Thesis (Ph. D.)--University of Florida, 1989. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 231-243).

Thesis (Ph. D.)--Columbia University, 1942. / Reproduced from type-written copy. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: p. 21-22.

Carbon-doped aluminium oxide, α-Al₂O₃ : C, is a highly sensitive luminescence dosimeter. The high sensitivity of α-Al₂O₃ : C has been attributed to large concentrations of oxygen vacancies, F and F⁺ centres, induced in the material during its preparation. The material is prepared in a highly reducing atmosphere in the presence of carbon. In the luminescence process, electrons are trapped in F-centre defects as a result of irradiation of the material. Thermal or optical release of trapped electrons leads to emission of light, thermoluminescence (TL) or optically stimulated light (OSL) respectively. The thermoluminescence technique is used to study point defects involved in luminescence of α-Al₂O₃ : C. A glow curve of α-Al₂O₃ : C, generally, shows three peaks; the main dosimetric peak of high intensity (peak II) and two other peaks of lower intensity called secondary glow peaks (peaks I and III). The overall aim of our work was to study the TL mechanisms responsible for secondary glow peaks in α-Al₂O₃ : C. The dynamics of charge movement between centres during the TL process was studied. The phototransferred thermoluminescence (PTTL) from secondary glow peaks was also studied. The kinetic analysis of TL from secondary peaks has shown that the activation energy of peak I is 0.7 eV and that of peak III, 1.2 eV. The frequency factor, the frequency at which an electron attempts to escape a trap, was found near the range of the Debye vibration frequency. Values of the activation energy are consistent within a variety of methods used. The two peaks follow first order kinetics as confirmed by the TM-Tstop method. A linear dependence of TL from peak I on dose is observed at various doses from 0.5 to 2.5 Gy. The peak position for peak I was also independent on dose, further confirmation that peak I is of first order kinetics. Peak I suffers from thermal fading with storage with a half-life of about 120 s. The dependence of TL intensity for peak I increased as a function of heating rate from 0.2 to 6ºCs⁻¹. In contrast to the TL intensity for peak I, the intensity of TL for peak III decreases with an increase of heating rate from 0.2 to 6ºCs⁻¹. This is evidence of thermal quenching for peak III. Parameters W = 1.48 ± 0:10 eV and C = 4 x 10¹³ of thermal quenching were calculated from peak III intensities at different heating rates. Thermal cleaning of peak III and the glow curve deconvolution methods confirmed that the main peak is actually overlapped by a small peak (labeled peak IIA). The kinetic analysis of peak IIA showed that it is of first order kinetics and that its activation energy is 1:0 eV. In addition, the peak IIA is affected by thermal quenching. Another secondary peak appears at 422ºC (peak IV). However, the kinetic analysis of TL from peak IV was not studied because its intensity is not well defined. A heating rate of 0.4ºCs⁻¹ was used after a dose of 3 Gy in kinetic analysis of peaks IIA and III. The study of the PTTL showed that peaks I and II were regenerated under PTTL but peak III was not. Various effects of the PTTL for peaks I and II for different preheating temperatures in different samples were observed. The effect of annealing at 900ºC for 15 minutes between measurements following each illumination time was studied. The effect of dose on secondary peaks was also studied in this work. The kinetic analysis of the PTTL intensity for peak I showed that its activation energy is 0.7 eV, consistent with the activation energy of the normal TL for peak I. The PTTL intensity from peak I fades rapidly with storage compared with the thermal fading from peak I of the normal TL. The PTTL intensity for peak I decreases as a function of heating rate. This decrease was attributed to thermal quenching. Thermal quenching was not observed in the case of the normal TL intensity. The cause of this contrast requires further study.

