摘要:The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000°C during the cooling to 100°C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200°C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.
摘要:High voltage lines are one of the main ways for carrying electric energy. To do so high voltage insulators are needed to insulate these lines from the supporting towers. Glass, ceramic and polymer insulators are widely used. Generally high voltage insulators are exposed to weather where humidity, from rain and moist, together with pollution allows accumulation of unwanted material on the surface of the insulator. Cleaning procedures are then needed to remove such material and avoid short-circuiting. The most commonly used cleaning methods are hand cleaning using chemicals that need turning off the main and water jet, which allows keeping the line in service. In this work we explore the possibility of using laser ablation for cleaning high voltage ceramic insulators. It is demonstrated that cleaning can be accomplished by a two-step process. First a Q-switched Nd: YAG laser is used to ablate the unwanted material. The second step is to use a free running Nd: YAG laser to restore the surface hydrophobicity of ceramic insulator, which is affected in the first process step.
摘要:A method for etching the surface of a Pyrex glass substrate using the Reactive Ion Etching process without the use of masks is reported. Variations in the machined surface on an auxiliary plate, manufactured in aluminum and placed below a Pyrex glass slide, were transferred to the upper surface of the substrate. SF6 as etching gas and low pressure chamber to promote the increase of mean free path of ions were used. Two etching ratios were found, general, that affects the entire surface of the substrate, and differential, which generates the relief on the surface of the glass. Differential etching depth showed a linear behavior with respect to time;the mean differential etching rate obtained was 43 nm/min. The same phase between the auxiliary plate machining and the etched pattern on the substrate is preserved. With this technique it was possible to manufacture convex and concave surfaces;some examples are given. The arithmetic mean roughness achieved with the proposed method was found to be N1 class, ideal for the development of optical corrector plates.
摘要:The corrosive properties of PVD TiN-Ti-Al type composite titanium nitride layer with titanium and aluminium sub-layers system on the AZ91D magnesium alloy and its sub-layers were investigated by using polarization method and impedance spectroscopy, specifically, in terms of the hydrothermal tightening effect. The aim was to explain the mechanisms which contribute to high anticorrosive properties obtained by hydrothermal tightening. It was stated that the hydrothermal treatment changes the surface topography of the examined layers, most probably due to the formation of a continuous titanium oxides film. Tightening significantly modifies the corrosion resistance of the particular component sub-layers of the TiN-Ti-Al layer which exhibits optimum electrochemical parameters. It was shown that the increase of the electrochemical parameters is controlled by tightening of the outside titanium nitride layer, whereas the aluminium sub-layer plays a critical role in creating proper conditions for the hydrothermal tightening of titanium nitride.
摘要:Surface engineering of magnesium alloys requires adequate strategies, processes and materials permitting corrosion protection. Liquid formulations containing corrosion inhibitors often are to be optimized according to the demands of the respective substrate and following the service conditions during its application. As an interdisciplinary approach, a combination of several techniques for instantly monitoring or elaborately analyzing the surface state of magnesium was accomplished in order to characterize the performance of new adsorbing sustainable amphiphilic polymers which recently were developed to facilitate a multi-metal corrosion protection approach. The application of established techniques like Contact Angle measurements and X-ray Photoelectron Spectroscopy investigations was supplemented by introducing related and yet faster online-capable and larger-scale techniques like Aerosol Wetting Test and Optically Stimulated Electron Emission. Moreover, an inexpensive setup was configured for scaling the inset and the extent of degradation processes which occur at local electrochemical circuits and lead to hydrogen bubble formation. Using these analytical tools, changes of the surface state of emeried AM50 samples were investigated. Even in contact with water, being a moderate corrosive medium, the online techniques facilitated detecting surface degradation of the unprotected magnesium alloy within some seconds. In contrast, following contact with a 1 weight% formulation of a polymeric corrosion inhibitor, surface monitoring indicated a delay of the onset of degradation processes by approximately two orders of magnitude in time. Mainly based on the spectroscopic investigations, the corrosion inhibiting effects of the investigated polymer are attributed to the adsorption of a primary polymer layer with a thickness of a few nanometers which occurs within some seconds. Immersion of magnesium for several hours brings up a protective film with around ten nanometers thickness.
