The behavior of model three phase solid/liquid/liquid systems has been studied in the external fields of shear or gravity. Observations of the deformation and break-up of solid-liquid clusters in a simple shear field has led to an investigation of various aspects of separation and coalescence phenomena: the interaction of solid particles and drops in simple shear, film thinning processes, the thermodynamics of engulfment and solid-liquid separation by the external fields. / A microrheological approach was used to determine which parameters are important to the behavior of these systems in simple shear. Among the most important were found to be the liquid/liquid interfacial tension, the incidence of three phase contact and/or the wettability of the solid surface. / The importance of these paramters was also investigated in the formation and stability of sphere-drop systems in a gravitational field, and the detachment of the liquid drop by surface and gravitational forces. / Extensions to existing theory have been made to include gravitational effects in the thinning of a liquid film which forms around a sphere. Finally, an asymptotic solution to the Laplace equation of capillarity has been developed which may be applied to various axisymmetric liquid/fluid interfaces not too far from spherical shape. / The findings in this thesis are highly relevant to various industrial processes (such as in the production of oil, minerals, paper, etc.) where three phase systems are encountered.

No description available.

No description available.

La fissuration à chaud par liquation peut se produire dans la zone affectée thermiquement lors du soudage. Deux facteurs influent ce phénomène : les contraintes thermiques dues au gradient de température et la perte potentielle de ductilité due à la présence d'un film liquide aux joints de grains en fonction de leur composition chimique. Des essais de ductilité à chaud (Gleeble) ont été utilisés pour étudier l'effet combiné de la teneur en bore et du temps de maintien sur la chute de la ductilité dans la plage de température de liquation pour l’acier inoxydable austénitique de type 316L. Il est démontré que les teneurs en bore élevées et les temps de maintien courts favorisent la perte de ductilité dans cette plage de température. En complément la spectrométrie de masse à ionisation secondaire a été utilisée pour tenter de corréler les variations de ductilité à la distribution du bore aux joints de grains. D'autres essais de fissuration à chaud en soudage (Varestraint, PVR) ont été effectués pour confirmer l'influence de la teneur en bore sur la sensibilité à la fissuration de l’acier 316L. Les résultats indiquent que des fissures apparaissent sur toutes les éprouvettes et que le chargement mécanique externe minimal pour créer les fissures de liquation diminue avec la teneur en bore. Plus la teneur en bore est élevée, plus le matériau est donc sensible à la fissuration à chaud par liquation. Un critère de fissuration à chaud par liquation a été déterminé en se basant sur les résultats des essais de ductilité à chaud et la simulation des essais de soudage. / Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used inattempt to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other hot cracking tests (Varestraint, PVR) have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels during welding. Results indicate that cracks appear on all specimens and that the minimum external mechanical loading for liquation cracking decreases with boron content. The higher the boron content is, the more the specimen exhibits tendency to hot cracking. A liquation hot cracking criterion has been determined, based on the results of the hot ductility tests and the simulation of welding tests.

Mémoire (M.SC.A.)--Université du Québec à Chicoutimi, 1986. / Document électronique également accessible en format PDF. CaQCU

No description available.

No description available.

Mixed-matrix hollow fiber membranes are being developed to offer more efficient gas separations applications than what the current technologies allow. Mixed-matrix membranes (MMMs) are membranes in which molecular sieves incorporated in a polymer matrix do separation between gas mixtures based on the molecular size difference and/or adsorption properties of the component gases vis-à-vis the porous structure and the nature of adsorption sites in the molecular sieve. The development of MMMs to deliver on its promises has however been slow. The major challenges encountered in the efficient development of MMMs are associated with some of the paradigm shifts involved in their processing. For instance, mixed-matrix hollow fiber membranes are prepared by a dry-wet jet spinning method. For an efficient large scale processing of hollow fibers the rheology and kinetics of phase separation of the MMM dopes are important control variables in the process design. Therefore, this research thesis aims to study the rheology and phase separation kinetics of mixed-matrix membrane dopes. In research efforts to develop predictive models for the shear rheology of suspensions of zeolite particles in polymer solutions it was found that MFI zeolite suspensions have relative viscosities that dramatically exceed the Krieger-Dougherty predictions for hard sphere suspensions. Our investigations show that the major origin of this discrepancy is the selective absorption of solvent molecules from the suspending polymer solution into the zeolite pores. Consequently, both the viscosity of the polymer solution and the particle contribution to the suspension viscosity are greatly increased. A predictive model for the viscosity of porous zeolite suspensions incorporating a solvent absorption parameter, α, into the Krieger-Dougherty model was developed. We experimentally determined the solvent absorption parameter and our results are in good agreement with the theoretical pore volume of MFI particles. In addition, fundamental studies were conducted with spherical nonporous silica suspensions to elucidate the role of colloidal and hydrodynamic forces on the rheology of mixed-matrix membrane dopes. Also in this thesis, details of a novel microfluidic device that enables measurements of the phase separation kinetics via video-microscopy are presented. Our device provides a well-defined sample geometry and controlled atmosphere for in situ tracking of the phase separation process. We have used this technique to quantify the phase separation kinetics (PSK) of polymer solutions and MMM dopes upon contact with an array of relevant nonsolvent. For the polymer solution, we found that PSK is governed by the micro-rheological and thermodynamic properties of the polymer solution and nonsolvent. For the MMM dopes, we found that the PSK is increased by increased particles surface area as a result of surface diffusion enhancement. In addition, it was found that the dispersed particles alter the thermodynamic quality of the dope based on the hydrophilic and porous nature of suspended particles.

