Synthesis and Optical Properties of Rare-Earth–Aluminum Oxide Glasses

Single-phase glasses containing 37.5 mol% Y₂O₃, 7 mol% La₂O₃, and 1 mol% Pr, Ho, Nd, Er, Sm, Tm, Eu, or Yb oxide substituted for part of the Y₂O₃ were synthesized by containerless melting. The spectral transmission and absorption cross sections of the glasses were determined at wavelengths from 360 to 3300 nm. The electronic transitions were broadened compared with results obtained in a crystalline yttrium aluminum garnet (YAG) host. The infrared transmission of the host glass extended to 6000 nm. The optical and physicochemical properties of these glasses are well suited for optical device applications.     

New Analytical Method for Maximum Temperature Assessment in an Exothermic Tubular Chemical Reactor

This paper deals with an analytical method to assess the maximum temperature value along a tubular chemical reactor at steady state. This reactor is provided with a jacket in which a counter current cooling liquid flows. The thermal behavior of the chemical reactor is calculated with the McCormack numerical method. Comparison of the exothermic reaction generated flux with the removed flux from the separating wall leads to a two-part reactor subdivision. In the first part, the reactor behaves as an adiabatic reactor followed by a zone in which the flux removed from the wall is not negligible and remains constant. In the second part, the reactor behaves like a simple heat exchanger without internal energy source. Analytical integration of mass and energy balance equations in each subsystem was used to determine the analytical expression of maximum temperature.     

Application of extended kalman filtering to chemical reactor fault detection

In this paper, we present a method for detecting faults that can appear in some parts of a chemical plant. This method is based on statistical information generated by the Extended Kalman Filter (EKF) and is designed to reveal any drift from the normal behavior of the process. Although this method was originally developed for linear systems, our contribution consists in extending it to unsteady state nonlinear systems such as stirred reactors in the presence of exothermic chemical reactions. We examined the abnormal behavior of a chemical reactor due to three different faults in its control parameters. Each fault is caused by an abrupt variation in the value of one of the following parameters: the cooling temperature, the stirring rate of the reaction mass, and the feeding flow rate of the reactant. The objective of this experimental study is to detect the presence of such faults on-line and to pinpoint the moment each occurs, as well as to determine the delay in detection with respect to the decision threshold.     

Microscopic observations of samples affected by delayed ettringite formation (DEF)

This article, which deals with the study of the microscopic modifications of DEF-affected materials, has two main objectives. The first one is to study the influence of sample preparation on the microcracks of specimens observed in Scanning Electron Microscopy (SEM). From the results of this study, it can be concluded that direct observations of the samples are inappropriate because they produce cracks that are not ascribable to the pathology. It is therefore preferable to use an indirect technique of observation such as the replica technique. This technique was developed in the 1980s and used to study the evolution of microcracking due to mechanical damage to the concrete. The results presented in this article show that it is possible to use this technique to study the microcracking associated with delayed ettringite formation. The second objective is to study ettringite formation during the swelling of DEF-affected specimens. The main results show that secondary ettringite is initially formed in the paste–aggregate interface even at low levels of expansion. For these levels of expansion, there is no trace of secondary ettringite or microcracks observable in the paste. However, for higher expansions, cracks filled with ettringite appear in the paste.     

Glass Formation and Polyamorphism in Rare-Earth Oxide–Aluminum Oxide Compositions

We report formation of single- and two-phase glasses from rare-earth oxide–alumina materials. Liquids with the Y₃Al₅O₁₂ and Er₃Al₅O₁₂ compositions underwent a liquid–liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error. Clear, brilliant, single-phase glasses were obtained from La₃Al₅O₁₂, ErLaYAl₅O₁₂, and compositions containing ≥5 mol% La₂O₃ substituted for the other rare-earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid–liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid–liquid phase transition is not observed. The results are discussed in the context of first-order liquid–liquid phase transitions (polyamorphism) and formation of single-phase glass from liquids that contain a high proportion of 4-coordinate aluminum ions.     

