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The development of quartz crystal microbalance based chemical sensorsDrake, Philip January 2000 (has links)
No description available.
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The computer simulation of dispersed two-phase flowHill, David Paul January 1998 (has links)
No description available.
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Studies of Ultrafast Relaxation and Photodissociation Processes in SolutionSalén, Peter January 2006 (has links)
<p>This thesis focuses on femtosecond studies of relaxation and photo-induced dissociation processes in the liquid environment. Measurements are performed using both polarization sensitive and magic angle transient absorption spectroscopy with excitation wavelengths of 387 nm and 258 nm and a white light continuum probe.</p><p>In the first three papers the photodissociation of the trihalides I<sub>3</sub><sup>-</sup> in acetonitrile and methanol as well as I<sub>2</sub>Br<sup>-</sup> in acetonitrile solution is investigated. These studies address such issues as the time scale for the production of the main photoproduct I<sub>2</sub><sup>-</sup>, rotational dynamics of the formed diatomic anions, the subsequent wavepacket dynamics of the coherently excited diiodide anion and vibrational relaxation in, and the geminate recombination of, the I<sub>2</sub><sup>- </sup>fragment. A nearly equal, bent geometry for the parent anion at the moment of bond breakage is proposed in all three solutions. However, the rotational temperature of the diiodide anion produced in the various solutions, reveals that motion along the bending coordinate of the dissociating triatomic anions plays an important role. The first signs of I<sub>2</sub><sup>-</sup> fragments can already be observed at delays of approximately 130 – 190 fs which indicates a faster dissociation than suggested in earlier publications. The production of I<sub>2</sub><sup>-</sup> seems fastest for I<sub>3</sub><sup>-</sup> in methanol, followed by I<sub>2</sub>Br<sup>-</sup> in acetonitrile and is slowest for I<sub>3</sub><sup>-</sup> in acetonitrile. It appears that vibrational relaxation of newly formed I<sub>2</sub><sup>-</sup> fragments happens on a short time scale of a few hundred femtoseconds from initially excited vibrational states centered around v = 60 to v = 20. This fast relaxation was never directly observed before in solution. After that it relaxes with a slower time constant of approximately 2 ps which is shorter than most former reported values. This biexponential behavior agrees well with earlier molecular dynamics simulations. The dependence of the dissociation product formation on excitation energy, parent anion and solvent is found to be relatively strong. These findings lead us to believe that the photo-induced dissociation of the triatomic anions I<sub>3</sub><sup>-</sup> and I<sub>2</sub>Br<sup>-</sup> in solution may very well resemble the gas phase process more than previously thought.</p><p>In paper IV electronic and vibrational relaxation rates of the cyanine dye Methyl-DOTCI are determined after excitation to high lying electronic states. The measurements are performed with two different excitation wavelengths and in various solvents. They reveal a fast electronic relaxation to the second excited electronic state which subsequently relaxes to the first excited electronic state with a time constant of about 10 ps. This relatively long relaxation time may partly be explained by the badly overlapping electronic wavefunctions obtained from theoretical calculations. Vibrational relaxation proceeds with a similar time constant of 10 ps but shows a marked solvent dependence with faster relaxation rates in alcohol solutions.</p>
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Studies of Ultrafast Relaxation and Photodissociation Processes in SolutionSalén, Peter January 2006 (has links)
This thesis focuses on femtosecond studies of relaxation and photo-induced dissociation processes in the liquid environment. Measurements are performed using both polarization sensitive and magic angle transient absorption spectroscopy with excitation wavelengths of 387 nm and 258 nm and a white light continuum probe. In the first three papers the photodissociation of the trihalides I3- in acetonitrile and methanol as well as I2Br- in acetonitrile solution is investigated. These studies address such issues as the time scale for the production of the main photoproduct I2-, rotational dynamics of the formed diatomic anions, the subsequent wavepacket dynamics of the coherently excited diiodide anion and vibrational relaxation in, and the geminate recombination of, the I2- fragment. A nearly equal, bent geometry for the parent anion at the moment of bond breakage is proposed in all three solutions. However, the rotational temperature of the diiodide anion produced in the various solutions, reveals that motion along the bending coordinate of the dissociating triatomic anions plays an important role. The first signs of I2- fragments can already be observed at delays of approximately 130 – 190 fs which indicates a faster dissociation than suggested in earlier publications. The production of I2- seems fastest for I3- in methanol, followed by I2Br- in acetonitrile and is slowest for I3- in acetonitrile. It appears that vibrational relaxation of newly formed I2- fragments happens on a short time scale of a few hundred femtoseconds from initially excited vibrational states centered around v = 60 to v = 20. This fast relaxation was never directly observed before in solution. After that it relaxes with a slower time constant of approximately 2 ps which is shorter than most former reported values. This biexponential behavior agrees well with earlier molecular dynamics simulations. The dependence of the dissociation product formation on excitation energy, parent anion and solvent is found to be relatively strong. These findings lead us to believe that the photo-induced dissociation of the triatomic anions I3- and I2Br- in solution may very well resemble the gas phase process more than previously thought. In paper IV electronic and vibrational relaxation rates of the cyanine dye Methyl-DOTCI are determined after excitation to high lying electronic states. The measurements are performed with two different excitation wavelengths and in various solvents. They reveal a fast electronic relaxation to the second excited electronic state which subsequently relaxes to the first excited electronic state with a time constant of about 10 ps. This relatively long relaxation time may partly be explained by the badly overlapping electronic wavefunctions obtained from theoretical calculations. Vibrational relaxation proceeds with a similar time constant of 10 ps but shows a marked solvent dependence with faster relaxation rates in alcohol solutions.
