Novel method for fabrication of room temperature polypyrrole–ZnO nanocomposite NO2 sensor

Nanocomposites of polypyrrole (PPy) and zinc oxide (ZnO) nanoparticles (NPs) were prepared by spin coating method. These nanocomposites were characterized by Fourier transform infrared (FTIR), Field emission scanning electron microscope (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis techniques, which proved the polymerization of pyrrole monomer and the strong interaction between polypyrrole and ZnO NPs. The nanocomposites were used for gas sensing to CH₃OH, C₂H₅OH, NH₃, H₂S and NO₂ at room temperature. It was revealed that PPy–ZnO nanocomposites with different ZnO weight ratios (10%, 20%, 30%, 40% and 50%) could detect NO₂ at low concentration with very higher selectivity and sensitivity at room temperature than the reported PPy. The PPy–ZnO nanocomposites responded to NO₂ at concentration as low as 10 ppm. PPy–ZnO nanocomposite containing ZnO (50%) showed the maximum sensitivity 38% with 92.10% stability to 100 ppm NO₂ gas at room temperature. The sensing mechanism of PPy–ZnO nanocomposites to NO₂ was presumed to be the effects of p–n junction between PPy and ZnO.     

Environmental scanning electron microscope observations of H2S attack on the protective oxide on an Ni-Fe alloy

Protective oxide layers on metals are frequently attacked by corroding agents. In this study, the attack of H₂S on the protective oxide on 60 wt-%Ni-40 wt-%Fe was studied. The oxide layer was prepared in a UHV system and the sulphidation was done in an environmental scanning electron microscope at an elevated temperature. The single crystal Ni-Fe sample had a (100) surface which was oxidized by O₂ exposure at about 800 K to produce an epitaxial Fe₂O₃ film. The breakup of the oxide was found to begin by pitting along surface features which are believed to correspond to atomic steps or step bunches. The areas where the oxide was more uniform were found to show better resistance toward the sulphidation.     

Effects of carbon content on the high temperature friction and wear of chromium carbonitride coatings

Chromium nitride-based coatings are often used in application at high temperature. They possess high wear and oxidation resistance; however, the friction coefficient is typically very high. Therefore, we doped CrN coatings by carbon with the aim to improve tribological properties at elevated temperature, particularly to lower the friction. CrCN coatings were prepared by cathode arc evaporation technology using constant N₂ flow and variable C₂H₂ flow. The coatings with a thickness of 3-4 μm were deposited on hardened steel substrates and high-temperature resistant alloy. The carbon content varied from 0 at.% (i.e. CrN) up to 31 at.%. The standard coating characterization included the nano-hardness, adhesion, chemical composition and structure (including hot X-ray diffraction). Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 700 °C. The coatings with carbon content 12-31 at.% showed almost identical tribological behaviour up to 700 °C.     

Effect of CuO as a dopant in TiO2 on ammonia and hydrogen sulphide sensing at room temperature

The heterogeneous nanocomposites of CuO doped TiO₂ nanoparticles were synthesized using sol gel method by varying the concentration of CuO as 0.1, 0.5 and 1 mol% for the sensing of ammonia and hydrogen sulphide. The substitutional doping of CuO in TiO₂ matrix was confirmed by the X-ray diffraction. Average crystallite size of the doped nanocomposites was found to reduce with increase in concentration of CuO. The 0.1 mol% CuO doped TiO₂ nanocomposites showed highest sensitivity to ammonia (97%) with response time of 2 s, while 1 mol% was selective to H₂S gas (77%) with response time of 45 s for 50 ppm of each gas at room temperature.     

Comparison of various C2Hx for high‐temperature lubrication by in situ pyrolysis

The ability of directed streams of three representative hydrocarbon gases ‐ acetylene C₂H₄, ethylene C₂H₄, and ethane C₂H₆ ‐ to provide extended‐duration lubrication to high‐temperature sliding contacts via surface deposition of pyrolytic carbon has been demonstrated. One order‐ and two order‐of‐magnitude reductions in friction coefficient and wear rate of self‐mated silicon nitride sliding contacts can be realised by this technique. The ability of these gases to provide ‘adequate’ lubrication at high temperature is illustrated through mapping the normal load/temperature/precursor flow rate space over which reduced friction may be maintained. Acetylene was the most effective precursor for pyrolytic carbon deposition, providing adequate lubrication over the broadest range of normal load/temperature/flow rate combinations, while ethane was the least effective. The boundary of the regions of adequate lubrication represents the locus of contact conditions with equal rates of lubricious carbon deposition and removal by wear. The shape of this boundary, as explored in the mapping study, supports a proposed model in which the removal rate is proportional to the product of normal load and sliding speed, while the deposition rate is proportional to the product of precursor flow rate and an Arrhenius temperature dependence.     

