轻质磁性材料的制备及在磁流变液中的应用

研究了使用化学镀的方法在轻质载体上包覆具有磁性的镍、钴等物质.该材料具有密度低的优点(有效密度为2～3 g/cm3).对比于几种羰基镍粉制备的磁流变液的沉降稳定性,使用该轻质磁性材料制备的磁流变液不用加防沉剂,其稳定性类似于加入较多防沉剂的羰基镍粉磁流变液.其在磁场下表观粘度比零磁场下的粘度有几十倍的变化.因此,使用该轻质磁性材料有望解决磁流变液普遍存在的沉降问题,得到综合性能良好的产品.     

磁流变体流变学特性研究

对所研制的矿物油介质和硅油介质磁流变体样品的零场粘度、磁流变性能、示功及速度特性进行了系统的测试和分析,并对其影响因素进行了详细的讨论.研制的磁流变体零场粘度小于0.5 Pa s(γ=81 s-1)且具有良好的粘温特性; 磁流变体的剪切应力接近和超过70 kPa(B=6000 Gs); 在智能减振器的应用试验中获得理想的示功特性曲线.     

α-Fe粉体浓悬浮体系的制备及磁流变效应

报道使用价格低廉的还原铁粉制备磁性粒子浓悬浮体系,对体系磁流变效应进行研究,并研究了磁性颗粒尺寸和氧化物对悬浮体系力学性质及沉降稳定性的影响.     

磁流变弹性体的研究进展

磁流变弹性体(Magnetorheological-Elastomer,MRE)由磁流变液(Magnetorheological-Fluid,MRF)发展而来。MRE材料克服了MRF的易沉降、稳定性差、颗粒易磨损等缺点,并具备了响应速度快、可逆性好、结构设计简单、制备成本低等优点。因此,MRE材料被广泛用于吸振隔振、振动控制以及应力位移传感器等领域。通过总结MRE材料的制备方法和相关性能,能够加速它的发展。本文汇总了近几年MRE材料的制备方法、性能及应用研究现状,并展望了未来的发展方向。     

温度对磁流变胶复合材料动态力学性能的影响研究与分析

磁流变胶(MRG)是新一代磁流变材料,其有效克服了磁流变液易沉降等缺点。磁流变胶是由软磁颗粒悬浮在凝胶状基质中形成的,其流变特性主要受磁场和温度两个因素控制。本文制备了含有羰基铁粉质量分数为60%的聚氨酯基磁流变胶。系统研究了温度对磁流变胶流变特性的影响。结果表明,温度对磁流变胶的粘弹性有显著影响。测量了频率分别为0.1、5和15 Hz,振幅分别为10%和50%的谐波应变信号在5个温度水平下的迟滞响应,分析了磁流变胶的粘弹性特性,并采用粘弹塑性模型预测了磁流变胶的非线性迟滞特性。分析结果表明,粘弹塑性模型能够准确预测磁流变胶在不同温度下的迟滞特性。     

金属核心/高聚物膜复合悬浮相电流变流体材料

针对电流变流体悬浮相材料的开发与研究,根据介质极化原理,设计开发了金属核心/高聚物膜复合悬浮相电流变流体材料,在乳液聚合与微胶囊包覆技术的基础上,制备出了金属核心/高聚物膜复合颗粒.并对这种金属核心/高聚物膜复合颗粒的电流变流体性能进行了测试与研究.从理论和实验上都说明了金属核心/高聚物膜复合悬浮相材料在改善电流变流体力学性能及稳定性方面具有潜力,是可以进一步提高与改进的电流变流体材料.     

磁性粒子浓悬浮体系沉降稳定性的光学表征

报道一种新的磁性粒子浓悬浮体系沉降稳定性的表征方法.对均匀分散的磁性粒子浓悬浮体系,采用定时光度测量法对其沉降稳定性进行表征,可以得到一定时间内粒子沉降的定量数据.此方法可用于低体积分数磁流变液沉降稳定性的表征.同时,对比分析表明,在磁性粒子浓悬浮体系中加入纳米级TiO2粒子,能使制备的磁流变液稳定性显著增强.     

