Síntese de MgAl2O4 por combustão assistida por micro-ondas: influência dos parâmetros de síntese na formação e na estrutura cristalina

Medeiros, Rodolfo L.B.A.; Macedo, Heloísa P.; Oliveira, Ângelo A.S.; Melo, Valci; Carvalho, Alexandre Fontes Melo de; Melo, M. A. F.

doi:10.1590/0366-69132016623621961

Cited by 6 publications

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References 19 publications

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“…5). The particles of the solids presented a format of thin sheets or plates with an irregular geometry and size, which is in accordance with the results obtained by Medeiros et al 40 . However, it was possible to notice that the particles from the sample MA0U presented a more smooth and homogeneous appearance, appearing a low porosity.…”

Section: (3)supporting

confidence: 91%

“…They observed that as the starch content increased in the blend, there was a decrease in crystallite size and an increase in the specific surface area of the solid as a consequence of the higher amount of gases released during the process. On the other hand, Medeiros et al 40 evaluated the influence of synthesis parameters by microwave-assisted combustion, such as fuel/oxidant ratio, microwave power and calcination temperature of the MgAl 2 O 4 powder structure. According to these authors, in order to form MgAl 2 O 4 with a higher degree of crystallinity and a smaller crystallite size, the combustion reaction must be performed with a fuel/ oxidant ratio less than 1:1, with the microwave operating at a power greater than 675 W, and after the synthesis realizing a calcination at 900 °C.…”

Section: Introductionmentioning

confidence: 99%

“…Once that Medeiros et al 40 used fuel/oxidation ratios equal to 0.8, 1.0 and 1.2 for the material synthesis and did not evaluate the influence of use a higher amount of urea during the preparation, this paper intends to investigate the effect of urea in excess on the synthesis by microwave-assisted combustion on the textual and structural properties of MgAl 2 O 4 . In order to do that, during the syntheses process, a mass of urea from 1.0 to 2.5 times the stoichiometric amount required was added, and the materials obtained were characterized by TGA, FTIR, XRF, XRD, BET, SEM and TEM.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Urea Excess on the Properties of the MgAl2O4 Obtained by Microwave-Assisted Combustion

et al. 2017

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In this paper, magnesium aluminate spinels were prepared by microwave-assisted combustion, using urea as fuel. In order to evaluate the effect of the urea excess used in the synthesis, its mass was added in a range of 1.0 to 2.5 times the stoichiometric amount required. The materials produced were characterized by TGA, FTIR, XRF, XRD, BET, SEM and TEM. The results demonstrated that magnesium aluminate spinel was formed in all solids, but the crystallinity degree and the specific surface area increased according to the amount of urea that was used in the synthesis. The use of excess fuel in the preparation was therefore advantageous, since it eliminated the need of the calcination step, at high temperatures, in order to stabilize the spinel phase and improve the crystallinity of the solid. The heat generated in the combustion process was sufficient to develop the formation of a nanocrystalline structure and produce high purity materials, with a save of 99.4% in energy.

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Section: (3)supporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of Urea Excess on the Properties of the MgAl2O4 Obtained by Microwave-Assisted Combustion

et al. 2017

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“…In microwave assisted combustion method the variation of synthesis parameters implies on the formation of undesirable secondary phases and affect the crystallinity and crystallite size of the material obtained. However, MgAl 2 O 4 with higher degree of crystallinity (66.60%) and small crystallite sizes (23.86 nm) can be obtained after adjustment of synthesis and calcination variables at 900 ºC for 3 h 10 .…”

Section: Introductionmentioning

confidence: 99%

Synthesis of MgAl2O4 by Gelatin Method: Effect of Temperature and Time of Calcination in Crystalline Structure

et al. 2017

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Magnesium aluminate can be obtained by the methods: ceramic method, sol-gel, co-precipitation, hydrothermal and combustion. However, this work presents a simple and low cost route to obtain MgAl 2 O 4 through the gelatin method. The main objective was to use gelatin as an organic precursor and to verify the influence of temperature and time of calcination on the structural and morphological properties of obtained materials. Al and Mg nitrates were used as metal precursors with Al/Mg = 2 ratio. Samples were calcined as follows: 700 ºC, 900 ºC and 1100 ºC during 2 and 4 h. The powders were characterized by TGA, XRD and SEM. A single phase material with a crystallinity of 39.18-90.40% and crystallite size in the range of 12.4 to 55.5 nm was obtained. The materials exhibited morphology in the form of plates and small agglomerates. It was found that increasing temperature and time of calcination favored the growth of crystallites and increased crystallinity.

