The influence of oxidation with nitric acid on the preparation and properties of active carbon enriched in nitrogen

The effect of oxidation by 20% nitric acid on the properties and performance of active carbons enriched with nitrogen by means of the reaction with urea in the presence of air has been studied. The study has been made on demineralised orthocoking coal and the carbonisates obtained from it at 600 or 700 °C, subjected to the processes of nitrogenation, oxidation and activation with KOH in different sequences. The amount of nitrogen introduced into the carbon with the aid of urea has been found to depend on the stage at which the process of nitrogenation was performed. The process of oxidation of the demineralised coal and the active carbon obtained from the former has been found to favour nitrogen introduction into the carbon structure. In the process of nitrogenation of the carbonisates the amount of nitrogen introduced has inversely depended on the temperature of carbonisation. The modifications of the processes permitted obtaining materials of different textural parameters, different acid-base character of the surface and different iodine sorption capacity.     

Mercury removal from aqueous solution and flue gas by adsorption on activated carbon fibres

The use of two activated carbon fibres, one laboratorial sample prepared from a commercial acrylic textile fibre and one commercial sample of Kynol^®, as prepared/received and modified by reaction with powdered sulfur and H₂S gas in order to increase the sulfur content were studied for the removal of mercury from aqueous solution and from flue gases from a fluidized bed combustor. The sulfur introduced ranged from 1 to 6 wt.% depending on the method used. The most important parameter for the mercury uptake is the type of sulfur introduced rather than the total amount and it was found that the H₂S treatment of ACF leads to samples with the highest mercury uptake, despite the lower sulfur amount introduced. The modified samples by both methods can remove HgCl₂ from aqueous solutions at pH 6 within the range 290-710 mg/g (ACF) which can be favourably compared with other studies already published. The use of a filter made with an activated carbon fibre modified by powdered sulfur totally removed the mercury species present in the flue gases produced by combustion of fossil fuel.     

Influence of processing parameters on atmospheric pressure plasma etching of polyamide 6 films

This study is designed to systematically investigate how various factors, such as treatment duration, output power, oxygen gas flux, jet to substrate distance, and moisture regain, influence atmospheric pressure plasma etching rate of polyamide 6 (PA 6) films. The etching rate increased as the output power, oxygen gas flux, and moisture regain increased. As the treatment time increased, the etching rate increased first and then decreased. When the substrate was too close or too far from the nozzle, the etching rate was almost not measurable. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show an increased surface roughness after the plasma treatment. X-ray photoelectron spectroscopy (XPS) shows a decreased carbon content and an increased oxygen content after the plasma treatment. T-peel strength shows an improved bonding strength between the PA 6 films and an adhesive tape after the plasma treatment.     

Effect of vapor attenuation in surface ablation of cobalt by pulsed UV laser

Numerical calculations based on a thermal model were presented, which describe the process of target heating and ablation of cobalt during irradiation by 30-ns laser pulses at 308 nm. The attenuation of laser by vapor has been taken into account in this model. As results of the calculations, the temperature distribution beneath the target surface and the temporal evolution of surface temperature were given. The dependence of ablation rate on laser fluence was also studied based on this model. The surface ablation of cobalt with pulsed excimer laser was investigated experimentally. Our model considering proper vapor attenuation has shown to be in good agreement with the experimental results. Received: 20 January 2000 / Accepted: 13 March 2000 / Published online: 5 July 2000     

Influence of jet-to-substrate distance on plasma etching of polyamide 6 films with atmospheric pressure plasma

In this study, polyamide 6 films were treated with different jet-to-substrate distances to investigate how it influenced the etching effect of plasma treatment. When the samples were too close or too far from the nozzle, the etching rate was almost not measurable. When the distance was 2 mm, the etching rate was larger than that of other distance. Decrease in contact angle was observed under 2 mm or 3 mm of jet-to-substrate distance. However, the contact angle had no change when jet-to-substrate distance was 1 mm or 6 mm. It can be seen that the peel strength increased when jet-to-substrate distance was 2 mm or 3 mm, and the peel strength was the largest when jet-to-substrate distance was 2 mm. However, the peel strength had no change when jet-to-substrate distance was 1 mm or 6 mm. These results were corresponding to SEM and XPS results.     

