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<p>Hydrogenated castor oil (HCO) crystals as a rheology modifier have been widely used in paints, cosmetics and household products. In this thesis, we are interested in the effect of crystal morphology on the suspension rheology of products. Three major types of micron-sized crystal morphologies have been observed: fiber, rosette and irregular crystal. Fibers show a high aspect ratio with the length ranging from 5 to 33 µm and width around 1~3 µm. The rosette (2~50 µm) is a three-dimensional spherulitic structure with nano-fibrous arms extruding from a heterogeneous central point. Irregular crystals with equivalent diameter ranging from 4 to 84 µm are hard solid and show irregular shapes. There is an additional fourth type of crystal morphology which is a nano-sized fibrous structure that is assumed to be broken down from arms of micron-sized rosettes and fibers. Due to the relatively small amount, the effects of nano-fibrous fragments on rheology were not considered separately in this work.</p> <p>The effect of temperature and shear history on the HCO crystal morphology has been studied. The energy barrier to nucleation for fibers is suggested to be higher than that of rosettes. Irregular crystals are thermodynamically less stable and tend to transform into stable polymorphs. A non-isothermal crystallization study showed that the formation of rosettes and fibers was favored by a slow cooling rate (1°C/min) while the formation of irregular crystals was favored by a fast cooling rate (5°C/min). Shear rates from zero to 100 s^-1 have been applied at cooling rates from 1°C/min to 5°C/min. Nucleation has been found to be promoted with the increase of shear rate. Morphological analysis indicated that the formation of fibers was favored by gentle shear (e.g., 1 s^-1), but fibers can be broken with the increase of shear time.</p> <p>Kinetics of isothermal crystallization of hydrogenated castor oil in water emulsions exhibiting multiple crystal morphologies has been studied in the temperature range of 55°C to 70°C. The induction time of nucleation increases with the increase of the isothermal temperature under which crystallization occurred. A linear increase in induction time with increased temperature was found for both fibers and rosettes. A modified Avrami model was developed by introducing the volume fraction of each type of morphology into three dimensional and one dimensional full Avrami models. It was found that the experimental trends for mixed crystal morphologies could be captured by the modified Avrami model.</p> <p>Due to the difficulty of obtaining samples with a single crystal morphology, rheological studies of suspensions containing mixtures of the three morphologies in a surfactant solution have been undertaken. The viscometry of dilute suspensions has shown that the magnitude of intrinsic viscosity is dominated by the fraction of a crystal morphology type, i.e. fiber > rosette > irregular crystal. A modified Farris model was fitted to the rheology data from mixtures of crystal morphology with interacting particles. A yield stress exists for concentrated suspensions followed by a shear thinning behavior with the increase of shear rate. A power-law relation has been found between yield stress and total particle volume fraction with a constant exponent of 1.5 regardless of crystal morphology.</p> / Doctor of Philosophy (PhD)

This thesis focuses on data-driven modeling and control of batch and batch-like processes. These processes are highly nonlinear and time-varying which, unlike continuous operations, are characterized by the finite duration of operation and absence of equilibrium conditions. This makes the modeling and control approaches available for continuous processes not readily applicable and requires appropriate adaptations of the available approaches to handle a) batch data structure for modeling and b) a control objective different than that of maintaining a steady-state operation as often encountered in a continuous process. With these considerations, this work adapted the batch subspace identification for modeling and control of a variety of batch and batch-like processes. A particular focus of this work was on the application of the proposed ideas on real engineering systems along with simulated case studies. The applications considered in this work are batch crystallization, a hydrogen plant startup dynamics in a collaboration with Praxair Inc. and a rotational molding process in collaboration with the polymer research group at McMaster University. For the seeded batch crystallization process, subspace identification techniques are adapted to identify a linear time invariant model for the, otherwise, infinite dimensional process. The identified model is then deployed in a linear model predictive control (MPC) strategy to achieve crystal size distribution (CSD) with desired characteristics subject to both manipulated input and product quality constraints. The proposed MPC is shown to achieve superior performance and the ability to respect tighter product quality constraints as well as robustness to uncertainty in comparison to an open loop policy as well as a traditional trajectory tracking policy using classical control. In another contribution, merits of handling data variety in a subspace identification framework was demonstrated on the crystallization process. The proposed approach facilitates the specification of a desired shape of the particle size distribution required at the termination of the batch process. Further, novel model validity constraints are proposed for the subspace identification