通过高剪切粘度建立碳分过程中纳米ATH的附聚动力学模型

碳分制备纳米氢氧化铝(ATH)的过程中,悬浮液粘度随ATH固含量的增加和粒度的减小而显著增大,悬浮液最终成为时变性非牛顿流体.离子浓度对悬浮液高剪切粘度的影响很小.在传统悬浮液流变模型的基础上建立了碳分过程中纳米ATH悬浮液流变模型,模型分析表明碳分过程的流变曲线接近U形,在ATH固含量达到一定程度后急剧升高.由于连续相性质对悬浮液高剪切粘度影响很小,高剪切粘度适宜建立碳分条件下的附聚动力学模型,模型分析表明附聚与过饱和度、温度和粒度等相关,附聚动力学曲线接近S形,当悬浮液ATH固含量增加和粒度减小时,附聚的倾向明显增大,模型分析与实际情况和文献相符.     

电化学和sol-gel法结合制备Cu-SiO2薄膜——不同pH值CuSO4硅溶胶中Cu的电化学行为

研究金属或半导体在溶胶中的电化学行为对电化学和溶胶-凝胶(sol-gel)法结合制备掺杂金属和半导体的复合凝胶薄膜有极大指导意义。用循环伏安(CV)和计时安培(CA)法研究了电化学和sol-gel法结合制备Cu-SiO2凝胶薄膜时不同pH值CuSO4硅溶胶中Cu在玻碳电极上的电沉积和电结晶行为。结果表明:在pH=1.0~3.0的CuSO4硅溶胶中,Cu2+的扩散系数在pH=2.0时最小,pH=1.0时较pH=3.0时大,这也是造成硅溶胶中pH=2.0时还原最难,pH=3.0时次之,pH=1.0时最易的原因;Cu在硅溶胶中的电沉积为Langmuir型吸附-三维瞬时成核机理;硅溶液中Cu2+的传递系数均大于0.9,存在吸附层;Cu2+在吸附过程的总放电量Qads随pH值增大而增大;Cu的成核数密度都随电位增大而增大,随pH值增大而减小,故pH值在1.0~3.0内越大越不利于制备Cu-SiO2薄膜。     

PVA/P(AA-AM)复合水凝胶的制备及性能

采用水溶液聚合方法合成了不同组成的丙烯酸-丙烯酰胺共聚物(P(AA-AM))。将聚乙烯醇(PVA)与所合成的P(AA-AM)共混,以戊二醛为交联剂,制备出了不同结构的PVA/P(AA-AM)复合水凝胶。采用扫描电镜观察了凝胶形貌,研究了复合水凝胶的结构与性能关系。结果表明,复合水凝胶溶胀性能与所用交联剂加量有关,复合水凝胶的溶胀度随着交联剂加量增加先增大后减小,在交联剂加量为0.5%时水凝胶溶胀度达到最大值。复合凝胶中的聚合物组成对溶胀度影响显著,随着P(AA-AM)含量提高,水凝胶的溶胀度逐渐增大。适当结构的复合水凝胶具有pH敏感性,敏感程度随着凝胶中P(AA-AM)含量的增加而增强。     

SiO_2气凝胶的合成与孔结构表征

采用溶胶-凝胶法结合超临界流体干燥技术制备了SiO2气凝胶,系统地考察了醇硅比、水硅比、体系pH值等制备条件对SiO2气凝胶胶凝时间、孔径分布及孔型结构的影响.结果表明,水硅比对气凝胶的孔径分布和孔型具有较大的影响;水用量增加.胶凝时间延长,气凝胶的孔径分布逐渐变窄,孔型趋于一致.乙醇不参与溶胶-凝胶反应,只对TEOS有助溶和稀释的作用,因此乙醇用量增加,溶胶的胶凝时间延长,但对体系反应的影响相对较小,不会引起气凝胶孔结构的剧烈改变.在较小pH值或弱碱性范围内,pH值对孔形结构的影响也比较小,体系pH值增大,胶凝时间缩短,制得的气凝胶孔径分布较窄,孔型均一.当pH值大于8.5后,不利于气凝胶网络结构的形成和均匀分布,胶凝时间随pH值的增大而延长,制备的气凝胶孔径和孔型分布都比较大.     

