多孔SiC陶瓷烧结体的导电特性

利用聚碳硅烷热分解形成的碳化硅，将工作碳化硅颗粒粘结在一起，形成多孔的碳化硅烧结体。文中给出了烧结体的微观分析，热分析和结构分析的结果。同时还给出了烧结时不同 量与常温电阻关系。对实验结果从掺杂，减少富碳和钝化表界面悬挂键几个角度进行了讨论，结果表明三者的影响对电阻率的变化趋势是一致的。     

碳气凝胶的制备及其电除盐性能的研究

在常压条件下通过溶胶-凝胶法和碳化、活化工艺制备碳气凝胶材料.用SEM和BET比表面积测量等手段对材料的表面形貌和微观结构进行分析表征,通过循环伏安法对材料的电化学性能进行研究.联系材料的微观结构和电化学性能,对碳气凝胶的电除盐过程和除盐机理进行了研究和分析,发现碳气凝胶是一种具有很大应用潜力的多孔电极吸附材料.     

PVC敏感膜电极对非离子表面活性剂的响应机理研究

本工作研究了ＰＶＣ敏感膜电极对几种聚氧乙烯类非离子表面活性剂的响应特性、响应机理和响应动力学，实验结果和理论研究表明：表面活性剂胶束的形成，使响应曲线上出现折点，并导致响应速度的控制步骤由络合离子在膜中的迁移过程转变为 带通过扩散阻挡层及膜／溶液界面反应两个过程共同作用。     

聚乙烯热解制备二氧化硅表面碳涂层的机理研究

利用反应分子动力学ReaxFF方法模拟了聚乙烯热解碳沉积二氧化硅基底的微观过程，通过分析沉积过程中碳结构、体系产物数目及碳碳径向分布函数的变化来揭示聚乙烯碳化机理。结果表明：碳结构的形成主要是远离基底芳香环的沉积成片生长和靠近基底的小分子碳的渗入、析出，连接在沉积的碳结构上。其中远离基底的聚乙烯热解有两个方向，一是直接热解为小分子的碳氢化合物(C₂H₄、C₃H₆、C₄H₈等),继而小分子碳氢化合物继续反应脱氢，重组形成碳链和碳环；二是未完全断链的碳氢长链(C>5),与碳氢小分子进行反应。研究温度和保温时间对沉积的影响得知，升温可以加快反应速率，但不改变整体的反应趋势。温度为2500K,在保证碳源充足的情况下，会有更多的碳形成稳定的碳环结构，持续生长。从ReaxFF动力学角度研究高分子聚合物制备碳材料的机理，可以为相关实验研究提供理论支持。     

不同生物质来源的多孔碳复合碳电极在钙钛矿太阳能电池中的应用

通过将生物质在惰性气体保护下高温热解/活化制备多孔碳材料,具有成本低,工艺简单等优点,并且是一种废物利用,减少环境污染的有效途径。将三种不同生物质通过高温热解/活化制备了多孔碳材料,将其与市售导电碳浆复合制成碳浆料后应用于钙钛矿太阳能电池(PSCs)背电极,研究了不同生物质多孔碳材料的形貌、结构和比表面积等对器件光电性能的影响。结果表明,基于不同生物质多孔碳材料的PSCs的光电性能取决于生物质多孔碳材料的形貌、结晶度、比表面积和形态以及钙钛矿/碳电极的界面接触。基于生物质多孔碳的复合碳电极结合研磨工艺制备的碳基PSCs,由于具有良好的界面性能获得最高10.18%的光电转换效率(PCE)(未复合生物质碳的PSCs的PCE为6.39%),室温下保存60天后,仍保留了初始PCE的96%。     

仿生制备多孔氮化硅陶瓷

以松木炭化后形成的多孔木炭为模板,经Y2O3/SiO2混合溶胶浸渍生物碳模板形成Y2O3/SiO2/C复合体,在高压氮气氛下(0.6MPa),1600°C碳热还原氮化制备出牛物形态多孔氮化硅陶瓷.借助XRD、SEM研究了烧结助剂、烧结温度、反应时间和烧结气氛对烧结产物显微结构和晶相的影响,探讨了多孔Si3N4陶瓷的反应过程和机理.结果表明,多孔si3N4陶瓷是由主晶相β-Si3N4和少量晶间玻璃相YsSi4n4O14组成;多孔Si3N4不仅保留了松木的管胞结构,还在孔道中生长出纤维状形貌的β-Si3N4颗粒;Si3N4的反应烧结过程包括α-Si3N4的形成、晶形转变(α-β相变)和晶粒生长三个阶段.在1450°C烧结的机理是气-固和气-气反应机理,在1600°C通过液相烧结的溶解-沉淀机理形成纤维状的多孔Si3N4陶瓷.     

