Material Science

The growth of silicalite zeolite layers by in situ crystallization on zircon porous supports has been investigated. Because of lower solubility in the mother liquor with respect to alumina substrates, zeolite weight gain with time is enhanced. Using the batch formulation 4.1 Na 2 O:50 SiO 2 :691 H 2 O:TPABr it was not possible to grow zeolite layers in an oriented fashion in the temperature range of 1401-1801C. It was observed that, unlike alumina substrates, porous zircon supports have a high affinity for oriented deposition of silicalite seeds (highly oriented 200/020 planes) by the dip-coating process. This phenomenon is a strong function of slip pH and concentration. Seed layers are prone to heavy mass losses during the hydrothermal process. A ''fixation'' process has been applied for the first time to fix the latter by reacting surface Zr-OH and Si-OH groups by condensation reactions between the support and the seed and among the seeds themselves. Such a fixed seed layer undergoes mostly crystal growth with minimal nucleation during the hydrothermal step, resulting in a dense highly oriented zeolite layer.

In this research, microstructure and mechanical properties of 5052Al/Al 2 O 3 surface composite fabricated by friction stir processing (FSP) and effect of different FSP pass on these properties were investigated. Two series of samples with and without powder were friction stir processed by one to four passes. Tensile test was used to evaluate mechanical properties of the composites and FSP zones. Also, microstructural observations were carried out using optical and scanning electron microscopes. Results showed that grain size of the stir zone decreased with increasing of FSP pass and the composite fabricated by four passes had submicron mean grain size. Also, increase in the FSP pass caused uniform distribution of Al 2 O 3 particles in the matrix and fabrication of nano-composite after four passes with mean cluster size of 70 nm. Tensile test results indicated that tensile and yield strengths were higher and elongation was lower for composites fabricated by three and four passes in comparison to the friction stir processed materials produced without powder in the similar conditions and all FSP samples had higher elongation than base metal. In the best conditions, tensile strength and elongation of base material improved to 118% and 165% in composite fabricated by four passes respectively.

In the present study, carbon nanotube (CNT)/zinc sulfide (ZnS) quantum dots (QDs) were synthesized followed by electrophoretic deposition on Al electrodes. First, surface of carbon nanotubes were modified using wet chemical routes to obtain Carboxyl-, Chlorine-and Aminemodified CNTs. Then, ZnS QDs were synthesized by hydrothermal method and attached to the CNTs. Although deposition weight of CNTs were improved considerably by surface modification, it decreased dramatically after attachment of ZnS QDs. Microstructure studies showed that a better coverage has been obtained on the Al substrate by the continuous layer of Carboxyl-modified CNTs. Moreover, ZnS QDs were coated on the surface of Carboxyl-modified CNTs properly.

The combustion process of TiO22MgC and 3TiO2-4Al-3C systems in a tubular furnace was investigated. TiC has been synthesized by the magnesiothermic reaction from a mixture of compacted powders of TiO2, Mg and charcoal as starting materials in the presence and absence of NaCl. The effects of temperature, pressure, and the stoichiometry ratio in the reaction yield have been studied. The results show that the synthesis of titanium carbide in the presence of sodium chloride has a better yield than other methods. Titanium carbide was also synthesized by aluminothermy reaction from a mixture of compacted powders of aluminum, titanium dioxide and charcoal. The reaction processes are modified to achieve a high yield of TiC. The final products were characterized by XRD and SEM.

