Crystal growth and dissolution of gypsum and analogous materials : a multi-scale approach

This thesis is concerned with the growth and dissolution of gypsum and analogous crystalline materials, with the aim of understanding the kinetic and mechanistic processes at the mineral-solution interface. The research conducted was a collaborative project sponsored by Saint-Gobain Gypsum. First, an image processing (IP) software package was developed to meet highly specialised IP needs and expedite the extraction of vital surface information from images produced in the growth and dissolution studies carried out in this thesis. A simple but powerful morphological analysis of characteristic etch pit features formed on the basal plane of gypsum was proposed, to aid the determination of intrinsic dissolution kinetics. Limiting the study to short times produced microscopic active features, which exhibited high and quantitative mass transport rates. At early times, the reaction was surface controlled, with the edge planes dominating the process, revealing anisotropic step propagation kinetics. With time, an increased contribution from mass transport was observed, suggesting that at later times, the basal plane dominated reaction kinetics. Common ion effects indicated a greater impact of Ca2+ than SO42- in reducing dissolution rates while inert ions enhanced dissolution in a directionspecific way. With this approach, microscopic phenomena were related to macroscopic measurements thus reconciling experimental length scales. Dissolution of the basal (010) and edge (001) surfaces of gypsum and polycrystalline anhydrite, were probed at the bulk scale by coupling the channel flow cell (CFC) technique which displays high mass transport rates, with off-line spectrometric measurements of dissolved Ca2+. Quantitative modelling of the diffusion-reaction within the CFC yielded a linear rate law for the dissolution process. Rates from the basal plane and anhydrite were found to be consistent with other bulk measurements, while the highly reactive edge plane exhibited high rates indicating a transport-limited process. Sodium trimetaphosphate, a common humid-creep inhibitor was found to significantly retard basal plane dissolution rates. Further CFC studies were carried out on industrially-relevant, chemically modified CaSO4 based materials, using a simple flux approach. It was found that models proposing a dissolution-precipitation pathway as the mode of action of humid-creep inhibitors were less plausible than those proposing a surface binding pathway. Finally, the influence of solution stoichiometry, r = (aCa2+ / aSO42-) on the growth kinetics of microscopic gypsum crystals was determined at a constant supersaturation. Crystal growth was found to be entirely controlled by surface kinetics over the range of r, with the edge planes dominating the process. The highest lateral rates were found at r = 1, diminishing sharply at r ≠ 1, and indicating strong plane-specific dependence on Ca2+ and SO42- availability. Additionally, dramatic changes in the morphology of grown crystals were observed. Propagation of steps on the basal face revealed a complex polynuclear layer-by-layer growth process for this surface. Macroscopic growth rates compared well to previous bulk measurements indicating that the approach used provided a comprehensive multi-scale view of gypsum growth processes.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Crystal growth and dissolution of gypsum and analogous materials : a multi-scale approach

