PFA/多孔PTFE/PFA三层驻极体膜的压电活性

通过升温至PFA熔融温度以上，在PTFE多孔膜的双面粘贴上一层PFA薄膜，形成具有封闭式孔洞的三层复合膜。以栅控电晕充电，等温表面电位衰减和准静态压电系数测量研究了这类复合膜的电荷稳定性及压电活性。利用扫描电镜（SEM）的结果对这种夹心结构复合膜的电荷稳定性和压电活性的结构根源进行了分析。     

压电微喷驱动振子振动的理论分析

压电驱动振子是由压电材料层和单晶硅层复合而成.以压电微喷驱动振子为研究对象,根据压电本构方程和弹性薄板弯曲理论,应用能量法对其进行了理论分析,建立了周边固支条件下压电驱动振子振动的理论模型,推导求解了驱动振子一阶固有频率及位移函数,MATLAB编程计算结果与ANSYS软件仿真结果误差为6.6%,表明了二者的一致性.分析了激励电压及压电驱动振子结构参数对轴向振动位移的影响,研究结果可为压电微喷液滴发生器的设计及控制提供理论依据.     

压电致动式圆片驱动装置结构分析与设计

根据压电致动的工作原理,建立了圆片微驱动装置的压电复合层薄板的机电耦合力学模型;应用弹性薄板的小挠度弯曲理论,推导出圆形压电复合层薄板的弹性曲面微分方程,提出由逆压电效应引起的平面应变可以等效为作用在压电复合层薄板上的横向荷载的设计方法;指出等效横向荷载取决于平行板电容器的边缘电场分布.推导了压电复合层薄板中性面的表达式.在求电场的超越方程数值解的基础上,建立了微驱动装置的有限元结构模型,并对某微泵驱动装置进行了计算仿真,得到令人满意的结果.     

复合双压电层FBAR的建模与仿真

在复合单压电层薄膜体声波谐振器(FBAR)的基础上,提出了一种新型的复合双压电层FBAR,它可以大大提高压电材料选择的灵活性。通过建模得到该结构的输入阻抗解析表达式,据此进行了仿真分析。仿真结果表明,基模谐振频率随双压电层结构中的较高声速压电膜的厚度所占比率的增加而加速增大,而相对带宽随较高机电耦合系数的压电膜的厚度与较低机电耦合系数的压电膜的厚度比的增加逐渐增加,并且复合双压电层FBAR出现了单压电层时所没有的模式。     

Teflon/Al_2O_3纳米复合膜的结构及微观摩擦学特性

为了提高聚四氟乙烯的耐磨损能力,用射频磁控溅射法交替溅射纯Teflon靶和Al2O3靶获得Teflon/Al2O3多层复合膜,通过PHI-5300 ESCA型X射线光电子能谱及原子力显微镜(AFM)对其结构、力学性能和微观摩擦磨损特性研究表明:Teflon/Al2O3多层复合膜不但具有Al2O3膜的较高硬度和抗磨损性能,而且具有纯Teflon膜的减摩性和高承载能力.同Al2O3相比,复合膜的综合性能优于纯Al2O3膜和纯Teflon膜.Teflon/Al2O3多层复合膜的研制,解决了弹性金属塑料瓦耐磨损能力差的问题.     