based control framework. In the collaborative work on hydrogen plant startup, it is recognized as a batch-like process due to its similarity to batch processes. Firstly, in this work a high fidelity model of the Hydrogen unit was developed with relevant startup and shutdown mechanisms. This setup is used to mimic the trends in the key process variables during the startup/shutdown operation. The simulated data is used to identify a state-space model of the process and validated on new simulated startup. Further, the approach was demonstrated on real plant data from one of the Praxair's plants. The predictive capabilities of the model provide ample handle for the plant operator for averting failures and abrupt shutdown of the entire plant. This is expected to have immense economic advantages. Finally, the subspace identification based modeling and control approach was applied to a lab-scale rotational modeling (RM) process. It is a polymer processing technique that is characterized by the placement of a polymer resin inside a mold, subsequent closure of the mold, followed by the simultaneous application of uni-axial (as is the case in the present work) or bi-axial rotation and heat. The resin is deposited on the mold wall where it forms a dense unified layer following which, the mold is cooled while still rotating the mold. Once demolding temperatures are achieved, the finished part is removed from the mold. Its potential as a manufacturing process for polymeric components is limited by a number of concerns including difficulties in process control, in particular, determining efficiently the process operation to yield the desired product consistently, and produce new products. This work has contributed by developing optimal control strategies for the process to achieve user-specified product quality and reject variability across batches. The results obtained demonstrate the merits of the proposed approach. / Thesis / Doctor of Philosophy (PhD)

The lithium disilicate (LS2) glass system provides the basis for a large number of useful glass-ceramic products. Microwave processing of materials such as glass-ceramics offers unique benefits over conventional processing techniques. Variable frequency microwave (VFM) processing is an advanced processing technique developed to overcome the hot spot and the arcing problems in microwave processing. In general, two main questions are addressed in this dissertation: 1. How does microwave energy couple with a ceramic material to create heat? and, 2. Is there a "microwave effect" and if so what are the possible explanations for the existence of that effect? The results of the present study show that VFM processing was successfully used to crystallize LS2 glass at a frequency other than 2.45 GHz and without the aid of other forms of energy (hybrid heating). Crystallization of LS2 glass using VFM heating occurred in a significantly shorter time and at a lower temperature as compared to conventional heating. Furthermore, the crystallization mechanism of LS2 glass in VFM heating was not exactly the same as in conventional heating. Although LS2 crystal phase (Orthorhombic Ccc2) was developed in the VFM crystallized samples as well as in the conventionally crystallized samples as x-ray diffraction (XRD) confirmed, the structural units of SiO4 tetrahedra (Q species) in the VFM crystallized samples were slightly different than the ones in conventionally crystallized samples as the Raman spectroscopy revealed. Moreover, the observed reduction in the crystallization time and apparent temperature in addition to the different crystallization mechanism observed in the VFM process both provided experimental evidence to support the presence of the microwave effect in the LS2 crystallization process. Also, the molecular orbital model was successfully used to predict the microwave absorption in LS2 glass and glass-ceramic. This model was consistent with experiments and indicated that microwave-material interactions were highly dependent on the structure of the material. Finally, a correlation between the Fourier transform infrared reflectance spectroscopy (FTIRRS) peak intensities and the volume fraction of crystals in partially crystallized LS2 glass samples was established. / Ph. D.

The dissertation describes and assembles the building blocks for sound and accurate models for solid-state polymerization process systems of condensation polymers, particularly poly(ethylene terephthalate) and nylon-6. The work centers on an approach for modeling commercial-scale, as opposed to laboratory-scale, systems. The focus is not solely on coupled polymerization and diffusion, but extends to crystallization, physical properties, and phase equilibrium, which all enhance the robustness of the complete model. There are three applications demonstrating the utility of the model for a variety of real, industrial plant operations. One of the validated simulation models is for commercial production of three different grades of solid-state PET. There are also validated simulation models for the industrial leaching and solid-state polymerization of nylon-6 covering a range of operating conditions. The results of these studies justify our mixing-cell modeling approach as well as the inclusion of all relevant fundamental concepts. The first several chapters discuss in detail the engineering fundamentals that we must consider for modeling these polymerization process systems. These include physical properties, phase equilibrium, crystallization, diffusion, polymerization, and additional modeling considerations. The last two chapters cover the modeling applications. / Ph. D.

