The effect of atmospheric plasma treatment of recycled carbon fiber at different plasma powers on recycled carbon fiber and its polypropylene composites

To increase the mechanical properties of recycled carbon fiber-reinforced polypropylene (PP) composites, recycled carbon fibers (RCF) were subjected to atmospheric plasma treatment at different plasma powers (100, 200, and 300 W). The changes on surface topography and roughness of RCF were examined by atomic force microscopy. Plasma treatment of RCF increased the roughness value of RCF. The variation of surface elemental compositions and tensile strength of RCF were determined by using X-ray photoelectron spectroscopy and tensile test, respectively. Plasma-treated RCF-reinforced PP composites were fabricated using high speed thermo-kinetic mixer. Plasma treatment of RCF at 100 W increased the tensile and flexural strength values of RCF-reinforced PP composites considerably by 17 and 11%, respectively. However, plasma treatment of RCF at higher plasma powers (200 W and 300 W) decreased tensile and flexural strength values of composites because of the etching of RCF. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47131.     

Electrochemical impedance spectroscopy and morphological analyses of pyrrole, phenylpyrrole and methoxyphenylpyrrole on carbon fiber microelectrodes

In this study, N-pyrrole (Py), N-phenylpyrrole (PhPy), and 1[4-methoxyphenyl]-1H-pyrrole (MPhPy) homopolymers were synthesized electrochemically onto carbon fiber microelectrodes (CFMEs). The influences of the substituent effect on electrochemical impedance spectroscopy (EIS) were studied comparatively. All the monomers were electrodeposited in 0.05 M tetraethyl ammonium perchlorate (TEAP)/dichloromethane (CH₂Cl₂) solution and characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The morphological study reveals that the polymers were deposited as a continuous and well adhered film to surface of the CFME. An equivalent electrical circuit for three different monomers on CFMEs was proposed and experimental data were simulated to obtain the numerical values of circuit components. All results support the high quality film deposition that resulted in desired electronic properties due to the electron donating behaviors of substituent group of phenyl and methoxy.     

Mitigating insider threat by profiling users based on mouse usage pattern: ensemble learning and frequency domain analysis

International Journal of Information Security - Exploring novel security layers in academia and industry is always a concern due to the types of malware developing currently. Adding a widely...     

Corrosion behaviour of multiwall carbon nanotube/magnesium composites in 3.5% NaCl

Corrosion behaviour of multiwall carbon nanotube (MWNT) modified pure magnesium (Mg) composites (MWNT/Mg) prepared by melt stirring technique was investigated by weight loss, H₂ gas collection and pH measurements, as well as electrochemical methods such as open circuit potential (OCP) monitoring, polarisation curves and electrochemical impedance spectroscopy (EIS). Results show that the corrosion rate of MWNT/Mg composites is significantly higher than the corrosion rate of pure Mg. The corrosion rate of the composites also depends on the degree of dispersion of MWNTs during melt stirring process. The role of the MWNTs in increasing the corrosion rate clearly can be attributed to their high cathodic activity. Characterization of the corrosion product layers indicates that dispersion of MWNTs in the matrix leads to a more homogeneous coverage of the surface by corrosion products, and the lowest thickness of the corrosion product layer. The corrosion product layers in all cases provide poor protection of the surface. The corrosion rate of pure Mg as well as Mg/MWNT composites significantly increases during 1-week immersion; this effect is the strongest for the composite with dispersed nanotubes and can be attributed to the increased cathodic kinetics with time.     

Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder

The production of tungsten by direct current reduction has been investigated. Experimental studies involved the electrochemical reduction of the solid tungsten compounds tungsten trioxide (WO₃) and calcium tungstate (CaWO₄) in the form of an assembled cathode of porous pellets attached to a current collector. Molten calcium chloride and a molten solution of calcium chloride and sodium chloride at eutectic composition, 48 pct mol NaCl, were used as the electrolytes. Reduced samples were characterized by means of X-ray diffraction analyses and scanning electron microscopy. The results of X-ray analyses, supported with thermodynamic computations, showed that WO₃ cannot be used without loss in processes that involve the use of CaCl₂ at high temperatures because it reacts with CaCl₂ by releasing volatile tungsten oxychloride. In the electrochemical reduction of CaWO₄, X-ray diffraction results indicated the presence of tungsten with significant concentrations of calcium compounds. Metallic tungsten was obtained after treating the reduced samples with dilute hydrochloric acid solutions.     