Heat pulse experiments have been made on Al₂O₃ single crystals in the temperature range 3.8° K to 35°K with the aim of gaining further insight into the nature of heat transport in solids at low temperatures. Short heat pulses were produced by heating a thin metal film evaporated on to one end of the crystal. The thermal pulse arriving at the other end of the crystal was detected by an indium film thermometer placed in a coil connected to a sensitive radio-frequency bridge, so that the variation of resistance was finally displayed on an oscilloscope. The pulses received at low temperatures (3.8°K to 8°K) show two quite separate parts, an initial sharp rise followed by a slow rise, starting at a definite delay time corresponding to the phonon velocity in the medium. The results up to 18°K do not show appreciable variation in delay time, showing that the heat pulse propagation has not entered a second sound region. As the temperature increases, the amplitude of the initial phonon pulse decreases very much compared with the amplitude of the slow rise. Above 18°K, the small sharp rise can no longer be seen clearly so that the delay time is no longer well defined, and at 30°K only the slow rise is observed. It is found that the conventional theory of heat conduction is inadequate to interpret our results at low temperatures, as it fails to predict the finite delay of the initial rise of the received pulse. A phenomenological approach is taken, using a modified heat equation which has an electrical transmission line analogy. Using Laplace transforms, a solution is obtained and the results calculated with a computer are compared with the experimental curves. It is found that the pulse shape can be interpreted quite satisfactorily, especially at the lowest temperatures. The thermal diffusivity, D, for different temperatures is found, and the apparent thermal conductivity, K, is calculated and compared with Herman's (1955) results. The solution of the modified heat equation is also calculated for liquid He II at 0.25°K and compared with the heat pulses observed by Kramers et al (1954); very good agreement is obtained. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Nanoporous alumina is a rather newly characterized material that so far has found limited use in the construction of bioreactors. The material has many advantages compared to conventional immobilization matrices. I have investigated its use in flow-through bioreactors. The rigidity and porous structure of the material makes it an excellent choice for multienzyme reactor construction. The total activity in a reactor is easily controlled by the number of membranes since the porosity makes the material less prone to increase flow system pressure. This bioreactor is suitable for characterization of new enzymes since the amount of immobilized enzyme is standardized and the enzyme may be reused many times. We designed a simple stepwise technique for covalent immobilization on this matrix in a monolayer to minimize mass transfer effects in the reactor function. The kinetic parameters for ten different substrates were investigated for immobilized alcohol oxidase and, as a second step, a two-step reactor was also designed by addition of horseradish peroxidase. This bienzymatic reactor was, in turn, employed for measuring injected alcohol concentrations. The use of the matrix for substrate specificity screening was proven for two new epsilon-class glutathione transferases from Drosophila melanogaster. Immobilized trypsin showed a substantially prolonged lifetime and its potential use as an on-line digestion unit for peptide mass fingerprinting was also demonstrated. Finally, I investigated the immobilization of the model enzyme lactate dehydrogenase by adsorption mediated by metal ion chelation similar to IMAC. Regeneration was here possible multiple times without loss of capacity. In conclusion, immobilization of enzymes on nanoporous alumina is a convenient way to characterize, stabilize and reuse enzymes.