Differences between nanoscale structural and electrical properties of AZO:N and AZO used in polymer light‐emitting diodes

Conducting atomic force microscopy and scanning surface potential microscopy were adopted to investigate the nanoscale surface electrical properties of N‐doped aluminum zinc oxide (AZO:N) films that were prepared by pulsed laser deposition (PLD) at various substrate temperatures. Experimental results demonstrated that when the substrate temperature is 150°C and the N₂O background pressure is 150 mTorr, the N‐dopant concentration on the surface is optimal. In addition, the root‐mean‐square roughness value of the film surface, the low contact current (<400 nA) conducting region as a percentage of the total area, and the mean work function value are 1.43 nm, 96.9%, and 4.88 eV, respectively, all of which are better than those of the optimal AZO film made by PLD. This result indicates that N‐doped AZO films are better for use as window materials in polymer light‐emitting diodes. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.     

Antibacterial activity of glass ionomer cement modified by zinc oxide nanoparticles

This study evaluated the antibacterial activity of zinc oxide nanoparticles incorporated into self‐cured glass ionomer cement (GIC) and light‐cured resin‐reinforced GIC on Streptococcus mutans biofilm. The GICs, Fuji II (GC America) and Fuji II LC (GC America), were incorporated with nanoparticles at concentrations of 0%, 1%, and 2% by weight, and the biofilm maturation time was one and seven days. Circular specimens of each GIC type were prepared. The antibacterial activity was evaluated by determining the number of colony forming units of S. mutans strain per milliliter. Morphology of the biofilm was analyzed by scanning electron microscopy (SEM). The data obtained for each GIC were analyzed by two‐way ANOVA (α = 5%). For chemically activated GIC, no significant difference was observed in relation to the time of biofilm maturation (p = 0.744), concentration of nanoparticles (p = 0.966), and their interaction (p = 0.800). The results from analysis of GIC modified by light‐polymerized resin showed that only of the maturing time significantly affected the number of adhered cells on the biofilm (p = 0.034, F = 4.778). The more mature the biofilm, higher the number of cells. SEM analysis showed no change in cell morphology in relation to the type of GIC, maturation time, and nanoparticles concentration. We conclude that the inclusion of zinc oxide nanoparticles at concentrations of 1% and 2% by weight into the GICs evaluated here, did not promote their antimicrobial activity against S. mutans.     

Novel method for fabrication of polyaniline-CdS sensor for H2S gas detection

In this paper, we report on the performance of a H₂S sensor based on polyaniline-CdS nanocomposites fabricated by a simple spin coating technique. The nanocomposites showed the sensitivity to H₂S gas at room temperature (300 K). The resistance of polyaniline-CdS nanocomposites showed a considerable change when exposed to various concentrations of H₂S. Maximum response up to 48% was achieved for 100 ppm H₂S for PANi-CdS sensor. Depending on the concentration of H₂S, the response time was in the range of 41 and 71 s, whereas the recovery time was in the range of 345-518 s.     

Influence of Mg doping on the morphology and optical properties of ZnO films for enhanced H2 sensing

