Tribological properties of surface-modified Pd nanoparticles for electrical contacts

A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2 wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20 N, 1.82 GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1 kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well.     

Nano force sensing using symmetric double stage micro resonator

A new approach is proposed to improve a graphical approach with considering intensity coupling loss coefficients in the analytical derivation of the optical transfer functions for a symmetric double stage vertically coupled microring resonator. An optimum transmission coupling condition is determined with considering terms of couplers intensity loss which leads to low insertion loss of 1.2 dB, finesse of 1525, the out of band rejection ratio of 61.8 dB. The resonating system is used as an optical force sensing system to make the benefit of the accuracy of measurements in micro and nano scales. The sensitivity of proposed force sensor in terms of wavelength-shift is 33 nm/nN and the limit of detection is 1.6 × 10⁻² nN. The proposed sensing system has the advantages of self-calibration and the low power consumption due to the low intensity.     

Parameters optimization on surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process

With the advance of contemporary technology, high precision surface finishing techniques for optical glasses are of great concern and developing to meet the requirements of the effective industrialized processes. Not only the used tools but also process parameters have great influence on the surface roughness improvements. In this paper, surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process has been presented. For the same purpose, a tool for executing ultra precision polishing was designed and manufactured. Taguchi's experimental approach, an L₁₈ orthogonal array was employed to obtain the optimal process parameters. ANOVA analysis has also been carried out to determine the significant factors. It was observed that about a 98.33% improvement on surface roughness from (R_a) 0.360 μm to (R_a) 0.006 μm has been achieved. The experimental results show that a surface finished achieved can satisfy the requirements for optical-quality surface (R_a < 12 nm). In addition, the influence of significant factors on surface roughness improvement has been discussed in this study.     

Simultaneous interferometric measurement of the absolute thickness and surface shape of a transparent plate using wavelength tuning Fourier analysis and phase shifting

The absolute optical thickness and surface shape of optical devices are considered as the fundamental characteristics when designing optical equipment. The thickness and surface shape should be measured simultaneously to reduce cost. In this research, the absolute optical thickness and surface shape of a 6–mm-thick fused silica transparent plate of diameter 100 mm was measured simultaneously by a three-surface Fizeau interferometer. A measurement method combining the wavelength tuning Fourier and phase shifting technique was proposed. The absolute optical thickness that corresponds to the group refractive index was determined by wavelength tuning Fourier analysis. At the beginning and end of the wavelength tuning, the fractional phases of the interference fringes were measured by the phase shifting technique and optical thickness deviations with respect to the ordinary refractive index and surface shape were determined. These two kinds of optical thicknesses were synthesized using the Sellmeier equation for the refractive index of fused silica glass, and the least square fitting method was used to determine the final absolute optical thickness distribution. The experimental results indicate that the all the measurement uncertainties for the absolute optical thickness and surface shape were approximately 3 nm and 35 nm, respectively.     

Compact and inexpensive iodine-stabilized diode laser system with an output at 531 nm for gauge block interferometers

A compact and inexpensive iodine-stabilized diode laser system with an output at 531 nm has been applied to long gauge block measurements. Although the optical frequency of the output beam was widely modulated (modulation width of ∼22 MHz), the coherence length and interference phase stability are sufficiently long and high, respectively, for the interferometric measurement of long gauge blocks of up to 1000 mm in length. The effective uncertainty of laser frequency in the interferometric measurement was theoretically and experimentally confirmed to be less than 10⁻⁹.     

