热压温度对纳米粘土增强炭／炭复合材料结构和性能的影响

The influence of hot-pressing temperature on the structure and properties of an organic modified nanoclay-reinforced carbon / carbon composite

采用热压与致密化工艺分别在1 000、1 100、1 200和1 300℃下制备出纳米粘土增强一维炭/炭复合材料(C/C)。利用XRD、激光拉曼光谱等研究纳米粘土的热转变规律,利用体密度、导热率、抗弯强度及模量等数据研究纳米粘土的热转变对C/C复合材料的影响。采用场发射扫描电镜分析试样微观形貌。结果表明,热压温度对纳米粘土增强C/C复合材料的结构和性能影响显著。1 200℃热压制备的C/C复合材料抗弯强度最大为230.1 MPa,模量最大为87.3 GPa。C/C复合材料中的纳米粘土1 200℃热压转变成莫来石、方石英、无序粘土、有序炭及无序炭。这些组分均匀分散在基体中,可改善基体炭结构以及基体炭和炭纤维的界面,提高复合材料的力学性能;1 300℃热压时纳米粘土中的Si O2与基体炭发生碳热还原反应,破坏了基体结构,导致材料的抗弯强度和模量降低,而反应产物Si C提高了材料的导热率。

A 1D-carbon/carbon composite （C/C） with an organic- modified nanoclay filler was fabricated by hot-pressing and densification at temperatures of 1 000, 1 100, 1 200 and 1 300 ℃. The organic modified nanoclay was prepared by substituting ions between the layers of an inorganic clay with an organic quaternary ammonium salt. The thermal transformation of the nanoclay fol- lowing the hot-pressing was investigated by X-ray diffraction and Raman spectroscopy and the effect of the transformation on the bulk density, porosity, thermal conductivity, flexural strength and modulus of the C/C were characterized. The microstructure of the specimens was observed by scanning electron microscopy. Results indicate that the hot-pressing temperature has a significant im- pact on the structure and properties of the nanoclay-reinforced C/C composite. The C/C composite with the nanoclay filler hot- pressed at 1 200 ℃ exhibited the best mechanical properties with a flexural strength of 230.1 MPa and modulus of 87.3 GPa. At this temperature, the nanoclay transformed into mullite, cristobalite, disordered nanoclay, ordered carbon and disordered carbon dispers- ed uniformly in the carbon matrix. This modified the structure of the carbon matrix and tightened the interface between the matrix and the fibers, thus increasing the mechanical properties of the C/C. Carbothermal reduction took place between SiO2 and the carbon matrix at 1 300℃, which damaged the matrix structure and decreased flexural strength and modulus of the composite. However, the presence of, the reaction product （SiC） increased the thermal conductivity.