Microwave permittivity of SiC-Al2O3 composite powder prepared by sol-gel and carbothermal reduction

SiC-Al2O3 composite powder was prepared by sol-gel and carbothermal reduction method. The powder synthesized was characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM） to confirm the phase formation, and the thermodynamic analysis was performed systematically. Moreover, the variation of its microwave permittivity with different atomic ratio of Al/Si was investigated in the frequency range of 8.2-12.4 GHz. The results show that, the powder obtained consists of spherical particles of 300-400 nm in diameter, which are composed of SiC and Al2O3 microcrystal with the grain size of approximately 45 nm. The results of XRD accord with those of the thermodynamic analysis. It is impossible for Al atoms to dissolve in the lattice of SiC during the carbothermal reduction process. Along with the increase of atomic ratio of Al/Si in the xerogel, the amount of Al2O3 in the powder synthesized increases, which reduces both ε＇, the real part of complex permittivity, and tg δ（ε＂/ε＇）, the dissipation factor, where ε＂ is the imaginary part of complex permittivity.     

零件厚度对激光相变硬化温度场的影响

以GCr15钢为例,采用有限单元法对激光相变硬化过程进行了数值模拟研究,建立激光相变硬化过程温度场的数学模型,分析了工件厚度及其下表面在自然散热和辅助水冷条件下对激光相变硬化温度场的影响.     

Si/C/N纳米微波吸收剂的制备

采用化学气相沉积方法,在1200℃～1600℃温度范围内,于不同的NH3流量条件下,合成了Si/C/N纳米粉体,研究了粉体的制备工艺、成分、相组成与其微波介电性能之间的关系.结果表明：NH3流量增加,粉体中N含量升高,随着合成温度的提高,粉体的晶化程度增强,主要为β-SiC相.在SiC晶格中固溶有N原子,且N原子的固溶量随合成温度升高而减少.Si/C/N纳米粉体中SiC微晶含量,以及SiC微晶中固溶的N原子浓度对粉体的ε＇,ε（＂）和损耗因子tgδ（ε＂/ε＇）起着重要作用.N原子固溶所导致的极化驰豫损耗和漏导损耗是Si/C/N纳米粉体具有吸波性能的主要机理.     

基于AT89S52单片机的温度测控系统

温度测控在工业领域具有广泛的应用,随着传感器技术等一系列相关技术的不断地发展,为智能温度测控系统功能、精度的提高和抗干扰能力的增强提供了条件.设计一种基于AT89S52单片机的温度测量系统的硬件结构及汇编程序,并且阐述其在冷库温度调控方面的应用.该系统结构具有价格低廉,精度高、微型化、抗干扰能力强、易扩展等一系列优点.     

基于AT89S52单片机的温度测控系统

温度测控在工业领域具有广泛的应用,随着传感器技术等一系列相关技术的不断地发展,,为智能温度测控系统功能、精度的提高和抗干扰能力的增强提供了条件.设计一种基于AT89S52单片机的温度测量系统的硬件结构及汇编程序,并且阐述其在冷库温度调控方面的应用.该系统结构具有价格低廉,精度高、微型化、抗干扰能力强、易扩展等一系列优点.