Friction and wear behavior of laser composite surfaced aluminium with silicon carbide

The present study concerns the wear behavior of laser composite surfaced Al with SiC and Al + SiC particulates. A thin layer of SiC and Al + SiC (at a ratio of 1:1 and dispersed in alcohol) were pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO₂ laser. Irradiation leads to melting of the Al substrate with a part of the pre-deposited SiC layer, intermixing and followed by rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance were evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in grain refined Al matrix. Part of the SiC particles are dissociated into silicon and carbon leading to formation of the Al₄C₃ phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface improves by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The mechanism of wear for as-received vis-à-vis laser composite surfaced Al has been proposed.     

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).     

Tribo-layer and its role in dry sliding wear of Ti–6Al–4V alloy

Dry sliding wear tests were performed for Ti–6Al–4V alloy under a load of 50–250 N at 25–500 °C on a pin-on-disk elevated temperature tester. Worn surfaces and subsurfaces were thoroughly investigated for the morphology, composition and structure of tribo-layers. Ti–6Al–4V alloy could not be considered to possess poor wear resistance at all times, and presented a substantially higher wear resistance at 400–500 °C than at 25–200 °C. The tribo-layer, a mechanical mixing layer, was noticed to exist on worn surfaces under various conditions. High wear rate at 25–200 °C was ascribed to no protective tribo-layer containing no or trace tribo-oxides. As more oxides appeared in the tribo-layers, they presented an obviously protective role due to their high hardness, thus giving a reasonable explanation for high wear resistance of Ti–6Al–4V alloy at 400–500 °C.     

DETERMINATION OF TRACE LEAD AND CADMIUM USING STRIPPING VOLTAMMETRY IN FLUIDIC MICROCHIP INTEGRATED WITH SCREEN-PRINTED CARBON ELECTRODES

A homemade fluidic microchip integrated with screen-printed carbon electrodes (SPCE) for direct detection of trace Pb(II) and Cd(II) has been designed. Analytes are accumulated and determined in a flow system with stripping voltammetry, and the methods of standardization are applied for self-calibration. The portable device produces a well-defined and reproducible electrochemical signal for monitoring Cd(II) and Pb(II), and limits of detection are low to 2.0 ppb and 3.0 ppb, respectively. Meanwhile, Pb(II) and Cd(II) in aqueous solutions are also qualitative measured with calibration both by internal standard and standard addition method. The proposed methodology possesses the advantages of simple, fast, high sensitivity, and stability. It has potential applications in the fields of environmental monitoring and biomedical science for real-time and online measurements.     

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.     

On-site calibration system for trace humidity sensors

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1 μmol mol⁻¹ and 350 μmol mol⁻¹ (equivalent to frost-point temperatures from −76 °C to −31 °C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20 °C to 60 °C and kept stable within 0.1 K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k = 2) of the generated value.     

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.     

Effects of sliding velocity on tribo-oxides and wear behavior of Ti–6Al–4V alloy

Dry sliding wear tests were performed for Ti–6Al–4V alloy on a pin-on-disc wear tester. The wear behavior of Ti–6Al–4V alloy at sliding velocities of 0.5–4 m/s was studied and the tribo-oxides and their function were explored. Ti–6Al–4V alloy presented a marked variation of wear rate as a function of velocity. With the rise and fall of wear rate, Ti–6Al–4V alloy underwent the transitions of wear mechanisms from the combination of delamination wear and oxidative wear at lower speeds to delamination wear at 2.68 m/s, and then to oxidative wear at 4 m/s. These phenomena were attributed to the appearance and disappearance of tribo-oxides. In spite of trace or a small amount, tribo-oxides would change the wear behavior, and even wear mechanism.     

