纳米流体导热系数影响因素分析

为了全面分析纳米流体的稳定性及导热系数影响因素,采用两步法配置了以去离子水和乙二醇为基液的氧化铝纳米流体,并添加了不同种类的分散剂.利用紫外可见分光光度计对纳米流体吸光度值进行测试,并基于Hot Disk热物性分析仪测试其导热系数.结果表明：吸光度法可有效评价纳米流体稳定性,但需要考虑分散剂对基液吸光度值的影响.超声波振荡可破坏粒子团聚,且当超声时间为1h时纳米流体稳定性最佳.分散剂、粒子体积分数、温度、基液等因素均会影响纳米流体的导热性能.当温度为50益时,添加质量分数0.2%的PVP分散剂,体积分数为0.5%的氧化铝-水纳米流体导热系数提高约20%.纳米流体可有效提供工质导热系数,提升系统散热性能.     

基于均匀设计法的碳纳米管纳米流体稳定性

研究碳纳米管质量分数、分散剂质量分数、pH值和超声振荡时间对碳纳米管纳米流体稳定性的交互影响和定量影响.配置12个碳纳米管纳米流体样品,测定各样品的Zeta电位值.样品的4因素取值通过均匀设计法确定,稳定性用Zeta电位表征.采用二次多项式逐步回归法处理数据,建立碳纳米管纳米流体稳定性与4个因素之间的回归模型.由模型分析可知,该4因素对碳纳米管纳米流体稳定性的影响是相互约束的.当超声振荡时间>3.411 h时,碳纳米管纳米流体的稳定性与碳纳米管质量分数正相关;当超声振荡时间<3.411 h时,碳纳米管纳米流体的稳定性与碳纳米管质量分数负相关.     

纳米流体热导率试验

采用自行设计的瞬态热线装置，测试了不同种类纳米流体的热导率，分析研究了粒子体积分数、粒径、温度、分散剂等因素对纳米流体热导率的影响.结果表明，低体积分数纳米流体的热导率比基液有较大幅度的提高，最大可达40%左右；纳米流体的热导率随着粒径的增大而减小，随着粒子体积分数的增大、温度的升高而增加，且分散效果越好的纳米流体热导率越大.试验热导率值大于常规固液混合物的H-C模型预测值，表明纳米流体具有不同于一般固液混合物的独特的优良导热特性.     

真空电弧纳米流体颗粒沉降及悬浮稳定性探讨

具有高度悬浮稳定性的纳米流体在工业应用上,才可确保纳米化的独特性与应用价值。本文旨在以自行发展的真空电弧纳米流体合成系统所制备出的纳米流体,探讨纳米流体中悬浮颗粒的沉降及悬浮稳定性。文中将分析此系统的主要制程参数对所合成Cu及Ti纳米流体悬浮稳定性的影响,如峰质电流、崩溃电压及放电幅等。针对所制备出的纳米流体检测其平均粒径、粒径分布、形貌特性、pH值、接口电位、沉降性及材料结构等特征,同时观察及量测静置时间与上述纳米流体特性变化的关连性。经由长时间检测纳米流体中颗粒的沉降及悬浮性变化,以验证此真空电弧纳米流体合成系统在所不同的制程参数条件下,所产出纳米流体的悬浮稳定性。     

羟基碳纳米管/乙二醇纳米流体性能研究

以光透过率作为纳米流体稳定性指标,同时采用L9(34)正交试验设计,分析超声振荡时间、分散剂种类和浓度等3个因素对羟基碳纳米管/乙二醇稳定性的影响,并对其黏度以及导热系数进行了测量。结果表明:3个因素对纳米流体稳定性的影响程度分别为:分散剂超声振动时间浓度。在纳米流体的质量浓度为0.07%、加入分散剂聚乙烯吡咯烷酮(PVP)和振荡时间为90min的条件下,得到的纳米流体稳定性最好。与基液相比,纳米流体的导热系数可提高1.34%,在-5～20℃时黏度随着温度的升高而显著降低。     

