Determination of phenyl acetic acid by cyclic voltammetry with electrochemical detection

The phenyl acetic acid (PAA) has been determined by cyclic voltammetry with electrochemical detection using CuGeO₃ nanowires as the glassy carbon electrode (GCE) modified materials. The electrochemical behaviors of the PAA at the CuGeO₃ nanowire modified GCE in neutral solution show that two pairs of electrochemical CV peaks are observed. Two anodic CV peaks are located at 0.31 V and −0.02 V for cv peak 1 and cv peak 2, respectively. The intensities of two anodic peaks vary linearly with the increase of the PAA concentrations from 0.01 to 2 mM. The detection limit is 82.1 μM and 9.1 μM for cv peak 1 and cv peak 2, respectively. The CuGeO₃ nanowire modified GCE exhibits good reproducibility, stability and sensibility.     

Thermopower detection of single nanowire using a MEMS device

We present a MEMS-based device on a silicon nitride membrane in order to measure the thermoelectric properties of a single nanowire. A temperature gradient along a nanowire was generated by a nanoheater, and the temperature was measured by Pt thermometers. A thermal simulation using a finite element method was conducted to analyze the temperature distribution over the MEMS device. The validity of the MEMS device was established by testing the Pt nanowires which had different symmetry configurations. From the test results of Pt nanowires, a convincing temperature calibration method was proposed and applied to an actual case of Bi₂Te₃ nanowire. We measured a Seebeck coefficient of −53 μV/K and electrical conductivity of 2.23 × 10⁵ S/m for a single Bi₂Te₃ nanowire with a diameter of 70 nm at 300 K. Our solid design for thermoelectric measurements based on a membrane structure enables the fast and high-yield characterization of one-dimensional nanostructures.     

Nano composite system based on fullerene-functionalized carbon nanotubes for simultaneous determination of levodopa and acetaminophen

In this paper we report an electrochemical sensor based on fullerene (C₆₀)-functionalized carbon nanotubes composite for the sensitive determination of the levodopa (LD) and acetaminophen (AC). A modified electrode by fullerene-functionalized carbon nanotubes (CNTs) composite has been fabricated and its electrochemical behavior was investigated by cyclic voltammetry, chronoamperometry and differential pulse voltammograms. The modified electrode shows electrocatalytic activity toward LD oxidation in phosphate buffer solution (pH 7.0) with a reduction of the overpotential of about 270 mV and an increase in peak current. These conditions are sufficient to allow determination of LD and AC in the samples at fullerene-functionalized carbon nanotubes composite. The differential pulse voltammetry data showed that the obtained anodic peak currents were linearly dependent on the LD concentrations in the range of 0.5–2000 μM, with the detection limit of 0.035 μM. The prepared electrode was successfully applied for the determination of LD and AC in real samples.     

Determination of ganciclovir as an antiviral drug and its interaction with DNA at Fe3O4/carboxylated multi-walled carbon nanotubes modified glassy carbon electrode

The electrochemical oxidation of an antiviral drug, ganciclovir (GCV) at Fe₃O₄/carboxylated multi-walled carbon nanotubes modified glassy carbon electrode (Fe₃O₄/cMWCNTs/GCE) was studied by voltammetric techniques. The influence of the effective parameters on the electrochemical behavior of GCV was investigated. Under optimized conditions, the proposed sensor was applied for low level GCV determination. The relationship between peak current and the concentration of GCV was linear in the range of 80–53,000 nM with a detection limit of 20 nM through square wave voltammetry (SWV). The interaction of GCV with calf thymus DNA was also explored by voltammetric and spectrofluorometric methods. Based on the obtained data the mode of binding of GCV to DNA was intercalative binding. The decrease in the SWV peak current of GCV in the presence of DNA was used for the determination of DNA. The modified electrode exhibited a good sensitivity, stability and pleasant reproducibility, and it was applied for the determination of GCV in spiked serum and urine, with satisfactory results.     

