Surface Review and Letters

This research work is an insight into the various properties of liner materials utilized in landfill sites to control the leachate. Although expansive clay soil is inorganic, it is problematic. The soil owes this aspect to erratic fluctuations in its behavior due to the movement of water. Urbanization, increase in population and industries generate enormous amounts of waste in different forms. Disposal of these wastes in the landfill without any scientific manner creates a major problem to the surrounding soil and groundwater. In this study, an attempt was taken to identify the effect of soil properties and groundwater quality due to the continuous generation of leachate in the dumping sites. To prevent such an environmental problem, highly impermeable sand–bentonite mixture is used as a liner material in the waste disposal sites. Therefore, various mixtures of sand–bentonite were prepared by varying sand contents and different sieve sizes, i.e. 2–0.075mm; 2–0.425mm and 0.425–0.075mm were used. And also to improve the strength and hydraulic conductivity of the liner materials, discrete random fiber is mixed with various proportions to these mixtures and examined.

Long tool life and high material removal rate (MRR) are the two essential requirements in rough cutting of materials. The rapid rate of the flank wear propagation in machining of nickel-based superalloys has induced the utilization of low cutting parameters when the goal was set to maximize the tool life based on the machining time or cutting length. However, this method may not provide an effective rate for the material being cut. This work presents two mathematical models to find the optimum cutting parameters results for the minimum flank wear and maximum MRR. Experimental tests were carried out based on the central composite design (CCD) in rough cutting of Inconel 625 by using TiAlN-coated insert. Maximum flank wear was measured to determine the tool wear propagation. The wear mechanisms which contribute in the tool wear were analyzed by using scanning electron microscope (SEM) to evaluate the effects of cutting parameters on the flank wear propagation. The results showed that cutting speed and depth of cut had the most significant effect on the tool wear. However, optimum cutting condition was achieved by reducing the cutting speed when feed rate and depth of cut maintained at the highest level. This was associated to the interaction of cutting speed and depth of cut, and predominant of abrasion and notching at their highest levels, respectively.

Carbon-doped titania (C:TiO₂) films were prepared by reactive magnetron sputtering using CO₂ as a carbon source. The as-prepared films were annealed at different temperatures in vacuum condition. A TiO₂ film using O₂ gas was also prepared for comparisons with C:TiO₂. The structure and composition of the as-prepared, the TiO₂ films and the annealed C:TiO₂ films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy, whereas the surface morphology of the C:TiO₂ films was measured by atomic force microscopy. Furthermore, photocatalytic properties of the films were evaluated by the degradation of methyl orange (MO). The results indicate that the photocatalytic property was improved when carbon was doped into TiO₂ films, and the C:TiO₂ films consist of anatase and TiO phases. The experimental results of the MO’s degradation confirm that the annealing process at various temperatures can modify the surface morphology of the films and the content of oxygen vacancies in the films. Consequently, the variations in surface topography and oxygen vacancy potentially enhance the photocatalytic activity of TiO₂ films.

Nanoscale dimples and periodic corrugations are observed on the fracture surface of Zr-based bulk metallic glass composite (BMGC). The nanoscale periodic corrugations display a curved shape, which is different from that observed in previous works. In addition, the crystallization behavior of ${\text{Zr}}_{64.13}$${\text{Cu}}_{15.75}$${\text{Ni}}_{10.12}$${\text{Al}}_{10}$ BMG was investigated. The second crystallization event of Zr-Cu-Ni-Al BMG can be controlled by annealing or tuning cooling rate. The in situ Zr-based BMGC was prepared via lowering cooling rate. The Zr-based BMGC displays completely brittleness.

Three different types of current-collecting plates for air-hydrogen PEM fuel cell were manufactured and tested: unmodified titanium plates; gold-plated titanium plates and titanium plates treated by carbon ions implantation. It was shown that the applied surface modifications reduce contact resistance between titanium plate and carbon gas diffusion layer. Total ohmic resistance of fuel cell is reduced by 1.8 and 1.4 times in case of gold-plated titanium and carbon-implanted titanium, respectively, in comparison with uncoated titanium. Although gold plating turned out to be more profitable than carbon ion implantation in terms of electrical characteristics, in the last case, the performance enhancement was reached without using precious metals, which at mass production must play more important role. This technology promises to reduce the cost of bipolar plates manufacturing, while maintaining high electrical performance of PEM fuel cells.