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Deposition and Applications of Titanium Oxide by Liquid Phase DepositionShih, Chung-min 15 July 2005 (has links)
Liquid Phase Deposited (LPD) TiO2 film technology and the characterization of films were described in detail in this thesis. The LPD-TiO2 film can be utilized in electrochromic, photocatalyst and gas sensor devices. The optimum parameters for deposition of LPD-TiO2 were studied.
First of all, we study the deposition properties and deposition parameter of LPD-TiO2 film. The effect of heating treatment on LPD-TiO2 film was investigated in this thesis. The as-deposited LPD-TiO2 film is amorphous and the TiO2 anatase phase can be obtained by annealing at 400 ¢J. The rutile phase can be observed at the annealing temperature of 900 ¢J. After annealing, the crystalling characteristic of LPD-TiO2 film can be improved and its refractive index can reach 2.46 annealed in O2 ambience. Its dielectric constant can be as high as 17 at annealing temperature of 700 ¢J in O2 ambience.
LPD-TiO2 film can deposit on GaAs substrate successfully. The GaAs was etched by the treatment solution during deposition. Therefore, Ga and As are contained in the LPD film. The C-V characterization can be improved at annealing 400 ¢J. But the leakage current increases with higher annealing temperature.
The electrochromic (EC) phenomena of TiO2 have been first reported by Inoue et al., where the films are prepared by hydrolysis of titanium tetraoxide. The film shows cathodic coloration and turns dark blue. The LPD-TiO2 film was deposited at 40 ¢J with (NH4)2TiF6 in the process of 0.1 M and 0.2 M boric acid. The films were transparent in the visible range and can be colored in a 1M LiClO4 + propylene carbonate solution. The deposition rate can be controlled quite well at 43 nm/hours. The 270 nm thickness LPD-TiO2 film gives the best electrochromic characteristic.
In order to further strength the feasibility and enlarge the application of LPD-TiO2 film. The characterizations of Nb, Au and Pt doped LPD-TiO2 film were investigated. The concentrations of Nb and Au in the film can be controlled by adjusting the concentrations of Nb and Au source solution added into the treatment solution, respectively. The Nb, Au and Pt species in the LPD-TiO2 film are Nb2O5, metallic Au and Pt(OH)x, respectively. The crystallite size of metal-doped LPD-TiO2 film is smaller than that of pure LPD-TiO2 film.
The photocalytic activities of undoped and Nb-doped LPD-TiO2 film were investigated. The photocatalytic activity of Nb-doped LPD-TiO2 film is about four times higher than that of pure LPD-TiO2 film.
The gas sensing properties of undoped and Nb, Au and Pt-doped LPD-TiO2 films were investigated for oxygen detection sensitivity. Experimental results show that the Nb-doped LPD-TiO2 film displays the highest in oxygen detection, and the Nb-doped LPD-TiO2 film has also a shorter response time.
