Vânia Caldas de Sousa

Combustion process in the synthesis of ZnO–Bi2O3

Abstract Combustion synthesis of homogeneous ZnO–Bi2O3 powder mixtures has been investigated, with emphasis on the reaction mechanism. The reaction uses salts containing the zinc and bismuth ion (oxidizer) and a fuel. The self-sustaining reaction leads to high temperatures that promote oxide formation and crystallization in a short period of time. The resulting ZnO–Bi2O3 powders show characteristics that favor applications in the field of electronic ceramics, such as varistors. Such characteristics, namely particle morphology and crystallinity degree, were accessed by X-ray diffraction and scanning electron microscopy, showing that combustion synthesis is a promising alternative method to produce adequate powders for the manufacture of varistors.

Obtainment of α-Tricalcium Phosphate by Solution Combustion Synthesis Method Using Urea as Combustible

The aim of this work is the synthesis of α-tricalcium phosphate by solution combustion synthesis using urea as combustible in the stoichiometric ratio and with excess of combustible. The salts Ca(O3)2.4H2O and (H4)2HPO4 were used as reaction precursors with Ca/P ratio of 1.5. The pH adjustment was made adding nitric acid. A porous foam composed by β-tricalcium phosphate, hydroxyapatite and α or β-dicalcium pyrophosphate were obtained as reaction product. X-ray diffraction was used to identify the phases. The obtainment of α-TCP was possible after a heat treatment where the material was held at 1250°C for 15 hours followed by quenching. Smaller particle size was obtained when four times the stoichiometric ratio of combustible was used in the reaction. α-TCP samples were immersed in SBF in order to verify the biocompatibility.

Combustion Synthesis of LSM Powders from a Precursor Solution with Mixed Fuels

For the combustion synthesis of strontium doped lanthanum manganite (LSM), different fuels can be used influencing the phase formation and also the powder morphology. Both are important features that can improve the material performance when used in a solid oxide fuel cell cathode. Urea and sucrose are fuels used to synthesize distinct LSM powders, thus the purpose of this work was to mix these fuels in order to obtain nanocrystalline LSM powders with a differentiated morphology, more convenient for the desired application. After calcination at 750°C for 3 hours the powder generated a pure phase LSM X-ray diffraction pattern and the micrographs taken in the transmission and scanning electron microscopes revealed a very peculiar morphology with specific surface area (BET) of 13 m²/g. Calcination led to a single phase and more crystalline material but showed no influence in the powder morphology.

Elaboration of Yttria-Stabilized Zirconia Films on Porous Substrates

The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.

Chemical Synthesis and Sintering Behaviour of Ca3Al206 Obtained by Polymeric Precursor Method

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.

Perovskites Used in Fuel Cells

Fuel cells are devices for energy generation with very high theoretical efficiency. Many researches were been carried out in the last few decades in order to develop reliable fuel cells. Solid oxide fuel cells (SOFC) and polymeric exchange membrane fuel cells (PEMFC) are those with more potential for commercial use. Specially for SOFC cathodes, many perovskites have been proposed as potential materials for this application. Nevertheless, other components of SOFC, such as the electrolytes, anodes and interconnects, have also been targeted with potential perovskites. More recently, the use of perovskites in PEMFC has also been proposed and studied. As many perovskite compositions can be used in SOFC components, some of the most important are discussed in this chapter and some recent works in perovskites for PEMFC are also referred. As a whole, in this chapter, the reader will find the relationship between the properties of perovskites with their compo‐ sitions and the main effects of dopant agents regarding the utilization of these materials in different components of SOFC and in electrodes of PEMFC.

Al2O3 and Al2O3-ZrO2 Fibers Obtained by Biotemplete with Low Thermal Conductivity

Certain porous materials have special properties and functions that cannot normally be obtained by conventional dense counterparts. Therefore, porous materials are now used in many applications such as final products and in various technological processes. Macroporous materials are used in various forms and compositions in everyday life; e.g. polymeric foams, packaging, lightweight aluminum structures in buildings, aircraft, and as a porous ceramic for water [1,2].

Electrochemical Impedance Spectroscopy: Evaluation of Drug Delivery System of Alpha-Tricalcium Phosphate Cement

Tricalcium phosphate cement (α-TCP) can be used in various fields of health, including as drug delivery systems. The application of a biomaterial based on α-TCP could enable both the constant drug delivery as support and shape damaged muscleskeletics tissues until which can be regenerated by the organism itself, replacing the biomaterial, while maintaining stable levels of the drug in the organism. The aim of this study was to evaluate the release of gentamicin sulfate using the technique of electrochemical impedance spectroscopy in drug delivery systems of α-TCP. The results obtained in vitro study validated the proposed methodology for assessment of controlled drug delivery systems on the basis of α-TCP.

Study of the Evolution of Phase Calcium Aluminate through the Method for Polymeric Precursors C12A7

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.

Microstructure and Thermal Conductivity of Porous Al2O3-ZrO2 Ceramics

The improvement on the development of porous ceramic materials has leaded to new technologies in thermal insulation, for example, composite materials for better performance of pressure vessels in rocket engines. Within this context, the present work aims to evaluate the ability of a refractory ceramic base alumina/zirconia through the processes of co-precipitation and replica method in an organic fiber template. The green body was burnt-out and sintered at 1200-1600°C to obtain the continuous porous ceramic fibers. In the FEG-SEM analysis, an interconnected porous structure with small grains was observed. The crystalline phases were determined by X-ray diffraction and compared to micro-Raman results regarding the crystalline structure confirms that there present in the material zirconia is composed of more than one phase. Porosity was calculated through a mercury porosimeter as 77.9%, and the Laser Flash method gave a thermal conductivity value of 1.61 K W.m−1.K−1 for the Al2O3-ZrO2 fibers.