摘要:Films fabricated by sputter deposit are extensively used in the semiconductor, optical and optoelectronic industries. However, studies to-date have focused only on analyzing the BFO films fabricated by sputter deposition. This paper’s research seeks to fill the gap in understanding the sputter effect on the target in order to fully understand the whole process of fabricating films by sputter deposition. In this study, 3 keV argon ions were continuously sputtered onto a target of multiferroic bismuth ferrite, BiFeO3, (BFO) with 5 mol% BaTiO3, in increasing time intervals. X-ray Photoelectron Spectroscopy (XPS) was applied to examine the sputtered surface after each sputter time interval. This paper makes the following findings. First, the surface-contaminant carbon was almost completely removed after 5120 seconds of sputtering. Second, the study observed two-component oxygen spectra remained after sputtering. Other than the chemi- and physic-sorbed oxygen, these two oxygen components perhaps resulted from the short and long O-Fe bonds due to the displacement of the Fe3+ ions. Third, sputtering resulted in a change of the oxidation states of bismuth from dominant Bi3+ state to equally weighted Bi3+ state and metallic Bi° state. The changes of the bismuth’s oxidation states, i.e., a non-stoichiometric BFO target might alter the film compositions deposited onto the substrate. This paper shows by introducing low pressure oxygen during the sputtering, the metallic Bio on the target can be re-oxidized.
摘要:A novel hybrid process for surface fluorination of polymers is being introduced. The process is based on ultra violet (UV) laser radiation, which on the one hand forms radicals out of an atmosphere of a partially fluorinated benzene, and on the other hand activates a polymer surface in the areas where the UV radiation hits the surface. The radicals can react with the polymer surface, hence altering the surface energy. With this process, a fluorine content of over 30% on the surface of bulk polystyrene can be achieved, while the smallest possible structure size was smaller than 1 mm.
摘要:The article is devoted to surface hardening of steels by alloying with the use of laser energy. Two combined technologies were proposed: first—laser alloying by nitride-forming elements followed by nitriding, and second—the local laser alloying followed by metallization in atmosphere of ammonia. It is shown that laser alloying in continuous radiation forms a layer with a homogeneous fine-grained structure with thickness of 600 microns. The subsequent nitriding increases the microhardness of the surface layer of low-carbon steels to 20,000 MPa, increases wear-resistance in a 3 - 15 times and crack resistance in a 1.5 times. Two-stage technology of metallization allows getting diffusion layer on the surface of steels with the thickness, which is 1.5 - 2 times higher than after traditional metallization. In addition, this method of surface modification can significantly reduce the temperature of diffusion metallization and reduce the processing time to 3 hours. The optimal regimes of both technologies, which provide homogeneous multiphase diffusion layers with high hardness and wear resistance, were determined.
摘要:The majority of naval ships are constructed of mild steel. Corrosion is a major concern in a maritime environment. This particular type of material degradation has recently received more attention by the marine industry. The present work aims to investigate the effect of recent coatings used in marine ship surfaces for preventing corrosion. Experiments were performed according to standard tests to evaluate and measure the coating adhesion to steel and to measure the corrosion wear rate if any for three types of coatings. An accelerated corrosion test was conducted to duplicate in the laboratory the field corrosion performance of a product. The results indicate that all tested types of paint have resulted in a reduction in the corrosion rate compared with the uncoated steel. A minimum corrosion rate of 0.8 mm/year for the coat “Hempadur 52,140” was obtained compared to 2.1 mm/year for the uncoated steel. A microscopic examination of the corroded steel surfaces was conducted which prevailed pitting behavior with different degree. The minimum corroded surface exhibited few pitting attack in comparison to other specimens. Although the pitting attack of the surface layer (paint), one can drive a conclusion that sample surface without coating is aggressively attacked by pits.
