By means of molecular simulation, we propose possible packing models for £\ and £\¡¬ phases in poly(9,9-di-n-hexyl-2,7-fluorene) (PFH). Simulated multi-chain unit cell structures are compared with experimental diffraction patterns of PFH where the unit cell structure (and the space group) of the high-temperature £\ crystals was identified as monoclinic (C2) and that of £\¡¬ phase (kinetically favored upon programmed cooling) triclinic (P1). Results show that £\ phase prefers to adopt bi-radial side-chain conformation whereas the £\¡¬ phase prefers tetra-radial one. Both models exhibit embracing behavior between adjacent chains in spite of differences in inter-chain distance. A group of embracing chains aligned along b-axis in £\ phase and the comparatively greater inter-chain distance in £\¡¬ phase are consistent with the observed faceting along (100) planes and the tensile cracking along the a-axis. A qualitative analysis of co-existing £\ and £\¡¬ phases reproduce the [001] SAED pattern quite well. In addition, we also show that arbitrary alternation of 40o and 140o in dihedral angle between neighboring monomers generates equally stable single-chain conformations in this case of linear alkyl side-chains.

Aluminum and its alloys are used in many aspects of modern life, from soda cans and household foil to the automobiles and aircraft in which we travel. Aluminum alloy systems are characterized by good workability that enables these alloys to be economically rolled, extruded, or forged into useful shapes. Mechanical properties such as strength are altered significantly with cold working, annealing, precipitation-hardening, and/or heat-treatments. Heat-treatable aluminum alloys contain one or more soluble constituents such as copper, lithium, magnesium, silicon and zinc that individually, or with other elements, can form phases that strengthen the alloy. Microstructure development is highly dependent on all of the processing steps the alloy experiences. Ultimately, the macroscopic properties of the alloy depend strongly on the microstructure. Therefore, a quantitative understanding of the microstructural changes that occur during thermal and mechanical processing is fundamental to predicting alloy properties. In particular, the microstructure becomes more homogeneous and secondary phases are dissolved during thermal treatments. Robust physical models for the kinetics of particle dissolution are necessary to predict the most efficient thermal treatment. A general dissolution model for multi-component alloys has been developed using the front-tracking method to study the dissolution of precipitates in an aluminum alloy matrix. This technique is applicable to any alloy system, provided thermodynamic and diffusion data are available. Treatment of the precipitate interface is explored using two techniques: the immersed-boundary method and a new technique, termed here the sharp-interface method. The sharp-interface technique is based on a variation of the ghost fluid method and eliminates the need for corrective source terms in the characteristic equations. In addition, the sharp-interface method is shown to predict the dissolution behavior of precipitates in aluminum alloys when compared with published experimental results. The influence of inter-particle spacing is examined and shown to have a significant effect on dissolution kinetics. Finally, the impact of multiple particles of various sizes interacting in an aluminum matrix is investigated. It is shown that smaller particles dissolve faster, as expected, but influence the dissolution of larger particles through soft-impingement, even after the smaller particles have disappeared.

A fundamental theoretical and experimental study on calcium sulphate scale formation in hydrometallurgical solutions containing various minerals was conducted. A new database for the Mixed Solvent Electrolyte (MSE) model of the OLI Systems® software was developed through fitting of existing literature data such as mean activity, heat capacity and solubility data in simple binary and ternary systems. Moreover, a number of experiments were conducted to investigate the chemistry of calcium sulphate hydrates in laterite pressure acid leach (PAL) solutions, containing Al2(SO4)3, MgSO4, NiSO4, H2SO4, and NaCl at 25–250ºC. The database developed, utilized by the MSE model, was shown to accurately predict the solubilities of all calcium sulphate hydrates (and hence, predict scaling potential) in various multicomponent hydrometallurgical solutions including neutralized zinc sulphate leach solutions, nickel sulphate–chloride solutions of the Voisey’s Bay plant, and laterite PAL solutions over a wide temperature range (25–250°C). The stability regions of CaSO4 hydrates (gypsum, hemihydrate and anhydrite) depend on solution conditions, i.e., temperature, pH and concentration of ions present. The transformation between CaSO4 hydrates is one of the common causes of scale formation. A systematic study was carried out to investigate the effect of various parameters including temperature, acidity, seeding, and presence of sulphate/chloride salts on the transformation kinetics. Based on the results obtained, a mechanism for the gypsum–anhydrite transformation below 100°C was proposed. A number of solutions for mitigating calcium sulphate scaling problems throughout the processing circuits were recommended: (1) operating autoclaves under slightly more acidic conditions (~0.3–0.5 M acid); (2) mixing recycled process solutions with seawater; and (3) mixing the recycling stream with carbonate compounds to reject calcium as calcium carbonate. Furthermore, aging process solutions, saturated with gypsum, with anhydrite seeds at moderate temperatures (~80°C) would decrease the calcium content, provided that the solution is slightly acidic.