Mg-9Gd-3Y镁合金PEO-EPD复合膜层组织结构与耐蚀性研究

为了提高镁合金的耐蚀性,本文利用扫描电镜分析了Mg-9Gd-3Y(GW93)镁稀土合金表面等离子电解氧化陶瓷层、等离子电解氧化-电泳复合膜层和电泳膜层的表面与纵截面形貌组织,利用傅立叶红外光谱仪(FT-IR)分析了电泳膜层有机官能团类型,用电化学测试手段和盐雾试验方法测试了该合金不同处理膜层的耐蚀性,讨论了电泳电压和固体粉料分数对等离子电解氧化-电泳复合膜层厚度、成膜速率和耐蚀性的影响.研究结果表明,随着电压、固体份的升高,等离子电解氧化-电泳复合涂层厚度和成膜速率呈增大趋势,腐蚀速率随着电压升高呈先减小后增大的趋势,随着固体份的增加呈降低趋势.电泳电压为70V,固体份为19%时,在等离子电解氧化膜层上生成陶瓷层与有机化合物层结合紧密的等离子电解氧化-电泳复合膜层,腐蚀电流密度比等离子电解氧化膜层降低两个数量级,自腐蚀电位正移200mV,耐蚀性提高近13倍.     

高性能PZT压电厚膜及MEMS微驱动器技术研究

运用混合溶胶-凝胶法制备了具有钛酸铅(PT)种子层的PZT基压电复合厚膜,包括(100)取向PZT压电厚膜,PZT纳米颗粒增强PZT压电复合厚膜((0-3)PZT)和氧化锌晶须增强PZT复合厚膜(ZnOw-PZT).通过结构表征,研究了工艺条件和膜厚对PZT基厚膜的生长、结晶、取向和微结构的影响,给出最佳工艺条件.并介绍了无阀型压电MEMS微泵、Ⅴ型阀式压电MEMS微泵、压电悬臂梁和三压电悬臂驱动的悬浮膜片式MEMS微镜等微器件的性能.     

Teflon/Al2O3纳米复合膜的结构及微观摩擦学特性

为了提高聚四氟乙烯的耐磨损能力，用射频磁控溅射法交替溅射纯Teflon靶和Al2O3靶获得Teflon/Al2O3多层复合膜，通过PHI－5300ESCA型X射线光电子能谱及原子力显微镜（AFM）对其结构、力学性能和微观摩擦磨损特性研究表明：Teflon/Al2O3多层复合膜不但具有Al2O3膜的较高硬度和抗磨损性能，而且具有纯Teflon膜的减摩性和高承载能力。同Al2O3相比，复合膜的综合性能优于纯Al2O3膜和纯Teflon膜。Teflon/Al2O3多层复合膜的研制，解决了弹性金属塑料瓦耐磨损能力差的问题。     

两层弹性软基底中压电薄膜的屈曲分析

硬薄膜软基底结构在压应力作用下通常会发生一种褶皱形式的屈曲失稳,这种结构在微纳机电系统、柔性电子器件等领域有非常广泛的应用。压电材料因其独特的力电耦合特性具有普通材料不可替代的作用,受到软基底-硬薄膜-软基底3层结构能进一步提高其弯曲性能的启发,从理论上分析了关于压电薄膜3层结构在压应力作用下的屈曲问题,结合线性扰动分析和能量法获得了3层结构压电薄膜屈曲的临界应变、波数、波长和幅值的解析表达式,并且与弹性薄膜3层结构进行了对比分析,发现压电薄膜比弹性薄膜有更强的抵抗屈曲变形能力。     

压电复合材料层合板弯曲变形及脱粘损伤的有限元分析

采用作者新近提出的四节点压电复合材料层合矩形板弯曲单元,对表面粘贴有压电驱动器的复合材料层合板在外加电场和外载荷作用下的弯曲变形进行了分析。通过与相关文献中结果的比较验证了程序的正确性和单元的有效性。研究了不同铺层形式(特别是非均衡性)对层合板弯曲变形的影响规律,并分析了压电驱动器部分脱粘对驱动变形的影响规律。结果表明:驱动器的脱粘损伤对层合板的弯曲变形会产生较大的影响,甚至可能会导致压电驱动器驱动功能(形状控制)的失效。     

