Towards Highly Stable Storage of Sodium Ions: A Porous Na3V2(PO4)3/C Cathode Material for Sodium‐Ion Batteries

A porous Na₃V₂(PO₄)₃ cathode material coated uniformly with a layer of approximately 6 nm carbon has been synthesized by the sol–gel method combined with a freeze‐drying process. The special porous morphology and structure significantly increases the specific surface area of the material, which greatly enlarges the contact area between the electrode and electrolyte, and consequently supplies more active sites for sodium ions. When employed as a cathode material of sodium‐ion batteries, this porous Na₃V₂(PO₄)₃/C exhibits excellent rate performance and cycling stability; for instance, it shows quite a flat potential plateau at 3.4 V in the potential window of 2.7–4.0 V versus Na⁺/Na and delivers an initial capacity as high as 118.9 and 98.0 mA h g^?1 at current rates of 0.05 and 0.5 C, respectively, and after 50 cycles, a good capacity retention of 92.7 and 93.6 % are maintained. Moreover, even when the discharge current density is increased to 5 C (590 mA g^?1), an initial capacity of 97.6 mA h g^?1 can still be achieved, and an exciting capacity retention of 88.6 % is obtained after 100 cycles. The good cycle performance, excellent rate capability, and moreover, the low cost of Na₃V₂(PO₄)₃/C suggest that this material is a promising cathode for large‐scale sodium‐ion rechargeable batteries.     

基于图象处理和傅里叶变换的三维多孔介质重构方法

本文基于傅里叶变换的截断高斯场方法的理论,通过从实际多孔介质二维切片的二元化图像中提取孔隙率和自相关函数来构造整个三维多孔结构.模拟结果显示通过傅里叶变换技术得到的随机过程确实满足高斯分布,且构造出的三维多孔结构的统计特性基本与二维切片类似,说明了该技术能够构造出符合要求的三维多孔介质,从而为进一步从孔隙尺度研究其内部传热传质过程奠定了基础.     

药型罩初始孔隙度对聚能射流行为的影响

 多孔材料药型罩由于其可压缩性,在压垮之前受炸药爆炸冲击压缩作用而使温度升高,为延迟射流的断裂时间提供了可能,估算了多孔材料药型罩压垮之前的冲击温升,并结合脉冲X光摄影研究了孔隙度对射流行为的影响。测试结果表明,一定的孔隙度范围内,射流的韧性随着孔隙度的增加而提高,射流直径随孔隙度的增加而变细。     

高温高压气体在低含水率介质中迁移的数值模拟

针对气液两相非等温渗流模型高度非线性的特点,发展了适宜的数值离散方法。根据相态转换准则和控制方程的性质,采用最低饱和度法简化算法。空间离散方面,使用有限体积法;时间离散方面,设计了一套包含合理求解顺序的Picard迭代法,解决了方程组强耦合的问题。利用上述数值方法对高温高压气体的迁移行为进行数值模拟,证明了气体在低含水率介质和等效孔隙度的干燥介质内的运动基本一致,并分析了空腔内的气液相态转变过程。在此基础上,研究了多孔介质孔隙度和渗透率对气体压强演化和示踪气体迁移的影响。研究表明,孔隙度越小（相同渗透率）、渗透率越高（相同孔隙度）,示踪气体的迁移距离越远,并给出了估算不同孔隙度和渗透率下迁移距离的半经验公式。     

Studies of Capillary Porosity of Clinker Phases During Hydration

The capillary porosity of clinker phases, i.e. 3CaOSiO₂, β2CaOSiO₂, 3CaOAl₂O₃ and 4CaOAl₂O₃Fe₂O₃, at the early stages of hydration has been studied by the methods of Differential Scanning Calorimetry and nitrogen adsorption (BET). It was established that pores of 3–70 nm were formed during the hydration of 3CaOSiO₂ and the maximum of their distribution was found at about 10 nm. The hydration of 2CaOSiO₂ is much slower and the porosity is one order of magnitude lower. During the hydration of 3CaOAl₂O₃ the content of crystalline hexagonal hydrates prevailed and the porosity was in the range 5–90 nm with the average pore diameter of about 16 nm. This average pore diameter was much smaller for thermoporosimetry and lay at about 7 nm. The hydrated 4CaOAl₂O₃Fe₂O₃ sample had the porosity in the range 3–90 nm with the maximum of the pores distribution at about 4 nm. There are some differences between the porosities measured by BET and thermoporosimetry. Principally thermoporosimetry gives no information about larger capillary pores in the range 30–50 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

环境温度和湿度对96-Al2O3陶瓷电阻率的影响

采用无压烧结技术,以0.25wt;CaO、1wt;MgO、2.75wt;SiO2为添加剂,在1500 ℃、1550 ℃、1600 ℃下烧结制备了Al2O3陶瓷,分别在150~400 ℃温度范围内和40;~100;的相对湿度环境下,对Al2O3陶瓷的直流电阻率进行检测.样品的相组成和显微结构通过X-ray衍射分析(XRD)和扫描电子显微镜(SEM)表征.结果表明,环境温度由150 ℃上升到400 ℃,样品的直流电阻率降低了约2~2.5个数量级;环境相对湿度从40;上升到100;,样品的直流电阻下降了约3~4个数量级.在相同测试条件下,1500 ℃烧结的Al2O3陶瓷样品由于小的晶粒尺寸和高的孔隙率,从而导致其具有更高的电阻率.     

