Study On Flame Aerosol Synthesis For Nanostructured Bismuth Telluride-Based Thermoelectric Material

Car spontaneous combustion accidents take place frequently in torridity summer as a result of heat from automobile engine of savings and oil tube ageing in engine cover,which threatens the safety of person and property.Thermoelectric(TE)materials,with low thermal conductivity,can play a role in isolating the external radiation heat.Meanwhile,the internal heat storage can be transformed into electric energy to further cool down.Conversion efficiency of TE materials is characterized by thermoelectric figure of merit ZT.Currently,methods to improve the ZT value are associated with doping,alloy,and nanostructuring.The main idea is that electron concentration can be modulated by doping to increase electrical conductivity,subsequently enhance ZT value of TE.And another train of thought is nanostructuring of bulk materials to increase phonon scattering by crystal boundaries artificially created as well as quantum limited effect and then improve ZT value.Experimentally proved nanostructuring of bulk materials can substantially reduce thermal conductivity of materials.Flame aerosol synthesis is an advanced technology owing to as-prepared particles with high purity,ultrafine diameter,and narrow size distribution.Firstly,CFD commercial software FLUENT is employed with reduced mechanism based on well-known GRI 3.0 with 24 species and elementary reactions of 20 steps to simulate temperature,velocity,and species profiles for ethylene comubstion.And the key factors affecting the stability of stagnation flame are discussed so as to find out the suitable conditions for synthesizing bismuth telluride-based materials.It is found by simulation that the stability of flat-structured flame caused by ethylene combusiton is greatly influenced by the initial temperature of premixed fuel gas and sheath nitrogen.In general,something that the flat-structured stagnation flame is destroyed and shift up to the nozzle of burner will occur with increasing the initial temperature of premixtures.Furthermore,the maximum temperature of combustion will be enhanced by elevating fuel gas.Similarly,increasing the flow rate of sheath nitrogen can also result in parallel changes in flame structure and temperature.For higher fuel-air ratio conditions,that is,poor-oxygen atmosphere,sheath nitrogen can not only effectively inhibit the secondary flame,but enhance the temperature of stagnation flame.Moreover,p type of purity-phase BiSbTe alloy is successfully synthesized using liquid-fed route of precursor under the condition obtained by simulation.It is found that the size of as-synthesized nanoparticles can be effectively controlled by changing the concentration of the precursor.In general,the particle size of nanoparticles can be controlled within 5nm observed by TEM with ultra narrow particle size distribution.The measurement for thermoelectric properties of bulk material consolidated with nanoparticles prepared by flame synthesis using cold-pressing under 50MPa show a very high power density of 45?W/cm2 for one thermoelectric module when a temperature difference of 45.7K between hot end and cold end is provide.