改善磁流体稳定性的研究

本研究从改进磁流体的制备方法入手,很好解决了磁流体中Ｆｅ３Ｏ４粒子的聚闭问题,并利用表面活性剂对Ｆｅ３Ｏ４粒子进行单独或复合包覆处理制备出了高稳定性的油基,水基及聚醚基磁流体。     

纳米Fe3O4磁流体的制备及其影响因素研究

通过液相共沉淀法制备了Fe3O4水基磁流体,选择油酸作为表面活性剂,获得油酸包覆的Fe3O4纳米粉,将其分散于有机溶剂中,制备了纳米Fe3O4有机基磁流体。采用X-Ray衍射分析仪和粒径分布仪分析了生成物的结构和粒径分布;用FT-IR和高分辨透射电镜表征了生成物的成分和形貌。结果表明:制得的立方晶体纳米Fe3O4平均粒径为16.3 nm,FT-IR图谱中1 593、1 736和2 926 cm-1等处的吸收峰很强烈,这充分说明该纳米粒子被油酸很好地包覆;选择油酸作为表面活性剂,起到表面改性和萃取出纳米粒子的作用;制得的油酸包覆纳米Fe3O4粒子能够稳定分散于有机溶剂中。     

阴离子表面活性剂分散制备水基磁流体

用化学共沉淀法制备了纳米级Fe2O4磁性粒子，用阴离子表面活性剂十二烷基苯磺酸钠（SDBS）对所制备的磁性粒子进行表面处理和溶液中分散处理制得稳定分散的Fe3O4磁流体。实验研究球磨时间、表面活性的加入量、溶液的pH值以及磁流体的固含量等诸多因素对纳米Fe3O4包覆结构和磁流体稳定性的影响，并分析了这些因素的影响机制。结果表明，纳米磁流体的稳定性与球磨时间和pH值之间存在一定的相关性，而磁性粒子固含量和SDBS用量对其稳定性起主导作用，并且在一定固含量下，SDBS用量对纳米粒子包覆结构起着决定性作用。制得的样品经过HRTEM和XPS等手段的表征，表明SDBS以化学和物理吸附在纳米Fe3O4粒子表面形成了Fe-O-S化学键，并以多层吸附的形式通过静电作用和空间位阻作用有效防止纳米粒子团聚，制得了稳定分散的纳米Fe3O4磁流体。     

全氟聚醚油基磁性液体的制备及耐腐蚀性能研究

采用电弧放电法,在50%CH4+20%H2+30%Ar的混合气氛中制备了C包覆Ni纳米粒子.以C包覆的Ni纳米粒子为磁性粒子、油酸为表面活性剂、全氟聚醚油和少量硅脂的混合液为基液制备了耐腐蚀、高粘度全氟聚醚油基磁性液体.制备的全氟聚醚油基磁性液体具有较好的耐腐蚀性能,磁性液体在25 ℃粘度为9～25 Pa·s,在85 ℃粘度为2～16 Pa·s,室温下饱和磁化强度为5.19～17.83 A·m2/kg.     

超声波技术在Fe3O4磁粒子制备中的应用

为制备磁粒子足够细小、均匀且稳定的磁性液体,将超声波技术引入Fe3O4磁粒子制备过程中,研究了化学共沉淀法制备Fe3O4磁粒子的不同阶段超声波功率对颗粒大小及磁性能的影响.结果表明:在共沉淀阶段引入超声波功率(40W)制备的Fe3O4磁粒子不易团聚,均匀细小;在包覆阶段引入超声波功率(40W)使表面活性剂在Fe3O4磁粒子表面形成稳定包覆层;在最佳条件下所制备Fe3O4磁粒子的平均粒径为10nm左右.     

磁流体制备过程对其稳定性的影响

在磁流体密封中,磁流体稳定性(磁流体中磁性粒子抗聚沉及磁流体抗被密封介质破坏的能力)的高低对磁流体密封承压能力、密封寿命等性能有明显的影响.针对影响磁流体稳定性的一些重要因素诸如磁流体中磁性粒子大小、表面活性剂与磁流体基液的相溶性以及磁流体基液的挥发性和与密封液体的乳化性等进行的研究已很多.但在上述问题已很好解决的情况下,磁流体的稳定性在很大程度上还取决于磁流体制备过程中的许多具体环节,本文就磁流体制备过程中几个对磁流体稳定性具有明显影响并带有普遍意义的问题进行分析和讨论.     

