Applied Surface Science (v.298, #C)

Corrosion resistance of siloxane–poly(methyl methacrylate) hybrid films modified with acetic acid on tin plate substrates: Influence of tetraethoxysilane addition by S.R. Kunst; H.R.P. Cardoso; C.T. Oliveira; J.A. Santana; V.H.V. Sarmento; I.L. Muller; C.F. Malfatti (1-11).
The aim of this paper is to study the corrosion resistance of hybrid films. Tin plate was coated with a siloxane–poly (methyl methacrylate) (PMMA) hybrid film prepared by sol–gel route with covalent bonds between the organic (PMMA) and inorganic (siloxane) phases obtained by hydrolysis and polycondensation of 3-(trimethoxysilylpropyl) methacrylate (TMSM) and polymerization of methyl methacrylate (MMA) using benzoyl peroxide (BPO) as a thermic initiator. Hydrolysis reactions were catalyzed by acetic acid solution avoiding the use of chlorine or stronger acids in the film preparation. The effect of the addition of tetraethoxysilane (TEOS) on the protective properties of the film was evaluated. The hydrophobicity of the film was determined by contact angle measurements, and the morphology was evaluated by scanning electron microscopy (SEM) and profilometry. The local nanostructure was investigated by Fourier transform infrared spectroscopy (FT-IR). The electrochemical behavior of the films was assessed by open circuit potential monitoring, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements in a 0.05 M NaCl solution. The mechanical behavior was evaluated by tribology. The results highlighted that the siloxane–PMMA hybrid films modified with acetic acid are promising anti-corrosive coatings that acts as an efficient diffusion barrier, protecting tin plates against corrosion. However, the coating properties were affected by the TEOS addition, which contributed for the thickness increase and irregular surface coverage.
Keywords: Tin plate; Hybrid organic–inorganic film coatings; Acetic acid; TEOS; EIS; Corrosion resistance;

Characteristics of microstructure and fatigue resistance of hybrid fiber laser-MIG welded Al–Mg alloy joints by Shaohua Yan; Yuan Nie; Zongtao Zhu; Hui Chen; Guoqing Gou; Jinpeng Yu; Guiguo Wang (12-18).
In this study, the microstructures, mechanical properties and fatigue strengths of the hybrid laser-MIG welded joints were investigated. The detailed microstructures of the hybrid welded joints were carried out using OM and TEM. The causes of the strengths loss of the hybrid welded joints were studied from aspects of solute strengthening, precipitates hardening, and grain boundary strengthening. The fatigue strengths of the hybrid welded joints, MIG welded joints, and base metals were investigated. The results showed that the fatigue strength of the hybrid welded joints was better than that of the MIG welded joint. The conditional fatigue strength (N f  > 107) of the hybrid welded joints could reach up to 84.6% of the base metal's conditional fatigue strength (130 MPa). The fatigue fracture surfaces were examined by SEM, and the result showed that the main reason for the decrease of the fatigue strength was porosity.
Keywords: Hybrid welding; Aluminum alloy; TEM; Fatigue;

Environmental pollution has an evidently adverse impact on the buildings that are constructed by the glass fiber reinforced cement (GRC) materials. In the present work, the stable, neutral TiO2/SiO2 hydrosols were prepared by using the Ti(SO4)2 as titanium source, HNO3 as peptizing agent, and SiO2 as stabilizer through a simple and low cost process. The morphologies and structures of TiO2/SiO2 hydrosol were further characterized by the TEM, SEM, XRD, and FTIR measurement. In the synthetic hydrosol, lots of nanoparticles with the diameters in the range of 10–20 nm can be observed. Ti―O―Si band were formed, as observed from the FTIR spectrum. The Na2O·SiO2 was detected from the SEM. After drying the TiO2/SiO2 hydrosol, the XRD shown that the TiO2 has an anatase structure and the SiO2 is amorphous. The TiO2/SiO2 hydrosol can be compactly coated on the GRC surface due to the existence of Na2O·SiO2 binder and exhibited high photocatalytic activity and stability in the degradation of Rhodamine B.
Keywords: Photocatalytic; Self-cleaning; Glass fiber reinforced cement materials; TiO2; SiO2; Hydrosol;

Titanate nanotubes with a high specific surface area were synthesized by the simple hydrothermal method and investigated as support for V2O5 catalyst in oxidative dehydrogenation of propane (ODP). The structures of pristine nanotubes as well as the prepared catalysts were investigated by XRD, Raman, FTIR, HRTEM, SEM, EDS, BET, and XPS techniques. The characterization of the as-synthesized nanotubes showed the synthesis of hydrogen titanate nanotube. The incipient wetness impregnation method was utilized to prepare VTNT-x (x  = 5, 10, and 15 wt.% vanadia supported on nanotube) together with VTi5 (5 wt.% vanadia supported on Degussa P25). The anatase phase was developed in VTNT-x catalysts upon calcination along with specific surface area loss. Higher vanadia loading resulted in the lowering of support capacity in maintaining vanadia in dispersed state such that eventually crystalline vanadia appeared. The measured catalyst activity demonstrates that in spite of major support surface area loss in VTNT-5 catalyst, the propylene yield is superior in comparison with VTi5 catalyst. The catalyst activity can be correlated with maximum reduction temperature.Deactivation of VTi5 and VTNT-5 as well as VTNT-15 were studied for 3,000 min time-on-stream. It was found that the activity of VTNT-5 catalyst remain unchanged while a decline in catalytic activity observed in VTi5 and VTNT-15 catalysts. The development of rutile was considered as being a major element in the deactivation of the investigated catalysts which is influenced by the presence of vanadium and reaction atmosphere.
Keywords: Propane oxidative dehydrogenation; Titanate nanotube; Deactivation; Vanadia; Anatase; Rutile;