Effect of bovine serum constituents on the surface of the tribological pair alumina/alumina nanocomposites for total hip replacement

Alumina has been widely used in the fabrication of hip joint replacement due to its excellent properties. But one of its drawbacks is the low fracture toughness, which can be enhanced with the addition of a second ceramic phase of nanometer size. Another property to be improved is its wear resistance under severe rubbing conditions. In this work Yttria Tetragonal Zirconia Polycrystal, Y-TZP (TZ-8YS, 100 nm), TiO₂ (PS-25, 50 nm) and Co (Nilaco, 28 nm) were added to Al₂O₃ (AKP 50, 300 nm). These starting powders were mixed and hot pressed, in order to fabricate alumina nanocomposites. Mechanical properties of the nanocomposites were estimated using the indentation method. Wear tests were carried out using a ball-on-plate tribometer, with a frequency of 1 Hz, at a load of 49 N, for 1 h. Alumina balls were used as the counterface. Distilled water and fetal bovine serum solution (FBSS) were the environments. The specific wear rate was within 10^?8 to 10^?7 mm³/N m and the coefficient of friction was around 0.3–0.7. Keeping in mind that wear is a process that starts on the surface and it is related to the physical chemistry of the surfaces, techniques such as scanning electron microscopy (SEM), and X-ray photoelectron spectrometry (XPS) were used to elucidate the role played by the proteins and phospholipids present in the fetal bovine serum solution and the new chemical specie formed on the surface.     

Study on tribological properties of UHMWPE irradiated by electron beam with TMPTMA and TPGDA as crosslinking agents

Trimethylolpropane trimethacrylate (TMPTMA) and tripropylene glycol diacrylate (TPGDA) used as crosslinking agents were blended with ultra-high molecular weight polyethylene (UHMWPE or UPE) in alcohol, respectively. Then UPE plates were made by compression molding and electron beam (EB) irradiation crosslinking methods. FTIR, Soxhlet extractor, DSC, Wear tester and SEM were used for the characterization of all specimens. FTIR analyses show that trans-vinylene (965 cm^?1) absorption increases in all specimens and the >C=C< stretching absorption decreases after irradiation. Soxhlet experiments reveal that gel fraction increases with the increasing dose. DSC results indicate that X_c of all the irradiated UPEs are higher than that of unirradiated UPEs because of the free radical and small molecular which can promote the crystallization. Wear rate of 100 kGy 1%TMPTMA/UPE and 1%TPGDA/UPE are 1.89×10^?7 mm³/(N m) and 4.28×10^?7 mm³/(N m), about 44.2% and 100% of that of 100 kGy UPE, respectively, illustrating that TMPTMA is beneficial to reduce the wear rate of UPE and TPGDA almost has no effect to reduce the wear rate of UPE before 100 kGy. SEMs of irradiated specimens are more smooth than that of unirradiated specimens. These can give some advice to improve tribological properties of UPE used in the friction field.     

Application of blue laser direct-writing equipment for manufacturing of periodic and aperiodic nanostructure patterns

This study presents the novel development of low cost, highly efficient blue laser direct-writing equipment for using mask-less laser lithography to manufacture periodic and aperiodic nanostructure patterns. The system includes a long-stroke linear motor precision stage (X, Y), a piezoelectric nano-precision stage (Y, θz), a 3-DOF (degrees of freedom) laser interferometer measurement system, and a blue laser direct-writing optical system. The 3-DOF laser interferometer measurement system gives the control system feedback for displacement (X, Y, θz) of the equipment. The laser processing equipment consists of a blue laser direct-writing optical head, a field-programmable gate array (FPGA) alignment interface, and an optical head servo controller. The optical head operates at a wavelength of 405 nm. Processing the nanostructures on thermo-reaction inorganic resists with precise control of the laser intensity, taking advantage of the threshold effect to exceed the limitations of optical diffraction, and reduces the nanostructure hole size. The equipment can be used to fabricate various periodic nanostructure patterns, aperiodic nanostructure patterns, and two-dimensional patterns. The equipment positioning accuracy is within 50 nm at a speed of 50 mm/s, and the minimum critical dimension can be achieved about 100 nm or so.     

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.     

