液态SiBCN前驱体转化陶瓷的抗氧化性能及机制

Oxidation behavior and mechanism of SiBCN ceramics derived from liquid polymer precursor

前驱体转化法制备的SiBCN陶瓷具有优异的耐高温抗氧化性能,有望作为高温热结构材料应用于航空航天领域。本文主要对前驱体转化法制备的SiBCN陶瓷在1 200、1 400℃下的抗氧化性能进行研究。采用XPS对陶瓷氧化前后化学键结合方式进行表征,分析了氧化前后化学结构的变化;采用XRD和SEM对陶瓷氧化前后表面相组成、微观形貌和截面氧化层进行分析,并通过氧化层厚度随时间变化对高温抗氧化动力学进行了研究。结果表明:SiBCN陶瓷经高温氧化后在表面形成了致密的氧化膜,氧化层主要以无定形态存在,且与基体结合紧密;陶瓷的高温氧化速率受氧扩散控制,其在1 200、1 400℃下的氧化动力学常数分别为0.0224μm^2/h和0.1045μm^2/h,小于SiC陶瓷的0.0449μm^2/h和0.1288μm^2/h。由于SiBCN陶瓷形成的BN(C)结构以及高温氧化后形成的SiO_xN_y致密氧化膜降低了氧气在氧化层中的扩散速率以及反应活性,使得SiBCN陶瓷具有比SiC陶瓷更加优异的高温抗氧化性能。

SiBCN ceramic shows excellent thermal stability,oxidation resistance and crystallization resistance.The oxidation behavior of SiBCN ceramics,derived from pyrolysis of polymeric precursor,was studied at 1 200℃ and 1 400℃ in air atmosphere.XPS was used to characterize the chemical bonding of SiBCN ceramic before and after oxidation experiments.XRD and SEM were employed to analyze the phase composition and microstructure of SiBCN ceramic before and after oxidation experiments.The oxidation kinetics was studied by measuring the thickness of oxide layers via SEM.The results show that,after oxidation experiments,dense protective oxide layers form on the surface of SiBCN ceramic to prevent further oxidation.And the diffusion of oxidant through the oxide layers is the rate-controlling process.The oxide layers thickness of SiBCN ceramic growth at 1 200 and 1 400℃ in air can be approximated by a parabolic rate law with rate constants of 0.0224 μm^2/h and 0.1045 μm^2/h,respectively.Which was thinner than SiC ceramic with rate constants of 0.0449 μm^2/h and 0.1288 μm^2/h,respectively.The BN(C)structure and the formed of dense SiOxNy layers made SiBCN ceramic have excellent oxidation resistance.