Effects of Melt Chemistry on the Spectral Absorption Coefficient of Molten Aluminum Oxide

Values of the spectral absorption coefficient (α) of liquid aluminum oxide were determined by transmission of a pulsed dye laser beam incident on continuous-wave (CW) CO₂-laser-melted pendant drops attached to sapphire filaments. Measurements were made on molten drops of Verneuil sapphire at wavelengths of 0.450 and 0.633 μm, at ambient oxygen partial pressures from 10^-10 to 1 bar in eight pure gases (Ar, CO, CO₂, H₂, H₂O, HCI, N₂ and O₂), in CO/CO₂ mixtures, and in H₂/H₂O mixtures, and at a temperature of ca. 2400 K. Specimens contaminated with iron, magnesium, silicon, and tungsten were also investigated in an oxygen atmosphere. At a wavelength of 0.633 μm, the value of α was greater than 50 cm^-1 under reducing or inert gas conditions. It decreased to a minimum at intermediate oxygen partial pressures of 5 × 10^-5 bar in CO/CO₂ mixtures and 5 × 10^-3 bar in H₂/H₂O mixtures, and increased at larger oxygen partial pressures. The specimens were opaque (α > 55 cm^-1) in hydrogen, in HCI at pressures above 0.04 bar. Specimens contaminated with 5000-10000 ppm of Fe, Mg, Si, or W were also opaque. At a wavelength of 0.45 μm the liquid aluminum oxide specimens were opaque in Ar and oxygen, and gave α= 46 cm^-1 in CO₂. The dynamic response when the ambient gas was changed from CO₂ to argon showed that the transmission maximum for = 0.45 μm was at p (O₂) < 0.1 bar.     

Spectral Absorption Coefficient of Molten Aluminum Oxide from.0.385 to 0.780 μm

The spectral extinction coefficient, k _λ, and the absorption coefficient, α_λ, of liquid aluminum oxide were determined from emission measurements on partially molten single-crystal sapphire filaments. Measurements were made at wavelengths from 0.385 to 0.780 μm in both argon and oxygen atmospheres and at 0.650 μm in a 10% H₂-90% N₂ mixture. The values of α_λ were found to vary with the time for which the specimen had been molten and achieved different steady-state values in the three processing atmospheres. A decrease in α_λ with wavelength (Urbach tail) was observed from 0.385 μm to about 0.420 μm in argon and 0.490 μm in oxygen, and approximately constant values were obtained at longer wavelengths. Steady-state values of α_λ at the optical pyrometer wavelength of 0.650 μm were 9 ± 2 cm⁻¹ in argon, 41 ± 8 cm⁻¹ in oxygen, and 14 ± 2 cm⁻¹ in the 10% hydrogen-90% nitrogen gas mixture.     

ESTIMATION AND LOCALIZATION OF MAXIMUM TEMPERATURE IN A TUBULAR CHEMICAL REACTOR BY LUENBERGER STATE OBSERVER

This study deals with an observer built for distributed parameter systems described by nonlinear representations. This observer was applied to a tubular chemical reactor in order to estimate the maximum temperature of the reactant mixture and its position in stationary and transient regimes. This estimation uses a Luenberger observer, while MacCormack's numerical method was used for resolution of the partial differential equations. Furthermore, to take into account the nonlinearity of the system, the gain of this estimator was proposed as a function of the position along the chemical reactor. This observer requires the values of both concentration and temperature at the inlet but only of temperature at the outlet. The convergence and robustness of this estimator were experimentally tested with initialization and modeling errors.     

Data Mining: A Key Contribution to E-business

Data mining consists of extracting knowledge from huge volumes of data, allowing better business decisions to be taken. In this paper, we show how data mining is integrated in the knowledge discovery process. We highlight its potential applications and the techniques that are often used to perform it. Association rule mining is presented as a case study. Furthermore, we show through an integrated architecture how data mining can contribute to e-business via the new technologies. Finally, we present some commercially-available architectures.