نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 25 (تابستان 1392)

Nowadays Cyanoacrylates glues are widely used in medicine and dentistry. The purpose of the present research is to investigate the role of nano-size SiO2 on the wear behavior of cyanoacrylates nanocomposite under stimulated artificialsaliva condition. Wear behavior of cyanoacrylate samples filled with different levels of nano-sized silica have been investigated using pin-on-disk tester. The wear mechanism of the samples was also evaluated using scanning electron microscopy (SEM). Besides, changes in hardness, temperature of mass reduction due to the destruction of the polymeras well as released energy content during polymerization have been studied. Furthermore, to investige the biocompatibility of the nanocomposite, cycotexicity test carried on using MTT method. The results have shown that an increase in nano-sized SiO2 content improves hardness and wear resistance of the cyanoacrylate based nanocomposites. It also reduces the increase in temperature during polymerization.Besides, the nanocomposite shows less cycotoxicity compering to the pure cyanoacrylate.

The ZnO thin films were prepared from zinc acetate dihydrate as main precursor by using sol-gel method and deposited by drainage and dip coating technique. Four different routes and coating techniques were used for the preparation of samples. The morphology and structural properties of the sol-gel made ZnO thin films were studied with respect to the preparation of sol-gel route, drainage and dip coating technique. The microstructure of the ZnO thin films and the powders were analyzed by X-ray diffraction. The ZnO thin films prepared in this study were amorphous while its powders were polycrystalline with various diffraction peaks in the X-ray diffraction patterns. The morphology of the film was examined by using scanning electron microscopy. The surface morphology of the ZnO thin films strongly depends on preparation route and deposition technique.

In the current investigation a Ni-B-WC composite coating was fabricated through electroless method and the effects of heat treatment on microstructure, hardness and tribological properties was studied. In this regard, electroless Ni-B-WC coating of 30 µm thickness was applied on the surface of Ck45 steel. Following that, the coated samples went through heat treatment for 1 h at 400 ˚C. X-ray diffraction and scanning electron microscopy were utilized in order to characterize the coating. Tribological behavior and hardness of the samples were studied by means of pin on disk and Vickers microhardness measurement device. The results revealed that the addition of WC particles leads to grain refinement and consequent microhardness elevation. Moreover, heat treatment resulted in nanocrystalline structure, therefore, hardness and wear resistance of the coating improved due to transformation on amorphous phase to crystalline structure and production of Ni3B phase.

Cerium based abrasives were studied for polishing glass surface. Raw materials used were Microsilica, Nanosilica, Silicon carbide, Cerium Oxide and Sodium Metasilicate. The procedure of powder processing was employed. Firing temperature 750ºC and 950 ºC were applied. Samples were prepared and firing temperature and strength was compared. Microscopy investigation and Image Analyzer revealed microstructure and grian distribution. XRD studies showed phases such as Ce2Si2O7, SiC and Na6Si8O19 From some reaction of CeO2 and SiO2.Then, values of density, percent by weight, volume of water absorption and the weight difference in grinding testwere measured. Finally the best composition was selected as sodium Metasilicate, Nanosilica, Silicon carbide and Cerium oxide and firing temperature of 950ºC, so that a suitable polishe for glass could be obtained.

In order to control the surface area and morphology of zinc oxide, wurtzite-type zinc oxide was successfully grown on gamma-alumina particles via heterogeneous precipitation method using urea hydrolysis as precipitation agent. Bayerite seed particles were added to system as the alumina precursor during the precipitation step. Also, the effect of alumina particles and zinc oxide content on morphology, surface area and UV absorption were investigated. Microscopic observations evidenced the formation of zinc oxide nanoflakes and nanosheets on alumina particles. The surface area measurements proved a reachable high surface area for this presented system and approach.

This paper aims at investigating the microstructure and failure mode of DP780 ferrite-martensite dual phase steel resistance spot welds between. Microstructural characterization, microhardness tests and the cross-tension shear tests were conducted. Results showed that the fusion zone microstructure exhibited mainly martensite with some Widmanstätten ferrite and bainite. A hardness reduction was observed in heat affected zone in respect to the base metal. Results showed that the mode of failure changed from interfacial fracture to pullout as the welding current was increased. Results indicate that there is a critical weld nugget size to ensure the pullout failure mode. Based on the failure mechanism of the spot welds in the cross-tension test, a simple analytical model is proposed to predict the minimum FZ size (DC) to ensure the pull-out failure mode. According to this mode, the sheet thickness, the hardness ratio of fusion zone to pull-out failure location (i.e. HAZ), the amount of shrinkage voids and porosity in fusion zone and the width of the HAZ are the main controlling factors for interfacial to pullout failure mode transition in cross-tension loading.

