M. de Souza

Rice Hull-Derived Silica: Applications in Portland Cement and Mullite Whiskers

Silica was extracted from rice hulls by three processing routes, starting with acid treatment followed by burning and milling. The amorphous white silica powder showed a surface area of 260 to 480 m2/g, purity above 99% and average particle size of 2.0 to 0.6 mm. This silica is suitable for the preparation of mullite whiskers employing the rare earth aluminosilicate glass technique. Due to its highly pozzolanic reaction, this prepared silica is used as an additive in high performance concrete.

Silica Derived from Burned Rice Hulls

Three new processes to obtain silica having high specific surface area from burned pre-treated rice hulls are presented and discussed. These procedures allow for the simultaneous recovery of biomass energy and the production of high quality silica at thermoelectric plants, without the risk of using corrosive substances in the burning process. The first method involves treatment of the hull with hot organic acid solutions before burning, the second with boiling water, both using an autoclave at temperatures close to150 °C, while the third method renders the hull fragile by treating it at 250 °C and reducing it to a fine powder before burning. The first two methods result in white amorphous silica that can show 500 m2/g of specific surface area. The third method, which does not remove the alkaline elements from the hull, produces an amorphous gray carbon-free powder whose specific surface area can be as high as 250 m2/g. An investigation of the specific surface area of the prepared silica indicates the alkaline elements are not mixed with silica in the hulls or combined as insoluble compounds. A comparison is made of these processes and the dissolution of silica by sodium hydroxide solutions is discussed.

Impure zirconia electrical conductivity enhancement by rare-earth minority ions in the Y2O3 RE2O3 ZrO2 system

Impure zirconia stabilized by 12 wt% yttria concentrate (85 wt% Y2O3 + 15 wt% rare-earth (RE)) was found to have high grain and grain-boundary electrical conductivities. The influence of the RE on the segregation of impurities was studied for four different compositions. Microstructure features are evidence for the enhanced segregation of impurities due to RE ions. The increased grain and grain-boundary conductivities are a consequence of the segregation of impurities.

Liquid phase sintering of RE2O3: YSZ ceramics Part I Grain growth and expelling of the grain boundary glass phase

Experiments on silicate liquid phase sintering of YSZ ceramics with addition of 0.5 mol % of rare earth ions have been done in order to study the effect of these ions on the kinetics of grain growth and the expulsion of glass through the grain boundaries. Kinetics follow a third power law in the following order YPr > YPrEr > YY > YEr. The expelled glass does not spread over the ceramic grains and its mass is inversely related to grain size. Glass phase separation inside the grain boundaries is found to be a necessary condition for glass expulsion.Experiments on silicate liquid phase sintering of YSZ ceramics with addition of 0.5 mol % of rare earth ions have been done in order to study the effect of these ions on the kinetics of grain growth and the expulsion of glass through the grain boundaries. Kinetics follow a third power law in the following order YPr > YPrEr > YY > YEr. The expelled glass does not spread over the ceramic grains and its mass is inversely related to grain size. Glass phase separation inside the grain boundaries is found to be a necessary condition for glass expulsion.

Designing reusable rule-based architectures with design patterns

Abstract Rule-based systems or production systems still have great importance in the construction of knowledge systems. In these systems, the domain expertise to solve a problem is encoded in the form of ‘if–then’ rules, enabling a modular description of the knowledge, thus facilitating its maintenance and updating. Although they have been extensively described in the Artificial Intelligence literature, their design process is at times repeated because of the lack of common software architecture and the restrictions offered by some off-the-shelf libraries and systems. This paper proposes a reusable architecture for rule-based systems described through design patterns. The aim of these patterns is to constitute a design catalog that can be used by designers to understand and create new rule-based systems, thus promoting reuse in these systems. Additionally, the use of the described patterns in the design of an intelligent tutoring system architecture is exemplified.

The ordering of aqueous suspensions of polystyrene spheres

Abstract We have measured the lattice parameter of policrystalline aqueous suspensions using the Debye-Scherrer method as a function of the concentration of spheres. Sistematic deviation in the lattice parameter higher than 12% as compared with the value of ( 2 N 0 ) 1 3 was found. A model for the equilibrium between crystallites is proposed.

Chemical dynamics and reverse saturable absorption in di-furfuryl ether solutions

We report on the chemical dynamics and nonlinear optical absorption of di-furfuryl ether (DFE) solutions. DFE molecules were derivatized from the room temperature furfuryl alcohol self-reaction, whose reaction kinetics was investigated with the Z-scan technique and laser-induced fluorescence. These molecules are shown to exhibit a pronounced reverse saturable absorption process. The magnitude of the excited-state absorption cross-sections and the intersystem crossing lifetime have been evaluated with 8 ns pulses at 532 nm.

Liquid phase sintering of Re2O3 YSZ ceramics: Part II Grain boundary electrical properties

Grain boundary electrical properties of Y2O3 stabilised zirconia with small additions of Er2O3 and Pr2O3 sintered via silicate liquid phase were studied by the impedance spectroscopy technique. Grain boundary specific conductivity of the praseodymium doped samples was found to be independent of sintering time, while the erbium doped sample showed high anomalous conductivity for the 1.0 h sintered samples. The electrical behaviour is explained considering the grain boundary to be a series association of the glass film and the space charge region. Specific conductivity and Debye length of the space charge region of erbium doped samples were found to be 6.7 × 10−8 S/cm and 0.25 nm, respectively.Grain boundary electrical properties of Y2O3 stabilised zirconia with small additions of Er2O3 and Pr2O3 sintered via silicate liquid phase were studied by the impedance spectroscopy technique. Grain boundary specific conductivity of the praseodymium doped samples was found to be independent of sintering time, while the erbium doped sample showed high anomalous conductivity for the 1.0 h sintered samples. The electrical behaviour is explained considering the grain boundary to be a series association of the glass film and the space charge region. Specific conductivity and Debye length of the space charge region of erbium doped samples were found to be 6.7 × 10−8 S/cm and 0.25 nm, respectively.

Photoluminescence spectrum of rare earth doped zirconia fibre and power excitation dependence

Abstract Recent studies in stabilished ZrO2 single crystals reveal that oxygen vacancies and/or their complexes are involved in the luminescent process [1]. Samples of rare earth doped zirconia fibres were pulled by the laser-heated pedestal growth (LHPG) method and their photo-luminescence was observed. We report the systematic study of the photoluminescence measured in several samples: ZrO2: Er3+, ZrO2: Er3+: Pr3+: Y3+, and ZrO2: Pr3+: Y3+. The experiments were carried out by pumping the samples with single and multiple UV lines of a Kr+ ion laser (337.5–356.4 nm). Emission spectrum broadening of Er3+ and Pr3+ has been observed and a reproducible strong changes in the luminescence behaviour occurs when the excitation power surpasses a certain value.

Mulita a partir de hidróxido de alumínio e de sílica da casca de arroz

Mullite was synthesised from aluminium hydroxide, Al (OH)3, previously purified from industrial rejects, and silica from acid-treated rice hulls burned at 500 oC. Although mullite synthesis started at 1300 oC, the reported experiments were performed at 1600 oC with 8.0 hours of soaking time. The apparent densities of the pure and yttria doped mullite were, respectively, 2.70 g/cm3 and 2.84 g/cm3, Yttria doped mullite microstructure shows few needle like grains as large as 30 m m. EDS analysis shows that yttria was incorporated in the mullite grains.