Dependence of atomic oxygen resistance and the tribological properties on microstructures of WS2 films by Shusheng Xu; Xiaoming Gao; Ming Hu; Jiayi Sun; Dong Jiang; Desheng Wang; Feng Zhou; Lijun Weng; Weimin Liu (36-43).
To study the anti-oxidation mechanism of WS2 films, the pure WS2, and Al doped WS2 composite films were prepared via radio frequency sputtering and the atomic oxygen (AO) irradiation tests were conducted using a ground AO simulation facility. The tribological properties of both films before and after AO irradiation were evaluated using vacuum ball-on-disk tribo-tester. The incorporation of a small fraction of Al dopant resulted in microstructure change from loose columnar platelet with significant porosity for pure WS2 film to very dense structure. In pure WS2 film, WS2 exists as crystalline phase with edge-plane preferential orientation, but nanocrystalline and amorphous phase coexists for the WS2-Al composite film. Even if large amount of AO transported into the interior through the longitudinal pores, the pure film showed good AO irradiation resistance owing to the basal plane of WS2 crystal exhibiting much higher anti-oxidation capacity than the edge-plane. The composite film also had excellent AO irradiation resistance due to the formation of effective thinner WO3 cladding layer in the sub-surface layer. Tribological results revealed that the composite films showed a significantly improved wear resistance, in comparison to the pure WS2 film. Besides, due to the effective AO resistance, the tribological properties of WS2 films remained almost unchanged before and after AO irradiation.
Keywords: Atomic oxygen resistance; WS2; Al doping; Microstructure; Tribological properties;

High-quality transparent conductive phosphorus-doped zinc oxide (PZO) thin films were fabricated on glass substrates by pulsed laser deposition (PLD) at different substrate temperatures. X-ray patterns indicated that (0 0 2) preferential growth was observed and P doping did not cause structural degradation of wurtzite ZnO. Hall effect results indicated that 350 °C was the optimum substrate temperature to get PZO thin films with the lowest resistivity (7.35 × 10−4  Ω cm). Photoluminescence spectra showed the UV luminescence peak resulting from the band-edge exciton transition observed for PZO thin films. UV–visible transmission spectra showed that PZO thin films had high transparence (about 85%). In addition, the influence of substrate temperature on bandgap shift in PZO thin films was systematically studied.
Keywords: Thin films; Laser deposition; X-ray diffraction; Electrical properties; Photoluminescence;

The evolution of vacancy–solute complex in Al–Mg based alloys with different Mg contents during aging process was studied by positron annihilation spectroscopy together with Vickers micro-hardness and transmission electron microscopy measurements. For quenched Al–Mg based alloys, no obvious change in positron lifetime is observed during natural aging process. While during artificial aging at 180 °C after subsequent quenching, the positron lifetime and Doppler broadening S parameter show a fast decrease after the initial 1 min aging. Further aging for more than 10 min causes increase of these parameters. Coincidence Doppler broadening measurement indicates formation of vacancy–Mg complexes even in the as-quenched samples. Natural aging at room temperature has no effect on these vacancy–solute complexes. It is believed that with artificial aging the microstructure of Mg transforms from uniformly scattered vacancy–Mg complexes to Mg clusters. The Vickers micro-hardness changes slightly during the artificial aging, which is supposed to be related with the formation of Mg clusters.
Keywords: Al–Mg based alloys; Positron annihilation spectroscopy; Vacancy–Mg complex; Vickers micro-hardness; TEM;

Influence of surface PMPC brushes on tribological and biocompatibility properties of UHMWPE by Dangsheng Xiong; Yaling Deng; Nan Wang; Yuanyuan Yang (56-61).
Extremely efficient lubrication has been observed between natural joint surfaces and the friction coefficients can reach as low as 0.001. However, attaining the ultra-low friction coefficients between articulating cartilage surfaces in any artificial joints remains a challenge for bio-tribologists. In order to obtain the ultra-low friction coefficients as in natural joints, a biomimetic zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) was grafted on the ultra high molecular weight polyethylene (UHMWPE) by UV radiation and self-polymerized to form brush-like structure. The results of total reflection (FT-IR/ATR) spectra and X-ray photoelectron spectroscopy (XPS) spectra indicated successful grafting of PMPC on to the UHMWPE surface (Polymerization of 2-methacryloyloxyethyl phosphorylcholine). The water contact angle of UHMWPE decreased from 80° to 15° after grafting PMPC for 45 min. Tribological properties were tested under high contact stress for a longer duration of time. The friction coefficient of the sample grafted with PMPC was found to be much lower than that of untreated UHMWPE at initial stage which increased gradually with the increase of the cycle till it attained the same level as that observed for untreated UHMWPE. The wear rate of modified samples was decreased by 37% and 46% in distilled water and saline, respectively. The highly hydrated PMPC layer provided efficient lubrication at the interface between the sliding couple leading to wear reduction of UHMWPE. Furthermore, blood compatibility of modified artificial joint materials was improved significantly, which has been attributed to the properties and structures of PMPC grafted on the UHMWPE surface.
Keywords: UHMWPE; Polymer brushes; Friction and wear; Blood compatibility;

