Ablation resistance and mechanism of SiC/ZrC-ZrB2 double layer coating for C/C composites under plasma flame

To improve the ablation resistance of carbon/carbon(C/C)composites,a SiC/ZrC-ZrB2 double layer coating was fabricated by pack cementation and slurry-sintering method.The ablation resistance of the SiC/ZrC-ZrB2 coating was tested under plasma flame above 2300°C.The results indicate that the SiC/ZrC-ZrB2 double layer coating exhibits superior ablation resistance than the ZrC-ZrB2 single layer coating.After being ablated under the plasma flame for 20 s,the mass and linear ablation rates of the ZrC-ZrB2 coating are 0.89 mg/s and 15.3μm/s,while those for SiC/ZrC-ZrB2 coating are 0.09 mg/s and 24.15μm/s,respectively.During ablation,the SiC inner layer can generate SiO2 glass and result in the formation of ZrO2-SiO2 molten film.Compared with the ZrO2 molten film formed on the ZrC-ZrB2 coating surface,the ZrO2-SiO2 molten film with lower oxygen diffusion rate and viscosity enables the SiC/ZrC-ZrB2 coating to have better self-healing ability.Therefore,the enhanced ablation resistance of the SiC/ZrC-ZrB2 coating can be attributed to the formation of dense ZrO2-SiO2 molten film under the plasma flame.

螺旋CT三维重建技术在基层医院复杂性肛瘘诊断中的价值

目的探索螺旋CT三维重建在基层医院复杂性肛瘘诊断中的价值。方法选取2020年6月-2022年6月我院收治的复杂性肛瘘患者98例,患者术前均给予MRI和螺旋CT三维重建技术检查,以手术结果作为金标准,分析螺旋CT三维重建技术对复杂性肛瘘内口、瘘管诊断的准确性以及肛瘘分级诊断的准确性。结果98例患者术中明确诊断为复杂性肛瘘,其中Ⅰ级、Ⅱ级、Ⅲ级分别为51例、36例、11例,共发现112个内口、132条瘘管。MRI、螺旋CT三维重建对复杂性肛瘘诊断准确率均为100.00%,对分级诊断准确率分别为98.98%、96.94%,对肛瘘内口、瘘管诊断准确率分别为93.75%、96.21%和91.96%、94.70%。以手术结果作为金标准,螺旋CT三维重建技术与MRI对复杂性肛瘘内口定位、瘘管检出、分级诊断准确性比较,差异无统计学意义(P>0.05)。结论螺旋CT三维重建技术对诊断复杂性肛瘘以及肛瘘分级有较高的准确性,同时可以明确肛瘘内口和瘘管的走行,有利于手术方案制定及实施,值得基层医院应用。

制备温度对ZrC-SiC复合涂层高温耐烧蚀性能影响

为提高C/C复合材料在超高温环境中的高温耐烧蚀性能,不同包埋温度1450,1550,1650,1750℃下在C/C复合材料表面制备了ZrC-SiC复合涂层。利用XRD、SEM和EDS等分析测试手段,对比研究了涂层的物相组成和微观结构,并借助等离子烧蚀设备进行烧蚀实验,分析讨论涂层的高温耐烧蚀性能和烧蚀机理。结果表明:1650℃包埋温度下的ZrC-SiC涂层与基体结合良好,其质量烧蚀率和线烧蚀率分别为0.129 mg/s和1.867μm/s,烧蚀性能最好。烧蚀后,ZrC-SiC涂层表面形成了ZrO2和SiO2熔融相,其中ZrO2分布在SiO2熔融物中,提高了氧化层的黏度和抗冲刷能力,使得ZrC-SiC涂层具有良好的高温耐烧蚀能力。