sol-gel法低温制备超细BaFe12O19磁粉

应用sol-gel法成功地低温合成了超细BaFe12O19磁粉。先驱体氢氧化物在醇：水比为1：1．7、Ba^2＋和Fe^3＋以的离子摩尔比为1．15：12的溶胶溶液中（以氢氧化钠NaOH为沉淀剂）制得。采用两步热处理法,先驱体氢氧化物在300℃预热处理1h,再在800℃热处理5h,X射线衍射分析（XRD）分析表明形成了BaFe12O19磁性粒子,粒子尺寸为42．0nm,接近理论单畴尺寸40nm。     

Molten salt synthesis of anisotropic BaFe12O19 powders

The formation mechanism, morphology, and magnetic properties of anisotropic BaFe₁₂O₁₉ powders prepared by the 0.8 Na₂SO₄-0.2 K₂SO₄ molten salt synthesis have been investigated. The reaction can be completed at temperatures lower than 845 °C which is the melting point of the 0.8 Na₂SO₄-0.2 K₂SO₄ salt mixture, due to the presence of the low melting phase related to the formation of BaSO₄ and Na₆CO₃(SO₄)₂. Even at temperatures lower than 845 °C, with the aid of the low melting phase, the morphology of ferrites was thin platelets. Magnetic properties such as coercivity, saturation magnetization, and remanent force are comparable to those found in other processing techniques. The orientation degree of the sintered body was very high due to anisotropic morphology; thus powders from molten salt synthesis are suitable for grain oriented ceramics.     

Zn-Ti取代的BaFe12O19铁氧体

采用标准陶瓷工艺,并进行湿压磁场成型和氧气氛烧结制备了高取向度、低介电损耗的各向异性Ｂａ（ＺｎＴｉ）ｘＦｅ１２－２ｘＯ１９多晶六角铁氧体,随着ｘ值增大,磁化强度减小,居里温度下降,磁晶各向异性常数减小。结果可以通过假设Ｚｎ＾２＋取代了四面体４ｆ１次点阵位和六面体２ｂ次点阵位上的ＦｅＴ＾３＋;Ｔｉ＾４＋取代了自旋向上的八面体１２ｋ,２ａ次点阵位上的Ｆｅ６３＋来解释。     

Synthesis of BaFe12O19 Powder by Modified Coprecipitation and Spray Pyrolysis Methods

Fine barium hexaferrite (BaFe₁₂O₁₉) powder consisting of platelike particles with the magnetoplumbite structure, 30–60 nm in size, is synthesized at 550°C via rapid oxidation of a suspension of barium and iron(II) hydroxides with NaClO. The magnetic properties of BaFe₁₂O₁₉ powders prepared by modified coprecipitation and spray pyrolysis processes are described. The coercivity of fine BaFe₁₂O₁₉ powders is shown to be lower than that of bulk material, which is due to the presence of a magnetically inactive layer of noncollinear spins in the basal plane of the hexagonal particles. BaFe₁₂O₁₉ particles less than 10 nm in size are shown to be in a superparamagnetic state.     

Magnetic and Photocatalytic Activity of Pure BaFe12O19 and BaFe12O19-TiO2 Hexagonal Ferrite Nanocomposites

Journal of Superconductivity and Novel Magnetism - Hard hexagonal barium ferrite BaFe12O19 (BaM), as well as core–shell structure BaFe12O19-TiO2 composite nanoparticles, was successfully...     

The effect of silica characterization on the microstructure of BaFe12O19 ferrites

The anisotropically formed BaFe₁₂O₁₉ ferrites were prepared from the hot-rolled mill scale and silica was added to the ferrite during fine milling in the range 0.15 to 0.50 wt%. These ferrites were sintered at 1220° C for 2 h. The grain growth of the ferrites is dominantly influenced by the sizes of the silica added. Coarse-grain ( 1m) silica tends to promote discontinuous grain growth, which increases drastically with slightly increasing amounts of silica added, while fine-grain ( 0.013m) silica tends to retain fine grain microstructures with the same increasing amount of silica. The average grain size of the ferrite without silica addition was 8 to 10m. The size was increased to as large as 30m on addition of 0.15% coarse-grain silica and the microstructure was full of extremely large grains on the addition of 0.50% coarse-grain silica.     

