【作者】 丁军；

【导师】 邓承继；

【作者基本信息】 武汉科技大学 ， 材料学， 2013， 博士

【摘要】 针对耐火材料工业广泛使用的含碳材料还需要改进和提高其亲水性和抗氧化能力、寻求新碳素材料替代不可再生的天然石墨、高温过程工业节能降耗对高性能轻质材料的需求，本文以熔盐的物理化学特性为基础，从材料的相组成和结构设计出发，一方面利用熔盐介质在天然石墨或木材炭化后的材料上原位反应生成碳化物或氮化物，解决天然石墨与水润湿性及抗氧化性的问题，同时为研发碳素替代材料提供新方向。另一方面利用熔盐的特性，将熔盐介质作为镁橄榄石轻质材料制备过程中的造孔剂和烧结助剂，利用熔盐与镁橄榄石之间化学反应活性成功制备了镁橄榄石轻质材料，且可有效去除杂质氧化铁，开发了轻质材料制备的新方法，拓展了熔盐的应用领域。（1）以NaF-NaCl为熔盐介质，在氩气保护下，1100-1400°C分别在天然石墨的表面成功地反应生成碳化硅纳米线或碳化钛层，改变了石墨原有的结构和性能，生成的纳米碳化硅或碳化钛起到了抗氧化作用，氧化后生成的氧化物层阻止了石墨的进一步氧化。在氮气气氛下，1100-1400°C在石墨表面生成了TiN晶须。TiN晶须以VLS的机制生长，其形貌分别有棒状、锥状和星型，其直径大约500-600nm。TiN晶须的生成提高了石墨的抗氧化性能。（2）在氩气保护下，900°C在KCl-KF熔盐介质中合成了保留木材天然多孔结构的TiC/C复合陶瓷，即在木材炭化的炭模板表面生成TiC层。生成的碳化钛的晶体形貌受到盐/钛摩尔比和反应温度的控制。同样在相同气氛和熔盐介质中，1250°C合成了SiC/C复合陶瓷，不仅保留了木材天然多孔结构，而且在炭模板表面以及孔隙内部形成了直径为10-100nm的SiC纳米线。TiC/C和SiC/C复合材料是耐火材料行业潜在的替代天然石墨的候选材料。（3）分别以NaCl和Na2CO3作为熔盐介质制备了镁橄榄石轻质材料，建立了轻质材料制备过程的动力学模型。NaCl作为熔盐时，适宜的制备温度为1100°C，合适的熔盐含量为40-50%。NaCl熔盐不参与化学反应，只提供镁橄榄石液相烧结环境，促进镁橄榄石的烧结和晶粒的长大。以Na2CO3为熔盐介质制备镁橄榄石轻质材料的合适温度是900-1100°C。Na2CO3熔盐的作用不仅提供镁橄榄石液相烧结环境，而且和镁橄榄石中的氧化铁反应，生成可溶于水的化合物和方镁石。含铁的化合物在溶水阶段排出，实现选择性去除铁的目的。生成的方镁石相有利于提高轻质材料的高温性能。更多还原

【Abstract】 The refractory materials contained carbon widely used in refractory industry has thedemand which still should be improved its hydrophilicity and antioxidant capacity, and foundnew carbon materials as substitution of non-renewable natural graphite. The energy-saving andcost-reducing of the high-temperature process industry need more high-performance lightweightmaterials. Based on the physical and chemical characteristics of the molten salt and the designtheory of the material composition and structure, the carbides or nitrides were produced by themolten salt method in natural graphite or wood-carbonized material through in situ reaction, sothe wettability and oxidation resistance of natural graphite were improved. The new direction ofthe research and development of carbon alternatives was issued. On the other hand, takingadvantage of the character of molten salt medium, we used the molten salt as a pore former andsintering aid for forsterite, and the lightweight materials of forsterite was successfully producedby the chemical reactivity between molten salt medium and forsterite, which could effectivelyremove iron oxide impurity. It is a new way to prepare lightweight materials, and expanding theapplications of the molten salt method.(1) Used NaF-NaCl as a molten salt and Si or Ti powders as raw material in argon, siliconcarbide nanowires and titanium carbide layer were successfully synthesized on the surfaces ofnatural graphite in the temperature range of1100°C to1400°C, respectively. The synthesizedsilicon carbide nanowires and titanium carbide should change the original structure andproperties of the graphite, and the graphite contained SiC nanowires or TiC layer had goodwettability with water. SiC nanowires or TiC layer were the antioxidant, and their oxide layers ofoxidation product would prevent further oxidation of the graphite. In nitrogen atmosphere andother same experimental conditions, TiN whiskers were successfully formed on the surface ofgraphite from1100°C to1400°C. TiN whiskers with different appearances such as rod, coneand star-shaped have grown with VLS mechanism, and the diameter of TiN whisker was about500-600nm. The generation of TiN whiskers has improved the oxidation resistance of thegraphite.(2) With the protection of argon, TiC/C composite ceramics which maintained natural porous structure of wood have successfully synthesized in KCl-KF molten salt at900°C, andTiC layer is formed on the surface of the charring carbon template. The morphology of thetitanium carbide crystals was controlled by the salt/Ti molar ratio and reaction temperature.Similarly, in the same atmosphere and molten salt system, the SiC/C composite ceramics havebeen compounded at1250°C, and retained the natural porous structure of wood. The diameter ofthe formed of SiC nanowires was from10nm to100nm on the surface of charring carbontemplate and inside its pores. The composite material of TiC/C or SiC/C was the potentialcandidate alternative material of natural graphite in the refractory industry.(3) Used NaCl and Na2CO3as molten salt medium respectively, the forsterite lightweightmaterials were prepared, and the dynamical models of the preparation process of the lightweightmaterials were issued. When NaCl acted as the molten salt, the proper temperature of preparationof the lightweight materials was1100°C, and the suitable content of the molten salt was40%to50%. NaCl didn’t participate in chemical reactions, and it just provided the environment for thesintering mechanism of the forsterite as liquid-phase sintering model, to promote the sinteringand grain growth of the forsterite material. The proper temperature to prepare forsteritelightweight materials in Na2CO3molten salt medium was900-1100°C. Na2CO3molten salt notonly provided the environment for forsterite sintering by the liquid phase model, but also reactedwith the iron oxide in forsterite and then generated a water-soluble compound and periclase.Iron-containing compound could be discharged when it dissolved in the water, which to achievethe purpose of removing iron selectively. The generated periclase phase is beneficial to improvethe refractory performances of the forsterite lightweight materials.更多还原