Highly oriented ZnO and Mg doped ZnO thin films were fabricated on Al₂O₃ substrate by sputtering at room temperature. The effect of Mg doping on the structural, optical, and morphological properties of ZnO film was investigated. The intensity of (002) peak in X‐ray diffraction measurements revealed the influence of Mg doping on the crystallinity and orientation of ZnO film. Photoluminescence (PL) results show that the Ultraviolet (UV) emission peak was shifted to lower wavelength side for Mg:ZnO film indicating the possibility for quantum confinement. UV–vis–NIR optical absorption revealed an improvement in optical transmittance from 70 to 85%, and corresponding optical band gap from 3.25 to 3.54 eV. Atomic force microscope (AFM) images revealed the nano‐size particulate microstructure of the films. The surface topography of Mg doped ZnO film confirmed decreased grain size with large surface roughness and increased surface area, favorable for sensing. Pure ZnO and Mg doped ZnO film were used as active layer and tested for its sensing performance to hydrogen. Compared to undoped ZnO, 22 at.% Mg doped ZnO film showed much higher sensor response to H₂ at a concentration as low as 200 ppm and at a lower operating temperature of 180°C. A linear sensor response was observed for H₂ concentration in the range of 100–500 ppm. Microsc. Res. Tech. 76:1118–1124, 2013. © 2013 Wiley Periodicals, Inc.     

Heat and mass transfer enhancement of the bubble absorption for a binary nanofluid

The main objective of this study is to enhance the heat and transfer process of absorption using the nanofluids as the working medium. Carbon nanotubes—ammonia nanofluids (the binary nanofluids) are prepared. The thermal conductivity of the binary nanofluids and the bubble absorption process enhancement are examined experimentally. The results show the thermal conductivity of the carbon nanotubes—ammonia nanofluid is higher 16% than that of NH₃/H₂O solution. And the carbon nanotubes—ammonia nanofluid has a great enhanced effect to the NH₃/H₂O absorption.     

System development and analysis for producing high quality gas and activated sludge char

For energy and resource utilization of dried sewage sludge, an integrated system with in-line connection of pyrolysis gasifier, plasma reformer, and fixed bed adsorber was developed. The plasma reformer was set to improve producer gas yield by destructing tar released from the pyrolysis gasifier. The fixed bed adsorber filled with the sludge char produced from the pyrolysis gasifier was installed for adsorption of un-treated tar. The pyrolysis gasifier produced sludge char, tar and gas. The sludge char showed 98.1 m²/g of specific surface area and 63.49 Å of mean pore size, which had a good distribution of micropore and mesopore with superior adsorption rate of light PAH tar. The concentrations of gravimetric tar and total light tar were 26.3 g/Nm³ and 10.9 g/Nm³, respectively. The analyzed light tar was in the order of benzene, naphthalene, benzonitrile, benzeneacetonitrile, anthracene and pyrene. Produced gas was composed of hydrogen, carbon monoxide, methane, and carbon dioxide. The plasma reformer displayed 83.2% of removal efficiency with 4.4 g/Nm³ of gravimetric tar at the outlet due to tar cracking and steam reforming reaction. The total amount of light tar was 1.3 g/Nm³. Among the reforming gas, the concentration of hydrogen, carbon monoxide, and methane was increased. Gravimetric tar at the outlet of the adsorber was 0.5 g/Nm³, which was 88.6% of removal efficiency. The total amount of light tar was 0.39 g/Nm³. Gas analysis results at the exit showed 50.5% H₂, 21.9% CO, 10.5% CH₄, 7.7% CO₂ and 0.1% C₂H₂ with a higher heating value of 13,482 kJ/Nm³. Therefore, sewage sludge can be converted into energy and resource by pyrolysis and gasification since the producer gas and sludge char could be utilized in a heat engine and adsorption tower for tar removal, respectively.

     

Effects of Adsorption of Some Surfactants on Antiwear Properties

The adsorption of organic polar compounds onto iron sulfide and onto iron oxide was investigated using a flow microcalorimeter. The effects of a combination of an iron sulfide surface and surfactants on wear were examined in air and argon atmospheres using a ball-on-dish friction machine. The polar interaction and reactivity between organic polar compounds and iron sulfide are important functions for wear reduction. This was shown from the results obtained in the measurement of the heat of adsorption, amount of adsorption, heat of desorption and iron content in the desorption solution. The adsorption of stearic acid on the steel ball sulfidized in H₂S reduced wear significantly in the air atmosphere. Surfactants contribute considerably to wear reduction when used with sulfur EP additives which form an iron sulfide film.     

