A geometric solution to the largest-free-sphere problem in zeolite frameworks

We have applied Delaunay triangulation to models of the known zeolite frameworks. We show that this well-established technique from computational geometry provides for each framework; (i) the location and shape of the open pores and channels, (ii) the diameter of the largest possible included sphere, and indirectly (iii) the diameter of the largest-free-sphere that can diffuse through the framework by at least one lattice translation. Since Delaunay triangulation naturally locates the empty spaces within a set of points, it provides a powerful computer-automated tool for determining the physical characteristics of pores and channels of zeolite frameworks. Such tools will further enhance the usefulness of large databases of hypothetical framework materials.

Here, we tabulate results for the 165 zeolite frameworks that are presently listed in the Atlas of Zeolite Frameworks. Of the known zeolites, refined as pure silicates, the largest included sphere occurs in the TSC framework, with a diameter of 16.39 Å. The largest-free-sphere has a diameter of 11.33 Å, for diffusion along the [0 0 1] direction in the VFI framework.     

Improved method to calculate Hansen solubility parameters of a polymer

An improved method to calculate Hansen solubility parameters δ_d, δ_p and δ_h, as well as the radius of interaction sphere for a given polymer is presented, starting from the idea that the solvents which dissolve a polymer, form in the interior of its solubility range a system of material points, their ‘masses' being given by the unity normed intrinsic viscosities of the polymer in the considered solvents. The mass centre coordinates of the material points system represent in fact Hansen solubility parameters of the polymer, and the radius of interaction sphere the distance from this centre to the farthest point of material points system mentioned.     

THE DISSOLUTION OR GROWTH OF A SPHERE

The problem of the dissolution or growth of an isolated, stationary, sphere in a large fluid body is analyzed. The motion of the boundary as well as the resulting motion in the liquid are properly taken into account. The governing equations are solved using a recently developed technique (Subramanian and Weinberg, 1981) which employs an asymptotic expansion in time. Results for the radius of the sphere as a function of time are calculated. The range of utility of the present solution is established by comparison with a numerical solution of the governing equations obtained by the method of finite differences.     

THE DISSOLUTION OR GROWTH OF A SPHERE

The problem of the dissolution or growth of an isolated, stationary, sphere in a large fluid body is analyzed. The motion of the boundary as well as the resulting motion in the liquid are properly taken into account. The governing equations are solved using a recently developed technique (Subramanian and Weinberg, 1981) which employs an asymptotic expansion in time. Results for the radius of the sphere as a function of time are calculated. The range of utility of the present solution is established by comparison with a numerical solution of the governing equations obtained by the method of finite differences.     

芳纶纤维复合材料切削性能与刀具选用

针对芳纶纤维复合材料的性能,进行了相应的车削、铣削和钻削基础工艺试验。结果表明,该材料呈现出切削力大、切削热不易散发、切削刀具磨损剧烈、树脂基材料影响切削性能、加工缺陷多,质量不稳定等切削性能;提出了相应切削刀具材料的选用原则,即应采用高硬耐磨的硬质合金或金刚石刀具材料进行切削;提出了车削、铣削、钻削加工该复合材料的刀具应具备的结构形式和几何参数。     

Prediction of methane storage in covalent organic frameworks using big-data-mining approach

A combination of computational materials screening and machine learning (ML) technique is being adopted as a popular approach to study various materials toward application of interest. In this work, we began with high-throughput molecular simulations to calculate the methane storage (6.5 MPa) and deliverable (6.5-0.58 MPa) capacities of 404,460 covalent organic frameworks (COFs) at 298 K. Then, the full data sets with 23 features were randomly split into training and test sets in a ratio of 20:80, which were applied to evaluate the prediction abilities of several ML algorithms, including gradient boosting decision tree (GBDT), neural network (NN), support vector machine (SVM), random forest (RF) and decision tree (DT). The results indicate that the RF model has the highest prediction accuracy, which was further employed to reduce the dimension of features space and quantitatively analyze the relative importance of each feature value. The binary classification predictors built using the features with the highest influence weight can give a successful identification of top-performing candidates from the test set containing 323,168 COFs with an accuracy exceeding 96%. The deliverable capacities of the identified COFs were found to outperform those reported so far for various adsorbents. The findings may provide a useful guidance for the design and synthesis of new high-performance materials for methane storage application.     

制备CS-Ca2+-SAL中空凝胶球及其对碳纳米的缓释行为

将海藻酸钠溶液(SAL)滴入壳聚糖-钙(CS-Ca2+)分散溶液中，海藻酸钠与壳聚糖分子链之间发生物理交联的同时，也与钙离子进行同步交联，可一步制备毫米级壳聚糖-钙-海藻酸钠(CS-Ca2+-SAL) 水凝胶球。通过调控原料用量比例、滴加速度和方式，成功制备内部中空，球壁均匀，表面致密的凝胶球。以荧光性碳纳米点为标记物，考察凝胶球的溶胀性能和缓释性能。结果表明，凝胶球在中性水溶液中12h溶胀率可达26.09%，并能保持完整球形结构。溶胀性能受到pH的影响显著，处于pH=1.2的溶液体系中溶胀率最小，处于pH =6.8溶液环境中溶胀率最大。荧光凝胶球在pH=7.1的Tris-HCl缓冲液中的释放率实验结果表明，对碳纳米的释放模型最符合Hixon-crowell溶蚀方程，说明凝胶球的缓释机制以溶蚀为主，扩散为辅。     