Design,realization and uncertainty analysis of a laser-based primary calibration facility for solar cells at PTB

A completely newly designed multi-functional facility for the primary calibration of reference solar cells and the spectral characterization of all solar cell types has been developed and built at PTB. The new facility is based on the successfully applied Differential Spectral Responsivity (DSR) method that allows the determination of the absolute spectral responsivity and nonlinearity of solar cells with the lowest uncertainties. By using a tunable laser system, the new setup avoids the main problem of monochromator-based systems: the low optical power level of the monochromatic beam. Thus it enables a significant reduction of the uncertainty for the short circuit current under standard test conditions I_STC of solar cells. It enables the calibration of World Photovoltaic Scale (WPVS) reference solar cells with an uncertainty of 0.4% (k = 2), the lowest value stated by any WPVS laboratory.     

A sensitive nanocomposite-based electrochemical sensor for voltammetric simultaneous determination of isoproterenol,acetaminophen and tryptophan

The electrooxidation of isoproterenol (ISPT), acetaminophen (AC) and tryptophan (Trp) and their mixture has been studied using an 8,9-dihydroxy-7-methyl-12H-benzothiazolo[2,3-b]quinazolin-12-one modified multiwall carbon nanotubes paste electrode (DMBQ-MCNTPE). The novel sensor exhibited potent and persistent electron mediating behavior followed by well separated oxidation peaks towards ISPT, AC and Trp with activation over-potential. The peak currents were linearly dependent on ISPT, AC and Trp concentrations using square wave voltammetry (SWV) method in the range of 0.04–400, 5.0–500, and 10.0–800 μmol L⁻¹, with detection limits of 0.009, 1.0, and 4.0 μmol L⁻¹, respectively. The modified electrode was used for the determination of ISPT, AC and Trp in biological and pharmaceutical samples.     

ICP-MS测定两种一枝黄花中12种微量元素

为确定两种一枝黄花中微量元素的差异,建立了微波消解-ICP-MS法,测定加拿大一枝黄花与一枝黄花中Ca、Mg、P、Fe、Mn、Ni、Cu、Zn、Se、Cr、Hg和Pb12种微量元素。方法的加标回收率为95.2%～107.1%,相对标准偏差在2.5%～8.9%之间,检出限在0.002～0.057μg.L-1之间,该方法具有良好的准确度和精密度。分析结果表明,加拿大一枝黄花与一枝黄花均含有Ca、Mg、P、Mn和Fe元素,前者中Ca、Cr、Mn、Zn、Pb、Ni含量较高,而后者中的Mg、P、Fe、Cu、Se含量较高。     

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.     

Identification and characterisation of steel corrosion using passive high frequency RFID sensors

High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.     

Optimization of degree of sphericity of primary phase during cooling slope casting of A356 Al alloy: Taguchi method and regression analysis

The present work presents the results of experimental investigation of semi-solid rheocasting of A356 Al alloy using a cooling slope. The experiments have been carried out following Taguchi method of parameter design (orthogonal array of L₉ experiments). Four key process variables (slope angle, pouring temperature, wall temperature, and length of travel of the melt) at three different levels have been considered for the present experimentation. Regression analysis and analysis of variance (ANOVA) has also been performed to develop a mathematical model for degree of sphericity evolution of primary α-Al phase and to find the significance and percentage contribution of each process variable towards the final outcome of degree of sphericity, respectively. The best processing condition has been identified for optimum degree of sphericity (0.83) as A₃, B₃, C₂, D₁ i.e., slope angle of 60°, pouring temperature of 650 °C, wall temperature 60 °C, and 500 mm length of travel of the melt, based on mean response and signal to noise ratio (SNR). ANOVA results shows that the length of travel has maximum impact on degree of sphericity evolution. The predicted sphericity obtained from the developed regression model and the values obtained experimentally are found to be in good agreement with each other. The sphericity values obtained from confirmation experiment, performed at 95% confidence level, ensures that the optimum result is correct and also the confirmation experiment values are within permissible limits.     