Improved wear resistance in alumina-PTFE nanocomposites with irregular shaped nanoparticles

Past studies with PTFE nanocomposites showed up to 600× improvements in wear resistance over unfilled PTFE with the addition of Al₂O₃ nanoparticles. Irregular shaped nanoparticles are used in this study to increase the mechanical entanglement of PTFE fibrils with the filler. The tribological properties of 1, 2, 5 and 10 wt.% filled samples are evaluated under a normal pressure and sliding speed of 6.3 MPa and 50.8 mm/s, respectively. The wear resistance was found to improve 3000× over unfilled PTFE with the addition of 1 wt.% nanoparticles. The 5 wt.% sample had the lowest steady state wear rate of K = 1.3 × 10⁻⁷ mm³/N m and the lowest steady friction coefficient with μ = 0.21.     

Spray pyrolysed Mn:Co3O4 thin film electrodes via non-aqueous route and their electrochemical parameter measurements

Present work explains the preparation of manganese incorporated cobalt oxide thin film electrodes on stainless steel by spray pyrolysis technique, via non-aqueous (methanolic) media. Structural, morphological and electrochemical characterizations of the prepared samples were made by means of XRD, SEM and electrochemical measurements. Structural elucidation confirms Co₃O₄ has face centred cubic and Mn₃O₄ has tetragonal body centred cubic structure with polycrystalline nature. Surface morphological observation shows the continuous semi porous film growth with spherical grains. Cyclic voltammetry reveals the mixed capacitive behaviour with maximum specific capacitance 605.35 F/g at the scan rate 1 mV/s in 1 M KOH electrolyte. Chronopotentiometric measurement gives energy density 33.5 Wh/kg, power density 2 kW/kg and Columbic efficiency 99.23%. Electrochemical impedance study was carried out in the frequency range 1 mHz to 1 MHz to see the internal resistance. Randles equivalent circuit was developed by using ZsimpWin software to search the circuitry parameters associated with the cell.     

The design of polyaniline based sensor for the qualitative estimation of malonaldehyde

The detection of contaminated food in every stage of processing required new technology for fast identification and isolation of toxicity in food. Since effect of food contaminant are severe to human health, the need of pioneer technologies also increasing over last few decades. In the current study, MDA was prepared by hydrolysis of 1,1,3,3-tetramethoxypropane in HCl media and used in the electrochemical studies. The electrochemical sensor was fabricated with modified glassy carbon electrode with polyaniline. These sensors were used for detection of sodium salt of malonaldehyde and observed that a high sensitivity in the concentration range ∼1 × 10⁻¹ M and 1 × 10⁻² M. Tafel plots show the variation of over potential from − 1.73 V to − 3.74 V up to 10⁻⁵ mol/L indicating the lower limit of detection of the system.     

Electrocatalytic determination of captopril using a modified carbon nanotube paste electrode: Application to determination of captopril in pharmaceutical and biological samples

A carbon paste electrode modified with carbon nanotube and benzoylferrocene (BF) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of captopril (CAP), was described. The electrode was employed to study the electrocatalytic oxidation of CAP, using cyclic voltammetry (CV), chronoamperometry (CHA) and square wave voltammetry (SWV) as diagnostic techniques. It has been found that the oxidation of CAP at the surface of modified electrode occurs at a potential of about 85 mV less positive than that of an unmodified CPE. SWV exhibits a linear dynamic range from 1.0 × 10⁻⁷ to 3.5 × 10⁻⁴ M and a detection limit of 3.0 × 10⁻⁸ M for CAP. Finally the modified electrode was used for determination of CAP in CAP tablet and urine sample.     

