An investigation on unusual interface properties of unprecedented ternary composites, formed by the inclusion of assorted proportions of B2O3 into TiO2/SiO2 structure, is conducted herein. The influences of B2O3 content and calcination temperature were evaluated. The precursor TiO2/SiO2 material was synthesized via a simple sol-gel procedure that was followed by B2O3 inclusion via maceration and calcination. The materials were fully characterized and their photocatalytic performance to degrade the Indigo Carmine dye investigated. The material prepared with a B/Ti molar ratio of 1 and at calcination temperature of 350 °C (B1-350) showed the best performance, with a superior photocatalytic activity than that of commercial TiO2. The presence of B2O3-TiO2-SiO2 interfaces in the structure of such material was of critical importance in producing a material with these attractive features. Finally, high resolution mass spectrometry monitoring allowed for the characterization of the main degradation products formed under these conditions.

O uso de ardósia em construções tem frequentemente resultado na produção de uma grande quantidade de resíduos particulados que tem pequeno valor mercadológico e grande potencial de danificação do meio ambiente. Neste trabalho, partículas de ardósia foram testadas como agente de reforço em polipropileno. Polipropileno e partículas de ardósia foram misturados em um misturador em diferentes frações. Anidrido maleico foi também usado durante a mistura para induzir modificações no polipropileno que levassem a um aumento na interação entre os componentes. As amostras foram caracterizadas por espectroscopia no infravermelho (FTIR) e microscopia eletrônica de varredura. Materiais contendo 5 e 10% de ardósia produziram amostras com características ópticas semelhantes à rocha original. As análises por FTIR e microscopia eletrônica de varredura sugeriram que as modificações químicas no polipropileno levaram a uma melhoria parcial das interações interfaciais entre as partículas de ardósia e o polímero. Propriedades mecânicas, avaliadas por meio de ensaios de resistência à tração, mostraram que a adição das partículas de ardósia não alterou significativamente a resistência mecânica do polipropileno. Assim sendo, a incorporação de partículas de ardósia em polipropileno surge como uma tecnologia potencial para a produção de sistemas com algumas propriedades mecânicas comparáveis ao polipropileno puro, baixo custo, propriedades ópticas próximas às da ardósia e habilidade de minimizar problemas ambientais decorrentes da presença de resíduos derivados de atividades industriais.

The use of slate rock in constructions often results in the production of large amount of residual powder that has very low economical value and can also damage the environment. In this work, slate powder was tested as a reinforcing agent for polypropylene. Polypropylene and slate powder were mixed in different ratios in a mixer. Maleic anhydride was also used during the mixing to induce chemical modification of polypropylene in order to improve interactions between the polymer and the inorganic powder. Samples were characterized by infrared spectroscopy and scanning electron microscopy. Samples obtained by adding 5 and 10 wt. % of slate powder in polypropylene had optical properties close to those of commercial slate. FTIR and electron microscopy results suggested that chemical modification of polypropylene led to a partial improvement on the interfacial interactions between slate powder and the polymer. Mechanical properties evaluated by using tensile tests showed that the slate powder did not affect substantially the mechanical strength of polypropylene. Therefore, the incorporation of slate powder in polypropylene emerges as a potential technology for production of systems with some mechanical properties comparable to pure polypropylene, low cost, optical properties close to pure slate and ability to minimize environment problems caused by the presence of residual powder derived from industrial activities.

Nos últimos anos tem-se verificado uma acentuada desaceleração no desenvolvimento de novos homopolímeros, e nota-se um crescente interesse no estudo e desenvolvimento de processos que misturam os polímeros já existentes, dando origem às blendas poliméricas. Neste trabalho, blendas de poliestireno e policarbonato foram preparadas por extrusão em diferentes proporções. O processo de separação de fases foi estudado através da combinação de ferramentas analíticas como microscopias de infravermelho (micro-FTIR), óptica, eletrônica de varredura, e análise térmica. Resultados obtidos a partir das microscopias eletrônica e óptica permitiram definir as correlações entre morfologia e grau de estabilidade das fases do sistema. A composição e proporção relativas das fases das blendas foram determinadas usando microscopia de infravermelho. Tais resultados foram utilizados no cálculo do parâmetro de interação polímero-polímero de Flory-Huggins.

In the last decade, a progressive reduction on the development of new homopolymers could be observed, while processes, such as blending, that combine commercially available polymers were emphasized. In this work, polycarbonate-polystyrene blends were extruded in compositions from 0% to 100% of polycarbonate in weight. The phase separation process was studied by combining a series of analytical techniques such as scanning electron, optical and infrared microscopy (micro-FTIR). Electron and optical microscopy allowed the determination of a correlation between phase morphology and the degree of phase stability of the system. The composition of the phases and information on phase stability were determined by using micro-FTIR. The Flory-Huggins interaction parameter could also be calculated from the micro-FTIR data.

