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.     

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.     

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.     

DFT and electrochemical studies of tris(benzimidazole-2-ylmethyl)amine as an efficient corrosion inhibitor for carbon steel surface

The corrosion inhibition properties of tris(benzimidazole-2-ylmethyl)amine (TBMA) were analyzed by DFT and electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy (EIS). DFT results clearly show that TBMA posses corrosion inhibition properties by having a delocalization region (N₁C₂N₃) in the benzimidazole ring that gives up their π electron density through its HOMO orbital to the metal LUMO to form a adsorption layer over the metallic surface; this has been proved by interacting the TBMA and its protonated structures with the surface of Fe₁₃ cluster, showing that the protonated moiety adsorbs strongly on the iron surface than that of the neutral structure. Electrochemical impedance data demonstrate that the interface between the electrode and the TBMA solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of adsorption layer over the iron surface.     

Structural characterization of amorphous hydrogenated-carbon nitride (aH-CNx) film deposited by CH4/N2 dielectric barrier discharge plasma: C, H solid state NMR, FTIR and elemental analysis

The chemical composition and bond structure of polymer like amorphous hydrogenated carbon nitride (aH-CN_x) thin films was studied by solid-state ¹³C and ¹H MAS NMR spectroscopy, FTIR spectroscopy and elemental analysis. The hydrogenated CN_x film was deposited on Si (100) substrate by CH₄/N₂ gas mixture dielectric barrier discharge (DBD) plasma. The broad ¹H signals obtained even at 33 kHz spinning speed with spinning side bands indicates the existence of a large proton proportion in the film. The ¹H and ¹³C signals are strongly broadened due to homo- and heteronuclear dipolar couplings and also due to amorphous nature of the deposited film. The local structure of the amorphous aH-CN_x film is dominated by C-C and C-N single bonds i.e. carbon is mainly in the sp³ hybridized state. The Fourier Transform infrared (FTIR) spectroscopy of the film indicates the typical regions for -C≡N, -(CO), -NH, vibrations together with overlapping NH and OH stretching bonds. CH₃ and C-N groups as well as species with CN conjugated double bonds are present in the deposited CN_x film. From elemental analysis it is obtained that the composition of the film is (in wt.%): C: 61.8, H: 8.4, N: 17.7.     

Sintering behaviors, magnetic and electric properties of Bi-Zn co-doped Co2Y ferrites

The Bi and Zn substitution effects on the sintering behaviors, magnetic and electric properties of hexagonal ferrites with a composition of 2(Ba_1−xBi_xO)·2(Zn_yCo_0.8−yCu_0.2O)·6(Fe_2−x/3Zn_x/3O₃) were investigated. The results showed that the addition of Bi and Zn can significantly promote Co₂Y densification. The Y phase may be triggered to decompose into M and spinel phases at high sintering temperatures (above 1050 °C) for samples with excess Bi (x = 0.2) substitution, which resulted in densification and magnetic properties degradation. Co₂Y ferrites with x = 0.1 and y = 0.4 sintered at 1050 °C show a relative density of 94%, a high initial permeability of 4.5, a quality factor (Q) of 50.     

Blue-emitting phosphor M2B5O9Cl: Eu (MSr, Ca) for white LEDs

Eu²⁺ doped M₂B₅O₉Cl (MCa, Sr) phosphors were prepared by a solid-state reaction method. Luminescent properties of as-synthesized phosphors were investigated under the excitation of near-ultraviolet (n-UV) light. Photoluminescence (PL) spectra revealed a blue emission band, and the emission band shifted to a longer wavelength region as Ca²⁺ substituted Sr²⁺. The photoluminescence excitation (PLE) spectra of M₂B₅O₉Cl: Eu²⁺ (MCa, Sr) showed broadband absorptions in the n-UV region. Moreover, the as-prepared phosphors were also compared with commercial BaMgAl₁₀O₁₇: Eu²⁺ (BAM) blue phosphor. The present phosphors showed a narrower full width at half-maximum and higher PL intensity than the reference BAM under the n-UV light excitation.     

Fracture properties of hydrogenated amorphous silicon carbide thin films

The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic-inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m⁻²) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited SiOSi suboxide bond formation that occurs in the films.     

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.