Fe3O4@SiO2磁性复合微球的制备与表征

采用化学共沉淀法制备Fe_3O_4颗粒,在其制备过程中控制Fe_3O_4核的长大时间,加入油酸钠作为表面修饰剂来控制Fe_3O_4核的尺寸,然后加入正硅酸乙酯(TEOS)生成纳米级Fe_3O_4@SiO_2复合纳米粒子和亚微米级Fe_3O_4@SiO_2复合微球。通过X射线衍射、透射电镜、能谱分析和红外光谱分析证实Fe_3O_4颗粒表面包覆有SiO_2,并研究了复合粒子的形貌和成分组成,然后进行了磁性能分析。结果表明,Fe_3O_4纳米颗粒、Fe_3O_4@SiO_2复合纳米粒子和亚微米级Fe_3O_4@SiO_2复合微球的饱和磁化强度分别为79.95、34.85和61.51 A·m2/kg,对应的剩磁分别为1.73、1.05和3.07 A·m2/kg,矫顽力分别为1083、755和2002 A/m,亚微米级复合微球的剩磁和矫顽力都显著增大。     

纳米Al_2O_3颗粒含量对Ni-Co基纳米复合电刷镀层组织和性能的影响（英文）

采用电刷镀技术制备了不同Al_2O_3颗粒含量的合金纳米复合电刷镀层,使用扫描电镜、硬度测试仪和摩擦磨损试验机测试了镀液中纳米Al_2O_3颗粒含量对镀层的沉积速度、纳米颗粒含量、硬度和摩擦学性能的影响。结果表明,随着镀液中纳米Al_2O_3颗粒含量的增加,电刷镀层沉积速度降低、表面形貌平整,显微硬度先提高而后降低,磨痕深度和摩擦系数先减小后增大。当镀液中纳米Al_2O_3含量为20 g/L时,镀层具有最优的组织和性能。     

纳米Fe_2O_3/KIT-6介孔结构材料的制备及非均相Fenton催化降解亚甲基蓝性能研究

采用等体积浸渍法设计制备纳米Fe_2O_3/KIT-6介孔结构非均相Fenton催化材料,并测试其对亚甲基蓝的降解性能。采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、小角X射线衍射(SAXRD)和氮气吸附脱附等方法表征其粒子尺寸、介孔有序性、比表面积及孔径分布等。结果表明,介孔KIT-6孔道内均匀分布着纳米尺寸的Fe_2O_3粒子,10%铁含量(质量分数)的纳米Fe_2O_3/KIT-6介孔结构材料具有最优的Fenton催化降解性能。这是因为适量的纳米Fe_2O_3负载使催化材料具有较大的比表面积和较多活性位点的同时具有一定的催化介质传质通道,同时减少纯纳米粒子在催化过程中的团聚,从而最终提高催化剂的Fenton催化降解性能。     

Cu/Sn-58Bi-xEr_2O_3/Cu钎焊接头微观组织和力学性能的研究

研究了不同含量的纳米Er_2O_3颗粒对Sn-58Bi钎料的铺展性能、钎焊接头微观组织和力学性能的影响。结果表明,添加微量的纳米Er_2O_3颗粒细化了Sn-58Bi钎料的微观组织、改善了Sn-58Bi钎料的铺展性能和力学性能。当纳米Er_2O_3颗粒的添加量为0.075%(质量分数)时,Sn-58Bi复合钎料得到了最佳的铺展性能,比Sn-58Bi钎料的铺展系数增大了5.1%;当添加量为0.05%(质量分数)时,Sn-58Bi钎料的组织明显细化且到了最大的抗拉强度89 MPa,比Sn-58Bi共晶钎料的抗拉强度增大了11.5%。     

转喷微注法制备Al_2O_3/7075铝基复合材料的组织及力学性能

通过转喷微注法制备Al_2O_3/7075复合材料,自行设计了转喷微注装置,利用氩气流将增强体颗粒注入熔融金属液,解决了增强体颗粒不易进入金属内部的问题。试验选用不同含量(质量分数分别为0、2%、4%和6%)的亚微米Al_2O_(3p)作为增强相制备Al_2O_3/7075复合材料,并对其组织性能进行观察与测试。结果表明,这种工艺制备成的Al_2O_3/7075复合材料的晶粒组织较不含Al_2O_3的基体合金小,当Al_2O_3的质量分数为4%时,Al_2O_3/7075复合材料的拉伸强度达到最高值182 MPa,较基体铝合金的拉伸强度提高了20%,硬度从HB76提升到HB113,提高了48%;如果进一步增加增强相含量,则复合材料拉伸性能开始出现下降的趋势。     