In the present study, ZnS-Mn nano-luminescent pigments were synthesized, using co-precipitation method. Polyvinylpyrrolidine (PVP) surface modifier and Mn dopant concentrations were considered as affecting parameters. The luminescent ink was loaded with two different concentrations of pigments. The obtained ink was silk-screened on different types of fabrics mainly treated cotton, cotton and nylon. Structure, microstructure, luminescent properties of nano-pigments, inks and fabrics and also rheological properties of the inks were investigated. The results showed that the ceramic ink prepared with nanoluminescent pigment had high photoluminescence (PL) intensity. Moreover, the optimum concentrations of Mn and PVP for obtaining maximum PL intensity were found as 2 and 5 wt%, respectively. SEM images of fabrics indicated that nanoparticles were loaded, nonuniformly, on the fibers. The treated linen and nylon fabrics showed maximum and minimum PL intensity, respectively, due to ink penetration depth in the fabrics. Furthermore, washing fastness estimated for all fabrics was in the proper range.

In the present study, combustion synthesis of cerium oxide nanoparticles was reported using cerium nitrate hexahydrate as starting material as well as urea, glycine, glucose and citric acid as fuels. The influence of fuel type on structure, microstructure, band gap, and corrosion inhibition was investigated. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) micrographs showed that CeO 2 nanoparticles with different morphologies were obtained depending on the fuel type. Microstructural changes from unreacted gel to sponge-like morphologies were resulted by varying the fuel type from urea, glycine, and Accepted Article This article is protected by copyright. All rights reserved. glucose to citric acid. In addition to Ce-O bonds, Fourier transformed infrared (FTIR) analysis showed carbon bonds of carbonaceous compositions from incomplete combustion which were declined during combustion reaction. Furthermore, corrosion analyses showed that samples synthesized using urea fuel released the most Ce +4 ions and could have better protection than other samples.

Solution combustion synthesis is proposed to fabricate spongy ceria by using two different fuels for combustion: glycine and urea. As-prepared samples are labeled as SCO Gl and SCO Ur. The acid-base properties of the cavities and surfaces of specimens are determined by measuring the pH of zero charges. Both SCO Gl and SCO Ur powders are decorated by the nanostructured Pd (NSPd) by the wetness incorporation. The NSPd-SCO Gl and NSPd-SCO Ur represent the high mass current density than NSPd as non-supported palladium for the electrooxidation of single-carbon molecules: methanol, formaldehyde and formic acid. The results show that the NSPd-SCO Gl and NSPd-SCO Ur are exceptional heterogeneous catalysts. The SCO as the support with porous structural network has been affected considerably on the electrochemical surface area, dispersion, and durability of NSPd. On the other hand, it can be effective for removing the poisoning species of the electrooxidation of single-carbon molecules on NSPd through the lattice oxygen, and the activation of an oxidation-reduction cycle between the high and low chemical valences of cerium, leading to improve the electrocatalytic efficiency of NSPd. Finally, it is confirmed the conversion of methanol to formaldehyde, and then to formic acid during electrooxidation by using cyclic voltammetry studies.

In this work, boehmite sol was prepared by a previously applied and validated method; hydrolysis of aluminum chloride hexa-hydrate. In order to obtain precise results, the effect of pH after adding precipitating agent, aging time, peptizing temperature and ultrasonic vibration time on the crystallite size of final precipitate were investigated in a narrow range. The preparation conditions applied in the production step of nanocrystalline boehmite affected on the desired alumina phase. Experiments were set based on the statistical design of experiments (Taguchi method). Furthermore the influence of calcination on crystallization and phase transformation of the precipitate was investigated using X-ray diffractometry (XRD) and simultaneous thermal analysis (STA) techniques. To evaluate the results, the obtained data were statistically analyzed. Considering the statisti cal analysis of experiments, the pH after adding precipitating agent is the major parameter affecting crystallite size...

In the present study, Inconel 625 alloy walls were fabricated by wire arc additive manufacturing method. Microstructure, hardness, tensile properties at room temperature and 700 ̊C, and high-cycle fatigue strength in both welding and building directions of samples were evaluated. The microstructure of the wall contained dendritic Ni-based solid solution along with MC carbide, Laves, and delta inter-dendritic phases. Moreover, the Vickers hardness value decreased from 380 HV near the substrate to 300 HV in the top layer. Also, yield and tensile strengths along the welding direction were 6.6 and 8.6% higher and the elongation was 23% lower than the building direction, respectively. Furthermore, fatigue test results with the stress ratio of 0.1 showed that the number of cycles to failure was slightly higher in the welding direction. Fractography of the samples illustrated that all fatigue cracks initiated from the surface. This confirmed the soundness of the walls manufactured by this ...

