The aim of the present investigation is to increase theunderstanding of the role played by the solvent in inhibitingor enhancing crystal growth. Drowning-out crystallizationexperiments has been performed by the controlled addition ofwater or ethanol water mixtures to a saturated solution ofbenzoic acid in ethanol-water mixtures. Crystal habitcontrolling factors have been identified.Seededcrystallization experiments have been carried out to evaluatethe effect of solvent composition on crystal habit at constantsupersaturation. The solubility of benzoic acid inethanol-water mixtures at the working temperatures has beendetermined. Electro-zone sensing determinations and microscopicmeasurements are used to characterize the final crystallineproduct. It has been found that the shape of the benzoic acidcrystals grown from ethanol-water solutions ranges from needlesto platelets. Platy particles possess a predominant basal plane(001), bound by (010) and (100) faces, while needles aredeveloped along the b-axis. Long needle-shaped particles havebeen produced at low initial bulk concentration and highethanol concentration in the feed. Small platelets are obtainedat high initial bulk concentrations and high waterconcentration in the feed. The effect of solvent composition on the growth rate hasbeen evaluated at constant supersaturation. Seed crystals arecharacterized by image analysis measurement both before andafter each experiment. Length and width dimensions have beenmeasured on the particle silhouette. The growth rate, thesolid-liquid interfacial energy and the surface entropy factorfor the (010) faces (length dimension) and (100) faces (widthdimension) have been estimated. The interfacial energy andsurface entropy factor decreases in the direction of increasingethanol concentration due to increasing solubility. The results suggest that at low ethanol concentration(xEtOH&lt;60%) growth proceeds by screw dislocation mechanism,and adsorption of ethanol molecules may reduce the growth rate.As the ethanol concentration increases above a critical value(xEtOH ≥60%), the growth mechanism shifts to surfacenucleation and the growth rate increases with increasingethanol concentration. It has been suggested that the observedeffect of the solvent composition on crystal habit is theresult of two conflicting effects here referred as the kineticand interfacial energy effects. High interactions of the pairethanol-benzoic acid seem to be responsible of the growthretardation (kinetic effect) exerted by the solvent. On theother hand, increased ethanol concentration leads to reduceinterfacial energy and increasing surface nucleation whichmight contribute to enhance growth kinetics. <b>Keywords:</b>drowning-out crystallisation, solventcomposition, benzoic acid, solubility, crystal growth,interfacial energy, surface entropy factor, growth mechanism,crystal shape distribution.

<p>The aim of the present investigation is to increase theunderstanding of the role played by the solvent in inhibitingor enhancing crystal growth. Drowning-out crystallizationexperiments has been performed by the controlled addition ofwater or ethanol water mixtures to a saturated solution ofbenzoic acid in ethanol-water mixtures. Crystal habitcontrolling factors have been identified.Seededcrystallization experiments have been carried out to evaluatethe effect of solvent composition on crystal habit at constantsupersaturation. The solubility of benzoic acid inethanol-water mixtures at the working temperatures has beendetermined.</p><p>Electro-zone sensing determinations and microscopicmeasurements are used to characterize the final crystallineproduct. It has been found that the shape of the benzoic acidcrystals grown from ethanol-water solutions ranges from needlesto platelets. Platy particles possess a predominant basal plane(001), bound by (010) and (100) faces, while needles aredeveloped along the b-axis. Long needle-shaped particles havebeen produced at low initial bulk concentration and highethanol concentration in the feed. Small platelets are obtainedat high initial bulk concentrations and high waterconcentration in the feed.</p><p>The effect of solvent composition on the growth rate hasbeen evaluated at constant supersaturation. Seed crystals arecharacterized by image analysis measurement both before andafter each experiment. Length and width dimensions have beenmeasured on the particle silhouette. The growth rate, thesolid-liquid interfacial energy and the surface entropy factorfor the (010) faces (length dimension) and (100) faces (widthdimension) have been estimated. The interfacial energy andsurface entropy factor decreases in the direction of increasingethanol concentration due to increasing solubility.</p><p>The results suggest that at low ethanol concentration(xEtOH<60%) growth proceeds by screw dislocation mechanism,and adsorption of ethanol molecules may reduce the growth rate.As the ethanol concentration increases above a critical value(xEtOH ≥60%), the growth mechanism shifts to surfacenucleation and the growth rate increases with increasingethanol concentration. It has been suggested that the observedeffect of the solvent composition on crystal habit is theresult of two conflicting effects here referred as the kineticand interfacial energy effects. High interactions of the pairethanol-benzoic acid seem to be responsible of the growthretardation (kinetic effect) exerted by the solvent. On theother hand, increased ethanol concentration leads to reduceinterfacial energy and increasing surface nucleation whichmight contribute to enhance growth kinetics.</p><p><b>Keywords:</b>drowning-out crystallisation, solventcomposition, benzoic acid, solubility, crystal growth,interfacial energy, surface entropy factor, growth mechanism,crystal shape distribution.</p>