Phase transformation during surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser

Surface ablation of cobalt-cemented tungsten carbide hard metal has been carried out in this work using a 308 nm, 20 ns XeCl excimer laser. Surface microphotography and XRD, as well as an electron probe have been used to investigate the transformation of phase and microstructure as a function of the pulse-number of laser shots at a laser fluence of 2.5 J/cm². The experimental results show that the microstructure of cemented tungsten carbide is transformed from the original polygonal grains of size 3 μm to interlaced large, long grains with an increase in the number of laser shots up to 300, and finally to gross grains of size 10 μm with clear grain boundaries after 700 shots of laser irradiation. The crystalline structure of the irradiated area is partly transformed from the original WC to βWC_1-x, then to αW₂C and CW₃, and finally to W crystal. It is suggested that the undulating ‘hill–valley’ morphology may be the result of selective removal of cobalt binder from the surface layer of the hard metal. The formation of non-stoichiometric tungsten carbide may result from the escape of elemental carbon due to accumulated heating of the surface by pulsed laser irradiation. Received: 13 July 2000 / Accepted: 27 October 2000 / Published online: 10 January 2001     

Laser removal of loose uranium compound contamination from metal surfaces

Pulsed laser removal of surface contamination of uranyl nitrate and uranium dioxide from stainless steel has been studied. Most of the loosely bound contamination has been removed at fluence levels below 0.5 J cm⁻², leaving about 5% fixed contamination for uranyl nitrate and 15% for uranium dioxide. Both alpha and beta activities are then sufficiently low that contaminated objects can be taken out of a restricted radiation area for re-use. The ratio of beta to alpha activity is found to be a function of particle size and changes during laser removal. In a separate experiment using technetium-99m, the collection of removed radioactivity in the filter was studied and an inventory made of removed and collected contamination.     

Behaviour of Self-Standing CVD Diamond Film with Different Dominant Crystalline Surfaces in Thermal-Iron Plate Polishing

Self-standing CVD diamond films with different dominant crystalline surfaces are polished by the thermal-iron plate polishing method. The influence of the dominant crystalline surfaces on polishing etfficiency is investigated by measuring the removal rate and final roughness. The smallest rms roughness of 0.14 μm is measured with smallest removal rate in the films with the initial （220） dominant crystalline surface. Activation energy for the polishing is analysed by the Arrhenius relation. It is found that the values are 170kJ/mol, 222kJ/mol and 214kJ/mol for the film with three different dominant crystalline surfaces. Based on these values, the polishing cause is regarded as the graphitization-controlling process. In the experiment, we find that transformation of the dominant crystalline surfaces from （111） to （220） always appears in the polishing process when we polish the （111） dominant surface.     

The effect of cerium and lanthanum surface treatments on early stages of oxidation of A361 aluminium alloy at high temperature

X-ray photoelectron spectroscopy analysis has been used to study the surface of A361 aluminium alloy after electrodeposition of cerium and lanthanum compounds followed by oxidation tests in air at 100-500 °C for 2 h. Cerium and lanthanum oxide deposits are found on the β-AlFeSi second phase particles and to a lesser extent on the eutectic Al-Si areas, while the α-Al phase is covered with a thin aluminium oxide film. This uneven deposition may be related either to a preferential nucleation and growth process on active interfaces or to the differing electrical conductivity of the phases and intermetallic compounds of the alloy. Initial stages of oxidation of A361 alloy disclosed thickening of the aluminium oxide layer and Mg enrichment at the surface, especially above 400 °C. Rare earth deposits revealed two different effects: reduced Mg diffusion and enhanced thickening of the aluminium oxide film. A distinctive behaviour of Ce oxide appears at 300-500 °C related with Ce(III) to Ce(IV) transition.     

