Journal of Advanced Materials in Engineering (Esteghlal)

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In this research, the reaction kinetics of TiH2 powder in contact with pure aluminum melt at various temperatures on the basis of measuring the released hydrogen gas pressure was studied. To determine the mechanism the reaction, after Solidification of samples, interface of TiH2 powder in contact with melt was studied. The results showed that PH2-time curves had three regions. In the first and second regions, the rate of reaction conforms to zero and first order, respectively. In the third region, hydrogen gas pressure remains constant and the rate of reaction becomes zero order. In the first and second regions, the main factors controlling the rate of reaction are diffusion of hydrogen atoms within titanium lattice and chemical reaction of titanium with aluminum melt, respectively. Based on the main factors controlling the rate of reaction, three temperature ranges can be considered for reaction mechanism, a) 700-750ºC, b) 750-800ºC and c) 800-1000ºC. In the temperature range (a), the reaction is mostly chemical reaction control. In the temperature range (b), the reaction is diffusion and chemical reaction control, and in the temperature range (c), the reaction is mostly diffusion control.

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In this research, DTA and TGA curves of titanium hydride powder in air with the heating rates of 5, 10, 20, 25, 30ºC/min were drawn, and XRD patterns of titanium hydride powder during heating rate 10ºC/min were prepared. Results showed that hydrogen comes out of titanium hydride in air during seven stages. And, by increasing heating rate, the mechanism of hydrogen emission from titanium hydride is almost fixed. Upon computation of activation energy of these stages, it was revealed that the mechanism does change at different temperatures. According to DTA curve at 10ºC/min, at temperatures lower than 460ºC, the mechanism is controlled by internal diffusion, at temperatures between 460-650ºC, it is controlled by physicochemical process, and at temperatures higher than 650ºC, it is controlled by chemical reaction. By increasing heating rate, the mechanism is changed at higher temperatures.

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The osseointegration of oral implants is related to the early interactions between osteoblastic cells and titanium surface. Chemical surface modification of titanium (Ti) implants is used to improve peri-implant bone growth, bone-to-implant contact, and adhesion strength. Thus, in this study, the surface topography, chemistry, and biocompatibility of polished titanium surface treated with mixed solution of three acids containing hydrochloric acid (HCl)- hydrofluoric acid (HF)- phosphoric acid (H3PO4) were studied under different concentration conditions. Moreover, Osteoblast cell (MG-63) was cultured on the and treated polished titanium surface. Also, in order to investigate titanium surface, SEM, AFM and EDS analyses were carried out. The results revealed that the surface of titanium treated with mixed solution containing the aforesaid acids had higher roughness, cell attachment, and proliferation than the controls

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In recent years, much research in the field of advanced materials synthesis using the mechanochemical process has been performed. In this study, Al2O3-TiN nanocomposite was produced by the mechanochemical method and using inexpensive material TiO2 (instead of pure titanium which is too expensive). Also, aluminum and titanium oxide powders were used as raw materials. Milling under N2 atmosphere with 5 atmospheric pressure was performed and the products were evaluated by the SEM and XRD. Milling results showed that in the first stage of the synthesis process, titanium oxide is reduced by aluminum and the process continues, producing titanium reaction with nitrogen. When the Al/TiO2 ratio molar is equal to 1.2 and 1.3, after 20 hours of milling, TiN peaks in the XRD appears. Moreover, the results showed that milling leads to the formation of fine and spherical particles.

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Refractory carbides are becoming a group of promising material due to their unique properties, such as high hardness, high wear and corrosion resistance, high thermal conductivity, high melting point, high strength even at high temperatures, and a high degree of chemical stability. Among these carbides, titanium carbide (TiC) is one of the most important engineering material, based on its promising properties. This paper presents a novel approach to preparing ultrafine TiC by sol–gel processing. This novel process would minimize kinetic barriers because carbon (coming from sucrose) was homogeneous dispersed in the precursor of TiO2 by sol–gel process. As a result, the increased contact area between reactants should make the reaction to complete at lower temperatures.

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In this study, pure powders such as molybdenum, silicon, aluminum and titanium carbide were utilized to produce MoSi2 compound, MoSi2 /20 Vol % TiC composite, MoSi2-x Al alloyed compound and MoSi2-x Al/20 Vol % TiC alloyed composite. The initial powders were mixed in specified ratios, and then, were activated by mechanical milling. Milled powders were compacted, synthesized and sintered in the temperature range of 1100 -1400 oC. SEM was used to investigate the microstructural change and XRD for identification of phases. Effect of aluminum addition on phase formation was investigated. Addition of aluminum by over 9 atomic percent resulted in the formation of Mo(Si,Al)2 in alloyed matrix.

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In recent years, much research has been performed in the field of nanomaterials synthesis using mechanochemical process. In this research, TixAly/Al2O3 ceramic matrix nanocomposite was produced by the mechanochemical method. Aluminum and inexpensive titanium oxide powders were used as raw materials, and milling was performed under N2 atmosphere. The results showed that reduction of TiO2 by Al is the first step of synthesis process, and then Ti reacts with residual Al. The synthesis after 10 hours of milling resulted in titanium aluminide and aluminium oxide. With the increase of milling time to 80 hours, titanium aluminide quantity was increased. Also, the results showed that the heating of samples containing titanium aluminide in the argon and nitrogen atmospheres does not lead to complete decomposition of aluminides.

