrogen-doped graphene oxide has potential applications for electrochemical sensors.     

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.     

The imaging mechanism of single-walled carbon nanotubes on Si/SiO₂ wafer in scanning electron microscopy

Scanning electron microscopy imaging of both suspended single‐walled carbon nanotubes (SWNTs) and contacted SWNTs with Si/SiO₂ substrate has been studied in this paper. The voltage contrast has been investigated by supplying external electric field around the samples. The results show that the image contrast of SWNTs attributes to both voltage contrast from the area surrounding SWNTs (tens of nanometres in both sides of the SWNTs) and electron beam induced emission from SWNTs themselves under low primary beam energy. Under high primary beam energy, however, EBIE dominates the image contrast due to the fact that the voltage contrast caused by implanted charges of the SiO₂ layer is weakened. Imaging under the primary beam energy lower than 1 keV offers widened diameter of SWNTs, which promises that the SWNTs are observable at very low magnification (lower than 100×). At a larger magnification, however, imaging under the primary beam energy higher than 10 keV can display more realistic images of the SWNTs. In addition, an appropriate external electric field can improve the images.     

Microstructure and properties of Fe–Al intermetallic coatings on the low carbon steel synthesized by mechanical alloying

Fe–Al coating was obtained on low carbon steel substrates using mechanical alloying and subsequent heat treatment. Light optical microscopy and a scanning electron microscope equipped with energy dispersive spectroscopy were used to conduct the microstructure characterization. Mechanical properties of the coatings were evaluated by microhardness measurements and wear tests. The corrosion behavior was determined by potentiodynamic polarization measurements in 3.5 % NaCl solution. The results of the mechanical and corrosion tests showed that the hardness and wear resistance of the coatings decreased with increasing the milling time, while increase in the milling time resulted in a significant increase in the thickness, porosity level, and corrosion resistance.     

Impact of polymer structure and confinement on the kinetics of Zdol 4000 bonding to amorphous‐hydrogenated carbon

The bonding of molecularly‐thin (10 Å) Zdol 4000 films to amorphous, hydrogenated carbon (CH_x) was investigated as a function of the Zdol structure, i.e., the ratio of the perfluoromethylene oxide (C₁) to perfluoroethylene oxide (C₂) monomer units in the backbone. The influence of the C₁/C₂ ratio on the intrinsic mobility of the Zdol polymer was also investigated by computing the energetic barriers to internal rotation about the C–O and C–C bonds in model compounds by both ab initio and molecular mechanics methods. The calculations indicate that increasing the C₁/C₂ ratio increases the relative flexibility of the Zdol polymer. The kinetic results demonstrate that the rate at which submonolayer Zdol films bond to CH_x is non‐classical (time‐dependent) regardless of the Zdol chain stiffness. The Zdol bonding rate can best be described by a kinetic equation of the form, dB/dt=k(t)A, where the rate coefficient, k(t) can be expressed as a power function in time: k(t)= k_B t ^-h. The values of the initial bonding rate constant, k _B, and the functional form of the time dependence, t ^-h, are both strongly dependent on the Zdol backbone flexibility. The magnitude of the initial bonding rate constants generally increase with increasing Zdol chain mobility. A discontinuous change in both the magnitude of k _B and the functional form of the time dependence is, however, observed at 64°C when the C₁/C₂ ratio is increased from 0.97 to 1.08. The bonding rate coefficient scales as t ^-0.5 for the relatively rigid Zdol backbone structures with C₁/C₂ < 1, while a t ^-1.0 time‐dependent bonding rate is observed for the more flexible Zdol backbones with C₁/C₂ < 1. The initial rate constant, k _B, also changes abruptly near C₁/C₂ ≈ 1, with k _B of the flexible Zdol chains (samples with C₁/C₂) being approximately an order of magnitude greater than the more rigid chains (C₁/C₂ < 1). These results indicate that the physical state of the confined Zdol film can be either liquidlike or solidlike depending upon the molecular stiffness of the backbone employed. The t ^-0.5 time‐dependent bonding rate is shown to be consistent with a one‐dimensional, diffusion‐limited reaction from a solidlike Zdol structure, whereas the t ^-1.0 bonding rate results when bonding occurs from a liquidlike Zdol film structure. The temperature dependence of the Zdol 4000 bonding rate coefficient for the Zdol backbone characterized by C₁/C₂ = 0.97 (solidlike at T = 64°C) was found to undergo a transition from a t ^-0.5 time dependence for T < 150°C, to a t ^-1.0 time dependence at T > 180. This transition occurs over relatively narrow temperature range (150 < T < 180°C) and is attributed to a 2D melting of the confined Zdol film.     

