Growth of oxide single crystals by topotactic reaction

Single crystals of MgO have been heated with crystals of Al₂O₃, Fe₂O₃ and TiO₂ on cut and polished faces, in known relative crystallographic orientations. The initial product in every case was a spinel phase witha ₀=8.38 Å, oriented with its axes parallel to those of MgO. Crystals reacted in different orientations gave the same product, but kinetic rates appeared to differ. CaO and TiO₂ crystals, treated in the same way, gave an unoriented product.     

Barium hexaferrite (M-phase) exhibiting superstructure

Barium hexaferrite (M-phase) prepared by the flux method is found to exhibit a $\text{√3}\text{a}\text{× √3}\text{a}$ superstructure similar to barium hexaaluminate.     

Barium hexaferrite nanoparticles: Synthesis and magnetic properties

Carbon combustion synthesis is applied to rapid and energy efficient fabrication of crystalline barium hexaferrite nanoparticles with the average particle size of 50-100 nm. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm with a surface area of 80 m²/g generates a self-propagating thermal wave with maximum temperatures of up to 1000 °C. The thermal front rapidly propagates through the mixture of solid reactants converting it to the hexagonal barium ferrite. Carbon is not incorporated in the product and is emitted from the reaction zone as a gaseous CO₂. The activation energy for carbon combustion synthesis of BaFe₁₂O₁₉ was estimated to be 98 kJ/mol. A complete conversion to hexagonal barium ferrite is obtained for carbon concentration exceeding 11 wt.%. The magnetic properties H_c∼3000 Oe and M_s∼50.3 emu/g of the compact sintered ferrites compare well with those produced by other synthesis methods.     

复相铁氧体材料的的放电等离子体烧结合成

采用化学共沉淀法制备了名义组成为xFe+BaFe12O19(0≤x≤1,△x=0.2)的共沉淀前驱体,研究了该前驱体在放电等离子体烧结条件下形成复相铁氧体材料的结晶行为和烧结体的磁性能.结果表明,所有烧结体中均没有Fe2O3中间相形成,x=0时烧结体为单相M型钡铁氧体(BaM),0相似文献   

Synthesis of barium hexaferrite by the co-precipitation method using acetate precursor

Fine particles of barium hexaferrite were synthesised by a chemical co-precipitation method using acetate-nitrate (barium acetate + iron nitrate) precursors. The thermal properties, phase composition and morphology of hexaferrite powders were studied. Simultaneous DTA/TG results confirmed by those obtained from XRD and VSM, indicated that the formation of barium hexaferrite occurs at a relatively low temperature of 710°C. This temperature is affected by the Fe³⁺/Ba²⁺ molar ratio. The SEM investigations revealed that the mean particle size of barium hexaferrite increases with increasing calcination temperature. In this system the Fe³⁺/Ba²⁺ molar ratio of 12 (stoichiometric ratio) is favourable.     

Barium hexaferrite nanoparticles: morphology-controlled preparation,characterization and investigation of magnetic and photocatalytic properties

In this paper, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized via a simple co-precipitation route. Six chelating agents such as three amino acids (proline, alanine, aspartic acid) and three surfactants (SDBS, PVP, and EDTA) were used. The result showed that the amino acids decrease the particle size and the best result was observed for alanine. Besides, the photocatalyst activity of as-prepared BaFe₁₂O₁₉ nanoparticles was evaluated by degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 200 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 30 emu/g.     

Microstructure and properties of Co2Z hexaferrite prepared by gel self-propagating method

The microstructure and properties of Ba₃Co₂Fe₂₄O₄₁ hexagonal ferrite sintered at relatively low temperature by the gel self-propagating method are investigated. XRD analysis and SEM pictures indicate that the formation and densification of Ba₃Co₂Fe₂₄O₄₁ hexaferrites can be achieved at relatively low temperature. Results from frequency spectra show higher initial permeability, stable cutoff frequencies and quality factor values for the sintered ferrites. The densification and microstructure are correlated to the magnetic properties. The electrical properties, such as resistivity and frequency dependence of dielectric constant, and relative mechanisms involved in generating these effects are discussed in this paper.     