液相等离子沉积非晶态碳膜的试验研究

应用简单的电镀槽，通过阴极/电解液界面前沿气泡鞘的形成而建立辉光放电，促成非晶态碳薄膜在电极表面的沉积。沉积物宏观上分布不均匀，在阴极浸入电解液的末端，由于电流的尖端效应，导致生成物为石墨。而远离末端为正常沉积区，表面平整光滑，生成物为非。晶态碳膜。结论：液相等离子沉积行为可发生在辉光放电条件下的阴极过程，从而可应用于非晶态薄膜如非晶态碳的制备。     

光热敏微胶囊的光信息记录与再现特性

采用界面聚合技术获得了新型光信息记录材料光热敏微胶囊。利用红外光谱及热显影技术对微胶囊光信息记录过程及再现特性进行了研究。实验结果表明,曝光瞬间自由基型光引发剂引发单体分子间交联聚合,从而造成不饱和碳碳双键含量呈双指数衰减,同时碳碳单键含量增加,从微观体现了微胶囊对光信息的记录;光聚合产物对染料分子形成包裹,降低了染料前体与显色剂的反应几率,造成曝光区微胶囊涂层显色密度的下降,与未曝光区显色密度形成明显的密度反差,从宏观体现了微胶囊对光信息的再现。     

用Fe粉坯连接SiC陶瓷的工艺研究

以Fe金属粉压坯作为连接材料,采用高温钎焊连接工艺连接反应烧结SiC陶瓷.通过正交实验得到了最佳连接工艺为：保温时间3 min,连接温度1250℃,降温速率为5℃/min,压坯厚度0.6mm（0.375g）.弯曲实验结果表明,采用该工艺得到的接头最大弯曲强度为13.6MPa.界面SEM分析表明,不同工艺下得到的接头界面微观结构相似,连接界面形成了2个反应层,相应的界面微观结构为SiC/反应层1,反应层2,反应层1/SiC.反应层1与SiC形成了紧密的连接,反应层1,反应层2界面处各相相互咬合在一起.     

微结构对碳/碳复合材料界面性能的影响

通过理论模型和界面顶出实验分析了微观结构对碳/碳复合材料界面性能的影响机制。使用高分辨Micro-CT系统获得C/C复合材料界面的微观结构特征,并对界面的微观结构特征进行统计分析,得到界面微观结构尺度分布的概率密度函数。对C/C复合材料的界面层建立力学分析模型,计算获得C/C复合材料界面力学性能,在计算过程中引入界面微观结构的随机性统计分布,获得C/C复合材料界面力学性能的分布规律。设计纤维束顶出实验,测试分析C/C复合材料的界面力学性能。将力学分析模型的计算结果与界面顶出实验获得的实验结果进行对比分析,表明通过模型计算获得的界面性能的均值和离散度与实验获得的结果具有较好的一致性。      

考虑多孔电极内气液分布的数学模型

给出了多孔电极内不同气液分布形状的溶液欧姆定律; 在单孔电极模型基础上定义了电化学反应的有效三相分界线长度概念,并给出了对应的计算方法;建立了基于多孔介质气液分布理论的一维电流和过电位数学模型,用数值迭代方法计算了沿电极面法线方向上的电流和过电位分布,分析了气体饱和度分布和有效三相分界线长度对它们的影响。     

Microscopic design and optimization of hydrodynamically lubricated dissipative interfaces

A homogenization-based topology optimization framework is developed, which can endow hydrodynamically lubricated interfaces with a micro-texture, to achieve optimal macroscopic responses by addressing both dissipative and nondissipative physics at the interface. With respect to the homogenization aspects of the problem, the thermodynamic consistency of the two-scale formulation is explicitly analyzed and verified. With respect to the topology optimization aspects, a variational approach to sensitivity analysis is pursued. Subsequently, these are employed in micro-texture design studies, which address microscopic and macroscopic objectives. The influence of dissipation on the optimization results is demonstrated through extensive numerical investigations, which also highlight the importance of working in a sufficiently flexible design space that can deliver nearly optimal micro-texture geometries.     

On the sintering with rigid inclusions

The sintering of porous matrices containing rigid, i.e. non-densifying, inclusions is discussed on the basis of the composite sphere model of Scherer. Recognizing that internal stresses are generated by the presence of the non-densifying inclusions, a new equation for the densification rate of the composite is proposed. It takes into account three contributions: (i) the free densification strain rate, which is independent of the stresses present, (ii) the strain rate due to the microscopic effect of the stresses on the sintering mechanism and (iii) the macroscopic deformation strain rate induced by the stresses. This result indicates that the presence of rigid inclusions may generate higher internal stresses in the densify ing compact than those calculated by the original Scherer's approach.     