Green synthesis of high conductivity silver nanoparticle-reduced graphene oxide composite films by D.A. Dinh; K.S. Hui; K.N. Hui; Y.R. Cho; Wei Zhou; Xiaoting Hong; Ho-Hwan Chun (62-67).
A green facile chemical approach to control the dimensions of Ag nanoparticles–graphene oxide (AgNPs/GO) composites was performed by the in situ ultrasonication of a mixture of AgNO3 and graphene oxide solutions with the assistance of vitamin C acting as an environmentally friendly reducing agent at room temperature. With decreasing ultrasonication time, the size of the Ag nanoparticles decreased and became uniformly distributed over the surface of the GO nanosheets. The as-prepared AgNPs/rGO composite films were then formed using a spin coating method and reduced at 500 °C under N2/H2 gas flow for 1 h. Four-point probe measurements showed that the sheet resistance of the AgNPs/rGO films decreased with decreasing AgNPs size. The lowest sheet resistance of 270 Ω/sq was obtained in the film corresponding to 1 min of ultrasonication, which showed a 40 times lower resistivity than the rGO film (10.93 kΩ/sq). The formation mechanisms of the as-prepared AgNPs/rGO films are proposed. This study provides a guide to controlling the dimensions of AgNPs/rGO films, which might hold promise as advanced materials for a range of analytical applications, such as catalysis, sensors and microchips.
Keywords: Silver nanoparticles; Reduced graphene oxide; Ultrasonication; Vitamin C; Dimension controlled; Composites; Films; Electrical property;

Langmuir–Blodgett films of cholesterol oxidase and S-layer proteins onto screen-printed electrodes by Juliana Aguilar Guimarães; Helen Conceição Ferraz; Tito Lívio Moitinho Alves (68-74).
Stable Langmuir monolayers of cholesterol oxidase (ChOx) and S-layer proteins were produced at the water–air interface and subsequently transferred onto the surface of screen-printed carbon electrodes by the Langmuir–Blodgett (LB) technique. The modified electrode surface was characterized by atomic force microscopy (AFM) and cyclic voltammetry (CV). AFM indicated the presence of deposited layers, showing reduction of surface roughness (RMS and Rt parameters). Significant changes in the shape of CVs were observed in modified electrodes compared to bare electrodes. The anodic peaks could be observed in cyclic voltammograms (CV), at a scan rate equal to 25 mV s−1, using electrodes with Z-type LB deposition. The presence of S-layer proteins in the ChOx LB film increases the oxidation peak intensity and reduces the oxidation potential. Altogether, these results demonstrate the feasibility of producing a cholesterol biosensor based on the immobilization of ChOx and S-layer proteins by LB technique.
Keywords: Cholesterol oxidase; S-layer proteins; Langmuir–Blodgett films; Biosensor;

Effect of impregnation protocol in the metallic sites of Pt–Ag/activated carbon catalysts for water denitration by A. Aristizábal; S. Contreras; N.J. Divins; J. Llorca; F. Medina (75-89).
The influence of the Pt precursor and the impregnation protocol in the catalytic behavior of 3%Pt–1.5%Ag supported on activated carbon for water denitration in a continuous reactor was studied. Pt(NH3)4(NO3)2 and H2PtCl6 were selected as Pt precursors. Five protocols were investigated: sequential impregnations (both sequences), co-impregnation, physical mixture of monometallic catalysts, and physical mixture of a bimetallic catalyst with a Pt monometallic catalyst. The samples were characterized by XRD, XPS, TPR, HRTEM and physisorption. It was found that the catalytic activity strongly depends on the synthesis protocol and the Pt precursor, which modify the particle size. Higher nitrate rates are achieved using H2PtCl6 than Pt(NH3)4(NO3)2; this is mainly related to the smaller metal particle size of the former, evidenced by HRTEM. Nitrate consumption rate is directly related with the mean particle size. The physical mixture of monometallic catalysts resulted in the highest nitrogen rate.
Keywords: Nitrate removal; Metal precursor; Chlorine; Synthesis method; Particle size; Catalytic reduction;

Recent experiments in the literature have observed Coulomb explosion (CE) in metals under femtosecond (fs) laser irradiation. This is different from the previous common belief that CE will be strongly inhibited in metals due to the existence of a large number of free electrons with good mobility and the associated screening effect. It is still not well understood why CE can occur in metals. CE requires a sufficiently high outwards pointing electric field in the metal near-surface region. Using a physics-based model, this study shows that during the early stage of fs laser–metal interactions, the emitted electrons due to fs laser irradiation are still very close to the metal target surface, whose effects also need to be considered. The emitted electrons will generate an additional outwards pointing electric field in the target near-surface region, and will also exert a repulsive force on the electrons flowing from the deeper region of the target towards its surface. These effects are helpful to the development of a large outwards pointing electric field in the target near-surface region. The model calculation considering the effects of emitted electrons shows that the electric field at around the target surface can exceed the CE threshold under the studied conditions. The study has provided a physical explanation for why CE can occur in metals under fs laser irradiation.
Keywords: Laser ablation; Laser-induced electron emission;