The vast majority of pharmaceutical drug products are developed, manufactured, and delivered in the solid-state where the active pharmaceutical ingredient (API) is crystalline. With the potential to exist as polymorphs, salts, hydrates, solvates, and cocrystals, each with their own unique associated physicochemical properties, crystals and their forms directly influence bioavailability and manufacturability of the final drug product. Understanding and controlling the crystalline form of the API throughout the drug development process is absolutely critical. Interfacial properties, such as surface energy, define the interactions between two materials in contact. For crystal growth, surface energy between crystal surfaces and liquid environments not only determines the growth kinetics and morphology, but also plays a substantial role in controlling the development of the internal structure. Surface energy also influences the macroscopic particle interactions and mechanical behaviors that govern particle flow, blending, compression, and compaction. While conventional methods for surface energy measurements, such as contact angle and inverse gas chromatography, are increasingly employed, their limitations have necessitated the exploration of alternative tools. For that reason, the first goal of this research was to serve as an analytical method development report for atomic force microscopy and determine its viability as an alternative approach to standard methods of analysis. The second goal of this research was to assess whether the physical and the mathematical models developed on the reference surfaces such as mica or graphite could be extended to organic crystal surfaces. This dissertation, while dependent upon the requisite number of mathematical assumptions, tightly controlled experiments, and environmental conditions, will nonetheless help to bridge the division between lab-bench theory and successful industrial implementation. In current practice, much of pharmaceutical formulation development relies on trial and error and/or duplication of historical methods. With a firm fundamental understanding of surface energetics, pharmaceutical scientists will be armed with the knowledge required to more effectively estimate, predict, and control the physical behaviors of their final drug products.

Fedmis Pty (Ltd) situated in Palaborwa, South Africa produces phosphoric acid using the wet process production process. For this study, two main areas of concern in the wet process phosphoric acid production were investigated. The first area is the formation of sludge in the system due to impurities that reduces the grade of the acid produced, thereby lowering the selling price. The second area is the crystallisation of the gypsum that influences filtration and thereby affects plant productivity. These two aspects were investigated separately as they occur in different steps of the production process at different acid concentrations. A major component of the acid sludge is known as x-compound, ((Fe,Al)3KH)14 (PO4)8.4H2O). The purpose of the investigation of x-compound is to determine what effects different ionic impurities have on its precipitation and to determine if these effects could be used to decrease the amount of sludge formation. Due to the complexity of the system and the wide variety of impurities only the major impurities were considered in this study. These impurities included potassium (K+), sodium (Na+), magnesium (Mg2+), aluminium (Al3+) and iron (Fe3+). For all the experiments investigating the effect of impurities, analytical reagents were used on laboratory scale. For the silica experiments, commercially available samples were used. For the experiments investigating the impurity effects on the precipitation of x-compound it was found that: <ul> <li> Agitation increases x-compound precipitation and can be used commercially to increase the precipitation rate to a point where sludge can be removed before transportation.</li> <li> Adding x-compound seeding crystals or magnesium ions also increases precipitation.</li> <li> Adding gypsum, sodium, hexafluorosilicates or fluorosilic acid reduces the precipitation, with sodium ions producing the lowest yield. This reduction is however not sufficient to be used commercially.</li> </ul> From the Raman study it became clear why x-compound precipitation is such a slow process. E At low acid concentrations, more H2PO4 - ions are present that form a complex with iron and aluminium. E As the acid concentration increases the concentration of H2PO4- ions decrease as the degree of dissociation of phosphoric acid decreases. The ferric- H2PO4- and aluminium- H2PO4- complexes become less stable and ultimately precipitation of the x-compound is favoured above solvation. E Addition of potassium impurities to the solutions had no visible effect on the Raman spectra and is suspected not to form a complex with the acid. From the silica sources investigated namely Dicalite, Serina Kaolin, Foskor silica and Aerosil 200 it can be concluded that none of the sources will be useful for the removal of potassium through formation of potassium hexafluorosilicates. For the determination of the concentration of impurities present in the production of phosphoric acid, the Fedmis monitoring program was initiated. It included the monitoring of Foskor rock analyses on a daily basis, and the monitoring of the 27%, 39% and 54% P2O5 phosphoric acid and precipitate, from these acid solutions on a weekly