Convergence of a dual‐porosity model for two‐phase flow in fractured reservoirs

A dual‐porosity model describing two‐phase, incompressible, immiscible flows in a fractured reservoir is considered. Indeed, relations among fracture mobilities, fracture capillary presure, matrix mobilities, and matrix capillary presure of the model are mainly concerned. Roughly speaking, proper relations for these functions are (1) Fracture mobilities go to zero slower than matrix mobilities as fracture and matrix saturations go to their limits, (2) Fracture mobilities times derivative of fracture capillary presure and matrix mobilities times derivative of matrix capillary presure are both integrable functions. Galerkin's method is used to study this problem. Under above two conditions, convergence of discretized solutions obtained by Galerkin's method is shown by using compactness and monotonicity methods. Uniqueness of solution is studied by a duality argument. Copyright © 2000 John Wiley & Sons, Ltd.     

一种室温下制备多孔锐钛矿型TiO2薄膜的方法

 采用具有锐钛矿晶粒的TiO2溶胶与聚苯乙烯球形粒子混合制得涂膜液,通过浸渍提拉法制备薄膜,然后在超声波振荡条件下,以甲苯为溶剂,将薄膜中的聚苯乙烯球选择性地溶解去除,在室温下获得了锐钛矿型多孔TiO2薄膜. 与致密的TiO2薄膜相比,该多孔TiO2薄膜具有较高的光催化活性. 该方法有以下两方面的优点: 一是实现了多孔TiO2薄膜的室温制备,增大了薄膜基材的选择范围; 二是可以通过添加不同粒径的聚苯乙烯球,较为方便地实现了对薄膜孔径的调节.     

基于巴西盘试验的海冰拉伸强度研究

海冰拉伸强度是其基本力学性能之一, 同时也是冰区船舶与海洋工程结构设计所需的重要参数. 对于脆性材料的拉伸强度测试, 巴西盘劈裂试验相比单轴拉伸试验在试样制备与加载上具有明显的优势. 为研究海冰的拉伸强度特征, 对渤海辽东湾沿岸的粒状冰开展了系统的巴西盘劈裂试验研究. 在加载过程中与试样破坏后, 分别对加载横梁的位移与加载力以及试样最终破坏模式进行了记录. 同时, 对试样的冰晶结构、盐度、温度以及密度进行了测量. 通过改变加载速率、试样厚度与试样温度以研究不同参数对试验结果的影响. 针对传统试验中试样的刚体假设, 考虑了试样变形对应力状态的影响并将其引入了理论模型. 试验过程中所有海冰试样均以劈裂模式破坏. 试验结果表明, 加载速率与试样厚度对拉伸强度的影响并不显著, 但孔隙率的影响较为明显. 当孔隙率由75‰降低至10‰时,拉伸强度由1.0 MPa升高至2.8 MPa. 与单轴拉伸试验所测得数据对比, 巴西盘劈裂试验所得到的拉伸强度随孔隙率的变化趋势相一致. 但该方法所得到的粒状冰拉伸强度要高于预期结果. 试验表明巴西盘劈裂试验中海冰试样的破坏模式与试验结果均较为合理, 可成为海冰拉伸强度的有效测试方法.      

Mechanical activation of precursors for nanocrystalline materials

Nanostructured materials win big scientific interest and increasingly economic meaning through their specific exceptional properties. Precursors that were compacted by pressing and sintering are normally used preparation of materials. In present work, the influence of mechanical activation by grinding on the structure as well as on compacting and sintering behavior of oxides from magnesium, aluminium and silicon has been investigated. Starting materials for each metal oxide differ in microstructure, dispersity, and porosity. The influence of mechanical activation on the destruction of crystalline structure to nanocrystalline, as well as to the amorphous stage and the compaction of powders with nano‐particles, as well as structures with nanoscale pores have been compared. The possibilities of the consolidation of nanostructured materials were investigated. The mechanical activation took place in a disc vibration mill. The mechanical activated materials as well as their pressing and their sintering products were characterized by density, particle‐sizedistribution, specific surface, pore‐structure, microstructure, and crystallite size by X‐ray powder diffraction (XRD). The mechanical activation of the model‐substances led, in most cases, to an improvement of the compaction properties; thus, this improvement can be achieved with subsequent sintering densities up to 98% of the theoretical density. From these experiments, generalizations transferable to other materials can be made.