粉末冶金和微波烧结法制备Al-CNTs-Al_2O_3纳米复合材料的工艺-显微组织-性能之间的关系（英文）

采用粉末冶金和微波烧结工艺制备Al-2CNTs-x Al_2O_3纳米复合材料。研究工艺引起的显微组织特征与材料的物理、力学性能以及超声参数之间的相互关系。研究发现,复合材料的致密化和尺寸变化等物理性能与纳米复合粉体的形貌和粒径密切相关。当Al_2O_3含量为10%(质量分数)、球磨时间大于8 h、颗粒被大量细化时,材料的密度最大。Al_2O_3含量、纳米强化相的分布和晶粒尺寸对材料的力学性能有显著影响,当Al_2O_3含量为10%(质量分数)、Al_2O_3纳米颗粒球磨时间为12 h、碳纳米管均匀分布时,可形成高密度位错和大量晶粒细化,从而获得最佳的硬度和强度。同时,纵波和横波速度及衰减随着Al_2O_3含量和球磨时间的增加而线性增加。超声速度和衰减的变化取决于碳纳米管和Al_2O_3在基体中分布的均匀程度及其较小的颗粒间距。经过较长的球磨时间,Al_2O_3含量越高,碳纳米管和Al_2O_3分布越均匀,超声波的速度和衰减越大。     

C/C-SiC-ZrC复合材料的制备及其力学性能

利用浆料浸渗技术将纳米ZrC粒子引入到CFRP先驱体中,裂解CFRP获得C/C-ZrC多孔体,然后采用液硅熔渗反应工艺制备了C/C-SiC-ZrC复合材料。使用SEM和XRD对材料微观形貌和组织进行了观察与分析。采用三点弯曲和单边缺口梁法(SENB)对C/C-SiC-ZrC复合材料的弯曲强度和断裂韧性分别进行了测试。结果表明:采用浆料浸渗技术可以将纳米ZrC粒子均匀的弥散在C/C-ZrC多孔体中,随着引入ZrC纳米粒子含量的增多,C/C-ZrC多孔体孔隙率增大。经液硅熔渗反应后,获得的C/C-SiC-ZrC复合材料具有不同微观组织结构。力学性能测试发现,当纳米ZrC粒子含量为5%(质量分数)时,复合材料弯曲强度和断裂韧性达到了最大值;当ZrC粒子含量超过5%时,其弯曲强度和断裂韧性有所下降,表明适量纳米ZrC粒子的引入,可以改善C/C-SiC-ZrC复合材料的力学性能。     

基础液对磁流变效应微砂轮微沟槽加工的影响

在磁流变液中添加金刚石磨料配置成抛光用磁流变工作液,对玻璃工件进行微沟槽加工试验。以磁流变工作液的剪切应力以及所加工的微沟槽形貌为分析评价指标,系统研究了基础液的种类(硅油、蓖麻油、液体石蜡、水)、黏度、含量对磁流变微沟槽加工的影响。结果表明,基础液对磁流变效应微砂轮的加工效果具有决定性的影响,以硅油作为基础液具有较好的去除率和加工精度;加工精度随着基础液粘度的增大而提高;基础液的含量有一个最佳值,当硅油的含量为59.3%时,磁流变效应微砂轮的材料去除率达到最大。     

Fe2O3在钛合金干滑动磨损及摩擦层形成中的作用

通过在Ti6Al4V合金滑动界面人工添加Fe_2O_3纳米颗粒及其与TiO_2、MoS_2的混合物,试图促进含Fe_2O_3摩擦层在室温下的快速形成;研究了Fe_2O_3、TiO_2、MoS_2在钛合金滑动过程中的作用,并探讨Fe_2O_3相对含量对钛合金磨损行为及磨损机制的影响。结果表明:干滑动下的Ti6Al4V合金耐磨性较差,磨面添加的TiO_2进一步加速磨损,MoS_2一定程度上降低了磨损但并不显著,而Fe_2O_3完全抑制磨损但增大了摩擦系数。高载下,富TiO_2、MoS_2颗粒并不能形成摩擦层,反而聚集在磨面犁沟或者凹坑处,而富Fe_2O_3则容易形成致密的摩擦层覆盖于磨损表面,这证实了钛合金高温耐磨性的改善是由于Fe_2O_3的出现。混合MoS_2+80%(质量分数)Fe_2O_3形成的摩擦层,兼具MoS_2的润滑性和Fe_2O_3的承载能力,给Ti6Al4V合金带来最佳的摩擦磨损性能。     