The sorption of p-nitrophenol (PNP) on two variable charge soils was studied under a series of batch experimental conditions of solution pH, contact time, and temperature. Their kinetic and equilibrium parameters were assessed. The optimum pH for sorption of PNP was 5.0 for Xuwen soil and 5.4 for Guangzhou soil, respectively. Langmuir and Freundlich models were successfully used to describe the sorption isotherms. Results implied that monolayer sorption and heterogeneous energetic distribution of active sites on the surface of the soils were possible. The kinetic data were fitted with pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The sorption process was well described by pseudo-second-order kinetic model, and the intra-particle diffusion was not the sole rate-controlling step. The negative standard Gibbs free energy (Δ r G m 0) values of the sorption implied that the sorption of PNP on soils was spontaneous, and the changes of the standard enthalpy (Δ r H m 0) showed that the sorption as endothermic. In addition, the soils were characterized by surface area, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy.
Keywords: Variable charge soil; p-Nitrophenol; Kinetics; Thermodynamics; Sorption;

Adsorption of water on the KNTN (0 0 1) surface: A density functional theory study by Wenhan Wang; Yanqing Shen; Xiaoou Wang; Zhongxiang Zhou; Weidong Fei (102-108).
We present a density functional theory study of water adsorption on K1−y Na y Ta1−x Nb x O3 (KNTN) surface terminations. The adsorption configuration and energy are determined and the bond formation between water molecule and KNTN surface are investigated by analysis of difference electron density and partial density of states. Our calculations reveal that the energetically favorable configurations for water monomer adsorption is at the K–Na bridge site on the K(Na)O-termination and the Nb top site on the Ta(Nb)O2-termination. With the coverage increasing, the water–surface interaction per water molecule decreases because of the formation of interwater hydrogen bonds, whereas the surface geometry becomes more roughness. The variation of bandgap for water adsorbed KNTN surface is also studied. We find that the interaction between water and surface would lead to a bandgap increase of KNTN surface, which is correlated to the electrons density redistribution.
Keywords: First principle; Perovskites; Water adsorption; Bandgap;

Effect of Mn doping on the microstructures and sensing properties of ZnO nanofibers by Yuzhen Mao; Shuyi Ma; Xiangbing Li; Caiyun Wang; Faming Li; Xiaohong Yang; Jing Zhu; Lin Ma (109-115).
Schematic diagram of Mn-doped ZnO nanofibers sensing mechanism: (a) nanofibers at air ambient, (b) nanofibers at acetone ambient.Zinc oxide (ZnO) nanofibers doped with manganese (Mn) are synthesized by electrospinning followed by calcinations at 580 °C for 150 min. The structure, morphology and element-composition are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the diameters of Mn-doped ZnO nanofibers are from 60 nm to 90 nm corresponding to the amount of Mn from 0 wt% to 2.0 wt%, respectively. XPS spectrum indicates that Mn2+ ions exist in divalent state. The gas sensing properties are significantly affected by the Mn-doped ZnO nanofibers and the operation temperature. The sensors exhibit excellent sensitivity, practical selectivity and stability to acetone with a fast response and recovery time at 340 °C.
Keywords: Nanofibers; Mn doping ZnO; Electrospinning; Acetone sensing;

Template-free method to prepare porous Cu-containing nanotubes with a good catalytic performance for styrene epoxidation by Chenhui Hu; Lihong Zhang; Junfeng Zhang; Liyuan Cheng; Zheng Zhai; Jing Chen; Wenhua Hou (116-124).
Cu-containing nanotubes with a large surface area and pore volume were prepared by using nanoscrolls derived from K4Nb6O17 as a support and a subsequent thermal transformation of Cu-containing nanoscrolls into Nb2O5 nanotubes. The method is facile and template-free. The catalytic performance of the resulted Cu-containing nanotubes was evaluated for styrene epoxidation in the presence of tert-butyl hydroperoxide (TBHP) and H2O2, respectively. It was found that Cu-containing nanotubes displayed a relative good catalytic performance with a styrene oxide (SO) selectivity of 46.9% by TBHP and a much higher SO selectivity of 94.6% by H2O2. Two possible mechanisms were put forward to explain the different catalytic behaviors in the two types of oxidation systems. Because of the thermal transformation of nanoscrolls into nanotubes, nanoscrolls may be a new kind of promising support for the design and assembly of novel heterogeneous catalysts.
Keywords: K4Nb6O17; Nanoscrolls; Nanotubes; CuO; Epoxidation;

Rapid and mask-less laser-processing technique for the fabrication of microstructures in polydimethylsiloxane by C.L. Sones; I.N. Katis; B. Mills; M. Feinaeugle; A. Mosayyebi; J. Butement; R.W. Eason (125-129).
We report a rapid laser-based method for structuring polydimethylsiloxane (PDMS) on the micron-scale. This mask-less method uses a digital multi-mirror device as a spatial light modulator to produce a given spatial intensity pattern to create arbitrarily shaped structures via either ablation or multi-photon photo-polymerisation in a master substrate, which is subsequently used to cast the complementary patterns in PDMS. This patterned PDMS mould was then used for micro-contact printing of ink and biological molecules.
Keywords: Ablation; Photo-polymerisation; Digital multi-mirror; Laser material processing; Microstructure fabrication; Micro-contact printing;