This thesis is concerned with the growth and dissolution of gypsum and analogous crystalline materials, with the aim of understanding the kinetic and mechanistic processes at the mineral-solution interface. The research conducted was a collaborative project sponsored by Saint-Gobain Gypsum. First, an image processing (IP) software package was developed to meet highly specialised IP needs and expedite the extraction of vital surface information from images produced in the growth and dissolution studies carried out in this thesis. A simple but powerful morphological analysis of characteristic etch pit features formed on the basal plane of gypsum was proposed, to aid the determination of intrinsic dissolution kinetics. Limiting the study to short times produced microscopic active features, which exhibited high and quantitative mass transport rates. At early times, the reaction was surface controlled, with the edge planes dominating the process, revealing anisotropic step propagation kinetics. With time, an increased contribution from mass transport was observed, suggesting that at later times, the basal plane dominated reaction kinetics. Common ion effects indicated a greater impact of Ca2+ than SO42- in reducing dissolution rates while inert ions enhanced dissolution in a directionspecific way. With this approach, microscopic phenomena were related to macroscopic measurements thus reconciling experimental length scales. Dissolution of the basal (010) and edge (001) surfaces of gypsum and polycrystalline anhydrite, were probed at the bulk scale by coupling the channel flow cell (CFC) technique which displays high mass transport rates, with off-line spectrometric measurements of dissolved Ca2+. Quantitative modelling of the diffusion-reaction within the CFC yielded a linear rate law for the dissolution process. Rates from the basal plane and anhydrite were found to be consistent with other bulk measurements, while the highly reactive edge plane exhibited high rates indicating a transport-limited process. Sodium trimetaphosphate, a common humid-creep inhibitor was found to significantly retard basal plane dissolution rates. Further CFC studies were carried out on industrially-relevant, chemically modified CaSO4 based materials, using a simple flux approach. It was found that models proposing a dissolution-precipitation pathway as the mode of action of humid-creep inhibitors were less plausible than those proposing a surface binding pathway. Finally, the influence of solution stoichiometry, r = (aCa2+ / aSO42-) on the growth kinetics of microscopic gypsum crystals was determined at a constant supersaturation. Crystal growth was found to be entirely controlled by surface kinetics over the range of r, with the edge planes dominating the process. The highest lateral rates were found at r = 1, diminishing sharply at r ≠ 1, and indicating strong plane-specific dependence on Ca2+ and SO42- availability. Additionally, dramatic changes in the morphology of grown crystals were observed. Propagation of steps on the basal face revealed a complex polynuclear layer-by-layer growth process for this surface. Macroscopic growth rates compared well to previous bulk measurements indicating that the approach used provided a comprehensive multi-scale view of gypsum growth processes.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Growth and Morphology of Small Ice Crystals in a Diffusion Chamber

Small water ice crystals are the main component of cold tropospheric clouds such as cirrus. Because these clouds cover large areas of our planet, their role in the radiation budget of incoming and outgoing radiation to the planet’s surface is important. At present, the representation of these clouds in climate and weather models is subject to improvements: a large part of the uncertainty error stems from the lack of precise micro-physical and radiation model schemes for ice crystal clouds. To improve the cloud representations, a better understanding of the life time dynamics of the clouds and their composition is necessary, comprising a detailed understanding of the ice particle genesis, and development over their lifetime. It is especially important to understand how the development of ice crystals over time is linked to the changes in observable variables such as water vapour content and temperature and how they change the light scattering properties of the crystals. Recent remote and aircraft based in-situ measurements have shown that many ice particles show a light scattering behaviour typical for crystals having rough surfaces or being of complex geometrical shapes. The aim of this thesis was to develop the experimental setup and experiments to investigate this further by studying the surface morphology of small water ice crystals using scanning electron microscopy (SEM). The experiments I developed study the growth of water ice crystals inside an SEM chamber under controlled environmental conditions. The influence of water vapour supersaturation, pressure and temperature is investigated. I demonstrate how to retrieve the surface topology from observed crystals for use as input to computational light scattering codes to derive light scattering phase functions and asymmetry parameters, which can be used as input into atmospheric models. Difficulties with the method for studying the growth of water ice crystals, such as the effect of the electron beam-gas ionization and charging effects, the problem of facilitating repeated and localized ice growth, and the effect of radiative influences on the crystal growth are discussed. A broad set of nucleation target materials is studied. In a conclusion, I demonstrate that the method is suitable to study the surface morphologies, but is experimentally very challenging and many precautions must be taken, such as imaging only once and preventing radiative heat exchange between the chamber walls and the crystals to avoid unwanted effects on the crystal morphology. It is also left as a question if a laboratory experiment, where crystals will need to be grown in connection to a substrate, can represent the real world well enough. Deriving the required light scattering data in-situ might be an alternative, easier way to collect data for modelling use

In situ characterisation for studying nucleation and growth of nanostructured materials and thin films during liquid-based synthesis

