Zn掺杂SnO2纳米线的制备与结构表征

利用化学气相沉积(CVD)方法,通过金属Sn粉和Zn粉在770℃下与氧气直接反应,以金为催化剂,成功地在硅片基底上制备了Zn掺杂的SnO2纳米线.对其制备参数进行了优化,获得了分布均匀、表面光滑的纳米线,其平均直径约为50nm,长度可达几十微米.并利用X射线衍射(XRD)、能谱分析(EDX)、场发射扫描电镜(FE-SEM)、透射电镜(TEM)和X射线光电子能谱(XPS)等设备对其形貌、结构特征进行了表征.     

甲烷气体检测系统的设计

甲烷是易燃易爆气体,是重要的工业原料和日常生活的燃气,同时也是温室效应最主要的气体之一,快速、实时检测甲烷的产生和泄漏及其体积分数具有十分重要的意义。将吸收式光纤传感技术、差分检测技术及计算机数据处理技术相结合,设计了时间双光路差分气体在线检测系统,可对气体体积分数进行实时在线连续检测。灵巧的波长切换机构,用低廉的LED作光源的时间双光路差分检测系统就可以实现甲烷气体的差分体积分数测量。以具有强大软件开发能力的V isual C++6.0为工具,基于用户界面设计出该监测系统的实时动态监控软件,实现了气体的实时在线检测。本系统的测量范围为0~25%,分辨力为50×10-6,并且测量灵敏度可调,最小灵敏度为142.35×10-6。     

高频地波雷达天线阵抗电离层干扰

高频表面波雷达是近年发展起来用于超视距监测大面积海洋环境的工具,但由于天线本身的特性和天线场的限制,发射天线辐射波束E面有一定的宽度或向上翘起一定角度,其辐射的电磁波能量除了沿海面绕射传播外,还有一部分能量以一定的角度向上半空间辐射,与电离层和所经路径上的散射体相互作用后,其后向散射信号又以原路径回到雷达,并对雷达形成严重的自干扰.本文基于自适应天线理论,在对功率倒置算法改进的基础上,介绍了一种自适应对消电离层自干扰新方法,雷达现场观测实验表明,本方法可以抑制电离层自干扰.     

采用高效LDO为亚微米CMOS负载供电

论述数字IC的供电问题.     

工频恒定电压下SF6气体中沿面放电发展过程研究

气体绝缘组合电器(GIS)中绝缘缺陷的存在会造成局部放电,导致设备劣化,进而危害到电力系统的稳定性。其中危害较严重的为绝缘子沿面放电缺陷,为探究其在工频恒定电压作用下的放电发展过程及规律,文中制作了“三结合”模型模拟SF 6中沿面放电缺陷并展开试验。保持工频电压在模型闪络电压的95%不变,每隔5 min记录一次局部放电信号,直至模型频繁发生闪络,分析各阶段放电统计参量的变化。结果表明沿面模型在闪络前的放电呈现放电重复率增加、放电量增加、放电间歇、放电再次增强的发展过程。放电间歇的产生与SF 6的强电负性、电场均匀化等均有一定关系。因此,需通过长时间放电检测以准确判定设备劣化阶段,并采取相应措施。     

Synthesis,characterization and photoactivity of bi-crystalline mesoporous TiO2

Mesoporous titania (meso-TiO₂) has received extensive attention owing to its versatile potential applications. This paper reports a low-temperature templating approach for the fabrication of meso-TiO₂ using the peroxo titanic acid (PTA) sol as precursor and Pluronic P123 as nonionic template. The TGA, XRD, N₂ sorption, FE-SEM and HRTEM were used to characterize the obtained samples. The results showed that meso-TiO₂ with high surface area up to 163 m²·g^–1 and large pore volume of 0.65 cm³·g^–1 can be obtained. The mesopore sizes can be varied between 13 and 20 nm via this synthesis approach. The amount of P123 and the calcination conditions were found to have great influence on the mesoporous and crystalline structures of meso-TiO₂. The photocatalytic activity testing clearly shows that the high surface area and bi-crystallinity phases of meso-TiO₂ play important roles in enhancing photocatalytic properties of meso-TiO₂ in photo-decomposing Rhodamine B in water.     

