Effect of boron content on the microstructure and electromagnetic properties of SiBCN ceramics

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was ?35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached ?29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.     

High performance X-band electromagnetic wave absorption of SiBCN metamaterials fabricated by direct pyrolysis

Electromagnetic wave (EMW)-absorbing ceramic metamaterials without doping absorbers were prepared by direct pyrolysis of polymer-derived SiBCN ceramics (PDC-SiBCN). The pyrolytic behavior of the ceramics, the effect of the pyrolysis temperature on the mechanical strength, and the EMW absorption properties of the metamaterials are discussed in detail. The mechanism of the enhanced EMW absorption by the metamaterials was further analyzed. The results indicated that PDC-SiBCN demonstrated the optimum impedance matching and absorption performance at a pyrolysis temperature of 1500 °C. The metamaterial can effectively absorb the full X-band when its thickness is in the range of 4.3–5.7 mm. When the thickness was adjusted to 4.7 mm, the minimum reflection coefficient (RC) reached − 26.6 dB. In addition, the flexural strength of the metamaterial was 31.2 MPa, and the compressive strength was 96.9 MPa, which is 60 times higher than that of the solid structure. This study provides a feasible guide for the simple fabrication of lightweight, high-strength, and high-performance EMW-absorbing materials.     

Adjustable iron-containing SiBCN ceramics with high-temperature microwave absorption and anti-oxidation properties

Quaternary siliconboron carbonitride (SiBCN) ceramics show excellent high-temperature stability and oxidation resistance, indicating great potential as high-temperature electromagnetic (EM) wave absorbing materials. In this contribution, an efficient and facile method was developed to prepare bulk iron-containing SiBCN (Fe–SiBCN) ceramics with remarkable EM wave absorption at high temperature by pyrolyzing boron and iron containing precursors (PSZV-B–Fe). The introduction of boron and iron not only improves the high-temperature stability but also influences the complex permittivity and EM wave absorption. The minimum reflection coefficient (RC_min) is −61.05 dB, and the effective bandwidth absorption (EAB) is 3.35 GHz (9.05–12.4 GHz). The RC_min will be decreased to −52.3 dB at 600°C as well as the EAB covers more than 67% of the X band (2.8 GHz). The high-temperature stable Fe–SiBCN ceramics with adjustable dielectric properties can be utilized as high-performance EM wave-absorbing materials in high-temperature and harsh environments.     

The effect of glow discharge plasma on the surface properties of Poly (ethylene terephthalate) (PET) film

In the present work, Poly (ethylene terephthalate) films have been exposed to glow discharge air plasma to improve their surface properties for technical applications. Surface energy values have been estimated using contact angle value for different exposure times and different test liquids. Surface composition and morphology of the films were analyzed by XPS and AFM. Crystallinity of the plasma treated samples were studied by XRD analysis. The improvement in adhesive strength was studied by measuring T-peel strength and lap shear strength tests. It was found that the plasma treatment modified the surfaces both in chemical composition and morphology. Change of chemical composition made the polymer surfaces to be highly hydrophilic, which mainly depends on the increase in oxygen-containing groups. The AFM and XRD observation showed that the surface roughness and crystallinity of the PET film increased due to plasma treatment.     

基于中子多重性方法的~(252)Cf中子强度测量算法及实验研究

252 Cf中子发射强度的获取在核技术应用中具有重要意义,为测量其绝对发射强度,分析了一种可能的替代测量算法,该算法基于252 Cf自发裂变的中子多重性分布,并结合中子在测量系统内的衰减时间行为,在不依赖测量系统探测效率和被测样品任何信息的条件下,可给出其中子强度测量值。利用5个252 Cf镀膜中子源在中子多重性测量装置上进行了实验测量,通过测量算法获取的中子强度值与账面记录值最大相对偏差为1.41%,其结果初步验证了该算法的正确性。     

一种仿252Cf中子源脉冲信号频谱分析的FPGA设计与实现

从252Cf自发裂变中子源之裂变中子在时间分布上相互独立的基本原理出发,针对随机核信号在时间上呈泊松分布,在幅度上服从高斯分布的这一特征,开展了基于FPGA技术的仿252Cf中子源随机核信号产生及其频谱分析系统的研究.通过比较仿252Cf中子源核信号与核信号的功率谱趋势,验证了仿252Cf中子源随机信号产生机制的可靠性...     

Development of Flexible Neutron-Shielding Resin as an Additional Shielding Material

A soft-type neutron-shielding resin has been developed by improving an existing hard-type neutronshielding material using the epoxy-based resin as an additional shielding material. A flexible heat-resistant neutron-shielding material has been developed, which consists of a new polymer-based resin with boron. The neutron shielding performance of the developed flexible heat-resistant resin with the ²⁵²Cf neutron source is almost the same as that of polyethylene. The outgases of H, H₂, NH₄, H₂O, CO, O₂, C₄H₁₀, and CO₂ from the developed resin have been measured at high temperature (up to 250°C) by thermal desorption spectroscopy methods. The soft-type resin and the newly developed heat-resistant resin will be applied to prevent the effects of neutron streaming and to control the movement of a vibrated pipe as the seal material around the plumbing in the future fast reactor and innovative fission reactor.     

Film growth by polyatomic C2H5 bombarding a diamond (1 0 0) surfaces: Molecular dynamics study

The deposition of polyatomic C₂H₅⁺ ions is studied using classical molecular dynamics simulations with a new improved Brenner potentials developed by Brenner. The simulation results show that when the incident energy is less than 65 eV, the deposition coefficient of H is larger than that of C atoms. When the incident energy is larger than 65 eV, the deposition of H is less than that of C atoms. With increasing incident energy, a transition from Csp3-rich to Csp2-rich in the grown films is found.     

应用锎源实验结果预估空间轨道单粒子翻转率

在实验研究的基础上,分析了应用锎源实验结果预估空间轨道单粒子翻转率的可行性。以静态存储器的锎源单粒子翻转截面为例,分3种情况预估了该器件在地球同步轨道上的单粒子翻转率。结果表明,若器件的锎源单粒子翻转截面小于10^-10 cm²/bit,在地球同步轨道上的单粒子翻转率则应小于10^-8d^-1•bit^-1。     

IDT6116单粒子敏感性评估试验技术研究

为评估IDT6116SRAM单粒子敏感性,采用地面试验方法和地面试验系统,利用脉冲激光、重离子和²⁵²Cf源3种不同的地面模拟源,对IDT6116SRAM器件进行单粒子敏感性试验研究,并对3种不同的模拟源的试验结果进行等效性分析比较,同时进行总剂量效应对单粒子效应影响的试验研究。研究结果表明：IDT6116SRAM抗单粒子翻转和锁定的能力较强;接受一定辐照剂量后的试验样品对单粒子翻转更加敏感,且翻转阈值略有降低,翻转截面略有增大。