超细α-Fe粒子对磁性粒子浓悬浮体系磁流变性能的增强

报道在磁性粒子浓悬浮体系中加入球磨超细α-Fe粒子对其磁流变性能的影响,主要研究其动态屈服应力的变化,沉降稳定性的改变以及超细粒子对相变结构的可能影响.超细α-Fe粒子的加入,能使磁性粒子浓悬浮体系的抗剪切能力有明显变化,悬浮稳定性增强.对其它几种超细粒子实验结果进行了简要讨论.超细粒子对磁流变性能影响程度取决于加入物与磁性颗粒的重量比例、加入物质的性质以及所加入超细粒子的尺寸.     

生物农药微胶囊壁材料研究

用原位聚合法对生物农药阿维菌素进行包囊,然后制备微胶囊制剂,并对用于该制剂的两种高分子囊壁材料-三聚氰胺甲醛树脂和脲醛树脂的性能进行了研究。结果表明,两种树脂皆为较好的生物农药用微胶囊缓释剂型的囊壁材料,其制备工艺简单,具有良好的稳定性、粒径大小与分布、悬浮性、缓释性等,包封率均达80％以上。其中三聚氰胺甲醛树脂悬浮性较脲醛树脂更好,缓释性更持久。     

海藻酸钠与丙烯酰胺微波共聚制备高吸水树脂

高吸水性树脂是近年来得到迅速发展的一类新型的功能性高分子材料,由于其能吸收自身质量数百倍至数千倍的水,且具有优良的保水性能,因此被广泛应用于农业、林业、卫生用品材料、工业用脱水剂,医用材料、水凝胶材料等。反相悬浮聚合法是目前制备高吸水性树脂较先进的方法,具有制备工艺简单,树脂的物理形态和吸水性能较好等优点。海藻酸钠是从褐藻中提取得到,由于其良好的生物降解性和生物相容性,     

Xanthan gum-coated soft magnetic carbonyl iron composite particles and their magnetorheology

The dispersion stability of carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by coating soft magnetic CI particles with an environmentally benign biopolymer of xanthan gum to reduce the density gap between the medium oil and dispersed particles. The sedimentation test of the MR fluid showed that the xanthan gum/CI composite particles improved the sedimentation drawback of the pristine CI-based MR fluid. The rheological properties of the MR fluid were also examined using a rotational rheometer to observe the typical MR characteristics, such as yield stress and shear viscosity.     

Two-layer coating with polymer and carbon nanotube on magnetic carbonyl iron particle and its magnetorheology

Magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids generally posses serious dispersion defects due to the large density mismatch between the CI particles and continuous oil medium, which restricts further MR applications. Polymer coating technology has been introduced in an attempt to reduce the density or prevent CI particle aggregation. In this study, a unique functional coating composed of a polyaniline layer and multiwalled carbon nanotube nest was fabricated on the surface of CI particles using a dispersion polymerization and solvent casting method to improve the sedimentation problem of CI-based MR fluids when dispersed in medium oil. The coating morphology was analyzed by scanning electron microscopy. The effect of the functional coating on the MR performance along with the sedimentation observations was investigated using a rotational rheometer. The results showed that the sedimentation of dispersed particles was improved considerably by the reduced density and rough morphology.     

Additive role of attapulgite nanoclay on carbonyl iron-based magnetorheological suspension

Attapulgite (ATP), a fibrous nanoclay mineral, was adopted as an additive in this study to improve the sedimentation problem of soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids caused by the density mismatch between the CI particles and medium oil. The MR characteristics of the two MR fluid systems with and without ATP were measured and compared using a rotational rheometer under different magnetic field strengths. Scanning electron microscopy indicated that ATP filled the interspaces among the CI particles, explaining the improved dispersion stability of the MR fluid based on the Turbiscan sedimentation measurements. Despite the slight decrease in MR characteristics, the MR fluid with the additive exhibited the typical MR performance of an increase in shear stress in an applied magnetic field.     

Soft magnetic carbonyl iron microsphere dispersed in grease and its rheological characteristics under magnetic field

Magnetorheological (MR) grease, comprised of a suspension of soft magnetic carbonyl iron (CI) microspherical particles dispersed in a grease medium, was fabricated by a mechanical stirring method. As potential medium oil for MR system, shear viscosity of the pure grease was measured as a function of temperature. Its MR characteristics were investigated using a rotational rheometer under an external magnetic field. Flow curve responses (shear stress and shear viscosity), yield stress, and elasticity were investigated using various magnetic field strengths ranging from 0 to 342 kA/m. It was confirmed that MR grease has a yield stress under no external magnetic field due to the inherent property of grease. In addition, CI based MR grease exhibited a characteristic of a Bingham fluid.     

