掺杂铈对锰锌铁氧体微波吸收特性的影响

采用溶胶-凝胶法制备了粒状锰锌铁氧体，对其掺杂稀土铈后．得到含铈的锰锌铁氧体Mn0.2Zn0.8Fe2-xCexO4(x=0，0．01,0．03，0．07),并研究了它们的吸波性能,结果表明,锰锌铁氧体在微波段具有很好的吸波性能，掺杂3mol％(x=0．03)铈能提高其吸波效率。     

宽频带双Y结微带环行器设计理论

本文研究了用于微波集成电路的具有双Y谐振器的宽频带环行器设计理论,理论参数与试验结果完全一致。这种具有双Y电路的微带环行器能成功地用于7GHz以下的频区,它的尺寸比用圆盘谐振器设计的微带环行器小一半,其典型性能是:插入损耗α_+≤0.5dB(0.6dB,max);隔离度α≥20dB(min);VSWR S≤1.25(1.30,max);相对带宽2δ_0≥40％。     

导体圆盘涂覆铁氧体层介质参数变异的电磁特性

采用基于频域矩量法(MOM)与解析法的Ansoft Designer软件,计算、分析了导体圆盘基底烧结铁氧体隐身层因裂纹介质参数出现变异的雷达X波段高频电磁特性.采用V极化波和H极化波2种情况入射,分别计算与分析,得出:在8-12 GHz 频带内,因裂纹产生介质参数变异对隐身电磁性能影响较明显.     

脉冲电流对球墨铸铁退火组织与性能的影响

在球墨铸铁的高温石墨化过程中采用脉冲电流为辅助手段,研究了脉冲电流对退火处理球墨铸铁力学性能以及渗碳体的石墨化、铁素体转变的影响.经脉冲电流处理后,球墨铸铁的硬度、抗拉强度降低,延伸率增加.SEM分析表明,脉冲电流加速了球墨铸铁的高温石墨化过程,促进了铁素体的转变.脉冲电流处理后石墨形核率的增加是加速渗碳体分解和铁素体转变的主要原因.     

共析钢温变形过程的组织球化与超细化

利用热模拟压缩变形、SEM和热磁法实验,研究了共析钢在600~700℃变形过程的组织演变规律,探讨了变形及随后保温过程对珠光体球化、组织超细化和渗碳体溶解、再析出的影响.实验表明:共析钢温变形过程中发生珠光体片层溶断,渗碳体逐渐球化,以及伴随铁素体动态回复再结晶的同时细小弥散渗碳体颗粒在基体析出的过程.提高温度有利于上述复合过程的进行.形变组织经过保温后,亚微米级别的等轴铁素体晶粒和渗碳体颗粒弥散分布的复相组织的均匀性程度有所提高.温变形过程中渗碳体溶解和在铁素体内再析出的事实得到证实.     

低碳钢中铁素体动态再结晶的粒子激发形核

利用淬、回火工艺得到具有弥散分布的渗碳体粒子 铁素体双相组织的低碳钢,采用Gleeble-1500型模拟机进行热压缩变形实验,研究了在700℃、0.01s-1条件下变形过程中渗碳体粒子对低碳钢铁素体动态再结晶过程的影响. 结果表明:在700℃、0.01s-1条件下变形时,存在以粒子激发形核机制为主的铁素体动态再结晶过程,在形变初期粒子激发形核主要在大尺寸渗碳体粒子(＞1μm)附近发生,大应变量下应变累积促进粒子激发形核在小尺寸渗碳体粒子(0.5～1μm)附近发生.     

Synthesis of nonstoichiometric M-type barium ferrite nanobelt by spark plasma sintering method

This study investigated the feasibility of ultrafast crystallization of M-type barium ferrite when the coprecipitation precursors in stoichiometric proportions as BaFe12O19, Fe(OH)3 and BaCO3 nanoparticles, had been heated by spark plasma sintering (SPS) process. The results show that SPS method may realize the ultrafast crystallization of M-type barium ferrite, absolutely prevent the crystallization of intermediate phase α-Fe2O3, and significantly decrease the crystallization temperature of M-type barium ferrite. The sintered samples obtained at 800℃ by sintering the precursors for 10 minutes are a kind of multiphase ferrites composed of major phase M-type barium ferrite and trace amount of BaFe0.24Fe0.76O2.88. It is discovered that M-type barium ferrites in the holes of the sintered samples are in nanobelt microstructure about 100-300 nm in width and several micrometers in length. These M-type barium ferrite nanobelts are non-stoichiometric and may be expressed as BaFe12 xO19 1.5x (-4.77≤x≤6.50). Their composistions suggest completely random Fe-rich or Ba-rich domains.     

碳钢高温变形两相区流变应力行为预测

部分钢铁材料在两相区高温变形时,流变应力往往不随变形温度升高而降低,而是在两相区内出现流变应力的谷值。为了弄清主要化学成分对两相区内流变应力行为的影响,通过热模拟压缩试验研究不同成分钢铁材料在两相区附近的变形行为,分析变形后的金相组织以及两相区附近流变应力的变化,获得铁素体相变开始温度Ar3和两相区内流变应力的降幅。通过回归拟合得到C、Si和Mn等主要合金元素对铁素体相变开始温度Ar3以及流变应力降幅的影响关系。     

Synthesis and characterization of carbon-coated cobalt ferrite nanoparticles

Cobalt ferrite nanoparticles (CFNPs) were prepared via a reverse micelle method. The CFNPs were subsequently coated with carbon shells by means of thermal chemical vapor deposition (TCVD). In this process, acetylene gas (C₂H₂) was used as a carbon source and the coating was carried out for 1, 2, or 3 h at 750°C. The Ar/C₂H₂ ratio was 10:1. Heating during the TCVD process resulted in a NP core size that approached 30 nm; the thickness of the shell was less than 10 nm. The composition, structure, and morphology of the fabricated composites were characterized using X-ray diffraction, simultaneous thermal analysis, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area diffraction. A vibrating sample magnetometer was used to survey the samples’ magnetic properties. The deposited carbon shell substantially affected the growth and magnetic properties of the CFNPs. Micro-Raman spectroscopy was used to study the carbon coating and revealed that the deposited carbon comprised graphite, multiwalled carbon nanotubes, and diamond- like carbon. With an increase in coating time, the intensity ratio between the amorphous and ordered peaks in the Raman spectra decreased, which indicated an increase in crystallite size.     

Influence of particle size and temperature on the dielectric properties of CoFe2O4 nanoparticles

The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated accord-ing to the Scherrer formula using X-ray diffraction （XRD） peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy （FESEM） images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe2O4 nanoparticle size, the dielectric per-mittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.