170℃高温用Fe3O4磁性液体的制备及其性能

采用化学共沉淀法制备了油酸包覆Fe3O4磁性颗粒,经过非离子表面活性剂的二次包覆后,将其均匀分散于具有优良耐高温性能的PAO合成油中,制成了合成油基Fe3O4磁性液体,将该磁性液体在大气环境中进行170℃长时间加热处理,对其密度、粘度、饱和磁化强度及挥发速率进行了测试,并用透射电镜进行形貌观察.结果表明:磁性颗粒呈球形,粒径在10nm左右;合成油基Fe3O4磁性液体随加热时间的延长,密度缓慢增加并逐渐趋于平缓,粘度快速增加,饱和磁化强度变幅仅为0.4%,挥发速率逐渐下降.     

微米 Ｃｏ 粒子对磁流体密封水性能的影响

为提高耐蚀水泵磁流体旋转密封的承压值,在Fe3O4油基磁流体中添加适量强磁性Co微米粒子,并研究磁流体中Co粒子体积分数对磁流体密封水性能和磁流体密封装置温升的影响。研究结果表明,随着磁流体中Co粒子体积分数增加,因Co粒子在密封间隙内密封极齿表面聚积形成的“柔性磁极”,导致密封间隙减小,磁流体密封承压值明显增大;随着磁流体中Co粒子体积分数的增加,磁流体密封的功耗将增大,磁流体密封装置的温度升高;磁流体密封装置的温升缘于密封间隙内Co粒子之间和Co粒子与旋转轴之间内摩擦所产生的摩擦热。     

受控部分还原法制备Fe3O4纳米粒子及其性能研究

采用受控部分还原法(CPRM)制备Fe3O4纳米粒子。由于反应乳液中的大分子表面活性剂限制了成核和核的生长过程,使得纳米粒子的粒径分布很好,且系统中纳米粒子的含量较微乳液法有明显提高。改变反应物浓度可使反应系统中的Fe2 稍过量,故采用CPRM时,反应系统无须惰性气体保护,合成的Fe3O4纳米粒子经TEM、X-ray、动态光散射和振动磁强计等进行表征,结果表明Fe3O4磁性粒子的平均粒径为16 nm,且粒径分布窄,具有极好的超顺磁性。CPRM法使得在一般条件下合成高质量的纳米粒子和Fe3O4磁流体成为可能。     

琼脂铁氧体水基磁流体的制备

采用化学共沉淀法,选择食用琼脂为稳定剂,NaOH作沉淀剂在水溶液中共沉淀FeCl2和FeCl3得到Fe3O4磁粒子,由此制备具有高度生物亲和性的琼脂水基磁流体。用古埃磁天平法对影响磁流体磁性和稳定性的主要因素进行了研究。结果表明:在FeCl2.7H2O和FeCl3.9H2O的数量比为1∶1.7,pH值为11,反应温度50℃,时间30 min,琼脂和Fe3O4质量比为1∶1.6的条件下,可得到磁粒子粒径约12 nm,饱和磁化强度16 mT,对空气不敏感的高稳定性水基磁流体。该磁流体可用作X射线造影剂。     

Cationic surfactants and other factors that affect enzymatic activities and transport

Surfactants influence functions of proteins in cell signalling. Because molecular mechanisms of surfactants are poorly understood, the cationic surfactant effect on three metabolically important enzymes--L-glutamate dehydrogenase, L-lactate dehydrogenase, and L-malate dehydrogenase--were investigated at a physiologically relevant pH range (6.5-7.4). How a cationic, a non-ionic, and an anionic surfactant could differentially influence these enzymes, and how these surfactants could influence the interfacial mass transport of these enzymes across a polycarbonate membrane in a separation cell were also investigated. Provided the charge density was the same, cationic surfactants affected enzymatic activities similarly, regardless of their molecular masses. Hence, a cationic surfactant behaved similarly to a hydrophilic anionic surfactant; however, the cationic surfactant also enhanced enzymatic activity at pH 6.5 and a moderately high concentration (150 ppm). The hydrophilic surfactant enhanced enzymatic activity and the hydrophobic surfactant depressed enzymatic activity. Addition of 0.1 ppm of the hydrophilic anionic surfactant decreased the amount of enzyme permeation through the membrane, but 0.1 ppm of the non-ionic surfactant had no effect, whereas 0.1 ppm of the hydrophobic surfactant increased enzyme permeation. These results have physiological and signalling implications in nanobiotechnology.     

Rheological measurement of redispersibility and settling to analyze the effect of surfactants on MR particles

The smart materials such as magnetorheological (MR) fluids are gaining wide popularity due to their superior control abilities. These abilities are strongly dependent about the stability of the MR fluid which needs to be sustained for the useful life of the system. In the present research work, experimental studies focusing on aggregation, redispersibility and settling of carbonyl iron-based MR fluids have been conducted to analyze the effect of surfactants on controlling settling and redispersibility. The experimental investigations were conducted by preparation of nine MR fluids samples using three types of surfactants (oleic acid, citric acid and tetramethylammonium hydroxide) and three different carrier fluids (water, silicone oil and DTE light mineral oil). The samples were prepared by mixing on rotational machine for 24 h and the homogeneity of the samples was visually inspected. The shear stress and viscosity variation of the homogenous mixture with respect to shear rate was obtained using magnetic rheometer. A new method is presented for measuring the settling of homogenous mixtures by measurement of the change in the magnetic field strength due to settlement of particles. The effect of surfactant type and its quantity on the stability of MR fluid is explored and the results of settling and redispersibility have been presented.     