水基ZnO纳米流体黏度及流变特性研究

实验通过“两步法”制备了水基氧化锌纳米流体,分析Zn O质量分数、温度、剪切速率、剪切应力对纳米流体黏度和流变特性的影响规律。实验数据得出,温度不变时,所制备流体黏度随浓度增加而增大。Zn O纳米颗粒的质量分数为0.4%时,纳米流体的黏度最小;质量分数为2.292%时,黏度最大。温度由15℃上升到55℃时,所制备流体黏度表现为非线性下降。在15℃时,纳米流体黏度最大;在55℃时,纳米流体黏度最小。在剪切率小于10 s^-1时,随着剪切率的增大,纳米流体的黏度均逐渐降低,超过10 s^-1后黏度趋于稳定。当温度为55℃,剪切率大于10 s^-1时,质量分数为0.4%的ZnO纳米流体具有最低的黏度特性。     

Sn/C纳米复合材料的合成及其电化学嵌放锂性能

用SnCl4和葡萄糖的水热反应合成SnO₂/碳质复合材料,然后在氮气气氛中热处理使SnO₂被碳热还原为Sn纳米粒子,制备得到Sn/C纳米复合材料.用X-射线衍射(XRD), 透射电镜(TEM)和X-射线电子散射能谱(EDX)对样品进行表征.结果显示Sn纳米粒子具有球形的形貌,并均匀地分散在无定形的碳材料中.对于Sn质量分数58.5%和32.3％的Sn/C复合材料,Sn纳米粒子的平均粒径分别为51和20 nm.电化学测试结果显示,Sn/C复合材料具有高的电化学贮锂可逆容量和良好的循环稳定性.讨论了Sn/C纳米复合材料的形成机理及其循环稳定性能改善的原因.     

纳米A12O3颗粒的制备及其悬浮液的分散稳定

以异丙醇铝为原料，甲苯为溶剂，氨水为pH值调节剂，采用溶胶-凝胶法制备了含有α和θ2种晶型的高纯纳米A12O3颗粒．产物经XRD，TEM以及BET测定和杂质含量分析，研究了不同pH值、分散剂种类及其用量对A12O3悬浮液分散稳定性的影响．研究结果表明：产物的主晶相是θ，次晶相是α；A12O3颗粒粒径为10～20nm，粒子呈球形或类球形，粒子尺寸分布较均匀，比表面积为82．31m^2／g；纯度≥99．95％；配制稳定的A12O3 CMP浆料的合适工艺条件为：在A12O3固含量为6％的浆料中，加入质量分数为10％的H2O2作为氧化剂，体积分数为0．99％的异丙醇胺作为分散剂，同时将浆料的pH值控制在3～4，能得到长时间不沉降的稳定浆料．     

氧化锆/氧化铝复合陶瓷悬浮体的制备及流变性能

选用Al2O3、ZrO2为粉体原料,在不同介质中测定了粉体的Zeta电位和粒度分布;研究了各种固含量条件下分散剂加入量对悬浮体流变性的影响.结果表明:在pH=10-11附近、分散剂的加入量为0.9%(质量百分数,下同)时复合陶瓷悬浮体的表观粘度呈现最低值;在优选实验条件下,固含量为85%的悬浮体表观粘度随剪切速率的增大而降低,带有明显的"剪切变稀"现象,呈现假塑性流体的特征.采用固含量85%的悬浮体,制备出氧化锆/氧化铝复合泡沫陶瓷.     

氧化铝纳米流体在车用热交换器中的试验研究

研究纳米流体在车用热交换器中的强化传热效果,测试不同纳米粒子体积分数的氧化铝纳米流体在板翅式机油冷却器中的传热和流动特性,并与水、防冻液（乙二醇）及纳米流体基础液体进行对比.试验结果表明,在同一热交换器中,纳米流体的传热系数明显高于其他3种液体.当冷、热侧介质温度为90和120 ℃时,纳米粒子体积分数为5%的纳米流体的传热系数分别比水、乙二醇和基础液体提高6.52%、18.88%和24.62%;当冷、热侧介质温度为120和135 ℃时,体积分数为5%的纳米流体的传热系数比体积分数为1%的纳米流体提高104.72%.在试验条件下,热交换器的换热量随纳米粒子体积分数的增大而增大,但流动阻力并未明显增加,初步证明了纳米流体应用于车用热交换器的可行性.     

