Browsing by Subject "Crystal Growth"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Modeling of continuum transport and meso-scale kinetics during solution crystal growth
    (2014-05) Wang, Wei
    Solution crystal growth is widely applied in many industries and fundamental research, and it is employed to crystallize materials ranging from inorganic molecules, small organic molecules, to large organic molecules. However, despite the broad application, fundamental factors regarding this crystal growth process are not well understood. In this thesis, numerical models are developed to study the influences of macro-scale mass transfer limitations and meso-scale growth kinetics on solution crystal growth. A parallel, finite element model is implemented to compute three-dimensional fluid flow and mass transfer during crystal growth and is especially applied to the growth systems in Atomic Force Microscopy fluid cells. This work assesses the parametric sensitivity of growth conditions to factors such as the strength of flow, the frequency of scanning motion, the size of the crystal, and the kinetics of the growing surface. Accounting for such effects will be very important to understand solution crystal growth and to interpret AFM measurements of growth dynamics. Additionally, a simplified two-dimensional numerical model focused on the region near the growing crystal surface and the AFM cantilever was developed based on the calculated results of the three-dimensional model. With this two-dimensional model, we provide basic understanding of the fluid flow and mass transfer where the AFM measurements were made, and simplified the revision of AFM measurements interpretation.A fundamental theoretical model based on the phase-field approach is developed to simulate nano-scale island growth and spiral step growth on crystal surfaces in a supersaturated liquid and is validated by comparison to zinc oxide nanowires synthesis experiments. Results obtained by this work help to explain how experimental factors affect the crystal growth and crystal microstructures and the correlation between island growth and spiral growth mechanisms.
  • Thumbnail Image
    Item
    Modeling the role of high-pressure on the optical floating zone technique and analysis of high-pressure, high-temperature diamond growth
    (2023-09) Dossa, Scott
    Far more than just pretty stones, single crystals increasingly underpin the technology we rely on every day. For the technologies of tomorrow, novel materials must be discovered and synthesis of known materials must be improved. Take diamond, for example: the favored material for the production of quantum bits owing to their unique physical, thermal, and electric properties. Only synthetic diamonds are suitable for this purpose. Synthetic diamonds are grown by transporting carbon through a solvent at high temperatures and pressures --the high-pressure, high-temperature (HPHT) method. Unfortunately, diamonds grown via HPHT contain large inclusions of the solvent used in their growth which greatly limits the resulting crystal quality. Reducing or eliminating solvent inclusions in synthetically grown diamonds is critical for the continued advancement of areas which rely on diamond. When discovering new materials, rather than improving production of traditional ones, the floating-zone system is an invaluable tool. Recently, a high-pressure gas has been added to optically heated floating-zone systems as this increases the range of phase space which can be utilized for growth. The high-pressure, optical floating-zone (HPOFZ) method has been used to achieve growth of completely new materials which could not be grown at ambient pressures and to make growth easier for existing materials. This advancement has also come with challenges. At high pressures, instability of the liquid zone as well as turbulent flow in the gas phase have been reported. Evaporation of volatile components from the liquid zone is also a concern at higher pressures due to the potential to stoichiometrically alter the crystal. To understand the challenges during growth with HPOFZ and the inclusion of solvent during HPHT diamond growth, we employ mathematical models to investigate each system. Our HPOFZ model realistically represents the shape of the liquid bridge and evaporation of volatile species arising due to the temperature and flow within the system. To fundamentally understand the role of pressure in HPOFZ growth systems, these calculations are done at pressures ranging from 1 to 300 bar. From these models we find system pressure significantly affects buoyant flows in the surrounding atmosphere. Both driving force and flow strength increase nonlinearly with pressure, with the Grashof number growing with the cube of pressure and the Reynolds number scaling with pressure to the 3/2 power. Species transport is also strongly affected by pressure with evaporation from the liquid scaling with pressure to the negative 2/5 power. The HPHT model focuses on the relationship between temperature, flow, and carbon transport and its effect on the growth characteristics of diamond. This model is the first to connect phase-change kinetics governing crystal growth to the continuum transport of carbon through the growth cell. Results show the importance of convective transport driven by buoyant flow in the solvent, which increases the growth rate by nearly an order of magnitude over that obtained under diffusion alone. Parametric studies show how crystal growth may be kinetically-limited or transport-limited, depending on the value of the macroscopic kinetic coefficient. Estimating this kinetic coefficient from growth experiments yields a phase-change Damk\"{o}hler number of unity, indicating a mixed regime where phase-change kinetics and transport are comparable and strongly coupled in this system. Mechanisms responsible for slowing growth as the crystal size increases are explained. Supersaturation inhomogeneities along the facets of larger crystals are predicted, which may be relevant to solvent inclusion formation during growth.
  • Thumbnail Image
    Item
    Protein crystallization using micro-fluidic devices
    (2009-08) Sugiyama, Masano
    X-ray diffraction is the most common way to determine protein structure at an atomic level. To determine the protein structure, a high-quality crystal of sufficient size is required. Obtaining such a crystal is difficult due to the multi-parametric phase space that needs to be screened to determine the best conditions for growth of a suitable crystal. In this work two microfluidic protein crystallization techniques have been developed and tested: the continuous-feed crystallization chamber and the phase diagram visualizer. The continuous-feed crystallization chamber (CCC) allows for kinetic path control through the crystallization phase diagram during crystallization. The CCC operates similarly to a continuously stirred tank reactor, where protein, salt, and buffer are fed at desired flow rates and concentrations to maintain desired conditions inside the chamber. A lumped kinetic model was developed, and parameters for heterogeneous nucleation kinetics were determined. Heterogeneous nucleation was found to have faster nucleation kinetics and slower growth kinetics than homogeneous nucleation, as expected. The lumped-model analysis gives a method to quantifying the effect of various crystallization variables by extraction of kinetic parameters. The phase diagram visualizer (PDV) determines the solution phase diagram for protein-precipitant systems in one experiment rather than many lengthy experiments as required for traditional methods. Laminar flow and diffusion in the PDV create significant gradients in concentration, so crystals form in only part of the chamber. By combining observation of the location of the crystal-rich regions with a computer simulation of flow and transport in the chamber, a solution phase diagram is generated. This PDV has been tested for the lysozyme-sodium chloride and lysozyme-soidum nitride system. Modeling results where used to design an improved PDV with grooves. This device has been fabricated and is to be tested in the next phase of experiments. These two microfluidic devices together can be used together to determine and execute an optimized growth strategy for a given protein or a condition change. The PDV will give a general road map of the phase space that will be traveled using the CCC.