In this investigation effect of preheating temperature of the GTAW process on weldability of the ferritic ductile cast iron has been studied. The ductile cast iron plates were welded in butt joint design by GTAW with ERNiCu-B wire in different preheats (100-600) temperature. The XRF was used for determining of the chemical analysis of the weld metals. The OM and SEM were used for study of the microstructure characteristics of weld metal, fusion line and HAZ at different samples. In addition tensile, hardness and impact test were used for determining of mechanical properties of the weld metal and HAZ of different samples. The OM and chemical analysis of different samples weld metals result shows, that by increasing of the preheat temperature, the solidification time, percent of dilution, percent of the Fe, Si, Mn, C elements in the weld metals were increased while the tensile strength and hardness of the weld metals were increased. The hardness of UMZ and PMZ were reduced when the preheating temperature increased. The SEM and OM of the HAZ result shows, that the HAZ width increased and the graphite nodule size and volume fraction of the ferrite phase in the microstructure were changed when the preheating temperature increased, also the hardness of the HAZ decreased and impact energy increased. In a general summary, the 400 is the appropriate temperature for preheating of the welding of the ferritic cast iron by GTAW.

This study investigates experimental and theoretical of a Schiff base-cobalt complex, namely Bis (N-(2-2aminoethylamino) ethanol) -2-Hydroxy-5-methoxybenzaldehyde) cobalt (III) chloride (CS) on corrosion inhibition of mild steel in 0.5 M HCl. Potentiodynamic polarization was applied to study inhibition efficiency. Results revealed that CS is a good inhibitor for mild steel corrosion in 0.5 M HCl; showing a maximum efficiency 84% at concentration of 400 ppm. FTIR observations of the mild steel surface applied to confirm the formation of protective film and the synergy effect of ions on the metal surface. The scanning electron micrographs (SEM) images showed significant effect of the inhibitor. Quantum chemical studies show CS is a softer base than corresponding ligand and also it shows superiority of complex over the corresponding ligand.

Corrosion of carbon steel in sodium chloride solution has been studied under ultraviolet illumination using weight loss, polarization, electrochemical impedance spectroscopy (EIS) and current transient tests. In polarization test an increasing in corrosion current density observed under UV illumination. Impedance spectroscopy indicate that the charge transfer resistance of system decreased by irradiation of UV light on carbon steel electrode. The weight loss of carbon steel in solution increased under UV light which confirms the results which obtained from electrochemical measurements. It was proposed that the essential effect of UV irradiation is on the oxide film, iron oxide, which forms on the surface and a little modification on the properties of solution. Therefore in presence of UV, the conductivity of oxide film might be increased and lead to higher metal dissolution and corrosion rate.

Sol-gel is chemical method for synthesis of nanometric powder that has been proposed in recent years. In the present investigation, synthesis of amorphous and nanometric powder with stoichiometric composition of cordierite in MgO-Al2O3-SiO2 system was prepared by tetraethyl orthosilicate and magnesium and aluminium chlorides. Particle size distribution of synthesised powder investigated by laser method. Structural investigation of gel derived powder at 100ºC and 1385ºC were characterized by FT-IR. The mechanism of cordierite formation was also studied using DTA and XRD techniques to follow the reactions occurring during gel heat treatment up to full cordierite conversion (1385ºC). XRD analysis revealed that spinel and cristobalite are formed at the beginning of heat treatment and then α-cordierite formed as the main crystalline phase in the sintered glass-ceramic by the reaction between spinel and cristobalite at crystallization peak temperature. The transformation of µ-cordierite to α-cordierite and a direct crystallization of α-cordierite from glass also occurred.

Activated carbon has broad application as surface absorber and can be produced from any carbon base materials such as shell walnuts. production process of activated carbon can be achived by chemical or physical methods.In this investigation phosphoric acid was used as a chemical agent.In order to obtaind proper condition iodine number factor wa evaluated as a scale for free surface of activated carbon.The suitable concentration of phosphoric acid was 50% to have best impregnation ratio of 0.5 and under this optimum conditios,carbonization process was carried out at temperature of 200 C soaking time of 4 hr,for activation the temperature of 500 C and soaking time of 1.5 hr was determind.The surface area of activated carbon at this optimum conditions was 430 m2/gr with poures surface area and volume of 306 m2/gr and 107 mm3/gr respectively.

In the present study, the effects of the length, thickness, welding current, welding sequence, holding time in the fixture and similarity of the base metals on welding residual distortion of dissimilar joint between carbon steel CK4 and stainless steel AISI409 were firstly investigated on the basis of a verified finite element model. Then, considering the welding current, fixing time and sequence of welding operation, the magnitude of welding residual distortion was minimized. The results showed that in the studied dissimilar joint, the minimum distortion occurred when the welding current was about 95A; fixing time was 120 sec and symmetric layout was used.