Poly (caprolactone) (PCL) has been widely studied as a model system for investigating polymer crystallization. In this thesis, PCL crystallization along with other phase transitions in PCL-based polymer blends are studied as Langmuir films at the air/water (A/W) interface. In order to understand the phase behavior of PCL-based blends, surface pressure induced crystallization of PCL in single-component Langmuir monolayers was first studied by Brewster angle microscopy (BAM). PCL crystals observed during film compression exhibit butterfly-shapes. During expansion of the crystallized film, polymer chains detach from the crystals and diffuse back into the monolayer as the crystals "melt". Electron diffraction on Langmuir-Schaefer films suggests that the lamellar crystals are oriented with the chain axes perpendicular to the substrate surface, while atomic force microscopy (AFM) reveals a crystal thickness of ~ 7.6 nm. In addition, the competition between lower segmental mobility and a greater degree of undercooling with increasing molar mass produces a maximum average growth rate at intermediate molar mass. PCL was blended with poly(t-butyl acrylate) (PtBA) to study the influence of PtBA on the morphologies of PCL crystals grown in monolayers. For PCL-rich blends, BAM studies reveal dendritic morphologies of PCL crystals. The thicknesses of the PCL dendrites are ~ 7-8 nm. BAM studies during isobaric area relaxation experiments at different surface pressure reveal morphological transitions from highly branched dendrites, to six-arm dendrites, four-arm dendrites, seaweedlike crystals, and distorted rectangular crystals. In contrast, PCL crystallization is suppressed in PtBA-rich blend films. For immiscible blends of PCL and polystyrene (PS) with intermediate molar masses as Langmuir films, the surface concentration of PCL is the only factor influencing surface pressure below the collapse transition. For PS-rich blends, both BAM and AFM studies reveal that PS nanoparticle aggregates formed at very low surface pressure form networks during film compression. For PCL-rich blends, small PS aggregates serve as heterogeneous nucleation centers for the growth of PCL crystals. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends). / Ph. D.

The phase behavior and phase separation kinetics in polymer solutions in binary mixtures of supercritical carbon dioxide (CO2) and organic solvents were studied for two systems. Solutions of polyethylene (PE) in CO2 + n-pentane were selected as one model system to study both the solid-fluid (S-F) and liquid-liquid (L-L) phase transitions as well as the interplay of these two types of phase separations on the final morphological and thermal properties of PE crystals. Solutions of polysulfone (PSF) in CO2 + tetrahydrofuran (THF) were selected as another model system because of the technological importance of this membrane forming polymer and because of the broad interest in developing new solvent/non-solvent systems for forming microporous materials. These phase boundaries were determined using a high-pressure view-cell and optical techniques over a temperature range of 90-165 oC and pressures up to 55 MPa for PE/n-pentane/CO2 system, and over a temperature range of 25 to 155 oC and pressures up to 70 MPa for PSF/THF/CO2 system. For PE solutions, it has been found that the addition of CO2 to the PE/n-pentane system shifts the L-L phase boundary to significantly higher pressures, but moves the S-F phase boundary only slightly to higher temperatures. The S-F phase boundary which represents the crystallization/melting process in the polymer solution was about 10 oC lower than the crystallization/melting temperatures of the neat polyethylene samples determined by differential scanning calorimetry (DSC). It was further found that the S-F phase boundary in n-pentane displays a unique sensitivity to the pressure-temperature conditions and moves to lower temperatures in the pressure range from 38 to 42 MPa. This effect even though not as augmented remains also for the S-F boundary in the solutions in CO2 + n-pentane mixtures. The miscibility of PSF in THF + CO2 was investigated at CO2 levels up to 14 wt %. This system shows lower critical solution temperature (LCST)-type phase behavior at low CO2 content, which is shifted to upper critical solution temperature (UCST)-type at higher CO2 levels along with an increase in the miscibility pressures. In contrast to the PE system, this system was found to display multiple miscibility windows. A "U"-shaped phase boundary in 92 % THF + 8 % CO2 mixture was observed to transfer to a "W"-shaped phase boundary at 10 wt % CO2, which was further separated into a double "U"-shaped phase boundary at 13 wt % CO2. The specific volume of the polysulfone solutions were found to display a variation parallel to this changing pattern in the phase boundaries, with reduced miscibility being accompanied with an increase in the specific volume. The phase separation kinetics in these two polymer solutions were investigated using time- and angle-resolved light scattering techniques. With the PE solutions, the focus was on the kinetics of S-F phase separation (crystallization) and miscibility and (melting) in n-pentane. Experiments were conducted with relatively dilute solutions at concentrations up to 2.3 wt %. The results show that the crystallization which was induced by cooling at constant pressure is dominated by a nucleation and growth process. In the majority of the experiments the particle growth process was