Co2+或Sn4+对MnZn功率铁氧体磁特性的影响研究

用普通陶瓷工艺制备了掺Co2+及Sn4+的MnZn功率铁氧体材料,研究了Co2+及Sn4+杂质掺入对MnZn功率铁氧体磁性能的影响.研究结果表明,由于Co2+具有大的正的磁晶各向异性常数K1,所以可与MnZn功率铁氧体负的K1进行补偿.当CoO掺入量为2×10-3时,可得到在20～120℃温度范围内具有非常平坦功率损耗-温度特性的MnZn功率铁氧体.Co2+的掺入还可以大大改善MnZn功率铁氧体的起始磁导率的温度特性.由于Sn4+掺入MnZn功率铁氧体时,Sn4+进入晶格中,减少了Fe3+Fe2+之间的电子跳跃,提高了材料电阻率.当SnO2掺入量为4×10-4时,可得到具有很低功率损耗的MnZn功率铁氧体材料.     

预烧温度对MnZn功率铁氧体烧结活性及温度稳定性的影响

采用氧化物陶瓷工艺制备了MnZn功率铁氧体.研究了预烧温度对MnZn功率铁氧体烧结活性及磁性能、温度稳定性的影响.结果表明,MnZn功率铁氧体预烧料粉体的活性随预烧温度的升高而降低.预烧料粉体的活性对其烧结样品的微观结构有很大影响.预烧温度在870℃时样品具有最佳的磁性能和温度稳定性.     

烧结对共沉淀预烧料制备MnZn高导铁氧体磁性能的影响

以共沉淀法预烧粉为原料,研究了烧结温度及烧结气氛对MnZn高导铁氧体磁性能的影响,采用SEM对其微观结构进行了表征。结果表明,随着烧结温度升高,MnZn高导铁氧体的μi增加;合适的烧结条件能促进晶粒生长,减少气孔产生,增大烧结密度,使晶界变细,提高初始磁导率和改善频率特性。当温度为1380℃,保温气氛为3.0%时,MnZn高导铁氧体的μi为13000,且有较好的频率特性,在150kHz时μi能维持在10000以上。     

SnO2掺杂对MnZn铁氧体微观结构和性能的影响

采用氧化物陶瓷工艺制备MnZn功率铁氧体,研究了SnO2掺杂对MnZn功率铁氧体微观结构及磁性能的影响。结果表明添加适量的SnO2可以有效提高晶粒均匀性和致密度。随着SnO2添加量的增加,起始磁导率先上升后下降,磁损耗先下降后上升。当添加量为0.5%(摩尔分数)时,μi达到最大值,损耗最低。此外,铁氧体损耗最低点所对应的温度随着SnO2掺杂量的增加向低温移动。通过对比一次掺杂和二次掺杂,发现一次掺杂的SnO2主要作用于晶粒内部,二次掺杂的SnO2主要作用于晶界处,而且一次掺杂所获得的样品性能更优。     

MnZn功率铁氧体研究进展

简要介绍了MnZn功率铁氧体的研究现状,分析了各种制粉方法,讨论了添加剂和不同烧结方式对MnZn功率铁氧体磁性能的影响.     

添加Ta2O5对MnZn功率铁氧体性能的影响

采用氧化物陶瓷工艺制备MnZn功率铁氧体,研究了不同Ta₂O₅含量对MnZn功率铁氧体微观结构和磁性能的影响. 结果表明：少量Ta₂O₅的加入可以使铁氧体烧结样品的晶粒尺寸增大,气孔率下降,起始磁导率、饱和磁感应强度和电阻率升高,损耗降低. 而加入过多的Ta₂O₅会导致异常晶粒长大,气孔率升高,起始磁导率、饱和磁感应强度和电阻率降低,损耗增大. 当Ta₂O₅含量为0.04wt%时,铁氧体烧结样品的晶粒尺寸大小均匀,气孔率最低,起始磁导率、饱和磁感应强度和电阻率达到最大值,损耗最低.     