Effect of Extraction Methods on the Properties of Althea Officinalis L. Fibers

In this study, the effect of extraction methods on the properties of Althea officinalis l. (marshmallow) fibers was investigated. For this purpose, obtaining the fibers from stem was done by water and chemical extraction. After the extraction process, mechanical and thermal properties of althea fibers were investigated and morphological structure was examined. Crystallinity indexes (CI) of fibers were determined. Scanning electron microscopy results revealed that extraction of althea officinalis fibers by alkali boiling in 5% NaOH solution led to removal of surface impurities and also according to X-ray diffraction results, crystallinity index of fibers was improved by 14%. Chemically extracted fibers showed 37% higher tensile strength when compared to water extracted fibers. Density measurements revealed that chemically retted fibers have higher density. Also, Fourier Transform Infrared Spectroscopy analysis showed that chemical extraction caused change of chemical composition by decreasing and/or disappearing of some peaks which belong to hemicellulose and lignin.     

Effect of acidic etching and fluoride treatment on corrosion performance in Mg alloy AZ91D (MgAlZn)

Fluoride activation of Mg AZ91D die-cast alloy surfaces by ammonium fluoride pre-treatment is an important procedure in industry. The procedure forms a fluoride rich layer on the surface enabling the formation of coatings in a uniform manner during further treatments. The present study explores the time dependence of the sequential two-step pre-treatment process – acid etching in H₂SO₄ (first step) and steeping in NH₄F (second step) – on the corrosion properties of AZ91D alloy. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) show the α phase to be selectively etched via a “peeling-off” mechanism that eventually leads to the undercutting and undermining of the β-phase network. After ammonium fluoride treatment, variations in structure and chemical composition of the fluoride rich layer were shown to depend on the underlying phase of the alloy surface by SEM and time-of-flight secondary-ion-mass-spectroscopy (ToF-SIMS). After step 1 (acid etching), electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution indicates greater charge transfer resistance (R_t) for samples of greater exposed β surface area. This greater R_t increases after step 2 (NH₄F steeping). Furthermore, the corrosion protection properties of F-coated AZ91D can be significantly enhanced by optimizing the durations of the two pre-treatment steps. Indeed, over extension of the duration of either step 1 or step 2 leads to deterioration of the overall corrosion resistance.     

Poly(N-methyl aniline) thin films on copper: Synthesis, characterization and corrosion protection

Poly(N-methyl aniline) (PNMA) coatings were synthesized on copper by electrochemical polymerization of N-methyl aniline in aqueous oxalic acid solution by using cyclic voltammetry. The optimum electrodeposition conditions (e.g. upper potential limit, scan rate and cycle number) were determined in order to obtain PNMA coatings to have the best corrosion performance. PNMA coatings were characterized by cyclic voltammetry, Fourier Transform Infrared-Attenuated Total Reflectance spectroscopy and scanning electron microscopy. Redox parameters found after electrochemical tests indicate a thin film character and diffusion controlled electroactive behavior of PNMA. Corrosion test results revealed that PNMA coating appears to enhance protection of copper in 0.1 M H₂SO₄ solution.     

Electrochemical decomposition of SiO2 pellets to form silicon in molten salts

Direct electrochemical reduction of porous SiO₂ pellets in molten CaCl₂ salt and CaCl₂-NaCl salt mixture was investigated by applying 2.8 V potential. The study focused on the effects of temperature, particle size of SiO₂ powder starting material and the behavior of cathode contacting materials during electrochemical reduction process. The starting materials and the electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy mainly. The studies showed that smaller particle sizes and higher temperatures had slightly positive effects in increasing the reduction rate within the ranges covered in this study. The results were interpreted from variations of current and accumulative electrical charge that passed through the cell as a function of duration of electrochemical reduction under different conditions. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO₂ in molten salts may become a method to produce silicon that could be used in solar energy utilization. Furthermore, X-ray diffraction analysis results indicated that the silicon produced at the cathode reacts with contacting materials; nickel, and iron in stainless steel to form Ni-Si and Fe-Si compounds due to very reactive nature of silicon especially at high temperatures.