磨料对磁流变工作液性能及加工效果的影响

本文研究了磁流变工作液中添加磨料种类、含量、粒度对其性能的影响,以及对磁流变效应微砂轮加工效果的影响。结果表明:添加磨料对磁流变效应的影响程度以氧化铈、碳化硅、金刚石、氧化铝的顺序增大,随着添加磨料含量增加、粒度增大,磁流变效应均被削弱。磁流变效应微砂轮加工微沟槽过程中,添加磨料对微砂轮加工性能的影响受到添加磨料对磁流变效应和磁流变效应微砂轮加工性能正反两方面的影响而出现最优加工效果。当磨料含量为3%时沟槽的宽度、深度和材料去除率都达到最大;当磨料粒度为W3.5时,加工沟槽的宽度最大;当磨料粒度为W7时,加工沟槽的深度和材料去除率最大。     

纳米铁酸锌/丙氨酸改性聚乳酸复合磁性微球的制备和表征(英文)

以改进液相化学法合成铁酸锌纳米磁流体来代替传统的铁氧化物磁粉,同时以D,L型丙交酯与丙氨酸为单体进行本体聚合,得到氨基酸改性聚乳酸,再以改性聚乳酸包封纳米磁流体构建磁性高分子微球。采用X射线衍射、傅立叶红外光谱仪、核磁共振仪、扫描电镜、透射电镜、振动样品磁强计、热重分析仪等对所合成的材料进行表征。结果表明:所制备的材料为尖晶石型的ZnFe2O4纳米晶,粒径为20～45nm,磁饱和强度为32×10-3A.m2;丙氨酸成功接枝到了聚乳酸链上;铁酸锌纳米磁流体/聚乳酸复合微球的分散性较好,粒径为80～300nm,聚乳酸的包覆率为45.5%,磁饱和强度为10.6×10-3A.m2,ZnFe2O4经改性聚乳酸封装后仍然保持较好的磁饱和强度。     

A Constitutive Equation for Magnetorheological Fluid Characterization

A microstructural model of the motion of particle pairs in MR fluids is proposed that accounts for both hydrodynamic and magnetic field forces. A fluid constitutive equation is derived, from the model that allows the prediction of velocity and particle structure fields. The analysis is similar to that of bead-spring models of polymeric liquids with replacement of the elastic connector force by a magnetic force. Results for simple shear flow are presented for the case when the two particles remain in close contact so they are hydrodynamically equivalent to an ellipsoid with an aspect ratio of two and only the component of the magnetic force normal to the connecting vector between the centers of the two particles affects motion. The model predicts oscillatory motion of the particle pairs at low magnetic fields. The fluid reaches a steady state at high magnetic fields. The time required to reach the steady state for a given shear rate reduces significantly as the field increases.     

基于非晶微米颗粒的磁流变液性能(英文)

采用成分为 Fe76Cr2Mo2Sn2P10B2C2Si4的自制非晶颗粒取代传统羰基铁粉作为分散相,制备非晶型磁流变液,以提高磁流变液的性能。对比非晶颗粒和羰基铁粉的软磁性能和密度,发现非晶颗粒具有较低的密度,在低磁场中具有较高的磁化强度和磁导率。测试颗粒体积含量为 20%的非晶磁流变液和羰基铁粉磁流变液的性能,可知非晶磁流变液在227 kA/m磁场强度下其饱和剪切屈服强度达41 kPa,抗沉降率为80%。在低磁场中(0~200 kA/m)基于非晶颗粒的磁流变液具有比羰基铁粉磁流变液更优的磁流变性能和沉降稳定性。     

Research on sheet-metal flexible-die forming using a magnetorheological fluid

Related studies showed that viscosity has a great effect on the formability of sheet metal in viscous pressure forming. However, the viscosity of viscous medium keeps constant in VPF. In this paper, a new flexible-die forming method for sheet metal using magnetorheological (MR) fluids, magnetorheological pressure forming (MRPF), is proposed, which enables the viscosity of flexible-die medium adjustable by changing the magnetic fields during the forming process. Squeezing tests of MR fluid show that its rheological behavior can be changed greatly under different magnetic fields. Magnetorheological pressure bulging tests of Al1060 sheet are conducted on the self-designed experimental apparatus. Experimental results show that MR fluids can be used effectively as a flexible-die medium to form the parts and its rheological behavior can be adjusted during bulging process. Variation of MR fluid's rheological behavior can lead to different forming pressure load paths and have an effect on sheet metal formability. For the same piston stroke of 8.0 mm, when the magnetic flux density is 0.180 T and 0.318 T, average dome height of bulging specimen is 8.71 mm and 10.61 mm, respectively. The value increases significantly by 21.8%. At the same time, the maximum thickness strain increases from −9.2% to −23.0%.     

