环境因素对聚酰亚胺薄膜及涂层侵蚀效应分析

目的采用不同表面改性方法处理聚酰亚胺,研究温度、湿度、紫外辐照和原子氧等环境因素对聚酰亚胺基体及涂层的侵蚀效应。方法用碱性溶液(NaOH)、硅烷偶联剂(KH-550)分别在水热及溶剂热条件下处理聚酰亚胺薄膜。用溶胶凝胶法制备二氧化硅溶胶,并在改性后的聚酰亚胺薄膜表面制备二氧化硅涂层。处理后样品的亲水性变化由接触角测量仪测定,透光率用紫外可见分光光度计表征,表面形貌用扫描电镜观察,表面结构变化由傅里叶变换红外光谱仪测定。环境效应试验用紫外老化箱和原子氧模拟试验装置进行评价,并用扫描电镜和材料显微镜表征环境因素对涂层产生的影响和破坏作用。结果实验得出的最佳表面处理条件为:(1)NaOH浓度0.1 mol/L,水热温度120℃,时间60 min;(2)20vol%KH-550+80vol%Et OH,溶剂热温度180℃,时间60 min。在此条件下处理后的聚酰亚胺基体与二氧化硅涂层界面结合较牢固。结论使用碱液水热处理与硅烷偶联剂溶剂热相结合的处理方法,可有效改善Si O2涂层与聚酰亚胺基体的界面粘附性。所制备的涂层均匀致密,具有很好的抗原子氧侵蚀能力,但在储运过程中必须注意环境湿度对涂层产生的破坏作用。     

Prevention of fouling and scaling in stationary and circulating liquid–solid fluidized bed heat exchangers: Particle impact measurements and analysis

Fluidized particles in liquid–solid fluidized bed heat exchangers are able to remove deposits from the walls and thus to prevent fouling or scaling. This fouling prevention ability is believed to depend strongly on the frequency and force of particle–wall collisions. This paper presents piezoelectric measurements of impacts on the wall in both stationary and circulating fluidized beds of various particle sizes and bed voidages. Two types of impacts were measured, namely by collisions of particles on the sensor and by liquid pressure fronts induced by particle–particle collisions close to the sensor. The characteristics of both impact types are used to analyze the total impulse and energy exerted by impacts on the wall for various fluidized beds.     

空间行波管电子枪中阴极热形变及冷启动特性研究

本文利用ANSYS软件对空间行波管的电子枪进行了稳态热分析,得到了电子枪阴极温度随灯丝功率的变化结果,计算结果与试验结果一致,验证了ANSYS热分析的正确性。在此基础上分析了阴极的热形变对电子枪性能参数的影响,同时模拟了电子枪中阴极的冷启动情况,得出阴极在-35℃条件下,在210s内阴极温度可以达到正常工作温度980℃。     

Mechanical properties and microstructure for 3 mol% yttria doped zirconia/silicon carbide nanocomposites

3 Mol% yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) is well known as a transformation toughening material with excellent mechanical properties at ambient temperature. However, the properties of 3Y-TZP drop down with increasing temperature. In this study, nanocomposite techniques were applied in order to improve mechanical properties of 3Y-TZP. 3Y-TZP/SiC nanocomposites were fabricated by hot-pressing, and effects of SiC particles on microstructure, transformation from tetragonal zirconia (t-ZrO₂) to monoclinic ZrO₂ (m-ZrO₂) and its mechanical properties were investigated. Fracture toughness of the nanocomposite was improved without decrease of strength. This should be due to not only crack deflection by dispersed SiC particles with high Young's modulus, but also the phase transformation of t-ZrO₂ accelerated by the residual stresses from coefficient of thermal expansion mismatch between 3Y-TZP and SiC.     

改善SiO2涂层与聚酰亚胺基体界面结合性能的研究

目的 利用硅烷偶联剂(SCA)有机官能基对有机物具有反应性或相容性的特点,探讨通过SCA改善SiO2涂层与聚酰亚胺(PI,Kapton)基体界面粘附力的实验方法,提高SiO2涂层与PI基体的结合强度,同时削弱因温度变化而引起的内应力.方法 水热条件下,用低浓度碱液对PI表面进行处理,选取γ-氨丙基三乙氧基硅烷(KH-550)、γ-(2,3-环氧丙氧)丙基三甲氧基硅烷(KH-560)和 γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)等三种不同的SCA,在溶剂热环境中与碱处理后的PI表面进行作用.用水汽辐照试验评价SCA与PI的结合状况.样品表面形貌用SEM扫描电镜和材料分析显微镜表征,表面润湿性用接触角测量仪测定,透光率用紫外可见分光光度计表征.结果 经0.1 mol/L NaOH水热处理后,Kapton表面的水接触角由77°下降为53°.KH-550溶剂热环境下,在Kapton表面形成均匀的水解层.水汽辐照试验后,该水解层依然保持完整,透光率没有下降.但KH-560和KH-570水解层出现脱落,透光率分别下降了4.4％和9.3％.结论 SCA虽然可以有效改善聚合物基体的润湿性,提高无机涂层与基体的界面粘附性,但在SCA选取上,必须考虑其与聚合物表面的相互作用.若SCA与聚合物基体的结合不牢固,反而更易造成涂层开裂、脱落,成为潜在的不稳定因素.     