Preparation of barium hexaferrite by a hydrothermal method: structure and magnetic properties

Barium hexaferrite, BaFe¹²O₁₉, was obtained in hydrothermal conditions from a water suspension of -FeOOH and Ba(OH)₂ · 8H₂O at a temperature about 315° C. X-ray and Mössbauer spectroscopy as well as electron microscopy investigations demonstrated the appearance of -Fe₂O₃ as an intermediate phase in the hydrothermal process. The magnetic characteristics of the obtained isotropic magnets are the following: coercive fieldH _c 159 kA m^–1, residual inductionB _r 0.26 T, maximum energy product (BH) _max12 kJ m^–3. The hydrothermal procedure for the preparation of barium hexaferrite in comparison with the conventional one is discussed.     

Barium hydroxyapatite nanoparticles synthesized by citric acid sol-gel combustion method

Barium hydroxyapatite (BaHAP) nanoparticles have been synthesized by citric acid sol-gel combustion method using citric acid as a reductant/fuel and nitrate as an oxidant at a relatively low temperature of 600 °C. The thermal decomposition of nitrate-citrate xerogel was investigated by thermogravimetric/differential thermal analysis (TG/DTA) technique. The yielding powders calcined at 600 °C have been characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and transmission electron microscope (TEM). The possible combustion process was presented.     

A new method for low temperature preparation of barium hexaferrite powders

The heating behaviour of lyophilized gels composed of ammonium pectate and Ba²⁺ and Fe³⁺ ions was investigated by differential thermal analysis, thermogravimetric analysis and X-ray diffractometry. The formation of barium hexaferrite was found to be complete after 22 h in an oxygen atmosphere at 600° C, whereas in air at 700° C it has been attained after 30 min only. Examination by scanning electron microscopy of the powders fired at temperatures below 800° C showed almost all of the particles to be less than 1 micron in diameter, a condition necessary for the attainment of high coercivity.     

Barium ferrite nanoparticles prepared by self-propagating low-temperature combustion method and its characterization

The barium ferrite particles were prepared using a self-propagating low-temperature combustion method using polyethylene glycol (PEG) as a fuel. The process was investigated with simultaneous thermo-gravimetric-differential thermal analysis (TG-DTA). The crystalline structure, morphology and the magnetic properties of the barium ferrite particles were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and SQUID susceptometer. The results show that the ignition temperature of PEG is lower compared with other combustion methods and gives nanocrystalline barium ferrite.     

Sol-gel法在烧结型NdFeB永磁材料表面制备耐蚀纳米MgO膜层的研究

以无机镁盐为前驱物,无水乙醇为溶剂,添加适量的表面活性剂,采用溶胶-凝胶法在烧结型NdFeB永磁材料表面首次成功制备了纳米MgO膜层.讨论了不同工艺条件对溶胶-凝胶稳定性的影响,采用DSC-TGA、XRD、腐蚀浸泡试验等手段对其进行表征,结果表明,前驱物镁离子浓度在0.03～0.15mol/L范围内,v(无水乙醇):v(表面活性剂(火棉胶))=(6:4)～(8:2)时,均能制备出透明、稳定的溶胶;通过最佳热处理工艺在烧结型NdFeB永磁材料表面形成了致密、耐蚀的纳米MgO膜层,且MgO的晶粒取向在{200}和{220}晶面上,在450℃热处理后的MgO平均晶粒尺寸为23.43nm.     