Knowledge about the nucleation, growth, and formation mechanisms during materials synthesis using sol-gel and solution-based methods is important to design a material with desired properties. We used aqueous chemical synthesis as an environmentally friendly and highly flexible route to tailored and reproducible synthesis of oxide nanomaterials and thin films. For studies of hydrothermal synthesis an in situ cell using synchrotron X-ray diffraction was used to investigate the formation mechanisms of SrxBa1-xNb2O6 piezoelectrics. Aqueous chemical solution deposition of phase pure oriented piezoelectric thin films demands strong control of processing parameters. An in situ cell for synchrotron X-ray diffraction studies of the annealing and crystallisation steps during aqueous chemical solution deposition was used to understand the nucleation and crystallisation of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). We discuss how the knowledge about nucleation and growth obtained by in situ characterisation can be used to design the optimal procedure for fabrication of oxide materials with desired properties

Improving continuous crystallisation using process analytical technologies: design of a novel periodic flow process

In this thesis novel configurations and operating strategies in the mixed suspension mixed product removal (MSMPR) crystalliser are investigated, aided by integrated process analytical technologies (PAT) and crystallisation informatics system (CryPRINS) tools. The MSMPR is an idealised crystalliser model that assumes: steady-state operation; well mixed suspension with no product classification, such that all volume elements contain a mixture of particles (small and large) and crystal size distribution (CSD) that is independent of location in the crystalliser and is identical of the product withdrawn; and uniform supersaturation thought, leading to constant nucleation and growth rates. Single-stage MSMPR designs with continuous recycle/recirculation and modified heat exchanger were investigated and found to minimise fouling, encrustation and transfer line blockages. In particular, a modified MSMPR with baffled heat exchanger was found to significantly reduce the temperature between incoming feed hot feed solution and the cooled crystalliser, leading to a significant reduction in fouling, encrustation and blockages. In addition, the concept of the periodic mixed suspension mixed product removal (PMSMPR) crystallisation process is demonstrated for the first time viz single- and multi-stage cascaded operations. This method of operation involves the periodic transfer of slurry (addition and withdrawal) at high flow rates from either a single stirred vessel or between a number of stirred vessels arranged in series. The PMSMPR is therefore characterised by periodic withdrawals of product slurry. Similar to the MSMPR, the product withdrawn from a PMSMPR has exactly the same composition as the vessel at the time of removal. The rapid withdrawal of slurry at high flow rates in PMSMPR operation leads to the prevention of particle sedimentation and blockage of transfer lines. The transfer of slurry (to/from) the PMSMPR is followed by a holding (or pause) period when no addition or withdrawal of slurry takes place. The holding period extends the mean residence time of the PMSMPR relative to a typical MSMPR, thereby increasing the yield and productivity of crystallisation as more time is allowed for consumption of available supersaturation viz crystal growth and nucleation. A state of controlled operation (SCO) in the periodic flow process, defined as a state of the system that maintains itself despite regular, but controlled disruptions was characterised using the PAT tools and CryPRINS within an intelligent decision support (IDS) framework. The crystallisation of paracetamol (PCM) from isopropyl alcohol (IPA) using different configurations of a single-stage continuous MSMPR crystalliser that incorporated continuous recycle and recirculation loop, and a novel design with baffled heat exchanger was investigated. Crystallisations of PCM-IPA carried out in the MSMPR without heat exchanger suffered from severe fouling, encrustation and blockage problems due to the high level of supersaturation (S = 1.39) in the crystalliser, which was required for the initial burst of nucleation to generate enough particles for later growth, as well as the large temperature difference between the incoming feed (45 oC) and the crystalliser (10 oC). Using the modified MSMPR design with baffled heat exchanger, the challenges of fouling, encrustation and blockage were significantly reduced due to the rapid lowering of the feed stream temperature prior to entering the crystalliser. In addition, the closed loop system led to conservation of material, which is a great benefit since large amounts of materials would otherwise be required if the MSMPR was operated with continuous product removal. This design is great for research purposes, in particular, to investigate process design and optimisation. Continuous crystallisation of PCM in the presence of hydroxyl propyl methyl cellulose (HPMC) additive was investigated in the modified MSMPR design with heat exchanger. HPMC was found to improve the crystallisation performance, leading to complete avoidance of fouling, encrustation and blockages at a concentration of 0.05 wt%. However, the yield of crystallisation was significantly reduced (28.0 %) compared to a control experiment (98.8 %, biased due to fouling/encrustation) performed without additive addition. Regardless, the productivity of crystallisation was more than four times that achieved in batch linear cooling (LC) (0.62 0.86 g/L-min) and batch automated dynamic nucleation control (ADNC) (0.24 0.25 g/L-min) runs. Aspects of the periodic flow crystallisation of single- and multi-component (co-crystals) molecular systems have also been examined to demonstrate the concept of state of controlled operation . The single component systems studied were PCM and glycine (GLY), each representative of compounds with slow and fast growth kinetics, respectively. The co-crystal systems investigated were urea-barbituric acid (UBA) and p Toluenesulfonamide-Triphenylphosphine oxide (p-TSA-TPPO). UBA is a polymorphic co-crystal system with three known forms (I, II and III). Form I UBA was successfully isolated in a three-stage periodic flow PMSMPR crystalliser. This study demonstrates the capability of periodic flow crystallisation for isolation of a desired polymorph from a mixture. p-TSA-TPPO exists in two known stoichiometric co-crystal forms, 1:1 and 3:2 mole ratio p-TSA-TPPO, respectively. The two crystalline forms exhibit solution mediated transformation, which proves to be a difficulty for separation. For this study, the implementation of temperature cycles in batch and flow control in semi-batch and periodic PMSMPR crystallisers were investigated to isolate pure 1:1 and 3:2 p-TSA-TPPO, respectively. Different regions of the ternary diagram of p-TSA, TPPO and acetonitrile (MeCN) were investigated. The desired co-crystal form was isolated all crystallisation platforms investigated. However, greater consistency was observed in the semi-batch and PMSMPR operations respectively. Periodic flow crystallisation in PMSMPR is a promising alternative to conventional continuous MSMPR operation, affording greater degrees of freedom operation, slightly narrower RTD profiles, consistent product crystal quality (size, shape and distribution), longer mean residence times, higher yield and productivity and significant reduction in fouling, encrustation and transfer line blockages over prolonged operating periods. Furthermore, the PMSMPR is a versatile platform that can be used to investigate a range of different molecular systems. Relative to batch operation, the PMSMPR can operate close to equilibrium, however, this is dependent on the system kinetics. In addition, retrofitting of batch crystallisers to operate as PMSMPRS fairly simple and require only subtle changes to the existing design space. The integrated array of PAT sensors consisted of attenuated total reflectance ultra violet/visible spectroscopy (ATR-UV/vis), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), focused beam reflectance measurement (FBRM), particle vision microscopy (PVM) and Raman spectroscopy. The results from the studies reported here illustrate very well the use of PAT and information system tools together to determine when the continuous and periodic MSMPR operations reaches a steady-state or state of controlled operation (i.e. periodic steady-state). These tools provided a better understanding of the variables and operating procedures that influence the two types of operations