摘要:Multi-walled carbon nanotubes (MWCNTs) were grown by plasma-enhanced chemical vapor deposition (PECVD) in a bell jar reactor. A mixture of methane and hydrogen (CH4/H2) was decomposed over Ni catalyst previously deposited on Si-wafer by thermionic vacuum arc (TVA) technology. The growth parameters were optimized to obtain dense arrays of nanotubes and were found to be: hydrogen flow rate of 90 sccm;methane flow rate of 10 sccm;oxygen flow rate of 1 sccm;substrate temperature of 1123 K;total pressure of 10 mbar and microwave power of 342 Watt. Results are summarized and significant main factors and their interactions were identified. In additiona computational study of nanotubes growth rate was conducted using a gas phase reaction mechanism and surface nanotube formation model. Simulations were performed to determine the gas phase fields for temperature and species concentration as well as the surface-species coverage and carbon nanotubes growth rate. A kinetic mechanism which consists of 13 gas species, 43 gas reactions and 17 surface reactions has been used in the commercial computational fluid dynamics (CFD) software ANSYS Fluent. A comparison of simulated and experimental growth rate is presented in this paper. Simulation results agreed favorably with experimental data.
摘要:The aim of this study is to report batch adsorption results of Cd (II) and Cr (VI) onto Algerian bentonite. The equilibrium adsorption process was achieved at about 120 min contact time. The kinetic and isotherms aspects of Cr (VI) and Cd (II) adsorption were investigated by varying operation parameters such as pH (0.5 - 6), initial Cd (II) and Cr (VI) concentrations (50 - 200 mg/l) and temperature (293.15 K - 343.15 K). The optimum conditions obtained were: pH = 6.0 and 4.0 for Cd (II) and Cr (VI) respectively, initial concentrations of Cd (II) and Cr (VI) = 50 mg/L and T = 293.15 K. The kinetic of the adsorption process was studied by application of the most important kinetic models namely the pseudo-first order, the pseudo-second order and Elovich equations. The results showed that the pseudo-second order model fitted well the adsorption data of Cr (VI) whereas, and the Cd (II) adsorption data fitted best the Elovich equation. The equilibrium data fitted best the Langmuir isotherm, and the maximum adsorption capacity was determined through this model and was found to be 13.17 and 12.61 mg/g for Cd (II) and Cr (VI) respectively. The temperature had a reverse effect on the Cd (II) and Cr (VI) adsorption;our results showed that the removal efficiency increased to82.4% and 55.70% for Cd (II) and Cr (VI)when the temperature decreasedto 293.15 K.The negative figures of the Gibbs free energy ΔG°ads values range from -15.23 kJ/mol to -14.37 kJ/mol for Cd (II) and from -9.70 kJ/mol to -9.64 kJ/mol for Cr(VI) at 293.15 K to 343.15 K showed that the adsorption process is spontaneous and favourable. These results confirmed the ability of the low-cost Algerian natural bentonite to efficiently and competitively adsorb the two toxic elements investigated: cadmium (II) and chromium (VI).
摘要:Polysulfone (PSF) membranes are frequently used in ultrafiltration, due totheirchemical and structural stability and mechanical robustness. Despite these advantages, successful utilization of this membrane technology has been greatly limited by the susceptibility of these membranes to fouling, due totheirhydrophobic nature. Here we report on the synthesis and characterisation of hydrophilic PSF membrane materials prepared by incorporation of polyvinyl alcohol, through chemical crosslinking to produce mechanically and chemically stable PSF hydrogels. The hydrogel composition was controlled at three different ratios to evaluate the effect of the PSF contributioni.e.25:75, 50:50 and 75:25. PSF hydrogels were characterized using high resolution scanningelectronmicroscopy (HR-SEM), cyclicvoltammetry (CV), and drop shape analysis techniques. The polysulfone hydrogels formed showed a decrease in contact angle by 50% for all hydrogels regardless of their polysulfone contribution, confirming an improvement in hydrophilic nature. The electron diffusion and ionic transport properties of thehydrogels as immobilised thin films in aqueous solutions,wereevaluated using cyclic voltammetry.