Precipitation strengthened nickel-base superalloys, such as IN 738, are very difficult to weld by fusion welding techniques due to their high susceptibility to heat-affected zone (HAZ) intergranular liquation cracking. An improvement in weldability could be realized by the deployment of innovative welding processes and/or the modification of the materials’ microstructural characteristics. Laser-arc hybrid welding is a relatively new welding process that appears to possess great potentials for joining the difficult-to-weld nickel-base superalloys. The research described in this Ph.D. dissertation was initiated to perform a systematic and comprehensive study of the cracking susceptibility of nickel-base IN 738 superalloy welds made by laser-arc hybrid welding process, and how to minimize it by using a combination of pre-weld microstructural modification and the application of various welding filler alloys. Laser-arc hybrid welding produced a desirable weld geometry in IN 738 Superalloy. Cracking did not occur exclusively in the fusion zone. Analysis of the fusion zone material using EPMA, SEM, TEM and EBSD revealed elemental partitioning pattern, the presence of secondary solidification reaction constituents and the grain structure of the fusion zone. Non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the HAZ that consequently resulted in extensive HAZ intergranular cracking. A very significant reduction in HAZ intergranular liquation cracking was achieved by the use of an industrially deployable and effective pre-weld thermal processing procedure developed during this research work. This novel procedure, designated as FUMT, was developed on the basis of the control of both boride formation and intergranular boron segregation in the pre-weld material. Propensity for HAZ intergranular liquation cracking in the weldments was also observed to vary depending on the Al+Ti+Nb+Ta concentration of the weld metal produced by different filler alloys, which can be attributed to variation in the extent of precipitation hardening in the weld metals. The newly developed FUMT treatment procedure, coupled with the selection of an appropriate type of filler alloy, is effective in reducing HAZ intergranular cracking both during laser-arc hybrid welding and during post-weld heat treatment (PWHT) of the laser-arc hybrid welded IN 738 superalloy.

Precipitation strengthened nickel-base superalloys, such as IN 738, are very difficult to weld by fusion welding techniques due to their high susceptibility to heat-affected zone (HAZ) intergranular liquation cracking. An improvement in weldability could be realized by the deployment of innovative welding processes and/or the modification of the materials’ microstructural characteristics. Laser-arc hybrid welding is a relatively new welding process that appears to possess great potentials for joining the difficult-to-weld nickel-base superalloys. The research described in this Ph.D. dissertation was initiated to perform a systematic and comprehensive study of the cracking susceptibility of nickel-base IN 738 superalloy welds made by laser-arc hybrid welding process, and how to minimize it by using a combination of pre-weld microstructural modification and the application of various welding filler alloys. Laser-arc hybrid welding produced a desirable weld geometry in IN 738 Superalloy. Cracking did not occur exclusively in the fusion zone. Analysis of the fusion zone material using EPMA, SEM, TEM and EBSD revealed elemental partitioning pattern, the presence of secondary solidification reaction constituents and the grain structure of the fusion zone. Non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the HAZ that consequently resulted in extensive HAZ intergranular cracking. A very significant reduction in HAZ intergranular liquation cracking was achieved by the use of an industrially deployable and effective pre-weld thermal processing procedure developed during this research work. This novel procedure, designated as FUMT, was developed on the basis of the control of both boride formation and intergranular boron segregation in the pre-weld material. Propensity for HAZ intergranular liquation cracking in the weldments was also observed to vary depending on the Al+Ti+Nb+Ta concentration of the weld metal produced by different filler alloys, which can be attributed to variation in the extent of precipitation hardening in the weld metals. The newly developed FUMT treatment procedure, coupled with the selection of an appropriate type of filler alloy, is effective in reducing HAZ intergranular cracking both during laser-arc hybrid welding and during post-weld heat treatment (PWHT) of the laser-arc hybrid welded IN 738 superalloy.