2D SAXS/WAXD analysis of pan carbon fiber microstructure in organic/inorganic transformation

Structure of PAN fibers during pre-oxidation and carbonization was studied using two dimensional small angle X-ray scattering/wide angle X-ray diffraction(2D SAXS/WAXD).The SAXS results show that during pre-oxidation between 180 ℃ and 275 ℃,the volume content of microvoids increases with the temperature increasing,which may be one of reasons for the decrease of tensile strength of pre-oxidized fibers.253 ℃ was the critical transition temperature,the length,diameter,aspect ratio and orientation distribution of microvoids increased with temperature before this temperature and decreased after this temperature.After the high temperature carbonization,lots of spindly microvoids formed.WAXD patterns demonstrate that the crystallite size of PAN fibers first increased before 230 ℃ and then decreased with the increase of temperature during the pre-oxidation.The diffraction peak of PAN fibers at 2θ≈ 17° almost disappeared at the end of preoxidation while the diffraction peak of aromatic structure at 2θ≈ 25° appeared at 253 ℃.During carbonization,the peak intensity at 2θ≈ 25° increased apparently due to the formation of graphite structure.The results obtained give a deep understanding of the microstructure development in the PAN fibers during pre-oxidation and carbonization,which is important for the preparation of high performance carbon fibers.     

过渡金属改性Mg-Al基固体碱催化剂上碳酸丙烯酯与甲醇合成碳酸二甲酯的研究

以共沉淀法制备了一系列不同价态过渡金属(Fe、Cu、Zr)改性的Mg-Al固体碱催化剂,考察了其对于甲醇与碳酸丙烯酯(PC)酯交换合成碳酸二甲酯的反应性能。采用XRD、N_2吸附-脱附、FT-IR、XPS、CO_2-TPD等手段对催化剂的物理化学性质进行了表征。结果表明,催化剂的碱强度、碱密度是影响催化活性的主要因素,不同价态过渡金属的加入可以调控Mg-Al固体催化剂的碱性。在考察的催化剂中,FeMgAl催化剂具有最高的表面碱密度,因此,表现出最好的催化性能。在温度为65℃、时间为4 h、甲醇与PC物质的量比为10∶1、催化剂用量为4%的反应条件下,PC转化率可达66.2%。     

一维高精度离散GDQ方法

GDQ method is a kind of high order accurate numerical methods developed several years ago, which have been successfully used to simulate the solution of smooth engineering problems such as structure mechanics and incompressible fluid dynamics. In this paper, extending the traditional GDQ method, we develop a new kind of discontinuous GDQ methods to solve compressible flow problems of which solutions may be discontinuous. In order to capture the local features of fluid flows, firstly, the computational domain is divided into many small pieces of subdomains. Then, in each small subdomain, the GDQ method is implementedand some kinds of numerical flux limitation conditions will be required to keep the correct flow direction. At the boundary interface between subdomains, we also use some kind of flux conditions according to the flow direction. The numerical method obtained by the above steps has the advantages of high order accuracy and easy to treat boundary conditions. It can simulate perfectly nonlinear waves such as shock, rarefaction wave and contact discontinuity. Finally, the numerical experiments on one dimensional Burgers equation and Euler equations are given.The numerical results verify the validation of the method.     

高性能聚丙烯腈碳纤维中纳米级微孔分析表征研究

高性能碳纤维由于其优异的性能,在各行各业中具有广泛应用。为深入研究碳纤维内结构与其性能之间的相关性,本文应用小角X射线散射研究了一系列典型的聚丙烯腈碳纤维样品,分析了样品内微孔的尺寸及取向,讨论了强度和模量与微孔的相关性,研究结果表明:高性能碳纤维的力学强度和模量与碳纤维内微孔缺陷的长度和长径比有关,控制碳纤维内微孔缺陷的长度有望实现高强碳纤维的制备,控制牵伸倍率从而控制碳纤维内微孔的长径比有望实现高模碳纤维的制备。     

溶液预凝胶化对再生纤维素水凝胶膜性能的影响

研究了溶液预凝胶化对纤维素/NaOH/尿素水溶液体系以浸没沉淀相转化法制备的再生纤维素水凝胶膜的影响.通过静态拉伸、扫描电子显微镜研究了预凝胶化温度、凝固浴温度、凝固浴组成对再生纤维素水凝胶膜结构和性能的影响.结果表明,与常规的浸没沉淀相转化法相比,使溶液预凝胶化可以提高所制备的水凝胶膜的机械性能.经60℃预凝胶30 min后制备的水凝胶膜,拉伸强度比未经预凝胶处理的水凝胶膜提高85%.凝固浴温度的升高和凝固浴中硫酸浓度的增大均会导致形成具有较大孔结构的纤维素水凝胶膜,机械性能也随之下降.     