We have reported the development of a silica based magneto-fluorescent hybrid of a newly synthesized dye and superparamagnetic iron oxide nanoparticles with ordered and radially distributed porous structure. The dye is synthesized by a novel yet simple synthetic approach based on Michael addition between dimer of glutaraldehyde and oleylamine molecule. The surfactant used for phase transformation of the dye from organic to aqueous phase, also acts as a structure directing agent for the porous structure evolution of the hybrid with radial distribution. The evolution of the radially distributed pores in the hybrids can be attributed to the formation of rod-like micelles containing nanoparticles, for concentration of micelles greater than critical micelle concentration. A novel water extraction method is applied to remove the surfactants resulting in the characteristic porous structure of the hybrid. Adsorption isotherm analysis confirms the porous nature of the hybrids with pore diameter ∼2.4 nm. A distinct modification in optical and magnetic property is observed due to interaction of the dye and SPION within the silica matrix. The integration of multiple structural components in the so developed hybrid nanosystem results into a potential agent for multifunctional biomedical application.
Keywords: Microporous; Hybrid; Magneto-fluorescent;

Formation of Au–Al alloy on silicon for polymer modulator electrode application by Yuanbin Yue; Jian Sun; Xuliang Zhao; Ying Xie; Xibin Wang; Lei Liang; Fei Wang; Changming Chen; Yunji Yi; Xiaoqiang Sun; Daming Zhang (137-141).
The formation of aurum–aluminum (Au–Al) alloy on silicon substrate and its use to be electrode of polymer electro-optic (EO) modulator were investigated. The surface morphology and crystallinity were studied by atomic force microscopy, scanning electron microscope, X-ray diffractometer (XRD) and energy dispersive spectrometer. The electrical resistivity was characterized by the four-probe method. XRD pattern confirmed the formation of AuAl phase. After annealed for 11 min at 575 °C, the Au–Al alloy film exhibited a root mean square roughness of less than 40 nm and a minimum electrical resistivity of 2.24 μΩ cm with no obvious change within 6 months. The scattering-parameter (S21) of a fabricated co-planar waveguide electrode polymer EO modulator was measured by vector network analyzer, and a 3-dB bandwidth of 5.2 GHz was observed. These physical properties promise good potentials of Au–Al alloy to be electrode of polymer EO modulators.
Keywords: Anneal; AuAl; Alloy; Modulator;

Spontaneous changes in contact angle of water and oil on novel flip–flop-type hydrophobic multilayer coatings by Go Kawamura; Tomoyuki Ema; Hisatoshi Sakamoto; Xing Wei; Hiroyuki Muto; Atsunori Matsuda (142-146).
Multilayer structures composed of poly(allylamine hydrochloride) (PAH) and Nafion were fabricated on glass substrates by layer-by-layer assembly. Some of the multilayers demonstrated spontaneous changes in contact angle of water and oil due to flip–flop movements of free sulfo groups in the Nafion layer, and the multilayers eventually possessed water repellency in air and oil repellency in water. The repellencies were enhanced by applying primer layers that were formed using SiO2 fine particles to increase surface roughness. Compared to typical hydrophobic and oleophobic surfaces, the multilayers showed practical levels for a use as soil release coatings.
Keywords: Wettability; Oleophobicity; Flip–flop movement; Soil release coating; Layer-by-layer;

(ZnO)1−x (CdO) x nanofibers were fabricated via electrospinning of polymer precursor by subsequent annealing in air. Field emission scanning electron microscopy (FESEM) showed the smooth and beadless nanofibers and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed the ZnO hexagonal and the CdO cubic structure. Diffuse reflectance spectroscopy (DRS) showed the band gap energy reduction by increasing the amount of CdO in (ZnO)1−x (CdO) x nanofibers that resulted in the photocatalytic activity under the visible light for dye degradation. Under the UV light CdO acted as both electron and hole sink in the (ZnO)1−x (CdO) x nanofibers and a possible photocatalytic activity mechanism was proposed. The effect of annealing rate on the nanofiber properties was also studied. Thermal gravimetric analysis (TGA) plot revealed that different heating rates influence on both peak position and maximum amount of decomposition. Improvement of the crystallinity and the increase in the photocatalytic activity were obtained by increasing the annealing rate from 3 to 20 °C/min.
Keywords: Degree of crystallinity; Electrospinning; Heating rate; ZnO–CdO;

The present work deals with a simulation of the growth kinetics of boride layers grown on Armco iron substrate. The formed boride layers (FeB + Fe2B) are obtained by the gas-boriding in the temperature range of 1073–1273 K during a time duration ranging from 80 to 240 min. The used approach solves the mass balance equations at the two growing fronts: (FeB/Fe2B) and (Fe2B/Fe) under certain assumptions. To consider the effect of the incubation times for the borides formation, the temperature-dependent function Φ(T) was incorporated in the model. The following input data: (the boriding temperature, the treatment time, the upper and lower values of boron concentrations in FeB and Fe2B and the experimental parabolic growth constants) are needed to determine the boron activation energies in the FeB and Fe2B layers. The obtained values of boron activation energies were then compared with the values available in the literature. Finally, a good agreement was obtained between the simulated values of boride layers thicknesses and the experimental ones in the temperature range of 1073–1273 K.
Keywords: Gas-boriding; Boride layers; Diffusion coefficient; Incubation time; Parabolic growth constant;