basis. From the investigation of the effect of these impurities on the solubility of potassium hexafluorosilicates, it was found that magnesium causes K2SiF6 to be the most soluble and fluoride the least. Unfortunately, the impurities did not help to reduce the potassium concentrations in the acid to below the required amount for sludge formation. For the calcium sulphate dihydrate surfactant experiments, the purpose of the investigation was to determine whether higher crystallisation qualities could be obtained to improve plant productivity. The investigation was limited to using surfactants with sulphate or phosphate functionalities and experiments were done on laboratory scale using analytical reagents. Atphos E3205, Atpol E3202 and Atpol E1231 are polyethoxylated alkyl phenol phosphate esters that had no visible effect on the crystal structure of the precipitated gypsum, but differences in the crystal sizes were observed. Smaller crystal structures with relatively equal masses compared to reference experiments are an indication of a growth inhibitor and a nucleation promoter as seen with Atphos E3205 and Atpol E3202. Increased crystal sizes were obtained using Atpol E1231. The use of Calsoline Oil caused a wider crystal size distribution in the precipitated crystals as thin and broad crystals with approximately the same length are found. The crystal mass obtained is also approximately the same as that of the reference experiment. Thus, it can be concluded that the surfactant affects the growth of the crystals and not the nucleation. Arlatone 1489, calcium gluconate monohydrate, Dowfax Hydrotrope and Tamol NN 8906 had no visible effect on the structure or size of the precipitated gypsum crystals. With the use of Nansa SS30, drastic effects were seen on the crystallisation of the calcium sulphate as small hexagonal rods were found. With an increase in surfactant concentration, there is a clear decrease in the mass of crystals obtained as well as crystal size. An increase in the crystal size distribution and a decrease in crystal size reduced the filtration rate dramatically. Experiments carried out for 24 hours exhibited the same trends where there is a decrease in yield with an increase in surfactant concentration. Higher yields were however obtained proving that mass transfer barriers were overcome. The results from these experiments again indicate that the surfactant affects crystal growth and nucleation. With the use of Dowfax 3B2 there is definite reduction in yield with an increase in surfactant concentration reaching a minimum at approximately 70% yield. Due to the presence of large amounts of smaller crystals and the almost constant yield obtained compared to the reference experiment, it can be concluded that this surfactant is a growth and not a nucleation inhibitor. As with Nansa SS30, experiments where Empicol LZ/D was used show a continuous decrease in the yield obtained with an increase in the surfactant concentration. At higher concentration of Empicol LZ/D, it seems as if this surfactant changed from a growth promoter to a growth inhibitor because although broad longer crystals are present, there are now also much smaller crystals formed. The crystal size distribution also broadens considerably. Overall, very high yields were obtained using Empimin KSN70 and the observed crystal size distributions were very narrow. The only difference was that the crystals appeared to be more porous or fibrous compared to the reference experiment. It is recommended that the experiments showing promise as crystal habit modifiers like Nansa SS30 and Empicol LZ/D be investigated in more detail as well as combinations of surfactants. Both the areas of concern in the process were investigated successfully. For the sludge formation problem, it is now clear what effects the precipitation of x-compound as well as what affect the impurities and operating conditions have. For the crystallisation of gypsum using surfactants, it was proven that surfactants could be used to affect crystal growth, shape and distribution and in this way influence filtration. / Dissertation (MSc(Chemical Engineering))--University of Pretoria, 2005. / Chemical Engineering / unrestricted

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24429号 / 理博第4928号 / 新制||理||1704(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 三宅 亮, 教授 野口 高明, 教授 下林 典正 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Les hydrates de gaz sont des composés cristallins stables à haute pression et à basse température, très répandus sur terre, notamment dans les fonds marins au niveau des marges continentales, où ils contribuent à la stabilité des sédiments par leur cohésion et leur adhésion aux surfaces minérales. Cependant, le comportement mécanique des hydrates en soi a été peu ou pas étudié à l’échelle du pore. L’objectif de cette thèse est d’étudier les conditions de stabilité et les propriétés mécaniques en traction de l’hydrate de méthane à l’échelle du pore, dans une configuration comparable à celle qu’on peut trouver dans les milieux poreux sédimentaires.Ici, nous étudions d’abord par microscopie optique les conditions de formation, de croissance et de dissociation de l’hydrate de méthane à l’interface eau/CH4 dans un micro-capillaire en verre utilisé à la fois comme un pore modèle et comme une cellule optique résistante à haute pression et à basse température. Ensuite, en développant une méthode originale in situ et sans contact : "dépression thermo-induite" on détermine les propriétés mécaniques en traction d’une coquille polycristalline d’hydrate de méthane. L’hydrate est nucléé à basse température sur l’interface