Vania Sousa - Academia.edu (original) (raw)

Papers by Vania Sousa

Sintering Techniques of Materials, 2015

Certain porous materials have special properties and functions that cannot normally be obtained b... more 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]. A growing number of applications that require advanced ceramics have appeared in recent decades, especially in environments where high temperatures, extended wear and corrosive environments are present. Such applications include the filtration of molten metals, high temperature insulation, support for catalytic reactions [3], filtration of particulates from exhaust gases of diesel engines and filtration of hot gases in various corrosive industrial processes, for example [4-6]. The advantages of using porous ceramic for these applications are generally a high melting point, suitable electronic properties, good corrosion resistance and wear resistance in combination with the characteristics acquired by the replacement of the solid material by voids in the component. Such characteristics include low thermal mass, low thermal conductivity, permeability control, high surface area, low density, high specific strength and a low dielectric constant [1,7]. These properties can be tailored for each specific application by controlling the composition and microstructure of the porous ceramic [8,9].

Materials Science Forum, 2010

The development of solid oxide fuel cell has shown that the thin film concept for the electrode s... more 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.

Materials Science Forum, 2012

Many studies have been reported in the literature related to YSZ films deposited on dense substra... more Many studies have been reported in the literature related to YSZ films deposited on dense substrate or applied directly on the SOFC anode. However, there are not a lot of studies about the YSZ deposition on the cathode. The present work aims to obtain yttria-stabilized zirconia (YSZ), using the spray pyrolysis technique, for their application as electrolyte in solid oxide fuel cells (SOFC). The films were obtained from a precursor solution containing zirconium and yttrium salts, dissolved in ethanol and propylene glycol (1:1), this solution was sprayed onto a heated LSM porous substrate. The substrate temperature was varied in order to obtain dense and homogeneous films. After deposition, the films were heat treated, aiming to crystallize and stabilize the zirconia cubic phase. The films were characterized by Scanning Electron Microscopy (SEM), thermal analysis, X-ray diffraction and Fourier transform Infrared Spectroscopy (FT-IR).

Key Engineering Materials, 2002

Key Engineering Materials, 2001

We present a novel approach to the multi-scale analysis of point-sampled manifolds of co-dimensio... more We present a novel approach to the multi-scale analysis of point-sampled manifolds of co-dimension 1. It is based on a variant of Moving Least Squares, whereby the evolution of a geometric descriptor at increasing scales is used to locate pertinent locations in scale-space, hence the name "Growing Least Squares". Compared to existing scale-space analysis methods, our approach is the first to provide a continuous solution in space and scale dimensions, without requiring any parametrization, connectivity or uniform sampling. An important implication is that we identify multiple pertinent scales for any point on a manifold, a property that had not yet been demonstrated in the literature. In practice, our approach exhibits an improved robustness to change of input, and is easily implemented in a parallel fashion on the GPU. We compare our method to state-of-the-art scale-space analysis techniques and illustrate its practical relevance in a few application scenarios.

Advanced Materials Research, 2014

The addition of different dopants affects the densification and electrical properties of TiO2 bas... more The addition of different dopants affects the densification and electrical properties of TiO2 based varistor ceramics. The nonlinear current (I) and voltage (V) characteristics of titanium dioxide are examined when doped with small quantities (0.5-2 at.%) of strontium oxide. This paper discusses the electrical properties of such an SrO doped TiO2 system, and demonstrates that some combinations produce electrical properties suitable for use as low voltage varistors. The high value of the nonlinear coefficient (α) (6.6), the breakdown field strength (Eb) (328 V/cm) and the leakage current (Ir) (0.22 mA/cm2) obtained in a system newly doped with SrO, are all adequate properties for application in low voltage varistors.