In this work TiO2-SiO2 glasses containing as much as 20 mol % of TiO2 were prepared via sol-gel process using titanium and silicon alkoxides, in the presence of chlorine, in the form of titanium tetrachloride or HCl. The gels were heat-treated until 800 °C. X-ray diffraction and Fourier transform infrared spectroscopy were used to understand the structural properties of TiO2-SiO2 oxides calcined at different temperatures and to evaluate the homogeneity of these materials. The degree of the compactness of the silica network is inferred from the frequency of the asymmetric stretching vibrations of Si-O-Si bonds. Formation of Si-O-Ti bridges, as monitored by the intensity of characteristic 945 cm-1 <FONT FACE=Symbol>¾</FONT> 960 cm-1 vibration, is particularly prominent if the method of basic two-step prehydrolysis of silicon alkoxide, addition of titanium alkoxide and completion of hydrolysis was used.

In this work we analyzed the "residual" performance of Portland cement concretes heat-treated at 600 °C after cooling down to room temperature. Concretes with characteristic compressive strength at 28 days of 45 MPa and of 60 MPa were studied. The heat-treatment was carried out without any imposed load. We measured the residual compressive strength and modulus of elasticity. The geometry of the structure was described by mercury intrusion porosimetry and nitrogen sorption tests. We observed a decrease of residual compressive strength and modulus of elasticity, with the raise of heat-treatment temperature, as a result of heat-induced material degradation. The results also indicated that the microstructural damage increased steadily with increasing temperature. Based on the results of this experimental work we concluded that residual mechanical properties of concrete are dependent of their original non heat-treated values.

We have developed a method to obtain polymer hybrids with control of inorganic content and molecular configuration. Hybrid poly(methyl methacrylate) (PMMA) was obtained via atom transfer radical polymerization (ATRP) initiated by octafunctional cubic silsesquioxanes using CuCl as catalyst. Two different ATRP initiators obtained by attaching specific chemical groups to the cubic silsesquioxane were employed to produce two types of hybrids with different architectures. While a-bromide ester groups generated a star-shaped polymer, the benzyl chloride groups produced longer and more linear polymeric chains containing the cubic silsesquioxane. These results were explained on the basis of the low initiation efficiency of benzyl chloride groups for PMMA, leading to polymers with molecular weights (Mn) and polydispersities (PDI) higher than the expected ones.

We evaluated the "residual" thermal conductivity of Portland cement concretes (with characteristic compressive strength at 28 days, f ck, of 20 MPa and 50 MPa) at room temperature after heat-treating at 180 °C, 300 °C and 600 °C. The description of the geometry of the structure was carried out using mercury intrusion porosimetry and nitrogen sorption. The results showed a decreasing tendency of residual thermal conductivity, which we attributed to heat-induced concrete degradation. Furthermore, the results from mercury intrusion porosimetry and nitrogen sorption tests showed that a coarser pore structure is produced with the raise of heat-treatment temperatures.

Materiais bioativos têm a capacidade de interagir com tecidos naturais, provocando reações que favoreçam o desenvolvimento de processos como: fixação de implantes, biocolonização, regeneração de tecidos anfitriões ou biodegradação do material. Grande parte dos materiais bioativos são cerâmicas. O objetivo deste trabalho envolve o desenvolvimento de novos biomateriais que apresentem níveis controláveis de reatividade a partir da combinação a nível nanométrico ou molecular de fases poliméricas e inorgânicas. Neste trabalho foram produzidos híbridos combinando álcool polivinílico (PVA) e tetraetil ortossilicato ou tetrametil ortossilicato dopados com sais de cálcio e alcóxido de fósforo. A caracterização do material produzido foi feita utilizando-se as seguintes técnicas: teste de inchamento por solvente, espectroscopia de infravermelho, microscopia eletrônica e análise térmica (DSC e TGA). O grau de reatividade foi determinado a partir da inserção das amostras em soluções aquosas por diferentes períodos de tempo. A partir do procedimento desenvolvido foram produzidos híbridos, na forma de filmes transparentes e flexíveis, de PVA-silicatos de cálcio e fósforo com composição variando de 25 a 100% em volume de PVA no híbrido e 40 a 80% molar de sílica na fase inorgânica. Os testes de imersão em solução aquosa demonstraram que os híbridos produzidos podem exibir reatividade controlável, variando de elevada degradabilidade até comportamento tipo gel, determinado através da avaliação da cinética de lixiviação e precipitação dos íons cálcio e fosfato. Os resultados mostraram ainda que o grau de reatividade dos materiais pode ser controlado através da manipulação de fatores estruturais como a densidade de ligações cruzadas, proporção das fases, densidade e composição da fase inorgânica, entre outros.

