Facile synthesis of tubular magnetic carbon nanofibers by hypercrosslinked polymer design for microwave adsorption

In this study, a simple and efficient method for fabrication of tubular magnetic carbon nanofibers (TMCF) has been developed. Firstly, tubular polymer nanofiber precursors are synthesized by confined self-condensation method. After carbonization of polymer and in situ transformation of FeCl₃ at high temperature, TMCF loaded with Fe nanoparticles is obtained. It has been found that carbonization temperature has significant effects on conductivity, specific surface area, pore volume, defects number in carbon component, and magnetic content of TMCF. The influence of composition, structure, and filler content on microwave absorption properties is revealed. Meanwhile, the microwave absorption mechanism has been analyzed in depth, which benefits from the designed unique structure. The TMCF obtained at 700°C exhibited best performance with the filler content of 15%. The minimum reflection loss is −47.33 dB@2.2 mm, the effective absorption bandwidth is 6.5 GHz (RL < 10 dB), and the matching frequency is 14.1 GHz. The obtained TMCF is lightweight and possess excellent microwave absorption ability, which can be widely used as highly efficient microwave absorber.     

Quantification of Mixtures of C2 and C3 Hydroxy Acids and Products of Glycerol Oxidation by High-Performance Liquid Chromatography and Quantitative 13C NMR

The aim of this study was to develop an improved general method for detecting and quantifying mixtures of hydroxy acids and other products of glycerol oxidation in aqueous media, to prevent the confusions that can occur due to similarities and interactions between these compounds depending on media conditions. Standard potential products of glycerol oxidation—glycerol, glyceraldehyde, dihydroxyacetone, glyceric acid, lactic acid, glycolic acid, glyoxylic acid, oxalic acid, tartronic acid, and mesoxalic acid—were analyzed by high-performance liquid chromatography (HPLC) and quantitative ¹³C nuclear magnetic resonance (NMR), in mixtures of known composition. The results obtained were concordant with the known compositions tested. HPLC was more accurate than quantitative ¹³C NMR for simple mixtures, but ¹³C NMR was required for complex mixtures containing dihydroxyacetone and glycerol, oxalic acid and mesoxalic acid, or glyoxylic acid and tartronic acid, pairs of compounds not well separated or detected by HPLC. As proof-of-concept, an unknown mixture generated by glycerol oxidation was analyzed by HPLC and quantitative ¹³C NMR. The results obtained were concordant and allowed accurate determination of the composition of the sample, which contained mesoxalic acid as the major product, with oxalic acid, tartronic acid, and glyceric acid as by-products.     

注塑材料在电机转子磁钢固定中的分析与应用

为提高电机转子磁钢固定的可靠性和经济性，本文采用了转子注塑工艺来对转子磁钢进行固定。通过对注塑材料的性能分析与验证确定注塑材料的可靠性。通过对转子注塑工艺进行验证，确定了注塑工艺参数，保证了注塑工艺的可行性。     

基于神经网络遗传算法的磁粒研磨TC4材料工艺参数优化

目的利用磁粒研磨光整加工技术提高TC4材料的表面质量,使用BP神经网络建立加工工艺参数和表面粗糙度之间的关系,使用遗传算法寻找最优工艺参数组合。方法使用双级雾化快凝法制备的金刚石磁性磨料对TC4材料工件进行L9(34)正交试验,借助Matlab软件建立结构为4-12-1的BP神经网络,根据正交试验结果训练BP神经网络,探究工艺参数主轴转速n、加工间隙δ、进给速率v、磨料粒径D和表面粗糙度Ra之间的关系。使用决定系数R2评判BP神经网络训练结果,基于训练好的BP神经网络使用遗传算法对工艺参数进行全局寻优。使用计算得到的优化工艺参数进行试验,并测量工件表面粗糙度,与计算得到的表面粗糙度做对比。结果BP神经网络的预测误差在1.5%以下,通过决定系数R2优化的模型可在训练样本较少的情况下进行有效可靠的预测。遗传算法优化的结果,在主轴转速为1021.26 r/min、加工间隙为1.52 mm、进给速率为1.04 mm/min、磨料粒径为197.91μm下,获得最佳表面粗糙度,为0.0951μm。使用调整后的工艺参数,在主轴转速为1020 r/min、加工间隙为1.50 mm、进给速率为1.0 mm/min、磨料粒径为196μm下,试验得到的表面粗糙度为0.093μm,与计算得到的最佳表面粗糙度误差为2.21%。结论采用磁粒研磨光整加工技术与寻优参数结合,可以有效提高TC4材料加工后的表面质量。     

