Journal of Advanced Materials in Engineering (Esteghlal)

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Anatase-to-rutile phase transformation was studied in milled and unmilled samples. Ball milling was carried out in two types of ball mills, planetary and tumbler, with a ball-to-powder ratio of 40:1 over 2-48 hours. First, the unmilled samples were heated in the furnace at various temperatures for different periods of time. The results revealed that the anatase-to-rutile transformation completed at 980 after 48 hours. The rate of transformation in milled samples was greatly higher than that of unmilled ones. Activation energy in unmilled samples was about 440 kj/mol. The rate of transformation in the planetary ball mill was higher than that in tumbler mill. In the former, transformation almost finished after 16 hours of milling while in the lattar, it did not finish even after 48 hours. XRD results revealed that the transformation proceeds through an intermediate srilankite phase in all milled samples. However, srilankite was not observed in the unmilled samples.

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In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..

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A powder mixtures of 18.72% wt, 17.67% wt Al2O3 and 63.6% wt zircon were prepared and milled in a planetary ball milled for one up to 10 hours in presence of air. After removal Iron impurity from as-milled samples, they were isothermally heated in temperature range of 1300-1450 0C for one hour in an air atmosphere. After cooling the samples, they were studied using XRD analyses. The XRD and PSA analyses were showed that the size of particles in the mixtures decreased with increasing of milling time and the mixtures became amorphous nature. The isothermal runs observed that pre-milling on the mixtures has great effect, wherever the zircon decomposition temperature and mullite formation temperature decreased to about 1300 0C in a one-hour-milled sample. The amount of tetragonal zirconia increased with increasing in milling time at 1300 0C, however the amount of tetragonal zirconia decreased with increasing of temperature up to 1450 0C. The amount of tetragonal zirconia at 1300 0C in the three hours milled samples was the highest value among all samples.

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In the present study, pure Aluminum powder with 5%wt Titanium Dioxide was mechanically milled at different times. Using phase analysis through X-ray diffraction (XRD), it was found that increasing of the milling times over 10 hours causes the reduction of Titanium by Aluminum and formation of Al2O3 in the structure. Also, it was shown that if the process persists, Aluminum reacts with Titanium and causes the formation of Al3Ti in the composition. The reactions were studied through the thermodynamic relations. Furthermore, after distribution of reinforcement particles in the matrix, using X-ray diffraction peak broadening, according to Williamson-Hall equation, the mean crystallite size and lattice strain were determined, and by scanning electron microscopy (SEM), the structure and morphology of the powder particles were studied.

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Silicon nitride has attracted a considerable attention because of its excellent properties such as high-temperature strength, good oxidation resistance, high corrosion resistance, good thermal shock resistance, high creep resistance and good thermal and chemical stability. There are several different fabrication methods for synthesizing Si3N4 particles. Such methods are mostly costly and kinetically slow and require lengthy heat treatment. In this study, Si3N4 compounds were synthesized by means of mechanical milling. In the mechanical milling route,Si powder (≤99.0%) was milled under nitrogen gas for 25 h and heated at various temperatures 1100-1200-1300 and 1400 C for 1 h at the nitrogen atmosphere at a rate of 200 ml/min. Silicon powder was also annealed under a similar condition in order to evaluate the impact of milling process on the low temperature synthesizing of Si3N4. Phase identification and microstructural characteristics of products were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The Fourier transform infrared spectroscopy and thermal analysis were used for characterization of the formed bands and thermal treatment of the sample, respectively. The obtained results exhibited that Si3N4 powder was fully formed with two kinds of morphologies including globular particles and wire with a width of 100–300 nm and length of several microns at sintering temperature of 1300 C. This was confirmed by the Si–N absorption bonds in the FTIR trace. Based on XRD results, 25 h milling reduced temperature of reaction remarkably in comparison with direct nitridation of Si powders for 1 h. With an increase in the reaction temperature, the Si3N4 samples had a phase transformation 𝛂→𝛃, and variation of the morphology followed the vapor–liquid -solid mechanism.

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In this research, ZrC nano particles were synthesized by self-propagating high temperature (SHS) using the mixed powder of ZrO2-C-Mg and NaF or NaCl diluent. The effect of different proportions of raw materials, milling time, composition of the diluent and also pickling on the synthesis of ZrC was investigated. Optimal amounts of magnesium and sodium fluoride for the synthesis of ZrC were 2.8 and 2 mol, respectively. Milling process of 120 minutes decreased the diffusion gap of raw material and increased the combustion reaction progress. XRD and SEM analysis showed that the NaF diluent more than NaCl caused a reduction in the size of the particles of ZrC and increased the progress of the combustion reaction. Synthesized samples were subjected to pickling in order to remove impurities of MgO by 37% HCl, and distilled water was used to wash off NaF and NaCl residues. ZrC particle size of different samples were in the range of 50-90 nm.