磁控溅射TiCN薄膜对Al-Cu-Mg-Ag合金组织与性能的影响

基于正交试验设计，在铝合金表面磁控溅射沉积TiCN薄膜，采用盐雾腐蚀、电化学腐蚀、硬度测试等探究磁控溅射工艺参数（钛靶功率、碳靶功率、氮氩比）对Al-Cu-Mg-Ag合金硬度与抗腐蚀性能的影响规律，并结合扫描电镜（SEM）、X射线衍射（XRD）等对其机理进行探讨。结果表明：磁控溅射工艺参数对合金的膜层硬度、盐雾最大腐蚀深度、腐蚀电流密度、膜基结合力的影响顺序分别为：氮氩比>C靶功率>Ti靶功率；C靶功率>氮氩比>Ti靶功率；C靶功率>氮氩比>Ti靶功率；Ti靶功率>C靶功率=氮氩比。C靶功率200 W、Ti靶功率100 W、氮氩比为1：40时，可以获得耐蚀性、硬度和膜基结合力综合性能优良的TiCN膜层。     

Effect of sintering additives on properties of Si3N4-BN composites fabricated via die pressing and precursor infiltration and pyrolysis route

The Si3N4-BN composites have been prepared via die pressing and precursor infiltration and pyrolysis route using borazine as precursor, and the effect of sintering additives on properties of the composites has been investigated. After sintering additives are adopted, the α to β phase transition of Si3N4 and the mechanical properties of the composites at both room temperature and high temperature are all increased with small extent. When using Y2O3+Al2O3 as additives, the phase transition of Si3N4 and the mechanical properties of the composites have better results. The β-Si3N4 content is 17.47%. The fl exural strength, elastic modulus and fracture toughness of the composites are 188.74 MPa, 84.34 GPa and 2.96 MPa?m1/2, respectively. After exposed at 1 000 ℃ in the air for 15 min, the fl exural strength of the composites is 154.62 MPa with a residual ratio of 81.92%. The elongated β-Si3N4 grains appear in all composites with different sintering additives. Relatively more rod like β-Si3N4 grains can be observed in composites with Y2O3+Al2O3 as additives, making it to possess better mechanical properties.     

Influence of mechanical milling on photocatalytic activity of g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> prepared by heating melamine

Using X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area measurement, ultraviolet-visible diffuse reflection spectra, and photoluminescence spectroscopy, the effect of mechanical milling on the photocatalytic activity of g-C₃N₄ photocatalyst was investigated. The rhodamine B, as a photodegrading goal, was used to evaluate the photocatalytic activity of g-C₃N₄. The experimental results indicate that the milling treatment is an effective method to improve the photocatalytic activity of g-C₃N₄. The enhanced photocatalytic activity was attributed to the improvement in catalyst’s surface area and dye adsorption on catalyst surface. Moreover, checking the luminescence properties of g-C₃N₄, it is found that the photocatalytic active sites on g-C₃N₄ are likely the same as luminescence sites.     

Self-cleaning glass coated with Fe^3＋ -TiO2 thin film

The self-cleaning glass coated with Fe^3 -TiO2 photocatalytic thin film was prepared by sol-gel process from the system Ti(OC4H9),-NH(C2H4OH)2-C2H5OH-H2O containing FeCl3. The microstructure and properties of the film were studied using differential thermal analysis-thermogravimetry(DTA-TG), X-ray diffration (XRD) and scanning electron microscope(SEM). The transmittance of the self-cleaning glass was measured by using UV-Vis spectrometer. The effects of content of Fe^3 and the thickness of Fe^3 -TiO2 thin film on the photocatalytic ac-tivity were examined. The results show that the photocatalytic thin films are mainly composed of Fe3O4 and TiO2 particles within 10-100 nm. The appropriate amount of Fe^3 is effective for improving the photocatalytic activities of TiO2. The best photocatalytic activity is obtained when the molar ratio of Fe^3 to TiO2 is 0. 005 and the glass is coated with 9 layers.     

