Effects of Al2O3 on phase equilibria in the olivine primary phase field of the MgO-"FeO"-SiO2-Al2O3 system in equilibrium with metallic iron

Liquidus temperatures and phase equilibria have been determined in the olivine primary phase field of the MgO-FeO-SiO2-Al2O3 system. Liquidus isotherms have been determined in the temperature range from 1748 to 1873K. The results are presented in the form of pseudo-ternary sections of the MgO-FeO-SiO2 with 2 and 3wt% Al2O3 in the liquid. The study enables the liquidus to be described for a range of SiO2/MgO ratios. It was found that liquidus temperatures in the olivine primary phase field decrease with the addition of Al2O3.

Effect of Al2O3 and Cr2O3 on loquidus temperatures in the cristobalite and tridymite primary phase fields of the MgO-"FeO"-SiO2 ststem in equilibrium with metallic iron

The effects of alumina and chromite impurities on the liquidus temperatures in the cristobalite/tridymite (SiO2) primary phase fields in the MgO-FeO-SiO, system in equilibrium with metallic iron have been investigated experimentally. Using high temperature equilibration and quenching followed by electron probe X-ray microanalysis (EPMA), liquiclus isotherms have been determined in the temperatures range 1 673 to 1 898 K. The results are presented in the form of pseudo-ternary sections of the MgO-FeO-SiO, system at 2, 3 and 5 wt% Al2O3, 2 wt% Cr2O3, and 2 wt% Cr2O3+2 wt% Al2O3. The study enables the liquidus to be described for a range of SiO2/MgO and MgO/FeO ratios. It was found that liquiclus temperatures in the cristobalite and tridymite primary phase fields, decrease significantly with the addition of Al2O3 and Cr2O3.

A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O. Applications to P-T sections and geothermometry

We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO–MgO–Al2O3–SiO2–H2O that is based on the Holland–Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe–Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P–T sections for metasediments at low temperatures (<400 °C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite + quartz + water equilibrium (2 clinochlore + 3 sudoite = 4 amesite + 4 H2O + 7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized detrital chlorite from the Zone houillère in the French Western Alps.

Development of a quasi-chemical viscosity model for fully liquid slags in the Al2O3-CaO-'FeO'-MgO-SiO2 system. Part 1. Description of the model and its application to the MgO, MgO-SiO2, Al2O3-MgO and CaO-MgO sub-systems

A structurally-based quasi-chemical viscosity model for fully liquid slags in the Al2O3 CaO-'FeO'-MgO-SiO2 system has been developed. The model links the slag viscosities to the internal structures of the melts through the concentrations of various Si0.5O, Me2/nn+O and Me1/nn+Si0.25O viscous flow structural units. The concentrations of these structural units are derived from a quasi-chemical thermodynamic model of the system. The model described in this series of papers enables the viscosities of liquid slags to be predicted within experimental uncertainties over the whole range of temperatures and compositions in the Al2O3 CaOMgO-SiO2 system.

Predicting coal ash slag flow characteristics (viscosity model for the Al2O3-CaO-'FeO'-SiO2 system)

A model has been developed which enables the viscosities of coal ash slags to be predicted as a function of composition and temperature under reducing conditions. The model describes both completely liquid and heterogeneous, i.e. partly crystallised, slags in the Al2O3-CaO-'FeO'-SiO2 system in equilibrium with metallic iron. The Urbain formalism has been modified to describe the viscosities of the liquid slag phase over the complete range of compositions and a wide range of temperatures. The computer package F * A * C * T was used to predict the proportions of solids and the compositions of the remaining liquid phases. The Roscoe equation has been used to describe the effect of presence of solid suspension (slurry effect) on the viscosity of partly crystallised slag systems. The model provides a good description of the experimental data of fully liquid, and liquid + solids mixtures, over the complete range of compositions and a wide range of temperatures. This model can now be used for viscosity predictions in industrial slag systems. Examples of the application of the new model to coal ash fluxing and blending are given in the paper. (C) 2001 Elsevier Science Ltd. All rights reserved.

Vitrocerâmicas de alta resistência mecânica obtidas a partir da cristalização do sistema SiO2-Al2O3-MgO-Li2O com adição de ZrO2 e B2O3

Pós-graduação em Engenharia Mecânica - FEG

Properties of glass-ceramics obtained from crystallization of the SiO2-Al2O3-MgO-Li2O system with addition of ZrO2

This paper presents the study results with glass-ceramics obtained from base glass (MgO-Al2O3- SiO2-Li2O system) with addition of ZrO2 as nucleating agent. The glass was melted at 1650 degrees C for 3 h and at a heating rate of 10 degrees C/min. The molten glass was poured into a graphite mold to obtain monolithic samples and also in water in order to obtain particulate material. Such material was grinded and then pressed by both uniaxial and isostatic pressing methods before being sintered. Both the monolithic and pressed samples were performed under two different conditions of heat treatment so that their nucleation and crystallization occurred. In the first one, the samples were heated to 1100 degrees C with a heating rate of 10 degrees C/min. In the second one, there was an initial heating rate of 10 degrees C/min up to 780 degrees C, which was kept for 5 minutes. After that, the samples were heated to 1100 degrees C at a heating rate of 1 degrees C/min. Microhardness analyses showed that base glass presented values around 7.0 GPa. The glass-ceramics obtained from the powder sintering showed microhardness values lower than those obtained from monolithic samples. The highest hardness values were observed in the samples which were treated with two heating rates, whose values were around 9.2 +/- 0.5 GPa. Moreover, the glass-ceramics which were produced with an only heating rate, presented values around 7.1 +/- 0.2 GPa, very close to those observed in the base glass.

A quasi-chemical viscosity model for fully liquid slags in the Al2O3-CaO-'FeO'-SiO2 system

A structurally based viscosity model for fully liquid silicate slags has been proposed and applied to the Al2O3-CaO-'FeO'-SiO2 system at metallic iron saturation. The model links the slag viscosity to the internal structure of melts through the concentrations of various anion/cation structural units (SUs). The concentrations of structural units are equivalent to the second nearest neighbor bond concentrations calculated by the quasi-chemical thermodynamic model. This viscosity model describes experimental data over the entire temperature and composition range within the Al2O3-CaO-'FeO'-SiO2 system at metallic iron saturation and can be extended to other industrial slag systems.

Decomposição térmica de espumas de poliuretano para fabricação de vitrocerâmica celular de Li2O-ZrO2-SiO2-Al2O3 (LZSA)

Characterization of the thermal decomposition of polyurethane (PUR) foams was performed by Fourier-transformed infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). Three main weight loss paths were observed by TGA, the residue being lower than 3 wt.% for 3 different PUR foams analyzed. FT-IR spectra indicated CO2, CO, NH3 and isocyanides as main decomposition products. PUR foams of different cell sizes were immersed in a slurry of the parent glass ceramic of composition Li2O-ZrO2-SiO2-Al 2O3 (LZSA) and submitted to heat treatment. The LZSA cellular glass ceramics obtained after sintering and crystallization resembled the original morphology of the PUR foams.

Structural and optical properties of Er3+ doped SiO2-Al2O3-GeO2 compounds prepared by a simple route

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)