The Synthesis of Single-Crystalline BaFe12O19 Nanoparticles by Molten-Salt Method with Surfactant NP-9

Single-crystalline barium ferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized by the molten-salt method. The particles of both samples with and without surfactant NP-9 possess hexagonal plate-like shape. However, BaFe₁₂O₁₉ nanoparticles without NP-9 during the preparation exhibit two different magnetic phases (soft and hard) reflected from the double magnetic hysteresis loops, and the soft magnetic phase was attributed to the defect region in the nanoparticles. Including the surfactant NP-9 in the preparation process, the soft magnetic phase was effectively suppressed, and only the hard magnetic phase was observed, reflected from the single magnetic hysteresis loop. Furthermore, the remanent magnetization and saturate magnetization were increased slightly by using NP-9. These results indicate that NP-9 is an effective additive for the preparation of high-quality single-crystalline ferrite nanoparticles.     

自蔓延高温合成钡铁氧体的研究

介绍了自蔓延高温合成技术合成BaFe12O19的过程，研究了热处理对产品性能的影响。用VSM对产物的磁性能进行了测量，用XRD对产物的物相进行了分析，用SEM对产物形貌和组织进行了观察。结果表明，采用自蔓延（SHS）高温合成的BaFe12O19具有良好的磁性能。     

自蔓延高温合成钡铁氧体的研究

介绍了自蔓延高温合成技术合成BaFe12O19的过程,研究了热处理对产品性能的影响.用VSM对产物的磁性能进行了测量,用XRD对产物的物相进行了分析,用SEM对产物形貌和组织进行了观察.结果表明,采用自蔓延(SHS)高温合成的BaFe12O19具有良好的磁性能.     

BaFe12O19铁氧体磁性涂层碳纤维研制

提出用ｓｏｌ－ｇｅｌ技术在碳纤维表面涂覆ＢａＦｅ１２Ｏ１９型铁氧体,制得磁性涂 连续碳纤维,利用红外吸收光谱鉴别了钡铁氧体的合成,并对纤维的磁性进行了初步理论分析。     

Sintering and electromagnetic properties of BaFe12O19 ferrite prepared by co-precipitation method

BaFe₁₂O₁₉ (BaM) was synthesized through the co-precipitation route. Pure phase BaM was formed after calcination of precipitated powder at 900 °C. BaM was sintered at three different temperatures; 1100, 1200, and 1300 °C to study the sintering kinetics by varying the sintering time from 1 to 4 h. Apparent porosity decreased, and bulk density increased with increasing sintering temperature and period. A bulk density of about 4.6 g/cm³ was achieved after sintering at 1300 °C/4 h. The rate-controlling mechanism of BaM densification was the diffusion of oxygen, and the activation energy for the sintering process was 274 kJ/mol. The grain size of BaM increased with rising sintering temperatures. Permittivity increased from about 11 to 17 and the permeability increased from about 10 to 16 with the increase in sintering temperature from 1100 to 1300 °C. Saturation magnetization was also enhanced to about 69 emu/g after sintering at 1300 °C/4 h. Therefore, BaM ferrite synthesized through the co-precipitation route can be effectively used for high-frequency applications after sintering at 1300 °C.

     

碳化硅表面钡铁氧体薄膜制备与吸波性能

采用柠檬酸盐溶胶-凝胶法在碳化硅表面形成钡铁氧体薄膜.XRD表明生成的铁氧体为六角磁铅型晶体BaFe12O19.测定了材料在0.1～6.0 GHz内的介电常数与磁导率.与单纯钡铁氧体比较,碳化硅表面沉积钡铁氧体薄层后复合相吸波频段宽化,吸波能力增强.     