Influence of TAC on Dispersion of Aqueous Nano Alumina Suspension

The stability of aqueous nano alumina powder suspensions with and without dispersant tri-ammonium citrate (TAC) was investigated by measuring zeta potential at different pH values. The isoelectric point (IEP) of alumina powder shifts towards more acidic pH range by adding TAC dispersant. The results illustrate that adsorption of TAC on alumina powder surface existed in the aqueous suspension, which leads to a high stability of the suspension.     

Experimental investigation on viscosity of Cu-H2O nanofluids

A procedure for preparing a nanofluid that a solid-liquid composite material consists of solid nanoparticles with sizes typically of 1–100 nm suspended in liquid was proposed. By means of the procedure, Cu-H₂O nanofluids with and without dispersant were prepared, whose sediment photographs and particle size distribution were given to illustrate the stability and evenness of suspension with dispersant. The viscosity of Cu-H₂O nanofluid was measured using capillary viscometers. The mass fractions(w) of copper nanoparticles in the experiment varied between 0.04% and 0.16% with the temperature range of 30–70 °C. The experimental results show that the temperature and SDBS concentration are the major factors affecting the viscosity of the nano-copper suspensions, while the effect of the mass fraction of Cu on the viscosity is not as obvious as that of the temperature and SDBS dispersant for the mass fraction chosen in the experiment. The apparent viscosity of the copper nano-suspensions decreases with the temperature increase, and increases slightly with the increase of the mass fraction of SDBS dispersant, and almost keeps invariability with increasing the mass fraction of Cu. The influence of SDBS concentration on the viscosity of nano-suspension was relatively large comparing with that of the nanoparticle concentration. Funded by Guangdong Provincial Natural Science Foundation (No. 04105950), Specialized Research Fund for the Doctoral Program of Higher Education (No. 20050561017), and Program for New Century Excellent Talents in University (No. NCET-04-0826)     

改性超细Al（OH）3水悬浮液的稳定性

选用六偏磷酸钠对超细Al（OH）3粉体进行湿法改性,利用红外光谱评价其改性效果.通过沉降量、沉降速率及透光率的测定,研究了分散剂、pH值、温度和搅拌速率对Al（OH）3水悬浮液体系的稳定性影响.结果表明,六偏磷酸钠湿法改性过的Al（OH）3粉体亲水性增强,在288 K,pH值为11的条件下,控制搅拌速率为600 r/min,加入0.2%的Tween-20可制得分散性和稳定性俱佳的改性Al（OH）3水悬浮液体系.     

质子化壳聚糖/磁性复合材料对含磷污水中磷的吸附特性

采用反相悬浮交联法制备出质子化壳聚糖/Fe_3O_4磁性复合吸附剂,研究了其对模拟含磷污水中磷的吸附特性。首先,考察了吸附时间对所有复合吸附剂的吸附特性的影响;选取其中吸附特性较好的E2吸附剂,考察了其吸附特性与含磷溶液初始浓度的关系;然后,进行了与溶液pH值、吸附剂类别、投加量、吸附时间、溶液初始浓度相关的正交试验。研究结果表明,原水pH值对吸附过程具有最明显的影响,最佳pH值为6,吸附剂和投加量的影响次之,影响最弱的是初始浓度和吸附时间。质子化磁性壳聚糖对磷的去除率最高达80%左右。吸附动力学研究结果表明,吸附过程能很好地符合Lagergren准二级动力学模型,由此证明吸附过程为化学吸附。     

硅溶胶制备纳米二氧化硅的工艺研究

以碱性硅溶胶和无机酸为原料,水和甲醇为反应介质,加入适宜的分散剂,反应体系在适宜的反应温度和pH值下反应一定时间,经过真空脱水干燥和超细筛网筛分得到稳定的纳米二氧化硅粉体。该方法的最佳工艺条件:反应温度50℃,pH=7.5~8.0,反应体系硅溶胶质量分数10%~20%,反应时间45 min。实验结果表明,制得纳米SiO2粉体的粒径为20~40 nm,比表面积大,分散性好,纯度在99%以上。该方法工艺简单,实用性强,适宜工业化生产。     

