Materials Science Forum Vol. 820

Abstract: In the past few years there is a considerable interest in the study and application of the mullite, due to its chemical, physical and mechanical properties, in which are correlated with the synthesis method used. Aiming to achieve better structural and morphological properties, many synthesis methods are being studied, in which the Pechini method is highlighted, which is today one of the most viable methods and successful technique used in the preparation of nanosized materials. Thus, this study proposes the production of mullite powders by the Pechini method. The influence of different routes of synthesis was investigated. The material was sintered at 1100oC/2h, 1200oC/2h and 1400/2h, and characterized by X ray diffraction (XRD) and thermal analysis (TG/DTG and DTA). The results showed that the synthesis route did not interfere in the formation of the formed phases, and the mullite for both routes, was formed from 1200oC.

Abstract: Magnetic catalysts are easily removed from the reaction process, thereby reducing the wastewater generation. Therefore, the study proposes to evaluate the performance of the nanomagnetic catalyst Ni_0.5Zn_0.5Fe₂O₄ in the transesterification reaction of the soybean oil to produce biodiesel, varying processing conditions (temperature, molar ratio of oil:alcohol and catalyst amount) on the catalytic reaction. The catalyst was synthesized by combustion reaction and characterized by XRD, BET, magnetic measurements and gas chromatography. The results revealed the inverse spinel phase formation, type B(AB)₂O₄, with isotherm profile classified as type V with hysteresis loop of type 3 (H3), and surface area of ​​48.39 m²g^-1. The magnetic hysteresis curve showed a characteristic behavior of soft magnetic material with saturation magnetization value of 55 emu/g. Chromatographic analysis confirmed that the magnetic nanoparticles are catalytically active and that the processing conditions directly influence the conversion into esters.

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: 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: Pseudoboehmite (PB) were synthesized through the sol-gel process, using aluminum nitrate as precursor. The pH adjustment of the precursor solution was made by using ammonium carbonate. After the precipitation, the material was dried at 70°C before characterization. The pseudoboehmite obtained were characterized by x-ray diffraction, scanning electron microscopy and afterwards by thermal analysis (DTA and TG). The pseudoboehmite was also calcined at 500^o C to obtain gamma-alumina. The specific surface area measurements through the BET process and the desorption-absorption of nitrogen as well the t plot in order to evaluate the pore volume of the calcined samples was realized. Finally, the results showed that the synthesized pseudoboehmite can be used to produce high specific surface material with a crystal structure of gamma-Al₂O₃ (around 324m2/g).

Abstract: The synthesis of ceramic materials from polymeric precursors has been the subject of numerous studies due to lower energy cost compared to conventional processing. The study aims to research and develop synthesis of calcium aluminate powders via the polymeric precursor method, in order to obtain the pure phase of hepta-aluminate dodecálcio (C₁₂A₇) with mayenita mineral name, since it has applications like: special cements and components for high temperature fuel cells. A study of the evolution of crystalline phases by X-ray diffraction was performed, the vibrational modes of atomic location in crystalline phases were studied by micro-Raman spectroscopy was also performed and images from scanning electron microscopy. From the characterizations carried out on the material can be seen that the sintering temperature of 1200°C was obtained pure phase, so the choice of synthesis shown to be effective due to the complexity of obtaining this phase pure.

Abstract: Tricalcium aluminate (C₃A) are used for different applications such as thermal insulation, cement, refractory concrete as binders or binders. The aim of this work is to study the synthesis and sintering behaviour of C₃A samples. The chemical synthesis was performed by means of polymeric precursor method from metalic nitrates dissolved in ethylene glycol and citric acid forming a polymeric resin. The evolution of the crystalline phases was accomplished by X ray Diffraction (XRD). Thermogravimetric (TG), Differential Thermal Analysis (DTG) and Thermal Expansion were performed in order to verify the thermal properties of the material. From the characterizations carried out it may be concluded that the synthesis of polymeric precursors via allowed obtaining pure phase of C₃A at 1000°C low temperatures. The temperature of 1350°C it possible to obtain materials having grain morphology with uniform size and densely packed.

Abstract: The main objectives of this work were the production of Ca₂MgWO₆ ceramic by sintering and the investigation of its reactivity to crude petroleum. A synthesis was prepared with stoichiometric amounts of CaO, MgO and WO₃. The reagents were characterized according to chemical composition. The synthesis was characterized by size distribution and thermal analysis. A green compact of the synthesis was calcined at 1200 °C and analyzed by XRD. The result showed that the calcined material consists predominantly of a complex perovskite-type Ca₂MgWO₆ ceramic. The calcined material was fragmented in a ball mill and used to prepare three green compacted to be sintered at temperatures of 1250, 1300 and 1350 °C. The sintered material was evaluated by linear shrinkage, microhardness, SEM, microanalysis by dispersive energy and stability tests in crude petroleum. The results showed that it is possible to produce a material with 74.5 % of Ca₂MgWO₆ and that is inert to crude petroleum.

Abstract: Among the vast applications in which the α-alumina can apply, the literature has reported researches which aim to achieve better features of these materials varying the obtainment methodology and some post-obtainment techniques. Thus, this paper aims to evaluate how different milling time lengths of 15, 30, 45 and 60 minutes alter the structure and morphology of α-alumina powders synthesized by combustion reaction. The time and temperature of the combustion reaction were evaluated during the synthesis of the alumina. The samples of non-milled and milled alumina were characterized by XRD and particle size analysis. The results showed that the maximum achieved temperature of reaction was 598°C. The milling time length variation did not alter the stable α-Al₂O₃ majority crystal phase present in all samples. The average particle diameter was reduced from 23.3 to 10.5 μm comparing the non-milled and the sample milled for 60s.

Abstract: This work aims to evaluate the immobilization of glucose oxidase (GOx) with CoFe₂O₄ nanoparticles and hybrids CoFe₂O₄/APTS. The nanoparticles were synthesized by combustion reaction and silanized using 3-aminopropyltrimethoxysilane (APTS). The samples were characterized by XRD, FTIR, magnetic measurements and immobilization of GOx. The results indicated single phase of spinel CoFe₂O₄ and the addition of APTS did not alter the structure of the ferrite. The characteristic bands of spinel and characteristic bands were observed in the silane silanized sample proving the silanization of nanoparticles of CoFe₂O₄. The CoFe₂O₄ nanoparticles and the hybrid had saturation magnetization of 58.0 and 53.0 emu/g and coercivity of 1.14 kOe and 1.15, indicating that the silanization does not interfere with the magnetism of the particles. The immobilized GOx was obtained with values of 0.047 and 0.050 mg/g efficiency of 84.86 and 80.30% for CoFe₂O₄/APTS and CoFe₂O₄.