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The Synthesis of Urea Formaldehyde Resin Based Carbon Microspheres and the Controlling of the Morphology

Author: WangDaLin
Tutor: WangChengYang
School: Tianjin University
Course: Chemical processes
Keywords: Urea-formaldehyde resin Carbon microspheres Microstructure Topography SEM analysis
CLC: TQ323
Type: PhD thesis
Year: 2011
Downloads: 135
Quote: 0
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Abstract


Granular carbon materials, carbon microspheres have high mechanical strength, high packing density, fluid flow properties. Urea-formaldehyde resin microspheres were prepared by the polymerization reaction of formaldehyde and urea, urea-formaldehyde resin-based carbon microspheres thus prepared after carbonization. How the carbon microspheres preparation process is to achieve the carbon microspheres micron or even nano-structured control, manual cutting carbon microspheres structure, depth study of the relationship between the performance of the material structure is of great significance. In this paper, the morphology of the structure and regulation of the carbon microspheres a useful exploratory study. By the change of the preparation conditions, urea-formaldehyde resin-based carbon microspheres of four different morphologies: solid carbon microspheres, hollow carbon microspheres with surface nano-structured carbon microbeads, flower-like carbon microspheres, the success achieved on the urea-formaldehyde regulation of the resin carbon microspheres morphology structure. And the use of SEM, FTIR, XPS hollow carbon microspheres, with the formation mechanism of the surface nano-structured carbon microspheres and flower-like carbon microspheres. Urea-formaldehyde resin microspheres as a precursor of carbon microspheres, provides a way to control carbon microspheres morphology structure, and control means simple, inexpensive raw materials. Formaldehyde and urea as raw materials starting point for the preparation of urea-formaldehyde resin-based carbon microspheres. Water as a reaction solvent, formic acid as the catalyst, the solution pH value is less than 2, so that formaldehyde and urea polymerization to generate urea-formaldehyde resin micro-ball, urea-formaldehyde resin microsphere diameter size less than 10μm, the dispersion is good, no bonding of microspheres, The sphericity is good, smooth surface. After curing by 2M hydrochloric acid, urea-formaldehyde resin microspheres, in accordance with the appropriate carbonization temperature program charring diameter of 2 to 4μm urea-formaldehyde resin-based carbon microspheres. XPS analysis revealed that carbon microspheres by carbonization of 400 to 1000 ° C, the thermal stability of the three main nitrogen-containing functional group sorted the pyridone / pyrrole lt; pyridine-N lt; Quaternary-N. By XRD and HRTEM test, urea-formaldehyde resin-based carbon microspheres with a typical amorphous structure. The pore structure of the carbon microspheres as the carbonization temperature trend meets polymer yl Carbons ships law: With the increase in the carbonization temperature, the beginning stage of the pore development stage, after reaching the surface area of ??the peak due to the shrinkage of the carbon skeleton, the hole structure with shrinkage. Urea-formaldehyde resin carbon microspheres containing both the hole and the microporous structure, holes are provided in the pore volume of the carbon microspheres, microporous specific surface area. When the carbonization temperature of 800 ° C to obtain the maximum specific surface area of ??395 m2 / g, the hole diameter peak 13.1nm. Template prepared urea-formaldehyde resin-based hollow carbon microspheres and hollow microspheres shell thickness regulation. By changing the concentration of hydrochloric acid curing urea-formaldehyde resin by hydrochloric Fabrication of Hollow carbon microspheres. As the curing increase of the concentration of hydrochloric acid, urea-formaldehyde resin base shell thickness of the hollow carbon microspheres gradually increases, eventually forming a completely solid body structure. Hollow carbon microspheres shell thickness can vary between 150nm to 1500nm. Urea-formaldehyde resin-based hollow carbon microspheres by different carbonization temperature of urea-formaldehyde resin microspheres SEM, XPS and FTIR characterization reveals the formation mechanism. A higher degree of crosslinking in the carbonization process, shell formation caused by hydrochloric acid curing urea-formaldehyde resin of the surface of the microspheres with the difference of the internal degree of crosslinking, to form the shell crosslinked high - kernel with a low degree of crosslinking of the core-shell structure microspheres, The hollow structure of the shell of the carbon microspheres, a low degree of crosslinking of the kernel forming carbon microspheres. Regulation and mechanism of urea-formaldehyde resin microspheres and its carbon microspheres surface nanostructures. Mentioned earlier, the preparation of urea-formaldehyde resin microspheres reaction solution pH of less than 2, when the initial pH value of the reaction solution 5:00, is a surface of the special structure of the urea-formaldehyde resin microspheres. Special in that the surface of the urea-formaldehyde resin is the large hole is formed by a series of mutually staggered a urea-aldehyde resin nano-sheet structure, the scale of the hole in the several hundreds of nanometers. These nano-sheet-like structures perpendicular to the surface of the microspheres, the hole formed perpendicular to the surface of the microspheres. Scanning electron microscopy analysis of the internal structure of the microspheres and urea-formaldehyde resin microspheres pressure mercury analysis, these big hole there is just the surface of the microspheres, the interior of a solid structure. On this basis, by continuously changing the concentration of formic acid in the initial reaction solution, the surface nano-structures having a large hole to the surface of a smooth continuous transition from a urea-formaldehyde resin microspheres. In order to study the mechanism of this morphology evolution of the structure, the use of SEM direct observation of the morphology of the surface nanostructures urea-formaldehyde resin microspheres evolution of the formation mechanism of the nanostructures urea-formaldehyde resin microspheres: urea-formaldehyde resin nano The banded structure is a precursor for the formation of this special structure. Polymerization of formaldehyde and urea generated strip urea-formaldehyde resin, of banded urea-formaldehyde resin solution by slow reunion, bifurcation, growth and ultimately the formation of the center was urea-formaldehyde resin microspheres radial to the surface of the microspheres. Such a surface nanostructures urea-formaldehyde resin microspheres after carbonization, the surface of the nanostructures and the radial structure of the microspheres keep. This is the first time we prepared this structure urea-formaldehyde resin microspheres and carbon microspheres regulation process is simple, does not use the template agent and structure-directing agent, has laid a good foundation for the urea-formaldehyde resin microspheres and the carbon microspheres performance cutting. By changing the formaldehyde and urea molar ratio to prepare flower-like urea-formaldehyde resin microspheres and the corresponding flower-like carbon microspheres. In the reaction solution pH values ??less than 2, the molar ratio of formaldehyde to urea in the range of 0.4 to 1.6, the morphology of the urea-formaldehyde resin microspheres to the smooth surface of the microspheres of urea-formaldehyde resin urea-formaldehyde resin microspheres from flower-like transformation. SEM direct observation of the morphology of the flower urea-formaldehyde resin microspheres evolution, the formation mechanism of the flower-like urea-formaldehyde resin microspheres: urea-formaldehyde resin wafer structure is the precursor to form a flower-like urea-formaldehyde resin microspheres. , Urea and formaldehyde in a molar ratio of formaldehyde with urea low polymerization product of the wafer structure. Urea-formaldehyde resin wafer structure is thermodynamically unstable and it is curled into a conical shape at the edge of the wafer first, these cone-shaped structure, with the curl will collide in the center of the wafer, and ultimately forming a flower-like urea-formaldehyde resin microballoons ball structure. The precursor carbonization flower-like urea-formaldehyde resin microspheres prepared after the flower-like carbon microspheres. Flower-like carbon microspheres diameter of 5μm or less. By nitrogen adsorption test, the flower-like carbon microspheres specific surface area of ??437 m2 / g, total pore volume and pore volume of 0.72cm3 / g and 0.60cm3 / g.

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