摘要:The surface of the AlSiC composite material consists of aluminum and silicon carbide areas. The uniformal metallization by nickel is necessary in order to provide solderability and high thermal conductivity of the surface. The process of chemical deposition of nickel coatings elaborated in the research center VIAM yields the uniformal highly adhesive metallization. The kinetics of the deposition process has been studied and the estimation of the coatings quality has been made in comparison with commercially available samples produced elsewhere.
摘要:The growth of the microscopic fungi on the solid surface has a great influence on technical materials destruction. The aim of this study was to determine the influence of two strains of micromycetesPenicillium palitansstrain6 andArthrinium phaeospermumstrain 10 on morphological and structural properties of carbon steel surfaces in the nutrient medium. The difference in consumption of chlorine byP. palitans6(0.07 wt%) andA. phaeospermum10(0.04 wt%) and the difference in accumulation of a newly formed elementmanganese forP. palitans6(0.01 wt%) andA. phaeospermum10(0.03 wt%) has been observed. A relation between the surface and interface fungal stimulated processes, the biotic oxidation of steel surface as well as formation of the mixed oxides on the biomodified steel surface has been determined. The morphology of surfaces was characterized by scanning electron microscopy, the structure—by the X-ray diffraction method, Fourier transformation infrared and X-ray fluorescence spectroscopy.
摘要:In orthopaedics and orthodontics, the growth of nanotubes of titanium oxide on titanium implants is a promising route for improving the osseointegration. Among the fabrication routes to produce nanotubes, anodization was generally preferred due to its simplicity and low cost. TiO2 nanotubes are formed by the simultaneous anodic reaction and chemical dissolution due to the fluoride species present in the anodization bath. In this work, the formation of TiO2 nanotubes was studied in stirred ethylene glycol-H2O electrolyte (90 - 10 v/v) containing NH4F at room temperature. In order to study the effect of NH4F concentration, voltage and anodization time, and to reduce the number of experiments, a design of experiments (DOE) based on a 2k factorial design with four replicates at the center point was used. The analysis of variance (ANOVA) was used to evaluate the effects of the factors of control and their interactions on the percentage of the titanium surface coated by nanotubes. The dimensions of nanotubes (length and diameter) were also evaluated using field emission gun scanning electron microscopy. The cristallinity and phase composition of the oxide layers was investigated by X-ray diffractometry. The electrochemical behavior of as-received and anodized titanium specimens was studied in Ringer’s solution. The statistical analysis showed that fluoride concentration is the most significant factor. The best condition according to the response surface analysis is the center point (1% NH4F, 20 V, 2 h). The nanotubular oxide layers presented an amorphous structure. Electrochemical tests showed that TiO2 nanotubes coated titanium is less corrosion resistant than as-received titanium.
摘要:Hydrogenated amorphous carbon coatings, deposited by low pressure plasma to minimize the wear of C100 steel components, were optimized and characterized. In order to ensure good adhesion of the films to the steel surface, a thin Ti interlayer was deposited, by magnetron sputtering, before the plasma deposition. The chemical characterization of the deposits was performed by means of RAMAN, XPS, RBS and ERDA analysis, while nanoindentation, nanoscratch and nanowear tests allowed to estimating the tribomechanical properties of the deposits, with the aim of evaluating their scuff-resistance. It was found that the optimized plasma deposited hydrogenated amorphous carbon coatings were well adherent to C100 steel and increased more than 70% its surface hardness.