硼硅酸玻璃对CaO-B2O3-SiO2玻璃陶瓷结构和性能的影响

采用在CaO-B2O3-SiO2（CBS）玻璃中添加硼硅酸玻璃的方式制备了低温烧结的CBS复相玻璃陶瓷,系统地研究了其对CBS玻璃陶瓷10MHz下的介电常数及热膨胀系数的影响规律。利用DSC,XRD和SEM微观结构分析方法,研究了试样的性能与结构的关系。研究结果表明：硼硅酸玻璃与CBS玻璃具有很好的相容性,硼硅酸玻璃的添加量在0～40%（质量分数,下同）的范围内均可在850℃烧结。硼硅玻璃能有效降低体系的介电常数,实现介电常数在5.6～6.6范围内可调;硼硅玻璃的添加量小于20%时,膨胀系数增加幅度较小,随着硼硅玻璃量的增加,膨胀系数显著增大,其原因是随着硼硅酸玻璃添加量的增加,生成了具有低介电常数、高膨胀系数的-αSiO2。     

Ti取代对MnZn功率铁氧体微结构及磁性能的影响

采用氧化物陶瓷工艺制备了MnZn功率铁氧体,研究亮磁性能的影响,由于Ti4 是非磁性离子,它对磁性离子Mn2 的取代,必将对材料的微结构、磁性能以及居里温度产生影响.结果表明,Ti4 取代Mn2 可提高MnZn铁氧体居里温度,适量的Ti4 取代,有利于提高致密度和起始磁导率,并降低磁损耗.为了得到优良的电磁性能,适宜的Ti4 取代量为0.5mol%.     

CaCO3、SnO2掺杂对MnZn铁氧体微结构和性能的影响

本文采用传统陶瓷工艺制备了高磁导率MnZn铁氧体材料.为获得高磁导率MnZn铁氧体材料,从分析材料微观结构入手,研究了适当的工艺条件以及CaCO3和SnO2不同的掺入比对高磁导率MnZn铁氧体材料性能的影响.研究结果表明,由于Ca2 离子存在于晶界,少量的CaCO3掺入会使铁氧体晶粒尺寸增加,均匀性改善,起始磁导率增加,而CaCO3掺杂过量,将会增加晶粒中的气孔率,从而降低起始磁导率.SnO2掺入后,由于Sn4 离子存在于晶界中,为满足电荷平衡的要求,引起晶界附近金属离子空位增多,从而加速畴壁的运动,提高材料的起始磁导率.     

升温速率和烧结温度对纳米晶MnZn粉体直接制备功率铁氧体性能的影响

采用纳米晶粉体直接造粒压制成块材烧结的方法制备MnZn铁氧体,研究了不同的升温速率和烧结温度对样品微观结构、磁性能的影响。研究表明,与传统的制备方法相比,直接烧结纳米晶MnZn铁氧体粉体,可以降低烧结温度。采用低的升温速率有利于提高样品的密度和初始磁导率,降低比损耗因子,并且低温烧结可以形成良好的微观结构和磁性能。     

含碱金属离子的CaO-B2O3-SiO2系玻璃陶瓷性能研究

研究了碱金属氧化物对CaO-B2O3-SiO2(CBS)系玻璃陶瓷的软化析晶温度以及材料的烧结、介电等方面性能的影响。结果表明:对于添加双碱的CBS玻璃,随双碱金属离子半径增大软化温度呈升高趋势,而析晶峰值温度呈降低趋势。Na2O和K2O添加对于改善CBS系玻璃陶瓷烧结性能效果更好,试样内部晶粒分布均匀、结构致密。烧成试样主晶相均为CaSiO3,CaB2O4和石英。试样的介电常数和介电损耗随频率的增加而减小。随着测试温度的升高,试样的介电常数略有增加,而介电损耗呈降低趋势。     

Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

Pressure sintering of MnZn and NiZn ferrites

Polycrystalline MnZn and NiZn ferrites suitable for recording-head applications have been prepared by pressure sintering (hotpressing). General conditions for pressure sintering and details of the apparatus are described. Also discussed are the effects of grain size and temperature, in the normal range of glass bonding, on the magnetic and physical properties of pressure-sintered MnZn ferrite. It was observed that the strength of the ferrite increased with decreasing grain size in the range studied (15 to 500 μm). An opposite effect was noted for resistance to material wear. Increases in permeability up to 30 percent were obtained by relieving residual machining stresses with anneals in the 500 to 900°C range. Similar increases in strength were observed for low-temperature anneals. However, at temperatures higher than 500°C, the strength was reduced strongly, with the amount of the reduction being dependent upon the surface finish of the ferrite and its geometry. In general, strength was reduced with coarser surface finish and increasing surface-to-volume ratios. Data on material wear and hardness as functions of grain size and composition are presented. Improvement in performance of video recording heads fabricated of pressure-sintered MnZn ferrite as compared to Alfesil and single-crystal MnZn ferrite is also demonstrated.     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.     

