Susceptor-assisted fast microwave sintering of TiN reinforced SiAlON composites in a single mode cavity

In the present study, 17 wt % TiN reinforced α-β SiAlON composites were sintered at low temperature by susceptor-assisted microwave heating. The effect of TiN addition on dielectrical properties of starting powders, as well as the influence of sintering temperature on phase evolution, microstructure development and mechanical properties of α/β-SiAlON-TiN composites were investigated. The obtained results showed that TiN addition increased the microwave absorbing properties which is reflected in the peak sintering temperature. Thus, the α:β ratio decreased and mechanical properties were improved, especially the fracture toughness of the composites. Furthermore, an estimate of energy consumption during microwave assisted sintering at the laboratory scale is presented. As a result, the highest values for relative density (97.1%), Vickers hardness (13.35 ± 0.47 GPa), and fracture toughness (7.52 ± 0.54 MPa m^1/2) were obtained by microwave sintering for 30 min at 1300 °C.     

2.5 GHz城市环境电磁态势的计算与补偿

复杂城市空间的电磁态势分布可以通过电磁场数值计算的方法进行预测。文章使用矩量法(MOM)结合一致性几何绕射理论(UTD)的方法对2.5 GHz频率下某小区环境中的电磁态势进行了仿真计算以及实际测量。场景中的树木结构在此频率下显示出比较强烈的波动性,对电磁仿真计算结果产生了不可忽略的影响,文中将其对仿真计算结果的影响进行了单独建模仿真,给出其产生影响的经验值,对仿真结果进行修正。修正结果与测量结果对比证明该经验值在该频率下可以有效补偿计算结果的缺失。     

Impact of Co doping on physical,structural, microstructural and magnetic features of MgZn nanoferrites for high frequency applications

Cobalt (Co) doped MgZn spinel nanoferrites with composition Mg_0.5Zn_0.5Co_x Fe_2-xO₄ at x = 0.0, 0.10, 0.20, 0.30, 0.40, 0.50 were prepared using sol-gel auto ignition method. The characterizations techniques such as FESEM, FTIR, XRD and VSM were used to determine the morphology, force constants, phase, structure and magnetic features of the samples. Lattice parameters, FWHM, d-spacing, crystallite size, micro strains and volume were investigated using high score plus software. Materials analysis using diffraction (MAUD) software was also used to study the Rietveld refinement properties of the Co doped MgZn ferrites. Physical properties such as porosity, X-ray and bulk density were also determined. Force constants of their respective absorption bands were calculated from FTIR of the Co doped MgZn nanoferrites. Single phase structure with cubic phase were observed for MgZn and Co doped MgZn at x = 0.0 whereas second phase was observed at higher Co concentrations respectively. FESEM show regular shape of the particles at low Co concentrations whereas agglomerations were observed at higher Co concentrations respectively. The magnetic properties of the Co doped MgZn ferrites were also investigated from VSM study. Magnetic remanence, coercivity, initial permeability, saturation magnetization, Bohr magneton and anisotropy constant were determined from VSM analysis. The coercivity, saturation magnetization, remanence, anisotropy constant and initial permeability were enhanced with the doping of ‘Co’ in MgZn nanoferrites. Response of the Co doped MgZn nanoferrites at high frequency regime was also evaluated. It can be seen that the response from all the Co doped MgZn nanoferrites was 2.84 GHz–5.96 GHz respectively and suggested the use of these nanoferrites for the operation of nanodevices in the X-band high frequency regime.     

Multistage homogenization process of aluminum alloy 2618

Single-, two-, and three-stage homogenization treatments of heat-resistant alloy 2618 were conducted in this study. Results reveal a low melting point Al₂CuMg phase and high melting point Al₂Cu phase in the as-cast aluminum alloy 2618. After single-stage homogenization at 495 °C for 10 h, the Al₂CuMg phase dissolves completely, but the Al₂Cu phase cannot be completely dissolved even once the homogenization time is prolonged to 18 h. After the alloy 2618 are homogenized using two stages: 495 °C for 10 h and 520 °C for 8 h, a portion of the Al₂Cu phase remains in the alloy. The Al₂Cu phase remains undissolved even after prolonged time. After the two-stage homogenization treatment at 495 °C for 10 h and 540 °C for 5 h, the high melting point Al₂Cu phase completely dissolves but overburn occurs. After the alloy 2618 are homogenized using three stages at 495 °C for 10 h, 520 °C for 5 h, and 540 °C for 3 h, the Al₂Cu phase completely dissolves and no overburn is detected. The three-stage homogenization treatment is an effective method for dissolving the high melting point Al₂Cu phase in the alloy 2618 and increasing their overburn temperature and solid solution temperature.     

