Mn-Zn铁氧体粉末压坯微波烧结致密性研究

采用频率为2.45 GHz的微波对Mn-Zn铁氧体粉末压坯进行烧结,研究微波加热过程样品的吸波性能和致密化特性,并探讨压坯在微波场中的加热机理,用扫描电镜对烧结样品的形貌进行观察。结果表明,Mn-Zn铁氧体粉末压坯在微波加热的初期(温度低于500)吸波性能较好,样品温度上升比较快,平均为15 ℃/min.;当温度高于500 ℃,加热速度逐渐下降,温度到800 ℃左右必须加大微波功率,样品温度才会继续上升;温度高于1 400 ℃,样品发生“热失控”;烧结温度对烧结密度的影响比较显著,密度随烧结温度的升高而增大,从1 250 的4.20 g/cm增大到1 400 ℃的4.93 g/cm;Mn-Zn铁氧体可在微波场中快速烧结致密,在1 400 微波烧结(保温时间为零)Mn-Zn铁氧体粉末样品组织致密、均匀。     

添加CaO对高磁导率Mn-Zn铁氧体磁性能的影响

以MnO、ZnO和Fe_2O_3为基础原料,固定其配比后,添加质量分数在01.0%的CaO,采用传统两步合成工艺制备Mn-Zn铁氧体,研究CaO对铁氧体微观结构和磁性能的影响。结果表明:随着CaO添加量的增加,Mn-Zn铁氧体的平均晶粒尺寸和烧结密度先增大后减小,2.2 MHz频率下的弹性磁导率先增大后急剧减小再略微增大,1T磁场强度下的饱和磁化强度先增大后减小,矫顽力先减小后增大;适量CaO可以改善Mn-Zn铁氧体的微观结构,降低铁心损耗;当CaO质量分数为0.4%时,Mn-Zn铁氧体在1T磁场强度下的饱和磁化强度最大,为46A·m~2·kg~(-1),2.2MHz频率下的弹性磁导率较大,为86.7,损耗功率较低,约为20kW·m~(-3),矫顽力较低,约为183.4kA·m~(-1),Mn-Zn铁氧体的综合磁性能较好。     

新型抗EMI材料及其传导干扰抑制性能评价

鉴于兆频带近场电磁干扰抑制材料需求的增加,采用气雾化制粉、粉末扁平化、绝缘压结、真空退火工艺制备出具有高频宽带分布磁导率特性的新型软磁合金复合材料.经测试,获得的典型材料在1.2 GHz时,μ＂,达到15左右.此外,采用平行线传输线测量S参数的方法评价了该复合材料的传导干扰抑制性能.试验表明：复合材料试样比铁氧体材料试样具有更佳的传导干扰抑制性能,损耗功率比在650 MHz以上超过铁氧体试样,最大值达0.7左右.     

开关电源用MnZn铁氧体磁损耗研究

文中研究了开关电源用MnZn铁氧体材料掺入SiO2-CaO、TiO2等杂质对电阻率、损耗的机制;分析了不同烧结温度、气氛对MnZn铁氧体材料功耗的影响;通过研究MnZn铁氧体材料在不同频率、温度下的功耗,表明了MnZn铁氧体材料工作在频率为100kHz时,磁滞损耗占磁芯损耗的主要成分。     

纳米Mn-Zn软磁铁氧体的制备与性能研究

纳米Mn-Zn软磁铁氧体以硝酸铁、硝酸锌、硝酸锰和柠檬酸为原料,利用溶胶-凝胶凝胶自蔓延燃烧工艺合成纳米级Mn-Zn铁氧体粉体.用X-衍射(XRD)分析了粉体的粒径大小和强度是否符合标准,利用高压投射电子显微镜、振动样品磁强计(VSM)、研究了烧结MnZn铁氧体的成相状态、磁性能.通过分析得到最佳制备条件:Mn:Zn=0.55:0.45、pH值为5、煅烧温度为200℃、煅烧时间为90 min.     

