TH-1169无溶剂高纯度环氧浸渍树脂的性能研究

通过改性高纯度环氧树脂,以特种潜伏性固化剂代替部分酸酐制备了单组份TH-1169无溶剂低粘度环氧浸渍树脂,并对其进行常规性能测试。结果表明：该树脂具有优异的贮存稳定性能、耐热性能、力学性能及电气绝缘性能。     

聚脲酰亚胺膜的制备、性能和液晶分子定向功能的表征

以均苯四甲酸酐(PMDA)、4,4’-二氨基二苯醚(ODA)和四甲基-双（γ-氨丙基）二硅氧烷(APDS)合成了氨端基聚酰胺酸预聚体,然后分别用甲苯二异氰酸酯（TDI）和二苯甲烷二异氰酸酯（MDI）扩链制得聚脲酰胺酸,经亚胺化制备了两种聚脲酰亚胺POAU(T)和POAU(M)。通过TGA和IR研究聚脲酰亚胺的热稳定性,测试聚脲酰亚胺在频率为0.1~105 Hz和温度50~300℃的介电常数(ε)和介质损耗(tanδ)。结果表明：聚脲酰亚胺分子链段中存在两个转变温度Tg,脲基链段的Tg为244℃(POAU(T))及243℃（POAU(M)）,酰亚胺环链段的Tg温度为329℃(POAU(T))及331℃(POAU(M))。预倾角测定（TBA）结果表明该聚脲酰亚胺是一种良好的液晶分子定向膜材料。     

纳秒脉冲介质阻挡放电等离子体对超声速燃烧室中凹腔性能的影响

为考察纳秒脉冲介质阻挡放电(NP-DBD)等离子体对超声速燃烧室中凹腔性能的影响,在凹腔后壁面上部区域布置表面介质阻挡放电激励器产生等离子体,基于NP-DBD等离子体高斯分布热源模型,采用3维数值模拟方法研究了等离子体作用下燃烧室壁面压力、凹腔阻力、质量交换率以及燃料分布的变化。研究结果表明,NP-DBD等离子体虽然降低了对称面处凹腔后缘波系强度,但结合凹腔后壁区域温度分布特征知等离子体热效应较弱,故整个凹腔波系受到影响较小;凹腔质量交换能力获得大幅提高,其阻力则略有减小;等离子体缩小了凹腔上方燃料的分布范围,凹腔下游燃料掺混效率有小幅提升。     

Structural and Dielectric Properties of Ca Doped Barium Iron Niobate

Ceramic materials with high dielectric constant are being used in many electric and electro-optics applications. Ca substituted barium iron niobate with general formula (Ba_1-xCa_x) (Fe_0.5Nb_0.5)O₃ with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by conventional solid state reaction method. Structural properties were investigated using X-ray diffraction and scanning electron microscope. Two types of phases were observed for 0.4 ≤ x ≤ 08. Dielectric constant and loss tangent were measured using impedance analyzer in the frequency range of 20 Hz–1 MHz at room temperature. Dielectric constant and loss tangent were found to decrease with increasing the frequency. A relatively good combination of dielectric constant and loss tangent was obtained for x = 0.2 (?_r = 1441 and tan δ = 0.19) at 10 KHz.     

The NMR sensitivity achievable with a slotted-tube resonator

The signal-to-noise ratio achievable with the slotted-tube resonator (STR), a fundamental type of high radiofrequency coil for nuclear magnetic resonance (NMR) experiments, was formulated in an equation. This equation is based on formulae presented by Hoult and Richards [J Magn Reson 24, 71 (1976)] and Hoult and Lauterbur [J Magn Reson 34, 425 (1979)]. The equation assumes that the sample is positioned within the homogeneous region of magnetic fluxB ₁ generated by the STR, and involves no unknown factors. The NMR sensitivity of an experiment with an STR can therefore be predicted, and the equation is applicable to any nuclear species, static field strength, and dimensions of the sample and STR.     

高压电机用环氧玻璃粉云母带

本介绍了介电强度达45MW／m以上的高压电机用环氧玻璃粉云母带的研制情况及应用。     

氰酸酯树脂的结构与性能

氰酸酯树脂是一种含三嗪环网状结构的高性能树脂;该结构赋予它优异的介电性能、较高的玻璃化温度、较低的收缩率和优异的力学性能。氰酸酯树脂有不同的化学结构,不同的结构它们表现出不同的物理性能。以上海慧峰科贸有限公司生产的不同型号、结构的氰酸酯树脂为例,叙述它们的各种性能。     

基于双频逆变拓扑结构的臭氧发生器电源研究

文章将成熟应用于感应加热电源的双频逆变拓扑结构运用于负载成容性的臭氧发生器电源，提出了一种新的多频臭氧发生电源，研究了这种电源的工作原理和电路的工作模态，通过对电路稳态工作过程波形的推导，得出了臭氧发生器介质层电压以及放电功率的表达式，并给出了仿真结果。     

Dielectric and Piezoelectric Properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-NaNbO<Subscript>3</Subscript>Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 – x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃] – xNaNbO₃(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant _r and dissipation factor tan measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures T_d and T_m are lowered due to introduction of NaNbO₃. P-E hysteresis loops show that 0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃ ceramics has the maximum P_r and E_c corresponding to the maximum values of electromechanical coupling factor K_p and piezoelectric constant d_33. The piezoelectric constant d₃₃ and electromechanical coupling factor K_p decrease a little, while the dielectric constant ₃₃^T/₀ improves much more when the concentration of NaNbO₃ is 8 mol%.     

Dielectric Properties of Niobium and Lanthanum Doped Lead Barium Zirconate Titanate Relaxor Ferroelectrics

The lead barium zirconate titanate (PBZT) relaxor ferroelectrics are ideal for high voltage capacitor applications due to their high dielectric constant, stability under DC bias, and temperature stability. In this study the composition (Pb_0.65Ba_0.35)(Zr_0.70Ti_0.30)O₃ was selected as the base composition. It exhibited typical relaxor characteristics such as frequency dispersion and diffuse phase transition. The dielectric constant is 6000 at room temperature and remains almost constant under electric field as high as 20 kV/cm. To further enhance the dielectric properties, various amounts of niobium oxide and lanthanum oxide dopants were added to the base PBZT to alter the defect structure and hence the dielectric properties. It was found that the dielectric constant of 1% Nb-doped samples was increased by 20–25% while maintaining similar voltage stability. This increase was attributed to the abnormal grain growth in the Nb-doped sample, and the correlation between microstructure and dielectric constant was drawn through a grain size study. The La addition only caused a monotonic decrease of dielectric constant and slightly improved voltage stability.