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Influence of base alloy composition on processing time during transient liquid phase bonding of nickel-base superalloysHunedy, Juhaina 22 August 2013 (has links)
An experimental investigation to study the influence of base metal composition on the time required to achieve complete isothermal solidification (tf) during TLP bonding of three Ni-base superalloys was performed. Alloys IN 738, DS Rene80 and DS IC 6 show similar behaviour when bonded at 1100 oC, with comparable tf. However, at higher temperatures, IN 738 requires extended period of time (as compared to DS Rene80 and DS IC 6) to achieve complete isothermal solidification. The prolonged tf in IN 738 appears to be caused by a more pronounced reduction in concentration gradient of the diffusing solute within the material during bonding. In contrast, the shorter complete isothermal solidification time experienced by alloy DS IC6 is attributable to its capability to better accommodate the diffusing solute, through the formation of densely packed second-phase precipitates in the diffusion affected zone (DAZ).
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Influence of base alloy composition on processing time during transient liquid phase bonding of nickel-base superalloysHunedy, Juhaina 22 August 2013 (has links)
An experimental investigation to study the influence of base metal composition on the time required to achieve complete isothermal solidification (tf) during TLP bonding of three Ni-base superalloys was performed. Alloys IN 738, DS Rene80 and DS IC 6 show similar behaviour when bonded at 1100 oC, with comparable tf. However, at higher temperatures, IN 738 requires extended period of time (as compared to DS Rene80 and DS IC 6) to achieve complete isothermal solidification. The prolonged tf in IN 738 appears to be caused by a more pronounced reduction in concentration gradient of the diffusing solute within the material during bonding. In contrast, the shorter complete isothermal solidification time experienced by alloy DS IC6 is attributable to its capability to better accommodate the diffusing solute, through the formation of densely packed second-phase precipitates in the diffusion affected zone (DAZ).
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LIQUID PHASE EXFOLIATION OF 2D LAYERED MATERIALS AND THEIR APPLICATIONWinchester, Andrew 01 May 2014 (has links)
In this work, several materials possessing a layered structure were investigated using a technique of exfoliation in liquid phase to produce few- to mono-layers of the material. Materials exfoliated in such a way included graphite, boron nitride, molybdenum disulfide and tungsten disulfide. Subsequent transmission electron microscopy and accompanying electron diffraction patterns revealed that few and mono layer forms of these materials have been realized through this exfoliation method. Ultraviolet-visible spectroscopy confirmed the shifting of the band gaps in molybdenum and tungsten disulfides that is predicted in reducing the number of layers of these materials and was also used to confirm the band gap of the boron nitride. As a potential application, exfoliated molybdenum disulfide was used in the construction of electrodes for electrical charge storage in an electrochemical double layer capacitor, or supercapacitor, style device. Cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy measurements were performed using three different electrolytes, which showed good capacitive behavior for these devices. Using the data from electrochemical impedance spectroscopy, equivalent circuit models were generated to represent the systems in different electrolytes. From this, it was determined that the capacitive behavior of these systems was partially diffusion limited.
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Gamma Initiated Iodination of MethaneLim, Heng-Soo 02 1900 (has links)
<p> The use of gamma radiation
to initiate the iodination of methane in liquid
phase was studied using a semi-batch technique
whereby the methane was bubbling through a
column of iodine solution in a reactor. Yields
of CH3I and CH2I2 lower than 10% and G < 500
were obtained as contrasted with the 60% yield
and G=7xl0^7 reported in the gas-phase reaction.
In view of the propensity of the iodine as a radical scavenger and the
endothermic nature of the reaction, various
attempts to improve the low yields were carried
out. Results are eiven that indicate the
chances of achieving a laree G value for
liquid-phase reaction are very low even if the
operating conditions are optimized. </p> / Thesis / Master of Engineering (MEngr)
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Simultaneous Gas Absorption and Liquid Phase Chemical ReactionPang, Kwok-Hing 03 1900 (has links)
The present apparatus was used to obtain rate data for the absorption of oxygen in a catalysed liquid phase reaction with acetaldehyde. The effects of several system parameters, namely, acetaldehyde concentration, catalyst concentration, partial pressure of oxygen and temperature on the rate of absorption were studied. An attempt was made to correlate absorption rates and product distribution with mathematical models based on the film theory and existing kinetic models proposed by Bolland and Bawn. Absorption rates predicted by these semi-empirical correlations are compared with experimental values. The differential equations involving diffusion with chemical reaction were solved on the digital computer IBM 7040 and the analog computer PACE TRlO. / Thesis / Master of Engineering (MEngr)
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