Bioactive materials have the capability of interacting with natural tissues by inducing interfacial reactions that can promote processes such as: attachment of implants, biocolonization, tissue regeneration or biodegradation of the material. Most of the bioactive materials are ceramics that usually are brittle, too stiff and difficult to process. The goal of this work is to develop novel biomaterials, obtained through the combination of nanometric polymer and inorganic phases, that can have tailored levels of bioactivity. In this work, inorganic-organic hybrids were produced by combining poly(vinyl alcohol) (PVA) with either tetraethoxy silane or tetramethoxy silane, doped with calcium salts and phosphorous alkoxide. The obtained materials were characterized by swelling experiments, infrared spectroscopy and microprobe analysis. The degree of bioactivity was determined by submitting the samples to water solutions for specific periods of time. The developed procedure proved to be able to yield flexible and transparent hybrid films with composition ranging from 25 to 100% volume fraction of polymer and also containing inorganic phases with compositions within 40 to 80% molar of silica. Results also showed that the obtained hybrids can exhibited degrees of bioactivity ranging from fast biodegradation to hydrogel behavior. It was also demonstrated that the degree of bioactivity can be controlled by manipulating structural factors of the hybrids such as the crosslink density, proportion of the phases and composition of the inorganic phase, among others.

The methodology of obtention of nanostructured glass, incorporated with lead compounds, obtained by sol-gel processing and the structural characterizations are presented. Specific surface area, porosity, pore morphology and pore size distributions of the gels were characterized with nitrogen sorption (BET) and mercury pycnometry. The pore size distributions of gels obtained using lead nitrate were more narrow than the ones observed for gels made with lead acetate. It was also observed the presence of a bimodal pore size distribution for gels produced using lead nitrate.

The oxide layer formed on the surface of a grain oriented silicon steel was characterized by SEM and EDS. 3% Si steel substrates were coated by two types of slurries: one formed by MgO and water and other formed by MgO, water and SrSO4. The ceramic films were evaluated by SEM, EDS and X-ray diffraction. Depth profiles of Fe, Si and Mg were obtained by GDS. The magnetic core losses (at 1.7 Tesla, 60 Hz) of the coated steel samples were evaluated as well. The use of MgO containing strontium reduced the volume fraction of forsterite particles beneath the outermost ceramic layer. It was observed a reduced magnetic core loss with the use of the slurry with MgO containing strontium.

A systematic methodology for microstructural description can help the task of obtaining the processing x microstructure x properties x performance relationships. There are, however, some difficulties in performing this task, which are related mainly to the following three factors: the complexity of the interactions between microstructural features; difficulties in evaluating geometric parameters of microstructural features; and difficulties in relating these geometric parameters to process variables. To solve some of these problems, it is proposed a methodology that embodies the following features: takes into account the different possible types of approaches for the microstructural description problem; includes concepts and tools of Total Quality Management; is supported on techniques of system analysis; and makes use of computer modeling and simulation and statistical design of experiments tools. The methodology was applied on evaluating some topological parameters during sintering process and its results were compared with available experimental data.

Received: August 15, 1998; Revised: March 30, 1999 In this work it was evaluated the influence of the type and concentration of the acid catalyst and the gelation temperature on the structure of pores of silica gels obtained with TEOS. The values of the major structural parameters related to the pores such as volume fraction of pore (VV), surface area per unit volume (SV), the average pore size (rP) and the connectivity of pores (GV), obtained in this work showed the possibility of tailoring the pore structure of silica gels by changing the processing variables. For the HF catalyzed gels the values of average pore radius varied from 6.8 nm to 21.6 nm, and the gelation time varied from 2 min to 140 min. For the gels obtained in this work the activation energy for gelation (E) was found to be 11.8 kcal/mole.

In this work it is carried out a review on structural parameters related to the evaluation of pore connectivity of nanostructures. The work describes parameters and methods of evaluation of geometric parameters. The concepts of connectivity are applied to silica gels and glasses obtained from sol-gel process. The study of pores connectivity was carried out using a combination of geometric modeling and experimental evaluation of specific surface area and pore volume. The permeability of the pore structure is evaluated and a permeability geometric factor, Pg, is proposed.

Fabrication of new optical devices based upon the incorporation of rare earth ions via sol-gel methods depends on elimination of dopant ion clusters and residual hydroxyl groups from the final material. The optical absorption and/or luminescence properties of luminescent rare earth ions are influenced by the local bonding environment and the distribution of the rare-earth dopants in the matrix. Typically, dopants are incorporated into gel via dissolution of soluble species into the initial precursor sol. In this work, Eu3+ is used as optical probe, to assess changes in the local environment. Results of emission, excitation, fluorescence line narrowing and lifetimes studies of Eu3+-doped gels derived from Si(OCH3)4 and fluorinated/chelate Eu3+ precursors are presented. The precursors used in the sol-gel synthesis were: tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Eu(III), Eu (III) trifluoromethanesulfonate, Eu(III) acetylacetonate hydrate, Eu (III) trifluoroacetate trihidrate, tris (2,2,6,6-tetramethyl-3,5- heptanedionate) Eu(III) and Eu(NO3)3.6H2O. The results were interpreted in terms of the evolution of the Eu3+ fluorescence in systems varying from solution to the gels densified to 800ºC. The lifetimes studies indicate that the fluorinated precursors are effective at reducing the water content in densified gels.