Influence of rare earth metals on the characteristics of anodic oxide films on aluminium and their dissolution behaviour in NaOH solution

The characteristics of oxide films on Al and Al1R alloys (R = rare earth metal = Ce, Y) galvanostatically formed (at a current density of 100 μA cm⁻²) in borate buffer solution (0.5 M H₃BO₃ + 0.05 M Na₂B₄O₇·10H₂O; pH = 7.8) were investigated by means of electrochemical impedance spectroscopy. EIS spectra were interpreted in terms of an “equivalent circuit” that completely illustrate the Al(Al1R alloy)/oxide film/electrolyte systems examined. The resistance of the oxide films was found to increase on passing from Al to Al1R alloys while the capacitance showed an opposite trend. The stability of the anodic oxide films grown in the borate buffer solution on Al and Al1R alloys was investigated by simultaneously measuring the electrode capacitance and resistance at a working frequency of 1 kHz as a function of exposure over a period of time to naturally aerated 0.01 M NaOH solution. Analyses of the electrode capacitance and resistance values indicated a decrease in chemical dissolution rate of the oxide films on passing from Al to Al1R alloys.     

Synthesis, characterization and densification of WCu nanocomposite powders

In the present investigation, W20-40wt.% Cu nanocomposite powders with average sizes ranging between 25 and 30 nm were synthesized by a soft chemical approach using tungsten hexacarbonyl [W(CO)₆] and copper acetonyl acetonate [Cu(acac)₂] as metal precursors. Particle size, morphology and distribution were measured using transmission electron microscope (TEM) and small angle X-ray scattering (SAXS). Surfactant coating on WCu composite powders was removed on heat treatment of powders at 450 °C in hydrogen atmosphere for 1 h. Elemental analyses of as-synthesized and annealed (at 450 °C) WCu nanocomposite powders were carried out using inductively coupled plasma-optical emission spectrometer (ICP-OES) and Leco gas analyzers. X-ray diffraction studies showed that the tungsten phase is amorphous while the crystal structure of copper phase is fcc in as-synthesized WCu nanocomposite powders. After annealing at 700 °C peaks corresponding to bcc tungsten are observed and peaks corresponding to fcc copper become sharper. Relative densities of 98.2%, 98.8% and 99.2% were achieved for W20wt.% Cu, W30wt.% Cu, and W40wt.% Cu composite powders respectively when sintered at 1000 °C.     

Microstructure characterisation and stress analysis of the Ti48Al2Ag coating on the near-α titanium alloy

The microstructure and phase composition of the protective Ti48Al2Ag coating produced on Timetal 834 by magnetron sputtering have been examined by scanning and analytical transmission electron microscopy (SEM, TEM). TEM investigations revealed that Ti48Al2Ag coating consists of two sublayers: outer columnar γ-TiAl and amorphous Ti₅Al₃O₂. Energy-dispersive synchrotron radiation diffraction was applied for stress analysis. The results show that there are tensile residual stresses present within the Timetal 834 substrate and compressive residual stresses within the γ-TiAl sublayer.     

Cutting simulation capabilities based on crystal plasticity theory and discrete cohesive elements

A material microstructure-level (MML) cutting model based on the crystal plasticity theory is adopted for modelling the material removal by orthogonal cutting of the Titanium alloy Ti6Al4V. In this model, the grains are explicitly taken into account, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the machined material. To obtain the material degradation process, the continuum intra-granular damage model and the discrete cohesive zone inter-granular damage model have been implemented. Zero thickness cohesive elements are introduced to simulate the bond between grain interfaces. The material model is validated by the simulation of a compression test and results are compared with experimental data from the literature. Simulation results demonstrate the ability of the MML cutting model to capture the influence of the material microstructure, in terms of initial grain orientation angles (GOA), on chip formation and machined surface integrity.     

Novel low temperature atmospheric pressure plasma jet systems for silicon dioxide and poly-ethylene thin film deposition

In this study, both low-density plasma quartz tube (QT) and high-density plasma metallic tube (MT) jet-electrodes with pulsed-type alternating-voltage (AC) generator were used to investigate the influences of the process parameters and electrode types on the microstructures and the corrosion behaviors of silicon dioxide (SiO₂) or poly-ethylene (PE, (CH₂CH₂)n) thin films. Tetraethoxysilane (TEOS) and ethylene (C₂H₄) were used as precursors for SiO₂ and PE thin film deposition. The TEOS precursor was vaporized by an ultrasonic oscillator and introduced into the AP plasma systems by argon (Ar) carrier gas. The main plasma working gas was Ar gas mixed with or without oxygen gas. The pulsed-type AC generator, with a frequency of 30 kHz, a voltage of 10 kV and a wattage of 300 W, was used to deposit SiO₂ and PE thin films on the silicon and AISI 1005 low carbon steel substrates at the room temperature, respectively. The high-density plasma MT jet-electrode with an Ar gas flow rate of 6 slm, a precursor flow rate of 40 sccm and an oxygen flow rate of 40 sccm revealed optimal plasma dissociation and chemical reaction efficiencies to synthesize effective atomic stoichiometry of SiO₂ (in-organic films) thin films. However, the low-density plasma QT jet-electrode with an Ar gas flow rate of 6 slm and an ethylene flow rate of 15 sccm appeared optimal plasma-induced polymerization efficiency to exhibit reasonable atomic stoichiometry of PE (organic films) thin films. Moreover, the optimal SiO₂ thin films deposited by MT jet-electrode possessed better corrosion resistant integrity than the optimal PE thin films synthesized by QT jet-electrode. It was also found that SiO₂ and PE thin films synthesized by the AP plasma method possess effective corrosion barrier characteristics like other deposition techniques.     

Antifogging and antireflective silica film and its application on solar modules

Superhydrophilic silica film with antifogging and antireflective properties was prepared by dip-coating the glass in SiO₂ nanoparticles sol. The transparent superhydrophilic film was composed of silica nanoparticles of about 20-30 nm in diameter. The combination of hydrophilic SiOH on the surface and nanoporous surface topography was believed to be responsible for the antifogging property. The nanopores also effectively reduced the refractive index of the film and resulted in the antireflective property. By sintering the multifunctional silica film, a pencil hardness of 2H could be obtained. Application of the functional film in full-sized photovoltaic modules (1580 × 808 × 35 mm) demonstrated an increase of the power output of about 2%, 5% and 8%, respectively, at incidence angles of 0°, 30° and 60°.     

Radio frequency plasma polymers of n-butyl methacrylate and their controlled drug release characteristics: I. Effect of the oxygen gas

The effect of oxygen gas on the chemical structure, surface property and controlled drug release characteristics of radio frequency (RF) plasma poly-n-butyl methacrylate (PPBMA) thin films was investigated. The ATR-FTIR and XPS spectra of the resultant PPBMA films showed relatively higher concentration of C-H, C-C and CC groups, but less intense peaks of CO and C-O functionalities, which imply that the oxygen gas had no significant influence on the chemical structure of the plasma films. Results of the SEM experiment revealed that a dome-like structure was observed in the case of deposition without oxygen, but in the case of deposition with oxygen, a smooth and dense surface was produced. Moreover, the hydrophilicity of PPBMA obtained from the deposition with oxygen was higher than that without oxygen. Drug release from PPBMA deposition coating without oxygen had biphasic patterns, a fast release followed by a slow release, but the one with oxygen exhibited a slow Higuchi release.