氧化铝悬浮液的分散行为及其影响因素研究

详细研究了氧化铝悬浮液的分散行为及固含量、pH值和聚丙烯酸(PAA)添加量对分散行为的影响。实验结果表明,固含量、pH值和PAA添加量对氧化铝悬浮液的分散行为有显著影响。粘度法及Zeta电位测试法所反映的悬浮液分散性随pH值和分散剂添加量的变化规律基本一致。当pH=9～10、分散剂添加量的质量分数为2.0%～2.5%时粘度最低、Zeta电位绝对值最大、分散效果最好。分散剂添加量存在最佳范围,且最佳范围不随固含量的变化而改变。随固含量的增加,粘度开始缓慢上升,到达一定程度后迅速增大。     

用电泳沉积方法制备LiCoO2薄膜

将LiCoO2粉末分散在异丙醇溶剂中电泳沉积,在铝箔阴极上制备出了LiCoO2薄膜.研究了pH值、悬浮液浓度、外加电压和时间等工艺参数对单位面积膜层质量的影响,初步探讨了Li-CoO2的电泳沉积机理.研究发现:悬浮液中不加HCl时,LiCoO2不能从异丙醇悬浮液中电泳沉积出来;LiCoO2的沉积量随悬浮液的pH值减小而增加,随悬浮液浓度、外加电压的增大和时间的延长呈线性增加.通过SEM分析发现,电泳沉积得到的LiCoO2薄膜不很致密,但作为锂离子电池正极材料使用是完全可以满足要求的.     

Cu-水纳米流体的分散行为及导热性能研究

通过测定Cu-水纳米悬浮液的Zeta电位和吸光度,采用Hotdisk热物性分析仪测量了其导热系数,探讨了不同pH值和分散剂浓度对Cu-水纳米悬浮液分散稳定性和导热性能的影响.结果表明,pH值和分散剂加入量是影响Cu-水纳米悬浮液分散稳定和导热系数的重要因素.最优化的pH值和分散剂加入量能显著提高水溶液中Cu表面Zeta电位绝对值,增大了颗粒间静电排斥力,悬浮液分散稳定性较好,导热系数较高.从分散稳定和导热系数提高两个方面来考虑,pH=9.5左右被选为最优化值,在0.1%Cu-H2O纳米流体中,0.07%SDBS被选为最优化浓度.另外,Cu-水纳米流体的导热系数随纳米粒子质量分数的增大而增大,呈非线性关系,且比现有理论(Hamilton-Crosser模型)预测值大.     

溶剂型丙烯酸酯压敏胶的流变性能研究

针对分子量不同的溶剂型丙烯酸酯共聚物压敏胶的流变性能进行研究,通过频率扫描、振幅扫描两种不同模式进行流变性能测试,并对其蠕变性能进行了测试,通过测试,分析了分子量对流变性能的影响。结果表明,分子量增大,区分频率值(f*)变小,零剪切黏度(η0)变大,样品的弹性变好;在振幅扫描模式下,随着分子量变大,样品的线性黏弹区域变大,弹性模量(G′)与黏性模量(G″)均变大,但弹性模量增大的幅度大于黏性模量,因此,随着分子量变大,样品逐渐从G′G″,样品由黏弹性液体流变行为逐渐向黏弹性固体流变行为转变;蠕变测试说明分子量增大,有利于改善样品的抗剪切变形能力与蠕变回复能力,蠕变回复时间也随之变大。     

溴化十六烷基三甲基铵在麦壳上的吸附研究

以麦壳为吸附剂,研究其对污水中阳离子表面活性剂溴化十六烷基三甲基铵(CTMAB)的吸附特性。考察了吸附剂用量、吸附时间、CTMAB初始浓度、溶液pH、吸附液盐度、温度等条件对吸附的影响。结果表明:随着麦壳用量的增加,吸附量逐渐减小;麦壳对CTMAB的吸附反应速率很快,40min即可达到吸附平衡;随着CTMAB初始浓度以及pH值的增加,吸附量均逐渐增大;随着Ca2+浓度的增大,吸附量逐渐减小;随着反应温度的升高,吸附量缓慢增大。麦壳对CTMAB的吸附符合Langmuir和Freundlich模型。     