Surface modification by gas nitriding for improving cavitation erosion resistance of CP-Ti by Haibin Li; Zhenduo Cui; Zhaoyang Li; Shengli Zhu; Xianjin Yang (164-170).
Gas nitriding process has been used to increase the surface hardness of titanium, in this study we used this technique to improve the cavitation erosion resistance (R ce) of commercial purity titanium (CP-Ti). We also studied microstructure, phase constituents, hardness and the effect of processing parameters on R ce of the treated samples. The results indicated that the R ce of the treated samples was related to the processing parameters. The sample treated at 850 °C for 4 h has the highest R ce, which was attributed to the compound layer (CL) with a hard, dense and free-defects microstructure. With increasing the nitriding temperature and duration, the R ce of the treated samples decreased due to the excessive oxide and defects formed in the CL. When the CL was removed, the treated sample exhibited an excellent cavitation erosion behavior. It was supposed to be due to the existence of the residual compressive stresses field in the nitrogen diffusion zone, which played an important role in preventing microcracks initiation and propagation to interior for cavitation damage.
Keywords: Titanium; Cavitation erosion; Gas nitriding; Diffusion zone;

Self-assembly of condensates with advanced surface by means of the competing field selectivity and Gibbs–Thomson effect by Vyacheslav Perekrestov; Yuliya Kosminska; Alexander Mokrenko; Taras Davydenko (171-175).
Copper and silicon layers were deposited using the accumulative plasma-condensate system. Their surface was found to possess the complex developed morphology using SEM technique. Competing processes of the field selectivity and Gibbs–Thomson effect are considered to describe the formation of the surface. The mathematical model is created on the basis of these effects which describes self-assembly of the surface at the form of adjoining elements of an elliptic section. The comparative analyses of theoretical and experimental results are given.
Keywords: Self-assembly; Quasi-equilibrium condensation; Surface morphology; Gibbs–Thomson effect;

An Al x O y /Pt/Al x O y multilayer solar absorber for use in solar-thermal applications has been deposited onto copper substrate by electron beam (e-beam) vacuum evaporation at room temperature. Different samples were annealed at different temperatures in air and characterized by spectrophotometry, emissometry, heavy ion elastic recoil detection analysis (HI-ERDA), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The Al x O y /Pt/Al x O y multilayer solar absorbers heated up to 500 °C were found to exhibit good spectral selectivity (α/ɛ) of 0.951/0.08. However, beyond 500 °C the spectral selectivity decreased to 0.846/0.11, possibly due to thermally activated atomic interdiffusion profiles. HI-ERDA has been used to study depth-dependent atomic concentration profiles. These measurements revealed outward diffusion of the copper substrate towards the surface and therefore, the decrease in the constituents of the coating. The decrease in the intensity of Pt grains and formation of CuO and Cu2O phases at 700 °C were confirmed by XRD and EDS.
Keywords: Depth profile; ERDA; Absorptance; Emittance;

TiO2-SnO2 heterostructures applied to dye photodegradation: The relationship between variables of synthesis and photocatalytic performance by Vagner R. de Mendonça; Osmando F. Lopes; Raul P. Fregonesi; Tania R. Giraldi; Caue Ribeiro (182-191).
This paper describes the synthesis of TiO2-SnO2 heterostructures and their application to water decontamination based on the photodegradation of Rhodamine B (RhB). The heterostructures were fabricated through two different routes, a hydrolytic sol gel and the polymeric precursor method, both of which induced the growth of SnO2 on commercial TiO2. The results show that the heterostructures presented higher photoactivity behaviors than commercial TiO2 nanopowders. The achievement of homogeneity during phase formation (i.e., of the SnO2 dispersion over the TiO2 nanoparticles) was a key parameter for obtaining higher photocatalytic activities per unit area. The main degradation mechanism was correlated with the process of •OH radical generation, which was related to the concentration and nature of the surface hydroxyl groups. Accordingly, the polymeric precursor method was shown to be more adequate for dispersing higher amounts of SnO2 in comparison with the hydrolytic sol gel method. Additionally, the polymeric precursor method delivered higher proportions of bonded surface hydroxyl groups, which were responsible for radical formation; in contrast, the hydrolytic sol gel method demonstrated the highest amount of adsorbed water.
Keywords: Heterostructures; Water decontamination; Sol–gel synthesis; Photocatalysis;

Properties of the surface of ceramic formed under laser irradiation of Al2O3–TiO2 compacts by P.A. Márquez Aguilar; M. Vlasova; A. Escobar Martínez; T. Tomila; V. Stetsenko (192-198).
The phase formation in the laser irradiation area from xAl2O3yTiO2 compacts and the properties of the surface layer have been investigated by the XRD, IR, and SEM methods. Main phases precipitating from eutectic melt are tialite, corundum, and rutile. A high temperature on the surface of specimens leads to the development of dissociation processes of these compounds and molecules of the gaseous medium. As dissociation products fly apart and pass through different temperature zone, there are formed different metal oxides, metal hydroxides, and thermolysis products. When these different oxides are deposited on the surface of the ceramic, they form layers with different adhesion degrees.
Keywords: Al2O3–TiO2 mixtures; Laser treatment; Phase formation; Surface products;