International Journal of Inorganic Materials, 1999

Halving the burden of malaria by 2015 and ensuring that 80% of people with malaria receive treatm... more Halving the burden of malaria by 2015 and ensuring that 80% of people with malaria receive treatment is among the health related targets of the Millennium Development Goals (MDGs). Despite political momentum toward achieving this target, progress is slow and many with malaria (particularly in poor and rural communities in Africa) are still without access to effective treatment. Finding ways to improve access to anti-malarial treatment in Africa is essential to achieve the malaria related and other MDG targets. During its work in Chad, Sierra Leone and Mali in the period 2004 to 2008, Médecins Sans Frontières showed that it was possible to significantly improve access to effective malaria treatment through: i) the removal of health centre level user fees for essential healthcare for vulnerable population groups, ii) the introduction of free community based treatment for children using malaria village workers to diagnose and treat simple malaria in communities where geographical and financial barriers limited access to effective malaria care, iii) the improved diagnosis and treatment of malaria using rapid diagnosis tests and artemisinin based combination therapy, at both health facilities and in the community. This paper describes and discusses these strategies and their related impact.

Journal of Materials Science: Materials in Electronics, 2004

This work illustrates the advancement of research on TiO 2-based electroceramics. In this work wi... more This work illustrates the advancement of research on TiO 2-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, in¯uences of the densi®cation, the mean grain size and the electrical properties of the TiO 2-based varistor ceramics. Dopants like Ta 2 O 5 , Nb 2 O 5 , and Cr 2 O 3 have an especial role in the barrier formation at the grain boundary in the TiO 2 varistors, increasing the nonlinear coef®cient and decreasing the breakdown electric ®eld. The in¯uence of Cr H Ti is to increase the O H and O H 2 adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O 2 adsorbed at the grain boundary. In this paper, TiO 2 and (Sn,Ti)O 2-based studies of polycrystalline ceramics, which show a non-linear I ±V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.

Environmental Progress & Sustainable Energy

Histology and Histopathology, 2011

J Mater Sci Mater Electron, 2010

J Mater Sci Mater Electron, 2006

A study was made to identify how the addition of Ta and Cr oxides influences the electronic prope... more A study was made to identify how the addition of Ta and Cr oxides influences the electronic properties of the TiO 2 varistor, aiming to obtain low voltage varistors. The results of an electric characterization, allied with a microstructural analysis, clarify and confirm the influence of these dopants on the varistors properties of these systems. This study, in which Cr 2 O 3 is used as dopant, clearly shows that the action of these dopants in the creation of electronic barriers is more efficient when these oxides are associated with Ta 2 O 5 , and that an breakdown electric field of 40 V/cm and a nonlinear coefficient of 12 can be obtained after heat treatment in an oxygen-rich atmosphere.

Materials Science Forum, 2015

The synthesis of ceramic materials from polymeric precursors has been the subject of numerous stu... more 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.

Materials Science Forum, 2006

Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO... more Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO2 varistors, increasing their nonlinear coefficient and decreasing their breakdown electric field. This paper discusses the microstructural and physical properties of Ta- and Cr-doped TiO2 systems in which imported tantalum oxide was replaced with an equivalent Brazilian raw material. Preliminary results confirm that this national oxide can be utilized to obtain electroceramics such as varistors.

Materials Science Forum, 2006

Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO... more Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO2 varistors, increasing their nonlinear coefficient and decreasing their breakdown electric field. This paper discusses the microstructural and physical properties of Ta- and Cr-doped TiO2 systems in which imported tantalum oxide was replaced with an equivalent Brazilian raw material. Preliminary results confirm that this national oxide can be utilized to obtain electroceramics such as varistors.