柔性石墨密封垫片的研究现状及发展趋势

主要介绍了柔性石墨的性能和制备工艺,制备工艺主要分为化学氧化法、电化学法、微波法、爆炸法和气相挥发法;总结了石墨与金属组成的复合垫片的主要结构形式,包括金属石墨缠绕垫片、石墨波齿复合垫片和金属与金属接触型垫片;还分析了石墨密封机理的研究现状,总结了现有的垫片泄露模型,并对石墨密封在核电等领域的应用前景和发展趋势进行了展望,指出未来石墨垫片发展的方向主要集中于石墨提纯、新密封结构开发,而有限元分析作为辅助的研究方法将成为热点课题之一。     

超声场中湿法制备纳米粉末的原理和方法

介绍了超声波在湿法制备纳米粉末中的应用机理，探讨了超声波对纳米颗粒的生成和团聚的影响，综述了超声场下湿法制备纳米粉末常用的方法，同时对超声在纳米材料制备上的应用作了展望。     

表面活性剂对电子束制备纳米镍粉的影响

在水溶液中,于常温常压下分别使用聚乙烯醇（PVA）和十二烷基三甲基溴化胺（DTAB）为表面活性剂,用电子束辐照方法制备了纳米镍粉;用X射线衍射仪、透射电镜、紫外可见分光光度计和红外光谱对所得产物进行了表征。结果表明：以PVA作表面活性剂得到相对纯的纳米镍粉,平均粒径约为12．6nm;而以DTAB为表面活性剂得到镍和三氧化二镍的混合物,平均粒径约为25nm;采用PVA为表面活性剂在产品的纯度和粒度上都优于DTAB。     

高分辨快原子轰击质谱法研究

本文介绍高分辩快原子轰击质谱技术（ＨＲＦＡＢＭＳ）。同时给出了内标物质和测量条件，讨论了数据处理方法。     

喷射打印和化学沉积成形微细电路中微滴可控喷射研究

针对智能纺织品中微细线路制备工艺复杂、成本高、柔性差等问题,提出了喷射打印与化学沉积技术相结合制作微细线路的方法。利用构建的气动式微滴喷射系统,以100μm的喷嘴对抗坏血酸和硝酸银溶液进行了可控稳定喷射及沉积成形试验。试验获得了两溶液可控稳定喷射的工艺参数,且微滴在基板上沉积的点阵均匀、成形线宽基本一致,成形银线具有一定导电性。     

EFFECT OF SURFACTANTS ON Ni-TiN NANOCOMPOSITE COATINGS PREPARED BY ULTRASONIC ELECTRODEPOSITION

Ni-TiN nanocomposite coatings were prepared by ultrasonic electrodeposition, and the effects of the surfactants on the coatings were investigated and the microstructure and micro rigidity of the coatings were characterized. Samples were also submitted to corrosion tests in 3% NaCl solution. The results showed that the surfactants had great effects on Ni-TiN nanocomposite coatings. The composite coatings prepared by ultrasonic electrodeposition with the surfactants were better than that of the coatings prepared without surfactants. The favorable properties of Ni-TiN nanocomposite coatings were prepared with the mixing of the non-ion and positive ion surfactants. The concentration of the mixing was 80 mg/L, and the ratio of the non-ion and positive ion surfactants was 1: 2.     

硅油基纳米Fe_3O_4磁性液体的制备

采用化学共沉淀法,成功制备了纳米Fe3O4微粒,主要研究了Fe2+与Fe3+不同物质的量比对Fe3O4微粒、粒径及磁化强度的影响,采用不同表面活性剂制备了硅油基纳米Fe3O4磁性液体。结果表明:Fe2+与Fe3+物质的量比对Fe3O4微粒性能影响显著,对微粒尺寸影响不大,均为纳米级,当Fe2+与Fe3+物质的量比为0.6时,其饱和磁化强度达到最大,为52.1 A.m2.kg-1;在无水乙醇中,聚乙烯吡咯烷酮(PVP)的分散效果虽优于油酸,但与硅油相溶性差、增粘作用明显的缺点限制了PVP的使用;而油酸由于亲油性好,更适合作为制备硅油基Fe3O4磁性液体的表面活性剂。