Determination of the chemical mechanism of chromate conversion coating on magnesium alloys EV31A by Sébastien Pommiers-Belin; Jérôme Frayret; Arnaud Uhart; JeanBernard Ledeuil; Jean-Charles Dupin; Alain Castetbon; Martine Potin-Gautier (199-207).
Magnesium and its alloys present several advantages such as a high strength/weight ratio and a low density. These properties allow them to be used for many aeronautical applications but they are very sensitive to corrosion. To solve this problem, conversion coatings are deposited on the surface before a protective top coat application. Several kinds of coatings exist but the best protective is chromium conversion coating (CCC). This process is now limited by several environmental laws due to the high toxicity of hexavalent chromium. However, in order to reduce hazardous impact onto the environment and to find alternative coatings, the chemical mechanisms of CCC deposition and protection on magnesium alloy are detailed for the first time in this work. The studied process includes 4 pre-treatments steps and a conversion immersion bath. The pre-treatment steps clean and prepare the surface for improving the coating deposition. The coating properties and its composition were characterized by voltammetry and XPS technics. A final layer of chromium(III) oxide and magnesium hydroxide composed the coating giving it its protective properties. Trapped orthorhombic potassium chromate has also been identified and gives to the coating its self healing property.
Keywords: Hexavalent chromium; Magnesium alloy; Mechanism of deposition; Conversion coating; Voltammetry; XPS;

Optimization of process parameters for the electrical properties in Ga-doped ZnO thin films prepared by r.f. magnetron sputtering by D.L. Zhu; Q. Wang; S. Han; P.J. Cao; W.J. Liu; F. Jia; Y.X. Zeng; X.C. Ma; Y.M. Lu (208-213).
Ga-doped ZnO (GZO) transparent conductive thin films have been deposited on quartz substrates by r.f. magnetron sputtering. The optimization of four process parameters (i.e., vacuum annealing temperature, r.f. power, sputtering pressure, and Ar flow rate) based on Taguchi method has been systematically studied in order to obtain the minimum resistivity. Compared to the optimal parameter set selected from orthogonal array by Taguchi method, the optimal prediction design can receive an improvement of 22.3% in electrical resistivity, and the corresponding resistivity is 8.08 × 10−4  Ω cm. The analysis of variance shows that vacuum annealing temperature is the most significant influencing parameter on the electrical properties in GZO films. X-ray photoelectron spectroscopy and photoluminescence results exhibit that the enhancement in electrical conductivity after vacuum annealing is ascribed to the variation of the chemical states of oxygen in GZO films. With the increase in annealing temperature, the content of absorbed oxygen and interstitial oxygen as acceptors will decrease.
Keywords: Ga-doped ZnO; Magnetron sputtering; Taguchi method; Vacuum annealing; Chemical states of oxygen;

The core–shell fluorinated-polyacrylate (PFA) emulsion was synthesized through emulsion polymerization method and the superhydrophobic PFA/SiO2 hybrid coating was successfully fabricated on the slide glass by spraying the mixture of PFA emulsion and hydrophobic SiO2 particles using ethanol as cosolvent. The PFA emulsion was characterized by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), water contact angle (WCA), transmission electron microscopy (TEM), and the effects of SiO2 content on the wetting behavior and surface morphology of PFA/SiO2 hybrid coating were investigated. To evaluate the stability of the hybrid coating, the acid and base resistance, weatherability and thermal stability were also studied. Results showed that the obtained PFA latex exhibited a core–shell structure with a particle size of 134.1 nm and a narrow polydispersity of 0.03. With the increase of dodecafluoroheptyl methacrylate (DFMA) content in the latex shell from 0 wt% to 31.8 wt%, the WCA of the PFA film enlarged from 85° to 104°, indicating that the introduction of fluorinated monomer was effective in reducing the surface energy. By adding different amount of SiO2 particles, the surface morphology and wetting behavior of the PFA/SiO2 hybrid coatings could be controlled. When the mass ratio of SiO2 to PFA emulsion was 0.2, the surface roughness (Rq) increased to 173.6 nm and the wetting behavior of the surface became superhydrophobic with a WCA of 153°, resulted from the corporation of low surface energy and the binary nano/microstructure on the surface. The as-prepared PFA/SiO2 hybrid coating showed good acid and base corrosion resistance, and it could keep superhydrophobicity after being heated at 250 °C for 2 h or exposed to ambient atmosphere for more than 3 months. Additionally, the superhydrophobic PFA/SiO2 hybrid coating could be applied to various substrates through spraying. This was a green and eco-friendly method in fabricating stable organic/inorganic hybrid superhydrophobic coating because none of toxic organic solvents were used during the whole process.
Keywords: Superhydrophobic; Emulsion polymerization; Fluorinated polyacrylate; Silica; Hybrid coating;