Journal of Materials Science-Materials in Electronics, 2002

Ceramic varistors are generally produced by the oxide mixing method or by chemical methods, such ... more Ceramic varistors are generally produced by the oxide mixing method or by chemical methods, such as sol–gel, precipitation and others. Chemical methods produce powders that are highly reactive, allowing for increased microstructural homogeneity and control of grain growth during sintering, which is essential for good varistor performance. The purpose of this work was to study the electrical characteristics of ZnO

Sintering Techniques of Materials, 2015

Certain porous materials have special properties and functions that cannot normally be obtained b... more 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]. A growing number of applications that require advanced ceramics have appeared in recent decades, especially in environments where high temperatures, extended wear and corrosive environments are present. Such applications include the filtration of molten metals, high temperature insulation, support for catalytic reactions [3], filtration of particulates from exhaust gases of diesel engines and filtration of hot gases in various corrosive industrial processes, for example [4-6]. The advantages of using porous ceramic for these applications are generally a high melting point, suitable electronic properties, good corrosion resistance and wear resistance in combination with the characteristics acquired by the replacement of the solid material by voids in the component. Such characteristics include low thermal mass, low thermal conductivity, permeability control, high surface area, low density, high specific strength and a low dielectric constant [1,7]. These properties can be tailored for each specific application by controlling the composition and microstructure of the porous ceramic [8,9].

Materials Science Forum, 2010

The development of solid oxide fuel cell has shown that the thin film concept for the electrode s... more 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.

Materials Science Forum, 2012

Many studies have been reported in the literature related to YSZ films deposited on dense substra... more Many studies have been reported in the literature related to YSZ films deposited on dense substrate or applied directly on the SOFC anode. However, there are not a lot of studies about the YSZ deposition on the cathode. The present work aims to obtain yttria-stabilized zirconia (YSZ), using the spray pyrolysis technique, for their application as electrolyte in solid oxide fuel cells (SOFC). The films were obtained from a precursor solution containing zirconium and yttrium salts, dissolved in ethanol and propylene glycol (1:1), this solution was sprayed onto a heated LSM porous substrate. The substrate temperature was varied in order to obtain dense and homogeneous films. After deposition, the films were heat treated, aiming to crystallize and stabilize the zirconia cubic phase. The films were characterized by Scanning Electron Microscopy (SEM), thermal analysis, X-ray diffraction and Fourier transform Infrared Spectroscopy (FT-IR).

Key Engineering Materials, 2002

Key Engineering Materials, 2001

We present a novel approach to the multi-scale analysis of point-sampled manifolds of co-dimensio... more We present a novel approach to the multi-scale analysis of point-sampled manifolds of co-dimension 1. It is based on a variant of Moving Least Squares, whereby the evolution of a geometric descriptor at increasing scales is used to locate pertinent locations in scale-space, hence the name "Growing Least Squares". Compared to existing scale-space analysis methods, our approach is the first to provide a continuous solution in space and scale dimensions, without requiring any parametrization, connectivity or uniform sampling. An important implication is that we identify multiple pertinent scales for any point on a manifold, a property that had not yet been demonstrated in the literature. In practice, our approach exhibits an improved robustness to change of input, and is easily implemented in a parallel fashion on the GPU. We compare our method to state-of-the-art scale-space analysis techniques and illustrate its practical relevance in a few application scenarios.

Advanced Materials Research, 2014

The addition of different dopants affects the densification and electrical properties of TiO2 bas... more The addition of different dopants affects the densification and electrical properties of TiO2 based varistor ceramics. The nonlinear current (I) and voltage (V) characteristics of titanium dioxide are examined when doped with small quantities (0.5-2 at.%) of strontium oxide. This paper discusses the electrical properties of such an SrO doped TiO2 system, and demonstrates that some combinations produce electrical properties suitable for use as low voltage varistors. The high value of the nonlinear coefficient (α) (6.6), the breakdown field strength (Eb) (328 V/cm) and the leakage current (Ir) (0.22 mA/cm2) obtained in a system newly doped with SrO, are all adequate properties for application in low voltage varistors.

