Experimental studies were undertaken to improve the radiation dose response and ease of manufacture of polymer gel dosimeters that use N-isopropyl acrylamide (NIPAM) as the monomer. An alternative carageenan gelling agent was tested in place of gelatin. Although the carageenan did reduce the gelling time for the dosimeter solution, the dose response of the dosimeters was unsatisfactory. An alternative antioxidant system, ascorbic acid and Cu2+, was investigated with the aim of reducing the toxicity of dosimeter materials and providing opportunities for commercial production of prepackaged dosimeter kits. Unfortunately, the new antioxidant was ineffective for the NIPAM-based dosimeters that were studied. Three cosolvents, glycerol, N-propanol and isopropanol, were used to increase the solubility of N,N’-methylene-bisacrylamide (Bis) crosslinker in polymer gel dosimeter recipes that use NIPAM. These cosolvents enabled the manufacture of polymer gel dosimeters with higher levels of dissolved crosslinker than was previously possible. Preliminary results using x-ray computed tomography to read the resulting gels are very promising, due to enhancements in dose sensitivity. Dosimeters with high N,N’-methylene-bisacrylamide content that used isopropanol or glycerol as cosolvents had good optical clarity prior to irradiation, but did not produce reliable optical CT results for non-uniformly-irradiated gels. Further experiments and recipe optimization are required to determine whether gels with cosolvents and high levels of N,N’-methylene bisacrylamide can be used effectively for verifying spatially non-uniform dose distributions using x-ray computed tomography. A mathematical model that includes inhibition of NIPAM-Bis polymerization was developed and the inhibition effects of MEHQ and oxygen in polymer gel dosimeters were simulated. Kinetic parameters were obtained from the literature and were estimated using experimental data obtained by our research group. Good agreement was obtained between model predictions and experimental data with and without oxygen contamination. Simulation results indicate that MEHQ has little influence on the duration of the inhibition period and the rate of polymerization when no oxygen contamination is present, so that removal of MEHQ from dosimeter recipes is not required. Effective oxygen removal is very important to achieve reliable dosimeter results. / Thesis (Master, Chemical Engineering) -- Queen's University, 2008-12-16 15:59:14.034

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Sandstone acidizing is a complex operation because the acidizing fluid reacts with a variety of minerals present in the formation that results in a wide range of reaction products. The hydrofluoric acid (HF) reaction rate differs widely from mineral to mineral because of the variation in the reaction rate and the area of contact with the injected fluid. The series of reactions occurring in sandstone makes it all the more difficult to find the exact individual reaction rate constants. An improved model that provides better estimates of the outcome of a sandstone acidizing treatment is developed following a review of previous sandstone acidizing models. The model follows the lumped mineral methodology and is based mainly on the kinetic approach. The use of accurate reaction-rate laws allows the model to effectively predict the consumption of acidizing fluid during the stimulation treatment. The consideration of a proper equation for the silica gel filming factor accounts for the fact that some clay becomes inaccessible to the acid when silica gel precipitates on their surface. The proposed model is shown here to be valid in extrapolating laboratory coreflood data and predicting the effluent acid concentration at various flow rates. The damage during sandstone acidizing can be minimized when stimulation treatments are designed according to the percentage of carbonate in the formation, type and amount of clay in the formation and the reservoir bottomhole temperature. Most of the available software for design and evaluation of acidizing treatments do not consider the temperature and mineralogy effects extensively. We studied one such software and developed recommendations to improve the design and evaluation of sandstone acidizing treatments by taking into account the multifaceted effects of temperature and mineralogy in increasingly deep and hot sandstone environments. These recommendations will be of great use in the times to come as most of the wells will have to be drilled at greater depths in search for new reserves.

