A.S.M.A. Haseeb

Gas Sensors Based on One Dimensional Nanostructured Metal-Oxides: A Review

Recently one dimensional (1-D) nanostructured metal-oxides have attracted much attention because of their potential applications in gas sensors. 1-D nanostructured metal-oxides provide high surface to volume ratio, while maintaining good chemical and thermal stabilities with minimal power consumption and low weight. In recent years, various processing routes have been developed for the synthesis of 1-D nanostructured metal-oxides such as hydrothermal, ultrasonic irradiation, electrospinning, anodization, sol-gel, molten-salt, carbothermal reduction, solid-state chemical reaction, thermal evaporation, vapor-phase transport, aerosol, RF sputtering, molecular beam epitaxy, chemical vapor deposition, gas-phase assisted nanocarving, UV lithography and dry plasma etching. A variety of sensor fabrication processing routes have also been developed. Depending on the materials, morphology and fabrication process the performance of the sensor towards a specific gas shows a varying degree of success. This article reviews and evaluates the performance of 1-D nanostructured metal-oxide gas sensors based on ZnO, SnO2, TiO2, In2O3, WOx, AgVO3, CdO, MoO3, CuO, TeO2 and Fe2O3. Advantages and disadvantages of each sensor are summarized, along with the associated sensing mechanism. Finally, the article concludes with some future directions of research.

Response of Ti–6Al–4V and Ti–24Al–11Nb alloys to dry sliding wear against hardened steel

Titanium alloys have been of great interest in recent years because of their very attractive combination of high strength, low density and corrosion resistance. Application of these alloys in areas where wear resistance is also of importance calls for thorough investigations of their tribological properties. In this work, Ti–6Al–4V and Ti–24Al–11Nb alloys were subjected to dry sliding wear against hardened-steel counter bodies and their tribological response was investigated. A pin-on-disc type apparatus was used with a normal load of 15–45N and sliding speed of 1.88 ms−1. In the steady state, it was demonstrated that Ti–24Al–11Nb had a substantially higher wear resistance (about 48 times) than that of the Ti–6Al–4V alloy tested under a normal load of 45 N. Severe delamination is found to be responsible for the low wear resistance of Ti-6Al-4V. In the case of Ti–24Al–11Nb, two wear mechanisms have been suggested: delamination with a lower degree of severity and oxidative wear. It is thought that the ability of Ti–24Al–11Nb to form a protective oxide layer during wear results in a much lower wear rate in this alloy.

Effect of mechanical factors on tribological properties of palm oil methyl ester blended lubricant

Abstract The effects of mechanical factors viz. applied load and temperature on the tribological performance of 5% palm oil methyl ester (POME) blended lubricant were studied using a steel–cast iron pair. Wear and frictional measurements were made using a stationary steel ball and a reciprocating cast iron plate in a modified universal wear and friction testing machine. The test conditions were contact pressure, 400 MPa; mean contact velocity, 0.34 m/s; reciprocating stroke, 80 mm; loads, 100–1100 N (fixed temperature); and temperature, 40–140°C (fixed load). Wear scar surfaces were investigated using scanning electron microscopy (SEM) to understand the wear mechanisms involved. Analysis of post bench test lubricating oils was performed using an ISL viscometer and TAN/TBN analyzers to investigate the lubricating oil degradation properties. Results showed that at lower loads (up to 500 N) and temperatures (up to 100°C), the wear rates under 5% POME lubricant are lower, whereas at higher loads and temperatures, the wear rates are higher. The friction behavior of POME as an additive in commercial lubricant indicates the prevalence of the boundary lubrication regime. The viscosity test results showed that 5% POME can improve the viscosity index (VI) properties of mineral-based lubricant up to 500 N load. However, in this investigation, corrosive wear and pits on the damaged surface are the dominant wear mode at higher temperature.

Dual‐Bath Electrodeposition of Cu/Ni Compositionally Modulated Multilayers

The electrodeposition of Cu/Ni compositionally modulated multilayers with sublayer thickness in the nanometer range has been carried out. The deposition was conducted under galvanostatic conditions using dual-bath technique. The structure of the multilayers was characterized by scanning electron microscopy, and conventional and high resolution transmission electron microscopy. Cu/Ni multilayers with distinct and continuous sublayers in the range of 100 to < 5 nm can be produced by dual-bath electrodeposition. Cu and Ni sublayers grow epitaxially on top of one another. The local variation in the growth rate of copper leads to a faceted morphology of the multilayers. The extent of this faceting is reduced as the sublayer thickness is decreased. A surface reaction like oxidation during transfer of the substrate does not adversely affect the crystallographic continuity at the interfaces between sublayers. The thin-film formation is discussed based on available growth models.

Tribological behaviour of quenched and tempered, and austempered ductile iron at the same hardness level

Abstract The tribological behaviour of ductile iron heat-treated by two different procedures viz. quenching and tempering, and austempering to an identical matrix hardness of 445 KHN is compared. Wear tests were carried out using a pin-on-disc type apparatus under dry sliding conditions at a linear speed of 1.18 m s−1. Applied load and sliding distance in the range of 7.5–30 N and 2×104–6×104 m, respectively, were used. It was observed that under all test conditions, austempered ductile iron exhibits a better wear resistance than quenched and tempered ductile iron, although both have an identical chemical composition and matrix hardness. The relative superiority of austempered ductile iron becomes even more pronounced at higher load and longer sliding distance. Microhardness measurement below the wear scar reveals that the hardness of austempered ductile iron increases while that of quenched and tempered iron decreases during the wear process. Metallographic study of the worn surfaces and X-ray investigation on wear debris indicate that oxidational wear is operative in both the samples. Stress-induced martensitic transformation of retained austenite as well as strain hardening of bainitic ferrite are thought to contribute to the improved wear performance of austempered ductile iron.

