Study of the sintering mechanism of kaolinite at 900 and 1050° C; influence of mineralizers

This paper presents a study, by means of isothermal dilatometry, of the often very important (10%) shrinkage phenomenon which occurs when heating clay ceramic materials, and especially of the influence of mineralizers on the shrinkage of kaolinite at 900 and 1050° C. We found that the isothermal shrinkage versus time curve of kaolinite at both temperatures was well described by the following equation: $$\lambda = \frac{t}{{\alpha + \beta t}}$$ where λ is the linear shrinkage (relative to the initial length of the bar),t the time, andα andβ two constants. The presence of various mineralizers at different concentrations did not affect the basic shape of this curve at either 900 or 1050° C, but affected the values of parametersα andβ. A sintering mechanism is proposed which takes into account the most recent data concerning the structural transformation of kaolinite in the 900 to 1050° C temperature range. The kaolinite sintering mechanism is of the viscous-flow type proposed by Frenkel [1] involving an amorphous phase, the viscosity of which increases with time due to its progressive recrystallization. The influence of mineralizers is then explained in terms of their action on the viscosity of the amorphous phase and their action on recrystallization.     

High extinction ratio and high-temperature 2.5-Gb/s floor-free 1.3-/spl mu/m transmission with a directly modulated quantum dot laser

For the first time with a directly modulated InAs-GaAs quantum-dot laser, high extinction ratio (up to 17 dB) and 25/spl deg/C-85/spl deg/C single-mode-fiber data floor-free transmissions are achieved at 2.5 Gb/s. Moreover, an interferometric technique showed a nearly constant Henry factor /spl sim/2 until a bias current six times the threshold current.     

Application of the Resources Model to the Supervision of an Automated Process

The present study was designed to ascertain how far flagging up potential errors can improve the automatic interpretation of technical documents. We used the resources model to analyze the supervised retro-conversion of architectural floor plans from the perspective of distributed cognition. Results showed that automated assistance helps users to correct errors spotted by the system and saves time. Surprisingly, they also showed that flagging up possible errors may make users less effective in identifying and correcting errors that go unnoticed by the system. Responses to a questionnaire probing the participants’ confidence in the system suggested that they were so trusting that they lowered their vigilance in those areas that had not been signaled by the system, leading to the identification of fewer errors there. Thus, although the participants’ confidence in the automated assistance system led to improved performances in those areas it highlighted, it also meant that areas to which the system did not draw attention were less thoroughly checked.     

Influence of high power diode laser surface melting on the pitting corrosion resistance of type 316L stainless steel

High Power Diode Lasers (HPDL) are becoming more and more attractive for industrial materials processing because of their high efficiency, low running costs, small sizes and low weight. Surface melting experiments have been carried out on 316L steel with a 1 kW HPDL, with application to modify its pitting corrosion resistance in NaCl 0.05 M. Surface modifications have been investigated with optical microscopy for the microstructure, microprobe analysis for the chemical content and X Ray Diffraction for phase transformations and residual stresses. Heat conduction characteristics, analysed with a 2D Finite element code, have driven to a 28% calculated absorption of the laser light generating nearly 400 m melted depth. A refinement and homogenization of structure together with -ferrite transformation and the dissolution of inclusions was found in the melted thickness, driving to enhanced pitting resistance (nearly + 0.2 V on the pitting potential values, and factor 2 decrease of the passive current density). This pitting resistance, investigated at different depths below the surface, was found to be little affected by the ferrite content (6% estimated value), and the fineness of the microstructure, but depreciated by the surface state without post-polishing. Therefore, it is believed that localized corrosion improvements can be mainly attributed to the dissolution of Al-base and Mn-base detrimental inclusions, despite the generation of up to 6% ferrite susceptible to drive to enhanced galvanic couplings with phase.     

Effect of several additives and their admixtures on the physico-chemical properties of a calcium phosphate cement

Combinations of citrate (C₆H₅O ₇ ^3-– ), pyrophosphate (P₂O ₇ ^4– ) and sulfate (SO ₄ ^2– ) ions were used to modify the physico-chemical properties of a calcium phosphate cement (CPC) composed of -tricalcium phosphate (-TCP) and phosphoric acid (PA) solution. The results obtained with only one additive at a time are similar to those previously published. New facts are: the positive effect of C₆H₅O ₇ ^3– ions on cement failure strain and their negative effect on cement pH. The position of the setting time maximum measured at an SO ₄ ^2– concentration of 0.09 M was not displaced by the addition of C₆H₅O ₇ ^3– and P₂O ₇ ^4– ions. However, the effect of SO ₄ ^2– ions on the setting time was depressed by C₆H₅O ₇ ^3– ions. Moreover, no increase in tensile strength was observed when increasing amounts of SO ₄ ^2– were added into a C₆H₅O ₇ ^3– -containing cement. The latter results suggest a competitive effect of C₆H₅O ₇ ^3– and SO ₄ ^2– on setting time and tensile strength. Anhydrous dicalcium phosphate (DCP; CaHPO₄) appeared in cement samples dried just after setting, but not in cement samples incubated for 24 h in deionized water before the drying step. It is believed that the setting reaction is stopped by the drying step, leaving a low internal pH in the sample, hence providing favorable conditions for the transformation of dicalcium phosphate dihydrate (DCPD) into DCP. Interestingly, even though C₆H₅O ₇ ^3– ions dramatically lowered the equilibrium pH of the cement with 5 ml of deionized water, they still prevented the occurrence of the transformation of DCPD into DCP.     

Improvement of conical corrugated horn analysis using Gaussianbeams

The classical analysis of a conical corrugated horn is extended out of the balanced hybrid conditions using a vectorial multimodal Gaussian beam expansion. An experimental validation is also presented     

The influence of preparation and doping on the reducibility of hematite by hydrogen

Samples of hematite and of hematite doped with 1 at% lithium and 1 at% vanadium are prepared by the hot kerosene drying technique. The doped samples are also prepared by an impregnation method. The various samples are used to study the reduction with hydrogen to form iron. The results indicate that the rates of reduction are strongly influenced by the particle size of the initial samples and by the repartition of the additive in the bulk and surface layer of the hematite particles. It has been shown that both additives can retard the rate of reduction. The lithium exerts its maximum influence when present in solid solution and vanadium when concentrated in the surface layer. The importance of a careful preparation of samples to be used for reduction studies, is stressed.     

Experimental investigation in the TOSQAN facility of heat and mass transfers in a spray for containment application

TOSQAN is an experimental program undertaken by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in order to perform thermal hydraulic containment studies. The TOSQAN facility is a large enclosure devoted to simulate typical accidental thermal hydraulic flow conditions in nuclear-pressurized water reactor (PWR) containment. The TOSQAN facility which is highly instrumented with non-intrusive optical diagnostics is particularly adapted to nuclear safety CFD code validation. The present work is devoted to studying the interaction of a water spray injection used as a mitigation means in order to reduce the gas pressure and temperature in the containment, to produce gases mixing and washout of fission products. In order to have a better understanding of heat and mass transfers between spray droplets and the gas mixture, and to analyze mixing effects due to spray activation, we perform detailed characterization of the two-phase flow.