Bio-silica incorporated barium ferrite composites: Evaluation of structure,morphology, magnetic and microwave absorption traits

A series of bio-silica incorporated barium-ferrite-composites with the composition of (x)Bio-SiO₂:(80-x)γ-Fe₂O₃:(20)BaO, where x = 0, 1, 2, and 3 wt% were prepared using the modified solid-state reaction method. The influence of different bio-silica (extricated from sintered rice husk) contents on the surface morphologies, structures, and magnetic characteristics of these composites were assessed. The relative complex permittivity and permeability were resolved using the Nicholson-Ross-Weir strategy in the frequency range of 8–13 GHz. Meanwhile, the reflection loss was estimated through the transmission/reflection line theory to assess the MW absorption properties of the composites. Incorporation of the bio-silica in the barium ferrite composites generated a new hexagonal phase (Ba₃Fe₃₂O₅₁) and a tetragonal phase (BaFeSi₄O₁₀) which led to a decrease in the saturation magnetization and significant shift in the MW frequency absorption peak positions.     

Influence of citric acid on the morphology and magnetic properties of barium ferrite thin films

Hexagonal barium ferrite (BaFe₁₂O₁₉) thin films were fabricated by spin coating of precursors from sol-gel methods. Different amount of citric acid was added. Weight loss and changes of chemical bonds during the heat treatment below 500 °C were recorded by thermogravity analyzer and Fourier transform infrared spectroscopy, respectively. The morphology of the films, i.e. the amount of acicular crystallites in the film, was controlled by adjusting the quantity of citric acid. The X-ray diffraction shows that the films are c-axis oriented, but the crystallization is less perfect with the increase of the citric acid. With the increase of the citric acid, the percentage of the acicular crystallites increased. At the same time, the coercivity force increased. The acicular crystallites were not exchange-coupled to the platelet crystallites. The citric acid was understood to form complex with iron ions and accelerate the exothermal auto-combustion. The c-axis oriented growth of the film was thus deteriorated.     

换能器辐射阻抗变化对匹配层参数的影响

匹配层换能器在实用中往往由于辐射阻抗的变化破坏了“最佳”匹配层参量的选取[1]。本文从反映阻抗概念给出了必要的匹配层厚度修正[2],并以实例计算证明了修正公式的实用意义。     

The structural and magnetic powders prepared by properties of barium ferrite the sol-gel method

In this paper,M-type hexagonal barium ferrite powders are synthesized using the sol-gel method.A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 C using thermo-gravimetric analysis and differential scanning calorimetry.The effects of the additives and the cacinating temperature on the magnetic properties are investigated,and the results show that single-phase barium ferrite powders can be formed.After heat-treating at 950 C for 4h with 3 wt% additive,the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g,respectively.     

The structural and magnetic properties of barium ferrite powders prepared by the solben gel method

In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.     

Analysis of the role of M-type hexaferrite-based materials in electromagnetic interference shielding

M-type hexaferrite has attracted much attention for its large magneto-crystalline anisotropic energy, exceptionally good chemical stability, corrosion resistance, high Curie temperature, and high coercivity. In this review paper, our goal is to examine the microwave absorption properties and related studies of M-type hexaferrite-based materials. The microwave absorption properties of hexaferrite-based materials in the S, X, and Ku-band are discussed with their corresponding reflection losses. Complementarity between magnetic loss and dielectric loss is found to have a great impact on the proper absorption of microwaves. The mechanisms corresponding to the microwave absorption in different morphologies and structural adaptations of hexaferrite have been elaborated in the article. The ongoing trends and future perspectives of these materials are also outlined.     

Reliable determination of the few‐layer graphene oxide thickness using Raman spectroscopy

We report on a reference‐free Raman spectroscopy method for a precise thickness determination of the multilayered graphene oxide flakes. The method is based on the normalization of the total integral intensity of D and G Raman bands to the integral intensity of the second‐order optical phonon peak of the silicon substrate in the Raman spectrum. The normalization provides discrete ratio values corresponding to the number of graphene oxide layers in the respective flakes with the intensity linearly increasing with the number of layers. This provides a fast and robust determination of the thickness of graphene oxide flakes in terms of the layer number up to high values. A comparison with conventional spectrally resolved reflectivity mapping shows similar sensitivity, while selectivity to particular functional chemical groups is a bonus of the Raman‐based method. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficiency and purity control in the preparation of pure and/or aluminum-doped barium ferrites by hydrothermal methods using ferrous ions as reactants

