沉积温度对碳化硅基体及其复合材料的影响

研究了沉积温度对化学气相渗透ＳｉＣ基体微观结构２及其纤维增强复合材料性能的影响。９５０℃沉积碳化硅为非晶态；１０００℃以上沉积出的碳化硅为结晶态，１０５０℃沉积碳化硅晶体取向为主：１２５０℃沉积碳化硅晶体取向为主。沉积温度升高，沉积深度和均匀性降低。     

Fabrication and Investigation on Double-Hollow Shell CoFe Oxide@TiO2 Nanocube with Superior Electromagnetic Properties

Electromagnetic wave absorbing materials are urgently required in the fields of medicine, communication, and military. However, the thickness, weight, narrow effective bandwidth, and weak absorbing ability of the materials restrict their further application. In this work, a double-layer hollow nanocube with a dielectric titanium dioxide (TiO2) shell and a magnetic CoFe oxide inner shell is prepared. Prussian blue (PB) is prepared by the hydrothermal method, and used as the template to prepare PB@CoFe PB analogue (PBA). After selective etching and further calcination, hollow CoFe oxide particles are obtained. The obtained particles are then coated with SiO2 and TiO2, respectively, and the intermediate layer is dislodged to obtain the final CoFe oxide@TiO2 with the hollow double shell structure. The obtained double-layer hollow structure can effectively capture the incident electromagnetic waves, and increase the propagation path. Moreover, the obvious enhancement of interface polarization and the improvement of impedance matching enhance the wave absorbing ability of the material. The analysis results show that, the structure is stable and the dispersion is good. The maximum reflection loss (RL) at 10 GHz is as high as -46.1 dB with the sample thickness of 1.6 mm. The light-weight and high-efficiency CoFe oxide@TiO2 absorber is promised to be used in commercial and military aerospace fields.     

全碳化硅功率模块开关瞬态特性及损耗研究

为了加快全碳化硅功率模块的实际工程应用,针对全碳化硅模块开通关断过程中电压电流变化率、栅极电压耦合、开通损耗和关断损耗开展了分析,并与传统IGBT功率模块进行了对比分析。在全碳化硅功率模块双脉冲试验的基础之上,研究了不同电压电流等级下开关瞬态特性和开关损耗,提取试验参数,获得了电压电流应力大小,为全碳化硅功率模块的工程应用提供有效参考。     

Luminescent Nanocrystalline Silicon Carbide Thin Film Deposited by Helicon Wave Plasma Enhanced Chemical Vapour Deposition

Hydrogenated nanocrystalline silicon carbide （SIC） thin films were deposited on the single-crystal silicon substrate using the helicon wave plasma enhanced chemical vapor deposition （HW-PECVD） technique. The influences of magnetic field and hydrogen dilution ratio on the structures of SiC thin film were investigated with the atomic force microscopy （AFM）, the Fourier transform infrared absorption （FTIR） and the transmission electron microscopy （TEM）. The results indicate that the high plasma activity of the helicon wave mode proves to be a key factor to grow crystalline SiC thin films at a relative low substrate temperature. Also, the decrease in the grain sizes from the level of microcrystalline to that of nanocrystalline can be achieved by increasing the hydrogen dilution ratios. Transmission electron microscopy measurements reveal that the size of most nanocrystals in the film deposited under the higher hydrogen dilution ratios is smaller than the doubled Bohr radius of 3C-SiC （approximately 5.4 nm）, and the light emission measurements also show a strong blue photoluminescence at the room temperature, which is considered to be caused by the quantum confinement effect of small-sized SiC nanocrystals.     