Steel machining chips as reinforcements to improve sliding wear resistance of metal alloys: Study of a model Zn-based alloy system

Two new steel-reinforced, metal-matrix composites (MMCs), Kirksite+1080 and Kirksite+M2 are developed by adding 25 wt% of AISI 1080/AISI M2 steel machining chips to a zinc-based alloy, Kirksite (4% Al and 3% Cu). The sliding wear resistance of the Zn alloy and the two MMCs, against AISI 52100 steel, is determined under increasing normal load (1–10 N) and temperature (25–150 °C), using a pin-on-disc configuration. The MMCs are found to exhibit superior wear performance under all test conditions. At room temperature, a maximum wear reduction in excess of 70% is obtained for the composites relative to the Zn-alloy at the highest load of 10 N. This reduction is as much as 86% at 150 °C and 1 N for the Kirksite+M2. The wear-reducing ability of the steel reinforcements is generally greater at the more severe contact conditions. The stability of the MMC matrices and recommended limits to the MMC operating temperatures are established using deformation measurements made via dynamic mechanical analysis. The principal wear mechanisms are analysed based on the sliding wear measurements, complemented by optical microscopy and SEM observations, and EDX microanalysis. The results show that the steel chip reinforcements are effective in improving the wear resistance of Zn alloys under severe conditions. Implications for use of low-cost machining chips as reinforcements to create MMCs for improved wear performance, and for recycling/reuse of these chips in advanced structural material systems are discussed.     

International comparison of volume measurement for a 1 kg silicon sphere between KRISS and NMIJ

1 kg single-crystal silicon spheres are presently used as primary density standards in many countries. The absolute density of the spheres is determined from the measurements of their mass and volume in conformity with the definitions of the SI base units. Since the mass of the spheres is almost 1 kg, a mass comparison with the prototype of the kilogram can be performed with very low uncertainty. Absolute volume measurements for the spheres therefore have a crucial role in realizing a reliable density traceability system. To confirm the reliability of the volume measurement, the volume of a silicon sphere was measured independently using optical interferometers at the Korea Research Institute of Standards and Science (KRISS, Korea) and the National Metrology Institute of Japan (NMIJ, Japan). An optical interferometer with an etalon scanning system was used at KRISS. On the other hand, an optical interferometer with an optical frequency scanning system was used at NMIJ. The volume was measured at 20 °C and 0 Pa, and the results are in agreement with each other within their uncertainties. Details of the two interferometers and the comparison results are described.     

Investigating the Machinability of Al–Si–Cu cast alloy containing bismuth and antimony using coated carbide insert

Surface roughness and cutting force are two key measures that describe machined surface integrity and power requirement evaluation, respectively. This investigation presents the effect of melt treatment with addition of bismuth and antimony on machinability when turning Al–11%Si–2%Cu alloy. The experiments are carried out under oblique dry cutting conditions using a PVD TIN-coated insert at three cutting speeds of 70, 130 and 250 m/min, feed rates of 0.05, 0.1, 0.15 mm/rev, and 0.05 mm constant depth of cut. It was found that the Bi-containing workpiece possess the best surface roughness value and lowest cutting force due to formation of pure Bi which plays an important role as a lubricant in turning process, while Sb-containing workpiece produced the highest cutting force and highest surface roughness value. Additionally, change of silicon morphology from flake-like to lamellar structure changed value of cutting force and surface roughness during turning.     

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.     

Thermal experimental verification on effects of nanoparticles for enhancing electric and dielectric performance of polyvinyl chloride

This paper presents investigation on the enhancement of dielectric constant characterization of polyvinyl chloride (PVC) by organic and inorganic nanoparticles under variant frequencies and thermal conditions. Dielectric spectroscopy has been experiment dielectric properties of polyvinyl chloride at various frequencies (0.01 Hz–1 MHz) and temperatures (20–80 °C); then, it has been specified the effective nanoparticles on dielectric constant performance compared with unfilled base matrix polymer. Therefore, it has been got optimum types and concentrations of nanoparticles that have been used for controlling and enhancing dielectric constant characterization of polyvinyl chloride.