A Thermodynamic Analysis of the Validity of Wenzel and Cassie＇s Equations ＊

Wettable properties of a considered solid on its contact angle （CA） can be analyzed theoretically using the classical Wenzel and Cassie＇s equations. However, recent strong interest in superhydrophobic surfaces has demanded a re-examination of the applicability of the two equations. We report a thermodynamic analysis to determine the universality, in particular, the limitations of the two equations. Using some special surfaces, we demonstrate that the two equations are valid for micro-scale heterogeneous structures, however they are invalid for macro-scale heterogeneous surfaces. Furthermore, the present calculations suggest that fundamental thermodynamic analysis is the most powerful and reliable approach to determine the comprehensive wettability for various structurally patterned surfaces.     

生态敏感区建筑遗产群保护规划方法探索——以浙江大学之江校区为例

任何程度的扩建和增建都可能对生态敏感区内的建筑遗产本身,或其所在的生态环境造成损失.本文将以位于西湖风景名胜区的浙江大学之江校区为例,对生态林保护区、建筑遗产群环境及其相互关系进行客观评价.评价基于ArcGIS分析平台,利用多因子叠加评价体系,分析和评估建筑遗产群所处的生态环境,在保证对生态环境、原有规划格局以及建筑遗产不受破坏的前提下,结合学校发展计划,提出空间引导与管制方案, 充分利用现有资源的潜质并从中获得最大效益.     

求解Stiff方程单步显式格式的拟B-稳定性

<正> 对于自治型 Stiff 常微分方程模型(dY)/(dt)=f(Y(t)),f:R~m→R~m,(1)J.C.Butcher 提出了 Runge-Kutta 方法的 B-稳定性概念.即在单调性条件〈Y-Z,f(Y)-f(Z)〉≤0,Y,Z∈R~m (2)满足的情况下,有定义1,R-K 方法称为 B-稳定的,如果 {Y_n}、{Z_n} 是 R-K 方法的两个解,有‖Y_n-Z_n‖≤‖Y_(n-1)-Z_(n-1)‖对任意自然数 n 成立.显然,由 B-稳定可推出 A-稳定.对于含高阶导数的方法,K.Burrage 提出了β阶可微单调性条件(-1)~(q-1)〈u,f~((q-1))(u)〉≤0,q=1,2,…,β,u∈R~m,(3)并研究了多值多导方法的代数稳定性.对于一般的非线性多导方法,直接讨论上述两种稳定性往往比较困难.为此,本文结合 B-稳定与 β 阶可微单调性条件,提出了一种单步显式多导(文中仅讨论二阶的情形,可推广到高阶的情形)方法的拟 B-稳定概念.     

微波消解-ICP-OES测定滇杨中的矿质元素

采用微波消解法消解样品,利用电感耦合等离子体-发射光谱法(ICP-OES)测定滇杨中的矿质元素.方法的RSD为0.5％-3.8％,加标回收率为96.7％-104.4％,表明该方法有良好的精密度和准确度.用该法对滇杨样品中的钙、镁、铁、锌、钾、锰、磷、硼、铜、钠、硅等11种矿质元素进行测定,发现铜含量明显偏低,不能达到植...     

甲烷无氧直接制备烯烃/芳烃研究进展(Ⅱ)

在"碳达峰、碳中和"的背景下,甲烷无氧直接制备烯烃/芳烃具有零二氧化碳排放、100％碳原子利用和富产氢等优势,是碳一化学和催化领域中一个热点研究课题.本综述基于作者在甲烷无氧直接制备烯烃/芳烃反应的研究工作,结合2018?2021年的相关文献,对目前甲烷无氧芳构化反应和甲烷无氧直接制备烯烃、芳烃和氢气反应的世界各国研究...