【作者】 费俊杰；

【导师】 王为民；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 二硼化钛(TiB2)是B和Ti的最稳定化合物,是一种具有优良物理化学性能的工程陶瓷材料,具有高熔点、高硬度、高模量、低比重和耐腐蚀等优点。与电解铝用传统碳素阴极材料相比,TiB2对金属铝液具有良好的润湿性,导电性好,且不与铝液发生化学反应。二硼化钛的这些特性使其作为理想的电解铝工业新型惰性可润湿性阴极材料而得到了广泛的研究。由于纯TiB2阴极材料烧结制备困难,且脆性较大,因此目前的研究重点主要集中于TiB2/C复合阴极材料。本文采用TiB2和石墨与炭黑两种碳源为原料,通过热压烧结制备TiB2/C复合阴极材料,并加入一定量短切碳纤维来实现材料的增韧补强。在保证材料对铝液完全润湿的前提下,重点研究了原料配比、碳纤维含量、热压烧结工艺参数对于材料显微结构、致密度、力学和电学性能的影响,研究材料结构与性能之间的关系。首先研究了短切碳纤维的表面除胶预处理工艺,分别采用真空热处理、浓硝酸氧化和丙酮清洗三种方法来对纤维表面胶层进行处理。发现丙酮清洗法可有效除去碳纤维表面胶层,且不会对碳纤维造成破坏。以TiB2、石墨与炭黑为原料,采用热压烧结分别制备了TiB2/C复合材料。研究发现：炭黑粒径较小、颗粒均匀,塑性流动能力较强,TiB2/炭黑材料的致密度高；但是TiB2晶粒容易被炭黑颗粒各自隔离,无法形成连接网络,导致材料力学电学性能很差。TiB2/石墨材料的综合性能较好,但是片状石墨在热压烧结过程中的塑性流动能力较差,其含量过高会导致材料致密度降低、导电性能和力学性能的下降。在此基础上,系统研究了TiB2含量、热压烧结温度和烧结时间对TiB2/石墨材料结构性能的影响。研究表明：随着TiB2含量的增加,TiB2晶粒之间逐渐相互结合形成连接网络,TiB2/石墨材料的致密度、导电性能和力学性能均上升；随着热压烧结温度的升高,TiB2晶粒之间的结合更加充分和紧密,材料的性能进一步提高;而随着烧结时间的延长,TiB2晶粒出现异常长大的现象,TiB2/石墨材料的综合性能呈现出先提高后下降的变化趋势。当TiB2含量为85wt%,石墨含量为15wt%,热压烧结温度为1950℃,烧结时间为1h,压力30MPa时,TiB2/石墨复合材料的综合性能最好为：抗弯强度为210.74MPa,断裂韧性为3.573MPa·m1/2,电阻率为30.02μΩ·cm,致密度为97.14%,维氏硬度为6.49GPa。在优化后的样品中掺加短切碳纤维来实现对TiB2/石墨材料的增韧补强作用。研究发现：随着纤维含量的增加,材料的弯曲强度下降,而断裂韧性先增后减。当碳纤维含量为3wt%时,材料的断裂韧性最高为4.61MPa·m1/2,相比不掺加纤维的样品提高了30%左右,而弯曲强度略微下降为197.02MPa。当碳纤维含量超过3wt%后,由于碳纤维之间相互堆积架接,孔隙增多,材料各项性能急剧下降。短切碳纤维对于TiB2/石墨材料的增韧机制主要有裂纹偏转、界面解离、纤维断裂和拔出等几种,通过这些能量耗散途径,使材料在破坏前大量吸收消耗外界的断裂功,提高材料韧性。更多还原

【Abstract】 As one of the most promising engineering ceramics, titanium diboride (TiB2) possesses excellent physical and chemical properties such as high melting point, high modulus, low density, good chemical stability, high hardness and excellent electric conductivity. Compared with the conventional cathode materials, TiB2ceramics exhibit unique properties such as good wettability with liquid aluminum and good resistance to sodium penetration, these properties make TiB2have been under wide studies as ideal cathode material for aluminum electrolysis. Duo to its bad toughness and difficulty of sintering of pure TiB2cathode material, now many researches focus on the TiB2/C composite cathode material primarily.In this paper, the titanium diboride-carbon (TiB2/C) composite was prepared by hot pressing sintering, the main experiment material were TiB2, graphite and carbon black, different content of short carbon fibers were added so as to reinforce TiB2/C composite. The dissertation mainly studied the influences of the ratio of row materials, carbon fiber content and sintering parameters to microstructure, density, mechanical and electrical properties of TiB2/C composite, the relationship between structure and properties was also studied.First of all, surface desizing pretreatment process of carbon fiber was studied. Three methods (vacuum heat treatment, oxidation with concentrated nitric acid, washed by acetone) were used to remove the glue line of carbon fiber, the results showed that the method of acetone washing can remove the surface glue line effectively without damaging carbon fiber.TiB2/C composite was prepared by hot pressing sintering using TiB2, graphite and carbon black as raw materials. The experimental results are as follow: TiB2/carbon black composite showed a high density because carbon black exhibited small particle size and had good ability of plastic flow, however, TiB2grain was likely to be separated by carbon black and could not form a connected network, this caused poor mechanical and electrical properties of TiB2/carbon black composite. TiB2/graphite composite exhibited better comprehensive performance, but high content of graphite would decrease density, mechanical and electrical properties of TiB2/graphite composite because of its low ability of plastic flow. Subsequently, the effect of TiB2content, sintering temperature and sintering time to TiB2/graphite composite’s structure and properties was studied systematically. It could be found that the increase of TiB2content improved the density, mechanical and electrical properties of composite duo to the connected network caused by more and more TiB2grain. TiB2/graphite composite showed a closer combination and better performance with the increase of sintering temperature. The abnormal grain growth was appear with the increase of sintering time, the comprehensive properties of composite appeared the trend from increasing to decreasing. When TiB2content was85wt%, graphite content was15wt%, sintering temperature was1950℃, sintering time was1h, sintering press was30MPa, TiB2/graphite composite exhibited best comprehensive properties as following:flexural strength was210.74MPa, fracture toughness was3.573MPa·m1/2, electrical resistivity was30.02μ(?)·cm, the relative density was97.14%, the Vickers hardness was6.49GPa.Different content (0-9wt%) of short carbon fibers were added into TiB2/graphite composite to reinforce TiB2/C composite. The results showed that flexural strength of composite decreased with the increase of carbon fiber, and fracture toughness appeared the trend from increasing to decreasing, TiB2/graphite composite with3wt%carbon fiber had the highest fracture toughness,4.61MPa·m1/2, which improved by30%than composite without fiber, and the flexural strength exhibited slight decrease of197.02MPa. When fiber content was over3wt%, the comprehensive properties of composite decreased sharply due to the increasing number of pores caused by the fiber bridging effect. Interface debonding, fiber fracture and pull-out were main toughening mechanisms of TiB2/graphite composite, all of these toughening mechanisms could consume much fracture energy and improve the fracture toughness of TiB2/graphite composite.更多还原