Carbon nanotube synthesis using magnetic fluids on various substrates

A new carbon nanotube synthesis method using a magnetic fluid is developed. The catalyst particles can be formed by simple spin coating of the magnetic fluid of Fe₃O₄ nano particles mixed with polyvinyl alcohol on substrates and subsequent heat treatment. A quantitative analysis of the catalyst particles distribution on Si substrate is carried out. The mixing of the magnetic fluid in polyvinyl alcohol gives viscosity to the solution, secures uniform particle distribution without agglomeration, and controls the catalyst particle density on the substrate. The distribution of the catalyst particles is mainly controlled by the NH₄OH concentration in the magnetic fluid solutions. Carbon nanotubes grown on various substrates of Si, alumina, and various metal plates revealed different morphologies due to the difference in the wetting of the catalyst particles on the substrate in the various particle-substrate systems.     

Research on magnetic testing method of stress distribution

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Y对TiAl合金显微组织及性能的影响

系统地研究了Ti-47Al-xY系[x（摩尔分数／％）分别为0、0．1、0．3、0．5、0．7、1．0]合金的显微组织及室温力学性能。结果发现：随着Y含量的增加，合金由柱状晶转变为等轴晶（x≥0．3），而且合金的晶粒尺寸和层片间距随着Y含量的增加而降低；当Y含量高于0．1％时，晶内弥散分布细小YAl2相颗粒的同时，YAl2相开始在晶界处偏析，且随着Y含量的增加，晶界偏析越来越严重；当Y含量达到1．0％时，晶界处YAl2相闭合成网络状。拉伸测试表明，Y含量为0．3％～0．5％的Ti-47Al合金有较高的强度和塑性。分析得知，YAl2相的尺寸及分布对性能起着重要的作用。一方面，组织的细化和晶内细小的YAl2相有利于性能的改善，另一方面，晶界处富集的大尺寸YAl2相显著恶化TiAl合金的性能，特别是在Y含量高于0．5％的TiAl合金中。     

Formation of structure and magnetic properties for YuNDKT alloys by thermomagnetic treatment

Conclusions The extreme dependence of magnetic properties on ITMT temperature is explained by the very effective action of a magnetic field on decomposition in a three-phase region, and at an ITMT temperature when '-phase precipitating from a solid solution is ferromagnetic and has a high I_s value there is a considerable effect on magnetostatic energy in the creation of '-phase particle anisotropy.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 48–51, March, 1981.     

磁场对纳米MnZn铁氧体前驱体形貌的影响

采用SEM，XRD，TEM，TG等手段研究了磁场对共沉淀法制备纳米MnZn铁氧体前驱体形貌及晶态结构的影响。结果表明，随着磁感应强度增大并达到某一临界值时，纳米颗粒形貌由球状向链状转变，继续增加磁感应强度将获得针状、棒状或纤维状的颗粒，10T强磁场下获得棒状颗粒呈现单晶结构。热重分析表明10T磁场下获得的纳米颗粒由于单维尺寸增加而导致活性降低。根据晶体生长理论，讨论了磁场影响纳米颗粒形核和长大过程的机理。     

Erosion-Corrosion of Carbon Steel Pipes in Oil Sands Slurry Studied by Weight-Loss Testing and CFD Simulation

Weight-loss testing and computational fluid dynamic simulation were combined to investigate the essential roles of fluid mechanics and the sand impact in erosion-corrosion (E-C) of an X65 pipe steel in oil sands slurry. Results demonstrated that the steel E-C is resulted from the synergistic effect of the hydrodynamic shear stress and mechanical impact stress exerted on the steel surface. At low impact angles, such as 30°, the effect of shear stress is dominant. The particle impact stress becomes dominant when the impact angle increases to a high value, such as 90°. It is demonstrated that the maximum of E-C of the steel occurs at approximately 45° of the slurry impingement.