Potential step study of electrooxidation of methanol in 1-butyl-3-methylimidazolium tetrafluoroborate

A potential step method was used to characterize the electrooxidation of methanol on a chemically modified electrode in an ionic liquid solvent. Two major findings were reported from this study. Firstly, the oxidation was dominant 2.2 s after the potential step. Before that, the double layer charging and adsorption were dominant. Therefore, there should be a waiting time of a few seconds if a methanol sensor is developed with a potential step method. Secondly, the oxidation of methanol on the electrode was diffusion controlled. The concentration of methanol affected the diffusion. The diffusion constant D₀ was 8.37 × 10⁻¹⁷ m²/s when the concentration was lower than 0.5 M and was 2.66 × 10⁻¹³ m²/s when the concentration was higher than 1.0 M. This suggests that the methanol concentration should be kept higher than a threshold in an ionic liquid based fuel cell.     

Tribological behavior of PEEK components with compositionally graded PEEK/PTFE surfaces

PEEK is a high strength engineering thermoplastic that suffers from a high friction coefficient and a friction induced wear mode. Past studies with 10 μm PEEK and PTFE powders resulted in composite solid lubricant that (at the optimal composition) had a wear rate of k = 2 × 10⁻⁹ mm³/Nm with a friction coefficient of μ = 0.12. A compositional grading of PEEK and PTFE is implemented in this study to create a bulk composite with the functional requirements of component strength, stiffness and wear resistance while providing solid lubrication at the sliding interface. The tribological performances of three functionally graded PEEK components were evaluated on linear reciprocating, rotating pin-on-disk and thrust washer tribometers. Wear rates comparable to samples of the bulk solid lubricant and comparable or improved frictional performance were achieved by compositionally grading the near surface region of PEEK components.     

Measurement of CFRP elastic modulus based on FBG reflectance spectrum analysis

Based on fiber Bragg grating (FBG) reflectance spectrum analysis, one novel method to measure the elastic modulus of carbon fiber reinforced plastics (CFRP) is proposed. Basic theory of the novel method is that CFRP uniform cantilever beam produces linear gradient strain which leads to FBG reflectance spectrum broadening under external loadings. Calculation model of the basic theory is put forward and validated by finite element method (FEM) simulation. In order to obtain actual data about the relationship between elastic modulus and FBG reflectance spectrum, experiment of CFRP uniform cantilever beam under external loadings is implemented. The experiment spectrum corresponding to external weight 20 g is chosen as the specimen to explain data processing procedure by self-adaptive method. 3 dB bandwidth and center wavelength of FBG are selected as the reference indexes in the procedure. Elastic modulus of CFRP which is used in the experiment is extracted and its value is 6.617 GPa. To validate the correctness of the elastic modulus, contrastive analyses between transmission matrix theory calculation and experiment spectrums with external weights 5 g and 10 g are also carried out. Absolute errors of 3 dB bandwidth and center wavelength in the comparison are all less than 5 pm which prove the feasibility and correctness of this novel elastic modulus measurement method.     

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.     

Development and evaluation of a two-axial shearing force sensor consisting of an optical sensor chip and elastic gum frame

We developed a promising shearing force sensor that is small in size and can measure shearing force along two axes independently. This sensor consists of an elastic gum frame and an optical sensor chip (6 mm × 6 mm × 8 mm). From the experimental results, the resolutions of the sensor along the x- and y-axes are found to be 0.070 N and 0.063 N. We also experimentally demonstrated that the sensor can separately measure shearing force along two axes. Finally, we demonstrated that the scale factor which correspond to resolution and linear portion which correspond to measuring range of the signals can be changed easily by using three types of elastic gum frame. This sensor can be embedded in the finger of a robot hand and use it to not only measure shearing force but also detect the slip phenomenon.     

