نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 15 (زمستان 1389)

Herein, we show that amorphous carbon nanoparticles (ACNPs) can be successfully transformed into multi-walled carbon nanotubes (MWCNTs) under an annealing at temperatures (1350-1380ºC), assisted by crystal defects via mechanothermal method.More importantly, the detailed observation of the morphologies and structures of the nanotubes and the related intermediate objects unveils that the transformation obeys following mechanism: nanoparticles first self-assemble into nanostructures with high-ultracrystal defects and then change into nanotubes via particle-particle coalescence and structural crystallization. Crystal phases were determined by X-ray diffraction (XRD). Scanning electron microscope (SEM) was applied to investigate the morphology. Themicrostructure of the CNT products were further observed by transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) with energy-dispersive X-ray spectroscopy (EDX). Raman spectra were taken at roomtemperature under ambient condition using an Almega Raman spectrometer with an Ar+ at an excitation wavelength of 514.5 nm.As a matter of fact, the method of mechanothermal guarantees the production of multi-walled carbon nanotubes (MWCNTs) for different applications, especially reinforcement materials because of ultra-high aspect ratio.

Age-hardenable Cu-Zr alloys are used in electrical and thermal conductive elements such as resistance welding electrodes. In the present study, mixtures of pure copper and zirconium powders in 1, 3 and 6 weight percents of Zr were milled for four differenthours. As milled powder mixtures were subsequently cold-pressed and followed by sintering at 450, 600 and 750°C. Vickers microhardness measurements were performed on as milled and sintered samples. Resulted microstructures were studied by opticalmicroscopy. Results showed that hardness in samples increased by milling time. Recovery and recrystallization processes are much slower in samples with higher Zr-contents and in those milled for longer times. These observations were attributed to the interactions of solute Zr atoms and also precipitated Zr-riched particles with recovery and recrystallization processes.

High refractoriness, chemical resistance to slag, production possibility of clean steel, environmental compatibility and low cost are some of the advantages of Dolomite refractories in steel industry. Because of availability of dolomite in Iran, production ofthese refractories is profitable. One kind of the Dolomite refractories is Doloma Graphite refractories that because of good resistance to corrosion and thermal shock have wide usage in cement and steel industries. In this research, the properties of Dolomite-Graphite refractories with different additives and tempering condition were evaluated. The samples were manufactured with different grain size distribution of Dolomite and various amounts of Graphite and resin. The raw materials and their thermalbehaviors were studied by XRF, XRD and STA. After preparing the samples, the physical and mechanical properties, slag corrosion and thermal shock resistances were evaluated. The properties of the samples were evaluated up to 11% total Carbon in thesystem. The reduction in MOR of the specimens, before and after heat treatment was determined as a measurement of thermal shock resistance. The slag corrosion test was conducted based on the crucible test, at 1600°C for 5 hrs. Then, the depth ofpenetration was measured. The obtained results showed that due to the gradual changes in thermal behavior of resin and its weight reduction, the low temperature properties of the system were affected. The results showed that CCS of the samples was increased at the beginning and then decreased, when Graphite was added to the system. The thermal shock and slag corrosion resistance were also improved by adding graphite to the system

Strontium Hexaferrite Bodies attracted more attention in various industries such as: microwave, Dc motors, agriculture (irrigation) and etc. In this research, the effect of chromium ion addition on phase analysis, microstructure and magnetic propertiesof strontium hexaferrite bodies prepared by solid state synthesis have been investigated. Results show that not only molar ratio of iron oxide and strontium oxide(n = 6) but also first firing temperature(1210oC) to form magnetic phase of strontium hexaferrite andsecond firing temperature (1220oC) to obtain suitable magnetic properties of strontium hexaferrite bodies at presences of chromium must be considered. XRD and SEM investigations showed that optimum amount of chromium is 0/3 (SrCr0/3Fe11/7O19).Magnetic coercivity, remanent magnetization and rectangularity ratio (Hk/HCj) of sample were 3995 Oe, 3719 Gs and 83/5%, respectively.

This paper aims at investigating the correlation among macro/microstructure haracteristics and mechanical properties in dissimilar resistance spot welding of AISI 304 austenitic stainless steel (SS) and AISI 1008 low carbon steel (CS). Macro andmicrostructural investigation, microhardness and tensile-shear test were performed. Results showed that the fusion zone microstructure was ranged from Ferrite-Austenite-Martensite to full martensite depending on the melting/dilution ratio of basemetals which in turn was governed by welding current. Fusion zone size in CS side is the determining factor for mechanical performance of CS/SS dissimilar welds. Generally there is a direct relation between mechanical performance (peak load and failureenergy) and FZ size of low carbon steel side. Generally, increasing the welding current increases the peak load and energy absorption. However, on expulsion observed in welding current higher than 12 kA, the energy absorption was dramatically reduced.

TiO2 has drawn much research attention in recent years because of possible applications to environmental purification, selfclean surface and solar energy converters. Anatase and rutile are the two major crystal phases of TiO2. Heat treatment can changecrystal structure and physical properties of TiO2 nanoparticles. In this work, the effect of particles size on anatase-rutile phase transformation due to heat treatment process has been studied. We have used powders with two different sizes with average sizesof 30 nm named as A and 70 nm named as B. The powders were annealed at 400, 500, 600, 700, 800, 900 and 1000°C for 2 h under ambient atmosphere and then cooled slowly. The titania powders obtained have been characterized using transmissionelectron microscopy (TEM), X-ray diffraction (XRD) and BET method. Grain size of samples and morphologic changes after heat treatment were observed by TEM, also particle size effect on the anatase-rutile phase transformation for A and B powders wereinvestigated by XRD technique. Phase transitions from anatase to rutile for powder A occurs at the lower temperature compared to powder B, that is probably due to difference of coarsening mechanism grain size for powder A and B.

In this investigation after leaching rhenium from flue dust molybdenite and contact with Amberlite ion exchange resin perrhenate and molybdate ions adsorb to the resin. In the first stage of desorption,molybdenum was carried out by solution with different concentration of sodium hydroxide, chloridric acid and potassium oxalate and in the second stage of desorption, rhenium by solution with different concentration of perchloric acid, nitric acid, chloridric acid,sulphuric acid,ammonium thiocyanate andammonium nitride.In extraction by ion exchange resin, in the stage desorption of molybdenium aim is to determin the conditions in order to have the most desorption was for molybdenum and the least was for rhenium and in the stage desorption of rhenium aim is to determin the conditions in order to have the most desorption was for rhenium. After batch experiments the most amount desorption of molybdenum was obtaind 91.1% by 7M sodium hydroxide and the most amount desorption of rhenium was alsoobtaind 79.3% by 1M perchloric acid.

The properties of the coatings depend strongly on the microstructural evolution during the thermal spraying process. In this research, the microstructural evolution and oxidation behavior of 316L stainless steel coatings deposited by flame spraying methodwas studied. Furthermore, the effects of the spraying distance and thickness on the microstructural evolution during the thermal spraying process were studied. Fabricated layers were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy(SEM) and microhardness testing. The test results indicated that the coatings consisted of porosity and oxidized phases. The increase in the levels of porosity and oxidized phases of the flame spraying coatings resulted in microhardness reductions. The results also inidated that by increasing the spraying distance to between 9 and 12 cm and decreasing the coatings thickness, there was a reduction in the coatings porosity levels and oxidized phases.