Nanocomposite polymer electrolyte based on rice starch/ionic liquid/TiO2 nanoparticles for solar cell application

Nanocomposite polymer electrolyte (NCPE) was prepared using solution cast technique. Rice starch (RS), lithium iodide (LiI), 1-methyl-3-propylimidazolium iodide (MPII) as ionic liquid and TiO₂ nanopowder (RS:LiI:MPII:TiO₂) were introduced to prepare the sample. The conductivity of 3.63 × 10⁻⁴ S/cm was achieved by introducing 30 wt.% of 1-methyl-3-propylimidazolium iodide (MPII) as ionic liquid and 2 wt.% of TiO₂. Temperature-dependent conductivity and dielectric behavior were analyzed in this work. Dye sensitized solar cell was fabricated using the nanocomposite film for this sample and analyzed.     

Application of L-DOPA modified carbon nanotubes as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid,adrenaline, acetaminophen and tyrosine

L-DOPA multi-wall carbon nanotube modified glassy carbon electrode (DOPA-MWCNT-GCE) was used as a bifunctional electrocatalyst for simultaneous quantitative determination of ascorbic acid (AA) and adrenaline (AD). Electrochemical experiments show that the modified electrode plays the role of an excellent bifunctional electrocatalyst for the oxidation of AA and AD in two different potentials. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k′, for the electrocatalytic oxidation of AA and AD at the DOPA-MWCNT-GCE surface were estimated. Through a different pulse voltammetric (DPV) method, the plot of the electrocatalytic current versus AA and AD concentrations emerged to be constituted of two linear segments with different sensitivities. In addition, detection limits of 1.5 μM for AA and 0.62 μM for AD were obtained. In DPV, the proposed bifunctional electrocatalyst could separate the oxidation peak potentials of AA, AD, acetaminophen (AC) and tyrosine (Tyr) present in a mixture though, at the bare GCE, the peak potentials overlap. Finally, DOPA-MWCNT-GCE was satisfactorily used for the determination of AA, AD, AC and Tyr in pharmaceutical preparations.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

Effect of silicon nitride coating thickness on fatigue of silicon microbeams

In this paper, two silicon nitride layers with thickness, 0.2 and 0.4 μm, are coated onto single crystal silicon (SCS) in order to achieve Si₃N₄/Si cantilever microbeams. The effect of LPCVD silicon nitride surface coatings on fatigue properties of SCS cantilever microbeams is investigated. Fatigue testing is conducted at both 40 Hz and 100 Hz. Typical S–N (strain amplitude–fatigue cycle) curves of the beams are achieved and correlated fatigue failure modes are investigated. It is found that thinner Si₃N₄ coating of 0.2 μm results in better fatigue lives of Si₃N₄/Si beams than thicker Si₃N₄ coating of 0.4 μm. Both thinner and thicker coated beams have major fatigue crack planes along {1 1 1} planes; however, thicker coated beams possess specific failure mode of delamination, which is not found in thinner coated beams. Delamination reduces the reinforcing effect of thicker Si₃N₄ coating and leads to its shorter fatigue life. For thicker coated beams, fatigue life at 100 Hz is longer than that at 40 Hz. The mechanism for delamination and the effect of cyclic frequency is investigated, and factors for better fatigue life are proposed.     

Electrochemical determination of sulfite and phenol using a carbon paste electrode modified with ionic liquids and graphene nanosheets: Application to determination of sulfite and phenol in real samples

Benzoylferrocene was used to construct a modified-graphene paste electrode. Also, hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) was used as a binder to prepare the modified electrode. The electro-oxidation of sulfite at the surface of the modified electrode was studied using electrochemical approaches. This modified electrode offers a considerable improvement in voltammetric sensitivity toward sulfite, compared to the bare electrode. Square wave voltammetry (SWV) exhibits a linear dynamic range from 5.0 × 10⁻⁸ to 2.5 × 10⁻⁴ M and a detection limit of 20.0 nM for sulfite. The diffusion coefficient and kinetic parameters (such as electron transfer coefficient and the heterogeneous rate constant) for sulfite oxidation were also determined. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of sulfite and phenol that makes it suitable for the detection of sulfite in the presence of phenol in real samples.     