Rolling contact fatigue using solid thin film lubrication

This paper addresses rolling contact fatigue (RCF) testing in ultra high vacuum (UHV) under high speed conditions. A ball–rod RCF test platform has been adapted for testing in UHV conditions that allows rapid accumulation of stress cycles, over 10 million cycles within 5 h of testing at 130 Hz rotation. The UHV environment and solid lubrication enables good vibration detection for the onset of spall. In this paper, approximately 0.2 μm of silver is applied to the balls and provides sufficient lubrication for up to 25 h of testing, or 50 million stress cycles in high vacuum at 130 Hz. Seventy-nine RCF tests using thin-film silver lubrication have been completed covering two ball sizes, and two rod and ball materials. 9.53 mm diameter Rex 20 steel and silicon-nitride (Si₃N₄) rods were tested against 7.94 mm diameter Rex 20 and 12.7 mm diameter M50 steel balls. It was found that ball size and material hardness did not affect the stress cycle life over a Hertzian contact stress range of 2.1–4.2 GPa and Rockwell C hardness range of 62–77. Rather, the key limiter to test length is lubrication depletion based on 79 tests and an average silver thickness of 0.2 μm. One of the two failure modes were observed for all tests: (i) early life spall of the silver coating, and (ii) depletion of silver lubrication followed by spall failure of both the ball and rod surfaces. A third-body storage model along with the Control Volume Fraction Coverage (CVFC) assumption and analysis was used to predict lubrication availability between asperities on the third body. There is good agreement between calculated and measured post-test lubrication thickness using the third-body storage model.     

Study of TiAlSiN coatings post-treated with N and C + N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C + N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5 μm thickness, were post-treated by implantations of N or C + N at an energy level of 50 keV. The dose range was between 5 × 10¹⁶ and 1 × 10¹⁸ ions cm^?2. After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6 wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C + N implantations. Particularly, the friction coefficient of the sample with 5 × 10¹⁷ C⁺ cm^?2 and 5 × 10¹⁷ N⁺ cm^?2 could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85 × 10^?7 mm³/Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C + N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C + N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.     

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.     

Tool wear analysis and improvement of cutting conditions using the high-pressure water-jet assistance when machining the Ti17 titanium alloy

This paper presents experimental results concerning the machinability of the titanium alloy Ti17 with and without high-pressure water jet assistance (HPWJA) using uncoated WC/Co tools. For this purpose, the influence of the cutting speed and the water jet pressure on the evolution of tool wear and cutting forces have been investigated. The cutting speed has been varied between 50 m/min and 100 m/min and the water jet pressure has been varied from 50 bar to 250 bar. The optimum water jet pressure has been determined, leading to an increase in tool life of approximately 9 times. Compared to conventional lubrication, an increase of about 30% in productivity can be obtained.     

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.     

Polymethacrylate optodes: A potential for chemical digital color analysis

The paper describes results of implementing a new kind of optical analytical method, digital color analysis (DCA), in which colorimetric polymethacrylate sensors (optodes) are used. The optodes are made of optically transparent polymethacrylate matrix with physically immobilized analytical reagent which is responsible for the extraction of the analyte into the sensing material and changing its color. The developed optodes can be used in determination of various analytes using both solid-phase spectrophotometer and naked eye. In order to improve accuracy and sensitivity of the naked-eye determination, it is possible to measure visible color changes using digital imaging of the polymethacrylate optode. The digital images then can be represented as basic color (e.g. RGB) data. The DCA determinations of Cu (II), Ag (I) and Co (II) have indicated that the developed optodes are linear in concentration ranges 0.02–0.30; 0.02–0.20 and 0.05–0.25 mg L⁻¹ appropriately with corresponding practical detection limits of 0.01; 0.02 and 0.07 mg L⁻¹.     

Determination of haloperidol drug in ampoules and in urine samples using a potentiometric modified carbon paste electrode

A modified carbon paste electrode for haloperidol drug based on haloperidol-phosphomolybdate (HP-PM) as an ion-exchanger dissolved in plasticizer DBP and its potentiometric characteristics were discussed. The electrode exhibited a good Nernstian slope of 56.9 ± 0.3 mV/decade with a linear concentration range from 3.2 × 10⁻⁶ to 1.0 × 10⁻² M for the haloperidol ion. The limit of detection (LOD) was 1.5 × 10⁻⁶ M. It had response time of 5–8 seconds (s), useable in pH range of 6.2–8.6 and temperature of 20–60 °C. The electrode shows clear discrimination of haloperidol drug from several inorganic ions, sugars and some common drug excipients. The sensor was applied for determination of haloperidol drug in urine and in pharmaceutical formulations using potentiometric determination, standard addition and the calibration curve methods. The results are satisfactory with excellent percentage recovery comparable or better than those obtained by other routine methods.     