Pb-Zn的电沉积及其多孔电极的制备

铅基合金由于低熔点、高密度以及在酸性溶液中有较高析氢过电位等,被广泛应用于有机电合成中。由于Pb-Zn镀层的硬度较纯Pb高,本研究采用多孔Pb-Zn电极。在柠檬酸和EDTA-2Na为络合剂的甲磺酸镀液中电沉积出Pb-Zn镀层,循环伏安曲线和阴极极化曲线表明,Pb-Zn是分步沉积的,且均受扩散控制。采用X射线衍射、扫描电镜、能谱分析等研究了Pb-Zn镀层及其多孔电极组成和结构。结果表明,Pb-Zn镀层由Pb和Zn的混合物组成,Pb-Zn镀层用体积分数10%的H2SO4腐蚀后,Pb-Zn镀层表面晶粒细化,得到多孔Pb-Zn镀层。小幅度恒电位阶跃实验表明,多孔Pb-Zn电极具有更大的比表面积。     

Forced Wetting Dynamics of Sodium Dodecyl Sulfate Glycerol Solution on Solid Substrates

The forced wetting dynamics of a sodium dodecyl sulfate glycerol solution on both intermediate hydrophilic and hydrophilic solid substrates was studied by using the Wilhelmy plate method. The dynamic contact angle θ _D at different contact line velocities U (θ _D–U relationship) was measured. The influences of the macroscopic properties including the surfactant solution concentration, the substrate surface free energy, and the surface tension on the θ _D–U relationship were investigated, and all three properties are important. An interesting phenomenon that θ _D initially increases then decreases with U was found in the experiment, which could not be explained by modern theoretical models. The microscopic effect of the surfactant adsorption on the solid–vapor interface near the three-phase contact line was used to explain this phenomenon. A modified molecular-kinetic model was proposed, and the model can well describe the experimental results.     

钯催化剂对锂空气电池氧析出和氧还原反应的催化机理的研究

锂空气电池以其超高的能量密度而备受关注, 然而充、放电过电位高等问题严重限制了其实际应用。金属钯作为催化剂可而降低锂空气电池的充、放电过电位, 但其充、放电反应催化机制尚不完善。本研究运用第一原理计算方法, 建立了钯/氧气/过氧化锂(Pd/O₂/Li₂O₂)的三相界面催化模型, 从微观角度揭示钯催化剂在锂空气电池充、放电反应中的催化机制。研究表明, Pd/O基底通过促进Li₂O₂在界面处的电荷转移提高自身对LiO₂吸附作用, 从而加速放电产物在电极表面的形成, 有效降低了充电过电位0.43 V。     

Gaseous reduction of an alloy oxide

Ni(Al, Fe)₂O₄ ceramic alloys were reduced by hydrogen gas at a pressure of 1 atm, and at temperatures between 450 and 800° C. The reaction rate was determined from the rate of advance of the porous metal product layer—unreduced oxide interface. A simple analysis was presented permitting assessment of both the interface reaction resistance and the gas transport resistant through the porous product scales. The reaction was under mixed control in all conditions studied. In a range of temperatures and reaction times, preferred grain-boundary attack was observed. The conditions under which this was observed depended strongly on the Al³⁺ content of the ceramic alloy. Al³⁺ also lowered the interface reaction rate and inhibited scale coarsening by formation of dispersed unreduced phases in the product scales.     

Lithium deintercalation in LiFePO4 nanoparticles via a domino-cascade model

Lithium iron phosphate is one of the most promising positive-electrode materials for the next generation of lithium-ion batteries that will be used in electric and plug-in hybrid vehicles. Lithium deintercalation (intercalation) proceeds through a two-phase reaction between compositions very close to LiFePO(4) and FePO(4). As both endmember phases are very poor ionic and electronic conductors, it is difficult to understand the intercalation mechanism at the microscopic scale. Here, we report a characterization of electrochemically deintercalated nanomaterials by X-ray diffraction and electron microscopy that shows the coexistence of fully intercalated and fully deintercalated individual particles. This result indicates that the growth reaction is considerably faster than its nucleation. The reaction mechanism is described by a 'domino-cascade model' and is explained by the existence of structural constraints occurring just at the reaction interface: the minimization of the elastic energy enhances the deintercalation (intercalation) process that occurs as a wave moving through the entire crystal. This model opens new perspectives in the search for new electrode materials even with poor ionic and electronic conductivities.     

Flow modeling of linear and nonlinear fluids in two scale fibrous fabrics

The fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium is the permeability. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. As permeability reflects both the magnitude and anisotropy of the fluid/fiber resistance, efficient numerical techniques are needed to solve linear and nonlinear homogenization problems online during the flow simulation. In a previous work the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and rheo-thinning resins. In the linear case only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as representative microscopic volumes exist in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, microscopic calculation must be carried out many times because the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. Thus, a nonlinear multi-scale problem results. In this paper an original and efficient offline-online procedure is proposed for the efficient solution of nonlinear flow problems in porous media.