Synergistic effects between sulfurized W-DLC coating and MoDTC lubricating additive for improvement of tribological performance

Low temperature ion sulfuration technology was used to obtain sulfurized layer on W doped diamond-like carbon (W-DLC) coating. The tribological behaviors of the pure W-DLC and sulfurized W-DLC coatings were investigated under PAO and MoDTC lubrication conditions. It shows that sulfurized W-DLC coatings can obviously improve their tribological performances under PAO with MoDTC lubrication. The primary reason is due to the formation of WS_x on the surface of sulfurized W-DLC coating, the decomposition of additives for formation a higher ratio of Mo sulfide/Mo oxide and the graphitization for a high ratio of sp²/sp³.     

A molecular-beam study of the tribological chemistry of carbon tetrachloride on oxygen-covered iron

Dc molecular-beam methods are used to examine the reactivity of carbon tetrachloride with oxide films grown on iron in ultrahigh vacuum. The incident CCl₄ beam flux is sufficiently low that the nature of the surface oxide is dictated by the annealing temperature allowing the reactivity of Fe₂O₃, Fe₃O₄ and FeO films to be examined. Carbon tetrachloride reacts rapidly with Fe₂O₃ and reaction with Fe₃O₄ commences at 620 K to evolve CO. The activation energy for this process is 20.6±1.0 kcal/mol. CCl₄ reacts with FeO above 790 K, also to evolve CO, and the activation energy for this reaction is 5.7±0.4 kcal/mol. X-ray photoelectron spectroscopy shows the formation of a halide after reaction at 900 K. These results are in accord with film-growth kinetics measured using a microbalance at high pressures, where it was found that it was not necessary to remove the oxide layer prior to reaction. This contrasts with the behavior of sulfur-containing molecules, where the oxide layer had to be removed before a film would grow. This effect may contribute to the additive synergies commonly found in extreme-pressure lubricant additives where one of the roles of the chloride may be to reduce the oxide layer.     

A single crystal of YALO3: Ce3+ as a fast scintillator in SEM

A new single-crystal scintillator intended for applications in a scanning electron microscope (SEM) is presented. It is a single-crystal disc of yttrium aluminium perovskite activated by trivalent cerium free of traces of Fe ions. The single crystals of YAlO₃: Ce³⁺ (YAP: Ce³⁺) were prepared by the Czochralski method in a reducing atmosphere of Ar and H₂ with an excess amount of Y³⁺ ions. Effective methods of purification and purity control of the raw material are described. The highest achievable concentration of Ce³⁺ ions in as grown crystals amounted to 0.3 wt%, concentration in the melt was 8–9 times higher. The best properties were found with samples of the maximum possible concentration of Ce³⁺. Compared with the previous aluminate Y₃ Al₅ O₁₂: Ce³⁺ (YAG: Ce³⁺) these samples showed higher efficiency, a shorter decay time of luminescence (40 ns) and an emission band in a more advantageous spectral region (378 nm). Because of high resistance to radiation damage, high chemical resistance and applicability to ultra-high vacuum it is also suitable for detection of other kinds of ionizing radiation.     

Modelling and experimental investigations of thin filmsof Mg phosphorus‐doped tungsten bronzes obtainedby ultrasonic spray pyrolysis

In this study, the synthesis of thin films of Mg phosphorus doped tungsten bronzes (MgPTB; MgHPW₁₂O₄₀·29H₂O) by the self‐assembly of nano‐structured particles of MgPTB obtained using the ultrasonic spray pyrolysis method was investigated. As the precursor, MgPTB, prepared by the ionic exchange method, was used. Nano‐structured particles of MgPTB were obtained using the ultrasonic spray pyrolysis method. The nano‐structure of the particles used as the building blocks in the MgPTB thin film were investigated experimentally and theoretically, applying the model given in this article. The obtained data for the mean particle size and their size distribution show a high degree of agreement. These previously tailored particles used for the preparation of thin films during the next synthesis step, by their self‐assembly over slow deposition on a silica glass substrate, show how it is possible to create thin MgPTB films under advance projected conditions of the applied physical fields with a fully determined nanostructure of their building block particles, with a relatively small roughness and unique physical properties.     

