Stefanovic, Ivan S.Nastasovic, Aleksandra B.Sandic, Zvjezdana P.Surucic, Ljiljana T....
10页
查看更多>>摘要：A novel magnetic polymer/bentonite composite was prepared by suspension copolymerization of glycidyl methacrylate and ethylene glycol dimethacrylate in the presence of magnetic bentonite (MB-PGME) and functionalized with ethylene diamine and hexamethylene diamine (MB-PGME-ED and MB-PGME-HD). The obtained samples were characterized in terms of structure as well as thermal, magnetic and morphological properties. The sorption of rhenium (Re) and tungsten (W) from aqueous solution onto MB-PGME-ED and MB-PGME-HD was investigated considering their contact time and different initial ion concentration, giving possibility for usage of these composites as commercial sorbents. The sorption system follows the pseudo-second order and intraparticle diffusion kinetic models. The results indicated a better fit with the Freundlich isotherm model.
Mathad, Shridhar N.Abbigeri, Megha B.Shashidharagowda, H.
16页
查看更多>>摘要：The Co1-xCuxMn2O4 samples were effectively synthesized by means of chemical reagents and highly scalable co-precipitation technique. X-ray diffraction investigation affirmed the tetragonal structure possessed by Co1-xCuxMn2O4 with crystal size ranging from 12 nm to 22 nm. The crystallite size and micro strain values were correlated using Williamson-Hall plot and size-strain plot method. SEM images showed highly porous, less dense, agglomerated grains with grain size from 3.93 mu m to 13.73 mu m. Vibrational characterization of the samples was completed using FTIR spectra and Raman spectra which affirm the tetragonal structure. The magnetic characterization demonstrates the ferromagnetic nature of the materials which varies with copper substitution.
查看更多>>摘要：Micro-silica is a highly efficient mineral additive whose role is reflected in improvements of microstructure packing, strength and durability of non-shaped composite building materials such as concrete and mortar. A comparative study of performances of rendering mortars with different quantities of micro silica was conducted. The experimental program included production of reference mortar based on Portland cement and quartz sand (CM) and three mortars with 5, 10, and 15 % addition of micro silica (SCM-5, SCM-10, and SCM-15). The effect that micro silica addition has on the thermal behavior and mechanical properties of mortars was discussed. Hydration mechanisms and thermally induced reactions were studied at temperatures ranging from ambient to 1100 degrees C by differential thermal analysis. The results were supported by X-ray diffraction analysis. The cementing efficiency of micro silica was assessed by cavitation erosion test. The changes in the morphology of mortar samples prior and upon cavitation testing were monitored by means of the scanning electron microscope imagining. It was found that 5 % of superfine micro silica (SCM-5 mortar) has positive effects on mechanical strengths (15 % increase in compressive strength) due to microstructure densification arising from the successive filling of voids by the micro silica. Addition of micro silica also improved the cavitation erosion resistance in comparison with reference cement mortar (SCM-5 showed cavitation velocity as low as 0.09 mg/min). This qualifies mortars with micro silica addition as building materials which can be safely employed in potential hydro-demolition environment.
查看更多>>摘要：Synthesis of silicon oxide (SiO2) via the sol-gel method and SiO2 coating ability on to Ti6Al4V alloy were investigated, in the novel study. Ti6Al4V alloy is the most used alloy in biomedical applications due to its many advantages. However, it has a minor disadvantage like releasing ions into the human body. In this study, the substrate material Ti6Al4V alloy samples were coated using the sol-gel method with alkoxysilane solutions (tetraethyl orthosilicate, TEOS; Si(OC2H5)(4) and glycidoxypropyltrimethoxysilane, GPTMS; C9H20O5Si) containing the unit of prepared Si(OR)(n) after the surface preparations were made. The prepared solutions were examined using thermal analysis methods and the process temperatures to be applied to the coatings were determined according to the results of the analysis. Coated samples were subjected to aging, drying, and sintering processes at specified temperatures. The morphologies and structures of the samples were investigated by using a scanning electron microscope with energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The sol-gel coating ability of the silicon oxide on the surface of the Ti6Al4V alloys has been discussed. The results demonstrate that cracks were observed in coating produced by TEOS precursor whereas the coatings used GPTMS precursor exhibited crack-free surface independently of dipping number. The crack formation tended to reduce with increasing dipping number of coatings produced by TEOS precursor. Distances between coating islets gradually became smaller as the number of dippings increased, and the continuity of the coatings increased. It has been observed that SiO2 coating layers produced with GPTMS are obtained in a more continuous and crack-free form than the layers produced with TEOS.
查看更多>>摘要：In this study, microstructure and mechanical properties of nickel matrix B4C reinforced functionally graded composites produced by powder metallurgy method were investigated. Samples with Ni+5% B4C, Ni +10% B4C, Ni+ 15% B4C and Ni+ 20% B4C compositions were sintered at 900 and 1050 degrees C for 60 minutes. Microhardness and wear tests along with optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction (XRD) analyses were carried out to determine the mechanical properties, microstructure and phase composition of the samples. The results indicated that hardness and wear resistance increased with increases of B4C amount in nickel matrix.