改进Sol-Gel法制备Y掺杂BST薄膜表面结构及介电性能研究

通过在溶胶前驱液中添加聚乙烯吡咯烷酮和在底电极Pt上形成界面仔晶层,对溶胶凝胶(Sol-Gel)法进行了改进,并以此在Pt/Ti/SiO₂/Si上制备了钇(Y)掺杂和非掺杂的Ba_0.6Sr_0.4TiO₃ (BST)薄膜,研究了薄膜的表面结构和介电调谐性能. X射线光电子能谱表明,BST薄膜表面元素都以两种或三种化学态出现,一种对应钙钛矿结构,其余的对应非钙钛矿结构. 和非掺杂相比,除了Ti2p外,Y掺杂对Ba3d、Sr3d和O1s具有明显的影响,Ba、Sr和O原子在非钙钛矿结构中的含量分别由41%、33%和51%减少到26%、29%和40%. 扫描电镜和原子力显微镜表明,Y掺杂BST薄膜光滑致密、无裂纹和无缩孔. 40V偏压和100kHz频率下的电压－电容曲线表明,Y掺杂提高了薄膜的介电调谐性能,调谐率大于43%、损耗0.0216及优化因子20. 对Y掺杂改性机理也进行了讨论.     

Dielectric properties of cobalt substituted M-type barium hexaferrite prepared by co-precipitation

Barium hexaferrite was synthesised via the co-precipitation method using high purity nitrates, oxides and carbonates of iron (III), barium (II) and ammonium hydroxide. Once a phase pure sample of barium hexaferrite was obtained, it was doped, by weight, with 1, 2, 3, 5, 10, 15, 20 and 30% cobalt oxide (Co₃O₄). The addition of cobalt to the BaM had the effect of reducing the permittivity and loss tangent until a doping of 10% whereupon it remained constant at around 9. Thermogravimetric (TG) studies of green bodies showed decarboxilation to occur at around 825°C and the transformation of residual Co₃O₄ to Co₂O₃ at around 900°C. The X-ray diffraction (XRD) studies confirmed the Co ions substituting in the iron sites until a doping level, of 10–15% where the structure underwent a transition to one more closely resembling the W-type hexaferrite. The measured densities were found to vary with doping levels, with a maximum of 4.45 g/cm³ at 1% Co doping.     

火焰发射光谱法测定光学材料钛酸钡锶中钡的研究

本文介绍了火焰发射光谱法测定光学材料钛酸钡锶中钡的方法,包括样品制备、测试条件、干扰试验及消除共存元素的干扰等。实验证明本方法准确、可靠。     

Synthesis of Nano-sized Barium Titanate Powder by Solid-state Reaction between Barium Carbonate and Titania

Size control of BaTiO3 in solid-state reaction between BaCO3 and TiO2 was demonstrated by varying the size of TiO2 and milling conditions of BaCO3. The smaller TiO2 particles had higher surface area, resulting in faster initial reaction. The mechanically milled BaCO3 particles accelerated the diffusion process and decreased the calcinations temperature. It can be deduced from the results that the size control is possible and nano-sized BaTiO3 particles with about 60 nm can be synthesized by using the conventional solid-state reaction between BaCO3 and TiO2.     

Properties of barium hexaferrite prepared by electric field assisted self-propagating high-temperature synthesis

We have prepared ferromagnetic barium hexaferrite powders by self-propagating high-temperature synthesis (SHS) in an electric field applied by a contactless method. Our results indicate that the field strength has a significant effect on the phase composition of the synthesis product. This effect is interpreted in terms of the decomposition kinetics of the solid oxidant and reactant diffusion. Microstructural examination demonstrates that an electric field has a marked effect on the morphology of SHS materials. The magnetic properties of the synthesized powders depend significantly on both the strength and direction of the applied field.     

火焰原子吸收光谱法测定光学新材料钛酸钡锶中钡和锶

本文介绍了火焰原子吸收光谱法测定光学新材料钛酸钡锶中钡和锶,研究样品制备、测试条件和共存元素干扰消除。本法的准确度和精密度均达到满意的结果。