Effects of pH and Oxidizer on Chemical Mechanical Polishing of AISI 1045 Steel

AISI 1045 steel has been widely used as the substrate for thin film deposition. In some cases, an ultra-smooth surface of AISI 1045 steel is needed and is even indispensible for the satisfactory deposition of thin film. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth surface of AISI 1045 steel. The effects of pH and H₂O₂ on the polishing performance of AISI 1045 steel were investigated. It is revealed that, with the increase of pH, the material removal rate (MRR) and the static etching rate (SER) of AISI 1045 steel gradually decrease due to the formation of passive iron oxides on the top surface, and thus the surface quality gradually improves. At pH 4.00, with the addition of H₂O₂, the SER of AISI 1045 steel is further suppressed; while the MRR of AISI 1045 steel first dramatically increases due to the formation of porous iron oxides with relatively low mechanical strength on the surface when the H₂O₂ concentration increases from 0 to 0.01 wt%, and then decreases since the porous iron oxides gradually grow compact when the H₂O₂ concentration further increases. The increase of the compactness of the iron oxides might be attributed to the crystallization of γ-FeOOH into α-FeOOH and even into α-Fe₂O₃ and the resulting polymerization of the amorphous iron oxides.     

The surface chemistry of alkyl and arylphosphate vapor phase lubricants on Fe foil

The surface chemistry of tributylphosphate (TBP) and tricresylphosphate (TCP) on a polycrystalline Fe surface was studied using temperature programmed reaction spectroscopy and Auger electron spectroscopy to illustrate some of the initial steps in the reaction mechanisms of alkyl and arylphosphate vapor phase lubricants. During heating, TBP [(C₄H₉O)₃P=O] adsorbed on the Fe surface decomposes via C–O bond scission to give butyl surface intermediates [C₄H₉–] that react via β-hydride elimination to desorb as 1-butene [CH₃CH₂CH=CH₂] and H₂ without appreciable carbon deposition onto the surface. The thermal decomposition of 1-iodobutane [I-C₄H₉] on Fe was observed to proceed via the same β-hydride elimination mechanism. In contrast to tributylphosphate, meta-tricresylphosphate (m-TCP) [(CH₃–C₆H₄O)₃P=O] decomposes on Fe via P–O bond scission to produce methylphenoxy intermediates [CH₃–C₆H₄O–]. During heating to 800 K, methylphenoxy intermediates either desorb as m-cresol [CH₃–C₆H₄–OH] via hydrogenation or decompose further to generate tolyl intermediates [CH₃–C₆H₄–]. Some of the tolyl intermediates desorb as toluene [CH₃–C₆H₅] via hydrogenation but the majority decompose resulting in H₂ and CO desorption and carbon deposition onto the Fe surface. The P–O bond scission mechanism of m-TCP was verified by showing that the temperature programmed reaction spectra of m-cresol yield products that are almost identical to those of m-TCP. These results provide insight into the origin of the differences in the performance of alkyl and arylphosphates as vapor phase lubricants. The alkylphosphates decompose via alkyl intermediates that readily undergo β-hydride elimination and desorb into the gas phase as olefins, thus removing carbon from the surface. In contrast, the arylphosphates generate aryloxy intermediates by P–O bond scission and aryl intermediates by further C–O bond scission. Neither of these intermediates can undergo β-hydride elimination and thus they decompose to deposit carbon onto the Fe surface. The higher efficiency for carbon deposition may be the primary reason for the superior performance of the arylphosphates over alkylphosphates as vapor phase lubricants.     

单层MoS2和WS2的太赫兹近场显微成像研究

采用太赫兹散射式扫描近场光学显微镜(THz s-SNOM)研究了化学气相沉积法制备的单层MoS₂和WS₂晶粒的太赫兹近场响应。在没有可见光激发时,未探测到可分辨的太赫兹近场响应,说明晶粒具有较低的掺杂载流子浓度。有可见光激发时,由于光生载流子的太赫兹近场响应,能够测得与晶粒轮廓完全吻合的太赫兹近场显微图。在相同的光激发条件下,MoS₂的太赫兹近场响应强于WS₂,反映了两者之间载流子浓度或迁移率的差异。研究结果表明,THz s-SNOM兼具超高的空间分辨率和对光生载流子的灵敏探测能力,对二维半导体材料和器件光电特性的微观机理研究具有独特的优势。