Papers by Keyword: Combustion Reaction

Abstract: Already, there are several processes to produce intermetalic alloy parts from powder , ex. metal injection molding (MIM) or additive manufacturing (AM). For these processes, pre-alloyed powder made by gas atomized powder is used because of their quality. As other way, intermetallic alloy can be produced combustion reaction process. On this process, ingredient metal powders are mixed and reacted by combustion. However, powders are fused by reaction heat, and they are difficult to keep the powder condition. There for, we are developed the process to produce intermetallic alloy precursor by slow combustion reaction. On this process, temperature of mixed powders increases slower than 0.2K/sec. while the combustion reaction, and powders are reacted without fusing. Using this process, TiAl presursor is synthesized. Relation of reacting condition and quality of the precursor is evaluated, and researched the practical usage of this precurser.

Abstract: This work intends to show the effect of the iron ion doping in LaCoO₃ perovskite, both in powders and in sintered samples obtained from combustion reaction route. The phase formation and particle morphology and particle size distribution of the powders were analysed by XRD, SEM and sedimentation techniques, respectively. Relative density, microstructure (secondary phases and grain size) and pore size distribution of LaCo_1-xFe_xO₃ sintered ceramics have been investigated by SEM/EDS and Hg porosimetry analysis. Although LaCo_1-xFe_xO₃ powders obtained from combustion reaction exhibited smaller grain sizes when sintered at high temperatures, they showed higher volume fraction of secondary phases. The presence of these crystalline phases in addition to the desired perovskite affected the microstructure acting as grain growth inhibitors by grain boundary pinning. It is believed by observing three grain junction pores that LaFeO₃ phase has a smaller dihedral angle than LaCoO₃. This fact would explain why LaFeO₃ presented a smaller driving force for sintering with higher tendency of pore and inclusion coarsening at higher temperatures (1400°C).

Abstract: The aim of this work is to show the effect of the iron ion doping in LaCoO₃ perovskite, both in powders and in sintered samples obtained from combustion reaction and solid state route. The phase formation and particle morphology and particle size distribution of the powders were analysed by XRD, SEM and sedimentation techniques, respectively. Relative density, microstructure (secondary phases and grain size) and pore size distribution of LaCo_1-xFe_xO₃ sintered ceramics were investigated by SEM/EDS and Hg porosimetry analysis. Although LaCo_1-xFe_xO₃ powders obtained from the combustion reaction exhibited smaller grain sizes when sintered at high temperatures, they showed a higher volume fraction of secondary phases. The presence of these crystalline phases in addition to the desired perovskite affected the microstructure acting as grain growth inhibitors by grain boundary pinning. It is believed that by observing three grain junction pores that the LaFeO₃ phase has a smaller dihedral angle than LaCoO₃. This fact would explain why LaFeO₃ presented a smaller driving force for sintering with a higher tendency of pore and inclusion coarsening at higher temperatures (1400°C).

Abstract: Nanotechnology has been important in improving of the properties of the materials used in the manufacture of magnetic devices, electromagnetic radiation absorbers, cell telephony, pigments and lately in catalysis in transesterification and esterification reactions to biodiesel obtaining. The objective of this work was to synthesize and characterize magnetic materials of spinel type compound of CuFe₂O₄, CoFe₂O₄, MnFe₂O₄, NiFe₂O₄ and FeFe₂O₄ and to check the catalytic effect on the methyl esterification reaction of soybean oil. The samples were obtained by combustion reaction and characterized by XRD, FTIR, BET and SEM. The results analysis revealed for nanoferrites the spinel phase formation and higher specific area to the sample CoFe₂O₄. Generally the samples presented in irregular agglomerates form. All samples were catalytically active in the esterification reaction, with the highest conversion obtained by the sample MnFe₂O₄ with 57%.

Abstract: The magnetic nanoparticles (MNP's) have chemical characteristics of acids or bases of Lewis or Brönsted and they allow their use in various processes, for example, in the biofuels synthesis. Thus, this study aimed to synthesize the MNP's of Ni_0.5Zn_0.5Fe₂O₄ and Ni_0.2Cu_0.3Zn_0.5Fe₂O₄ to be used as catalysts in the transesterification reaction by methyl and ethyl route. In samples preparing we used the combustion reaction method and characterization by XRD, FTIR and BET. The catalytic reaction was conducted in a high pressure reactor on the conditions: 180°C for 1 hour, oil:alcohol molar ratio 1:12 and 2% of catalyst. The results indicate the formation of spinel inverted phase for the studied samples. In catalytic activity we observed an increase of 85% in conversion when we added Cu⁺² to Ni_0.5Zn_0.5Fe₂O₄ system with conversion of 13.9% by methyl route and 10.8% by ethyl route.