Microstructure and tribological performance of self-lubricating diamond/tetrahedral amorphous carbon composite film

In order to smooth the rough surface and further improve the wear-resistance of coarse chemical vapor deposition diamond films, diamond/tetrahedral amorphous carbon composite films were synthesized by a two-step preparation technique including hot-filament chemical vapor deposition for polycrystalline diamond (PCD) and subsequent filtered cathodic vacuum arc growth for tetrahedral amorphous carbon (ta-C). The microstructure and tribological performance of the composite films were investigated by means of various characterization techniques. The results indicated that the composite films consisted of a thick well-grained diamond base layer with a thickness up to 150 μm and a thin covering ta-C layer with a thickness of about 0.3 μm, and sp³-C fraction up to 73.93%. Deposition of a smooth ta-C film on coarse polycrystalline diamond films was proved to be an effective tool to lower the surface roughness of the polycrystalline diamond film. The wear-resistance of the diamond film was also enhanced by the self-lubricating effect of the covering ta-C film due to graphitic phase transformation. Under dry pin-on-disk wear test against Si₃N₄ ball, the friction coefficients of the composite films were much lower than that of the single PCD film. An extremely low friction coefficient (∼0.05) was achieved for the PCD/ta-C composite film. Moreover, the addition of Ti interlayer between the ta-C and the PCD layers can further reduce the surface roughness of the composite film. The main wear mechanism of the composite films was abrasive wear.     

Analysis of mechanism of carbon removal from GaAs(1 0 0) surface by atomic hydrogen

Etching of carbon contaminations from the GaAs(1 0 0) surface by irradiating with atomic hydrogen, which is one of the key reactions to promote high-quality thin films growth by molecular beam epitaxy (MBE), has been investigated by mass spectrometry (MS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It is shown that during the cleaning process at room temperature a total reduction of the Auger carbon signal, accompanied by desorption of methane as major reaction product, can be observed. The reaction pathways as well as the processes responsible for the observed carbon removal are discussed in detail to give a support for etching and growth quality enhancement not only in thin films epitaxy but in all atomic hydrogen promoted gas-phase III-V semiconductor processes.     

Characterization of AZ91 magnesium alloy and organosilane adsorption on its surface

Oxide formation on a clean AZ91-Mg alloy surface has been characterized by X-ray photoelectron spectroscopy (XPS), while the chemical composition of a mirror-polished sample was assessed by scanning Auger microscopy (SAM) and scanning electron microscopy (SEM) at different microstructural regions, referred to as the grain boundary, matrix and particle regions. XPS and SAM confirmed that Mg and Al are always present in the surface regions probed, whereas bulk characterization with energy dispersive X-ray (EDX) analysis was necessary to detect the additional alloying elements, Mn and Zn. Coating by 1% solutions of BTSE, γ-GPS and γ-APS at their natural pH values gave etching of the surface Mg oxide. Adsorption occurs on the different regions, but the attachment is weak, especially because of the fragile nature of the underlying substrate. However, increasing the concentration of BTSE to 4% formed a thicker and denser coating with better prospects for substrate protection.     

AFM investigation on surface evolution of amorphous carbon during ion-beam-assisted deposition

Hydrogen-free amorphous carbons (a-C) have been prepared on mirror-polished Si(1 1 1) wafers through thermally evaporated C₆₀ with simultaneous bombardments of Ne⁺ ions. The time evolution of film surfaces has been characterized by atomic force microscopy (AFM) at two temperatures of 400 and 700 °C, respectively. Based on the topography images and the root-mean-square (rms) roughness analysis, it is found that the a-C surfaces present roughening growth at the initial stage. With increasing growth time, the cooperative nucleation of the islands and pits appears on the surfaces, suggesting three-dimensional growth, and then they continue to evolve to irregular mounds at 400 °C, and elongated mounds at 700 °C. At the steady growth stage, these surfaces further develop to the structures of bamboo joints and ripples corresponding to these two temperatures, respectively. It is believed that besides ion sputtering effect, the chemical bonding configurations in the amorphous carbon films should be taken into considerations for elucidating the surface evolutions.     

Gas adsorption on a single walled carbon nanotube-model simulation

We simulate the conduction variation of a gas-adsorbed carbon nanotube by a hybridization model, which has been previously used to simulate the gas adsorption on a nanographite ribbon. Two energy parameters, hybridization interaction and orbital energy level, are employed to simulate and distinguish the adsorbed gases. Two mechanisms, carrier localization and charge distribution, coexist in the gas adsorption process and provide a qualitative explanation for the current increase or decrease in gas adsorption experiments for the carbon nanotube.     