eau/CH4, qui est rapidement recouverte d’une "croûte" polycristalline d’hydrate. À partir de cette croûte, l’hydrate pousse de part et d’autre de l’interface : dans l’eau sous forme "d’aiguilles" cristallines, dans le gaz, sous forme de "filaments" cristallins, et enfin entre le substrat et le gaz sous forme d’un "halo". Le halo qui est un film polycristallin avançant sur le substrat, en chevauchant un film d’eau, ralentit et finit par s’immobiliser et s’accrocher au substrat. À partir de ce moment, "la coquille" polycristalline, constituée de la croûte et du halo, forme une barrière entre l’eau et le gaz. Les tests de traction sont effectués par génération d’une dépression dans le compartiment eau en augmentant la température à pression de méthane constante.Les propriétés élastiques en traction de la coquille (module élastique et contrainte de rupture) sont déterminées en fonction de la taille des grains, contrôlée ici par les deux paramètres : le sous-refroidissement par rapport à la température d’équilibre, et le temps de mûrissement. On trouve un comportement élastoplastique à caractères ductile et fragile mélangés. Nos données de contrainte de rupture s’insèrent dans un écart de cinq ordres de grandeurs de taille de grain, et de trois ordres de grandeurs de la contrainte de rupture (entre des données de simulation à l’échelle nanomètrique et des données expérimentales à l’échelle millimétrique). L’effet de taille de grain sur la contrainte de rupture de l’hydrate de méthane peut être un facteur contribuant à la déstabilisation des pentes continentales. / Gas hydrates are ice-like crystals stable at high pressure and low temperature. They are ubiquitous on earth, notably at the edges of continental shelves, where they contribute to the mechanical stability of marine sediments, by hydrate cohesion and hydrate adhesion to mineral particles. However, the mechanical behavior of gas hydrates at pore scale has been hardly or not at all studied. The purpose of this thesis is to study the stability conditions and the tensile mechanical properties of methane hydrate at pore scale in a representative pore habit of gas hydrate in a sedimentary medium.Here, using optical microscopy, first the formation, growth and dissociation conditions of methane hydrate are investigated across a water/CH4 interface in glass micro-capillaries used both as a pore model and as an optical cell resisting high pressure and low temperature. Then by developing a contactless and an in situ method, "thermally induced depressing", tensile mechanical properties of polycrystalline methane hydrate shell are determined. At low enough temperature, the hydrate nucleates as a polycrystalline "crust" over the water/CH4 interface. From this crust, the hydrate continues growing on both sides of the interface: in the water as "needle like crystals", in the gas as "hair like crystals", and finally between the gas and the substrate as a polycrystalline film, the "halo". The halo advances slowly on the substrate, riding over a water film, and comes to rest and adheres to the substrate. From then on, the "shell" (crust and halo) isolates the water from the gas. Tensile tests are carried out by generating a depression in the water compartment by increasing temperature at constant methane pressure.Tensile elastic properties of the shell (elastic modulus and the tensile strength) are determined as a function of the grain size, controlled here by two parameters, supercooling compared to the equilibrium temperature and the annealing time. We find elastoplastic behavior, with mixed ductile and brittle characteristics. Our data on tensile strength contribute to fit the gap of five orders of magnitude of grain size, and three orders of magnitude of tensile strength (between molecular simulations at nanometre scale and current experiment at millimetre to centimetre scale). The effect of grain size on the tensile strength of methane hydrate could be a factor contributing to the destabilization of continental slopes.

Research on salts species formed by evaporation of aqueous solution of Na2 in the early 1930s. The thermodynamic, crystallographic and many other physical and chemical properties of most of the species formed from this solution has been known for decades. However, there was no complete information or reliable data to confirm the existence of a unique double salt that is rich in sodium carbonate, up until five years ago when a research identified the double salt (~2Na ₂ CO ₃ • Na ₂ SO ₄) from the ternary system Na₂CO ₃Na₂SO ₄ H₂O. Crystallization of this double salt so called sodium sulfate dicarbonate (~2Na ₂ CO ₃ • Na ₂ SO ₄) is known to be a primary contributor to fouling heat transfer equipment in spent-liquor concentrators used in the pulp and paper industry. Therefore, understanding the conditions leading to formation of this double salt is crucial to the elimination or reduction of an industrial scaling problem. In this work, double salts were generated in a batch crystallizer at close to industrial process conditions. X-ray diffraction, calorimetry, and microscopic observation were used to investigate the stability of the salts to in-process aging, isolation and storage, and exposure to high temperature. The results show that care must be taken during sampling on evaporative crystallization. Two apparent crystal habits were detected in the formation of sodium sulfate dicarbonate; the favored habit may be determined by calcium ion impurities in the system. The results also verify that sodium sulfate dicarbonate exists as a unique phase in this system and that remains stable at process conditions of 115-200℃