Preparation and sintering of nano Fe coated Si3N4 composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N₂. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si₃N₄. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. Foundation item: Project(50804016) supported by the National Natural Science Foundation of China     

GNR-TiO_2/g-C_3N_4异质结构的制备及其性能研究

采用二次凝胶-溶胶法和水热法合成了具有光催化效应的GNR-TiO_2/g-C_3N_4异质结构,并对其性能进行了研究.研究结果表明:GNR-TiO_2/g-C_3N_4异质结构表现出强的光催化活性,并在可见光照射下,对有机物亚甲基蓝有良好的催化效果.这主要归因于石墨烯纳米带作为载体,不仅增加了异质结构的比表面积,还使空穴-电子对的再结合率降低.     

Ablation and radar-wave transmission performances of the nitride ceramic matrix composites

The 2.5 dimensional silica fiber reinforced nitride matrix composites (2.5D SiO_2f/Si₃N₄-BN) were prepared through the preceramic polymer impregnation pyrolysis (PIP) method. The ablation and radar-wave transparent performances of the composite at high temperature were evaluated under arc jet. The composition and ablation surface microstructures were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the 2.5D SiO_2f/Si₃N₄-BN composites have a linear ablation rate of 0.33 mm/s and high radar-wave transparent ratio of 98.6%. The fused layer and the matrix are protected by each other, and no fused layer accumulates on the ablation surface. The nitride composite is a high-temperature ablation resistivity and microwave transparent material. Supported by the State Key Laboratory of Advanced Ceramic Fibers & Composites Foundation (Grant No. 2004js51488.0101.kg01.3) and the Innovation Foundation of National University of Defense Technology for Graduate Students (Grant No. 0603)     

Effect of annealing on microstructure and properties of Si_3N_4-AlN composite ceramics

Aiming at developing novel microwave-transparent ceramics with low dielectric loss,high thermal conductivity and high strength,Si3N4-AlN(30%,mass fraction) composite ceramics with La2O3 as sintering additive were prepared by hot-pressing at 1 800 °C and subsequently annealed at 1 450 °C and 1 850 °C for 2 h and 4 h,respectively.The materials were characterized by XRD and SEM.The effect of annealing process on the phase composition,sintering performance,microstructure,bending strength,dielectric loss and the...     

First-Principles Study of the High-Temperature Behaviors of the Willemite-Ⅱ and Post-Phenacite Phases of Silicon Nitride

The structural and elastic properties of the recently-discovered wⅡ- and δ-Si_3N_4 are investigated through the plane-wave pseudo-potential method within ultrasoft pseudopotentials.The elastic constants show that wⅡ- and δ-Si_3N_4 are mechanically stable in the pressure ranges of 0-50 GPa and 40-50 GPa,respectively.The α→wⅡ phase transition can be observed at 18.6 GPa and 300 K.The β→δ phase transformation occurs at pressures of 29.6,32.1,35.9,39.6,41.8,and 44.1 GPa when the temperatures are100,200,300,400,500,and 600 K,respectively.The results show that the interactions among the N-2s,Si-3s,3p bands(lower valence band) and the Si-3p,N-2p bands(upper valence band) play an important role in the stabilities of the wⅡ and S phases.Moreover,several thermodynamic parameters(thermal expansion,free energy,bulk modulus and heat capacity) of δ-Si_3N_4 are also obtained.Some interesting features are found in these properties.δ-Si_3N_4 is predicted to be a negative thermal expansion material.The adiabatic bulk modulus decreases with applied pressure,but a majority of materials show the opposite trend.Further experimental investigations with higher precisions may be required to determine the fundamental properties of wⅡ- andδ-Si_3N_4.     

Fabrication of Fine-Grained Si3N4-Si2N2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

1 IntroductionAs high-temperature structure materials ,nitride ce-ramics possess the excellent mechanical properties ,highmelting temperature ,low density, high elastic modulusand strength, and good resistance to creep, wear andoxidation[1-3]. The intrinsic brittleness and hardness ofsilicon nitride ceramics , however , make it difficult andcostly to machine into complex-shaped components[4 ,5].The fracture toughness of sintered silicon nitride ceramicsmust beimprovedif these ceramics areto be…