observed to last for about 1 minute with a slight dependence on the crystallization pressure. The phase separation kinetics in PSF solutions were conducted only in a solvent mixture containing 90 wt % THF and 10 wt % CO2. Polymer concentrations were varied up to 3.3 wt %. This system was also observed to undergo phase separation by only nucleation and growth mechanism under these conditions upon reducing the pressure at constant temperature. Several experiments were conducted using a multiple rapid pressure drop technique to identify the depth of the metastable region. PE crystals that were produced by crossing the S-F boundary by different paths were collected and characterized by field emission scanning electron microscopy (FESEM) and DSC. Crystallization was carried out either by cooling at constant pressure, or by cooling without pressure adjustment, or by first crossing the L-L boundary via pressure reduction at a constant temperature followed by cooling. For crystal recovery, the system was depressurized to ambient conditions irrespective of the path. It was found that all of the crystals formed from these solutions show multiple melting peaks in their first DSC heating scans, which however collapse into one crystallization peak in the cooling scans and one melting peak in the second heating scans. The temperatures corresponding to the multiple melting peaks were lower than the single melting temperature of the original PE sample and the melting temperature observed in the second heating scans for all samples. The multiple melting peaks were attributed to the presence of different lamellar thickness that are formed in the crystallization, final depressurization and sample collection stages. Depending upon the crystallization path some differences were noted. The crystals formed by first going through L-L phase separation displayed predominately double melting peaks in the first DSC scan. It was observed that the overall crystallinity is increased by more than 10 % to about 75 % compared to the crystallinity of the original PE sample, which is about 63 %. FESEM characterization showed that the prevailing morphology is composed of plate-like lamellae that show different level of agglomeration depending on the crystallization conditions. The overall structures of the particles were ellipsoid for crystals formed from dilute solutions. For crystals formed from the 1% PE solution, crystal sizes ranged from 4 mm ´ 10 mm for crystals formed at 14 MPa to 30 mm ´ 45 mm at 45 MPa. The crystals formed from 5 wt % solutions in n-pentane at pressures in the range of 38-54 MPa showed different morphologies with features of shish-kebab like structures which were however absent in crystals formed from n-pentane + CO2 solutions. The crystals that were formed from first crossing the L-L phase boundary followed by cooling showed two distinct particle size ranges that were attributed to crystals formed from the polymer-rich and polymer-lean phases that evolve when the L-L phase boundary is crossed. / Ph. D.

Magnetic alloys that are amorphous exhibit soft magnetic properties; hence they play an essential role in electronic and electrical systems and devices. They are used in applications that include electrical power generation and transmission, electronic motors, solenoids, relays, magnetic shielding, and electromagnets. This work was an attempt to investigate the solid-state formation of Co-C amorphous alloys, their thermal stability and magnetic properties. Amorphous Co-C alloys with compositions of 2 to 40 at.% C were successfully synthesized from elemental Co and C (graphite) using mechanical alloying, a solid-state powder processing technique. All alloy compositions were milled for up 40 hours. After 20h of milling some of the alloys (≤ 20 at.% C) had partially amorphized, while the higher concentrations had completely amorphized. After 40h of milling, complete amorphization was observed in all alloys, except for the 2 and 5 at.% C alloys. The thermal analyses of the milled powders showed very interesting results. DSC results indicated that alloys with compositions through 20 at.% C crystalized in two steps; the lower temperature event precipitated metastable cobalt carbide from the amorphous phase, followed by the eventual transformation to fcc cobalt and graphite from both the remaining amorphous and the metastable carbide at the higher temperature. Two types of carbides were observed - Co3C in the 2 and 5 at.% C alloys, and Co2C in the higher carbon alloys through 20 at.% C. For compositions above 20 at.% C, only one step crystallization was observed, that of the decomposition of the amorphous phase to amorphous carbon and cobalt – primarily fcc phase. Activation energy calculations show that the low temperature carbide precipitation was controlled by carbon diffusion, while the high temperature decomposition reaction forming cobalt and amorphous carbon was controlled by cobalt diffusion. Room temperature magnetic measurements of the milled powders were made using vibrating sample magnetometer (VSM). High saturation magnetization (Ms) and very low coercivity (Hc) are desired for efficient performance of soft magnets. But in this study, Ms decreased with both carbon composition and milling time. It decreased from 195 Am2/kg for the un-milled pure Co to between 178 and 44 Am2/kg for the alloys, with the worst being the 40 at.