PH-Responsive and Self-Healing Hydrogels Fabricated with Guar Gum and Reactive Microgels

Hydrogels (MR gels) with pH-responsive and self-healing properties were prepared via guar gum solutions and reactive microgel. The reactive microgel was characterized through scanning electron microscope (SEM), laser particle-size analysis measurements, and FTIR. Compared with general hydrogels cross-linked by borax (B gels), the MR gels exhibit superior properties on the aspects of viscosity, viscoelasticies, and temperature resistance. Furthermore, the viscosities of MR gels increase with the rising pH value, and it can dynamically reconstruct after being destructed by external force. In addition, the microstructure of the MR gel was characterized by SEM, which confirms that the reactive microgel indeed as cross-linker and each microgel can cross-link several chains as if the chains were grafting from the microgels. These features show that the addition of reactive microgels can enhance the strength of MR gels significantly and indicate that the MR gels have a great potential application in hydraulic fracturing, especially in high-temperature oil fields.     

Iron oxide/MCM-41 mesoporous nanocomposites and their magnetorheology

Mesoporous nanocomposite materials of magnetic iron oxide-containing MCM-41 (IO/MCM-41) were prepared by simple thermal oxidation of Fe-containing MCM-41 initially prepared by a direct synthesis route using Fe³⁺ salt. The magnetic saturation of the fabricated nanocomposite materials was measured using a vibrating sample magnetometer, while surface morphology and inner framework of the composite materials were studied using a field emission scanning electron microscope and a transmission electron microscope to confirm their mesoporous nanocomposite formation. The fabricated magnetic materials were then adopted as a magnetorheological (MR) fluid, where the IO/MCM-41 magnetic nanocomposites were dispersed in a nonmagnetic medium oil in addition to as an additive for carbonyl iron-based MR fluid. Their MR properties of flow curve along with yield stress and viscoelastic properties under applied magnetic fields were investigated using a rotational rheometer.     

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

In this study, magnesium ferrite (MgFe₂O₄) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe₂O₄ nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe₂O₄ nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe₂O₄ nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe₂O₄ nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.     

Nitrogen-Containing Hydrochar: The Influence of Nitrogen-Containing Compounds on the Hydrochar Formation

Hydrothermal carbonization (HTC) of fructose and urea containing solutions was conducted at 180 °C to study the influence of nitrogen-containing compounds on the conversion process and HTC products properties. The concentration of fructose was fixed, while the concentration of urea was gradually increased to study its influence on the formation of nitrogen-containing hydrochar (N−HC). The degradation of urea has an important influence on the HTC of fructose. The Maillard reaction (MR) promotes the formation of N−HC in acidic conditions. However, in alkaline conditions, MR promotes the formation of bio-oil at the expense of N−HC. Alkaline conditions reduce N−HC yield by catalyzing fragmentation reactions of fructose and by promoting the isomerization of fructose to glucose. The results showed that adjusting the concentration of nitrogen-containing compounds or the pH value of the reaction environment is important to force the reaction toward the formation of N−HC or N-bio-oil.     

A Parameter Identifying Method for Magnetorheological (MR) Fluids Dampers

In order to speed up the commercial process of magnetorheological(MR) dampers, it is necessary to set up the theoretical foundation of the design of MR dampers. In this thesis, we studied the mechanical property of MR fluids, the design roles of MR dampers and the experimental modeling of MR dampers. Based on a prototype MR dampers working in flow mode, an experimental modeling method for MR dampers is put forward. Employing a nonlinear sequential filter to identify the model parameter of viscous plastic model carries out the modeling method.We performed numerical simulation with eqs. (5) and (7), present the simulation results in Fig.3. The good agreement between the test data and results computed shows that the modeling method is correct     

Structures and Properties of Silicon Oxide Clusters by Theoretical Investigations

In this paper, we outline our computational work in the area of silicon oxide clusters. To reduce the computational cost, we designed an economic basis set for silicon oxide systems, and reliable structures were obtained by this approach. To reveal the formation mechanism of silicon nanowires, we investigated the structures and properties of silicon suboxide clusters in particular monoxide clusters that play an important role in the oxide-assisted growth. And to improve our understanding of the silicon dioxide clusters and to bridge the gap between gas phase and solid phase silica, we proposed several models based on the two-membered ring (2MR), three-membered ring (3MR), four-membered ring (4MR), the hybrid of the 2MR and 3MR, or the 3MR and 4MR.