Magnetic and microwave absorption properties of polymer composites with amorphous Fe-B/Ni-Zn ferrite nanoparticles

In this study, polymer composites containing amorphous Fe-B submicrometer particles and Ni-Zn ferrite nanoparticles were fabricated. A polymer composite of mixed particles showed high permeability of μ^′r=13.7 at 0.5 GHz and μ^″r=8.3 at 1.2 GHz. In addition, this composite exhibited good microwave absorption properties (R.L. < −20 dB) in the frequency range of 0.65-1.12 GHz for absorber thickness of 2.38-4.06 mm. It is concluded that this polymer composite can be used for fabricating microwave absorbers in the UHF range, and would result in thinner microwave absorbers than any other microwave absorbers reported thus far.     

复合表面活性剂对油包水型高内相乳状液流变性和稳定性的影响

为了研究复合表面活性剂对油包水型高内相乳状液流变性和稳定性的影响,选用由PIBSA-TEA和油酸二乙醇酰胺、椰子油酸二乙醇酰胺、失水山梨醇单油酸酯等小分子表面活性剂组成的复合表面活性剂制备HCEs,并检测所制得HCEs的流变性和储存稳定性。结果表明:表面活性剂对HCEs的剪切应力和储能模量有较大的影响。采用复合表面活性剂制备的HCEs具有较高的剪切应力和储能模量。但是,复合表面活性剂制备的HCEs储存稳定性明显下降。在油相黏度比较高时,复合表面活性剂制备的HCEs储存稳定性有一定的提高。     

锰锌铁氧体纳米粒子的制备和磁性能研究

以金属离子的硫酸盐溶液和氨水溶液为原料,采用水热法制备了粒径为6～16nm的锰锌铁氧体纳米粒子.采用XRD、TEM、TGA和VSM等方法对产物以及产物的磁性能进行了表征.结果表明,锰锌铁氧体(Mn1-xZnxFe2O4)的居里温度随着锌的相对含量x的增加而单调的降低.锰锌铁氧体的磁化强度先随着锌的相对含量x的增加而增大,当锌的相对含量＞0.6时,磁化强度随着锌的相对含量x的增加而减小.测量了锰锌铁氧体磁流体的饱和磁化强度,计算了锰锌铁氧体(Mn0.4Zn0.6Fe2O4)纳米粒子的磁矩,其值为1.01×10-19A·m2.     

Dielectric properties of Al-substituted Co ferrite nanoparticles

A series of polycrystalline spinel ferrites with composition, CoFe_2−x Al _x O₄ (0 ≤ x ≤ 1), have been synthesized by sol-gel method. The effect of Al-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. The particle size, D, decreases with increase in Al-content. The lattice parameter, a and X-ray density, d _x , decreased with increase in Al-content. The dielectric properties for all the samples have been studied as a function of frequency in the range 100 Hz–10 MHz. Dielectric properties such as dielectric constant, ɛ′, dielectric loss, ɛ″ and dielectric loss tangent, tan δ, have been studied for nanocrystalline ferrite samples as a function of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrites proposed by this technique possess lower value than that of the ferrites prepared by other methods for the same composition. The low dielectric behaviour makes ferrite materials useful in high frequency applications.     

橡胶沥青复合材料动态剪切流变特性

在橡胶沥青复合材料中加入不同的胶粉含量,其动态力学特性发生明显改变。利用三参量流变模型,推导了橡胶沥青复合材料黏弹性的动态剪切流变参数。通过Origin软件自定义拟合功能,对黏度预估模型的4个待定参数进行了拟合。采用动态剪切流变仪(DSR),在不同温度下对不同胶粉含量的橡胶沥青复合材料试样进行测试,并将实验结果与三参量流变模型得到的理论结果进行对比。结果表明,实验结果与理论结果吻合较好。随着测试温度的升高或胶粉含量的降低,橡胶沥青复合材料的黏度、储存模量和损耗模量均呈现降低的趋势,而损耗因子呈增大的趋势。     

Magnetic-field effect on the rheological properties of strontium ferrite suspensions

The effect of a magnetic field and surfactants on the rheological properties of strontium ferrite suspensions has been studied. An applied magnetic field is shown to raise the suspension viscosity, which is attributable to the formation of three-dimensional chain structures made up of ferrite particles. After the magnetic field is removed, these structures do not fully break down, which leads to hysteretic behavior of the suspension viscosity. The introduction of polyelectrolytes reduces the viscosity of the suspension both in a magnetic field and after the field is removed. This is due to the formation of an electrical double layer on the particle surface, which reduces interparticle friction and the strength of the three-dimensional structures. The results of this study may be useful in devising processes for enhancing the texture and density of highly anisotropic strontium ferrite materials produced by wet pressing.     

