内网安全技术分析与标准探讨

论文通过对内网安全技术和产品的分析,给出了内网安全的威胁模型,并对其技术和产品标准化进行了探讨。     

纳米氧化铁的制备工艺及其进展

总结了当前制备纳米氧化铁的各种方法,对一些传统的方法进行了详细分类,介绍了一些交叉制备的方法,阐述了液相制备的一些新方法等,同时对各种制备方法的工艺原理及特点进行了比较,说明了各种方法的优缺点.     

Preparation and properties of unidirectional boron nitride fibre reinforced boron nitride matrix composites via precursor infiltration and pyrolysis route

The unidirectional boron nitride fibre reinforced boron nitride matrix (BN_f/BN) composites were prepared via the precursor infiltration and pyrolysis (PIP) route, and the structure, composition, mechanical and dielectric properties were studied. The composites have a high content and fine crystallinity of BN. The density is 1.60 g cm⁻³ with a low open porosity of 4.66%. The composites display good mechanical properties with the average flexural strength, elastic modulus and fracture toughness being 53.8 MPa, 20.8 GPa and 6.88 MPa m^1/2, respectively. Lots of long fibres pull-out from the fracture surface, suggesting a good fibre/matrix interface. As temperature increases, both of the flexural strength and elastic modulus exhibit a decreasing trend, with the lowest values being 36.2 MPa and 8.6 GPa at 1000 °C, respectively. The desirable residual ratios of the flexural strength and elastic modulus at 1000 °C are 67.3% and 41.3%, respectively. The composites have excellent dielectric properties, with the average dielectric constant and loss tangent being 3.07 and 0.0044 at 2-18 GHz, respectively.     

Microwave dielectric properties of BaO-2(1 − x)ZnO-xNd2O3-4TiO2 (x = 0-1.0) ceramics

Microwave dielectric properties of (1 − x)BaZn₂Ti₄O₁₁-xBaNd₂Ti₄O₁₂ (x = 0-1.0) ceramics were investigated by the solid-state reaction with the purpose of finding a microwave ceramics with high dielectric constant (?_r), high quality factor (Q × f) and low temperature coefficient of resonant frequency (τ_f). A two phase system BaZn₂Ti₄O₁₁-BaNd₂Ti₄O₁₂ was formed and SEM photographs show equiaxed BaZn₂Ti₄O₁₁ grains and columnar BaNd₂Ti₄O₁₂ grains. The microwave dielectric properties were strongly determined by the chemical composition. As increasing x from 0 to 1.0, the phase composition varied from pure BaZn₂Ti₄O₁₁, to the two phase system BaZn₂Ti₄O₁₁-BaNd₂Ti₄O₁₂ and then to pure BaNd₂Ti₄O₁₂. Therefore, the ?_r raised from 29.1 to 82.0 and the Q × f values decreased from 54,630 GHz to 8110 GHz, and the τ_f values increased from −29 ppm/°C to 94 ppm/°C. 0.8BaZn₂Ti₄O₁₁-0.2BaNd₂Ti₄O₁₂ ceramics sintered at 1250 °C for 2.5 h had ?_r = 39.1, Q × f = 37,850 GHz and τ_f = −9 ppm/ °C.