Papers by Author: Ana Cristina Figueiredo de Melo Costa

Abstract: This study aims to evaluate the hydrophobicity of vulcanized silicone rubber coatings at room temperature (RTV SR) with loads of alumina trihydrate (ATH) and nanosilica (NS) in the polymeric silicone rubber matrix, in order to obtain coatings ATH/NS/RTV SR to cover the surface of glass electrical insulators. The coatings were characterized by scanning electron microscopy (SEM), testing in salt spray chamber, loss test and recovery of hydrophobicity. These coatings showed varying sizes of agglomerates and heterogeneous distribution of particles within the matrix RTV SR. In the test in salt spray chamber smaller leakage current values was observed for the insulator coating with the ATH/NS loads. In the loss and recovery of the hydrophobicity test the best result was observed for insulating load RTV SR / 20: 1 (ATH: NS).

Abstract: This work involved a study of the reproducibility of the process of combustion synthesis to produce Ni-Zn ferrites. The structural, morphological and magnetic characteristics of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and magnetometry using an alternating gradient magnetometer (AGM). The XRD diffractograms of the samples indicated that they are monophasic, crystalline, with crystallite sizes ranging from 21 to 38 nm, and have a homogeneous morphology consisting of agglomerates of spherical particles. The samples behaved as soft magnetic materials, with magnetization levels ranging from 37 to 47 emug^-1. The combustion synthesis was found to be efficient in producing Ni-Zn nanoferrites, yielding reproducible results.

Abstract: This study proposes to evaluate the influence of the variation of sintering temperature on microstructural characteristics and magnetic ferrite Ni_0,5Zn_0,5Fe₂O₄ sintered by microwave energy. The samples were sintered at 900, 1000, 1100 and 1200°C for exposure time of 10 minutes, with rate 50°C/minutes and characterized by density and porosity, X-ray diffraction, scanning electron microscopy and magnetic measurements. The results indicate that the values of density and apparent porosity were 4.2, 4.5, 4.4 and 4.5 g/cm³ and 3.4, 2.1, 2.2 and 2.4% for the sintering temperatures of 900, 1000, 1100 and 1200°C respectively. The formation of the ferrite phase Ni_0,5Zn_0,5Fe₂O₄ been identified for all conditions of sintering, with grain sizes of 52, 62, 71 and 58nm and saturation magnetization values of 63, 68, 69 and 27 emu/g to temperatures sintering 900, 1000, 1100 and 1200°C respectively.

Abstract: The influence of particle size of the load in the structure and morphology of the composite is an important factor in their final properties. This study will evaluate the behavior of the load of nickel ferrite calcined at different temperatures (700, 900 and 1200 ° C) with the polyamide matrix 6. In the preparation the polymer matrix was previously been dried in a vacuum oven at 80 ° C/48hs for eliminating humidity, and then the load was incorporated in the form of powders calcined at three temperatures in the mass concentration of 50%. Thereafter, the mixture was compressed to obtain composites, which were characterized by XRD and SEM. The results show XRD characteristic peaks of nickel ferrite and polyamide 6, showing that the calcination caused an increase in crystallinity of the load. SEM results show that the calcination caused an increase in the size of the agglomerates of the load, favoring significant changes in the morphology of the composite.

Abstract: This paper proposes to assess the efficiency of ZnAl₂O₄ obtained by combustion reaction on the process of esterification and transesterification of soybean oil to biodiesel production. In the synthesis it was used three heating conditions: spiral resistance, muffle furnace, and microwave oven. In order to investigate the influence of the heating source on the structure, morphology, and on the catalytic activity, the samples were characterized by XRD, FTIR, granulometric analysis, TGA, carbon content, TEM, and gas chromatography. The results showed that it was possible to obtain the ZnAl₂O₄ cubic phase with traces of ZnO. The ZnAl₂O₄ monophasic was just obtained by the synthesis carried out in the microwave oven and in the electrical resistance. All the samples showed a typical morphology of dense agglomerates and low carbon content. The samples also presented low catalytic activity in the esterification and transesterification process under the adopted conditions.