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In this study, at first Al-Al2O3 composite powders having different volume fractions of Al2O3 (0, 10, 20, 30 and 40 vol.%) were produced by low energy mechanical alloying, which were used as foam materials. Then, composite foams with 50, 60, and 70 percent of porosity were produced by space-holder technique. Spherical carbamide particles (1-1.4 mm) were used to achieve spherical porosities. In order to investigate the compressive behavior of foams, the compression test with strain rate of 10-3 S-1 was performed on the foam samples. The results showed that the compressive properties depended on the volume fraction of Al2O3 and porosity fraction. Generally, by decreasing the porosity fraction, the compressive properties were improved. The composite foams containing 10 vol.% Al2O3 showed superior compressive properties in comparison to other foams studied in this work.

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In this study, the effect of Al₂O₃ addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al₂O₃-ZrB₂ composite was investigated. For this purpose, the thermite mixture of Al, ZrO₂, H₃BO₃ and different amounts of Al₂O₃ (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650 °C. The results showed that by increasing the Al₂O₃ content up to 6 wt.%, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB₂ particles with finer grain size was observed.

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In this study, synthesis of silicon nitride by mechanical alloying and the effects of important parameters of milling time and heat treatment temperature, time and rate are presented. Silicon micro powder and nitrogen gas were used as precursor materials. Synthesized phases, morphology and particle size were investigated by X-ray diffraction pattern (XRD) and Field emission scanning electron microscopy (FE-SEM), respectively. X-ray fluorescence analysis (XRF) was used for silicon nitride purity investigation.The optimum sample was produced at 30 h milling time, heat treatment at 1300 ℃ and 22 ℃/min heating rate conditions. X-ray fluorescence analysis showed more than 98% purity.

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In this paper, milling was investigated as a method for production of Mn-Ga binary alloys and the effect of milling process on phase formation of Mn:Ga samples with 2:1 and 3:1 ratio within 1, 2 and 5 hour milling times was studied. For Mn:Ga samples, according to the results, Mn_1.86Ga compound with tetragonal structure and I4/mmm space group was a stable phase. Also, some amounts of  Mn₃Ga compound with orthorhombic structure and Cmca space group was observed in the Mn:Ga solution. The effect of Ge addition, with the purpose of  replacing Ge with Ga was also studied in Mn:Ga:Ge (3:0.5:0.5) sample. Although improved magnetic properties is expected with the addition of Ge, but increasing the coercivity was occurred, and saturation magnetization did not change significantly in the studied sample. Ge addition caused elimination of the possibility of formation of asymmetric orthorhombic Mn₃Ga phase. In return, two new structures of Mn₁₁Ge₈ and MnGaGe were appeared. This phase change was confirmed by studying magnetic behaviour of samples. This behavior can be caused by unbalanced electrostatic forces resulting from Mn-Mn exchange interaction in Mn₃Ga orthorhombic structure and substitution of some Ge atoms with Ga.

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Investigating the effect of Al₂O₃-TiB₂/Fe complex reinforcement (CCMR) on the mechanical properties of aluminum composites was the goal of this study. For this purpose, the Al₂O₃-TiB₂/Fe reinforcement powders were synthesized during milling and subsequent annealing. Different volume percentages of the produced reinforcement powders (1.25, 2.5 and 5 vol.%) were added to aluminum matrix, milled for 10 h and then hot extruded. The structural phasic and mechanical investigations of the specimens were carried out using X-ray diffraction, scanning electron microscopy and tensile test. The results showed that the metallic component (Fe rich phase) in this new type of reinforcement stuck the ceramic parts (Al₂O₃-TiB2) to aluminium matrix, and has an importance role in the flexibility of the product. The best volume percentage of CCMR in aluminium matrix was about 2.5%. This nanocomposite had a combination of strength and ductility of about 500 MPa and 6%, respectively.
 

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Despite a great thermodynamic driving force, copper cementation by aluminum from sulfate solutions involves a relatively slow kinetics due to the presence of the passive oxide film on the surface of aluminum. The previous studies have confirmed the positive effect of the presence of small amounts of chloride ion on reducing the scale of this problem. In this paper, the effect of concurrent ball milling on the kinetics of this process has been investigated. The cementation experiments were carried out in a polyamide jar with alumina balls inside by planetary ball milling. The studied parameters were ball number (0, 4), temperature (25-55 °C) and time (0-240 s). All experiments were conducted at constant condition of [Cu²⁺] = 6 g/L, [Cl⁻] = 75 mg/L, rotation speed of 160 rpm, average aluminum particle size of 279 µm and [H⁺] = 1.94×10^-3. The results showed that concurrent ball milling reduces the induction period of the cementation process to less than 120 s.  The apparent rate constant of cementation showed the positive influence of simultaneous milling on the kinetics of the studied cementation process. Moreover, activation energies of the induction and main periods were calculated to be respectively 86 and 26 kJ.mol^-1, indicating the shift of the reaction mechanism from chemical control to mass transfer control.
 

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