In the present study, CdSe quantum dots were synthesized via hydrothermal method using cadmium chloride and selenium oxide as starting materials, 3-mercaptopropionic acid as a surface modifier, and sodium borohydride, ascorbic acid, trisodium citrate dehydrated, tartaric acid and 2-aminobenzenecarboxylicacid as reducing agents (RAs). The effect of synthesis parameters such as the reducing agent type, synthesis temperature and time, primary pH value, and MPA surface modifier concentration was studied on the photoluminescence properties (PL). Results showed that PL spectra were considerably affected by the type of RA and the synthesis parameters. Moreover, hydrothermal synthesis in the presence of sodium borohydride as a RA with proper synthesis conditions led to the formation of CdSe particles in the quantum dot size range below 5 nm with the bandgap of above 3 eV.

In this research, microstructure and mechanical properties of 5052Al/Al 2 O 3 surface composite fabricated by friction stir processing (FSP) and effect of different FSP pass on these properties were investigated. Two series of samples with and without powder were friction stir processed by one to four passes. Tensile test was used to evaluate mechanical properties of the composites and FSP zones. Also, microstructural observations were carried out using optical and scanning electron microscopes. Results showed that grain size of the stir zone decreased with increasing of FSP pass and the composite fabricated by four passes had submicron mean grain size. Also, increase in the FSP pass caused uniform distribution of Al 2 O 3 particles in the matrix and fabrication of nano-composite after four passes with mean cluster size of 70 nm. Tensile test results indicated that tensile and yield strengths were higher and elongation was lower for composites fabricated by three and four passes in comparison to the friction stir processed materials produced without powder in the similar conditions and all FSP samples had higher elongation than base metal. In the best conditions, tensile strength and elongation of base material improved to 118% and 165% in composite fabricated by four passes respectively.

Gas atomized Mg-Zn 4.3 Y 0.7 (at%) alloy powders were consolidated by using a magnetic pulsed compaction (MPC) process, and obtained by rapid solidification not to lose the fine microstructure during the generally conducted thermal consolidation process. MPC is known as one of the most rapid pressing process with the GPa range. The effects of the discharging voltage and thermal pressure on the microstructure, hardness, density and compressive strength were investigated. The experimental results showed that the density increased with increasing the voltage although the sample MPCed still consists of pores especially between the powder boundaries even at the maximum pressure of this investigation. The density was improved further up to 96% to the cast value by the MPC at the maximum voltage. Uniform and fine microstructure formed in the alloy powders as atomized was almost maintained even after the thermal MPC.

In the present study, friction spot welding or refill friction stir spot welding was performed to consolidate dissimilar AA5754 Al and AZ31 Mg alloys. The intermetallic compounds of Al 12 Mg 17 and Al 3 Mg 2 were primarily found in the weld, distributed at the interface between the base materials and in the Al top sheet. The distribution of the intermetallic compounds and the interfacial area between the base materials affect the lap shear strength of the weld. It is concluded that the material flow induced by tool movement plays an important role in both the distribution of the intermetallic compounds and the interfacial area between the base materials.