Viscosity of kaolin slurries: Effects of dispersant and urea-intercalation

Good fluidity (low viscosity) of highly concentrated kaolin is highly needed in paper-coating industry. We put forward an effective route to improve the viscosity concentration of Beihai kaolin slurries. The effects of various factors such as solid content, pH, dispersant content, and urea-intercalation on the viscosity of kaolin slurries were investigated. The results revealed that the viscosity of kaolin slurries significantly decreased with decreasing solid content or with increasing pH and dispersant content. It was worth noting that urea-intercalation was proven to be an efficient method for promoting the dispersion of highly concentrated kaolin as compared with adding dispersant. The intercalation ratio of urea-intercalated kaolin was increased from 17.36% with 2% of urea addition to 81.30% with 6% of urea addition. Meanwhile, the viscosity concentration of raw kaolin slurry was improved from 65.0% to 70.13% after the intercalation of urea with 6% addition, which was attributed to finer particle size, increased pH value and more negative charges of urea-intercalated kaolin. Therefore, the route is effective to improve the dispersion of highly concentrated kaolin for paper-coating.     

Preparation of SiO_2 Nanoparticles by Silicon and Their Dispersion Stability

1Introduction Nanoparticleshavesomespecialpropertiesinopti cal,electric,thermal,andmagneticaspects[1].AfterRoyandKormarnenifirstputforwardtheconceptofnano recombination[2]in1984,therecombinationofinorganicnanoparticlesandorganicpolymerhasbeenanactivere se…     

碳纳米管的表面修饰及分散机理研究

为了探讨多壁碳纳米管(MWCNTs)在水性体系中的分散性及分散机理,以阿拉伯胶(GA)为分散剂(SAA),采用SAA超声处理法对MWCNTs进行表面修饰,制备了分散性能良好的MWCNTs悬浮液.采用紫外分光光谱吸光度法(UV-vis)定量分析及TEM测试表征了GA对MWCNTs分散性能的影响,结果表明:当GA质量浓度为0.45g/L时,悬浮液中MWCNTs质量浓度达到最大值,为初始质量浓度的90.67%,且悬浮液相当稳定,静置80h,MWCNTs质量浓度仅降低11.45%.通过测定等温吸附曲线对GA的吸附分散机理进行了分析和讨论,结果表明:GA在MWCNTs表面为典型的"SL"型两阶段吸附,当GA质量浓度为0.45g/L时,在MWCNTs表面达到吸附饱和状态.GA能够通过其分子长链的包覆作用改善MWCNTs的亲水性和分散性.     

Study on the two and three-parameter working stability regions of 3Y-TZP suspension

We determined the variation tendency of viscosity (η) at various solids load- ing (α) for 3Y-TZP suspension as a function of dispersant concentration (Cw) using vis- cosity measurement, measured the diameter of particles as a function of Cw in very dilute suspension using light scattering method, and obtained the surface features of the sedi- ment of suspension with different Cw using SEM. We also discussed the influence of the microstructure of adsorbed polymer layers on particles and their interactions in the dis- persing medium on the stability of suspension. Then two different stable states and two different unstable states for 3Y-TZP suspension were given. Accordingly, the (Cw, η), (Cw, α), and (α, η) two-parameter, and (Cw, α, η) three-parameter stability maps were con- structed. Based on the DLVO theory calculations, the dispersant concentration, particle distance (r), and interparticle potential energy (VT) maps with various solids loading for 3Y-TZP aqueous suspension were also constructed. In (Cw, r) two-parameter coordinate system, the stable motion region map for particles was established. The Cw, α, and VT,max (the highest potential energy) surface of the potential barrier map was obtained through calculation and simulation on the basis of the surfaces of Cw, r, VT maps introduced above. The (Cw, α) two-parameter stability map was then obtained from the Cw, α, VT,max map. The results showed that this theoretical map can qualitatively prove the experimentally obtained results—the existence of different dispersed states of particles in suspension system and the variation tendency of suspension stability with changing each parame- ter—were reasonable.