The Synthesis Of Urea Formaldehyde Resin Based Carbon Microspheres And The Controlling Of The Morphology

Carbon microspheres have been drawing considerable attention for their high mechanical strength, high packing density and low flow resistance, compared with granular carbon materials. The controlling of surface chemistry and surface morphology not only widen the type of carbon microspheres, but also is very important for practical applications. In this dissertation, carbon microspheres were synthesized through polymerization of urea/formaldehyde, followed by drying and carbonization. Valuable researches have been carried to tailoring the surface morphology of carbon microspheres. By changing the synthesized parameters, four different type carbon microspheres, solid carbon microspheres, hollow carbon microspheres, carbon microspheres with surface nanostructures, flower-like carbon microspheres were prepared. Based on the results of SEM、FTIR、XPS,the mechanism of the formation of hollow carbon microspheres, carbon microspheres with surface nanostructures, flower-like carbon microspheres was proposed.Solid carbon microspheres were prepared from urea formaldehyde resin. Urea formaldehyde resin microspheres were prepared by condensation of urea and formaldehyde in aqueous solution. The diameter of obtained urea formaldehyde resin microspheres was below 10μm and showed perfect spherical morphology with smooth surface. After carbonization with suitable temperature program,the diameter of the obtained carbon microspheres has shrank to 2~4μm. Based on the results of XPS for carbon microspheres obtained at the temperature range from 400~1000℃, the sequence of the thermal stability of nitrogen functional groups is pyridone-N<pyridine-N<quaternary-N. The results of HRTEM and XRD demonstrated the presence of amorphous carbon phase within the carbon microspheres. As the carbonization temperature increasing, the changes in pore structures of carbon microspheres were consistent with other polymer based carbon materials. In the initial stage, the pore structures were developed. After the BET surface area increased to maximum,the pore volume and BET surface showed decline trends.Template free synthesis way to hollow carbon microspheres. Hollow carbon microspheres were prepared by changing the HCl concentration for urea formaldehyde resin stabilization. The shell thickness of hollow carbon microspheres was increased until the formation of solid carbon microspheres as the concentration of HCl for urea formaldehyde resin stabilization. Based on the results of SEM、FTIR and XPS for samples obtained by carbonizing at different temperature,the mechanism of hollow carbon microspheres was proposed. Due to the difference of crosslinking degree between the surface and interior, urea formaldehyde resin microspheres with core-shell structures in which shell had high crosslinking degree and core had low crosslinking degree, were formed. After carbonization, the core became the hollow structures while the shell became the carbon shell.The controlling of surface morphology of urea formaldehyde resin microspheres and carbon microspheres. Urea formaldehyde resin microspheres with novel surface structures were obtained when the pH value of initial solution is about 5. A series of urea formaldehyde resin nanoplates perpendicular to the surface were formed, which allowed for the formation of the macropore channel oriented perpendicular to the surface. The results of mercury intrusion porosimetry demonstrated the pore in the surface of urea formaldehyde resin microspheres is not real pore,the interior of the urea formaldehyde resin microspheres is solid. The surface morphology of urea formaldehyde resin microspheres was successfully tailored by continuous changing the concentration of formic acid in initial solution. The evolution from urea formaldehyde nanoplates to urea formaldehyde resin microspheres with nanostructures was directly observed by SEM. Based on the SEM results, the mechanism of the formation of urea formaldehyde resin microspheres was proposed: (1) the formation of urea formaldehyde oligomers primary plates, (2) the aggregation of plates to form flower-like superstructures, (3) repeated branching on the plates of flower-like superstructures to form regular hierarchical microspheres. The novel surface nanostructures and original radial pattern was obtained after carbonisization. This method provided a new way to tailor the surface morphology of urea formaldehyde resin microspheres and carbon microspheres.Flower-like carbon microspheres was synthesized by changing the formaldehyde urea molar ratio. With the pH value of initial solution below 2, flower-like urea formaldehyde resin microspheres was formed when the formaldehyde urea molar ration is 0.4. The evolution from urea formaldehyde micro-disk to flower-like urea formaldehyde resin microspheres was directly observed by SEM. Based on the SEM results, the mechanism of the formation of flower-like urea formaldehyde resin microspheres was proposed: (1) the formation of urea formaldehyde resin micro-disk, (2) the rolling distortions (3) the crumpling and growing. The flower-like structures were obtained carbonisization. This method provided a new way to synthesis the flower like urea formaldehyde resin microspheres and flower like carbon microspheres.The BET surface area, the total pore volume and mesopore pore volume of flower like carbon microspheres are 437 m2/g, 0.72cm3/g and 0.60cm3/g, respectively.