The effects of nickel and carbon concentrations on the wear resistance of Fe–Ni–C austenitic alloys

The effects of nickel and carbon concentrations on the wear resistance of Fe–xNi–yC (x = 14–20 wt.%, y = 0.6–1.0 wt.%) were investigated with respect to strain energy initiation of the martensitic transformation and hardness. The strain energy needed to initiate the martensitic transformation increased with increasing carbon and nickel concentrations, except in 1.0 wt.% C alloys. The wear resistance of the material decreased with increasing carbon concentration up to 0.9 wt.% C. This effect is most likely due to decrement of the martensite volume fraction with increasing carbon concentration induced by the incremental strain energy required to begin the martensitic transformation. In the case of 1.0 wt.% C, the improved wear resistance may be due to carbide precipitation.     

Evaluation of performance of nanofluid using multiwalled carbon nanotubes for machining of Ti–6AL–4V

Machining of titanium alloys generate very high temperature in the cutting zone. This results in rapid tool wear and poor surface properties. Therefore, improvement in cutting performance in machining of titanium alloys is very much dependent on effectiveness of the cooling strategies applied. In the present work, performance of nanofluid using multiwalled carbon nanotubes (MWCNTs) dispersed in distilled water and sodium dodecyl sulfate (SDS) as surfactant is evaluated for turning operation on Ti–6Al–4V workpieces. Turning operations were carried out under three different conditions – dry, with conventional cutting fluid and with nanofluid. Nanofluid application was limited to 1 L/h and it was applied at the tool tip through gravity feed. Various machining responses like cutting force, surface finish and tool wear were analyzed while turning at optimum cutting parameters as 150 m/min, 0.1 mm/rev and 1 mm depth of cut. Later on, machining performance of nanofluid is confirmed at low cutting speed of 90 m/min. Nanofluid outperformed conventional cutting fluid with 34% reduction in tool wear, average 28% drop in cutting forces and 7% decrease in surface roughness at cutting speed of 150 m/min.     

Mapping erosion–corrosion of carbon steel in oil–water solutions: Effects of velocity and applied potential

In this study, the erosion–corrosion performance of carbon steel was investigated in crude oil, reservoir water, and a mixture of both solutions at a range of applied potentials, velocities and impact angle. The application of such work is to upstream and downstream oilfield conditions, where the proportions of hydrocarbon and water may vary during the extraction process over time. Following exposure of the carbon steel in the crude oil, the extent of erosion was greater than that of corrosion, whilst in the reservoir water, the erosion and corrosion contributions were similar. Regimes of erosion–corrosion were proposed based on the variation in erosion behaviour at various impact angles and applied potentials in the environments studied. Mechanistic changes were identified on erosion–corrosion maps as a function of velocity and applied potential at various impact angles, indicating important transitions in erosion–corrosion processes in the oil/water environments.     

Electrochemical determination of hydrogen peroxide using a novel prussian blue–polythiophene–graphene oxide membrane-modified glassy carbon electrode

A polythiophene–graphene oxide compound membrane and Prussian blue were deposited sequentially on the surface of a glassy carbon electrode by cyclic voltammetry. Due to its excellent electrocatalysis and its analogy with peroxidase enzymes, Prussian blue has been widely used in amperometric biosensors. The polythiophene–graphene oxide compound membrane exhibited good electroconductibility and a large specific surface area. The fabricated Prussian blue/polythiophene/graphene oxide/glassy carbon electrode was characterized by transmission electron microscopy, scanning electron microscopy, and cyclic voltammetry. Under the optimal experimental conditions, the detection of hydrogen peroxide was studied by its amperometric current–time curve. Due to the presence of polythiophene–graphene oxide compound membrane and Prussian blue, the hydrogen peroxide sensor shows a linear calibration range of 1.0?×?10^?6–1.0?×?10^?4?mol?L^?1, detection limits of 3.2?×?10^?7?mol?L^?1 at a signal-to-noise ratio of 3, and recoveries from 95.0 to 105.0%. The results show that the modified glassy carbon electrode has potential practical application for the determination of hydrogen peroxide based on its sensitivity and long-term stability.     

