硼掺杂各向同性热解炭材料的制备、微观结构及抗氧化性能研究

IMR OpenIR

	硼掺杂各向同性热解炭材料的制备、微观结构及抗氧化性能研究
	许力
学位类型	博士
导师	成会明 ; 白朔
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	硼掺杂各向同性热解炭化学气相沉积微观结构抗氧化性能 Boron Doping Isotropic Pyrolytic Carbon Chemical Vapor Deposition Microstructure Oxidation Resistance
摘要	"各向同性热解炭具有密度低、耐高温、自润滑、优异的力学性能和摩擦磨损性能、耐腐蚀及良好的生物相容性等优点，具有重要的工业价值。目前作为高性能机械密封材料已广泛应用于机械、航天、航空、船舶等领域。但由于各向同性热解炭在高温氧化性气氛中会被氧化，故其高温应用受到了极大的限制。在热解炭材料中引入硼元素将显著影响材料的理化性能，尤其对提高热解炭材料的抗氧化性能有十分明显的作用。目前对各向同性热解炭材料掺杂硼的研究还处于空白状态，亟需开展硼掺杂各向同性热解炭材料的研制工作，以拓展各向同性热解炭材料的应用领域，满足装备技术发展对高性能材料的需求。本论文以CH4、H2和BCl3为原料，采用硼碳化学气相共沉积方法制备硼掺杂各向同性热解炭，对其制备工艺、微观结构及抗氧化性能进行了较为系统的研究： 1. 对硼掺杂各向同性热解炭的关键制备工艺参数（沉积温度和气源条件）进行了研究。通过优化制备工艺参数制备出致密、均匀的硼掺杂各向同性热解炭，材料中的硼含量可在0～5 at. %范围内调控。硼元素的掺杂对材料的微观组织结构具有较大的影响：随着硼碳源比率的增大，材料的生长单元由颗粒状碳结构逐渐向球团状碳结构转变，但由于生长单元随机取向并杂乱堆积，材料在宏观上仍呈各向同性性质。硼掺杂各向同性热解炭材料的生长机理基本遵循粘滞小滴机理，但由于BCl3的加入会影响粘滞小滴的脱氢炭化过程，因此使生长单元从颗粒状向球团状转变。 2. 硼掺杂各向同性热解炭属于乱层结构炭，但硼元素对石墨片层生长和重排的催化作用提高了材料的石墨化度。随着硼含量的增加，材料中的碳化硼颗粒含量增加。碳化硼颗粒由尺寸几十纳米到几百纳米、具有五次对称性形貌特征的碳化硼微晶组成，其颗粒形状与其生长机理密切相关。硼在材料中的存在形式除了碳化硼相之外，还可以在石墨片层中取代碳原子以B-C键合形式存在。硼掺杂各向同性热解炭材料的石墨化受热激发和硼催化共同控制，硼在其石墨化过程中起到了极为重要的作用。 3. 硼掺杂各向同性热解炭具有优异的抗氧化性能，其起始氧化温度比各向同性热解炭提高近200℃，氧化失重速率仅为未掺硼材料的5%～11%。硼含量和微观结构（孔隙结构、生长单元等）对材料的抗氧化性能都具有重要的影响。硼掺杂各向同性热解炭材料的本征抗氧化能力的提高及材料中以取代形式存在的硼和碳化硼优先氧化形成的氧化硼膜，使材料的抗氧化能力显著提高。"
其他摘要	"Isotropicpyrolytic carbon is of great industrial value, due to its low density,high temperature stability,self-lubrication, excellent mechanical propertiesandtribological properties, high corrosion resistance, goodbiocompatibility, etc. Recently, it has been widely usedashigh-performancemechanical sealmaterials in mechanical, aerospace, aviation, shipping and other fields.However, isotropic pyrolytic carbon is easy to be oxidized at high temperature, resulting in the limited application of this material. Introducing boron into carbon would significantlyaffect thephysical and chemical properties, in particular, to improve theoxidation resistance ofcarbon materials. However, there has little work on boron doping in isotropicpyrolyticcarbon, so it is very necessary to carry out research and development to expandthe application ofisotropicpyrolyticcarbon and meetthe demandsofhigh-performance carbon materials. In this dissertation, a chemical vapor co-deposition process was used to fabricate boron-doped isotropic pyrolytic carbon, using methane (CH4), hydrogen (H2) and boron trichloride (BCl3) as reactant gases, and the deposition process, microstructure and oxidation behavior of the boron-doped isotropic pyrolytic carbon were studied. 1. Key deposition parameters, including temperature and gas condition, have been investigated. By optimizing the deposition parameters, dense and uniform coating of boron-doped isotropic pyrolytic carbon can be obtained with boron content up to 5 at. %. Boron doping has a remarkable effect on the microstructure of the deposits. With the increase of the gas ratio of boron to carbon source, the growth unit of boron-doped isotropic pyrolytic carbon would change gradually from spherical carbon structures to the agglomeration of wrinkled graphitic sheet structures. Because they are both arranged and packed in a random way, the materials obtained are macroscopically isotropic. The growth mechanism of the boron-doped isotropic pyrolytic carbon follows the droplet theory, and the addition of BCl3 would affect the carbonizing process of the viscid droplets, then induce the microstructure change the growth units. 2. The boron-doped isotropic pyrolytic carbon is a turbostratic carbon material. Due to a strong catalytic effect of boron on the growth and rearrangement of graphitic plane, the graphitization degree of the boron-doped carbons has been improved. The content of boron carbide particles increased with the increase of boron content. The boron carbide particle is composed of microcrystals showing a five-fold symmetrical morphology and a size of about tens to hundreds of nanometers. Its shape is closely related to its growth mechanism. Besides boron carbide, boron can also substitute carbon atoms and form B-C bonds. The graphitization of the boron-doped isotropic pyrolytic carbon is controlled both by thermal excitation and catalytic graphitization of boron, and the catalytic effect of boron plays a more crucial role. 3. The boron doped isotropic pyrolytic carbon obtained exhibits excellent oxidation resistance. Compared to the pyrolytic carbon, the onset of oxidation of the doped pyrolytic carbon is increased to about 200℃, and the rate of weight loss is lowered to about 5%～11%. Both boron content and microstructure（pore structure and growth unit）have a great influence on the oxidation resistance of the material. Improved intrinsic oxidation resistance and protection from a layer of glassy boron oxide coating formed on the oxidation surface should be responsible for the improvement of the oxidation resistance of the boron-doped isotropic pyrolytic carbon."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64427
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	许力. 硼掺杂各向同性热解炭材料的制备、微观结构及抗氧化性能研究[D]. 北京. 中国科学院金属研究所,2012.