Effects of PyC shell thickness on the microstructure,ablation resistance of SiCnws/PyC-C/C-ZrC-SiC composites

SiC nanowires/pyrocarbon (SiCnws/PyC) core-shell structure toughened C/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4 μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion (CTE) decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4 μm,but increased when the PyC thickness was up to 2.4 μm.Especially when the PyC thickness was 1.4 μm,the linear and mass ablation rates of the composites were 71.25 ％ and 63.01 ％ lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.     

兰州肉苁蓉多糖的组成分析及抗氧化活性

对兰州肉苁蓉多糖进行组成分析和抗氧化活性研究.采用沙生植物兰州肉苁蓉肉质茎鲜样,使用传统水提醇沉法进行兰州肉苁蓉粗多糖(CLP)的提取,利用DEAE-纤维素阴离子交换色谱柱法对粗多糖CLP进行洗脱,得到中性糖CLP-1和酸性糖CLP-2.用高效凝胶渗透色谱法(HPGPC)和高效液相色谱法(HPLC)对其分子量和单糖组成...     

可食性西瓜皮基膜制备与性能分析

为促进果蔬加工副产物的资源化利用,以西瓜皮为基材,添加海藻酸钠为增稠剂,甘油为增塑剂,采用流延法制备了可食性西瓜皮基膜。研究了西瓜皮浆料质量分数、海藻酸钠和甘油的添加量对膜感官品质、拉伸性能和阻隔性能的影响。结果表明:制备可食性西瓜皮基膜的最佳配方为西瓜皮浆料质量分数55%,海藻酸钠质量分数0.35%,甘油体积分数0.20%,此时膜的综合性能最佳,感官品质得分为90分,其他主要性能指标为厚度0.072 mm,抗拉强度18.09 MPa,断裂伸长率18.92%,水蒸气透过系数3.068×10~(-12)(g·cm)/(cm~2·s·Pa),氧气透过系数4.042×10~(-17)(cm~3·cm)/(cm~2·s·Pa)。利用西瓜皮可制备综合性能良好的可食性膜,用于食品包装等领域。     

Effects of air oxidation on mesophase pitch-based carbon/carbon composites

Mesophase pitch-based carbon–carbon (C/C) composites were fabricated by cycles of impregnation/carbonization using two different preforms. Air oxidation was used as a stabilization process prior to carbonization. In order to study the effects of air oxidation, composites without air oxidation were also fabricated for comparison. The results showed that the effect of air oxidation was different for different preforms. For 2-dimensional (2D) punched carbon cloth preforms, air oxidation could greatly shorten the fabrication period, and had significant effects on the matrix microstructures. Without air oxidation, the carbon matrix of the composites consisted of small domains with a mosaic texture. With air oxidation, the matrix consisted of domains mingled with flow domains. However, air oxidation had little effect on composites prepared from 2D carbon felts preforms, and the corresponding carbon matrix in the composites consisted of mainly small domains with a mosaic texture irrespective of air oxidation.     

Influence of CLVD thermal gradient on the deposition behavior,microstructure and properties of C/C-ZrC composites

Chemical liquid vapor deposition (CLVD) is a rapid preparation method, but it is rarely involved in fabrication of C/C-UHTCs composites and its technology parameters are hardly discussed. In the present study, C/C-ZrC samples were prepared by CLVD process, and the effects of thermal gradient on the deposition behavior, microstructure and properties were investigated. Results exhibited the density, ZrC content and uniformity of the composites increased as the thermal gradient decreased from 30.4 to 9.8?°C/mm, indicating the deposition behavior was improved gradually. When the thermal gradient was 30.4?°C/mm, the deposition behavior of the specimen was poor, which resulted in the high porosity, small numbers of ZrC blocks and uneven distribution. Therefore, the specimen had a low flexural strength with brittle fracture and poor ablation resistance. As the thermal gradient decrease to 9.8?°C/mm, there was an excellent deposition in the composites, and the composites possessed large amounts of ZrC particles and their dispersion were improved remarkably. In this case, the composites displayed a non-brittle fracture with high strength, and the linear and mass ablation rates were reduced, which indicated an improvement of anti-ablation property. Nevertheless, the deposition was deteriorated evidently when the thermal gradient reached to 0?°C/mm. The density, ZrC content and uniformity of the sample became poor, leading to the decline of mechanical property and ablation resistance.     

基于RFID的监狱智能定位系统的设计与实现

为解决在押犯人管理困难的问题,该文介绍了一种基于射频识别技术的CC1110 RSSI定位系统。系统主要由腕带标签、读卡器、无线中继和服务器组成。标签主要负责对读卡器发送相关信息,读卡器负责接收标签的数据并转发给无线中继,中继通过以太网把读卡器传送过来的数据发送给服务器,服务器负责对数据的处理、分析并进行相关管理操作。该系统结构简单、硬件成本较低、易部署、适应性较强。实际测试表明,该系统能够用于监狱在押人员的定位,降低非视距误差。     

Mannich碱柴油清净剂的研究进展

介绍了Mannich碱柴油清净剂的合成条件、清净性能及在其它方面的应用,报道了Mannich碱清净剂的研究进展,评述了一些以Mannich碱为主剂的柴油清净剂的清净功效,并展望其应用前景。     

裂解炉炉管温度实时在线监测与分析

为了实时准确获取裂解炉炉管表面真实温度,介绍了一种基于近红外比色测温技术的炉管表面温度实时在线监测系统。论述了系统器件校准和环境背景影响消除的原理和方法,并通过一次和二次补偿因子校准使系统测量误差达到测量值的±0.5%或±5℃。系统应用于裂解炉取得了炉管实时监测及运行历史数据。结果表明:该系统可实时准确获取炉管表面真实温度,分析炉管表面温度分布特性,跟踪炉管温度运行历史,预测炉管运行周期,为加热炉安全稳定运行提供保障,实现节能降耗及效益提升。     

SiC coating toughened by SiC nanowires to protect C/C composites against oxidation

A dense SiC coating toughened by SiC nanowires was prepared on carbon/carbon (C/C) composites using a two-step technique of chemical vapor deposition (CVD) to protect them against oxidation. The morphologies and crystalline structures of the coatings were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. SiC nanowires played a role in decreasing the size of the cracks and improving the thermal shock resistance of the coating. The result of thermal shock between 1773 K and room temperature for 21 times indicates that, compared with the SiC coating without SiC nanowires, the average size of the cracks in the SiC coating toughened with SiC nanowires reduced from 5 ± 0.5 to 3 ± 0.5 μm. The weight loss of the SiC coated C/C composites decreased from 9.32 to 4.45% by the introduction of SiC nanowires.