高纯度氮化硼纳米管的宏量合成及其对莫来石陶瓷的强韧化研究

Mullite ceramic has been widely utilized as refractory material, high-temperature structure material, infrared transparent window material and microelectronic substrate due to its high melting point, excellent resistance to corrosion and creep, low thermal conductivity and thermal expansion coefficients, and etc. However, mullite ceramic is basically brittle, which restrict its practical applications. It was found that carbon nanotubes (CNTs) could strengthen and toughen ceramics. Boron nitride nanotubes (BNNTs) have very similar structure and Young’s modulus with CNTs, but possess better thermal and chemical stability. Thus, BNNT can be expected to act as an ideal toughening agent for ceramics. Nevertheless, very few work on the toughening of ceramics with BNNTs is reported (and even no on the toughening of mullite ceramics), because there is no commercial BNNTs product yet at present. In this project, we intend to synthesize BNNTs in large scale and with high purity through improved solid-reaction method, and then fabricate mullite nanocomposite ceramics by spark plasma sintering method using BNNTs as toughening agent. The effects of material prescription and sintering processing parameters on the microstructure and properties of the composites will be systematically investigated. The toughening behavior and mechanism will also be investigated in detail based on the study of interfaces between BNNTs and ceramics matrix.

莫来石具有熔点高、耐腐蚀、抗蠕变性好、热传导系数和热膨胀系数低等特点，可广泛应用于耐火材料、高温结构材料、红外透明窗口和微电子基底材料等领域，但其室温强度和韧性较差，严重制约该材料的应用。研究发现碳纳米管（CNTs）能较好地补强增韧陶瓷材料，而氮化硼纳米管(BNNTs)与CNTs的结构非常相似，具有相似的弹性模量，且热稳定性和化学稳定性优于CNTs，是一种理想的增韧材料。但目前市场上缺乏商业化的BNNTs产品，实验室制备的BNNTs量少且通常夹杂有颗粒，限制了BNNTs作为增韧相复合陶瓷的研究和应用。本项目拟通过改进课题组开发的固相反应法，宏量化制备具有较高纯度的BNNTs；然后以BNNTs为增韧相，采用放电等离子烧结法（SPS）制备莫来石纳米陶瓷复合材料。系统研究BNNTs添加量、烧结制度等对材料结构和性能的影响，并深入研究BNNTs与基体的界面结构，探讨BNNTs的增韧机制。

莫来石陶瓷具有诸多优良性能，如低热导率、耐腐蚀和抗蠕变性能好等，然而脆性大的缺陷限制了其应用。与碳纳米管结构相似的氮化硼(BN)纳米管因具有优良力学性能和更好的抗氧化性能而备受关注。本项目针对莫来石陶瓷韧性差的问题，系统地研究了高纯BN纳米管、掺碳BN微纳复合结构的制备工艺和技术，将其用于莫来石陶瓷的增韧，探讨了增韧机制。并采用热压烧结技术制备了莫来石复合陶瓷和高铝硅陶瓷材料。通过BN纳米管、碳化硅颗粒、氧化锆相变、以及它们之间的协同作用进行强韧化研究，从晶粒、晶界、缺陷等显微结构层次探讨协同强韧化机制。研究发现BN纳米管可以有效增韧莫来石陶瓷，当BN纳米管的添加量为0.8 wt.%时，莫来石陶瓷的断裂韧性达到4.9MPa·m1/2，提高了29%，硬度和抗弯强度达到13.4GPa和376.7MPa；BN纳米管的桥联、拔出和断裂等多种机制对强韧化起了重要的作用。研究发现进行复合化后莫来石陶瓷的韧性和强度得到显著的提高，莫来石/氧化锆复合陶瓷的断裂韧性和弯曲强度分别为12.08MP·am1/2和674.05MPa，Al2O3-莫来石-ZrO2-SiC复合陶瓷断裂韧性和弯曲强度分别为12.3MP·am1/2和970MPa。增韧机制为裂纹偏转、裂纹分支、裂纹桥联、晶粒拔出和相变增韧机制的协同效应。