Modification of dielectric and mechanical properties of rubber ferrite composites containing manganese zinc ferrite

Spinel ferrites constitute an important class of magnetic materials. Polycrystalline ferrites are a complex system composed of crystallite grain boundaries and pores. Manganese zinc ferrites have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. Composite materials are ideally suited for many modern applications where ceramic materials have some drawbacks. The mouldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ (MZF) were synthesized for different ‘x’ values in steps of 0.2. These pre-characterized ceramic ferrites were then incorporated in a natural rubber matrix. The dielectric properties of the ceramic manganese zinc ferrite and RFC were also studied. A program based on G programming was developed with the aid of LabVIEW package to automate the dielectric measurements. The dielectric permittivity of the RFC were then correlated with that of the corresponding dielectric permittivity of the magnetic filler and matrix by a mixture equation, which helps to tailor properties of the composites.     

镍铁氧体/聚苯乙烯复合材料的制备与性能

采用高分子凝胶法制备了纳米镍铁氧体,然后用热压法制备了镍铁氧体/聚苯乙烯复合材料.镍铁氧体的结构、形貌和复合材料的电磁性能分别采用X射线衍射仪(XRD)、透射电镜(TEM)和HP8510网络分析仪进行了研究.结果表明,当煅烧温度为600℃时,镍铁氧体晶相生成.随着煅烧温度的升高,镍铁氧体晶体晶型趋向完整.在X波段,复合材料的复介电常数和复磁导率值随着镍铁氧体煅烧温度的升高而增大.1000℃煅烧的镍铁氧体所制备的镍铁氧体/苯乙烯复合材料在11.47GHz处的最小反射率为-12.67dB.     

Synthesis and electrical properties of polymer composites with polyaniline nanoparticles

Nano-sized polyaniline (PANI) particles dispersed in aqueous solution were prepared using both poly(vinyl alcohol) (PVA) and poly(styrene sulfonic acid) (PSSA) as polymeric stabilizers. Size of the spherical PANI particle synthesized using PVA with a HCl dopant (PANI-HCl/PVA) was about 150 nm in diameter, and that with PSSA (PANI-PSSA) was about 50 nm, with a uniform size distribution. Doping level of the PANI-PSSA measured by UV–visible spectrometer was higher than that of PANI-HCl/PVA. The PVA based composite films using both PANI-HCl (PANI-HCl/PVA) and PANI-PSSA (PANI-PSSA/PVA) were prepared by a casting method for different PANI content and their electrical conductivities were measured. A percolation threshold of PANI concentration for conductivity of composite was found only around 10 wt.% of PANI for the PANI-PSSA/PVA, and furthermore, the PANI-PSSA/PVA became more conductive above the threshold point than PANI-HCl/PVA.     

Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni_0.8−xCu_0.2Zn_xFe₂O₄ with x = 0.1-0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7-48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value (M_s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn²⁺ ions to occupy octahedral sites. The decrease in the coercivity (H_c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn²⁺ ions compared to Ni²⁺ ions. Temperature dependence of the molar magnetic susceptibility (χ_M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature (T_C) with increasing zinc.     

钴铁氧体纳米粒子制备及其镧掺杂的磁性能研究

为了制备性能良好的钴铁氧体及改善其磁性能,通过改进的溶胶凝胶自蔓延燃烧法成功地制备了钴铁氧体(CoFe2O4)及掺镧(La)钴铁氧体纳米粒子.采用X射线衍射(XRD),透射电镜(TEM)、能谱分析(EDS)、振动样品磁场计(VSM)对所得粒子进行了结构、形貌、成分及磁性能表征.测试结果表明,利用改进的溶胶凝胶法制得钴铁氧体粒度均匀,且成相温度较低,500℃煅烧1h时平均粒径12nm左右;通过掺杂稀土镧元素对所得铁氧体的相结构有较强的影响,所得掺镧钴铁氧体与目标产物一致;所得钴铁氧体具有较高的矫顽力(737.33Oe),并且通过稀土元素镧的掺杂提高了钴铁氧体的矫顽力.     

Preparation and electromagnetic properties of zinc ferrite/expanded graphite composites

An effective process for the synthesis of nano spinel zinc ferrite/expanded graphite composites was developed in order to get an electromagnetic interference shielding material. Firstly, expandable graphite was prepared using sulfuric and nitric acid solutions. Then, the precursor of the composites was produced by chemical co-precipitation method, followed by heating treatment. The obtained composites were characterized by X-ray diffraction and scanning electron microscopy. The dielectric and magnetic properties were determined using vector network analyzer and vibrating sample magnetometry. The results showed that ferrite nanoparticles with the sizes of about 50–150 nm were uniformly dispersed on the surface and interspace of EG. The magnetic properties of the composites changed by adjusting the ferrite/EG ratio and the composites had high dielectric constant in the range of 2–18 GHz. These properties of the prepared composites suggest that they can be used as a promising electromagnetic interference shielding material.     

