Sergio Cava

Interfacial photoluminescence emission properties of core/shell Al2O3/ZrO2

This research investigated the synthesis of the Al2O3/ZrO2 core-shell system using a polymeric precursor method. The interfacial features emission show the possibility for control of the luminescence behaviour. X-ray diffraction (XRD) patterns are well defined for α-Al2O3 and for γ-Al2O3, core structures and a zirconia shell phase for high concentrations. Photoluminescence (PL) spectra (λexc = 350.7 nm) reveal that the effect of the zirconia coating on the alumina was more effective for α-Al2O3 than for γ-Al2O3 which may be related to the zirconia coating process on alumina. The image transmission electron microscopy (TEM) shows an amorphous region of 10 nm which is attributed to a ZrO2 shell layer.

Fingerprints of short-range and long-range structure in BaZr1−xHfxO3 solid solutions: an experimental and theoretical study

A microwave-assisted hydrothermal method was applied to synthesize BaZr1-xHfxO3, (BZHO) solid solutions at a low temperature, 140 °C, and relatively short times, 160 min. The detailed features of the crystal structure, at both short and long ranges, as well as the crystal chemistry doping process, are extensively analysed. X-ray diffraction measurements and Raman spectroscopy have been used to confirm that pure and Hf-doped BZO materials present a cubic structure. Extended X-ray absorption fine structure (EXAFS) spectra indicate that Hf(4+) ions have replaced the Zr(4+) ions on the 6-fold coordination and a subsequent change on the Ba(2+) 12-fold coordination can be sensed. X-ray absorption near-edge structure (XANES) spectroscopy measurements reveal a local symmetry breaking process, associated to overlap of the 4d-2p and 5d-2p orbitals of Zr-O and Hf-O bonds, respectively. Field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM) show the mesocrystalline nature of self-assembled BZHO nanoparticles under a dodecahedron shape. In addition first principle calculations were performed to complement the experimental data. The analysis of the band structures and density of states of the undoped BZO and doped BZHO host lattice allow deep insight into the main electronic features. The theoretical results help us to find a correlation between simulated and experimental Raman modes and allow a more substantial interpretation of crystal structure.

THE EFFECT OF TITANIUM DIOXIDE NANOPARTICLES OBTAINED BY MICROWAVE-ASSISTED HYDROTHERMAL METHOD ON THE COLOR AND DECAY RESISTANCE OF PINEWOOD

This study aimed to synthesize titanium dioxide nanoparticles by microwave-assisted hydrothermal method to incorporate them to the structure of Pinus elliottii wood. The color changes and the decay resistance of impregnated wood was investigated. The titanium dioxide nanoparticles were impregnatedinto Pinus elliottii wood by vacuum-pressure and simple immersion methods. Furthermore, Pinus elliottii wood was treated with chromated copper borate solution tocompare their effectiveness to the titanium dioxide treated wood. The titanium dioxide nanoparticles impregnated by vacuum-pressurewere presented especially on the wood surface, forming a homogeneous coating. The titanium dioxide nanoparticles did not change the natural color of wood and, at the same time, decreased the degree of the white rot fungus (Ganoderma applanatum) colonization in the wood structure and the wood decay,compared to the untreated one. The titanium dioxide treated wood samples provided similar protection against decay in comparison to wood treated with chromated copper borate. The impegnation with titanium dioxide nanoparticles can be a good alternative to decrease/avoid the fungi proliferation,providing to Pinus elliottii wood a self-cleaning mechanism.

Functionalized pink Al2O3:Mn pigments applied in prosthetic dentistry

Statement of problem The color of dental poly(methyl methacrylate) (PMMA) is conventionally rendered by organic and inorganic pigments, which are usually not bonded to the polymer network. Functionalized ceramic pigments can be used to color PMMA, allowing improved chemical interaction with the resin matrix. Purpose The purpose of this in vitro study was to synthesize, functionalize, and characterize pink manganese‐doped alumina ceramic pigments. The hypothesis tested was that functionalized ceramic pigments would render pink coloration to a translucent PMMA without jeopardizing its mechanical properties. Material and methods Pink alumina powders doped with 1 or 2 mol% of manganese (Al2O3:Mn) were prepared by means of a polymeric precursor method. Pigment (Pig.) particles were functionalized with a silica coating method followed by silanation before preparation of PMMA‐based composite resins (5 wt% pigment). The color of composite resins (Pig.1% and Pig.2%) and PMMA controls (Pink and translucent [Trans]) was evaluated (CIELab color coordinates), and their mechanical properties were tested (3‐point bending). Results The microstructure of the pigment particles showed approximately 55‐nm nanocrystals of manganese‐doped &agr;‐alumina clustered into irregular porous particles up to 60 &mgr;m. The composite resins and pink PMMA showed similar color parameters (CIE a* pink=20.1, Pig.1%=14.6, Pig.2%=16.0, Trans=0.19, P<.001; CIE b* Pink=17.0, Pig.1%=18.6, Pig.2%=19.0, Trans=2.52, P<.001). No statistical differences were observed in mechanical properties among groups (&sgr;f pink=98.4, Pig.1%=98.1, Pig.2%=98.8, trans=89.1, P=.136). Conclusions The addition of the functionalized pink ceramic pigments to a translucent PMMA yielded similar coloration to that of the regular pink PMMA used in dentistry and did not jeopardize its mechanical properties.

