by Lam King Shun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (p. 103-107). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / by Lam King Shun.

Heavy metals and hydrocarbons are persistent pollutants in the environment. Problems associated with the cleanup of sites contaminated by metals and hydrocarbons have demonstrated the need to develop remediation technologies that are feasible, quick, and effective in a wide range of physical settings. Experiments were conducted to investigate the efficiency of silica encapsulation and the factors that influence its performance. Analysis was done by ICP-OES and GC-FID for metals and hydrocarbons respectively. This technology was tested using sodium silicate and ChemcapTM. Soils and water contaminated with hydrocarbons and heavy metals were successfully remediated by silica encapsulation. The silica coating was stable under both acidic and alkaline conditions. A new product that is based on sodium silicate formulation was developed and was more effective at encapsulating hydrocarbons and heavy metals. Laboratory tests indicated that it is more effective in an acidic medium and it continues to strengthen with time. Metal encapsulation was affected by the sizes of metal ions and the presence of hydrocarbons.

Silica is one of the most abundant elements on the planet, has flexible bonding properties and generally excellent stability. Because of these properties, silica has been a vital component in technologies ranging from ancient glassware to modern supercomputers. Silica is able to form a wide range of materials both alone and as a component of larger material frameworks. Porous silica based nanomaterials are rapidly growing in importance because of their many applications in a wide variety of fields. This thesis focuses on the synthesis of silica based porous nanomaterials: nanocrystalline zeolites, mesoporous silica nanoparticles, and iron oxide core/shell nanocomposites. The synthetic conditions of these materials were varied in order to maximize efficiency, minimize environmental impact, and produce high quality material with far reaching potential applications. The materials were characterized by physicochemical techniques including Transmission Electron Microscopy, Dynamic Light Scattering, Powder X-Ray Diffraction, Solid State NMR, and Nitrogen Adsorption Isotherms. The materials were evaluated and conditions were controlled to produce high yields of quality nanomaterials and hypothesize methods for further synthetic control. The products will be used in studies involving nanoparticle toxicity, environmental remediation, and drug delivery.

No description available.

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a timeconsuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. The above two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The composite fouling experiments were performed in a novel closed-loop circulation system simulating the effect of feed composition of successive stages of evaporation cycle in a single run. In addition, the fouling-loop system was operated in a constant composition mode to study the effects of thermal hydraulic conditions on composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2. Some of the highlights of the obtained results are as follows: ??? Identification of a complex interactive process in calcium oxalate monohydrate ??? silica (COM-SiO2) systems by investigation of the kinetics and thermodynamics of COM-SiO2 coprecipitation in water and sugar solutions, and an understanding of the mechanisms of these interactions; ??? Development of a novel fouling-loop system, which is simple, efficient and cost effective for the study of the effect of juice composition on scale formation in various stages of juice evaporation; ??? Elucidation of composite fouling mechanisms, e.g., a feed composition dependent fouling mechanism is proposed; ??? Isolation and verification of the existence of certain species in composite deposits, which is known to be thermodynamically unstable. In other words, it is established that calcium oxalate trihydrate is stable under certain conditions; ??? Evaluation of the role of thermal hydraulic operating parameters in determining the characteristics of subcooled flow boiling heat transfer and in determining the strength of the composite deposit; ??? Development and validation of an empirical model to predict the subcooled flow boiling heat transfer coefficients in water and sugar solutions; ??? Development of an analytical model incorporating the effects of operating parameters for COM and SiO2 composite fouling in sugar solutions. This model predicted the experimental data better than available models. Results of this work are significant, not only because they have made a valuable contribution to advance the fundamental understanding of heat exchanger fouling, but also because they may play a key role in the development of scale control and removal strategies to minimize the composite fouling in Australian sugar mill evaporators. For example it was found that, in order to effectively minimize the rate of composite fouling and reduce the scale tenacity, it would be necessary to control thermal hydraulic operating conditions, especially the fluid velocity, and to adjust the initial CaOx/SiO2 supersaturation ratio to the optimum value. To achieve the optimal CaOx/SiO2 ratio, certain device can be developed to sequentially measure oxalic acid and SiO2 concentrations in juice so that the correct proportions of chemicals can be added. Model simulations of the composite fouling rate may also effectively and economically provide comparative and relevant information essential for process optimisation and evaporator design

The present research is focused on investigating particle interactions between valuable and gangue materials, and the effect of these interactions on selectivity in flotation. This is a very important issue to operations at several mines across the world (e.g., at Century Mine operated by Zinifex Ltd in Australia). Particle interactions between valuable and gangue minerals with subsequent aggregation have significant impact on flotation performance. Valuable minerals may be depressed if heavily covered with hydrophilic gangue minerals and/or gangue minerals may misreport to the concentrate.

This thesis presents a study of applications and techniques for molecular dynamics simulations. Three studies are presented that are intended to improve our ability to simulate larger systems more realistically. A comparison study of two- and three-body potential models for liquid and amorphous Si0��� is presented. The structural, vibrational, and dynamic properties of the substance are compared using two- and three-body potential energy models against experimental results. The three-body interaction does poorly at reproducing the experimental phonon density of states, but better at reproducing the Si-O-Si bond angle distribution. The three-body interaction also produces much higher diffusivities than the two-body interactions. A study of tabulated functions in molecular dynamics is presented. Results show that the use of tabulated functions as a method for accelerating the force and potential energy calculation can be advantageous for interactions above a certain complexity level. The decrease in precision due to the use of tabulated functions is negligible when the tables are sufficiently large. Finally, an investigation into the benefits of multi-threaded programming for molecular dynamics is presented. / Graduation date: 1999

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Dionisios G. Vlachos and Raul F. Lobo, Dept. of Chemical Engineering Includes bibliographical references.

The undesirable expansion of concrete because of a reaction between alkalis and certain type of reactive siliceous aggregates, known as alkali-silica reactivity (ASR), continues to be a major problem across the entire world. The renewed interest to minimize distress resulting from ASR has emphasized the need to develop predictable modeling of concrete ASR behavior under field conditions. Current test methods are either incapable or need long testing periods in which to only offer rather limited predictive estimates of ASR behavior in a narrow and impractical band of field conditions. Therefore, an attempt has been made to formulate a robust performance approach based upon basic properties of aggregate and concrete ASR materials derived from dilatometry and a kinetic-based mathematical expressions for ASR behavior. Because ASR is largely an alkali as well as a thermally activated process, the use of rate theory (an Arrhenius relationship between temperature and the alkali solution concentration) on the dilatometer time-expansion relationship, provides a fundamental aggregate ASR material property known as “activation energy.” Activation energy is an indicator of aggregate reactivity which is a function of alkalinity, particle size, crystallinity, calcium concentration, and others. The studied concrete ASR material properties represent a combined effects of mixture related properties (e.g., water-cementitious ratio, porosity, presence of supplementary cementitious materials, etc.) and maturity. Therefore, the proposed performance-based approach provides a direct accountability for a variety of factors that affect ASR, such as aggregate reactivity (activation energy), temperature, moisture, calcium concentration, solution alkalinity, and water-cementitious material ratio. Based on the experimental results, the following conclusion can be drawn concerning the performance-based approach to evaluate ASR potential of aggregate and concrete using dilatometer method; (i) the concept of activation energy can be used to represent the reactivity of aggregate subjected to ASR, (ii) the activation energy depends on the reactivity of aggregate and phenomenological alkalinity of test solution, and (iii) The proposed performance-based model provides a means to predict ASR expansion development in concrete.

Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology. In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques. In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.</p>