Processing and characterization of large diameter ceramic SiCN monofilaments from commercial oligosilazanes
Processing and characterization of large diameter ceramic SiCN monofilaments from commercial oligosilazanes
复制标题
DOI：
10.1039/c5ra17300k
复制
发表时间：
2015-12
期刊：
影响因子：
3.9
通讯作者：
O. Flores;R. Bordia;S. Bernard;T. Uhlemann;W. Krenkel;G. Motz
中科院分区：
文献类型：
--
作者：
O. Flores;R. Bordia;S. Bernard;T. Uhlemann;W. Krenkel;G. Motz
本文报道了用两种化学性质不同的聚硅氮烷（ML33S和HTTS）通过前驱体制备大直径陶瓷SiCN单丝的方法。粒径在35 ~ 150 μm范围内可控的连续聚合物纤维的熔融纺丝和热解成陶瓷SiCN纤维的过程不受聚硅氮烷化学结构差异的影响。相比之下，硅-乙烯基基团将必要的电子束固化剂量从ML33S（无乙烯基）的600 kGy降低到HTTS衍生聚合物纤维的200 kGy。固化步骤提高了可处理性，这对在1100℃氮气中进一步热解和提高陶瓷收率很重要。从这两种体系得到的陶瓷SiCN纤维具有相似的机械和热性能，表明聚硅氮烷类型对这些性能的影响很小。本文首次全面研究了纤维直径对SiCN纤维抗拉强度的影响。平均强度从90 μm直径的~ 800 MPa增加到30 μm直径的~ 1600 MPa。弯曲应力松弛（BSR）测试表明，SiCN单丝在高达1000°C时不会发生应力松弛，其抗蠕变性能等于或优于由化学气相沉积（CVD）生产的市购SiC单丝。抗氧化性能也可与市售的无氧CVD SiC纤维（SCS-6）相媲美。在本研究中，陶瓷纤维在低温（1100℃）下热解，具有高氧含量（13 ~ 29 wt%）。降低氧含量，提高热解温度，可望提高其高温抗蠕变性能和抗氧化性能。
This work reports the processing of large diameter ceramic SiCN monofilaments via the precursor route using two chemically different polysilazanes ML33S and HTTS self-synthesized from respective commercially available oligosilazanes. The melt-spinning of continuous polymer fibers with controllable diameters from 35 to 150 μm and their pyrolysis to ceramic SiCN fibers is not influenced by differences in the chemical structure of the polysilazanes. In contrast, the necessary e-beam curing dose is reduced by Si-vinyl groups from 600 kGy for ML33S (vinyl free) to 200 kGy for HTTS derived polymer fibers. The curing step leads to an enhanced handleability important for further pyrolysis at 1100 °C in nitrogen and to an increase in ceramic yield. The resulting ceramic SiCN fibers from both systems have similar mechanical and thermal behavior, indicating quite a low influence of the polysilazane type on these properties. For the first time a comprehensive investigation of the effect of fiber diameter on the tensile strength is reported for SiCN fibers. The average strength increases from ∼800 MPa for 90 μm diameter fibers to ∼1600 MPa for the 30 μm diameter fibers. Bend Stress Relaxation (BSR) tests demonstrated that no stress relaxation occurs up to 1000 °C for SiCN monofilaments and the creep resistance is equal to or better than commercially available SiC monofilaments produced by chemical vapour deposition (CVD). The oxidation resistance is also comparable to commercially available oxygen free CVD SiC fibers (SCS-6). The ceramic fibers in this study were pyrolyzed at low temperature (1100 °C) and have high oxygen content (13 to 29 wt%). The high temperature creep resistance and oxidation resistance is expected to improve if the oxygen content is reduced and the pyrolysis temperature increased.