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Papers by Amir Hossein Emami

Research paper thumbnail of An engineering design based on nano/micro-sized composite for CaTiO3/CaCu3Ti4O12 materials and its dielectric and non-Ohmic properties

Ceramics International, 2019

In this research, the dielectric and non-Ohmic properties of nano/micro-sized CaTiO 3 /CaCu 3 Ti ... more In this research, the dielectric and non-Ohmic properties of nano/micro-sized CaTiO 3 /CaCu 3 Ti 4 O 12 composites (NCTO/MCCTO) with different weight percent of CTO (0, 7, 15, and 30 wt%) were examined as a new engineering design. NCTO was prepared after high energy ball milling of calcined CaCO 3 and TiO 2 mixture. Microsized CCTO was synthesized after calcination of CaCO 3 , CuO, and TiO 2 mixture at 1000°C. According to the TEM, BET, and SEM analyses; the mean particle size of NCTO and MCCTO was 80 nm and 2.5 μm, respectively. The NCTO/MCCTO powder composites were prepared from direct mixing of pre-synthesized NCTO and MCCTO. After the sintering of green body composites at 1100°C for 5 h, both relative density and grain size of NCTO/ MCCTO composites decreased with the increase in NCTO content. It was found that the abnormal grain growth in the sintered MCCTO changed to the normal grain growth in NCTO/MCCTO composites. The best dielectric properties (ϵ r : 7050, tanδ: 0.02) was observed for NCTO/MCCTO with 15 wt% CTO. This unique dielectric constant was ascribed to the large grain size of CCTO, and the reduced dead zone of CTO with a low dielectric constant. Due to uniform distribution of CTO with the small size of 0.3-1.5 μm at grain boundaries of CCTO with a large grain size of 5 μm, the number of active interfaces were increased sharply and consequently the maximum breakdown electric field of 7 kV/cm and the nonlinear coefficient of 15 were obtained for NCTO/MCCTO with 15 wt% of NCTO. Therefore, the MCCTO-NCTO composite with 15 wt% of NCTO is a promising candidate for the capacitor and energy storage applications.

Research paper thumbnail of Rapid mechanochemical synthesis of nickel-vanadium carbide nanocomposite powder by magnesiothermic reaction

Ceramics International, 2018

In the present study, in-situ production of Ni-VC nanocomposite powder synthesized from several r... more In the present study, in-situ production of Ni-VC nanocomposite powder synthesized from several raw materials including NiO, V 2 O 5 , Mg and C, was carried out through mechanochemical approach by means of magnesiothermic reaction. Due to high adiabatic temperature (T=3964 K), this reaction is known as a self-propagating reaction or MSR. Raw materials were mixed at 1:1:6:2 stoichiometric ratios of nickel oxide, vanadium oxide, magnesium and graphite, respectively. Milling process was carried out in a high-energy planetary ball mill under argon atmosphere with various ball-to-powder weight ratios (15:1, 20:1 and 25:1) for the aim of obtaining the optimum ball-to-powder weight ratio to reduce the synthesis time. After milling for 30 min and 40 min, combustion occurred in the milling vial for 25:1 and 20:1 ball-to-powder weight ratios, respectively. The microscopic properties of milled nanocomposite powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD patterns, after combustion reaction, anticipated products including nickel, vanadium carbide (VC) and magnesium oxide (MgO) were totally produced. To remove undesirable MgO phase, leaching process (1M HCl at 80 °C for 1 h) was used. According to XRD and X-ray-mapping analyses before and after the leaching process, HCl dissolved MgO phase thoroughly. Additionally, crystallite size and lattice strain were calculated based on Williamson-Hall method; these values were calculated 54 nm and 0.00615 for VC, while they were 40 nm and 0.00595 for nickel, respectively. Moreover, according to TEM micrograph, the morphology of the particles after leaching process was found to be spherical with the size of 50±5 nm.