Analysis of load-speed sensitivity of friction composites based on various synthetic graphites

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient (μ) of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-test-rig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 μm. Other particle sizes which resulted in good performance were 38 and 169 μm. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of μ following an orthogonal L₉(3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ～80–250 μm.     

A study on erosion of upper bainitic ADI and PDI

Ductile iron containing ∼3.5 wt.% C and 2.1–4.2 wt.% Si (2.1, 2.8 and 4.2 wt.%) was studied. Three sets of specimens with differing Si contents were made into austempered ductile iron (ADI) and pearlite ductile iron (PDI) through heat treatment. These specimens were then eroded with Al₂O₃ particles and SiO₂ particles of 275–295 μm grit size to understand the relationship between erosion rate and microstructure. The ADI specimens were upper bainitic matrices that were austempered for different periods of time at 420 °C. The heat treatment of PDI was conducted at 870 or 930 °C for 1 h then forced air cooled or oil quenched to room temperature.Two types of wear curves, single peak curves and double peak curves, were found when plotting the erosion rate figures derived from the experimental results. 2.1 wt.% Si and 2.8 wt.% Si ADI tempered for a long period of time, due to their decreased retained austenite content and increased carbide content, had a single peak erosion rate curve. This embrittlement effect caused the impact angle of maximum erosion rate to increase from ∼30 to ∼45°. Decreasing the interspacing of the lamellae cementite promoted the hardness and improved the low-angle erosion wear resistance of PDI. The high hardness and brittleness of the matrix reduces the high-angle erosion resistance and the peak erosion rate occurs at a higher angle.For 2.1Si-ADI and 2.8Si-ADI tempered for a short duration, increasing the volume fraction of martensite in the matrix increases the erosion rate at an impact angle of 30°, but the maximum erosion rate is found at 75°. This results in a curve with a double peak. The double peak curve was also observed for high silicon ADI tempered for a long duration. The high solid solution hardness of 4.2Si-ADI, due to low retained austenite content and the presence of carbide in the matrix, results in poor erosion resistance. When this material is austempered for a long period, the erosion rate curve shifts from a single peak curve (30°) to a double peak curve (30°; 60°).     

WC–ZrO2 composites: processing and unlubricated tribological properties

In the present work, we report the processing and properties of WC–6 wt.% ZrO₂ composites, densified using the pressureless sintering route. The densification of the WC–ZrO₂ composites was carried out in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y-stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. An important observation is that a transition in friction and wear with load is noted. The dominant mechanisms of material removal appear to be tribochemical wear and spalling of tribolayer.     

Silver nanoparticles/polymethacrylic acid (AgNPs/PMA) hybrid nanocomposites-modified electrodes for the electrochemical detection of nitrate ions

AgNPs/PMA hybrid nanocomposite materials with different Ag loadings have been synthesized using a simple chemical route assisted by UV irradiation. The hybrid composites were characterized by means of SEM and TEM, UV–vis spectroscopy and XPS. The as synthesized hybrid samples, composed of small Ag nanoparticles (AgNPs) embedded within the PMA (poly-methacrylic-acid) matrix, have been used to modify the working electrode of disposable screen printed carbon electrodes (SPCEs). It has been observed that hybrid composite with the lowest Ag loading forms dendritic silver structures on the surface of working electrode, whereas at higher loadings massive structures were formed. The electrocatalytic properties of the AgNPs/PMA/SPCEs were investigated toward the reduction of nitrate at neutral pH. Based on these modified electrodes, both voltammetric and amperometric sensors were developed for the electrochemical sensing of nitrate. Voltammetric sensor showed a wide linear range (0–20 mM) and high sensitivity (130 μA mM⁻¹ cm⁻²).     