A new understanding of carbon nanotube growth: Activation and deactivation of a catalyst by Yueling Zhang; Qing Yu; Xidong Wang; Yajun Tian (221-224).
Due to the crucial role of a catalyst in growth of carbon nanotubes (CNTs) by a chemical vapor deposition, it is important to understand the activation and deactivation of a catalyst for controlling production of CNTs. Using molecular benzene as the carbon source and Fe–Co/γ-Al2O3 as catalyst, multi-CNTs were synthesized with a thermal analyzer coupled a mass spectrometer in different atmospheres of N2 and H2. Very different thermogravimetry behaviors (TG-DTG) were observed during CNT growth, indicating that CNTs experienced very different activation and deactivation processes. In a N2 atmosphere, a catalyst particle was activated jumpily, then about half of catalyst surface was covered by the produced CNTs generated on one side of a catalyst, leading to trigger deactivation immediately following activation; in a H2 atmosphere, a catalyst was activated gradually, and deactivation developed gradually, the total CNT yield in H2 was higher than in N2, suggesting H2 suppressed the deactivation development of a catalyst by cleaning the amorphous carbon over a catalyst. In combination of the mass spectral measurements, the activation and deactivation mechanism of a catalyst in an inert and reducing reaction atmospheres gas were revealed.
Keywords: Chemical vapor deposition; Thermal analysis–mass spectroscopy technique; Carbon nanotubes; Interface dynamics; Model;

Synthesis; characterization and antimicrobial effects of composites based on multi-substituted hydroxyapatite and silver nanoparticles by Aurora Mocanu; Gabriel Furtos; Sorin Rapuntean; Ossi Horovitz; Chirila Flore; Corina Garbo; Ancuta Danisteanu; Gheorghe Rapuntean; Cristina Prejmerean; Maria Tomoaia-Cotisel (225-235).
Nano hydroxyapatite doped with zinc (0.2 wt%), silver (0.25 wt%) and gold (0.025 wt%), (HAP), has been obtained by an innovative wet chemical approach, coupled with a reduction process for silver and gold. The synthesized multi-substituted nano HAP was freeze-dried and calcined at 650 °C. Nano HAP has been characterized by XRD, FTIR spectroscopy and imaging techniques: TEM, SEM and AFM. Then, nano HAP was mixed with previously synthesized silver nanoparticles (AgNPs), in the amount of 9 wt%, to give a novel material (HAP-Ag). The AgNPs were prepared by the reduction of silver nitrate with glucose in alkaline medium. TEM and UV–Vis confirmed the formation of AgNPs with an average size of 12 nm. Further, organic matrix composites were obtained from a filler made of HAP and/or HAP-Ag and a mixture of monomers (such as bis-GMA and TEG-DMA), which were polymerized at various compositions in AgNPs content up to 5.4 wt%. Antibacterial activities of these composites were investigated against several different pathogenic species: Escherichia coli, Staphylococcus aureus, Staphylococcus spp., Bacillus cereus, and Candida albicans, using the Kirby–Bauer disk-diffusion method. Antibacterial activities are enhanced with increasing of silver content within composites. These effects clearly reveal that AgNPs can be effectively utilized in combination with multi-substituted HAP and polymeric matrix, both used as carriers, in order to improve their efficiency against various pathogenic species. These composites can be considered a promising antimicrobial material for coating of orthopedic and dental implants or used as bone cements in surgical applications.
Keywords: Multi-substituted nano hydroxyapatite; Silver nanoparticles; Nano composites; Antibacterial effects; Pathogenic species;

The adsorption and pathway processes of atomistic Nb, Si, and N at high-symmetry sites on NbN (0 0 1) and (1 1 1) surfaces were studied using first-principle method, which is based on the density functional theory. This investigation presents some of the results obtained. The potential energy surface (PES) was obtained by calculating the adsorption of Nb, Si, and N atoms on NbN (0 0 1). The most energetic site for the Nb atom adsorbed on NbN(0 0 1) was the site ‘on-top of face–center cubic’ (HL), whereas those for N and Si were both at the site ‘between TopN and HL’ (TopN-HL). The minimum energy paths of the single atom on NbN (0 0 1) surface diffusion were obtained using the PES calculation results. The Nb and Si atoms were diffused from the TopN to the HL position. The N atom was diffused from the TopNb, whereas the TopN–HL to HL position. The diffusion energies of the Nb, Si, and N atoms on the NbN (0 0 1) surface were 0.32, 0.69, and 1.32 eV, respectively. The pathways of the atomistic diffusion involved the diffusion of atoms from the FCC to the HCP site on the NbN (1 1 1) surface. The results showed that the diffusion energy of Si on the Nb layer was smaller than that on the N layer. Si and N can easily form stable structures while bonding on the N layer. Moreover, Si atoms can stabilize the activity of N atoms while promoting the spread of Nb atoms during deposition.
Keywords: Niobium nitride; Surface adsorption; Surface diffusion; Density functional calculation;

It has generally been believed that the formation of the S phase or expanded austenite γN with enough thickness depends on the temperature (lower than 480 °C) and duration of the process. In this work, we attempt to produce nitrogen expanded austenite layer at high temperature in short time. Nitriding of AISI 316L austenitic stainless steel was carried out at high temperatures (>520 °C) for times ranging from 5 to 120 min. The microstructures, chemical composition, the thickness and the morphology of the nitrided layer, as well as its surface hardness, were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, optical microscopy, scanning electron microscopy, and microhardness tester. The corrosion properties of the untreated and nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results confirmed that nitrided layer was shown to consist of γN and a small amount of free-CrN and iron nitrides. High temperature plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the austenitic stainless steel, and it can critically reduce processing time compared with low temperature nitriding.
Keywords: Plasma nitriding; AISI 316L austenitic stainless steel; XPS;