Browsing by Subject "Nonthermal plasma"
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Item Decontamination of Particulate Foods Using Intense Pulsed Light and Other Non-Thermal Technologies(2020-01) Chen, DongjieLow-moisture particulate foods comprise a wide range of food products such as milk powder, protein powder, egg powder, whey powder, spice, flour, grain, and seeds. Various pathogens or toxins such as C. sakazakii, Salmonella spp., Bacillus cereus spores, and deoxynivalenol (DON) were infected in particulate food matrices. These contaminants are physiologically dormant and metabolically quiescent in low moisture particulate foods and are therefore resistant to conventional thermal process. Conventional heating processes used to eliminate foodborne pathogens may cause some degrees of undesirable flavor and quality changes on particulate food products that are unacceptable for uses by consumers and food industries. This dissertation research focuses on developing non-thermal microbiocidal technologies for dry particulate foods. Lack of knowledge related to continuous nonthermal techniques on low-moisture particulate foods prevents the technology from applications in food industry. In this study, an intense pulsed light (IPL) treatment system was developed, processing parameters such as relative humidity, temperature, water activity, pulsed duration, voltage, pulsed frequency, and residence time, etc., were evaluated on different low-moisture particulate foods. After several generation-improvement of the IPL system and processes, the results showed a maximum of 4 log10 CFU/g reduction of microbe could be obtained after 60s IPL treatment on the conditions of 1 Hz and 3000 voltage. Furthermore, additional one log10 CFU/g microbial reduction could be achieved when combining IPL with TiO2 based catalysts. Food products such wheat, wheat kernels, and NFDM could be potentially subjected to IPL with minimized quality loss. For milk powder process, the IPL step can be fitted after spray drying. On the other hand, cold atmospheric plasma was able to inactivate be used to inactivate ~3 log10CFU/g of C. sakazakii in non-fat dry milk after only 120 s. However, the throughput of the system was limited and thereby, difficult to scale up. With respect to plasma activated water, the system was effective in degrading DON (34.6 %) in germinating barley samples while maintaining sample quality after 5 min. For microwave or catalytic microwave treatments, the results indicated microwave treatment below 60 °C was feasible to inactivate pathogens in wheat kernels up to 5 log10CFU/g at the water activity level of ~0.8. Therefore, the process can be fitted in a step after tempering. In summary, several nonthermal technologies specifically used for particulate food pasteurization were developed in the current research, optimized conditions for disinfection and particulate sample preservation were comprehensively investigated. The findings from this research has filled the key knowledge gaps of preventing the technology from commercialization.Item Nonthermal plasma synthesis of aluminum nanoparticles(2017-08) Pearce, BenjaminAluminum nanoparticles are an intriguing material because of their high reactivity and high energy density, making them ideal for propellant materials such as rocket fuel. In addition, nanoaluminum is also a promising abundant, low cost material for plasmonic applications with a plasmonic response that can extend from the visible region of the light spectrum down to ultraviolet wavelengths of light. Nonthermal plasmas are a promising tool for synthesizing nanocrystalline materials without the need for high temperatures or solvents. Their ability to add electrons to the surface of nanoparticles within the plasma helps reduce agglomeration and form aerosols with tighter size distributions than other competing aerosol synthesis techniques. Nanoparticles containing crystalline elemental aluminum were synthesized using a nonthermal plasma containing trimethylaluminum (TMA) vapor, argon and hydrogen gases. The percentage of hydrogen flowing with respect to total gas flow was required to be at least 70% in order to form crystalline aluminum. In addition the ratio of H2 to TMA flow rates needed to be a minimum of 60. 7% of the nanoparticles' aluminum atoms were in elemental aluminum form with the remaining ones in the form of alumina (Al2O3) or an aluminum hydroxide according characterization by air-free X-ray photoelectron spectroscopy. Air-free X-ray diffraction of the nanoparticles indicated the average crystallite size of the elemental aluminum in the particles was on the other of a few nanometers.Item Nonthermal Plasma Synthesis Of Nanoparticles And Double Probe Diagnostic(2023-04) Xiong, ZichangNanoparticles are tiny particles that range in size from 1 to 100 nanometers. Their large surface area-to-volume ratio allows them to interact with their surroundings in unique ways. Nonthermal plasmas are particularly attractive sources for nanoparticle synthesis. In these plasmas, energetic plasma electrons decompose molecular gaseous precursors, producing radicals, which lead to the nucleation and growth of nanoparticles. This thesis investigates the feasibility of double probe measured in nonthermal dusty plasma and the mechanism of particle trapping and heating in nonthermal plasma synthesis of nanoparticles. This thesis also studies ICP synthesized size-tunable y-Al2O3 nanocrystals and reducing iron oxide particles by a MW hydrogen plasma. Double probes are utilized to diagnose the plasma properties of an argon:silane plasma containing nanoparticles. We demonstrate good stability of current-voltage characteristics over several minutes of operation. In addition, we developed a zero-dimensional global model to investigate the effect of the presence of nanoparticles on the plasma properties. Critical processes were investigated in nonthermal plasma synthesis of nanoparticles. We present experimental and computational evidence that, during their growth in the plasma, sub-10 nm silicon particles become temporarily confined in an electrostatic trap in radio-frequency excited plasmas until they grow to a size at which the increasing drag force imparted by the flowing gas entrains the particles, carrying them out of the trap. Furthermore, a nanoparticle heating model was used to study the temperature increase of a particle exposed to a plasma by exothermic surface reactions. y-Al2O3 is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. We report a single-step synthesis of size-controlled and monodisperse, facetted y-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small 3.5 nm, below the predicted thermodynamic stability limit for y-Al2O3. CO2 emissions from the steel production account for 8% of the global anthropogenic CO2 emissions and are a key challenge towards achieving a carbon-neutral future. We report an electrified process for reducing iron ore particles using atmospheric pressure hydrogen plasma powered by microwave energy. Iron ore particles were reduced steadily on a mesh exposed to the plasma. Moreover, in-flight iron ore reduction was achieved using the atmospheric pressure hydrogen microwave plasma, which is more than 100 times faster than the previously reported flash in-flight iron ore reduction by a thermal hydrogen technique.