Porous spherical LiFePO4·LiMnPO4·Li3V2(PO4)3@C@rGO composites as a high-rate and long-cycle cathode for lithium ion batteries

The porous spherical LiFePO₄·LiMnPO₄·Li₃V₂(PO₄)₃@C@rGO (Sample-G) composites are prepared via a spray drying process. The results show that the composites consist of orthorhombic olivine-type LiFe_0.5Mn_0.5PO₄ and monoclinic Li₃V₂(PO₄)₃, which are evenly distributed. In particular, nanoparticles are embedded in graphene nanosheets, which are interconnected and stacked to form a porous sphere structure with an interior three-dimensional conductive network, resulting in the huge improvement on electrochemical performance and structural stability. Due to the increased Li⁺ diffusion coefficient, the composite possesses 98.6 and 82.9 mAh g⁻¹ with capacities retention of 81.6% and 71.8% at 10 and 20C after 1000 cycles, respectively. The mutual cross-doping effect between LFP·LMP·LVP and a porous sphere structure with a 3D conductive network inside provides a practical method for improving the cycling and rate performance.     

Three-dimensional microstructure analysis of numerically simulated cementitious materials

In order to predict the transport properties of porous media, such as permeability and electrical conductivity of cementitious materials, a better understanding of the microstructural characteristics, including the geometrical and topological properties, is required. In this contribution, the microstructure of cementitious materials is simulated by using the cement hydration model HYMOSTRUC. In this computer-based numerical model, the hydrating cement grains are modeled as gradually growing spheres, which become in contact while growing. The simulated porous medium can be described as a series of sections taken from three orthogonal directions, in which each unit (pixel) is filled either with a solid or a fluid phase (pores). Various algorithms based on a random walk process are utilized to determine the local geometrical information, such as gravity center's coordinate, perimeter and area of each individual pore. The percolating path of the fluid in three dimensions is traced by using an overlap algorithm. Both three-dimensional (3D) geometrical information and topological space characterization including branch node network and genus of the pores are derived. Calculation results of these algorithms are compared with results obtained by other microstructural models at various degree of hydration.     

Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design

Simple explicit relations are presented for the onset of competing fracture modes in ceramic coatings on compliant substrates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near-contact area. The critical load relations are expressed in terms of well-documented material parameters (elastic modulus, toughness, hardness, and strength) and geometrical parameters (coating thickness and sphere radius). Data from selected glass, Al₂O₃ and ZrO₂ coating materials on polycarbonate substrates are used to demonstrate the validity of the relations. The formulation provides a basis for designing ceramic coatings with optimum damage resistance.     

熔盐体系表面张力的分子关联模型

将Ｒｅｉｓ提出的硬球表面张力模型用于计算纯熔盐和混合熔盐体系的表面张力将硬球直径视为温度的函数，对２３个纯熔盐体系的表面张力进行了关联，得到相应的分子参数，表面张力的关联总体平均偏差为０４８％应用ｖａｎｄｅｒＷａａｌｓ理论－１混合规则，将Ｒｅｉｓ的表面张力模型推广到混合熔盐体系，对２７个二元熔盐混合体系的表面张力进行了预测和关联，总体平均偏差分别为３３８％和１０４％，其结果能满足工业应用的需要     

聚丙烯/硅－铝空心球增强材料的力学性能

用刚性无机粒子硅-铝（Si-Al）空心球填充增强聚丙烯,研究了Si-Al空心球的含量、粒径及偶联剂对PP/Si-Al空心球增强材料力学性能的影响,结果表明,填充40%以下的Si-Al空心球的增强PP的缺口冲击强度、拉伸强度、拉伸弹性模量、弯曲强度和弯曲弹性模量均显著提高;Si-Al空心球为20%时,增强PP的冲击强度达到最大值,与填充粒径10μmSi-Al空心球相比,填充粒径5μmSi-Al空心球的增强PP的缺口冲击强度和拉伸弹性模量高。填充经偶联剂A和C表面处理的Si-Al空心球有利于提高增强PP的缺口冲击强度、弯曲强度及弯曲弹性模量。填充刚性无机粒子Si-Al空心球不仅能提高PP的力学性能,而且能降低PP的成本,为Si-Al空心球的应用开辟了新途径。     

球形补偿器及其在低压蒸汽管道中的应用

介绍球形补偿器的特点、使用范围、几个典型参数的确定，并用工程实例说明了球形补偿器在低压蒸汽管道中的应用。     

Networks of materials: Construction and structural analysis

Modeling and analysis of the materials universe is an emerging area of research with many important applications in materials science. The main goal is to create a map of materials which allows not only to visualize and navigate the materials space, but also reveal complex relationships and “connections” among materials and potentially find clusters of materials with similar properties. In this paper, we consider the problem of mapping and exploring the materials universe using network science tools and concepts. The networks are based on the open-source materials data repository AFLOW.org where each material is represented as a node, and each pair of nodes is connected by a link if the respective materials exhibit a high level of similarity between their Density of States (DOS) functions. We discuss the importance of similarity measure selection, investigate basic structural properties of the resulting networks, and demonstrate advantages and limitations of the proposed approaches. Materials networks, similarity measures, DOS function, materials informatics, network analysis, clique.     