Abstract: The present work aims to study the magnetic properties of nanoferrita cobalt obtained by combustion reaction. The structural feature as well as the magnetic behavior when in the presence of a magnet and magnetic measurements was investigated. The resulting samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), magnetic behavior when in the presence of a magnet and magnetic measurements. The results indicated the phase single the spinel ferrite CoFe₂O₄, with high intensity of diffraction peaks indicating that the samples are crystalline and nanoparticle formation. The characteristic bands of spinel were observed for nanoferritas CoFe₂O₄. The ferrite nanoparticles were strongly attracted when in presence the magnet presenting a saturation magnetization of 58.0 emu/g, coercivity of 1.14 kOe.

Abstract: This paper proposes to investigate the influence of the type of container on the structure, morphology and measures magnetic nanoparticles of the Zn_0.6Fe_0.4O synthesized by combustion reaction, for use as diluted magnetic semiconductors (DMSs). For synthesis were used as containers stainless crucibles and porcelain. The heating was realized in a muffle furnace at 500 °C. During the reactions, were performed measurements of the maximum temperature and total time of combustion reaction. The synthesized samples were characterized by XRD, SEM and magnetic measurements. The maximum temperatures obtained were 478 and 456 °C and total reaction time of 285 and 195 s for the samples synthesized in the crucible of stainless steel and porcelain, respectively. In both containers were possible to obtain single phase material with average crystallite size of 26 to 37 nm, irregular agglomerates formed by, behavior ferrimagnetic whose, saturation magnetization values of 1.6 e 2.0 emu/g respectively.

Abstract: In this paper, a novel processing method (reactive precursor method) to manufacture high-melting point porous Al-Ti intermetallics is investigated. Especially, morphological control of porous structure is focused. In the reactive precursor process, precursors are made by blending aluminum and titanium powders. The precursor is heated to ignite an exothermic reaction (so called “combustion reaction”) between the elemental powders. Pore formation is a well-known intrinsic feature of the combustion reaction, and we tried to control the pore morphology. Fundamentally, the closed-cell structure can be obtained when the maximum temperature during the reaction exceeds the melting point of the reaction product. By blending the exothermic agent powder in the precursor, the maximum temperature is increased and the reaction products are melted. The porosity is controlled by the maximum temperature. In contrast, an open-cell porous structure can be obtained when the maximum temperature is below the melting point of the reaction product. Microwave heating turned out to be an effective method to create an open cell structure. A powdery substance that does not react with other elemental powders (heat-absorbing agent powder) decreases the temperature during the reaction. Closed, open and bimodal-sized open pores have been achieved by the reactive precursor process so far.

Abstract: This research aims to synthesize ZrO₂ by combustion reaction in batches of 15 g of the product and to evaluate the calcination influence on the structural and morphological characteristic about synthesized sample. For the synthesis of ZrO₂, the stoichiometry of phase was established in accordance with the propellants and explosives chemical concept, whereas the stoichiometric coefficient φ =1. After the synthesis, the sample as synthesized was calcined at 600 and 700°C and subsequently characterized by XRD, SEM, textural analysis (BET) and FTIR. The results have shown to the sample as synthesized and then calcined at 600°C the majority phase formation of orthorhombic zirconia with monoclinic phase dashes. The temperature increase to 700°C, has been transformed a part of the orthorhombic ZrO₂ to a monoclinic phase, contributing to a surface area reduction of the samples, showing irregular agglomerates in morphology, with adsorption/desorption isotherms type IV and mesoporosity characteristic.

Abstract: The aim of this study is to evaluate the effect of temperature during the synthesis of alumina by combustion in a muffle furnace. The alumina was characterized by X-ray diffraction, particles size distribution and scanning electron microscopy. The results showed that the synthesis temperature of the alumina can affect the structure of the produced samples. The size distribution of the median particle diameter reached higher value for the alumina synthesized at 500°C with 16.07 μm, the range of the total distribution of particles is introduced to the large alumina synthesized 500 and 600°C and close synthesized when 700 and 800°C. The phase of the alumina was identified only after the synthesized sample at 800°C with crystallite size of 22.16 and 6.75 μm synthesized samples 800 and 900°C, respectively. With respect to morphology, increased synthesis temperature was not enough to significantly change.