原料粉体粒径对NiCuZn软磁铁氧体微观结构和磁性能的影响

通过改变二次球磨时间(1～6 h)调控原料粉体粒径,采用固相烧结法制备NiCuZn软磁铁氧体,研究了原料粉体粒径对软磁铁氧体微观结构和磁性能的影响。结果表明：粉体粒径随着二次球磨时间的延长而减小,尺寸分布逐渐集中;制备的软磁铁氧体晶粒尺寸的均匀性先变好后变差,晶界先变清晰后变模糊;随着粉体粒径的减小,NiCuZn软磁铁氧体的起始磁导率、饱和磁感应强度、相对密度及电阻率均先增大后减小,功率损耗先减小后增大;当二次球磨时间为3 h时,粉体粒径主要集中在2.5～3.5μm,平均粒径为3.237μm,烧结制备的软磁铁氧体的晶界较为清晰,晶粒尺寸均匀,起始磁导率、饱和磁感应强度最大,分别为1 385 H·m^-1和360 mT,功率损耗最小,为284 kW·m^-3。     

粉末注射成形材料微波烧结过程的有限元模拟

基于传统电阻加热烧结过程的建模与模拟,通过对粉末注射成形材料微波烧结过程的机理分析,结合电磁场、热力学以及连续介质力学原理,确定了微波烧结全过程的数学模型和模拟方法;通过建立合理的力学模型和控制方程,采用COMSOL Multi-physics软件模拟微波烧结过程,并将模拟结果与试验结果进行了对比。结果表明:氧化锆粉末成形件在微波烧结初始阶段加热缓慢,当温度升至400℃之后,成形件内部温度持续急剧升高;当加热至1 360℃时,烧结件的相对密度高达92%,可满足粉末烧结工艺要求;建立的数学模型能有效模拟微波烧结过程中粉末成形材料内部的电场、温度场分布以及密度的衍化过程。     

各向同性钡—锶铁氧体合金

本文从合金成分、成形方法、压坯密度、烧结温度等方面。研究了各向同性钡-锶铁氧体永磁合金的生产工艺参数对合金磁性能的影响。     

铁基合金粉末低温温压工艺研究

对铁基合金粉末低温温压工艺进行了较为系统的研究,考察了粉末温度、模具温度、润滑剂含量和压制压力对温压密度的影响。结果表明：较佳的模具、粉末温度分别为120℃和100℃;粉末中较佳的润滑剂含量为0．65％;当压力为686MPa时,Fe-1．5Cu-0．5C和Fe-1．5Ni-0．5Mo-0．5Cu-0．5C粉末压坯密度分别达到了7．42,7．41g／cm^3;两种粉末的温压坯件经过烧结后密度进一步提高,合金元素镍、钼等具有优良的烧结强化效果。     

多场耦合作用下粉末成型固结技术及其装备的发展

综述多场耦合作用下粉末冶金零件的制备技术及其装备,包括力、温度两场耦合的温压成型,磁、力两场耦合的动磁压制成型,强电场、温度场和应力场耦合的放电等离子烧结方法,以及强电场、磁场、温度场和应力场四场耦合作用下的多场耦合粉末成型.讨论多场耦合粉末固结成型装备的发展方向.     

截止波导介质腔介电常数测量理论与方法研究

本文提出了用截止波导介质谐振腔测量微波材料相对介电常数和微波损耗的方法.利用开波导法给出了腔中TE0ml谐振模的电磁场,导出了利用此模测量介电常数和微波损耗的公式;通过测量频率和谐振曲线,就能算出材料的复介电常数,并对谐振模TE0ml进行了讨论;比较了这种测量方法与原有的短路金属板介质谐振腔法的优劣,结果表明采用截止波导介质谐振腔测量材料的微波损耗时更有优越性.     

A Facility for Probe Measurements of the Dispersion Characteristics of Polycrystalline Ferrite Plates

A facility for probe measurements of the dispersion characteristics of polycrystalline ferrite plates is described. The measurements are based on the analysis of a fringe pattern of a microwave field under the superposition of a few electromagnetic waves in the studied sample, which was placed in a magnetizing field. It is shown that experimental fringe patterns enable the restoration of dispersion characteristics of polycrystalline ferrite plates within a frequency band of 2–7 GHz at magnetizing fields of 2–3.2 kG.     

Determination of dielectric constant and loss of high-K thin films in the microwave frequencies

A method to determine the dielectric constant and loss of high-K thin film dielectrics in the microwave frequency region using the extended cavity perturbation technique is presented. The feasibility of the technique is demonstrated by the determination of the dielectric constant and loss for reactively sputtered TiO₂ thin films on borosilicate glass substrates. The dielectric constant and loss is measured at 8.98, 9.96 and 10.97 GHz using a TE_10n rectangular cavity. Using this technique, the dielectric properties of TiO₂ films deposited under varying oxygen percentage in the sputtering atmosphere from 20% to 100% were measured. The dielectric constant and loss are found to be dependent on both the oxygen partial pressure as well as frequency of measurement. The film deposited at 50% of oxygen had a higher dielectric constant, ε_r = 44.35 at 8.98 GHz, where as the film deposited at 100% oxygen showed the lowest value of dielectric constant, ε_r = 21.36 at 10.97 GHz. The dielectric loss tangent varied from 0.004 to 0.019 depending on frequency and oxygen partial pressure. However this technique is applicable only for thin films coated on low K dielectric substrates.     