The synthesis of hexagonal barium ferrite (BaFe₁₂O₁₉) was studied under hydrothermal conditions by a method in which a significant amount of ferrous chloride was introduced alongside ferric chloride among the starting materials. Though all of the Fe²⁺ ions in the starting material were converted to Fe³⁺ ions in the final product, Fe²⁺ was confirmed to participate differently from the Fe³⁺ used in the conventional method in the mechanism of forming barium ferrite. Indeed the efficiency of the synthesis and the quality of the product and the lack of impurities such as Fe₂O₃ and BaFe₂O₄ were improved when Fe²⁺ was included. However, the amount of ferrous ions that could be included to obtain the desired product was limited with an optimum ratio of 2:8 for FeCl₂/FeCl₃ when only 2 h of reaction time were needed. It was also found that the role of trivalent Fe³⁺ could be successfully replaced by Al³⁺. Up to 50% of the iron could be replaced by Al³⁺ in the reactants to produce Al-doped products. It was also found that the ratio of Fe²⁺/M³⁺ could be increased in the presence of Al³⁺ to produce high quality barium ferrite.     

纸质胶带胶层厚度在线测量

在纸质胶带生产过程中 ,胶层厚度及均匀性是很重要的技术指标 ,因此需要对胶层厚度进行在线测量。介绍了一种红外纸质胶带胶层厚度测量仪。它是依据胶质对一定波长的红外光具有特征吸收的原理 ,采用了能量比参考平衡技术 ,使仪器性能稳定、可靠     

Characterization of inner layer thickness change of a composite circular tube using nonlinear circumferential guided wave:A feasibility study

The feasibility of using the nonlinear effect of primary circumferential guided wave (CGW) propagation for characterizing the change of inner layer thickness of a composite circular tube (CCT) has been investigated. An appropriate mode pair of the fundamental and double-frequency CGWs (DFCGWs) has been selected to enable the second harmonics of primary wave mode in the given CCT to accumulate along the circumferential direction. When changes in the inner layer thickness (described as the equivalent inner layer thickness) take place, the corresponding nonlinear CGW measurements are conducted. It is found that there is a direct correlation between change of equivalent inner layer thickness of the CCT and the relative acoustic nonlinearity parameter (Δβ) measured with CGWs propagating through one full circumference, and that the effect of second-harmonic generation (SHG) is very sensitive to change in the inner layer thickness. The experimental result obtained demonstrates the feasibility for quantitatively assessing the change of equivalent inner layer thickness in CCTs using the effect of SHG by primary CGW propagation.     

First order reversal curves analysis of the temperature effect on magnetic interactions in barium ferrite with La–Co addition

First order reversal curves (FORCs) distributions are a powerful tool for investigating hysteresis and interactions in magnetic systems and have been widely applied. La–Co substitution in barium hexaferrites has also been extensively studied. The most effective substitution to improve the magnetic properties (coercive field and energy product) is given by x=y=0.2 in the formula Ba_1-xLa_xFe_12-yCo_yO₁₉. In this work, this stoichiometry is initially used to obtain a state where more than one phase is present. The magnetic behavior as a function of temperature was studied in order to have an insight into the magnetic interactions that originate a decrease in the magnetic performance of Ba hexaferrite magnets. The sample was structurally characterized by X-ray diffraction (XRD) and magnetically studied in a SQUID magnetometer. FORC distributions were used to study the dependence of the magnetic interactions with the temperature. FORC diagrams performed on the sample at different temperatures exhibit similar characteristics, such as the spread in the h_c–h_u plane and a spread out of the h_c-axes. These features are interpreted in terms of exchange-interacting particles and dipolar interactions, respectively. As the temperature decreases, stronger interactions are noticed among hard and soft phases.     

Effect of doping MnO2 on magnetic properties for M-type barium ferrite

The crystalline structure and magnetic properties of M-type barium ferrite doped with small amounts of MnO₂ (0, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 wt%, respectively) have been investigated by means of XRD, SEM and VSM. The results show that the crystalline structures of barium ferrite are still M-type hexagonal structure and Mn ions are distributed homogeneously in both the grains and the grain boundaries. The saturation magnetization and magnetocrystalline anisotropy constants both reach the highest values when x=0.75 wt%. The displacement of Fe ions from 4f₁ to 2b site is mainly responsible for the appearance of the maximum values.     

Improving the property of calcium ferrite using a sonochemical method

Power ultrasonic vibration was applied to the solidification of calcium ferrite (CF) melt in this study. The results indicated that power ultrasound can promote the formation of CF by accelerating the solidification process. Ultrasonic vibration greatly refined the CF grains, resulting the grain size decreased from 1893 to 437 μm. Meanwhile, ultrasonic vibration significantly enhanced the compressive strength, reduced the reduction time and improved the reducibility of CF slags. With ultrasonic treatment, the ultimate compressive strength of samples increased from 37.5 to 67.8 MPa, and the reduction time decreased from 225 to 136 min.     