Enhancement of hard magnetic properties of BaFe12O19 nanoparticles

Barium hexaferrite nano particles are prepared through glycine assisted sol–gel auto combustion method with a minimal glycine to nitrate ratio and the pH values of 4, 6 and 9. X-ray diffraction patterns reveal the formation of hexagonal magneto-plumbite structure of BaFe₁₂O₁₉ with a weak intensity of secondary phase in the case of pH 4 and pH 6 samples. Interestingly disappearance of secondary phase at pH 9 sample is noticeable feature. Scanning electron microscope micrographs of the samples show the formation of characteristic hexagonal shape of barium hexaferrite. Constituent elements and chemical composition are analyzed using energy dispersive X-ray spectrum. Fourier Transform Infra Red and Raman spectra show the different metal–oxygen stretching vibration modes corresponding to octahedral, tetrahedral and trigonal bipyramidal sites of BaFe₁₂O₁₉. Magnetization studies show increase in saturation magnetization, squareness ratio, coercivity values on increasing the pH of the solution. 10 % enhancement of Curie temperature is observed (T_c = 495 °C of pH 9 sample) in comparison to its bulk counterpart T_c = 450 °C reported earlier. Enhancement of magnetic properties is achieved by optimizing pH and suitable choice of post annealing temperature during synthesis of nanoparticles of barium hexaferrite.     

Effect of Cr substitution on microwave absorption of BaFe12O19

The chromium substituted barium hexaferrites were prepared by self-propagating combustion method. The crystalline structure, complex permittivity, complex permeability, and hyperfine parameters of BaFe_12−xCr_xO₁₉ (x varies from 0.2 to 1.0 in a step of 0.2) were measured with X-ray diffraction, vector network analyzer and Mössbauer spectroscopy. At 850 °C, only a part of Cr³⁺ ions are permitted to enter the lattice of barium ferrite. With further calcination at 1000 °C, all Cr³⁺ ions enter the lattice. After substitution, the complex permittivity is increased. The Cr³⁺ ions substitute for the Fe³⁺ ions on the 2a site, and simultaneously lead to a quadrupole splitting on the 4f₁ site. These changes decrease the anisotropy field, which are accordant with the spectra of μ″. In the crystalline cells of the substituted barium ferrites, some Fe²⁺ ions are formed. It results in a bigger dielectric loss.     

并流共沉淀法合成Dy_(2)O_(3)-ZrO_(2)纳米粉体EI北大核心CSCD

采用并流化学共沉淀法合成了Dy_(2)O_(3)掺杂ZrO_(2)(DySZ)纳米粉体材料,系统研究稳定剂掺杂量、阳离子浓度、反应系统pH值和煅烧温度对粉体材料物相组成、晶体结构和微观形貌的影响。结果表明:不同合成工艺条件下,DySZ粉体材料均具有纳米尺度特征,球形颗粒尺寸为10~30 nm,Dy_(2)O_(3)的掺杂可以起到稳定晶型的作用;稳定剂掺杂量对DySZ粉体的物相组成具有明显影响,掺杂量为10%(质量分数)时可合成单一四方相结构的DySZ粉体;DySZ粉体材料的四方度和微观形貌对稳定剂掺杂量、阳离子浓度、反应体系pH值和煅烧温度均不敏感,但其平均晶粒尺寸随稳定剂掺杂量、阳离子浓度和反应体系pH值的升高略有降低,随煅烧温度的提高而显著增加。     

BaFe12O19的溶胶-凝胶合成及其微波性能研究

采用柠檬酸sol-gel工艺，以硝酸铁、碳酸钡、柠檬酸等为原料合成了BaFe12O19，并对其介电常数及其磁导率在1MHz-6GHz下的变化规律进行了研究。结果表明，要在实验过程中避免Ba(NO3)2的生成，既要增大体系中柠檬酸的浓度，更要提高体系的pH值。BaFe12O19的开始生成温度为700℃；其磁导率实部都随微波测试频率的增加而变小，磁导率虚部随测试频率的变化曲线上显示了一个由自然共振引起的共振峰。