% C sample milled for 40h. The Ms drop as function of composition made sense, as its related to the volume fraction of cobalt in the alloy. However, the Ms drop as a function of milling time is unclear. In the case of Hc, its value did drop from 12.7 kA/m for the un-milled pure Co to between 7.5 and 1.3 kA/m when the C content is less than 15 at.%. These gains are not significant enough to favor the use of these alloys as soft magnets. Amorphous metal alloys tend to have strengths that are much higher than their crystalline counterparts, and they have hardness values comparable to those of particulate ceramic materials used to reinforce metal matrices. The Co-C amorphous alloy with 40 at.% C that had been milled for 40h (the most stable of all the samples) was used to reinforce cobalt matrix by powder processing methods that included spark plasma sintering (SPS) at temperatures below those of crystallization. Volume fraction ranged from 1 to 20 % reinforcement. The densities of these composites were between 81 and 85 % of theoretical values, hence there were substantial porosities. Despite this the matrix strengthening of the cobalt matrix, as assessed by Vickers microhardness tests, was significant. Hardness increased from 210 HV for unreinforced matrix to 537 HV for the 20 vol.% amorphous. The primary contributor to the strengthening appears to be boundary strengthening by the particles whose average size of about 4 microns is comparable to the grain size of the matrices of the composites. The hardness data fits the Hall Petch-like relationship based on particle spacing. Having a reinforcement particle with a chemistry similar to that of the matrix as is the case in this study, has the potential to improve interfacial bonding and also minimize the difference between the components' coefficient of thermal expansions, which are major issues with the use of ceramics to reinforce metal matrices. The microstructures of the composites indicated good bonding at their interfaces. / Doctor of Philosophy / Magnetic alloys that are amorphous (have no long-range atomic order) exhibit soft magnetic material properties (easily magnetized and demagnetized); hence they play an essential role in electronic and electrical applications. This work investigated the solid-state formation of Cobalt-Carbon (Co-C) amorphous alloys, their thermal stability and magnetic properties. Amorphous Co-C alloys with compositions of 2 to 40 atomic weight % of C were successfully synthesized from elemental Co and C (as graphite) using a mechanical alloying technique (high-energy milling to alloy materials by impact). All alloy compositions were milled for up 40 hours. After 20h of milling some of the alloys (≤ 20 atomic weight % of C) had partially become amorphous, while the higher concentrations had completely become amorphous. After 40h of milling, complete amorphization was observed in all alloy compositions, except for the 2 and 5 atomic weight % of C alloys (2-5 atomic weight % of C). Thermal analyses (Differential Scanning Calorimetry, DSC) of the milled powders showed that alloys with compositions through 20 atomic weight % of C crystalized via a low temperature precipitation of a metastable cobalt carbide from the amorphous phase, followed by a high temperature transformation to a face centered cubic (fcc) cobalt and graphite phase from both the remaining amorphous and the metastable carbide. Activation energy calculations showed that the low temperature carbide precipitation was controlled by carbon diffusion, while the high temperature decomposition reaction forming cobalt and amorphous carbon was controlled by cobalt diffusion. High saturation magnetization (Ms) and very low coercivity (Hc) are desired for efficient performance of soft magnets. Thus, room temperature magnetic measurements of the milled powders were made using vibrating sample magnetometer (VSM). But in this study, Ms decreased with both carbon composition and milling time. The Ms drop as function of composition made sense, as its related to the volume fraction of cobalt in the alloy. However, the Ms drop as a function of milling time is unclear. In the case of Hc, its value did drop from 12.7 kA/m for the un-milled pure Co to between 7.5 and 1.3 kA/m when the C content is less than 15 atomic weight %. These gains are not significant enough to favor the use of these alloys as soft magnets. Amorphous metal alloys tend to have strengths that are much higher than their crystalline counterparts, and they have hardness values comparable to those of particulate ceramic materials used to reinforce metal matrices. The Co-C amorphous alloy with 40 atomic weight % of C that had been milled for 40h was used to reinforce cobalt matrix by powder processing methods (including spark plasma sintering (SPS) at temperatures below those of crystallization). The densities of these composites were between 81 and 85 % of theoretical values and hence there was substantial porosity. Despite this the matrix strengthening of the cobalt matrix, as assessed by Vickers microhardness tests, was significant. The primary contributor to the strengthening appeared to be boundary strengthening by the particles whose average size of about 4 microns was comparable to the grain size of the matrices of the composites. Having a reinforcement particle with a chemistry similar to that of the matrix has the potential to improve interfacial bonding and also minimize the difference between the components' coefficient of thermal expansions, which are major issues with the use of ceramics to reinforce metal matrices. The microstructures of the composites indicated good bonding at their interfaces.