A new powder processing approach to produce oxidation resistant molybdenum alloys for high temperature use has been developed. Oxidation protection is provided by fine dispersion of silica glass particles within a molybdenum matrix. As the molybdenum oxidizes, the glass is exposed and melts to form a self-healing protective oxide coating. Additionally, homogeneously dispersed Mo5SiB2 and/or Mo2B provide boria upon oxidation which reduces glass viscosity and allows flowing glass to coat the surface while remaining solid internally. This is similar to the oxidation protection used in Mo-3Si-1B (wt%) systems; however embedding the glass directly into the Mo matrix and eliminating the Mo3Si (A15) phase provides the same volume of glass at lower volume fractions of brittle phases and also without embrittling Si impurities in solution in Mo. Additionally the glass composition can be tailored for different applications and different temperatures beyond that achievable in Mo-Si-B based systems. A variety of microstructures, compositions and additional components for improved oxidation protection are also explored, and mechanisms of the oxidation protection are discussed.

Out of the known refractory metals and alloys, molybdenum (Mo) and its alloys are very important due to their unique combination of properties which render them suitable for various applications. Owing to their good creep properties, minimum damage from neutron irradiation and good compatibility with the liquid alkali metals, molybdenum and its alloys are well suited candidates for structural components in the newly developed Compact High Temperature Reactor (CHTR). However, to fabricate components for structural application from molybdenum and its alloys, the processing response needs to be established. The present thesis is an attempt to address this issue in a more generic manner. The study have been specifically aimed to examine the hot deformation behaviour of molybdenum and two of its alloys (Mo-TZM and Mo-TZC) over a high temperature range, for obtaining stable microstructure with good mechanical properties. The thesis basically addresses the following (i) the thermos-mechanical response of the material with change in deformation conditions, and (ii) the evolution of microstructure during hot deformation, and identification of associated mechanisms. Chapter 1 of the thesis includes an introduction of the material system and alloys with a detailed survey of the literature on the deformation behaviour of refractory metals and alloys that are used as structural materials in nuclear reactors. More emphasis is given to molybdenum and two of its alloy Mo-TZM and Mo-TZC. Chapter 2 includes the detail of the experimental techniques and analysis procedures that are followed in the course of investigation. The hot deformation behaviour of molybdenum in temperature range 1400 - 1700°C and strain rate range 0.001 - 10.0s-1 is discussed in chapter 3. The stress - strain behaviour has been further analysed to obtain strain rate sensitivity maps. The micro-mechanisms operative in different deformation domain has been analysed extensively by Electron Back Scatter Diffraction (EBSD) technique. Different restoration processes which include dynamic recrystallization, recovery and grain growth have been identified in different domains of deformation conditions. Chapter 4 of this thesis is dedicated to the hot deformation behaviour of Mo-TZM alloy. Deformation behaviour was studied under identical conditions as molybdenum. Mo-TZM showed higher strain rate sensitivity and high temperature strength than molybdenum. Dynamic recovery is the most predominant mechanism in Mo-TZM alloy as revealed through the analysis of stress strain curve as well as EBSD based investigation. At higher temperature and strain rates dynamic recrystallization has also been observed. The effect of excess carbon which results in Mo-TZC alloy, deformation behaviour has been investigated in chapter 5. The analysis of stress – strain curves in this case indicates the predominance of dynamic recrystallization over a range of deformation conditions. The mechanism has been identified as particle simulated nucleation (PSN). The significant growth of the deformed grains is observed at the highest temperature of deformation. A comparison of deformation behaviour of alloying addition in molybdenum alloys has been discussed in chapter 6. The results of deformation behaviour of molybdenum and its alloys has been compared vis-a-vis with another similar class of alloys based on Niobium (Nb) and apparent similarities and differences in the deformation behaviour has also been discussed in chapter 6. Finally, the overall summary of the thesis has been presented in chapter 7.

Laser application in the field of biological and medical sciences has significantly grown, thereby strengthening the field of Biophotonics. Research conducted in Biophotonics focuses on the concept of using light especially in the visible and near infrared regions of the electromagnetic radiation for the evaluation of living systems. In this thesis new discoveries are presented about low level laser therapy, optical trapping, transmission spectroscopy, luminescence spectroscopy and structured illumination microscopy (SIM), displaying the impact each technique has on HIV infected cells. The results showed that the irradiation of HIV-1 infected TZM-bl cells with low power red laser reduces HIV-1 infection. The outcomes of this study further proved that when irradiation is used in conjunction with efavirenz, an antiretroviral drug, HIV-1 infection could be reduced to undetectable levels in TZM-bl cells. Through the coupling of transmission spectroscopy with optical trapping, and separately, use of luminescence spectroscopy, label free diagnosis of HIV in infected cell samples was achieved. This finding affirms that HIV-1 infection can be detected in a label free manner when using laser based techniques. Furthermore, the photoluminescence spectrometer system was employed to generate a decay curve, which was necessary so as to have some understanding on lifetime of the luminescent signal in infected TZM-bl cells. Finally, in order to confirm that indeed TZM-bl cells were infected, an established super-resolution microscopy system SIM was used to detect HIV-1 infection in TZM-bl cells. Indeed in the infected cells viral molecules p24 and gp41 were detected through SIM, while they were not detected in uninfected cells. In future studies, super resolution microscopy would be coupled to an optical trapping system in order to confirm that each trapped cells is whether infected or uninfected so as to improve HIV diagnosis. / College of Science, Engineering and Technology / Ph. D. (Science, Engineering and Technology)