Abstract: Through different field of application and productive growth that membrane technology has been presented in the last years, the aim of this work is to prepare and characterize anisotropic porous ceramic membrane. The membrane were done with alumina, prepared by combustion reaction in microwave oven from urea as combustible and after deposited on support based on a commercial alumina. The results showed that it was obtained α-alumina as unique phase with average agglomerate size of 10µ and surface area of 33 m²/g. The alumina morphology was constituted by pre-sintering particles with hard agglomerates and/or aggregates. In relation to the membranes, it was observed a longitudinal section without cracks and uncovers support surface, also it can be observed grain formation well distributed and a layer of alumina with approximately 35.25µm. In relation to the permeate flux, the membrane presented initially values relatively high that is decrease with the permeation time, due to adsorption of water in the internal surface of the pores of the membrane, experiencing a decrease in size.

Abstract: This research was incorporated the hydroxyapatite in a mineral trioxide aggregate sealer, with the aim of studying this influence in the structure, morphology and radiopacity of the cement to obtain osteoconductive material. The samples were characterized by X ray diffraction (XRD), spectrometry fluorescence X ray (EDX), spectroscopy transform infrared Fourier (FTIR), scanning electron microscopy (SEM) and radiographic appearance. Through the results obtained by XRD for the new sealer observed the formation of phases HAp and MTA evidenced by the presence of phases: CaO, SiO₂ and Bi₂O verified also by EDX. Through FTIR was observed the presence of absorption bands related to links Ca-O, Si-O and Bi-O present in MTA and P-O present in HAp. The morphology visualized by SEM consists of irregular agglomerates with the formation of pre-sintered particles. The sample MTA/HAp3% presented radiopacity viable for their application as endodontic cement.

Abstract: The aim of this work is to evaluate the esterification and transesterification activity of ZnAl₂O₄ catalysts obtained by different ways of heating during the combustion synthesis using glycine as fuel. Samples were prepared according to the propellants and explosives theory using a vitreous silica crucible as container, and as heating source, plate, muffle furnace and microwave oven. After synthesis, the samples were structural and morphologically characterized by: XRD, nitrogen adsorption and carbon content analysis, and employed in the esterification and transesterification reactions, the percentage of biodiesel formed (FAME) was determined by gas chromatography. The samples obtained on the plate, muffle furnace and microwave showed that even using different heating ways, led to the formation of ZnAl₂O₄ as majority phase, with crystallite sizes of 11, 15 and 10 nm, respectively. The samples present values of surface area ranging from 16 to 77 m²/g, particle size from 17 to 81 nm, and carbon content lower than 11%. The forms used for heating influenced the esterification and transesterification reactions, showing that there was a gap in the production of biodiesel, which is a promising indication that this material has potential to be used as catalysts on the biodiesel production.

Abstract: This study aimed to assess the performance of the solid catalyst Ni_0.4Cu_0.1Zn_0.5Fe₂O₄, synthesized by combustion reaction, over the methyl esterification reaction of the fatty acids present in cottonseed oil. The catalyst was characterized by XRD, FTIR pyridine absorption, Raman spectroscopy, and SEM. The reactions were conducted at 140 and 180°C with molar ratios of 1:3, 1:6 and 1:9, with 2% of catalyst and reaction time of 2 h. The XRD results showed that the single phase ferrite was obtained with surface area of 87 m²/g and with mesoporous characteristic. It was observed from the FTIR pyridine absorption only the presence of Lewis acid sites. The Raman spectra confirm the presence of the inverse spinel phase. The results indicated that at 180°C and molar ratio of 1:9, the conversion of free fatty acids was about 87%.

Abstract: This paper aims to synthesize and characterize nanosized nickel and zinc ferrites (NiFe₂O₄ and ZnFe₂O₄) samples by a combustion reaction method, using glycine as fuel. The performance in HT-WGRS reaction the samples was investigated. The results showed that the combustion reaction was effective in the production of major phases of the spinel ferrite (crystallite sizes of 44 and 27 nm) and presence of the secondary phases, such as Ni and ZnO, with surface area 3 and 115 m²/g for NiFe₂O₄ and ZnFe₂O₄, respectively. HT-WGSR activity was achieved (80%) to NiFe₂O₄ ferrite in the temperature range of 300 - 500°C.