Non-Classical Nucleation Phenomena Study And Following Process Monitoring and Optimization in Solution Crystallization Process

Nucleation is a crucial step in the solution crystallization process. Despite their good development, classical nucleation theory and two-step nucleation theory cannot explain all the nucleation phenomena, especially for the non-classical nucleation phenomena which include oiling out, gelation and non-monotonic nucleation. Accordingly, for the non-classical nucleation systems, the crystallization processes are seldom designed based on the nucleation monitoring and supervision. In this thesis, crystallization process optimization was conducted to study the mechanism of non-classical nucleation phenomena and in-line process monitoring technology development. Two kinds of non-classical nucleation phenomena with non-monotonic nucleation rate and gel formation were investigated, and accordingly, two nucleation pathways that self-induced nucleation and jellylike phase mediated nucleation were proposed based on the analysis of in-line spectral monitoring and off-line sample characterizations. Results indicated the agitation level would affect the pre-nucleation clusters’ existence in the non-monotonic nucleation system, and the properties of solvent determined the formation of jellylike phase and the transformation to crystals. Motion-based objects tracking model and the state-of-the-art neural network Mask R-CNN were introduced to monitor the onset of nucleation and following the crystallization process. Combined with a cost-effective camera probe, the developed real-time tracking system can detect the nucleation onset accurately even with ultrasonic irradiation and can extract much more information during the whole crystallization process. Subsequently, ultrasonic irradiation and seeding were used to optimize a non-classical nucleation system that accompanied oiling out phenomenon. Different frequencies and intensities of ultrasonic irradiation and seeds addition time were screened to optimize the nucleation step, which proved their effectiveness of promoting nucleation and narrowing the metastable zone widths of oiling out and nucleation. A fine-tuning of nucleation step was carried out in a mixed suspension mixed product removal (MSMPR)-tubular crystallizer series. The nucleation step was optimized in the MSMPR stage with the aid of principal component analysis, which enabled the growth of crystals in the tubular crystallizer with preferred polymorphism, shape, and size. The study in this thesis provides insights into non-classical nucleation mechanism and nucleation based crystallization process design and optimization