Les évolutions de microstructures du nouvel alliage chinois Ti B19 ont été étudiées au cours de divers traitements thermiques et des relations entre microstructures et propriétés mécaniques ont été établies. Les cinétiques de transformations isothermes ont été établies par des mesures de résistivité électrique. Les structures et microstructures ont été caractérisées par DRX synchroton, Microscopies Optiques et Electroniques (MEB, MET). Les cinétiques de transformation et les caractéristiques microstructurales. Les cinétiques de transformation isothermes ont été obtenues, analysées (loi JMAK), et cet ensemble de résultats a conduit à l'établissement du diagramme TTT de l'alliage TiB19. Enfin il a été montré que la vitesse de chauffage a une très forte influence sur les transformations mises en jeu, et qu'une pré déformation plastique accélère les cinétiques de transformation (introduction de nouveaux sites de germination). Enfin les cinétiques de transformation ont été caractérisées en refroidissement continu depuis le domaine monophasé bêta. Une première approche de la modélisation des cinétiques de transformation a été menée en utilisant le loi JMAK et le principe d'additivité de Scheil. Enfin les relations entre microstructures et propriétés sont discutés / The phase transformations and microstructure evolutions has been characterized for different thermal treatments, and the relationships between final microstrures and properties have been investigated in the new metastable Ti-B19 alloy. The isothermal phase transformation kinetics and the influence of different heat treatment phaths have been establisheb by using in-situ electrical Resistivity. The structures have been determined by synchrotron X-Ray Diffraction and the microstructures were observed by SEM and TEM. The results show that phase transformation kinetics and microstructure characteristics are strongly dependent on the aging temperature (ranging from 300 to 700°C). The global isothermal phase transformation phase transformation kinetics has been got and anallyzed with JMAK equation, and the TTT diagram of Ti-B19 alloy has been established. We have also shown that the heating rate has remarkable influence on the isothermal phase transformation behaviors and the pre-deformation accelerates the transformation kinetics. The microstructure evolutions during cooling are obviously dependent on the cooling rates. A first attempt has been made to calculate the transformation kinetics during cooling using JMAK law and Scheil principle. Finally, the relationship between mechanical properties and microstructure has been discussed

A fundamental theoretical and experimental study on calcium sulphate scale formation in hydrometallurgical solutions containing various minerals was conducted. A new database for the Mixed Solvent Electrolyte (MSE) model of the OLI Systems® software was developed through fitting of existing literature data such as mean activity, heat capacity and solubility data in simple binary and ternary systems. Moreover, a number of experiments were conducted to investigate the chemistry of calcium sulphate hydrates in laterite pressure acid leach (PAL) solutions, containing Al2(SO4)3, MgSO4, NiSO4, H2SO4, and NaCl at 25–250ºC. The database developed, utilized by the MSE model, was shown to accurately predict the solubilities of all calcium sulphate hydrates (and hence, predict scaling potential) in various multicomponent hydrometallurgical solutions including neutralized zinc sulphate leach solutions, nickel sulphate–chloride solutions of the Voisey’s Bay plant, and laterite PAL solutions over a wide temperature range (25–250°C). The stability regions of CaSO4 hydrates (gypsum, hemihydrate and anhydrite) depend on solution conditions, i.e., temperature, pH and concentration of ions present. The transformation between CaSO4 hydrates is one of the common causes of scale formation. A systematic study was carried out to investigate the effect of various parameters including temperature, acidity, seeding, and presence of sulphate/chloride salts on the transformation kinetics. Based on the results obtained, a mechanism for the gypsum–anhydrite transformation below 100°C was proposed. A number of solutions for mitigating calcium sulphate scaling problems throughout the processing circuits were recommended: (1) operating autoclaves under slightly more acidic conditions (~0.3–0.5 M acid); (2) mixing recycled process solutions with seawater; and (3) mixing the recycling stream with carbonate compounds to reject calcium as calcium carbonate. Furthermore, aging process solutions, saturated with gypsum, with anhydrite seeds at moderate temperatures (~80°C) would decrease the calcium content, provided that the solution is slightly acidic.