The structural properties of Al doped ZnO films depending on the thickness and their effect on the electrical properties

In this study, the structural and electrical properties of AZO films with different film thickness deposited by r.f. magnetron sputtering were interpreted in relation with film growth process. The result shows that the grain size increases during film growth, which is accompanied by decrease of compressive stress, indicating the enhancement of crystallinity. The relationship between grain size and compressive stress follows the same tendency for the samples regardless of deposition temperature, which implies the strong dependencies between the grain size and the compressive stress. The XPS analysis shows that the defects such as chemisorbed oxygen and segregated Al₂O₃ cluster at grain boundary are reduced with increase of film thickness or deposition temperature, leading to increase of carrier concentration and mobility. The mobility increase is accompanied by grain size increase and compressive stress reduction, indicating the influences of grain boundary and crystallinity on the mobility.     

Effects of oxygen deficiency on the acoustic anomalies and phase transition behaviors of barium titanate single crystals

The acoustic behaviors of oxygen-reduced barium titanate (BaTiO_3-δ) single crystals with δ∼0.04 were investigated as a function of temperature by using Brillouin spectroscopy. The longitudinal acoustic mode of the moderately-reduced BaTiO₃ (BTO) showed two pronounced anomalies at approximately 112 °C and −11 °C, which correspond to the cubic-tetragonal and tetragonal-orthorhombic phase transition temperature, respectively. These temperatures were lower by more than 10 °C compared to those of the pure BaTiO₃ suggesting that the disorder introduced by oxygen vacancies lowers the phase transition temperatures. The paraelectric phase of the reduced BaTiO₃ were characterized by substantial softening of the longitudinal acoustic mode and the growth of central peaks centered at zero frequency. These anomalies were observed in a certain temperature range above the Curie temperature, indicating that pretransitional precursor polar clusters exist in the cubic phase and that their dynamics are responsible for the acoustic anomalies caused by electrostrictive coupling between the strain and the polarization. The relaxation time of the precursor polar clusters derived from the central peak exhibited a critical slowing-down behavior showing that their dynamics becomes more sluggish as temperature approaches the Curie point.     

The influence of impurity on the critical thickness of the CeO_2 buffer layer for coated conductors

The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and ela...     

Preparation, characterization and magnetic properties of the doped barium hexaferrites BaFe12−2xCox/2Znx/2SnxO19, x=0.0-2.0

A series of powders of M-typed barium hexaferrites doped with Co, Zn and Sn of general formula BaFe_12-2xCo_x/2Zn_x/2Sn_xO₁₉ (x=0-2.0) were prepared by the co-precipitation/molten salt method. The structures, particle morphology and magnetic properties of the products were characterized by X-ray powder diffraction, vibrating sample magnetometer and ESEM/EDX. The results show that the crystallinity of the samples decreases with increase in the doping amount x. When x is less than 0.6, it is possible to obtain perfectly crystallized hexagonal BaFe_12-2xCo_x/2Zn_x/2Sn_xO₁₉, where the diameters of the particles are around 500 nm. The saturation magnetization of pure barium ferrite BaFe₁₂O₁₉ produced with this method is 71.9 A m² kg⁻¹ at room temperature and the intrinsic coercivity (H_c) is 367.8 kA m⁻¹. The doped barium hexaferrite powder obtained when x is between 0.3 and 0.4 exhibits high saturation magnetization and a temperature dependence of coercivity close to zero.     

矩形掺杂光子晶体中电磁波的模式和缺陷模

利用一维矩形掺杂光子晶体中电磁波横向受限的条件,推导出电磁波在其中各个模式满足的关系式,利用它研究了电磁波各模式的特性.利用特征法研究了电磁波的缺陷模随模式量子数和矩形边长的变化规律,得出了一维矩形掺杂光子晶体缺陷模的新结构.     

Al掺杂ZnO薄膜的厚度对其结构及磁学性能的影响

采用直流磁控共溅的方法在玻璃基底上制备了不同厚度的Al掺杂ZnO薄膜,并在真空和空气中分别退火.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)对系列薄膜的结构和磁性进行了表征.XRD结果显示:随着膜厚的增加,晶粒尺寸逐渐增大,薄膜的内应力逐渐减小.在空气退火的薄膜样品中观察到了室温的铁磁性,薄膜的饱和磁化强度M_s 随着膜厚的增加而增大,而矫顽力H_c却随着膜厚的增加而减小. 关键词： Al掺杂ZnO薄膜 薄膜厚度 应力 铁磁性