Thesis (M.Sc.(Engineering)--University of the Witwatersrand, Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, 2012,. / The objective of this research was to improve alumina (Al2O3) mechanical and electrical properties by reinforcement using multi-walled carbon nanotubes (MWCNTs) and titanium carbide (TiC). The objective of the study was achieved with interesting and challenging difficulties along the way. The MWCNTs were initially coated with boron nitride (hBN) in order to improve the Alumina-CNTs interface which was previously discovered to be weak and also to protect them from reacting with Al2O3 during sintering. The coating of CNTs with hBN was done using nitridation method. This method was unsuccessful since it was not possible to coat each CNT individually. Dispersing hBN coated CNTs proved to be impossible without pealing the off the hBN coating. The “flaking off “of the hBN coating from the CNTs revealed that the CNT-hBN interface was weak; therefore uncoated CNTs were used for this study. The starting powders (Al2O3, TiC and CNTs) were individually dispersed before they were mixed together. TiC and Al2O3 were dispersed using an ultrasonic probe which was done successfully. The CNTs were dispersed by an ultrasonic probe and then attritor milled with the use of polyvinylpyrolidone (PVP) as a dispersant. The dispersed Al2O3 and TiC (30 wt%) powders were mixed in a planetary ball mill. The composite powder was sieved and sintered using SPS with temperature and pressure programmed to be 1700˚C, 35MPa respectively. In making the Al2O3+CNT composite powder, the already dispersed Al2O3 and CNTs (1 wt%) were mixed in a planetary ball mill, after sieving the powder it was sintered using SPS at 1600˚C, 35MPa (programmed conditions). Lastly in making the Al2O3+CNT+TiC composite, the already dispersed TiC, CNTs and Al2O3 were all mixed in a planetary ball mill, after sieving it was sintered using SPS at 1650˚C, 35MPa (programmed conditions). For comparison of properties, dispersed monolithic Al2O3 was also sintered using SPS at 1600˚C, 35 MPa. The density results showed that the monolithic Al2O3 was 99.8% dense, , Al2O3+CNTs was 99.4%, Al2O3+TiC+CNTs was 99.2% and Al2O3+TiC sample was 99.0%. The mechanical properties of the samples were measured using the indentation method. The hardness and fracture toughness of the samples were; Al2O3= 3.3MPa√m (17 GPa), Al2O3+CNTs = 4.2MPa√m (18 GPa), Al2O3+TiC = 4.8 MPa√m (23 GPa) and Al2O3+TiC+CNT= 5.0 MPa√m (23 GPa). The electrical properties showed that incorporating CNTs and TiC into Al2O3 improved Al2O3 electrical conductivity. The measured electrical conductivity of the ceramic samples were; Al2O3 iii ≈ 0 Sm-1, Al2O3+CNTs= 30 S.m-1, Al2O3 +TiC + CNTs = 6855 S.m-1 and Al2O3+TiC = 9664 S.m-1. The CNTs improved Al2O3 mechanical properties slightly inhibiting grain growth by pinning the grain boundary movement and also by crack bridging. The Al2O3 electrical conductivity was increased by the CNTs network that was located along the alumina grain boundaries. The TiC improved Al2O3 mechanical properties slightly inhibiting grain growth and through crack deflection mechanism. The addition of TiC into Al2O3 increased the electrical conductivity by serving as a conducting continuous secondary phase. The results show that the CNT-hBN interface is weak. The addition of CNTs and TiC into monolithic Al2O3 slightly improved its mechanical and electrical properties but it density was slightly compromised. CNTs and TiC slightly improved monolithic alumina hardness by in inhibiting Al2O3 grain growth and the fracture toughness through crack deflection and crack bridging mechanisms. The CNTs network located at the Al2O3 grain boundaries not only aided in improving Al2O3 hardness but also served as transport medium for electrons hence increasing the Al2O3 electrical conductivity. Addition of TiC into Al2O3 increased its electrical conductivity by conducting electrons from one TiC grain to the adjacent grain. The large increase in electrical conductivity upon addition of TiC is due to the presence of a continuous TiC phase within Al203.

Thesis (Ph. D.)--Uppsala universitet, 2006. / Description based on contents viewed Feb. 5, 2007; title from title screen. Includes bibliographical references (p. 53-57).

In this thesis, the growth and fabrication of the self-assembly ordered porous alumina have been investigated. First, well-ordered honeycomb array can be obtained in large area under well-anodizing condition. The diameter of formed porous alumina was about 40 to 80 nm. Pore diameter can be tuned by different voltage and electrolyte. After we got such an ordered-arrangement porous alumina array, the following analysis of the material optical properties were characterized. In the luminescence behavior, photoluminescence (PL) measurements showed a strong PL peak in blue. The PL peak was at 420 nm excited by He-Cd laser. Material transmittance was also detected, the result showed that material was transparent above 400 nm. On the other hand, the porous alumina membrane can be used as a mask. For working as negative mask, we evaporated the metal such as Au or Ti into the membrane and the metal filled into the porous to adhere to the semiconductor substrate. After lifting-off the membrane, the metal nanadots was formed on the substrate. The size and the position of these metal nanodots were distinctly-controlled by the mask. For working as replica mask, we have used the membrane as an etching mask to transfer the pattern to the semiconductor substrate successfully. This technique has the advantages of low cost and large area for nano-fabrication.