Relationship between magnetic properties and microwave-absorbing characteristics of NiZnCo ferrite composites

The complex permeability and permittivity of the constituent materials of the microwave absorbers play a key role in determining the reflection or attenuation properties of the incident microwave. The real and imaginary (loss) components of _r and _r in the frequency range 1–12 GHz, and their relationship with microwave-absorbing properties, have been investigated in the NiZnCo ferrite composites. The composite specimens were prepared by moulding and curing a mixture of prereacted ferrite powder and silicone rubber. The quantitative estimation of microwave-absorbing properties was made by plotting the observed material constants (_r, _r) on the calculated solution map of impedance-matching. It was found that the CoO content influences the first matching frequency and the first matching thickness in the NiZnCo ferrite composites, but does not influence the second matching frequency and second matching thickness.     

Cofiring properties and camber development of ferroelectric/ferrite multilayer composites

The multilayer ferroelectric/ferrite composites were prepared and their interaction, camber development, and interface microstructure were investigated. The results show that no chemical reaction between the ferroelectrics and ferrite materials existed. The camber is because of a mismatch shrinkage of the composites and were observed at the temperature range from 800°C to 900°C. A simple model was established to describe camber. The investigation of camber development showed that the camber developed firstly toward ferrite and then toward ferroelectrics, finally the composites become flat at 950°C. The multilayer ferroelectric/ferrite composites can be cofired at 950°C and the interface is continuous with no delamination and cracks.     

Thermal stability of composites containing HCl-doped polyaniline and Fe nanoparticles

HCl-doped polyaniline (HCl-PANI) powder was mechanically mixed with Fe nanoparticles to obtain the HCl-PANI–Fe composite. The composite pellets containing 30 and 50 wt% Fe nanoparticles were heated in air at 50, 100, 150 and 200 °C for times up to 60 min. The heat treatment degrades the crystallinity of the HCl-PANI and promotes the oxidation of the Fe nanoparticles. After heat-treating, the aromatic structure of PANI is retained in the HCl-PANI and HCl-PANI–Fe pellets. However, the heat treatment causes the dopant dedoping from the polymer backbones. The HCl-PANI–Fe composite pellets heated are in a higher reduction state compared with the unheated ones. Thermogravimetric analysis reveals that a weight loss decreases with increasing the Fe nanoparticle content at the same heating temperature. The weight loss increases rapidly within the first 5-min isothermal time at 200 °C. The conductivity decreases with increasing the heat-treating temperature. A rapid decrease in the conductivity happens within the first 20-min heat-treating time for the HCl-PANI–30 wt% Fe composite and within the first 10-min heat-treating time for the HCl-PANI–50 wt% Fe composite at 200 °C. The composites exhibit a narrow hysteresis curve typical for superparamagnetic nanoparticles and the magnetization behavior is independent of the heat-treating conditions.     

Magnetic properties of nickel ferrite nanoparticles prepared using flotation extraction

A method has been proposed for the preparation of nickel ferrite nanoparticles in a system of direct sodium dodecyl sulfate micelles using ion flotation. Amorphous nickel ferrite nanoparticles with the overall composition xNiFe₂O₄ · yFe₂O₃ · zH₂O, containing dodecyl sulfate anion impurities, have been prepared. According to transmission electron microscopy results, the size distribution of the synthesized nanoparticles has a maximum in the range 4 to 6 nm, and the ferrite is X-ray amorphous. The blocking temperature of the synthesized nanoparticles is 25 K. The ferrite possesses superparamagnetic properties, with a specific saturation magnetization of 15 A m²/kg at 5 K.     

Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.     

The role of aggregation of ferrite nanoparticles on their magnetic properties

We have studied the magnetic properties of aggregates of Mn0.5Zn0.5Gd(x)Fe(2-x)O4 ferrite nanoparticles, with x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20. The scanning electron microscopy micrographs show significant aggregation of the nanoparticles in all samples. Zero field cooled and field cooled magnetization measurements were conducted on all samples from 400 K down to 5 K. Most zero field cooled curves were found to exhibit the usual behavior but with wide peaked regions. For some x values, the field cooled magnetization was found to increase slowly with decreasing temperature, and becomes nearly constant at low temperatures. The measurements of magnetization versus applied magnetic field were conducted on all samples at 5 K and 305 K in the field range from -15000 to 15000 Oe. At 305 K the magnetization for all samples was observed to saturate, while at 5 K the magnetization did not reach saturation for some values of x. The saturation magnetization values were suggested to be proportional to the size of particles. These results were discussed and suggested to be due to the inter-particle dipolar and exchange interactions between the particles in the aggregates, the large particle size distribution and the surface magnetization effects.