利用海南石英砂资源制备氮化硅陶瓷及氮化硼纳米管增韧

As an outstanding member in ceramic family, silicon nitride (Si3N4) possess excellent properties such as high strength, large thermal conductivity, low thermal expansion coefficiency, good anti-corrosion and anti-oxidation resistance. But similar to the other family members, Si3N4 is also brittle and toughening is very essential for improving its performance. With the creation and development of nanomaterials and nanotechnology, carbon nanotubes (CNTs) are used more and more popularly for reinforcing and toughening ceramics. Recently, more and more concerns have been putting into boron nitride nanotubes (BNNTs) due to their analogous graphite structure and excellent mechanical properties as CNTs. More importantly, BNNTs have better anti-oxidation performance than CNTs. However, very few research work is reported on the utilization of BNNTs for toughening ceramics. There are about 2 billion tons of proved reserves of high-quality quartz-sand resource in Hainan province, but most of them are merely used as clay source for building brick in a low-efficiency and low added-value way. In this proposal, we intend to fabricate α-Si3N4 powder via a carbothermal reaction route by using the abundant quartz-sand resource in Hainan as the main raw material, and then fabricate high-performance Si3N4 ceramics. The Si3N4 ceramics toughened with BNNTs will also be investigated. The BNNTs will be provided based on the large-quantity synthesis method, i.e. a solid-state reaction method developed by us previously. Also, the toughening mechanism will be studied in detail.

氮化硅是陶瓷家族中一种具有优良综合性能的陶瓷,如高强度、高热导率、低热膨胀系数、耐腐蚀和抗氧化等。但氮化硅陶瓷也同样具有脆性大这一陶瓷共同的缺陷，增韧成了一种提高其性能的必然手段。随着纳米材料和技术的兴起和发展，碳纳米管被越来越多地用于陶瓷材料的增韧添加相，而与碳纳米管具有相似结构和高力学性能的氮化硼纳米管，因为具有的更好的抗氧化性能而受到关注，但目前鲜有关于氮化硼纳米管作为陶瓷材料增韧添加相的报道。海南省具有丰富优质的石英砂资源，保守储量达到20亿吨，但主要被用做粘土砖的原料，未能实现优质资源的高效和高附加值利用。本项目拟利用海南省的石英砂资源作为硅源，采用碳热还原法，开发出从石英砂到α-Si3N4再到高性能Si3N4陶瓷的制备工艺和路线；并利用申请人开发的固相反应法，比较大量合成BN纳米管，将其作为添加相对Si3N4陶瓷进行增韧研究，并探索其增韧机理。

氮化硅具有高强度、高热导率、低热膨胀系数、耐腐蚀和抗氧化性能好等优良性能，但也具有脆性大的缺陷，开发新的技术对其进行增韧具有重要意义。氮化硼纳米管因为具有与碳纳米管相似的结构和优良力学性能，且具有更好的抗氧化性能而受到关注，但目前鲜有关于氮化硼纳米管作为氮化硅陶瓷增韧相的报道。本项目多方面系统地研究了高纯氮化硼纳米管、氮化硼微纳复合结构和莫来石晶须的制备工艺和技术，并将它们用于氮化硅陶瓷和莫来石陶瓷的增韧，探讨了增韧机制；并采用冷冻干燥技术多方位探索了由莫来石晶须互锁结构构成的具有高强高孔隙率的莫来石多孔陶瓷的制备工艺、以BN纳米片修饰碳纤维改善碳纤维的抗氧化性能和微波吸收性能等。研究发现BNNTs可以有效增韧Si3N4陶瓷，Si3N4陶瓷的断裂韧性从7.2 MPa·m1/2 提高到10.4 MPa·m1/2，增幅44.4%，抗弯强度依然保持在711 MPa以上的一个较高水平；而BN微纳复合结构可提高Si3N4陶瓷的硬度等性能，因为其促进了长柱状β-Si3N4晶须的长大。研究发现莫来石晶须和碳化硅晶须对莫来石陶瓷增韧效果较好，莫来石陶瓷的断裂韧性可提高到5.47 MPa·m1/2（个别样品达到6.66 MPa·m1/2）。增韧机制主要包括纳米管或晶须的桥联、拔出和断裂、裂纹的偏转等。