نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 27 (زمستان 1392)

In this research، titania nanoparticles were produced from titanium tetraisopropoxide (TTIP) in acidic environment by sol/gel method and deposited on natural cotton and sack fiber. After elimination of cellulose by heating of the sample، fibery and layered nanostructures were obtained. The effect of pH on crystal structure and particle distribution was determined and pH for most suitable deposition process was reported. X-ray diffraction patterns revealed that at low acidity، pure anatase and at high acidity، mixture of rutile and anatase phases were precipitated. Transmission electron microscopy illustrated production of sharp-edge particles of 10 to 15 nm at pH=1. 85. Although synthesis was at room temperature، diffraction pattern rings showed considerable degree of crystallinity. Specific area measurement by BET indicated 214 m2g-1. Scanning electron micrographs of the deposited layers revealed replication of the fiber topographies on the final deposition. After elimination of the cellulose from the cotton and the sacks، remaining TiO2 nanoparticles had fibery and layered-like appearance.

In this research, was synthesized barium titanate nanoparticles performed by hydrothermal method with a high degree of crystallinity. Phase development, morphology of barium titanate powder particle and grain were investigation by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy, respectively. X-ray diffraction analysis confirmed the formation of barium titanate phase with high crystallinity. Also, the images of SEM and TEM high crystallinity and also nanoparticles synthesized powders are well visible. The results showed which optimum temperature for the synthesis of barium titanate of precursors such as BaCl2.2H2O and TiO2 is 180°C up to 3 hours with 13.6 pH. The average grain size of barium titanate synthesized using Scherrer equation was calculated equal to 20 nm. Also, according to the results of TEM, the grain size was estimated in the range of 30-40 nm, with the value obtained by Scherrer equation is partly similar.

In gravity casting of aluminum alloys, turbulent mold filling, reactions between the molten metal and molding materials, melt cooling rate and fluidity as well as inadequate feeding to compensate the solidification shrinkage cause different types of defects. Volumetric defects are among the most important problems in the casting processes and include gas and shrinkage defects which are formed during solidification of the melt. These defects strongly reduce the quality of thin wall castings and have adverse effects on their mechanical properties. In this study, the influence of using nano-ceramics mold coating on sand molds on these defects was investigated and the defects formed in thin samples cast using nano-ceramic mold coating, micro-ceramic mold coating, graphite mold coating and sand mold without coating were compared using x-ray radiography method. The results could lead to production of higher quality AL4-1 alloy components using nano-ceramic coatings.

Equal channel angular pressing (ECAP) is the most promising and effective method of severe plastic deformation thechniqus. In addition, materials with low doctility show severe cracking during ECAP and back pressure has been used in some research to overcome this problem. In this paper finite element has been used for simulation of ECAP with back pressure and the possibility of using ECAP die with inclined upper channel wall instead of back pressure. Results show that inclined up channel wall with 10 mm length and 5 degree inclination needs lower pressing foece and exert 100Mpa pressure on upeer side of sample. Therefore, die with inclination is suitable substitude for ECAP whith back pressure.

Stir casting (vortex technique) is one of the simplest methods for producing metal matrix composites. Due to the formation of agglomerated particles and large amounts of porosities, these fabricated composites have very low mechanical properties. The effects of hot extrusion and warm ECAP on the microstructure and mechanical properties of these composites have been investigated in this study. The experimental results indicated the appreciable effects of these secondary processes on the tensile and ultimate strengths, ductility, relative density, hardness, and microstructures of the as-cast composites. In addition, it was revealed that warm ECAP (at 200 °C) and hot extrusion (at 500 °C) have completely different effects on properties of as-cast composites.

In this research by carbothermal reduction process and VLS mechanism, silicon carbide whiskers were produced. Pitch and silica by product of a manufacturer (as an inexpensive material) and ferrosilicon (as catalyst) were used as starting materials. Primary mixtures were synthesized at 1300°C and 1400°C in tube furnace under the argon atmosphere. The products were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns indicated the presence of SiC in the reaction products. The SEM analysis showed that SiC whiskers have been obtained. The SiC crystallite sizes were less than 50 nm. In the next step, primary mixtures were milled in a planetary ball mill at 5hr milling time. The activated powders were synthesized at 1400°C. The XRD patterns showed that by milling the starting materials, the peaks width was increased while their intensity decrease and it showed a reduction of about 5-10 nm in crystallite size, which shows more nucleation or faster growth of SiC whiskers.