A unique method of preparing TiO₂/sericite composite particles material was investigated by coating anatase TiO₂ on the surface of sericite via chemical precipitation method. The results of X-ray diffraction, scanning electron microscope, infrared spectra and X-ray photoelectron spectroscopy indicated that TiO₂ coated uniformly on the surface of sericite, and Si-O-Ti chemical bonds are formed during the thermal treatment process. The hiding power of Ti/SE-CPM composite is up to 85% of TiO₂ white pigments, and the oil absorption value was equal to TiO₂ white pigments. All these data demonstrated that the obtained Ti/SE-CPM samples have similar excellent properties compared with anatase TiO₂ white pigments. Therefore, this study provides a feasible way of reducing the usage of TiO₂ while maintaining similar pigment properties, which, of course, will reduce the cost, protect our environment and has a potential application in large-scale production of white pigments.

Hierarchical heterostructure of rutile TiO₂ nanoflower array on anatase TiO₂ sheet was fabricated by a two-step method. Anatase TiO₂ sheet was synthesized by a modified dip coating method, followed by the formation of rutile TiO₂ nanoflower array via a wet chemical route. Studies by X-ray diffraction and scanning electron microscopy indicated the formation of hierarchical heterostructure. Tests on degradation of methylene blue under UV light illumination showed that the hierarchical TiO₂ film exhibited superior photocatalytic performance to those with monophased anatase and rutile TiO₂ films and commercial P25 film. It was attributed to efficient separation of photogenerated charge carriers and prevention of the unfavorable multiple electron transfer on biphase interface. Investigation on the influence of addition of scavengers on photocatalysis suggested that hydroxy radicals and superoxide anion radicals dominated the photocatalytic degradation of MB. The hierarchical TiO₂ film exhibited excellent photocatalytic stability in cycling tests.

In this paper, a symmetrical MIM tunnel junction diode with a novel material combination, vanadium–vanadium sequioxide–vanadium (V–V₂O₃–V) is fabricated and electrically characterized. Analysis of the measured current-voltage ($I$–$V)$ characteristics of the fabricated MIM diode revealed an ultra-high diode sensitivity of $-$9.24${\text{V}}^{-1}$ at an applied bias of $-$0.104V. Based on the measured $I$–$V$ characteristics, theoretical predictions were performed showing that the diode’s dynamic resistance can be tuned for matching to coupled antennas, in rectenna structures, whilst maintaining high levels of sensitivities using practically realizable V₂O₃ insulator thicknesses.

In this paper, we present a new method that is capable of manufacturing microfluidic chips of polymethyl methacrylate (PMMA) rapidly and cheaply. This technique, which we call Tape adhering-Laser Cutting and Sealing Integration (TLCSI), only utilizes a CO₂ laser and a piece of double-sided tape to produce a microfluidic chip in several minutes. It only has three main steps. First, the double-sided tape sticks to the surface of a PMMA substrate. Second, the microchannel should be cut on the surface of the double-sided tape. At last, a PMMA cover plate with liquid pools is pressed onto the surface of the double-sided tape and a CO₂ laser is used to cut edges of the chip for sealing the chip. We present a qualified microfluidic chip with regular microchannels and sealing strength of 1.2Mpa. Compared with most current fabrication methods, TLCSI is a quick and cost-effective way to produce microfluidic chips of PMMA.

Nickel oxide nanoparticles (NiO NPs) were synthesized through template free sol–gel method. Synthesized particles were calcined at 300^∘C, 500^∘C and 700^∘C for 2h and further the particles were characterized for its thermal, functional, structural, morphological and optical properties. The peak broadening analysis was undertaken in order to calculate the variation in size and strain components of the particles with the calcinations temperature. The Debye–Scherer, Williamson–Hall and Size-strain plot methods were employed in peak broadening analysis and were compared with TEM results. All the NiO NPs crystallite size and lattice strain value were found to be in good agreement with all the models. The TEM analysis revealed that the calcinations at 700^∘C NiO NPs have sphere like structure of less than 20nm particles size value. The strong peak observed at 360.5nm bandgap emission relates to the bandgap of 3.44eV which is because of the near band edge emission.

In this paper, first we investigate the heating-responsive shape memory effect in an acrylonitrile butadiene styrene (ABS). Subsequently, after surface treatment (via dipping in acetone/water solution of different concentrations and for different dipping time) of pre-stretched samples, we demonstrate the feasibility to form strip shaped wrinkles atop the surface upon heating of pre-stretched ABS for shape recovery. The influential factors, such as acetone concentration and dipping time in surface treatment, are revealed and discussed.