Self-assembled formation of uniform InP nanopore arrays by electrochemical anodization in HCl based electrolyte

Attempts were made to optimize the electrochemical anodization process for the formation of high-density, regular and straight nanopore arrays on InP. The structure, shape and size of the pores were very sensitive to substrate orientations, electrolyte concentrations and anodization voltages. Among (1 1 1)A, (1 1 1)B and (0 0 1) substrate orientations, the most uniform and most straight nanopore arrays were obtained on (0 0 1) substrates at anodization voltages of 5-7 V by using 1.0-1.5 M HCl electrolyte containing HNO₃. The pore depth could be controlled up to 80 μm by the anodization time.     

Influence of the vacuum level upon the growth of carbon nanotubes on silicon carbide surface

We have investigated the influence of the vacuum level upon the growth of carbon nanotubes (CNTs) on 6H-SiC () surface.CNTs of about 160 nm in length were formed densely and uniformly on the 6H-SiC surface during annealing at 1700 °C in a high vacuum (∼10⁻² Pa). CNTs of about 1 μm in length were formed during annealing at 1700 °C in an ultra-high vacuum (∼10⁻⁷ Pa). However, CNTs were not formed and SiO₂ layers were formed on the SiC surface at 1700 °C in air. It is found that longer CNTs can grow up in an ultra-high vacuum, moreover, a little aligned and low-density graphite layers, or carbon nanofibers can also grow up.     

Surface diffusion of carbon atom and carbon dimer on Si(0 0 1) surface

Carbon (C) atom and carbon dimer (C2) are known to be the main projectiles in the deposition of diamond-like carbon (DLC) films. The adsorption and diffusion of the C adatom and addimer (C2) on the fully relaxed Si(0 0 1)-(2 × 1) surface was studied by a combination of the molecular dynamics (MD) and Monte Carlo (MC) simulation. The adsorption sites of the C and C2 on the surface and the potential barriers between these sites were first determined using the semi-empirical many-body Brenner and Tersoff potential. We then estimated their hopping rates and traced their pathways. It is found that the diffusion of both C and C2 is strongly anisotropic in nature. In addition, the C adatom can diffuse a long distance on the surface while the adsorbed C2 is more likely to be confined in a local region. Thus we can expect that smoother films will be formed on the Si(0 0 1) surface with single C atoms as projectile at moderate temperature, while with C2 the films will grow in two-dimensional islands. In addition, relatively higher kinetic energy of the projectile, say, a few tens of eV, is needed to grow DLC films of higher quality. This is consistent with experimental findings.     

Surface modification of a polyamide 6 film by He/CF4 plasma using atmospheric pressure plasma jet

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.     

Electroless deposition of copper and fabrication of copper micropatterns on CVD diamond film surfaces

Electroless deposition of copper on as-grown and amino-modification diamond substrates was investigated. The compact and uniform copper films were successfully electrolessly deposited on as-grown and amino-modification diamond substrates after activation by Pd/Sn colloid nanoparticles. The adhesion interaction between copper films and diamond substrates was roughly estimated by the ultrasonic treatment. The results showed the higher adhesion interaction between copper films and amino-modification diamond substrates than that between the copper films and as-grown diamond substrates due to the greater attractive force between the Pd/Sn colloid nanoparticles and amino-modified diamond surface. The favorable copper micropatterns were successfully constructed on diamond film surfaces by means of the catalyst lift-off method and the copper lift-off method. Furthermore, the electrochemical behavior of copper-modified boron-doped diamond (BDD) was studied for glucose oxidation in 0.2 M sodium hydroxide solution by using cyclic voltammetry, and the result indicated that copper-modified BDD exhibited high catalytic activity to electrochemical oxidation of glucose in alkaline media.     

Realization of controllable etching for ZnO film by NH4Cl aqueous solution and its influence on optical and electrical properties

ZnO films were deposited on c-plane Al₂O₃ substrates by pulsed laser deposition. The etching treatments for as-grown ZnO films were performed in NH₄Cl aqueous solution as a function of NH₄Cl concentration and etching time. It was found that NH₄Cl solution is an appropriate candidate for ZnO wet etching because of its controllable and moderate etching rate. The influence of etching treatment on the morphology, optical and electrical properties of the ZnO films has been investigated systematically by means of X-ray diffraction, atomic force microscope, photoluminescence and Hall effect. The results indicated that the surface morphology and optical properties of the films were highly influenced by etching treatment.