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“…No caso da síntese do Al 2 O 3 , vários trabalhos já relataram o uso de diferentes tipos de combustíveis [15][16][17]. Em estudo anterior realizado na preparação do MgAl 2 O 4 , observou-se que o excesso de combustível e a utilização de potência abaixo de 675 W resultaram na obtenção de tamanhos de cristalitos entre 10 e 20 nm [18]. Entretanto, ainda não foram estudadas as influências da potência do micro-ondas e da razão combustível-oxidante na formação e nas propriedades dos óxidos de alumínio.…”

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Estudo da influência da razão combustível/oxidante e da potência do micro-ondas na formação da α-Al 2 O 3 via reação de combustão

et al. 2017

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ResumoOs óxidos de alumínio (Al 2 O 3 ) nanoestruturados vêm recebendo apreciável atenção nos últimos anos em diversas áreas. Em especial, a α-Al 2 O 3 que é uma fase estável, se destaca por sua estabilidade térmica e química em diversas aplicações. Entre as técnicas de síntese da α-Al 2 O 3 , o processo de combustão assistida por micro-ondas tem recebido notável importância por se tratar de um método rápido, com facilidade de processamento e baixo custo, que possibilita a obtenção de pós cerâmicos com boas características estruturais. Apesar da sua simplicidade em termos de processamento, vários parâmetros podem influenciar nas propriedades finais dos pós cerâmicos. Neste sentido, o objetivo deste estudo foi avaliar a influência da razão combustível/oxidante (R co ) e da potência do micro-ondas (P mic ) na quantidade de α-Al 2 O 3 formada, no tamanho de cristalito e na cristalinidade dos pós formados. Para isso, foram utilizados três R co (1:1, 2,5:1 e 5:1) e três P mic (450, 675 e 900 W) para realizar as reações de combustão. Os materiais obtidos foram calcinados a 900 ºC por 2 h para verificar a influência dos parâmetros na formação da α-Al 2 O 3 . Para avaliar melhor a influência dos parâmetros da síntese foi utilizado o planejamento fatorial 2² com quatro pontos centrais. As técnicas de difração de raios X e de microscopia eletrônica por varredura foram utilizadas para investigar a estrutura cristalina e a morfologia dos pós formados. Os resultados mostraram que tamanhos de cristalitos de 10 a 13 nm foram obtidos utilizando mistura pobre em combustível (R co de 1:1), independente da potência utilizada. A influência dos parâmetros de síntese também foi observada na morfologia, onde espécies de carbonatos de alumínio foram observadas após a reação de combustão quando o experimento foi realizado usando mistura rica em combustível. Palavras-chave: α-Al 2 O 3 , combustão, micro-ondas, planejamento fatorial. Abstract Nanostructured aluminum oxides (Al 2 O 3 ) have received considerable attention in recent years in several areas. In particular, α-Al

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Síntese de MgAl2O4 por combustão assistida por micro-ondas: influência dos parâmetros de síntese na formação e na estrutura cristalina

Cited by 6 publications

References 19 publications

Effect of Urea Excess on the Properties of the MgAl2O4 Obtained by Microwave-Assisted Combustion

Effect of Urea Excess on the Properties of the MgAl2O4 Obtained by Microwave-Assisted Combustion

Synthesis of MgAl2O4 by Gelatin Method: Effect of Temperature and Time of Calcination in Crystalline Structure

Estudo da influência da razão combustível/oxidante e da potência do micro-ondas na formação da α-Al 2 O 3 via reação de combustão

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