摘要:Binder is an important ingredient in pigment coating as it is used to impart adhesion, gloss and flexibility to the dried film as well as binding the pigment particles together. The aim of this work was to synthesize polymeric binders via radical copolymerization of acrylic acid (AA) with maleic anhydride (MA) and with 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). The chemical structures of the prepared binders were characterized by FTIR and 1HNMR analysis. The rheology of the prepared binders was also investigated. The prepared binders were applied in paper coating suspensions and their effects on optical, mechanical, and physical properties in addition to printability of the coated paper were studied. The results showed that acrylic maleic anhydride copolymers increased the adhesion, gave good film forming properties and good surface activity which increased print quality of paper coating. It was also found that MA/AA (50:50) and the blend between MA/AA (50:50) with AMPS:AA (30:70) have more suitable coating film properties and have highest pick resistance which is resemble to the commercial binder.
摘要:Surfactants used for formulation metal working fluids. In the present paper, the inhibitive effect of synthesized anionic surfactant P-decyloxy p-sodium sulphonateazobenzene with chemical structure H21C10O-Ph-N=N-Ph-SO3Na and 1-ethyl-1-dodecyl-2-sulphonate-4-(hydroxyl ethyl)-piprazine on the corrosion of carbon steel in sulphuric acid solution is measured by the weight loss method. The relationships between the concentrations of these inhibitors and their surface properties, thermodynamic properties, surface coverage and inhibiting efficiency, have been investigated. The results indicate that P-decyloxy p-sodium sulphonate azobenzene is superior to 1-ethyl-1-dodecyl-2-sulphonate-4-(hydroxyl ethyl)-piprazine at high acid concentration. These inhibitors blend with coupling agent to produce water miscible cutting fluid. Values of surface tension of these additives were measured in water phase and consequently CMC was determined for all inhibitors. The efficiency of these inhibitors depends on their chemical structure and the presence of hydrophilic group to association of the surfactant with metal surface, hence very good wetting properties. The anti-corrosion characteristic of surfactants increases with increasing polar linkages in the aromatic moieties forming chelated and coordinated layer. This is due to the increase in number of sites to chemisorption on the metal surface. These studies have led to much clear evidence of the intimate relationship between the chemical structure of the surfactants and their efficiency. More confirmation for suggested mechanism was investigated by measuring the area occupied per molecule of the surfactant at aqueous phase. The results indicate that the amphoteric surfactant more efficient than anionic surfactant. The antioxidants activities of different dosages of inhibitors were evaluated and suggested mechanism according to their thermodynamics parameters. The oxidation of the oil has been carried for different time intervals. The degradation of the oil has been monitored by total acid formation.
摘要:Nanocomposite films based on poly (3,4-ethylenedioxy thiophene) (PEDOT), functionalized single-walled carbon nanotubes and different dopants were studied. It was fabricated by a simple oxidative electropolymerization method. The dopant substances used were SDS (Sodium dodecyl sulfate) and tiron (1,2-Dihydroxybenzene-3,5-disulfonic acid disodium salt hydrate). These nano-composite films were grown electrochemically from aqueous solutions such that constituents were deposited simultaneously onto substrate electrode. The synthetic, morphological and electrical properties of the nanocomposite films obtained were compared. Scanning electron microscopy (SEM) revealed that the composite films consisted of nanoporous networks of SWCNTS (single-walled carbon nanotubes) coated with polymeric film. Cyclic voltammetry (CV), electro-chemical impedance spectroscopy (EIS) and FT-IR spectroscopy demonstrated that these composite films had similar electrochemical response rates to pure polymeric films but a lower resistance and much improved mechanical integrity. The negatively charged functionalized carbon nano-tubes (CNTSF) served as anionic dopant during the electropolymerization to synthesize polymer/CNTSF composite films. The specific electrochemical capacitance of the composite films is a significantly higher value than that for pure polymer films prepared similarly. Using these composite films, the modified electrodes with improved properties were obtained. (In this paper, for simplicity, the SWANTs-COOH group will be noted CNTsF which means functionalized carbon nanotubes.)
摘要:Development of novel functional devices has been expected by modification for Si surface. This study investigated immobilization and roles of the Si surface with flowing surfactant by in situ ATR-FTIR method. This result suggested that the surfactant prevented oxidation of the hydrogen-terminated Si surface from the higher concentration in aqueous solution. These would guard the Si surface against H2O molecules.