Research paper thumbnail of An investigation of the reduction mechanisms and magnesiothermic reactions in ZrC-Ni nanocomposite synthesis

Materials Chemistry and Physics, 2019

In the present study, the effects of preactivation stage and graphite content on the reduction an... more In the present study, the effects of preactivation stage and graphite content on the reduction and synthesis mechanisms of ZrO2-NiO-Mg-graphite system were evaluated. For this purpose, the powder mixture with stoichiometric ratio was exposed to milling process. After the combustion it was found that the synthesis did not occur completely. By adding 10 wt.% Mg to the mixture and further milling, the synthesis was completed and NiZr intermetallic compound was formed. Preactivation stage was carried out to complete the synthesis and reduction process of the composite samples. It was determined that after 6 h of preactivation, combustion time increased due to increase of oxide particles surface area and presence of graphite as a barrier between Mg and oxide particles. To confirm this, the mechanochemical process was performed with different graphite contents. It was realized that by increasing the graphite content as a postponing agent to levels higher than the stoichiometric limit, the synthesis was completed after 1200 min of milling without the presence of intermetallic compound.

Research paper thumbnail of A low temperature mechanochemical synthesis of nanostructured ZrC powder by A magnesiothermic reaction

Ceramics International, 2015

Nanostructured ZrC powder was synthesized by the mechanochemical process in a high-energy ball mi... more Nanostructured ZrC powder was synthesized by the mechanochemical process in a high-energy ball mill by a magnesiothermic reaction. The effects of various amounts of Mg (stoichiometric and over-stoichiometric) on synthesis efficiency of the ZrC powders were investigated. The synthesized powders were studied by X-ray diffraction (XRD), differential thermal analysis (DTA), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Zirconium carbide (ZrC) was produced after 30 h milling. Thermodynamic calculation showed the reaction to be a mechanically induced self-sustaining one (MSR). DTA analysis indicated that the temperature of exothermic reaction decreases significantly after 12 h milling.

Research paper thumbnail of An engineering design based on nano/micro-sized composite for CaTiO3/CaCu3Ti4O12 materials and its dielectric and non-Ohmic properties

Ceramics International, 2019

In this research, the dielectric and non-Ohmic properties of nano/micro-sized CaTiO 3 /CaCu 3 Ti ... more In this research, the dielectric and non-Ohmic properties of nano/micro-sized CaTiO 3 /CaCu 3 Ti 4 O 12 composites (NCTO/MCCTO) with different weight percent of CTO (0, 7, 15, and 30 wt%) were examined as a new engineering design. NCTO was prepared after high energy ball milling of calcined CaCO 3 and TiO 2 mixture. Microsized CCTO was synthesized after calcination of CaCO 3 , CuO, and TiO 2 mixture at 1000°C. According to the TEM, BET, and SEM analyses; the mean particle size of NCTO and MCCTO was 80 nm and 2.5 μm, respectively. The NCTO/MCCTO powder composites were prepared from direct mixing of pre-synthesized NCTO and MCCTO. After the sintering of green body composites at 1100°C for 5 h, both relative density and grain size of NCTO/ MCCTO composites decreased with the increase in NCTO content. It was found that the abnormal grain growth in the sintered MCCTO changed to the normal grain growth in NCTO/MCCTO composites. The best dielectric properties (ϵ r : 7050, tanδ: 0.02) was observed for NCTO/MCCTO with 15 wt% CTO. This unique dielectric constant was ascribed to the large grain size of CCTO, and the reduced dead zone of CTO with a low dielectric constant. Due to uniform distribution of CTO with the small size of 0.3-1.5 μm at grain boundaries of CCTO with a large grain size of 5 μm, the number of active interfaces were increased sharply and consequently the maximum breakdown electric field of 7 kV/cm and the nonlinear coefficient of 15 were obtained for NCTO/MCCTO with 15 wt% of NCTO. Therefore, the MCCTO-NCTO composite with 15 wt% of NCTO is a promising candidate for the capacitor and energy storage applications.

