No description available.

No description available.

No description available.

A series of derivatives of the brominated alcohol 3-bromo-2,2- bis(bromomethy 1)-1 -propanol were prepared with a view to eventual use of such derivatives as flame retardants. The derivatives took the form of alkoxide compounds of main group elements, except for a few compounds of non-main group elements, which were added for their known application in the flame retardant field. Many of these derivatives were liquids at room temperature, so were of limited use for flame retarding polymers etc., but were of interest due to the trends shown in their spectra. Of the solid derivatives, the fully substituted monomeric boron and silicon compounds were tested by high temperature DSC & TGA techniques. The silicon derivative showed potential for application in ABS-type polymers, and would be worthy of further study. The simple orthoborate did not perform as well. The other solid species produced were tested by DSC to 400 C and the results reviewed. Derivatives of the brominated diol 2,2-bis(bromomethyI)-l,3- propanediol were also prepared, with the same aim. Some reactions of tetrahydroborate with 1,2-dihydroxybenzene or sulphur were studied. The spirocyclic bisdiol borate anion was successfully prepared via this route, although the target of the monodioldihydro species was not formed. The reactions with sulphur were aimed at producing an active borane-type species, but were also of interest for the structural problems they raised. No definite conclusions were reached regarding the product of these reactions, however. Some work was also performed on a novel route to carboranes by reacting a carbene with a borane anion. The preliminary reactions did not indicate the presence of any carborane species.

No description available.

The project synthesizes phase pure Yttria particles using flame spray pyrolysis, and to experimentally determines the effect of various process parameters like residence time, adiabatic flame temperature and precursor droplet size on the phase of Yttria particles generated. Further, through experimentation and based on the understanding of the process, conditions that produce pure monoclinic Y2O3 particles were found. An ultrasonic atomization set-up was used to introduce precursor droplets (aqueous solution of yttrium nitrate hex hydrate) into the flame. A hydrogen-oxygen diffusion flame was used to realize the high temperature aerosol synthesis. The particles were collected on filters and analyzed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Individual process parameters (flame temperature, residence time, precursor concentration, precursor droplet size) were varied in continuous trials, keeping the rest of the parameters constant. The effect of the varied parameter on the phase of the product Yttria particles was then analyzed. Pre-flame heating was undertaken using a nozzle heater at variable power. Precursor solution concentrations of 0.026 mol/L, 0.26 mol/L, and 0.65 mol/L were used. Residence time was varied by means of burner diameter (9.5 mm and 1.6 mm ID). Large precursor droplets were removed by means of an inertial impactor. The higher flame temperatures and precursor heating favor the formation of monoclinic yttrium oxide. The fraction of the cubic phase is closely related to the particle diameter. All particles larger than a critical size were of the cubic phase. Phase pure monoclinic yttrium oxide particles were successfully synthesized. The end conditions included a precursor concentration of 0.65 mol/L, a pure hydrogen-oxygen flame and a 1.6 mm burner. The precursor droplets entrained fuel gas was passed through a round jet impactor and preheated at full power (130 VA). The particles synthesized were in the size range of 0.350 to 1.7 µm.

Techniques have been developed for measuring the temperature, stable species concentrations, and atomic radical concentrations during a transient combustion event. They combine the features of direct sampling with two spectroscopic techniques to produce relatively simple diagnostic techniques to obtain time-resolved measurements. In this study, a transient event was provided by a propagating hydrogen/air flame. Stable species were detected downstream of the sampling orifice by electron impact fluorimetry, while temperatures and atomic hydrogen concentrations were measured by atomic resonance absorption spectroscopy. The calculation of stable species concentrations from time-varying fluorescence signals was straightforward, however conversion from absorption measurements to temperatures and atomic radical concentrations required the development of a computer model of the radiation source and the absorption by the sample. The model of the source was validated by comparing predicted and recorded spectra of hydrogen Lyman-α emissions, while the absorption model for the sampled gas was tested by comparing the temperatures predicted by absorption measurements with those recorded at a range of known temperatures. These direct sampling spectroscopic techniques minimize time-history distortions inherent in other direct sampling techniques, and are capable of tracking local temperatures and species concentrations during the passage of a propagating flame front. / Graduation date: 1990

The project synthesizes phase pure Yttria particles using flame spray pyrolysis, and to experimentally determines the effect of various process parameters like residence time, adiabatic flame temperature and precursor droplet size on the phase of Yttria particles generated. Further, through experimentation and based on the understanding of the process, conditions that produce pure monoclinic Y2O3 particles were found. An ultrasonic atomization set-up was used to introduce precursor droplets (aqueous solution of yttrium nitrate hex hydrate) into the flame. A hydrogen-oxygen diffusion flame was used to realize the high temperature aerosol synthesis. The particles were collected on filters and analyzed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Individual process parameters (flame temperature, residence time, precursor concentration, precursor droplet size) were varied in continuous trials, keeping the rest of the parameters constant. The effect of the varied parameter on the phase of the product Yttria particles was then analyzed. Pre-flame heating was undertaken using a nozzle heater at variable power. Precursor solution concentrations of 0.026 mol/L, 0.26 mol/L, and 0.65 mol/L were used. Residence time was varied by means of burner diameter (9.5 mm and 1.6 mm ID). Large precursor droplets were removed by means of an inertial impactor. The higher flame temperatures and precursor heating favor the formation of monoclinic yttrium oxide. The fraction of the cubic phase is closely related to the particle diameter. All particles larger than a critical size were of the cubic phase. Phase pure monoclinic yttrium oxide particles were successfully synthesized. The end conditions included a precursor concentration of 0.65 mol/L, a pure hydrogen-oxygen flame and a 1.6 mm burner. The precursor droplets entrained fuel gas was passed through a round jet impactor and preheated at full power (130 VA). The particles synthesized were in the size range of 0.350 to 1.7 µm.

The purpose of this study was to investigate the thermochemical properties of a transient supersonic flame. Creation of the transient flame was controlled by pulsing air in 200 millisecond intervals into a combustor filled with flowing methane. The combustor was designed following well-known principles of jet engine combustors. A flame holder and spark plug combination was used to encourage turbulent mixing and ignition of reactant gases, and to anchor the transient flame. Combustion created a high temperature and pressure environment which propelled a flame through a choked de Laval nozzle. The nozzle accelerated the products of combustion to a Mach number of 1.6, creating an underexpanded transient flame which burned for approximately 25 milliseconds. Qualitative information of the flame was gathered by two optical systems. An intensified charge-coupled device (ICCD) was constructed from constitutive components to amplify and capture the chemiluminescence generated by the transient flame, as well as the spatial structure of the flame at specific phases. To gather temporal data of a single transient event as it unfolded, a z-type schlieren optical system was constructed for use with a high speed camera. The system resolves the data in 1 millisecond increments, sufficient for capturing the transient phenomenon. The transient system was modeled computationally in Cantera using the GRI-3.0 reaction mechanism. Experimental conditions were simulated within the zero- dimensional computation by explicit control of the reacting gas mass flow rates within the system. Results from the computational model were used to describe the ignition process. The major limitation of the zero-dimensional reactor model is homogeneity and lack of spatial mixing. In this work a Lagrangian tracking model was used to describe the flame behavior and properties as it travels within the zero-dimensional reactor towards the nozzle. Following this, the flow expansion through the de Laval nozzle was calculated using one-dimensional isentropic relations. The computed reactor model data was then contrasted to experimental results from the ICCD and high speed schlieren images to fully describe the events in the transient supersonic flame.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Noel T. Clemens. Vita. Includes bibliographical references. Also available from UMI.