酰化胶原溶液的流变行为研究

应用流变学的方法研究了酰化胶原溶液的流体力学性能。结果表明,酰化胶原溶液属于假塑性流体,随着剪切速率的增大,表现出明显的剪切变稀行为。当温度从25℃升高到30℃,酰化胶原分子的热运动增加,分子间的物理缠结逐渐降低,导致酰化胶原溶液的剪切粘度、弹性模量(G′)、粘性模量(G″)和复数粘度逐渐降低,而损耗因子却不断升高。酰化胶原溶液的柔量随温度升高而升高,表明其抵抗变形的能力逐渐降低。基于数学模型的拟合结果表明,幂律方程、Carreau和Cross方程可有效描述溶液的稳态测试曲线,Lenovo、Burger和Herschel-Bulkley方程分别对动态频率、蠕变和触变曲线具有较好的拟合效果。     

聚丙烯木塑复合材料蠕变行为的模拟与预测

通过三点弯曲蠕变试验,研究了聚丙烯木塑复合材料在23℃左右室内环境五种应力水平下的短期蠕变行为,并采用四元件模型对其蠕变行为进行模拟。依据时间-温度-应力等效原理,以5MPa为参考应力水平,将其它四种应力水平下的蠕变曲线移位成5MPa应力水平下的主曲线,从而可以预测聚丙烯木塑复合材料在5MPa应力水平下大约3年内的蠕变行为。     

纳米纤维素对两性蠕虫胶束线性黏弹性的影响

对两性蠕虫胶束（Z-WLM）溶液添加不同类型纳米纤维素（NCs）后的耐温性能进行了研究,并通过线性流变学方法分析了不同浓度的NCs对Z-WLM的动态黏弹性、触变性、蠕变性等流变行为的影响。研究结果表明,质量分数为4wt%的芥酸酰胺丙基二甲基甜菜碱表面活性剂溶液可形成蠕虫胶束（WLM）结构,具有剪切稀释性、黏弹性、蠕变性及良好的触变回复性等特性。与其它类型NCs相比,长径比大、羧基含量高的NCs对WLM溶液拥有更好的增黏作用,同时可增加体系的松弛时间、弹性模量,延长其剪切黏度及动态模量触变回复时间,改善其蠕变回复性和耐温性,适用于70~100℃的中高温油藏增产作业使用。随着NCs添加量的增加,复合体系的黏弹性和蠕变回复性增强,触变回复性减弱。      

Monte Carlo simulation of the effect of fiber characteristics on creep life of a fiber tow

Fatigue of reinforced ceramics at elevated temperatures was numerically evaluated with a fiber dominated, power-law creep model. A Monte Carlo simulation of fiber creep in a uniaxially loaded tow was used to examine the influence of fiber radius, elastic modulus, and strength on creep respose. The simulation permitted variation of both the average magnitude and dispersion of fiber characteristics while maintaining constant power-law creep parameters. A linear increase in creep life was predicted for an increase in mean fiber radius, and a linear decrease in creep life was predicted for an increase in the standard deviation of fiber radii. A linear increase in creep life was predicted for both an increase in mean fiber elastic modulus and standard deviation of elastic moduli. Characteristic fiber strength and Weibull modulus were predicted to have a significant effect on creep life of a SiC fiber low. An increase in either the characteristic strength or Weibull modulus was predicted to result in an increase in creep life.     

早龄期水泥混凝土拉伸徐变实测与模型

该研究研发了混凝土早龄期拉伸徐变测量装置,并能够测量直接拉伸强度和拉伸弹性模量。对测得的拉伸徐变进行模拟,采用现存模型对数据进行验证,认为现存模型不能够精确预测混凝土早龄期拉伸徐变。根据实测拉伸徐变数据对现存模型进行修正,建立了更能代表实际工程情况、用于混凝土结构物应力计算的拉伸徐变模型,提供了可用于结构物应力计算的松弛模量。     

基于流变特性的含铝凝胶燃料制备工艺研究

为提升液固燃料的结构稳定性,以无机纳米颗粒为凝胶剂制备了环氧丙烷基凝胶基质,在基质中引入微米铝粉,得到含铝凝胶燃料。通过测定凝胶基质的弹性模量G′₀和线性区范围γ_c,分析了超声和热处理对纳米颗粒成胶的影响。针对不同含铝量的凝胶燃料,在不同剪切速率（0.1～2 000.0 s^-1）下,进行了旋转剪切测试,并研究了剪切历史对燃料流动曲线的影响。结果表明,超声和加热对纳米颗粒的成胶效果皆有促进作用。低剪切速率（γ<100 s^-1）下,剪切历史会使得凝胶体系黏度增高;超过100 s^-1后,黏度较无剪切历史的样品低。流动曲线显示,含铝凝胶燃料在100 s-1附近出现增稠现象,而更高的剪切速率直接导致凝胶结构在短时间内出现不可逆破坏,致使黏度迅速降低。     