查看更多>>摘要：Intergranular and intragranular cracks that usually form during sintering of yttrium manganite (YMnO3) ceramic samples hinder the densification process of this ceramic and deteriorate its magnetic and ferroelectric properties. To overcome this problem, mechanochemically synthesized YMnO3 powder was sintered using two different processes: Conventional Sintering (CS) and Pulsed Electric Current Sintering (PECS). All samples were characterized by XRD, SEM and FESEM and their magnetic and ferroelectric properties were investigated. Apart from their phase composition, conventionally sintered ceramic samples showed cracks throughout their whole volume, reaching a maximum relative density of 85 %. However, it was found that PECS process could significantly reduce the presence of cracks within samples whose relative density reached 99.8 %.
Erden, Mehmet AkifTasliyan, Mehmet FurkanAkgul, Yasin
12页
查看更多>>摘要：Developments in sintering of powder mixtures contributed growth of steel production via powder metallurgy. This study aims to improve the mechanical and tribological properties of carbon steels produced via powder metallurgy. For this purpose, P/M carbon steel was alloyed with 3 % Manganese. Then, this alloyed steel was reinforced with particles such as titanium carbide (TiC), titanium nitride (TiN) and titanium carbonitride (TiCN) in different proportions (0.5 and 1 %) and combinations. The effect of these additives on the mechanical properties of PM steels was determined by conducting tensile and hardness tests. Wear tests were performed to understand the tribological properties of samples. Also, microstructural properties, fracture surfaces, and worn surfaces of samples were examined using a Scanning Electron Microscope. Results show that the hardness and tensile strength of carbon steel increased by nearly 158 % and 62 % respectively, while the wear resistance improved by 4 times with the addition of 3 % Mn and 0.5 % TiCN.
Ismail, Nur Quratul AiniSa'at, Nor KamilahZaid, Mohd Hafiz Mohd
10页
查看更多>>摘要：The influence of sintering time on the microstructure and electrical properties of ZnO-CoO-SLS (soda lime silica) glass varistor based ceramics has been investigated. With increased sintering time, the density of the sintered pellets increased from 5.060 to 5.644 g/cm(3) resulting in an increase of the nonlinear coefficient and barrier height of the ZnO-CoO-SLS glass varistor ceramics from 6.742 to 8.252 and 0.846 to 0.955 eV, respectively. The breakdown voltage is inversely proportional to the leakage current. The breakdown voltage increases from 183.7 to 278.6 V/cm and the leakage current decreases from 5.832 to 4.324 mu A/cm(2) as the sintering time is increased from 60 to 150 minutes but as the increase sintering time of 150 minutes their value decreases to 222.8 V/cm and increases to 5.078 mu A/cm(2). The high nonlinearity of 7.366 with lowest leakage current of 4.324 mu A/cm(2) has been achieved from the varistor sintered at 150 minutes, breakdown voltage of 278.6 V/cm and barrier height of 0.954 eV.
查看更多>>摘要：B2O3 was used to reduce the sintering temperature of steatite (named MSB) dielectric ceramics. Electrical properties of this composition have been studied using impedance spectroscopic method to get better understanding of the electrical conduction, dielectric relaxation mechanism, and microstructure -electrical properties relationship of the materials as a function of temperature and frequency. These samples were prepared by a solid-state reaction technique and their single phase formation was confirmed by the X-ray diffraction technique. Dielectric and complex impedance spectroscopic studies were carried out in a wide frequency (102-106 Hz) and temperature (30-500 degrees C) range. The dielectric constants decrease with increasing frequency for each sample, and then stabilize at frequencies lower than 100 kHz. The dielectric constant increases with the addition of B2O3. The nature of frequency dependence of ac conductivity of MSB follows the Jonscher power law and calculated DC conductivity follows Arrhinius behavior. The Nyquist plot (Z" vs ZMODIFIER LETTER PRIME) revealed the presence only of the grain boundary effect from 350 degrees C onwards. The occurrence of single arc in the complex modulus spectrum of MSB compositions confirms the single-phase characteristics, and also confirms the presence of non-Debye type of multiple relaxations in the material.
查看更多>>摘要：Montmorillonite based clay was acid activated. Nicotine was adsorbed on untreated and acid activated clay from its aqueous solution at either pH=6 or pH=9.26 (unadjusted pH solution). The XRD analysis revealed that the 001 basal spacing of montmorillonite after nicotine adsorption was around 1.38 nm, regardless of clay treatment or pH of adsorption. The obtained values for basal spacing indicate that nicotine is in monolayer arrangement. In order to investigate electrochemical properties, untreated and acid activated clay, with and without nicotine, were used as modifier of carbon paste electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to study electrochemical response of clay-modified electrodes toward ferrocyanide probe. The nicotine-modified untreated clay used as paste electrode showed enhanced electrochemical response toward ferrocyanide probe in comparison to electrode based on clay without nicotine. On the other hand, adsorbed nicotine on acid activate clay resulted in lower electrode activity. Electrochemical response of adsorbed nicotine was studied at different pH. Nicotine oxidation at each of investigated samples followed the same trend regardless of clay treatment or pH at which adsorption was performed. For all samples, nicotine oxidation peak potential showed linear dependence on pH in pH range from 3.7 to 9.0, with slopes close to the value of 59 mVdec(-1) expected for equal number of protons and electrons involved in the reaction. The nicotine reduction process was best resolved at pH = 1 at potential around -1.35 V, while the following cathodic wave observed at potential around-1.5 V was ascribed to the cathodic hydrogen reduction. Mechanism of electrochemical oxidation was not influenced by pH of adsorption, i.e., nicotine form. The amount of adsorbed nicotine was not correlated with the electrochemical activity suggesting that only small number of adsorbed nicotine was involved in electrochemical response.
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