Fabrication of Functional Ceramics Composite Strengthened by Carbon Nanotube

碳纳米管(CNT)-陶瓷复合材料通常是用陶瓷粉末制备的。多壁碳纳米管(MWCNT)分为两种，不同于石墨素(石墨片)的厚度。一种是薄壁多壁碳纳米管(Thin-MWCNT)，到目前为止，几乎所有的复合材料都是以它为原料制备的。另一种是厚多壁碳纳米管(Thick-MWCNT)。薄壁MWCNT倾向于形成凝聚的团簇。厚多壁碳纳米管比薄多壁碳纳米管更硬，凝结更少。陶瓷粉末大于凝聚的碳纳米管的缝隙，很难进入其内部。碳纳米管-陶瓷复合材料中含有凝聚的碳纳米管，其强度随碳纳米管含量的增加而大大降低。一些陶瓷前驱体通过加热转化为陶瓷晶体，并有望引入到凝聚的碳纳米管中。碳纳米管的分散性较好，可以得到由前驱体衍生的复合材料。本文以碳纳米管为前驱体制备了薄壁碳纳米管-羟基磷灰石(HA)/氧化铝复合材料。羟基磷灰石的前驱体是6摩尔的CaHPO_4·2H_2O和4摩尔的Ca(OH)_2的混合物，氧化铝的前驱体是氢氧化铝。薄壁MWCNT-HA复合材料的强度和韧性均高于HA。然而，由于HA是一种强度不高的陶瓷，其强度还不足以提高到工业应用的水平。由薄壁碳纳米管和氢氧化铝制备的复合材料没有达到很好的分散性，随着薄壁碳纳米管含量的增加，复合材料的强度迅速下降。氧化铝前驱体没有进入凝聚的薄壁碳纳米管的内部。制备的厚壁碳纳米管-氧化铝复合材料不仅具有足够的工业应用强度和韧性，而且具有高导电性、低摩擦系数和良好的吸波性能。成功地将前驱体与厚壁碳纳米管混合，防止了碳纳米管的凝聚分散。

Carbon nanotube (CNT)-ceramics composites have been usually fabricated with the ceramics powders. There is two kind of multi-walled carbon nanotube (MWCNT) distinguished from thickness of grapheme (graphite sheet). One is thin multi-walled carbon nanotube (thin-MWCNT) and has been starting material for almost all composites prepared until now. Another is thick multi-walled carbon nanotube (thick-MWCNT). Thin-MWCNT tends to make the coagulated cluster. Thick-MWCNT is stiffer and less coagulated than thin-MWCNT. Ceramics powder is greater than gaps of the coagulated CNT and hard to go its inside. CNT-ceramics composites result in containing the coagulated CNT, and their strength is greatly decreased with increasing it. Some of ceramics precursors are transformed into ceramics crystal by heating and expected to be introduced inside of the coagulated CNT. Better dispersion of CNTs can result in the composite derived from the precursor.In this paper, the thin-MWCNT-hydroxyapatite (HA) and alumina composites were prepared using the precursors. The precursor of hydroxyapatite was mixture of 6 moles of CaHPO_4 2H_2O and 4 moles of Ca(OH)_2 and that of alumina was aluminum hydroxide. Strength and toughness of the thin-MWCNT-HA composite were higher than that of HA. However, the strength was not enough to be improved for industrial application because HA is not strong ceramics. The composite synthesized from the thin-MWCNT and aluminum hydroxide did not achieve good dispersion of them and its strength was rapidly decreased with increasing thin-MWCNT. The alumina precursor did not put into inside of the coagulated thin-MWCNT. The thick-MWCNT-alumina composite had enough strength and toughness for industrial applications and advanced properties such as high electric conductivity, low friction coefficient and good absorption of electromagnetic wave. The precursor and thick-MWCNT were successfully mixed to prevent the coagulated dispersion of CNT.