| Boron carbide has been used for high-temperature structural material, functional material, gradient absorbing material and so on, and has found extensive uses in various industries including space, nuclear energy, electronics and advanced weapon, due to its high melting point, chemical inertness, high modulus, large neutron capture section, low density, outstanding thermal and electrical properties. However, the limitation in the use of B4 C pertains to its high chemical stability, which is mostly due to the difficulty of sintering B4 C because of the strong covalent bonds that exist within its crystalline lattice, poor plasticity, large grain boundary migration resistance, and small surface tension at the solid state. Furthermore, it is difficult to fabricate boron carbide in processed forms by the common method. The technique of preceramic polymer conversion offers a number of potential advantage:(1) a suitable polymer could have a precisely controlled stoichiometry with a composition which could be systematically varied to optimize ceramic properties;(2) the polymer could be formed into a desired shape and be converted to a ceramic with possible retention of form;(3) the polymer could undergo low temperature decomposition, enabling ceramic formation under milder conditions than those used in conventional techniques.Hollow microspheres not only have some characteristics of low density, high specific surface area, but also contain lots of guest molecule or large size objects and produce some peculiar properties based on microscopic package effect. The combination of these properties gives rise to numerous applications, such as the controlled delivery and transportation of dyestuff, cosmetics, medicine, sensitive reagents and protein, lightweight filler, high selective catalyst, catalyst carrier and so on. However, we discover that there are not reports about boron carbide hollow ceramic microspheres up to now.A kind of large molecular weight polymer poly(6-norbornenyldecaborane)(PND) as a kind of boron carbide preceramic polymer, was synthesized by the ruthenium-catalyzed ring-opening metathesis polymerization(ROMP) reaction of 6-norbornenyldecaborane with the catalyst Grubbs II. The synthesized polymer precursor whose average molecular weight was up to 2.834×104 had a high ceramic yield of 75 % at 750 oC. Unfortunately, this polymer could only be soluable to in the polar organic solvent because of its rigidity. To solve this problem, we tried to design a new kind of poly(norbornenyldecaborane-co-hexadiene)(P(NB-co-DE)) copolymer as boron carbide preceramic polymer, which combined the flexible groups in the polymer chain by the method of copolymerization reaction of 6-norbornenyldecaborane with 1,5-hexadiene. The copolymer, which had a good solubility and film-forming ability, was freely soluble in most organic solvents and with a high ceramic yield of 74 % at 700 oC.Furthermore, we used these polymers to fabricate polymer hollow microspheres by a triple orifice droplet generator and stirring. By using the triple orifice droplet generator, we obtained two kinds of polymer hollow microspheres that were monodisperse, which showed that the two kinds of precursor polymer we synthesized both had an excellent sphere forming ability and could be used to fabricate boron carbide ceramic materials in the processed forms. Besides, we researched and discussed the pyrolysis conversion process of the polymer precursor from the starting polymer to the resulting ceramic material by kinds of characteristics. |
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