Effect of metallised carbon content of collector strip on the wear of contact wire–collector strip pair in railway systems

Among the topics related to the interaction between the contact wire of the overhead line and the collector strip, the wear that takes place at the contact interface, depending on both electrical and mechanical quantities, represents an important aspect of maintenance costs, affecting the mean lifetime of collectors, in terms of travelled kilometers (in terms of tenth of thousands), and contact line duration, in terms of years (between 15 and 40). Due to its importance in the global maintenance of both rolling stock and infrastructure, this topic deserved the attention of several regulations in the last decade. In order to investigate the effects of electro-mechanical wear on both contact wire and contact strip, a new test equipment has been designed and installed at Politecnico di Milano. A series of tests have been performed, involving different kinds of collector strip materials and contact conditions, tested at varying speeds and current intensities. This investigation concerned different collector strip configurations intended for 3kV D.C. lines. The combination of different contents of copper and metallised carbon in the collector has been found to influence the wear rate of both collector strip and contact wire. Differences in wear up to four times for the former and up to six times for the latter have been found depending on the composition of the collector. Copyright © 2006 John Wiley & Sons, Ltd.     

A capillary absorption spectrometer for stable carbon isotope ratio (13C∕12C) analysis in very small samples

A capillary absorption spectrometer (CAS) suitable for IR laser isotope analysis of small CO(2) samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO(2) near 2307 cm(-1) (4.34 μm). This initial CAS system can achieve relative isotopic precision of about 10 ppm (13)C, or ～1 per thousand (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20-100 picomoles of entrained sample within the hollow waveguide for CO(2) concentrations ～400-750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ～2 Torr. Overall (13)C∕(12)C ratios can be calibrated to ～2 per thousand accuracy with diluted CO(2) standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ～10 s. The CAS is meant to work directly with converted CO(2) samples from a laser ablation-catalytic combustion micro-sampler to provide (13)C∕(12)C ratios of small biological isolates currently operating with spatial resolutions ～50 μm.     

Effects of carbon content and sliding ratio on wear behavior of high-vanadium high-speed steel (HVHSS) under high-stress rolling–sliding contact

This study developed a wear tester to investigate the wear properties of high-vanadium high-speed steel (HVHSS) with approximately 9% vanadium and different carbon contents under rolling–sliding condition. The carbon content significantly affected microstructure of matrix and mechanical properties of HVHSS, and therefore played an important role in wear resistance. Nevertheless, the wear failure mode was mainly related to sliding ratio, which varied from fatigue wear to sliding wear with increasing sliding ratio. The wear behavior was affected by the interaction of carbon content and sliding ratio. The high-stress rolling–sliding contact not only caused severe wear but transformed austenite to martensite.     

Role of thermal,mechanical and oxidising treatment on structure and chemistry of carbon black and its impact on wear and friction: Part 2 – Boundary lubrication condition

Mineral oil formulations with zinc dialkyl dithiophosphate (ZDDP) and dispersant (poly isobutylene succinimide ashless dispersant or ‘PIBSA’) and fully formulated oils with and without carbon black were subjected to thermal and mechanical treatment and tribologically tested on TE 77 (high frequency reciprocating rig or ‘HFRR’) machine to examine the frictional performance during the test. These results were compared to oils without carbon black and oils with diesel soot. Results indicate that oils with just ZDDP and dispersant had the highest friction that remains constant for the duration of the test while oils with carbon black in the milled and oxidised condition had the lowest coefficient of friction and the smallest surface roughness in the tribofilm. The mechanism of wear with treated carbon black and diesel soot was found to be polishing wear as evidenced by the scanning probe microscopy images of the tribofilms. Tribofilms were analysed with X-ray absorption near edge structure (XANES) and it was seen that oils without carbon black or even with untreated carbon black had sulphates at the surface, while the oils with carbon black that were treated had a higher proportion of sulphides. A combination of both FeS and ZnS was found in the tribofilms along with short chain phosphates of Zn.