Mechanism and behavior of fiber-reinforced asphalt mastic at high temperature

Abstract

The rheological behaviour and reinforcement mechanism of asphalt mastic mixed with fibres at high temperature were investigated in this study. Fibres, including basalt, polyester and glass, were added to asphalt mastic. Repeated creep and multi-stress creep tests were conducted to characterise the high-temperature properties of the mastic, and numerical simulation was performed with ABAQUS software to analyse the reinforcement effect of fibres. Test results indicate that the fibres have excellent reinforced performance; for example, the accumulated strain and its change rate decrease, and its creep stiffness modulus increases after the fibres are mixed into the mastic. The creep recovery rate increases, and its creep residual value decreases at a high stress level. The creep stiffness modulus under different loading cycles can be expressed by a power function. Numerical simulation shows that the fibres effectively absorb mastic stress; hence, creep strain in the mastics decreases. The Burgers model was utilised to present the rheological behaviours of mastics with fibres; the model parameters were estimated.     

Strain mechanisms in grey cast iron

Grey cast iron exhibits a continuous stress-strain curve on which elastic and plastic strains cannot be identified. Tensile straining is analysed here in the case of a grey cast iron solidified by continuous casting. It is demonstrated that the main damaging processes are directly related to strain components which can be macroscopically identified. The amount of microcracking is evaluated by the decrease in elastic stiffness. On complete unloading, a small increase in the elastic stiffness is recorded; however, the initial value is not recovered. Deformation due to localized plastic strains is evaluated by recording the tangent modulus. For stresses inducing negligible creep strains the tangent modulus decreases linearly for increased applied stress. Under low stress amplitude, however, an elastic range is clearly observed. Both mentioned strain mechanisms are fully responsible for the non linear behaviour of the material. Furthermore, it is demonstrated that as a consequence of these strain mechanisms, the stress-strain curve of a prestrained grey cast iron is directly related to the initial stress-strain curve of the same material.     

Thermoplastic multiphase composites: Tensile and creep behavior

It is shown that the strength of the investigated composite in which the concentration of chlorinated polyethylene can be as high as 60% (i.e., under the assumption that the matrix is formed by low-density polyethylene) is fairly well predicted by using the Smith-Nielsen lattice model. In turn, the experimental values of the modulus of elasticity for various compositions based on low-density polyethylene and chlorinated polyethylene can be predicted within the framework of the Hashin-Shtrikman variation fork and the creep of the same systems is predicted according to the power law. The concentration dependences of the elastic modulus and creep compliance for the investigated thermoplastic materials are S-shaped due to their multiphase structure. Thus, the elastic and creep properties of the composites can be successfully predicted for a fairly broad range of compositions. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 49–54, November–December, 2006.     

单晶高温合金DD6不同状态下的元素分布与力学行为

选择3mm/min和8mm/min两种抽拉速率通过螺旋选晶法制备[001]方向的DD6单晶高温合金,测试合金枝晶间与枝晶干的元素分布,研究了两种工艺合金的持久性能和断裂特征;利用EPMA电子探针测试了3mm/min抽拉速率DD6合金经0.1%、0.2%、0.5%蠕变应变后枝晶间与枝晶干的元素分布,并通过纳米压痕仪测试了枝晶间与枝晶干的弹性模量和硬度。结果表明,抽拉速率较小时DD6合金枝晶组织更粗大,元素偏析程度较大,抽拉速率对合金持久寿命的影响不大;随着蠕变应变的增加,合金枝晶间与枝晶干弹性模量和硬度的差值逐渐增大,这与合金元素的再分布紧密相关,特别是与难熔元素Ta、Hf、Mo和Nb随着蠕变应变的变化而发生再分布有关。     

Mechanical properties of ZnS nanobelts

Mechanical properties of ZnS nanobelts were measured at room temperature by direct nanoindentation experiments. It was found that the ZnS nanobelts achieve 79% increase in hardness but 52% decrease in elastic modulus compared to bulk ZnS. The nanobelts were found to exhibit creep under indentation. Indentation cracking was preferred along the belt growth direction. Indentation deformation behavior and fracture mechanisms of the ZnS nanobelts are discussed in conjunction with their crystalline structure, size effect, and surface-to-volume ratio.