一种适用于SiC基变换器的桥臂串扰抑制方法

在对碳化硅基变换器中的桥臂串扰产生机理进行深入分析的基础上,提出一种新型有源箝位桥臂串扰抑制方法,并构成适用于碳化硅(Silicon carbide,SiC)基桥臂电路的串扰抑制驱动电路。给出其等效电路模态分析,讨论了关键参数的设计方法。设计制作了串扰抑制驱动电路模块板,并在1kW永磁同步电机(Permanent magnet synchronous motor,PMSM)驱动实验平台上进行了验证。实验结果表明,该方法能够有效抑制SiC基变换器中的桥臂串扰。     

飞艇载荷舱电子设备散热研究

在分析平流层飞艇载荷舱传热特性和高空环境特性的基础上,提出了采用基于开放式二氧化碳制冷和冷板相结合的平流层飞艇载荷舱电子设备冷却方案。所提出的方案能避免单纯采用冷板散热所面临的制冷量不足的问题。同时,通过建立理论计算模型并结合VC++编程软件,获得了飞艇上升过程中所需要携带的二氧化碳的量的理论值,并分析了气瓶内二氧化碳的状态变化及造成制冷量损失的因素。结果表明:通过计算所得的理论量能够满足飞艇上升过程的制冷要求,且在低储存温度、大管径、低背压的情况下制冷量损失较小。该研究结果为平流层飞艇载荷舱电子设备的冷却提供技术参考。     

多路传感器系统的软件补偿和校准技术的研究

分析了多路传感器系统的软件补偿和校准技术的发展趋势,并根据国内测试校准压力传感器的要求,对自补偿和自校准技术加以研究,同时提出了适合应用的解决方案。     

燃烧产物二氧化碳高温辐射的窄谱带模型参数

窄谱带模型法与CG近似及LS近似结合能够很好处理非灰、非等温、非均匀介质的辐射传输问题,在飞行器发动机燃烧室及尾喷焰高温辐射传输问题研究中多被采用。二氧化碳是含碳类推进剂主要的燃烧产物,其辐射特性的研究一直受到国内外重视,但其现有的窄谱带模型数据不完整或分辨率太低。本文利用最新的高分辨率高温燃气光谱数据库HITEMP(序列号:3153),并将其中的谱线光谱参数外推到300～3000K的温度范围内,计算得到了一个新的、完整的、分辨率较高的二氧化碳窄谱带模型参数库。以本文计算的模型参数为基础,采用窄谱带模型计算了各种光学路径下的发射率、穿透率,其结果与实验值符合很好。      

三维网络碳化硅多孔陶瓷的制备

以中间相沥青添加55%(质量分数,下同)的Si粉混合物为原料,制备了含Si的炭泡沫模板。在高温反应烧结炉中,氩气气氛下1500℃保温1～6h,结合反应烧结工艺制备了碳化硅多孔陶瓷。利用扫描电子显微镜(SEM)和X射线衍射分析仪(XRD)对碳化硅多孔陶瓷的微观形貌、物相组成进行了观察,并对熔融Si与C的反应机理进行了探讨。结果表明:碳化硅多孔陶瓷的微观结构与炭泡沫模板的微观结构一致,烧结温度1500℃下,随着保温时间的延长,多孔陶瓷的弯曲强度先增大后减小,而孔隙率先减小后增大;在保温4h的条件下制备的碳化硅多孔陶瓷主要由β-SiC相组成,最大弯曲强度为26.2MPa,对应的孔隙率为45%。内部熔融的Si与外部熔融的Si同时与C反应生成SiC,最后两者结合在一起形成致密的SiC多孔陶瓷。     

多孔Si3 N4 表面Al-Y-Si-O-N 陶瓷涂层的制备和表征

采用溶胶-凝胶法,利用Al2O3-Y2O3-SiO2溶胶中氧化物与基体中的Si3N4颗粒反应制备一层致密A1-Y-Si-O-N陶瓷涂层.主要研究了烧结温度对陶瓷涂层的组织和性能的影响,利用XRD和EDS分析涂层的相组成和微区元素组成,通过SEM观察涂层的微观形貌.结果显示:在1 400℃烧结时,能够制备出较为致密的陶瓷涂层,涂层由β -siMon,Si2ON,SiO2和非晶相组成;与基体相比,试样的吸水率下降了32.8％～90％,强度提高了2.1％～25.9％.