In this research, microstructures and hardness profiles across the interface of friction stir welded joints between monolithic 2024-T4 aluminum alloy (AA) and Al/Mg 2 Si metal matrix cast composite (MMC) and effects of one and two welding passes on these parameters were investigated. Results showed that there were complicated patterns of materials flow in the stir zone (SZ) especially in samples welded in two passes. This region was free of defects like voids and tunnel defects in samples welded in one pass. But some defects were formed in samples welded in two passes. Stirring caused fragmentation and rearrangement of Mg 2 Si large particles in the stir zone and thermo mechanically affected zone (TMAZ) of MMC, respectively. Eutectic phase has formed on the grain boundaries of 2024 AA in thermo mechanically affected zone due to high heat input to the joint area during welding. In samples welded in one pass, hardness increased from the base metal to the stir zone on the MMC side, reached a maximum in the middle of the joint interface and decreased at about 2 mm away from the joint interface center on 2024 AA side. But, hardness variation in the sample welded in two passes was complicated and there was alternating decrease and increase in hardness value at the joint interface.

In this research, joining austenitic to martensitic stainless steels and effect of welding power on microstructure and mechanical properties of the joint were investigated. Microstructure of the weld was studied using optical microscopy (OM) and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) linked to SEM was used to determine chemical composition of phases and distribution of chromium (Cr), nickel (Ni) and iron (Fe) at the joint interface. Microhardness and tensile strength tests were performed. Finally fracture surface of samples were studied by SEM. Results showed that an interlayer composed of 80% ferrite and 20% martensite has formed at the joint interface and there were three different zones in the heat affected zone (HAZ) of two steels. Different forms of austenite phase including widmanstatten austenite (W c ), allotriomorphic austenite (A c ) and intergranular austenite (I c ), delta ferrite (d-ferrite) and chromium carbide (Cr 23 C 6 ) have formed in the HAZ of austenitic stainless steel. Fractography of tension samples indicated that in all samples fracture occurred in austenitic stainless steel HAZ. The strength and hardness of the joint increased and HAZ length decreased with increasing of welding power.

The dissimilar joining of CP-copper to 304 stainless steel was performed by gas tungsten arc welding process using different filler materials. The results indicated the formation of defect free joint by using copper filler material. But, the presence of some defects like solidification crack and lack of fusion caused decreasing tensile strength of other joints. In the optimum conditions, the tensile strength of the joint was 96% of the weaker material. Also, this joint was bent till to 180º without any macroscopic defects like separation, tearing or fracture. It was concluded that copper is a new and good candidate for gas tungsten arc welding of copper to 304 stainless steel. 摘 要：采用不同焊丝对工业纯铜和 304 不锈钢进行钨极氩弧焊接。结果表明，采用铜做焊丝时，焊缝无任何缺 陷生成，而采用 304 不锈钢和 Ni−Cu−Fe 合金为焊丝材料时，焊缝中有凝固裂纹和未熔化区存在。在最优条件下， 焊缝的抗拉强度能达到铜材的 96%。焊缝在弯曲到 180°下也没有分离、撕裂和断裂等现象发生。这表明铜是一种 较好的工业纯铜与 304 不锈钢 GTA 焊的焊丝材料。 关键词：钨极氩弧焊；工业纯铜；304 不锈钢；异种材料连接；显微组织；力学性能 (Edited by YUAN Sai-qian)

In this research, titanium carbo-nitride coatings were synthesized on the surface of Ti-6Al-4V alloy by nitro-carburizing route and the detachment mechanism of the coatings were investigated. For this purpose, rectangular blocks were embedded in a carbon containing graphite cup. Then, the cup was placed in a tubular furnace containing nitrogen gas. After coating in different temperatures between 1200 and 1400 ̊C for 20 to 60 min soaking times, structure and microstructure of the coatings were investigated by X-ray diffraction, Raman analysis and scanning electron microscope equipped with energy dispersive spectroscopy (EDS). Moreover, the effect of coatings on the corrosion resistance of the alloy in an aqueous solution containing 5.2 mol HCl, 3.2 mol HNO3 and 3.2 mol HF was investigated. Results showed that the maximum thickness of the titanium carbo-nitride coating for the sample treated at 1400 ̊C for 60 min was about 50 μm. However, the possibility of coating detachment increase...