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In this research, Ti-6Al-4V alloy was brazed with 410 stainless steel by three different filler metals as silver-base, nickel-base, and titanium-base alloys. In order to obtain optimum clearance, brazing was done in three different clearances of 0.02, 0.04 and 0.06 mm. Also, the strength and hardness of the brazing zone were investigated. The results of shear strength showed that the brazed samples with titanium-base alloy at the clearance of 0.02 mm had the maximum strength among the different samples which was 149.5 MPa.

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With various features such as strong oxidation, biocompatibility and acceptable mechanical properties, titanium dioxide (TiO₂) is among the materials that are frequently used in biological and medical applications. Nowadays, with the aim of increasing the efficiency of titanium dioxide and practical use of this material, doping it with elements such as silver, zinc and iron has been favored. In this study, Ag-TiO₂ and ZnO-TiO₂ nanoparticles were prepared by the sol–gel method and were evaluated and compared.In order to identify the present phases in the structure, X-ray diffraction analysis was used. Also for the characterization of the nanoparticles, Ultraviolet–visible spectroscopy (UV-Vis), Energy-dispersive X-ray spectroscopy (EDS), Field Emission Scanning Electron Microscope (FESEM) and Zeta Potential were used. Inaddition, the antibacterial activities of nanoparticles were investigated and compared. The results showed that sol-gel method could successfully produce nanoparticles of Ag-TiO₂ and ZnO-TiO₂ with the expected combination. The investigation of antibacterial properties of these particles revealed that at lower inhibitory concentrations, Ag-TiO₂ composition has a higher antibacterial activity than ZnO-TiO₂ one.

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In this research, TiAl/Al₂O₃ composite was synthesized from mechanically activated TiO₂-Al powder mixtures using microwave heating.The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on the ignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti₃Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product.The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.

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In this research titanium nitride (TiN) films were prepared by plasma assisted chemical vapor deposition using TiCl₄, H₂, N₂ and Ar on the AISI H13 tool steel. Coatings were deposited during different substrate temperatures (460^°C, 480 ^° C  and 510 ^°C). Wear tests were performed in order to study the acting wear mechanisms in the high(400 ^°C) and low (25 ^°C) temperatures by ball on disc method. Coating structure and chemical composition were characterized using scanning electron microscopy, microhardness and X-ray diffraction. Wear test result was described in ambient temprature according to wear rate. It was evidenced that the TiN coating deposited at 460 ^°C has the least weight loss with the highest hardness value. The best wear resistance was related to the coating with the highest hardness (1800 Vickers). Wear mechanisms were observed to change by changing wear temperatures. The result of wear track indicated that low-temprature wear has surface fatigue but high-temperature wear showed adhesive mechanism.

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TiO₂/MWCNT nanocomposite thin films containing different percentages of multi-walled carbon nanotubes were coated on fluorinated tin oxide substrates by sol-gel dip coating method. Results of X-ray diffraction analysis indicated that the crystal structure of the coatings was anatase TiO₂. It was also understood that the size of crystallites reduced with CNT but structural properties and equilibrium phase remain intact. Field emission scanning electron microscope images showed that CNTs dispersed uniformly among 45 nm spherical TiO₂ particles of close relations. These images also showed that CNT promoted cracks on the coated surface. Results of the UV-Vis spectroscopy showed that the visible light range adsorption  increased with CNT and the absorption edge did not significantly differ with the pure TiO₂ layers.. Results of the photoluminescence spectroscopy revealed that the presence of CNT could reduce the pair electron–electron holes recombination which is considered totally undesirable.
 

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In the present study, alkali roasting and oxalic acid leaching were used to extract titanium dioxide from ilmenite, and the effect of ethanol and ascorbic acid on the purity and recovery of titanium dioxide was investigated. In this research, ilmenite was alkali roasted with sodium carbonate for 4 hours at 900˚C. Then, the roasted ilmenite was leached with distilled water for 1 hour at room temperature. Finally, leaching with a mixture of 0.47M oxalic acid and different amounts of ascorbic acid and ethanol was performed at 65˚C. The results showed that using ethanol caused an increase in the amount of recovery and ascorbic acid increased the purity of the extracted titanium dioxide; also, the presence of these two factors at the same time simultaneously increased the amount of purity and recovery of the final product. Eventually, by choosing 0.47M oxalic acid, 0.005M ascorbic acid, and 48% ethanol as the appropriate conditions for leaching media and increasing the leaching time and temperature to 16 hours and 80˚C, it was possible to get titanium dioxide purities which were as high as 93.3% and 90.9%, respectively.

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In this study, the formation of the Al₃Ti intermetallic compound at the junction interface of aluminum-titanium was investigated during deposition and annealing. The results illustrated that during the deposition process, one thin layer of Ti₃Al₂ intermetallic compound was created at the junction interface. During the annealing at 550 °C, this layer was transformed to the  Al₃Ti intermetallic phase and the layer growth occurred. By performing annealing at higher temperatures, the growth rate of Al₃Ti intermetallic layer was increased; at the same time, the formation of Kirkendall cavities and  coupling in the cavities and fragmentation of diffusional coupling from the junction with aluminum were observed

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In order to improve the oxidation and hot corrosion resistance of steels, various elements including aluminum, chromium, silicon, titanium or combination of these elements can be diffused on to the surface of steel. In this study, aluminum and titanium were simultaneously co-deposited onto the AISI 430 ferritic stainless steel substrate by the pack cementation process. Coating was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coating consised of two layers with the thickness of approximately 14 microns. The results obtained by XRD showed the existence of FeTi, TiO₂, AlTi, Al₃Ti and Al₅Ti phases in the coating. Isothermal oxidation and cyclic oxidation were carried out at 1000^○C. It was showed that the diffusional coating of aluminum-titanium led to the improvement of cycle and isothermal oxidation resistance.

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