In this paper reinforced multilayered Al/Zn composite with silicon carbide nano particles was produced by accumulative roll bonding (ARB) process for the first time; and investigated mechanical property and microstractural evolutions. In this process after manufacturing of sandwich sample (zero pass), applied about 50% thickness reduction in per passes which is equivalent to 0.8 von-misess plastic strain. This process was donning up to 8 cycles and results to production of an aluminum metal matrix composite with uniform distribution of zinc fragments and silicon carbide nano particles in matrix with 257 MPa tensile strength.

Cordierite is a main phase in engineering that uses in various indestrials. In this study, high purity cordierite was successfully synthesized via sol-gel method using TEOS, Al(NO3)3.9H2O, Mg(NO3)2.6H2O as starting materials and the different steps of transformation to cordierite are analyzed by DSC, FT-IR spectrometry and X-ray diffraction at different temperatures. FTIR spectroscopy result showed the presence of hydroxyl groups in the synthesized powder and have evidenced the characteristic bands for α-cordierite at high temperatures which supported the XRD result. XRD result showed that α-cordierite was obtained with cristobalite and spinel phase as a minor impurity.

MgO – Cr2O3 Refractories are used in Refining Furnaces of Copper Smelters. These Alkaline Refractories in contact with Slag Alkaline and Acidic Oxides and in 1350 oC Temperature are extremely influenced by molten Slag, in this case the high dencity layer of Slag can be seen inside the Refractory Spinel and Periclase grains. In MgO – Cr2O3 Refractories, the penetration of Copper, Iron Oxides and Silica result in the growth of Spinel Magnesia Chromite (Fe,Mg)(Cr,Al,Fe)2O4 and formation of Phase Magnesium Ferrite (Fe2MgO4), in such a way that the Refractoriness temperature of penetrated area decrease from 1900 to 1400 oC and the Bonding Structure of Refractory changes to Liquid from Solid. The results of studies done by Scanning Electron Microscopy (SEM) and phase analyzer (XRD) showed that the tested Refractory Materials, the formation of Fe2SiO4 easy melting Silcate phase and Magnesium Ferrite Alkaline phase are distinguished as the factory of Chamical Corrosion. According to the obtained results the Refractory with the higher Molecular density is less affected by penteration of Alkaline and Acidic phases of Slag.

Application of based andalusite refractories in industries is related to special properties of andalusite such as thermal stability of andalusite crystals and no changes on density after firing. In this research effect of different amount of Aluminum powder with optimized percent of Graphite and SiC were added to andalusite and physical and mechanical properties were investigated by density, porosity and CCS curves and microstructure, phase analysis and formation temperature of Al4C3 were investigated by (SEM), (XRD) and (DSC) respectively.The results showed that in coke atmosphere Al4C3 formed from 635°С and in presence of andalusite, Al4C3 reacted with andalusite, and SiC were formed from 1450°С and higher temperature. Also with mullitization of andalusite from 1400°С and formation of amorphous phase SiO2, in presence of carbon and Al, SiC and Al2O3 were formed. increase in the amount of Al and formation of Al4C3 and SiC at 1450°С, led to improvement of physical and mechanical properties of the samples.

Nano-CaZrO3 was successfully synthesized at 800 oC using the molten-salt method, and the effect of raw materials particle size on the formation of CaZrO3 were investigated. Na2CO3, CaCl2, nano-ZrO2 and micro-ZrO2 were used as starting materials. On heating, Na2CO3 reacted with CaCl2 to form NaCl and in situ CaCO3. Na2CO3–NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that in both nano- and micro-ZrO2 inclusive samples, CaZrO3 started to form at about 700 oC and that, after the temperature was increased to 1000 oC, the amounts of CaZrO3 in the resultant powders increased with aconcomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples containing nano- and micro-ZrO2 heated for 3 h at 800 oC and 1000 oC, were single-phase CaZrO3 with 70–90 nm and 400–450 nm particle size, respectively. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt synthesis.