The Au/Ti/HfO₂/$n$-GaAs metal/insulating layer/semiconductor structures have been fabricated using standard thermal atomic layer deposition. We experimentally showed whether or not the HfO₂ interfacial layer grown on the $n$-GaAs wafer modifies the barrier height (BH) of the device at the room temperature. Besides, we investigated the measurement based on temperature dependence of the device parameters from the current–voltage ($I$–$V$) characteristics of the diode in 60–400K range with steps of 10K. The X-ray photoelectron spectroscopy (XPS) have been carried out to characterize the surfaces of both $n$-GaAs wafer and HfO₂ thin films. The series resistance value from the temperature-dependent $I$–$V$ characteristics decreased with decreasing temperature, which is a desired positive result for the devices developed from the MOS capacitor. The BH value of 0.94eV (300K) has been obtained for the device with the HfO₂ layer which is a higher value than the value of 0.77eV (300K) of the device without HfO₂ layer. Therefore, we can say that the HfO₂ thin layer at the metal/GaAs interface can also be used for the BH modification as a gate insulator for GaAs MOS capacitor and MOSFETs. When the temperature-dependent $I$–$V$ characteristics at low temperatures have been considered, it has been observed that the current prefers to flow through the lowest BHs due to the BH inhomogeneities.

A low-temperature hydrothermal method was developed to synthesize red phosphor lanthanum molybdate doped with ${\text{Eu}}^{3+}$ ions. SEM, XRD, FTIR, Raman, UV–Vis DRS and photoluminescence patterns were employed to characterize information of the sample’s morphologies, phase structure and properties. The calcination temperature was determined by TG-DTA results. Thorough energy transfer happened between ${\text{Fe}}^{3+}$ ions and phosphors in water solution. So, the prepared materials provide an excellent sensing platform for ferric ions, which have potential applications in biotechnology and environmental protection.

The composites were obtained by the argon-arc cladding (AAC) of the Deloro22-Si₃N₄-Fe pre-placed powders on a TA1 titanium alloy substrate, which improved the wear resistance of the substrate. Such composites were investigated by means of the scanning electron microscope (SEM), the microscope and the high resolution transmission electron microscope (HRTEM). The results indicated that the amorphous phases were produced in such AAC composites, increasing the wear resistance. With addition of Y₂O₃, lots of the micro/nanoscale particles were formed, which further improved the wear resistance of such AAC composites.

In order to improve the mechanical compatibility and cytocompatibility of titanium implants, tantalum coatings were prepared using plasma spraying technology. Tantalum coatings have been deposited via atmospheric plasama spraying (APS) and vacuum plasma spraying (VPS) methods, and then their morphologies, porosities, bonding strengths and elastic modulous were investigated. In vitro cytocompatibility of the two coatings was evaluated via human bone marrow stromal cells (hBMSCs). The results show that oxidation phenomenon was observed for the APS tantalum coatings, while less oxidation was found in the VPS tantalum coatings. Compared with APS tantalum coatings, the VPS tantalum coatings have a more compact microstructure and less impurity content, resulting in a better bonding with the titanium substrate. VPS tantalum coatings were measured to have a lower elastic modulus and a higher hardness than APS Tantalum coatings. Electrochemical corrosion of the coatings were examined and the VPS tantalum coating showed improved chemical stability. Besides, bone marrow stem cells (BMSCs) adhere to and spread well on the surface of both VPS and APS tantalum coatings without significant difference. The proliferation rate of BMSCs is higher on VPS tantalum coating surface than on APS tantalum coatings. Our results suggest that VPS tantalum coatings are more suitable for the application of surface modification of titanium implant due to their lower elastic modulus and better chemical stability for higher mechanical compatibility and cytocompatibility.

In this paper, the development and the formation of the mild steel immersed in seawater that covered with enamel coating are investigated. The wire beam electrode (WBE) was applied to evaluate pitting corrosion and local inhomogeneous corrosion that happened on the coated surface of metal substrate. This method can obtain Maps that can show corrosion potential and galvanic current distributions and the specific values can be calculated from the WBE surface that was covered by enamel coating. Corrosion potential–current and electrochemical noise were successfully measured by using a WBE scanner and electrochemical workstation. This new linkage-test method means that the combined WBE-$R_n$ has ability to characterize and analysis the process of enamel coating failing more accurately [Ref. 1; Ref. 2; Ref. 3; Ref. 4]. To some extent, the method can also predict the tendency and location of corrosion occurring. It was found that the coating has a good protective effect on the surface of the metal substrate because the corrosion potential is very positive and the corrosion current is very small. At the same time, in the course of the test, the distribution of the anode current is heterogeneous, as time increases, the original single anode current region gradually expands and is connected with the other anode regions in the final. In addition, corrosion often occurs at the boundary of the electrode (WBE) and then to the central area.