Research paper thumbnail of Rapid mechanochemical synthesis of nickel-vanadium carbide nanocomposite powder by magnesiothermic reaction

Ceramics International, 2018

In the present study, in-situ production of Ni-VC nanocomposite powder synthesized from several r... more In the present study, in-situ production of Ni-VC nanocomposite powder synthesized from several raw materials including NiO, V 2 O 5 , Mg and C, was carried out through mechanochemical approach by means of magnesiothermic reaction. Due to high adiabatic temperature (T=3964 K), this reaction is known as a self-propagating reaction or MSR. Raw materials were mixed at 1:1:6:2 stoichiometric ratios of nickel oxide, vanadium oxide, magnesium and graphite, respectively. Milling process was carried out in a high-energy planetary ball mill under argon atmosphere with various ball-to-powder weight ratios (15:1, 20:1 and 25:1) for the aim of obtaining the optimum ball-to-powder weight ratio to reduce the synthesis time. After milling for 30 min and 40 min, combustion occurred in the milling vial for 25:1 and 20:1 ball-to-powder weight ratios, respectively. The microscopic properties of milled nanocomposite powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD patterns, after combustion reaction, anticipated products including nickel, vanadium carbide (VC) and magnesium oxide (MgO) were totally produced. To remove undesirable MgO phase, leaching process (1M HCl at 80 °C for 1 h) was used. According to XRD and X-ray-mapping analyses before and after the leaching process, HCl dissolved MgO phase thoroughly. Additionally, crystallite size and lattice strain were calculated based on Williamson-Hall method; these values were calculated 54 nm and 0.00615 for VC, while they were 40 nm and 0.00595 for nickel, respectively. Moreover, according to TEM micrograph, the morphology of the particles after leaching process was found to be spherical with the size of 50±5 nm.

Research paper thumbnail of An investigation of the reduction mechanisms and magnesiothermic reactions in ZrC-Ni nanocomposite synthesis

Materials Chemistry and Physics, 2019

In the present study, the effects of preactivation stage and graphite content on the reduction an... more In the present study, the effects of preactivation stage and graphite content on the reduction and synthesis mechanisms of ZrO2-NiO-Mg-graphite system were evaluated. For this purpose, the powder mixture with stoichiometric ratio was exposed to milling process. After the combustion it was found that the synthesis did not occur completely. By adding 10 wt.% Mg to the mixture and further milling, the synthesis was completed and NiZr intermetallic compound was formed. Preactivation stage was carried out to complete the synthesis and reduction process of the composite samples. It was determined that after 6 h of preactivation, combustion time increased due to increase of oxide particles surface area and presence of graphite as a barrier between Mg and oxide particles. To confirm this, the mechanochemical process was performed with different graphite contents. It was realized that by increasing the graphite content as a postponing agent to levels higher than the stoichiometric limit, the synthesis was completed after 1200 min of milling without the presence of intermetallic compound.

Research paper thumbnail of A low temperature mechanochemical synthesis of nanostructured ZrC powder by A magnesiothermic reaction

Ceramics International, 2015

Nanostructured ZrC powder was synthesized by the mechanochemical process in a high-energy ball mi... more Nanostructured ZrC powder was synthesized by the mechanochemical process in a high-energy ball mill by a magnesiothermic reaction. The effects of various amounts of Mg (stoichiometric and over-stoichiometric) on synthesis efficiency of the ZrC powders were investigated. The synthesized powders were studied by X-ray diffraction (XRD), differential thermal analysis (DTA), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Zirconium carbide (ZrC) was produced after 30 h milling. Thermodynamic calculation showed the reaction to be a mechanically induced self-sustaining one (MSR). DTA analysis indicated that the temperature of exothermic reaction decreases significantly after 12 h milling.