Development of a simple ‘temperature versus sliding speed’ wear map for the sliding wear behaviour of dissimilar metallic interfaces

The variation in wear behaviour during limited debris retention sliding wear of Nimonic 80A versus Stellite 6 (counterface) between room temperature and 750 °C, at sliding speeds of 0.314, 0.654 and 0.905 m s⁻¹, was investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to transfer and oxidation of Stellite 6-sourced debris to the Nimonic 80A and resultant separation of the Nimonic 80A and Stellite 6 wear surfaces. Between room temperature and 450 °C, this debris mostly remained in the form of loose particles (with only limited compaction), whilst between 510 and 750 °C, the particles were compacted and sintered together to form a wear protective ‘glaze’ layer.At 0.654 and 0.905 m s⁻¹, mild oxidational wear due to transfer and oxidation of Stellite 6-sourced debris was only observed at room temperature and 270 °C (also 390 °C at 0.654 m s⁻¹). At 390 °C (450 °C at 0.654 m s⁻¹) and above, this oxide was completely absent and ‘metal-to-metal’ contact resulted in an intermediate temperature severe wear regime—losses in the form of ejected metallic debris were sourced almost completely from the Nimonic 80A. Oxide debris, this time sourced from the Nimonic 80A sample, did not reappear until 570 °C (630 °C at 0.654 m s⁻¹), however, were insufficient to eliminate completely severe wear until 690 and 750 °C. At both 0.654 and 0.905 m s⁻¹, the oxide now preventing severe wear at 690 and 750 °C tended not to form ‘glaze’ layers on the surface of the Nimonic 80A and instead supported continued high wear by abrasion. This abrasive action was attributed to the poor sintering characteristics of the Nimonic 80A-sourced oxide, in combination with the oxides’ increased mobility and decreased residency.The collected data were used to compose a simple wear map detailing the effects of sliding speed and temperature on the wear of Nimonic 80A slid against Stellite 6, at these speeds and temperatures of between room temperature and 750 °C.     

Erosive smoothing of abrasive slurry-jet micro-machined channels in glass,PMMA, and sintered ceramics: Experiments and roughness model

Abrasive slurry jet micro-machining (ASJM) was used to machine channels in glass, PMMA, zirconium tin titanate, and aluminum nitride. The channel roughness was measured as a function of the ASJM process parameters particle size, dose, impact velocity, and impact angle. The steady-state roughness of the channels was reached relatively quickly for typical ASJM abrasive flow rates. The roughness of channels having depth-to-width aspect ratios up to about 0.25 could be reduced by approximately 35% compared to the roughest channel by decreasing particle impact velocity and angle. However, machining at such conditions reduced the specific erosion rate by 64% on average. It was therefore quicker to post-blast reference channels (225 nm average root mean square (R_rms) roughness) using process parameters selected for peak removal. It was also found that the roughness of reference channels could be reduced by about 78% by post-blasting using 3 μm diameter silicon carbide particles at 15° jet incidence. The smoothest post-blasted channels had an R_rms roughness of about 23 nm in glass, PMMA, and zirconium tin titanate, and 170 nm in aluminum nitride. Computational fluid dynamics was used to predict the particle impact conditions that were used in a model to predict the steady-state roughness due to ductile erosion with an average error of 12%.     

AC conduction mechanism and battery discharge characteristics of (PVC/PEO) polyblend films complexed with potassium chloride

New K⁺ ion-conducting polymer blend electrolyte films based on amorphous polymer poly(vinyl chloride) (PVC) and semicrystalline polymer poly(ethylene oxide) (PEO) complexed with KCl salt were prepared using a solution-cast technique. The maximum value of ionic conductivity of a PVC/PEO:KCl (42.5:42.5:15) system is 8.29 × 10⁻⁶ S/cm at 303 K. The absorption edge was found at 4.30 eV for undoped film, while it was observed at 4.03 and 3.93 eV for 10 and 15 wt% KCl doped films, respectively. The direct band gaps for these pure and salt doped PVC/PEO films were found to 4.10, 3.86 and 3.74 eV, respectively, whereas the indirect band gaps were determined as 4.15, 3.72 and 3.64 eV. Transference number values showed that the charge transport in this electrolyte system is predominantly due to ions (t_ion = 0.97). The discharge capacity for PVC/PEO:KCl (42.5:42.5:15) polymer blend electrolyte system is 11 μA/h.     