Investigation of some dielectric properties of phosphate glasses doped with iron oxides,by a microwave technique

The effects of iron ions on dielectric properties of lithium sodium phosphate glasses were studied by non-usual, fast and non-destructive microwave techniques. The dielectric constant (ε′), insertion loss (L) and microwave absorption spectra (microwave response) of the selected glass system xFe₂O₃·(1 − x)(50P₂O₅·25Li₂O·25Na₂O), being x = 0, 3, 6, … , 15 expressed in mol.%, were investigated. The dielectric constant of the samples was investigated at 9.00 GHz using the shorted-line method (SLM) giving the minimum value of ε′ = 2.10 ± 0.02 at room temperature, and increasing further with x, following a given law. It was observed a gradual increasing slope of ε′ in the temperature range of 25 ? t ? 330 °C, at the frequency of 9.00 GHz. Insertion loss (measured at 9.00 GHz) and measurements of microwave energy attenuation, at frequencies ranging from 8.00 to 12.00 GHz were also studied as a function of iron content in the glass samples.     

Measurements of beam current density and proton fraction of a permanent-magnet microwave ion source

A permanent-magnet microwave ion source has been built for use in a high-yield, compact neutron generator. The source has been designed to produce up to 100 mA of deuterium and tritium ions. The electron-cyclotron resonance condition is met at a microwave frequency of 2.45 GHz and a magnetic field strength of 87.5 mT. The source operates at a low hydrogen gas pressure of about 0.15 Pa. Hydrogen beams with a current density of 40 mA/cm(2) have been extracted at a microwave power of 450 W. The dependence of the extracted proton beam fraction on wall materials and operating parameters was measured and found to vary from 45% for steel to 95% for boron nitride as a wall liner material.     

Microwave Sensing of Moisture Content in Concrete Using Open-Ended Rectangular Waveguide

The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC.     

Development of a compact cylindrical reaction cavity for a microwave dielectric heating system

This paper describes a compact reaction cavity for a microwave-assisted synthesis system. The microwave dielectric heating is a key technology to improve synthesizing yield, however, the large size of the microwave generation and reaction parts in an all-in-one system is a major obstacle when applying the technique to various systems, of which the installation space is limited. For this particular problem, a compact stand-alone cylindrical reaction cavity was developed in the current study. A microwave excited from a monopole probe, which is inserted into the side of the cavity, is transferred to a reaction mixture through the upper hole of the cavity. The cavity is miniaturized by filling it with an alumina ceramic dielectric. Fine-tuning of the resonance frequency becomes available by controlling the length of the inserted screw between the probe and the upper hole. The physical properties of the cavity were simulated using high frequency structural simulator (HFSS) and the produced cavity was tested using an Agilent E8357A network analyzer. The test results show that the developed cavity is able to send enough energy to various solvents.     

微波加热含碳红铁矿粉升温特性研究

本文通过对含碳红铁矿粉进行微波加热磁化焙烧,研究含碳铁矿粉在微波场中的升温特性。研究了微波加热还原含碳红铁矿粉的升温特性。结果表明,含碳红铁矿粉具有较好的微波加热特性。在一定的粒度、功率、配碳量的条件下,分析各个因素对含碳铁矿粉吸收微波能力的影响。     

Influence of frequency tuning and double-frequency heating on ions extracted from an electron cyclotron resonance ion source

The electromagnetic field within the plasma chamber of an electron cyclotron resonance ion source (ECRIS) and the properties of the plasma waves affect the plasma properties and ion beam production. We have experimentally investigated the "frequency tuning effect" and "double frequency heating" on the CAPRICE ECRIS device. A traveling wave tube amplifier, two microwave sweep generators, and a dedicated experimental set-up were used to carry out experiments in the 12.5-16.5 GHz frequency range. During the frequency sweeps the evolution of the intensity and shape of the extracted argon beam were measured together with the microwave reflection coefficient. A range of different ion source parameter settings was used. Here we describe these experiments and the resultant improved understanding of these operational modes of the ECR ion source.