International Journal of Inorganic Materials, 1999

Halving the burden of malaria by 2015 and ensuring that 80% of people with malaria receive treatm... more Halving the burden of malaria by 2015 and ensuring that 80% of people with malaria receive treatment is among the health related targets of the Millennium Development Goals (MDGs). Despite political momentum toward achieving this target, progress is slow and many with malaria (particularly in poor and rural communities in Africa) are still without access to effective treatment. Finding ways to improve access to anti-malarial treatment in Africa is essential to achieve the malaria related and other MDG targets. During its work in Chad, Sierra Leone and Mali in the period 2004 to 2008, Médecins Sans Frontières showed that it was possible to significantly improve access to effective malaria treatment through: i) the removal of health centre level user fees for essential healthcare for vulnerable population groups, ii) the introduction of free community based treatment for children using malaria village workers to diagnose and treat simple malaria in communities where geographical and financial barriers limited access to effective malaria care, iii) the improved diagnosis and treatment of malaria using rapid diagnosis tests and artemisinin based combination therapy, at both health facilities and in the community. This paper describes and discusses these strategies and their related impact.

Journal of Materials Science: Materials in Electronics, 2004

This work illustrates the advancement of research on TiO 2-based electroceramics. In this work wi... more This work illustrates the advancement of research on TiO 2-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, in¯uences of the densi®cation, the mean grain size and the electrical properties of the TiO 2-based varistor ceramics. Dopants like Ta 2 O 5 , Nb 2 O 5 , and Cr 2 O 3 have an especial role in the barrier formation at the grain boundary in the TiO 2 varistors, increasing the nonlinear coef®cient and decreasing the breakdown electric ®eld. The in¯uence of Cr H Ti is to increase the O H and O H 2 adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O 2 adsorbed at the grain boundary. In this paper, TiO 2 and (Sn,Ti)O 2-based studies of polycrystalline ceramics, which show a non-linear I ±V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.

Environmental Progress & Sustainable Energy

Histology and Histopathology, 2011

J Mater Sci Mater Electron, 2010

J Mater Sci Mater Electron, 2006

A study was made to identify how the addition of Ta and Cr oxides influences the electronic prope... more A study was made to identify how the addition of Ta and Cr oxides influences the electronic properties of the TiO 2 varistor, aiming to obtain low voltage varistors. The results of an electric characterization, allied with a microstructural analysis, clarify and confirm the influence of these dopants on the varistors properties of these systems. This study, in which Cr 2 O 3 is used as dopant, clearly shows that the action of these dopants in the creation of electronic barriers is more efficient when these oxides are associated with Ta 2 O 5 , and that an breakdown electric field of 40 V/cm and a nonlinear coefficient of 12 can be obtained after heat treatment in an oxygen-rich atmosphere.

Materials Science Forum, 2015

The synthesis of ceramic materials from polymeric precursors has been the subject of numerous stu... more 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.

Materials Science Forum, 2006

Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO... more Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO2 varistors, increasing their nonlinear coefficient and decreasing their breakdown electric field. This paper discusses the microstructural and physical properties of Ta- and Cr-doped TiO2 systems in which imported tantalum oxide was replaced with an equivalent Brazilian raw material. Preliminary results confirm that this national oxide can be utilized to obtain electroceramics such as varistors.

Materials Science Forum, 2006

Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO... more Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO2 varistors, increasing their nonlinear coefficient and decreasing their breakdown electric field. This paper discusses the microstructural and physical properties of Ta- and Cr-doped TiO2 systems in which imported tantalum oxide was replaced with an equivalent Brazilian raw material. Preliminary results confirm that this national oxide can be utilized to obtain electroceramics such as varistors.

Journal of Materials Science-Materials in Electronics, 2002

Ceramic varistors are generally produced by the oxide mixing method or by chemical methods, such ... more Ceramic varistors are generally produced by the oxide mixing method or by chemical methods, such as sol–gel, precipitation and others. Chemical methods produce powders that are highly reactive, allowing for increased microstructural homogeneity and control of grain growth during sintering, which is essential for good varistor performance. The purpose of this work was to study the electrical characteristics of ZnO