Effect of SiC particles on the friction and wear behavior of Ti3Si(Al)C2-based composites

The non-lubricated, sliding friction and wear behavior of Ti₃Si(Al)C₂ and SiC-reinforced Ti₃Si(Al)C₂ composites against AISI 52100 bearing steel ball were investigated using a ball-on-flat, reciprocating tribometer at room temperature. The contact load was varied from 5 to 20 N. For monolithic Ti₃Si(Al)C₂, high friction coefficients between 0.61 and 0.90 and wear rates between 1.79 × 10⁻³ and 2.68 × 10⁻³ mm³ (N m)⁻¹ were measured. With increasing SiC content in the composites, both the friction coefficients and the wear rates were significantly decreased. The friction coefficients reduced to a value between 0.38 and 0.50, and the wear rates to between 2.64 × 10⁻⁴ and 1.93 × 10⁻⁵ mm³ (N m)⁻¹ when the SiC content ranged from 10 to 30 vol.%. The enhanced wear resistance of Ti₃Si(Al)C₂ is mainly attributed to the facts that the hard SiC particles inhibit the plastic deformation and fracture of the soft matrix, the oxide debris lubricate the counterpair, and the wear mode converts from adhesive wear to abrasive wear during dry sliding.     

Modified nanoporous carbon as a novel sorbent before solvent-based de-emulsification dispersive liquid–liquid microextraction for ultra-trace detection of cadmium by flame atomic absorption spectrophotometry

Combination of different extraction methods is an interesting work in the field of sample pretreatment. In the current study, for the first time, solid phase extraction combined with solvent-based de-emulsification dispersive liquid–liquid microextraction (SPE-SD-DLLME) was developed for preconcentration and trace detection of cadmium in water samples using flame atomic absorption spectrophotometry (FAAS). The adsorbed cadmium ions on prepared SPE (75 mL of aqueous solution) were eluted by optimized elution solvent and introduced to the second microextraction step. The effective variables of SPE including the pH of sample, flow rates, type, concentration and volume of the eluent and the effect of potentially interfering ions of the separation of cadmium were evaluated and optimized. Also, several factors that influence the SD-DLLME step such as pH, neocuproine concentration (the cadmium binding ligand), type of dispersed/de-emulsifier solvent, volume of disperser/de-emulsifier solvent and type and volume of extraction solvents were investigated. SPE-SD-DLLME provides a preconcentration factor of 165 for cadmium ions. Calibration plot was linear in the range of 0.1–50 μg L⁻¹ with correlation of determination (r²) of 0.988. The precision and limit of detection of proposed method were 5.1% (RSD%, n = 8) and 0.03 μg L⁻¹, respectively.     

High-precision and high-speed positioning of 100 G linear synchronous motor

The present paper describes a moving permanent magnet linear synchronous motor (MPM LSM) that can move with an acceleration above 100 G (=980 m/s²), and is also capable of high-precision and high-speed positioning. The MPM LSM consists of a mover including permanent magnets and a double-sided electromagnet stator. It can produce a thrust of 4.56 × 10³ N and has a working range wider than 1 m. The MPM LSM mover is improved for light weight and is driven using a suitable phase lead for flux weakening. The combination of the improved mover and the suitable phase lead provides motion at an acceleration above 100 G and a velocity above 12 m/s. The positioning characteristics of the improved MPM LSM are examined using a controller with two suitable phase lead functions. The control system shows a positioning accuracy and a positioning resolution of 500 nm, which is similar to the vibration amplitude of the sensor output in open loop. In 300-mm step positioning, the improved MPM LSM shows an acceleration above 660 m/s² and a velocity above 8.3 m/s. It takes less than 101 ms to reduce the positioning error to less than 5 μm. The temperature rise during positioning is also examined experimentally. Continuous positioning for longer than 30 minutes increases the temperature of the MPM LSM, but by less than 6 °C.     