Effects of calcining and sintering parameters on the magnetic properties of high-permeability MnZn ferrites

For asymmetric digital subscriber line (ADSL) technology applications, new MnZn ferrites are required with not only high initial permeability, but also with low hysteresis material constant /spl eta//sub B/. The effects of calcining and sintering temperatures and oxygen equilibrium partial pressure on the magnetic properties of MnZn ferrites are studied in this work. It was found that raising the calcining temperature required a rise in the sintering temperature to simultaneously achieve maximum permeability and the lowest /spl eta//sub B/ value. Both grain size and porosity had an effect on the initial permeability of the samples. Porosity had an even larger effect on the /spl eta//sub B/ value than the initial permeability. Oxygen equilibrium partial pressure also had an important effect on the initial permeability and /spl eta//sub B/ value. In our testing range, both the initial permeability and the /spl eta//sub B/ value decreased with increasing value of A (oxygen parameter). In order to optimize synthesis conditions for the high initial permeability and low /spl eta//sub B/ value, it was best to calcine the sample at 950/spl deg/C and sinter it at 1370/spl deg/C, with A=7.55.     

Reducing dielectric losses in MnZn ferrites by adding TiO/sub 2/ and MoO/sub 3/

We investigated the complementary effects of TiO/sub 2/ and MoO/sub 3/ additives on the magnetic properties, the core loss, and the dielectric properties of MnZn ferrites. We analyzed the composition factors influencing the permeability of MnZn ferrites. A high initial permeability base ZnO-MnO-Fe/sub 2/O/sub 3/ composition ratio was selected. Electrical and dielectric analyses indicated that the introduction of TiO/sub 2/ can improve the high-frequency loss properties of MnZn ferrite cores, but such introduction will also have a negative effect on the magnetic properties of the sintered samples. Introduction of MoO/sub 3/ can alleviate the negative influence of TiO/sub 2/ and also reduce the internal polarization intensity. As a result, the dielectric constant and corresponding dielectric loss may be reduced. We give experimental results in the paper.     

低B2O3掺杂Bi—CVG铁氧体的结构与性能

采用传统固相反应法制备了Y1.05Bi0.75Ca1.2Fe4.4-xV0.6BxO12（Bx：Bi—CVG）系列铁氧体试样。借助XRD、SEM及MATS等技术手段研究了烧结助剂B20,对Bi—CVG铁氧体的体积密度、相组成、微观结构及磁性能的影响。研究结果表明,掺B可以有效降低Bi—CVG铁氧体的烧成温度,提高材料的烧结密度并且影响其微观结构和磁性能。在1040℃×6h条件下烧结、B掺杂量为x=0．025时,制备出综合性能良好的Bi—CVG铁氧体材料：室温时D=5．11g／cm^3,DR.T=97．2％,Bs=37．30mT,Br=25．54mT,Hc=0．87kA／m。     

纳米掺杂和直接掺杂Li2O-SiO2复合助烧剂对X7R型BaTiO3基陶瓷显微结构和介电性能的影响

以Li2O-SiO2（LSO）复合组分作为助烧剂,比较纳米掺杂和直接掺杂对X7R型BaTiO3基陶瓷显微结构和介电性能的影响,并进一步研究直接掺杂LSO的用量及烧结温度的影响,同时通过缺陷化学理论探讨了陶瓷的烧结机制。实验结果表明与纳米掺杂相比,直接掺杂助烧剂能够使掺杂元素进入晶格产生离子空位等缺陷,减少了物质迁移所需的活化能,从而有效促进陶瓷致密化过程,显著改善陶瓷的微观形貌及其介电性能。陶瓷样品的介电常数随着LSO助烧剂掺杂量的增加先增大后减小;当助烧剂掺杂量为0.08%（摩尔分数）时,样品可在1200℃烧结,室温介电常数达到4855,且容温特性满足X7R标准。通过直接掺杂能够使助烧剂十分均匀地分布在陶瓷材料中,可以显著减少助烧剂的用量,达到明显降低烧结温度的目的,并起到助烧兼改性的作用。     

Bi-Mo复合掺杂对MgCuZn铁氧体烧结特性和磁性能的影响

为改善MgCuZn铁氧体的低温烧结特性并提高其软磁性能, 采用传统氧化物法制备MgCuZn铁氧体材料, 研究了Bi-Mo复合掺杂对其烧结特性和软磁性能的影响. 结果表明: 复合掺杂Bi₂ O₃和MoO₃适量时(分别为0.6wt％和0.1wt％), 在较低的烧结温度(1020℃)就能获得较高的烧结密度(<4.75g/cm³), 起始磁导率可达1240, 且具有较高的品质因数(100kHz下为33.8). 通过主成分优选、有效的掺杂技术及工艺条件可以提高MgCuZn铁氧体的综合性能, 使其可应用于多层片式电感中.