Anodisation of copper in thiourea- and formamidine disulphide-containing acid solution.: Part I. Identification of products and reaction pathway

Abstract The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV–vis spectroscopy, XPS and EDAX analysis, and structural information on copper–thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range −0.30≤E≤0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)–thiourea soluble complexes, and Cu(I)–thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E≥0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced.

Enhanced Ethanol Gas Sensing Properties of SnO2-Core/ZnO-Shell Nanostructures

An inexpensive single-step carbon-assisted thermal evaporation method for the growth of SnO2-core/ZnO-shell nanostructures is described, and the ethanol sensing properties are presented. The structure and phases of the grown nanostructures are investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. XRD analysis indicates that the core-shell nanostructures have good crystallinity. At a lower growth duration of 15 min, only SnO2 nanowires with a rectangular cross-section are observed, while the ZnO shell is observed when the growth time is increased to 30 min. Core-shell hierarchical nanostructures are present for a growth time exceeding 60 min. The growth mechanism for SnO2-core/ZnO-shell nanowires and hierarchical nanostructures are also discussed. The sensitivity of the synthesized SnO2-core/ZnO-shell nanostructures towards ethanol sensing is investigated. Results show that the SnO2-core/ZnO-shell nanostructures deposited at 90 min exhibit enhanced sensitivity to ethanol. The sensitivity of SnO2-core/ZnO-shell nanostructures towards 20 ppm ethanol gas at 400 °C is about ∼5-times that of SnO2 nanowires. This improvement in ethanol gas response is attributed to high active sensing sites and the synergistic effect of the encapsulation of SnO2 by ZnO nanostructures.

Fretting wear of metallic multilayer films

Fretting wear behaviour of electrodeposited Cu/Ni multilayer films with 10 and 5 nm thick sublayers has been investigated against a hardened steel ball as the counter body and compared with that of the constituents, Cu and Ni. The wear tests were carried out by using a ball-on-flat geometry at a translation frequency of 8 Hz and slip amplitude of 100 μm. Friction force was recorded on line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy and energy dispersive X-ray microanalysis. It has been observed that the frictional and wear mechanisms are very different for copper, nickel and Cu/Ni multilayers. Fretting of copper creates a relatively smooth wear scar mainly by mechanical ploughing of the asperities on steel counterbody (abrasive wear) and shows a very little third body interaction. Fretting of nickel involves adhesive wear resulting in a large transfer of steel to nickel, which is attributed to the strong chemical interaction between nickel and the steel counterbody. Fretting on multilayers involves a strong third body interaction resulting in ploughing mainly by debris (abrasive wear). The coefficient of friction is approximately 0.45 for copper, and approximately 0.8 for nickel as well as for multilayers. The values of the coefficient of friction for nickel and Cu/Ni multilayers found under the present fretting conditions are approximately double the corresponding values reported earlier for sliding wear conditions. It has been found that Cu/Ni multilayer is more resistance to fretting wear than the constituents, copper and nickel. Furthermore, the fretting wear resistance of Cu/Ni multilayers with 5 nm thick sublayer is better than that of the multilayers with 10 nm thick sublayers.

Addition of cobalt nanoparticles into Sn‐3.8Ag‐0.7Cu lead‐free solder by paste mixing

Purpose – The purpose of this paper is to investigate the effects of addition Co nanoparticles on the characteristic properties of Sn‐3.8Ag‐0.7Cu solder.Design/methodology/approach – Cobalt (Co) nanoparticles were added to Sn‐Ag‐Cu solders by thoroughly blending various weight percentages (0‐2.0 wt%) of Co nanoparticles with near eutectic SAC387 solder paste. Blending was done mechanically for 30 min to ensure a homogeneous mixture. The paste mixture was then reflowed on a hot plate at 250°C for 45 s. The melting points of nanocomposite solder were determined by differential scanning calorimetry. Spreading rate of nanocomposite was calculated following the JIS Z3198‐3 standard. The wetting angle was measured after cross‐sectional metallographic preparation.Findings – No significant change in melting point of the solder was observed as a result of Co nanoparticle addition. The wetting angles of the solder increased with the addition of nanoparticles, while the spreading rate decreased. Although the wetting...

Anodisation of copper in thiourea-containing acid solution: Part II. In situ transversal imaging observations. Kinetics of anodic film growth

Abstract The formation of anodic films during the anodisation of copper, at different applied potentials E, in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea was investigated following the corroding electrode profile by on line in situ imaging. For E 0.07 V, the main reactions are the electro-decomposition of formamidine disulphide and Cu(I)–thiourea complexes yielding a copper sulphide-containing film (film II) and the electrodissolution of copper as aqueous Cu(II) ions through film II. The relative contribution of these processes depends on thiourea concentration in the solution, the applied electric potential and anodisation time. The growth kinetics of films I and II were determined from the evolution of the average film height 〈h〉 obtained from in situ imaging. The kinetics of film I fit a parabolic rate law, whereas those of film II approach a linear 〈h〉 versus anodisation time relationship. The rupture of film II assists the localised corrosion of copper. Likely physical mechanisms for the formation of these anodic films are discussed.