This research extended the knowledge of the solid phase transformation and the resulting influence on impact toughness and pitting corrosion resistance in super austenitic stainless steel (SASS) SANICRO® 35. A time-temperature-transformation diagram (TTT diagram) was assembled by performing isothermal heat treatments in the temperature range of 650-1050 °C for different periods of time, ranging from 5 min to 500 min. Microstructural analysis via LOM-DIC, SEM-EDS shows that the nose temperature of dominating σ phase is located in between 900-950 °C. Minor nitrides including π phase and Cr2N with the nose temperature of 900 °C and 850 °C, respectively, were detected after prolonged heat treatment times. Area fraction of precipitates was calculated by analyzing micrographic images in the software ImageJ. Charpy impact tests indicate that the impact toughness degrades with increasing area fraction of precipitates but at a higher rate at the early stage of precipitation. Despite a much-lessened area fraction, fine precipitates decorating the grain boundaries in a continuous pattern impose significant negative effect on impact toughness. Pitting corrosion resistance was indicated by critical pitting temperature (CPT) as per ASTM G150mod (3M MgCl2). Pitting corrosion resistance deteriorated with increasing amount of σ phase due to the Cr- and Mo-depleted surrounding area, but it is more dependent on the distribution pattern of precipitates, as well as the secondary phase type. The lowest CPTs were measured after heat treatment for 500 min at 800 °C and 850 °C where nitrides including Cr2N and π phase were formed and the small precipitates were distributed on grain boundaries continuously. Auxiliary simulation of TTT diagram via TC PRISMA shows drastic variation from experimental results in regard of time scale. The enhancement pre-factor for the interfacial mobility and interfacial energy can be modified to approach the experimental results. / Detta arbete utfördes för att undersöka fasomvandlingar och dess inflytande på slagsegheten och gropfrätningsmotståndet för det superaustenitiska rostfria stålet (SASS) SANICRO® 35. Ett tid-temperatur-transformationsdiagram (TTT-diagram) har tagits fram genom att utföra isotermiska värmebehandlingar mellan 650-1050 °C med olika hålltider från 5-500 minuter. Mikrostrukturanalys genom LOM-DIC, SEM-EDS undersökning visar att nosen för den dominerande σ-fasen ligger mellan 900-950 °C. Mindre nitrider, som π-fas och Cr2N, med nosarna vid 900 °C respektive 850 °C observerades vid längre hålltider. Areafraktionen av utskiljningar beräknades genom analys av mikrobilder med programmet ImageJ. Slagprovning visade att slagsegheten minskar med ökande fraktion utskiljningar men med en tydligare försämring i början av fastransformationen. Trots att de utgör en betydligt mindre areafraktion så kan mindre utskiljningar som följer korngränserna också påverka materialet signifikant negativt. Gropfrätningsmotståndet testades genom att mäta Critical Pitting Temperature (CPT) enligt ASTM G150mod (3M MgCl2). CPT minskade med ökande andel σ-fas p.g.a. den Cr- och Mo-utarmade zon som omger de utskilda partiklarna. Det finns även en stark koppling mellan lägre CPT och distributionen av utskiljningarna samt andra typer av faser. Lägst CPT uppmättes efter 500 minuter vid 800 °C och 850 °C då små nitrider inklusive Cr2N och π-fas bildats längs med stora delar av korngränserna. Simulering av TTT-diagram i TC PRISMA visade en drastisk skillnad i tiden till utskiljning/mängden utskiljningar jämfört med de experimentella resultaten. Diffusionförstärkningsfaktorn (eng. “mobility enhancement pre-factor”) och ytenergin kan minskas för att bättre överensstämma med de experimentella resultaten.