双磁极式磁粒研磨机理分析及试验研究

目的解决平面磁粒研磨中压力不均匀和需要反复调整研磨间隙的问题,设计双磁极式研磨方法。方法首先对双磁极式研磨方法机理进行分析,并对研磨区域单颗磨粒进行受力分析,寻找影响研磨压力的主要因素;其次利用Ansoft Maxwell软件对两种研磨方法进行磁场仿真,分析两种研磨方法的研磨区域磁场梯度变化,通过面积积分法对比磁感应强度的影响程度;最后设计试验装置,通过试验对理论分析及有限元分析的结果进行验证,对比研磨前后工件表面粗糙度及微观形貌变化。结果双磁极式研磨方法中磨粒的研磨压力完全由磁场力提供,与研磨区域磁感应强度成正比,研磨区域磁感应强度比"铣削式"研磨方法提高约34.56%。两种方法在相同试验条件下对SUS304不锈钢板研磨40 min,双磁极式研磨方法研磨后,工件表面原始纹理基本被去除,表面粗糙度值由原始的0.25μm下降至0.16μm,下降率为36%,比"铣削式"研磨方法提高约80%,粗糙度曲线波动平缓,波峰波谷高度差变化均匀且表面形貌光滑平整。结论双磁极式研磨方法研磨区域磁场梯度变化明显,利于磨粒流动更新,研磨压力相对稳定,表面粗糙度下降率高,研磨后工件表面形貌光整,与"铣削式"研磨方法相比具有较明显的优势。     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

GSH-responsive polyglutamic acid nanocarriers for dual targeted cancer therapy

In order to reduce the toxic side effects of chemotherapeutic drugs and improve the targeting and efficiency of cancer treatment, the development of drug delivery system has received great attention. In this study, second generation polyglutamic acid dendrimers (G₂) are used as basic materials to produce porous nanoparticles through cross link by crosslinkers containing disulfide bonds. The crosslinked products (G₂)_n have negative electricity and abundant voids, which enable them to adsorb the electronegative anticancer drug DOX. At the same time, in order to transport DOX to the tumor site, we modified FA on DOX and encapsulated it in magnetic mesoporous silica (FA-DOX-MSNs). Therefore, the final nanoparticles (FA-DOX-MSNs/(G₂)_n) not only have dual targeting ability to transport DOX to the tumor site, but also have reductive responsiveness that can release drugs responsively in the tumor cells. In addition, it has good biocompatibility and endocytosis ability.     

Reduction in Microsegregation in Al-Cu Alloy by Alternating Magnetic Field

The microsegregation behavior of the Al-4.5 wt%Cu alloy solidified at different cooling rates under the alternating magnetic field(AMF) was investigated.The experimental results showed that the amount of non-equilibrium eutectics in the interdendritic region decreased upon applying the AMF at the same cooling rate.The change in microsegregation could be explained quantificationally by the modifications of dendritic coarsening,solid-state back diffusion and convection in the AMF.The enhanced diffusivity in the solid owing to the AMF was beneficial for the improvement in microsegregation compared to the cases without an AMF.In contrast,the enhanced dendritic coarsening and forced convection in the AMF were found to aggravate the microsegregation level.Considering the contributions of the changes in above factors,an increase in solid diffusivity was found to be primarily responsible for the reduced microsegregation in the AMF.In addition,the microsegregation in the AMF was modeled using the analytical model developed by Voller.The calculated and experimental results were in reasonable agreement.     

Study on surface magnetization recover ilmenite from titanaugite using surfactant sodium oleate

ABSTRACT

Separation of ilmenite from titanaugite was investigated by magnetic coating. By enlarging magnetic difference between ilmenite and titanaugite, ilmenite was efficiently recovered. Scanning electron microscope and vibrating sample magnetometer results indicated that magnetite selectively coated onto ilmenite surface and increased its magnetism, which resulted in different magnetic separation behavior between ilmenite and titanaugite. FTIR and contact angle measurements confirmed that the adsorption difference of sodium oleate resulted in a stronger hydrophobicity on magnetite and ilmenite than titanaugite. Interaction energy analysis illustrated that hydrophobic association interaction on ilmenite was stronger than that on titanaugite, and which led to the selective coating of magnetite onto ilmenite.     

用于阀芯类零件去毛刺的磁极板优化设计与实验研究

目的 为解决阀芯类零件节流边毛刺去除不均匀和效率低下的问题，对磁极板尺寸和曲率进行规律性研究和实验验证。方法 首先，用Maxwell仿真软件对磁极板的各个参数进行规律性仿真，得出合适的磁极板尺寸;其次，为提高加工区域的磁感应强度值，设计了曲面磁极板，并对其相关参数进行仿真;最后对优化后的装置进行磁感应强度测试，并使用液体磁性磨具对45钢和阀芯棱边毛刺进行去除实验。结果 根据仿真结果发现，磁极板长度比工件大20 mm时，工件轴向磁场分布最均匀，磁极板厚度对磁场影响较小，磁极板宽度应根据加工间隙进行选择。曲面磁极板可以加强加工区域的磁感应强度值，曲率半径越小，加工区域获得的磁感应强度值越大，其中半圆形磁极板效果最佳。对装置的磁感应强度测试也表明，将工件置于磁场中后，其表面磁感应强度值最高达600 mT左右，满足加工需求。最后通过加工实验发现，在转速为500 r/min的条件下，阀芯节流边的毛刺去除效果理想，且轴向加工均匀。结论 该装置可以对阀芯这类导磁性回转类零件产生良好的加工效果。