Surface modification is a process that is applied to the surfaces of titanium substrates in order to improve the biocompatibility after implanting in the body. Two methods were used in the present work: Anodisation and gel oxidation. Anodisation was performed at room temperature in strong mineral acids (sulphuric acid (H2SO4) and phosphoric acid (H3PO4)), an oxidising agent (hydrogen peroxide (H2O2)), mixed solutions of the preceding three, and a weak organic acid mixture (β-glycerophosphate + calcium acetate). The parameters used in anodisation were: Concentrations of the electrolytes, applied voltage, current density, and anodisation time. Gel oxidation was carried out by soaking titanium substrates in sodium hydroxide (NaOH) aqueous solutions at different concentrations (0.5 M, 1.0 M, 5.0 M, and 10.0 M) at 60??C for 24 h, followed by oxidation at 400??, 600??, and 800??C for 1 h. Conceptual models representing changes in the microstructure as a function of the experimental parameters were developed using the anodisation data. The relevant parameters were: Applied voltage, current density, acid concentration, and anodisation time: ?? The model for anodisation using the strong acid (H2SO4) illustrates the growth rate of the film, identification of the threshold for the establishment of a consistent microstructure, and prediction of the properties of the film. ?? For the oxidising agent (H2O2), two models were developed: Current-control and voltage-control, the applicability of which depends on the scale of the current density (high or low, respectively). These models are interpreted in terms of the coherency/incoherency of the corrosion gel, arcing, and porosity. ?? The model for the strongest acid (H3PO4) is similar to that of H2O2 in current-control mode, although this system showed the greatest intensity of arcing and consequent pore size. ?? Anodisation in mixed solutions uses Ohm??s law to explain four stages of film growth in current-control mode. These stages describe the thickness of the gel, its recrystallisation, and the achievement of a consistent microstructure. ?? Anodisation in weaker organic acids allows the most detailed examination of the anodisation process. Both current density and voltage as a function time reveal the nature of the process in six stages: (1) instrumental response, (2 and 3) gel thickening, (4) transformation of the amorphous gel to amorphous titania, (5) recrystallisation of the amorphous titania, and (6) subsurface pore generation upon establishment of a consistent microstructure. Gel oxidation was done at low and high NaOH concentrations followed by oxidation. Three models were developed to represent the gel oxidation process: (1) Low concentration, (0.5 M and 1.0 M NaOH), (2) Medium concentration (5.0 M NaOH), and (3) high concentration (10.0 M NaOH). For the low concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase and (2) a dense layer of rutile forms. For the high concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase, (2) a dense layer of anatase forms and raises up the existing porous anatase layer, and (3) the dense and porous anatase layers transform to dense and porous rutile layers, respectively. The main difference between the two is the retention of crystalline sodium titanate in the higher NaOH concentration. Anodised and gel oxidised samples subsequently were soaked in simulated body fluid in order to study the precipitation of hydroxyapatite in the absence and presence of long UV irradiation, which has not been investigated before. With the anodised surfaces, the porous and rough titania coating facilitated both the precipitation of hydroxyapatite and the attachment of bone-like cells. UV irradiation showed greatly enhanced hydroxyapatite precipitation, which is attributed to its photocatalytic properties. With the gel oxidised surfaces, the greatest amount of hydroxyapatite precipitation occurred with the presence of both anatase and amorphous sodium titanate. Rutile suppressed precipitation.

Surface modification is a process that is applied to the surfaces of titanium substrates in order to improve the biocompatibility after implanting in the body. Two methods were used in the present work: Anodisation and gel oxidation. Anodisation was performed at room temperature in strong mineral acids (sulphuric acid (H2SO4) and phosphoric acid (H3PO4)), an oxidising agent (hydrogen peroxide (H2O2)), mixed solutions of the preceding three, and a weak organic acid mixture (β-glycerophosphate + calcium acetate). The parameters used in anodisation were: Concentrations of the electrolytes, applied voltage, current density, and anodisation time. Gel oxidation was carried out by soaking titanium substrates in sodium hydroxide (NaOH) aqueous solutions at different concentrations (0.5 M, 1.0 M, 5.0 M, and 10.0 M) at 60??C for 24 h, followed by oxidation at 400??, 600??, and 800??C for 1 h. Conceptual models representing changes in the microstructure as a function of the experimental parameters were developed using the anodisation data. The relevant parameters were: Applied voltage, current density, acid concentration, and anodisation time: ?? The model for anodisation using the strong acid (H2SO4) illustrates the growth rate of the film, identification of the threshold for the establishment of a consistent microstructure, and prediction of the properties of the film. ?? For the oxidising agent (H2O2), two models were developed: Current-control and voltage-control, the applicability of which depends on the scale of the current density (high or low, respectively). These models are interpreted in terms of the coherency/incoherency of the corrosion gel, arcing, and porosity. ?? The model for the strongest acid (H3PO4) is similar to that of H2O2 in current-control mode, although this system showed the greatest intensity of arcing and consequent pore size. ?? Anodisation in mixed solutions uses Ohm??s law to explain four stages of film growth in current-control mode. These stages describe the thickness of the gel, its recrystallisation, and the achievement of a consistent microstructure. ?? Anodisation in weaker organic acids allows the most detailed examination of the anodisation process. Both current density and voltage as a function time reveal the nature of the process in six stages: (1) instrumental response, (2 and 3) gel thickening, (4) transformation of the amorphous gel to amorphous titania, (5) recrystallisation of the amorphous titania, and (6) subsurface pore generation upon establishment of a consistent microstructure. Gel oxidation was done at low and high NaOH concentrations followed by oxidation. Three models were developed to represent the gel oxidation process: (1) Low concentration, (0.5 M and 1.0 M NaOH), (2) Medium concentration (5.0 M NaOH), and (3) high concentration (10.0 M NaOH). For the low concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase and (2) a dense layer of rutile forms. For the high concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase, (2) a dense layer of anatase forms and raises up the existing porous anatase layer, and (3) the dense and porous anatase layers transform to dense and porous rutile layers, respectively. The main difference between the two is the retention of crystalline sodium titanate in the higher NaOH concentration. Anodised and gel oxidised samples subsequently were soaked in simulated body fluid in order to study the precipitation of hydroxyapatite in the absence and presence of long UV irradiation, which has not been investigated before. With the anodised surfaces, the porous and rough titania coating facilitated both the precipitation of hydroxyapatite and the attachment of bone-like cells. UV irradiation showed greatly enhanced hydroxyapatite precipitation, which is attributed to its photocatalytic properties. With the gel oxidised surfaces, the greatest amount of hydroxyapatite precipitation occurred with the presence of both anatase and amorphous sodium titanate. Rutile suppressed precipitation.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 139-148). Also available via World Wide Web.

Thesis (Ph. D.)--Ohio University, March, 1995. / Title from PDF t.p.