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.

Síntese e caracterização do sistema ZrO2-SiO2 com adição de cobalto para uso como pigmentos cerâmicos

Co-doped ZrSiO4 powders were synthesized by the polymeric precursor method to obtain ceramic pigments. The effect of different Co2+ contents on the t-ZrO2 to ZrSiO4 phase transition was studied by X-ray diffraction and differential thermal analysis. UV-Vis spectroscopy of the samples allowed comparing the band shift with the phase transition. Moreover, a study of the thermal stability and intensity of the blue to red color change of the synthesized powders with the presence of cobalt in relation to the calcination temperature was accomplished and compared to the phase transition. The results allowed to identify the t-ZrO2 to ZrSiO4 phase transition.

Physico-chemical description of titanium dioxide–cellulose nanocomposite formation by microwave radiation with high thermal stability

Titanium dioxide–cellulose nanocomposites were nucleated and grown by decomposition of titanium isopropoxide in ethanol media together with wood cellulose fibers into the microwave-assisted solvothermal (MAS) system; the low temperature and fast formation time of the nanocomposites stand out in this methodology. The MAS method was successfully applied in the synthesis of TiO2 with anatase structure in wood cellulose fibers to produce TiO2–cellulose nanocomposites based on hydrolysis, condensation and subsequent polymerization of titanium nanoparticles on cellulose fibers. Through scanning electron microscope it was possible to confirm nanocomposite formation by impregnation/nucleation/growth of titanium dioxide (TiO2) nanoparticles on the fiber walls. The nanocomposites X-ray powder diffraction showed peaks of crystalline titanium dioxide anatase phase associated to additional cellulose diffraction remarks, as well as the absence of the CaCO3 phase, proving the nanocomposite design concept. This means that the inclusion of TiO2 nanoparticles on fibers does not alter the crystalline structure of cellulose, also confirmed by Fourier-transform mid-infrared spectroscopy. Based on the thermogravimetric analysis, nanocomposites are thermally more stable than pure cellulose, reaching a 19% difference of mass loss reduction.

Resistência biológica e colorimetria da madeira termorretificada de duas espécies de eucalípto

Os objetivos deste estudo foram os seguintes: a) observar o efeito de termorretificacao sobre a durabilidade natural da madeira de Eucalyptus tereticornis e Corymbia citriodora apos ataque de fungos causadores de podridao-branca (Trametes versicolor eGanoderma applanatum); b) avaliar parâmetros colorimetricos apos a submissao das madeiras a tratamentos termicos e aos fungos T. versicolor e G. applanatum. Para realizacao do estudo, corpos de prova de ambas as especies foram submetidos aos tratamentos: T1 - testemunha; T2 - autoclave (120 °C) a 1,5 kgf/cm2 durante 1 h; T3 - estufa laboratorial (180 °C) por 4 h; e T4 - termico combinado [120 °C (1 h) + 180 °C (4 h)]. Posteriormente, os corpos de prova foram submetidos ao apodrecimento acelerado, sendo expostos as duas especies de fungos por 16 semanas. Apos esse periodo, foram avaliadas a perda de massa e as variaveis colorimetricas, atraves dos parâmetros L*, a*, b*, C* e ho antes e depois do ataque pelos fungos. De acordo com os resultados, E. tereticornis e C. citriodora foram classificados como altamente resistentes a fungos apodrecedores, exceto no tratamento testemunha de C. citriodora submetido ao ataque de G. applanatum, o qual foi classificado como resistente. Com os tratamentos T3 e T4, a perda de massa foi reduzida em ambas as especies de madeira. As maiores mudancas nos parâmetros colorimetricos ocorreram devido ao tratamento termico e a pouca variacao observada com o ataque dos fungos apodrecedores. Houve reducao da variavel claridade (L*) e queda das matrizes vermelho (a*) e amarelo (b*), razao por que o tratamento termico mostrou-se como alternativa para protecao e escurecimento da madeira de eucalipto, tornando-a mais proxima de padroes de coloracao de madeiras nobres.

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].

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.