Characterizing porous protein crystal materials for applications in nanomedicine and nanobiotechnology

2018 Summer.Includes bibliographical references.Protein crystals are biologically derived, self-assembling, porous structures that have been used for decades in structure determination via X-ray diffraction. Recently, however, there has been increased interest in utilizing protein crystals for their unique material properties—most notably, their highly ordered porous structure, innate biocompatibility, and chemical plasticity. The diverse topologies of protein crystals and the relative ease with which their chemical properties can be altered via genetic mutation or chemical modification offers a wider and more dynamic design palette than existing chemically-synthesized nanoporous frameworks. These traits make protein crystals an attractive new material for applications in nanomedicine and nanobiotechnology. The intent of this project is to demonstrate the application potential of porous protein crystal materials for use in nanostructured devices. This work highlights our efforts to: experimentally and computationally investigate macromolecular transport and interaction energies within a large-pore protein crystal environment using time-lapse confocal microscopy, bulk equilibrium adsorption, and hindered diffusion simulation; assess the cytocompatibility of various cross-linking chemistries for the production of biostable protein crystal materials for use in biologically sensitive environments; and create multifunctional textiles by covalently attaching various cross-linked protein crystals to cellulose fibers in woven cotton fabrics. By pursuing this research, we hope to better understand porous protein crystal materials and leverage that knowledge to design advanced nanostructured devices for applications in medicine and biotechnology

Adipic Acid Sonocrystallization in Continuous Flow Microchannels

Crystallization is widely employed in the manufacture of pharmaceuticals during the intermediate and final stages of purification and separation. The process defines drug chemical purity and physical properties: crystal morphology, size distribution, habit and degree of perfection. Particulate pharmaceuticals are typically manufactured in conventional batch stirred tank crystallizers that are still inadequate with regard to process controllability and reproducibility of the final crystalline product. Variations in crystal characteristics are responsible for a wide range of pharmaceutical formulation problems, related for instance to bioavailability and the chemical and physical stability of drugs in their final dosage forms. This thesis explores the design of a novel crystallization approach which combines in an integrated unit continuous flow, microreactor technology, and ultrasound engineering. By exploiting the various benefits deriving from each technology, the thesis focuses on the experimental characterization of two different nucleation systems: a droplet-based system and a single-phase system. In the former, channel fouling is avoided using a carrier fluid to segment the crystallizing solution in droplets, thus avoiding the contact with the walls. In the latter channel blockage is prevented using larger channel geometries and employing higher flow rates. The flexibility of the developed setup also allows performing stochastic nucleation studies to estimate the nucleation kinetics under silent and sonicated conditions. The experiments reveal that very high nucleation rates, small crystal sizes, narrow size distributions and high crystal yields can be obtained with both setups when the crystallizing solution is exposed to high pressure field as compared to silent condition. It is concluded that transient cavitation of bubbles and its consequences are a significant mechanism for enhancing nucleation of crystals among several proposed in the literature. A preliminary study towards the development and design of a growth stage is finally performed. Flow pulsation is identified as a potential method to enhance radial mixing and narrow residence time distribution therefore achieving optimal conditions for uniform crystal growth. The results suggest that increasing values of Strouhal number as well as amplitude ratio improve axial dispersion. Helically coiled tubes are identified as potential structures to further improve fluid dynamic dispersion