摘要:Seeking ways to diminish Egypt’s dependency on foreign oil imports, we had to look for the obvious resources to exploit. Oil shale is one of Egypt’s resources that are left abandoned and not used. This project is aiming at introducing both experimental analysis for oil shale in Egypt and the best production technique for it. This study is about experimentally analyzing different samples of potential oil shale fields in Egypt. Samples that are analyzed in this project are from two locations in Egypt: Quseir-Safaga and Abu-Tartur Western Desert, and they are compared to one of the best oil shale fields in the world, which is from Green River Formation Colorado. The experiments were done using AUC lab retort to experimentally determine the critical temperature that will lead to the maximum production using sudden and gradual change in temperatures, which turned out to be sudden change at 500°C. Thereafter, the degree of API gravity was calculated for each run. Then the oil samples were determined for impurities and liquid chromatography results in the Egyptian Petroleum Research Institute. Part two of the study plan has been included to determine the ultimate ways of producing efficiently, ecologically and economically.
摘要:Using density functional theory, the adsorption of CO, CO2, NO and CO2 gas molecules on different chiralities and diameters of single carbon nanotubes is investigated in terms of energetic, electronic properties and surface reactivity. We found that the adsorption of CO and CO2 gas molecules is dependent on the chiralities and diameters of CNTs and it is vice versa for NO and NO2 gas molecules. Also, the electronic character of CNTs is not affected by the adsorption of CO and CO2 gas molecules while it is strongly affected by NO and NO2 gas molecules. In addition, it is found that the dipole moments of zig-zag CNTs are always higher than the arm-chair CNTs. Therefore, we conclude that the zig-zag carbon nanotubes are more preferred as gas sensors than the arm-chair carbon nanotubes, especially for detecting NO and NO2 gas molecules.
摘要:Quantum energies which are used in applications are usually composed of repulsive and attractive terms. The objective of this study is to use an accurate and efficient fitting of the repulsive energy instead of using standard parametrizations. The investigation is based on Density Functional Theory and Tight Binding simulations. Our objective is not only to capture the values of the repulsive terms but also to efficiently reproduce the elastic properties and the forces. The elasticity values determine the rigidity of a material when some traction or load is applied on it. The pair-potential is based on an exponential term corrected by B-spline terms. In order to accelerate the computations, one uses a hierarchical optimization for the B-splines on different levels. Carbon graphenes constitute the configurations used in the simulations. We report on some results to show the efficiency of the B-splines on different levels.
摘要:The fight against dirt settling on the hulls of ships and more generally on all underwater structures is more than 2000 years. The need for effective antifouling paints, which prevents the establishment and growth of marine organisms on submerged structures, is universally recognized. In this work, we synthesize two perfluorinated surfactants from simple monomers. After describing the reactions, we discuss the different analyzes of the proton nuclear magnetic resonance (1H NMR), the fluorine nuclear magnetic resonance (NMR I9F), gel permeation chromatography (GPC) and the light scattering (LS) at a fixed angle 90. The glass transition temperature of the two surfactants diethylallylphosphonate and allylamine are obtained by Differential Scanning Calorimetry (DSC). Antifouling paint properties were followed by exposure of the plates to the marine environment by visual observation.
摘要:P-type (100) oriented silicon wafers were etched with vapors of concentrated Hydrofluoric acid in a reaction chamber under continuous vapor-flow at standard temperature and pressure. The surface morphology of the etched samples was examined by scanning electron microscope and pore size analyzer. The radius of the pores and quantum dots were found to be 6 nm and 4 nm respectively. Etched samples emitted red luminescence when exposed to ultra violet (UV) light. The red luminescence emitted by the etched surface has been assigned to energy states induced by quantum confinement of holes.