Enhancing electrical conductivity and electrical thermal characteristics of a PEDOT:PSS thin layer by using solvent treatment and adding Ag nanoparticle solution

A method of enhancing the electrical conductivity of 3,4-ethylenedioxythiophene:poly styrene sulfonate (PEDOT:PSS) by combining solvent treatment (adding high polar solvent: 5 wt% ethylene glycol) and adding a small amount of silver (Ag) nanoparticles in a solution was investigated. The main purpose of this was to apply a PEDOT:PSS conductive layer to micro-thermal devices driven by electricity and, for this, to reduce the layer thickness (for low stiffness) while maintaining necessary high electrical conductivity. Layers with thicknesses of less than about 10 μm were examined for electrical conductivity and temperature when electricity was applied. The solvent treated PEDOT:PSS had suitable electrical resistance to generate appropriate temperature properties. The added Ag nanoparticles reduced the electrical resistance by 30–70% over the measured thickness range. The electric conductivity applied with this method was 200–260 Ω⁻¹ cm⁻¹ for thicknesses of 1–2 μm (conductive area: 12 mm × 10 mm) and the generated temperature increase was 20–50 °C at applied voltages of 3–5 V. These characteristics are considered to be suitable to use the conductive layer as a heating element. In addition, the method we used scarcely degraded the transparency of the layer. Measurements of the conductive area in a layer with conductive atomic force microscope (AFM) indicated that the added Ag nanoparticles contributed to increasing the conductive areas and distributing them more uniformly.     

An investigation into the effect of film thickness on nanowear with amorphous carbon-based coatings

A sample oscillation module linked to a nanoindentation unit was used to perform nano-scale wear testing on a series of sputtered Cr doped amorphous C films deposited over a range of thicknesses (10, 20, 50, 150, and 2000 nm) under conditions relevant to MEMS and micro-scale engineering devices. A ruby sphere was used as the counter-body. Specific wear rates (defined as volume of worn material per unit applied load per unit of slid distance) were quantified and the effect of film thickness, applied load and test duration was investigated. Specific wear rate reduced exponentially with decreasing film thickness over the range of 10–2000 nm. The lowest wear rates were in the range of 0.1–6.1 × 10^?17 m³ N^?1 m^?1. Specific wear rate reduced with increased applied load over the range of 0.1–10 mN. The data scatter of replicated testing reduced along with the reduction of wear rate. A rapid reduction of specific wear rate was observed during the first 3000 oscillation cycles. This was analogous to the ‘running in’ process observed with macroscopic tribology systems.     

Wear behaviour of dental enamel at the nanoscale with a sharp and blunt indenter tip

Two different diamond nanoindenter tips, a rounded conical (～1200 nm radius) and a sharp cube corner (20–50 nm radius) were used to abrade bovine enamel. Square abraded areas (2 μm × 2 μm, 5 μm × 5 μm, 10 μm × 10 μm) were generated with loads that varied from 50 μN to 500 μN depending on the indenter tip. In addition normal and lateral forces were simultaneously measured along 10 μm single scratched lines with the sharp cube corner tip. SEM (scanning electron microscopy) and TEM (transmission electron microscopy) were also used to characterise the worn areas and debris. Two different wear mechanisms were observed depending on the geometry of the tip. The rounded tip generates a predominantly elastic contact that mainly compresses and plastically deforms the superficial material and generates severe shear deformation within the sub-surface material which, under certain conditions, fractures and removes material from the sample. The sharp tip cuts into and ploughs the enamel creating a wedge or ridge of material ahead of itself which eventually detaches. This sequence is repeated continuously for every passage of the sharp indenter tip. The different mechanisms are discussed in terms of abrading tip contact angle and enamel microstructure.     

Tribological properties of Ni3Al produced by pressure-assisted volume combustion synthesis

The production of Ni₃Al was performed under an uniaxial pressure of 150 MPa at 1050 °C for 1 h. The formation temperature of Ni₃Al was determined to be 655 °C. The presence of Ni₃Al was confirmed by XRD analysis. SEM analysis revealed that the Ni₃Al phase has very low porosity. The relative density and microhardness of test materials were 97.8% and about 359±31 HV_1.0, respectively. The specific wear rate of Ni₃Al was 0.029 mm³/N m for 2 N, 0.017 mm³/N m for 5 N and 0.011 mm³/N m for 10 N, respectively. The distribution of alloying elements was determined by energy-dispersive spectroscopy (EDS).     

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.