一种监测月球尘埃沉积质量的方法

月球探测过程中,由于自然悬浮和人类活动激起的月尘沉积在航天器表面,致使航天器敏感部件性能下降,需要实地监测长期探测过程中月尘的沉积质量,进而对其影响进行预估。通过对月尘遮挡效应的研究,设计利用测量太阳电池短路电流来监测月尘沉积量的方法。     

Preparation of α-SnWO4 hierarchical spheres by Bi3+-doping and their enhanced photocatalytic activity under visible light

Bi-doped α-SnWO₄ porous spheres assembled by thin plates were prepared by a simple hydrothermal process without any template. The effects of Bi³⁺ ions on the microstructure and photocatalytic activity of α-SnWO₄ were investigated. The doping of Bi can induce a shape transformation from nanoplates of pure α-SnWO₄ to hierarchical spheres of Bi-doped samples. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic de-colorization of methyl orange (MO) under visible light irradiation. Bi-doped α-SnWO₄ samples exhibit better photocatalytic property than pure α-SnWO₄, and the optimal Bi-doping concentration is around 0.5 at%. The enhanced photocatalytic properties of Bi-doped α-SnWO₄ spheres can be ascribed to the porous hierarchical structure and the introduction of defects induced by Bi-doping, which improve visible-light absorption and allow the efficient charge separation of the photogenerated electron-hole pairs. Bi-doped α-SnWO₄ has a great potential in industrial water treatment due to its satisfactory recyclability and stability.     

在聚酰亚胺表面构筑含微纳米SiO2颗粒涂层的方法研究

目的 研究一种将St?ber法制备的SiO2纳米微球分散在含硅溶胶体系中,在聚酰亚胺(PI,Kapton)表面制备含SiO2微纳米颗粒涂层的新方法,并利用该涂层提高Kapton薄膜的使用寿命和抗原子氧(atomic oxygen,AO)侵蚀能力.方法 用正硅酸乙酯(TEOS)在碱性条件下制备St?ber微球,用3-氨丙基三乙氧基硅烷(APTES)在酸性条件下制备含硅溶胶.将St?ber微球均匀分散到溶胶中,用提拉镀膜方法在经低浓度NaOH水热处理后的Kapton薄膜表面,制备含SiO2微纳米颗粒的涂层.在束流密度为1.43×1016 atoms/(cm2·s),辐照时间为6 h的AO环境中进行模拟试验.用SEM扫描电镜和AFM原子力显微镜表征试验前后样品的表面形貌.结果 AO辐照后,原始Kapton薄膜的质量损失和AO侵蚀率分别为1.39 mg/cm2和3.17×10?24 cm3/atom,且Kapton表面被严重侵蚀;而有涂层的Kapton样品,质量损失和AO侵蚀率分别下降为0.10 mg/cm2和0.22×10?24 cm3/atom,侵蚀率只相当于原始Kapton的6.9％.结论 采用St?ber与sol-gel相结合的方法,提高了所制备涂层中SiO2的含量.模拟试验表明,该涂层提高了样品的抗AO侵蚀能力.此制备方法简单实用,对于长寿命航天器中聚合物材料的AO防护,具有一定的研究意义.     

Liquid phase formation in the system SiC,Al2O3, Y2O3

The liquid phase formation in the system SiC–Al₂O₃–Y₂O₃ was investigated via differential thermal analysis (DTA) combined with thermogravimetry (TG). For this purpose mixtures of various alumina and yttria mol ratios and 10 and 20 mol% silicon carbide were densified and heat treated at different temperatures. It was shown that silicon carbide in the examined amounts has low influence on the melting temperature of the oxide phase. The compositions and microstructures formed were studied by SEM, EDX and XRD. The results were compared to thermodynamic calculations.     

适用于Ka波段圆形电子注行波管的半圆形卷绕微带线慢波结构

提出了一种基于开槽介质基底的卷绕微带线慢波结构.由于金属曲折微带线印制在介质基底的半圆形槽中,这种卷绕微带线慢波结构非常适合圆形电子注行波管,从而使得采用这种新型慢波结构的行波管可以利用传统的周期永磁磁场进行聚焦.文章对提出的卷绕微带线慢波结构的色散特性,耦合阻抗,传输特性及注-波互作用进行了分析.和传统的平面微带线慢波结构相比,提出的卷绕微带线慢波结构具有更低的相速、更弱的色散和更高的耦合阻抗,从而使得其适合于低电压、宽频带、小型化的毫米波行波管.将同步电压及直流电流分别设置为6 550 V及0.1 A的情况下,基于该卷绕微带线慢波结构的Ka波段行波管在35 GHz处能够输出42.32 W的功率,对应增益为26.26 dB,且均匀聚焦磁场只需0.4 T.