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.     

Lubricating property of MQL grinding of Al2O3/SiC mixed nanofluid with different particle sizes and microtopography analysis by cross-correlation

With the increased requirements for environmental protection, energy conservation, and low consumption, nanofluid minimal quantity lubrication (MQL) grinding, which is an environment-friendly machining method, has been paid increasing attention. Improving the lubricating property of nanofluids effectively is currently a main research trend. Meanwhile, optimizing mixed nanoparticle (NP) size ratio is an effective way for enhancing the lubricating property of MQL grinding. In the experiment, different sizes (30, 50, and 70 nm) of Al₂O₃ and SiC NPs were mixed, and nanofluids were prepared at 2% (volume fraction) mixed NPs and base oil. The prepared nanofluids were then used in MQL grinding on a hard Ni-based alloy (inconel 718). The experiment was then evaluated by specific grinding force, removal rate of workpiece, surface roughness, morphology of grinding debris, and contact angle. The effect of the sizes of the Al₂O₃/SiC mixed NPs on MQL grinding performance was discussed in accordance with the period and amplitude, as well as cross-correlation coefficient, of the workpiece surface cross-correlation function curve profile. Experimental results suggest that different Al₂O₃/SiC mixed NP sizes affect the nanofluid MQL grinding performance variably. The highest removal rate of the workpiece [189.05 mm³/(s N)] and the lowest RSm (0.0381 mm) were achieved when the Al₂O₃/SiC mixed NP size ratio was 70:30. The lowest Ra (0.298 μm) was obtained at 50:30. Meanwhile, the highest length ratio of the profile support (90%), the best morphology of abrasive dusts, and the largest wetting area of liquid drops were acquired at 30:70. Furthermore, a cross-correlation analysis of the workpiece surface profile curve under three size ratios (30:70, 50:30, and 70:30) was carried out. The cross-correlation function curve of the workpiece surface profile under 30:70 attained the shortest period, the largest amplitude, and the largest cross-correlation coefficient (0.67), thereby indicating good workpiece surface quality. Therefore, 30:70 was the best size ratio of the Al₂O₃/SiC mixed nanofluid.     

Subpixel edge location method proposed to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio

A subpixel edge location method based on orthogonal Jacobi–Fourier moments is proposed in this paper to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio. The effectiveness of the proposed method is proved through the performance test of a micro-hole measuring machine with optical spherical coupling probe. Test results indicate that a blind micro-hole of 400 μm in diameter can be experimentally measured at the depth of 2000 μm with a repeatability of 40 nm and an extremity resolution of 42 nm.     

Structural and photoluminescence studies of rutile TiO2 nanorods prepared by chemical bath deposition method on Si substrates at different pH values

The effects of pH on the structural, morphological and optical properties of TiO₂ nanorods were investigated. Nanorods were fabricated on p-type (1 1 1)-oriented silicon substrates and all substrates were seeded with a TiO₂ seed layer synthesized with a radio-frequency reactive magnetron sputtering system (the TiO₂ seed layer was also examined in this research). Chemical bath deposition (CBD) was performed to grow rutile TiO₂ nanorods on Si substrate at various pH values (0.5, 0.7 and 0.9). Raman spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analyses showed the tetragonal rutile structure of the synthesized TiO₂ nanorods. Optical properties were examined photoluminescence spectroscopy, which indicated a high-intensity UV peak centered at around 390 nm for all samples compared with visible defect peaks. Experimental results showed that the TiO₂ nanorods grown at pH 0.7 exhibited the optimal structural properties. Moreover, the CBD method enabled the formation of photosensitive and high-quality rutile TiO₂ nanorods with few defects for future optoelectronic nanodevice applications.     

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).     

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.