A parametric study of the relationship between microstructure and wear resistance of Al–Si alloys

Wear tests were conducted on three commercial grade Al–Si alloys, a die cast 383 with 9.5 wt.% Si, a sand cast A390 with 18.5 wt.% Si and a spray cast alloy with 25 wt.% Si under dry sliding conditions. In addition, heat treatment processes were used to modify the microstructure and hardness of 383 alloy. This selection of materials and heat treatments provided a broad range of samples with different silicon weight percentage, morphology, size, and alloy hardness for comparison purposes. Using a method of pair-wise comparison, it was found that the effect of the individual contribution of each microstructural feature on the wear resistance could be isolated.Block-on-ring tests were performed under a controlled atmosphere of 5% relative humidity at a constant speed of 1 m/s. A mild to severe wear transition occurred at loads above 150 N irrespective of the alloy composition and microstructure. The mild wear regime consisted of two sub-regimes that were named as the first sub-regime of mild wear (MW-1) at low loads and the second sub-regime of mild wear (MW-2) at higher loads. The steady state wear rates (W) in each sub-regime of the mild wear showed a power-law dependence to the applied load (L) as W = CLⁿ, where C is the wear coefficient, and n is the wear exponent. The wear coefficients, C₁ of MW-1 and C₂ of MW-2, and the transition loads L₁ and L₂, which denoted the start and end of the transition zone between MW-1 to MW-2, were sensitive to microstructure.Pair wise comparisons showed that an increase in the Si content from 9.5 to 25 wt.% increased the transition load L₁ by 140%, but had only a minor effect on C. An increase in alloy hardness from 31.6 to 53.5 kg/mm² provided a very significant increase in the transition loads (e.g., 400% increase in L₁), but did not have a notable effect on the values of C (only 3% increase). On the other hand, a decrease in the silicon particle aspect ratio from 3.75 to 1.98 increased L₁ by 25% and reduced C₁ by 25% (and C₂ by 31%). A decrease in the silicon particle size from 45.8 to 3.1 μm had the most significant effect on both wear parameters by reducing C₁ by 35% and C₂ by 58%, and increasing the transition load L₁ by 71%.     

Non-contact temperature measurement of silicon wafers based on the combined use of transmittance and radiance

We propose a non-contact temperature measurement method that combines the temperature dependence of transmittance below 600 °C and radiation thermometry above 600 °C. The combined method uses a polarization technique and the Brewster angle between air and a dielectric film such as SiO₂ or Si₃N₄ grown on silicon wafers. A prominent feature of this method is that both measurements of transmittance and radiance are performed with the same geometrical arrangement.For a semitransparent wafer, the measurement of p-polarized transmittance at the wavelengths of 1.1, 1.2 and 1.3 μm enables temperature measurement in the range from room temperature to 600 °C. For an opaque wafer above 600 °C, the p-polarized radiation thermometry at the wavelength of 4.5 μm allows the temperature measurement without the emissivity problem. The combined method with the use of transmittance and radiance is valid in the entire temperature range irrespective of variations of film thickness and resistivity.     

The capability of ultrafiltrated alkaline and organosolv oil palm (Elaeis guineensis) fronds lignin as green corrosion inhibitor for mild steel in 0.5 M HCl solution

The inhibitive effect of ultrafiltrated oil palm fronds (OPF) lignins on the corrosion of mild steel in 0.5 M HCl solution has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP) and weight loss measurement. The presence of smaller lignin fractions reduces remarkably the corrosion rate of mild steel. The highest corrosion inhibition efficiency for all ultrafiltrated lignins were attained at maximum concentration of 500 ppm (IE_P.Soda: 87% > IE_P.Organosolv: 83% > IE_P.Kraft: 81%). The results from this corrosion test clearly reveal that all ultrafiltrated lignins behaved as a mixed-type inhibitor with predominant anodic (organosolv lignin) or cathodic (alkaline lignin) effectiveness. It was deduced that the inhibition process was spontaneous and the inhibitors were mainly physically adsorbed onto the mild steel surface.