AbstractTitle of Thesis: SIZE MODIFICATION AND COATING OFTITANIUM DIOXIDEUSING A PREMIXED HYDROGEN/AIR FLAMESeungchan Lee, Master of Science, 2006Thesis directed by: Dr. Sheryl H. Ehrman.Department of Chemical Engineering.A study was conducted of the effect of flame processing on the size distribution oftitania nanoparticles, and a flame process was developed for producing TiO2/SiO2core-shell particles from aqueous suspensions of TiO2and SiO2nanoparticles. Both wereperformed using a premixed hydrogen/air flame. At the adiabatic flame temperature of2400 K, the number mean diameter of titania primary particle increased considerablyfrom an initial value of 44 nm to 96 nm, presumably by atomic diffusion, and viscousflow coalescence. Moreover, the majority of product particles from this high flametemperature were smooth and spherical. Based on the results of size modificationexperiments, coating experiments were performed. The dominant morphology observedin the product particles from coating experiments was silica coated titania. The silicacoating was very smooth and dense. The total particle size and the shell volume of theproduct particles were in reasonable agreement with values predicted from the atomizeddroplet size distribution and the droplet concentration.SIZE MODIFICATION AND COATING OF TITANIUM DIOXIDE USINGA PREMIXED HYDROGEN/AIR FLAMEbySeungchan LeeThesis submitted to the Faculty of the Graduate School of theUniversity of Maryland, College Park in partial fulfillmentof the requirements for the degree ofMaster of Science2006Advisory Committee:Professor Sheryl H. Ehrman, Chair / AdvisorProfessor Michael R. ZachariahProfessor Mikhail AnisimovProfessor Srinivasa R. Raghavan©Copyright bySeungchan Lee2006iiAcknowledgementsI am deeply grateful for the meticulous guidance and true encouragement of myacademic advisor, Dr. Sheryl H. Ehrman. I also would like to thank Dr. Michael R.Zachariah, who is my co-advisor. He, who has extensive knowledge in various areas anda passion for research, always has been a paragon to me.Korea Science and Engineering Foundation (KOSEF), an affiliated organizationof the Ministry of Science and Technology, had given financial support from September,2004 to May, 2006. I am very thankful for their unconditional financial aid.Finally, many thanks to members of my research group and Dr. Zachariah’sresearch group, particularly Ranjan Pati, Sunmin Kin, and Kyle Sullivan; my friends; myfamily, my father Jongsun Lee, my mother Chaewha Moon, and my sister Hyojung Lee.iiiTable of ContentsList of Tables vList of Figures vii1. Introduction 11.1 Overview of Thesis 11.2 Background 4Photoactivity of TiO2Nanoparticles 4Particle Size and Light Scattering 6Synthesis of Core-Shell Systems 72. Experimental 82.1 Overview 82.2 Experimental Procedure 83. Theoretical Consideration 143.1 Residence Time 143.2 Sintering Rate 174. Results and Discussion 234.1 Flame Temperature Effect on TiO2Particle Size Modification 234.2 Characterization of SiO2Coated TiO2Particles with HRTEM 27SiO2Shell Volume 27Particle Morphology 345. Conclusion 406. Recommendations for Future Work 42ivProduction of CeO2and Al2O3Core-Shell System with PremixedHydrogen/Oxygen Flame 42Product Particle Size Control by Using Various Droplet Size 43Appendices 44Appendix A: Droplet Size Measurement 44Appendix B: Temperature Profile 48Appendix C: Standard Operation Procedure 50Appendix D: Index to TEM Holder 53References 54vList of TablesTable 2.2.1 10Experimental conditions of TiO2size modification experiments. The flow ratesare presented at standard pressure and temperature of 0 ˚C.Table 2.2.2 11The flame and solution conditions of coating of TiO2experiments. The flow ratesare presented at standard pressure and temperature of 0 ˚C.Table 3.1.1 14Reynolds number of gas flow in the tube at each flame condition. The flow ratesare presented at standard pressure and temperature of 0 ˚C.Table 3.1.2 16Calculations of residence time in the flame and post-flame zone.Table 3.2.1 19Property data of titania and silica.Table 3.2.2 22The characteristic coalescence time of TiO2with respect to the adiabatic flametemperature and the particle diameter.viTable 3.2.3 22The characteristic coalescence time of SiO2with respect to the adiabatic flametemperature and the particle diameter.Table 4.1.1 24Number mean diameters of initial TiO2particles and product particles from theadiabatic flame temperature of 1800 K, 2000 K, and 2400 K.Table A.1 45Estimated volume mean particle diameter of sodium chloride.Table D.1 53Index to TEM grid holder.viiList of FiguresFigure 1.1.1 2Schematic illustration of the process of making TiO2/SiO2core-shell particles.Figure 2.2.1 8Schematic illustration of the experimental apparatus.Figure 2.2.2 12Cold finger configuration.Figure 3.2.1 21The time needed to heat up an individual TiO2particle from 298 K up to 2100 Kwhen there is negligible surface resistance.Figure 4.1.1 23Transmission electron microscope image of initial titanium oxide nanoparticlesand the particle size distribution.Figure 4.1.2 25Transmission electron microscope image of size modified titanium oxidenanoparticles and the particle size distribution (adiabatic flame temperature of1800 K).viiiFigure 4.1.3 26Transmission electron microscope image of size modified titanium oxidenanoparticles and the particle size distribution (adiabatic flame temperature of2000 K).Figure 4.1.4 26Transmission electron microscope image of size modified titanium oxidenanoparticles and the particle size distribution (adiabatic flame temperature of2400 K).Figure 4.2.1 28Plot of theoretical prediction of silica shell volume.Figure 4.2.2 28Enlargement of Figure 4.2.1 with total particle diameter from 202.5 nm to202.6 nm and with SiO2shell volume from 2.695 x 10-21m3to 2.699 x 10-21m3.Figure 4.2.3 30Comparison of computed values with the measurements from TEM analysis.Experimental condition of 0.36 g SiO2+ 0.6 g TiO2in 80 ml deionized water.Error bars represent measurement uncertainty and in some cases the same size orsmaller than data point markers.ixFigure 4.2.4 31Comparison of computed values with the measurements from TEM analysis.Experimental condition of 1.8 g SiO2+ 0.6 g TiO2in 80 ml deionized water.Same definition for error bars as in Figure 4.2.3.Figure 4.2.5 32Comparison of computed values with the measurements from TEM analysis.Experimental condition of 3.6 g SiO2+ 0.6 g TiO2in 80 ml deionized water.Same definition for error bars as in Figure