Phase stability and magnetic properties of SrFe18O27 W-type hexagonal ferrite

W-type ferrite is a member of the hexagonal ferrite family and a potential permanent magnet material. However, its synthesis conditions are not fully understood yet. Samples were sintered either at 1400°C in air and quenched, or at 1300°C at reduced oxygen partial pressure. The precise stability conditions of this W-type ferrite were investigated in the temperature range of 1200°C-1400°C using thermogravimetry, XRD, and electron microscopy. At 1300°C, the ferrite is stable at oxygen partial pressures of . At more oxidizing conditions, the ferrite decomposes into M-type ferrite and hematite, while at more reducing atmospheres Sr₄Fe₆O₁₃ and magnetite are formed. The nonstoichiometry δ of SrFe_18−δO₂₇ was derived from thermal analysis data at 1300°C as function of oxygen partial pressure and was found to be mainly due to cation vacancies. Magnetization measurements show that this W-type ferrite exhibits M_s = 103 emu/g at T = 4 K, which agrees well with a ferrimagnetic spin arrangement according to Gorter's model. As alternative, Zn-substituted W-ferrite was found to be stable in air at 1200°C with a large M_s = 123 emu/g at 4 K.     

稀土元素对W型钡铁氧体微波吸收特性的作用

采用化学共沉淀法制备W型钡铁氧体,研究稀土元素Dy、Nd、Pr掺杂对铁氧体微波特性的作用.发现:稀土元素的掺入能有效调整铁氧体的微波电磁参数,使自然共振频率向高频移动,并明显提高试样的高频弛豫特征,同时减小复介电常数,以利于阻抗匹配.在一定范围内增大Dy的掺杂量x,有利于进一步获得低介电损耗和高磁损耗,用数值计算模拟方法得到x=0.05时匹配厚度下铁氧体在2～18GHz范围的反射率曲线:吸收峰值达-52.34dB,吸收率小于-10dB的带宽7.9GHz,结果表明稀土Dy掺杂有利于制备轻、薄铁氧体吸波材料.     

柠檬酸对钡铁氧体晶相变化的影响

采用柠檬酸溶胶-凝胶法制备超细晶粒钡铁氧体,选择柠檬酸与金属硝酸盐摩尔比(CA/MN)分别为1,1.2,1.4和2制得一系列钡铁氧体磁性粉末,通过热重分析(TGA)、X射线衍射(XRD)及扫描电镜(SEM)检测手段对产品的物相组分及显微结构进行了表征。结果表明,CA/MN在钡铁氧体晶相变化过程中起关键性作用,在430℃预烧、1280℃煅烧、同时保温2~5h的热处理条件下,随CA/MN增大,钡铁氧体的晶相由W相转变为M相,转变点在CA/MN=1.3左右。产生该现象的主要原因是,随着柠檬酸量的增加,自蔓延燃烧产物团聚程度增大,进而促使γ-Fe2O3向α-Fe2O3发生转化,导致W型铁氧体成相温度升高,在相同煅烧条件下,引起钡铁氧体晶相的转变。     

W型试样在测量断裂韧度中的合理性分析

Ｗ型试样在核反应堆压力容器用材料的断裂韧度测试中具有良好的应用前景。本文利用弱塑性有限元方法,通过与标准比例的紧凑拉伸试样（ＣＴ试样）的比较,分析满足Ｊ主导条件的Ｗ型试术在测量断裂韧度中的合理性。研究表明,在常用的裂纹长度和韧带长度范围内,Ｗ型试样在断裂韧度的测量中是合理而可行的。     

W型铸铝水冷机座压铸新工艺

本文介绍了一种环保能源牵引电机及发电机定子机座的制造方法。通过压铸模具的设计,在内筒体上铸出W型水道和W型阴槽及焊缝保护法兰;在外筒体上铸出W型阳槽,内外筒体压力铸造;然后在压力状态下通过W型导向,对内外筒体进行预热压装;最后内外筒体进行组焊制成电机定子水冷机座。本工艺结构巧妙,工序简单,防漏水、窜水,结构可靠。     

Optimization of structural,electrical, and magnetic properties of ytterbium substituted W-type hexaferrite for multi-layer chip inductors

The rare earth (Yb³⁺) substituted W-type hexagonal ferrites with composition CaPb_2-xYb_xFe₁₆O₂₇ (x = 0.0, 0.5, 1.0, 1.5, 2.0) were synthesized by a facile and cost-effective sol-gel auto combustion method with post heat treatment. The synthesized hexagonal ferrites were characterized by a variety of analytical techniques, and an impedance analyzer was used to investigate the effects of Ytterbium on structural, magnetic, spectral and dielectric properties. The relationship between their impedance, structure and dielectric properties was investigated. The X-ray diffraction patterns verify the presence of single-phase W-type hexagonal ferrites. Physical properties such as D_bulk (bulk density), D_xrd (X-ray density), and P (porosity) of the CaPb_2-xYb_xFe₁₆O₂₇ W-type hexagonal ferrites were calculated. The bulk density of all the samples was decreased, and X-ray intensity was increased with the Ytterbium replacement in the W-type hexaferrite. By adding Yb³⁺ ions, the lattice parameters, cell volume and X-ray density were reduced due to the substitution of ytterbium with smaller ionic radii compared to the lead ion with large ionic radii. The AC-conductivity was increased from (1.523 × 10^?5 to 6.699 × 10^?5) Ωcm^?1. The dielectric constant and tangent loss was found to decrease substantially. The magnetic properties were found to enhance by the substitution of Yb³⁺. The low coercivity value of Yb³⁺ substituted W-type hexagonal ferrites are suitable for magnetic recording media operated at a high-frequency regime. The enhancement of electrical, dielectric and magnetic characteristics suggests these materials as promising for multi-layer chip inductors (MLCIs) circuit applications.     

宽带毫米波微带天线的设计与分析

根据微带天线的设计技术要求,介绍了微带天线带宽的影响因素。在矩形毫米波微带天线设计与分析的基础上,分别设计出 C 型和 W 型两种宽带毫米波开槽微带天线。利用仿真软件对3 种天线的输入回波损耗、驻波系数、相对带宽和方向性等技术参数进行仿真优化和比较分析。仿真与实验结果表明,3 种天线的设计均满足技术要求,C 型和 W 型开槽微带天线较矩形微带天线的相对带宽大幅提高,且具备良好的定向辐射特性。     

W形火焰燃烧技术及燃烧调整

介绍了W形火焰燃烧器的组成和结构,W形火焰燃烧技术及调整方法。     

W型火焰锅炉对低挥发份煤的适应性及其燃烧系统设计分析

文中分析了低挥发份煤的主要特征及如何组织其煤粉混俣物与燃烧系统以满足对着火稳定及提高燃尽度的要求,而Ｗ型火焰锅炉是满足这一要求的最佳选择,文中并对Ｗ型火焰锅炉燃烧设备的设计作了分析。