摘要:Silicon wafers (p-type) were etched under continuous flow of HF vapors in a reaction chamber at standard temperature and pressure. Etched surface of the silicon wafer was found emitting red luminescence when exposed to ultra violet (UV) light. XRD and Atomic Force Microscopy of the etched samples were carried out to study the surface of the etched silicon. It is noticed that etching has removed the stress induced atomic layers of silicon at grain boundaries and layer of porous silicon has been formed at the surface of silicon wafer which has higher inter planer distance than the silicon itself. The size of dots observed on the surface of etched silicon is of the order of few nm. The red emission from the surface of etched silicon appears to be due to the energy states induced by quantum confinement.
摘要:This paper describes a simple form, the theory to determine the crystallization fraction during the phase transformation of a solid, at a constant heating rate, from data obtained by impedance spectroscopy, where the change of the applied alternating voltage and measured current are proportional to the microstructural changes at the sample, corresponding to the volume fraction of a series layer model of two phases. To determine the volume fraction of each phase present in the sample, electrical data are obtained: conductivity and permittivity at DC, which are modeled by an electrical circuit composed by 2-RC, taking into that the permittivity and the occupied volume correspond to the filling fraction of each phase. By Cathodic Ersion or Sputtering, samples were obtained in film form of about 500 in thickness, composed of an alloy of Sb2Te3, in amorphous phase. To ensure the existence of the phase transformation in the sample, phase transition tests are performed by changes in: Reflection Optics, Electrical Resistivity and X-Ray Diffraction, showing clearly the presence of such a transformation. In the final part of this work, it completely shows the experimental results, giving a clear and precise idea of the kinetics of phase transformation of Sb2Te3 alloy, by impedance spectroscopy technique, which proves to be a simple and practical calculation tool.
摘要:In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.
摘要:The refolding of denatured hen egg white lysozyme (HEWL) was examined by surfactants at a high final refolded HEWL concentration (1 mg/mL). Hexadecyltrimethylammonium bromide (CTAB) and sucrose fatty acid monoester (DK-SS) were used to dissolve denatured HEWL without denaturants such as guanidine hydrochloride (GuHCl) and urea. When denatured HEWL was perfectly dissolved in buffer solutions containing surfactants and dithiothreitol (DTT), the concentration of CTAB was about one-twentieth times less than that of DK-SS. The concentration of CTAB strongly affected the refolding yield, and the maximum refolding yield was obtained at 0.88 mM CTAB, which is around the critical micelle concentration of CTAB. The refolding yield was influenced by the molar ratio of oxidized glutathione (GSSG) to DTT, and the maximum refolding yield was obtained when [GSSG]/[DTT] was 1.5. The refolding yield was markedly dependent upon the solution pH of HEWL, and exhibited 80% at pH 5.2.
摘要:Black-colored titanium was obtained by anodic oxidation of a commercially pure grade-1 titanium sheet in a 0.06 M NH4NO3 solution, followed by heat treatment at 773 K for 1 h in a vacuum furnace. The resulting oxide layer on the titanium substrate was examined by X-ray photoelectron spectroscopy, X-ray diffraction, glow discharge spectroscopy, and scanning electron microscopy. It was found that the oxide layer on the black-colored titanium sheet was several micrometers thick and mainly consisted of rutile TiO2 exhibiting a sponge like nanoporous structure. It is considered that the black-colored appearance of the titanium sheet is due to the sponge like nanoporous structure of the oxide layer absorbing the incident light. The photocatalytic activity of the black-colored titanium sheet was examined by observing the decomposition of a methylene blue (MB, C16H18N3SCl) solution under ultraviolet irradiation due to the existence of rutile TiO2. The sheet also exhibited photocatalytic activity under visible light irradiation. It is believed that the photocatalytic response upon irradiation with white light is due to carbon doping of the titanium oxide layer on the titanium substrate.
表面工程材料与先进技术期刊(英文)的期刊信息
创刊时间:2011
地区:CN
语言:中文
热门主题:LT
SUB
COATINGS
WEAR
CORROSION
SURFACE
NANOTUBES
TITANIUM
LASER
MICROSCOPY