含Euxyl K220的复合防腐剂在化妆品中的防腐效果研究

为寻求新型复合防腐剂,研究了含有Euxyl K220的不同种类复合防腐剂在化妆品基质中的作用效果并进行评价。选择4种防腐剂按照不同方法复配,利用微生物挑战性试验验证复配后的复合防腐剂在化妆品基质中的防腐效果。结果发现,对羟基苯甲酸甲酯质量分数低于0.1%时,含Euxyl K220的复合防腐剂抑制细菌效果稍好,抑制霉菌效果较差,不能通过挑战性试验,而当存在Euxyl PE9010时,抑制细菌、霉菌效果均较好,能通过挑战性试验;对羟基苯甲酸甲酯质量分数在0.1%~0.2%时,含Euxyl K220的复合防腐剂抑菌效果最好,Euxyl K220在相对较低的质量分数(0.08%)下即能通过挑战性试验。研究制备的对羟基苯甲酸甲酯(质量分数0.2%)和Euxyl K220(质量分数0.08%)复合防腐剂,以及对羟基苯甲酸甲酯(质量分数0.05%)、Euxyl K220(质量分数0.1%)和Euxyl PE9010(质量分数0.2%)复合防腐剂应用于受试样品中均通过了挑战性试验且用量较低,该两种新型复合防腐剂的应用可行性较高。     

220kV丽江变电所注浆加固地基失败原因探讨

由于注浆加固软土层是挤密、劈裂、渗透的复合过程,因而采用传统、单一的渗透注浆理论来计算与实际情况有较大的偏差.把软土体看作遵循Tresca屈服准则的理想弹塑体,同时结合浆液的柱状扩散情况,利用圆筒形扩张理论来计算浆液扩散半径和注浆压力.并以220kV丽江变电所注浆加固地基为例,分析其注浆失败的原因.     

220kV变电站电晕噪声抑制技术研究和应用

变电站电晕放电会导致变电站工频电磁场及无线电干扰水平超标,对周围环境造成噪音和电磁污染,影响居民生活和工程的环境评价,因此必须对其进行治理。根据相关设备、金具的实际布置形式和外形结构图纸,结合变电站电晕实测结果,同时考虑相间影响和周围带电导体作用,采用有限元软件ANSYS建立了220 kV变电站典型放电位置的三维电场有限元仿真计算模型,计算了金具表面的电场分布,得到了其表面的场强最大值和分布规律。根据计算结果优化了金具的结构、尺寸和参数,并提出了电晕噪声抑制措施。仿真结果表明采取优化和抑制措施后,金具的电场分布畸变有较大改善,表面最大场强下降到3 000 V/mm以下。研究成果为变电站的防晕降噪设计提供了重要参考,为绿色电网和变电站的建设提供了依据。     

60 GHz无线通信技术发展现状及趋势研究

60 GHz无线通信技术以其丰富的频谱资源和高速的数据传输速率,成为目前无线通信领域的研究热点之一。首先介绍了60 GHz无线通信技术的概念内涵、特点优势和应用场景;接着重点阐述了60 GHz无线通信技术形成的产业联盟和通信标准;然后分析了60 GHz无线通信技术发展面临的问题;最后根据信息技术的发展形势,展望了60 GHz无线通信技术的发展趋势。     

室外微蜂窝小区3.5GHz 电波传播特性仿真和分析

射线跟踪方法是研究室外微蜂窝小区电波传播的有效方法。基于入射及反弹射线法/ 镜像法对室外微小区环境中3. 5GHz 电波传播的路径损耗进行了仿真和分析,仿真结果与文献所给的结果一致性良好,验证了该 方法的正确性。提出了一种新型的射线管判收方法,可有效判断到达接收机的所有射线管。分析了仿真中得到的接收功率、均方根时延扩展、波达方向等传播参数,并比较了视距传播(LOS)和非视距传播(NLOS)的传播特性,这些分析结果可为3. 5GHz 频段无线通信系统的覆盖提供相应的理论依据。     

辐射对220kV主变压器室温度场分布的模拟研究

采用计算流体力学(CFD)技术,对220kV主变压器室温度场进行模拟计算,对比分析了不考虑辐射条件和考虑辐射条件的室内温度场的模拟结果,得出辐射条件是模拟220kV主变压器室温度场分布必须考虑的条件之一.