Facile and controllable preparation of mesoporous TiO<Subscript>2</Subscript> using poly(ethylene glycol) as structure-directing agent and peroxotitanic acid as precursor

This work demonstrated that mesoporous TiO₂ (meso-TiO₂) with controllable mesoporous and crystalline structures can be facilely prepared by using poly (ethylene glycol) (PEG) as structure-directing (SD) agent and peroxotitanic acid (PTA) as precursor. Meso-TiO₂ with high specific surface area (157 m²?g^-1), pore volume (0.45 cm³?g^-1) and large mesopore size of 13.9 nm can be obtained after calcination at 450°C. Such meso-TiO₂ also shows relatively high thermal stability. BET surface area still reaches 114 m²?g^-1 after calcination at 550°C. In the synthesis and calcination process, PEG that plays multiple and important roles in delivering thermally stable and tunable mesoporous and crystalline structures shows to be a suitable low-cost SD agent for the controllable preparation of nanocrystalline meso-TiO₂. The photocatalytic activity tests show that both high surface area and bi-crystallinity of obtained meso-TiO₂ are important in enhancing the performance in photo-decomposing Rhodamine B in water.     

研发硬质合金的集成计算材料工程

用于研发硬质合金的集成计算材料工程是将微观(10~(-10)10~(-8)m)、细观(10~(-8)10~(-4)m)、介观(10~(-4)10~(-2)m)和宏观(10~(-2)10 m)等多尺度计算模拟和关键实验集成到硬质合金设计开发的全过程中,通过成分-工艺-结构-性能的集成化分析,把硬质合金的研发由传统经验式提升到科学设计,从而大大加快硬质合金材料的研发速度,降低研发成本.本文详细阐述了第一性原理计算、CALPHAD方法、相场模拟和有限元模拟等计算模拟方法及各种微结构表征和性能测定的实验方法,论述了其在硬质合金研发中所发挥的具体作用.基于集成计算材料工程,提出了从用户需要、设计制备和工业生产的3个层面研发硬质合金的具体框架.通过应用实例,展示了集成计算材料工程在新型硬质合金研发中的强大功能,为新型硬质合金的设计和开发提供了新模式.     

Unexpected liquefaction under isotropic consolidation of idealized granular materials

The drained isotropic compression behaviour of very loose and fully saturated monodisperse glass beads in triaxial compression is investigated in this paper. Short cylindrical samples were prepared by moist-tamping technique and isotropically compressed in a classical axisymmetric triaxial machine. Very loose glass bead samples exhibit numerous local collapses with sudden volumetric compaction and axial contraction of very large amplitude and experience ultimately global collapse with spontaneous liquefaction under undetermined external isotropic stress. Excess pore pressure instantaneously generated at the beginning of the collapse phenomenon, and rapidly dissipated with the usual drainage system, shows a global complex system with local dynamic instability. The dynamic time evolution of the excess pore pressure \(\varDelta U\) consists in a first and fast transient phase I at constant volume and constant axial strain with large spikes \(\varDelta U^{peak}\), followed by an intermediate second phase II of large increase of volumetric compaction and axial contraction at stabilizing \(\varDelta U_{stable}\) or constant effective stress \(\sigma ^{\prime }\) and finally a third and longest phase III of excess pore water pressure dissipation at nearly constant axial strain toward the initial back-pressure. For local collapses, the second phase is totally missing. Upon ignoring the local collapses, very loose idealized granular materials have a unique and global isotropic compressibility behaviour, independently of the void ratio at the end of the fabrication stage; and liquefaction-free for dense state below a threshold void ratio at fabrication \(e_{30}^{liq}\), representing the transition from global instability with total failure to local instability with partial collapse. This paper provides the first reported spontaneous liquefaction instability under isotropic consolidation. It gives the necessarily conditions for an isotropic liquefaction and emphases some usually hidden or partially developed mechanisms underlying the diffuse instability phenomenon and adds a new intriguing layer to the complex behaviour of idealized granular materials in classical drained triaxial isotropic compression.