Creeping motions of a composite sphere in a concentric spherical cavity

An analytical study is presented for the quasisteady translation and steady rotation of a spherically symmetric composite particle composed of a solid core and a surrounding porous shell located at the center of a spherical cavity filled with an incompressible Newtonian fluid. In the fluid-permeable porous shell, idealized hydrodynamic frictional segments are assumed to distribute uniformly. In the limit of small Reynolds number, the Stokes and Brinkman equations are solved for the flow field of the system, and the hydrodynamic drag force and torque exerted by the fluid on the particle which is proportional to the translational and angular velocities, respectively, are obtained in closed forms. For a given geometry, the normalized wall-corrected translational and rotational mobilities of the particle decrease monotonically with a decrease in the permeability of its porous shell. The boundary effects of the cavity wall on the creeping motions of a composite sphere can be quite significant in appropriate situations. In the limiting cases, the analytical solutions describing the drag force and torque or mobilities for a composite sphere in the cavity reduce to those for a solid sphere and for a porous sphere.     

Spontaneous Crystallization in Athermal Polymer Packings

We review recent results from extensive simulations of the crystallization of athermal polymer packings. It is shown that above a certain packing density, and for sufficiently long simulations, all random assemblies of freely-jointed chains of tangent hard spheres of uniform size show a spontaneous transition into a crystalline phase. These polymer crystals adopt predominantly random hexagonal close packed morphologies. An analysis of the local environment around monomers based on the shape and size of the Voronoi polyhedra clearly shows that Voronoi cells become more spherical and more symmetric as the system transits to the ordered state. The change in the local environment leads to an increase in the monomer translational contribution to the entropy of the system, which acts as the driving force for the phase transition. A comparison of the crystallization of hard-sphere polymers and monomers highlights similarities and differences resulting from the constraints imposed by chain connectivity.     

基于CPM模型的路用混凝土组成设计方法

针对基于三重球模型的混凝土组成设计方法存在参数计算复杂,在实际工程中使用不便,对其中抗压强度模型和浆体/骨料模型的计算简化处理,提出了一种基于可压缩堆聚模型(CPM)模型的路用混凝土组成设计方法,通过设计实例表明:该方法简单实用,级配优化合理,水泥用量少,混凝土各项指标能够满足设计要求.     

Infrasorb: Optical detection of the heat of adsorption for high throughput adsorption screening of porous solids

The demand for fast screening methods in modern materials chemistry led to the development of a room temperature operated high-throughput tool for adsorption screening. Within five minutes a porosity screening of a large sample pool can be realized. Using a variety of different porous materials (activated carbons, porous polymers, metal-organic frameworks, zeolites) and the test gas n-butane, the reliability of the new instrument is shown. Furthermore, possible applications in the determination of n-butane capacities and BET surface areas are given as well as the application in synthesis or product control.The presented data exhibit high quality factors for the correlation of integrated signal intensity (heat of adsorption) and specific surface areas (above 0.97). As an example for the applicability of other gases that can be used with this tool, screening measurements using cyclohexane as test gas are also presented. The developed automated screening tool is an important step to overcome the bottle-neck between high-throughput syntheses technologies developed in the last decades and measurement of adsorption properties.     

Modeling of the Structure of Porous Disperse Systems

The globular and chaotic sphere arrangement models of the structure of disperse system are compared. It is necessary to take into account the history of interparticle contacts. The globular model is modified to refine the expressions for integral parameters of the chaotic sphere arrangement model. An example of structural calculations is given.     

Pore Network Drying Model for Particle Aggregates: Assessment by X-Ray Microtomography

Convective drying of disordered glass bead packings has been investigated both experimentally and numerically. X-ray microtomography (XMT) and image analysis techniques have been used to determine the three-dimensional spatial distribution of the liquid and solid phases at the pore scale within the wet particle aggregates. The evolution of the liquid distribution in the aggregate has been tracked during the drying process. Particle center coordinates and radii have been extracted from the X-ray images using binarization and segmentation techniques. Based on this geometric data for a real aggregate, a pore network approximation of the pore space has been generated from a Voronoi tessellation about particle centers by designating Voronoi edges as interconnected cylindrical pores with radii computed from the distance between neighboring particles. This three-dimensional irregular pore network takes into account both the geometrical and topological characteristics (pore size distribution and connectivity) of the actual pore space. Drying simulations have been carried out for the pore networks obtained from the XMT and results are presented as phase distributions and moisture profiles. The simulated liquid phase distributions are in qualitative agreement with the experimental result, which indicates that pore network models are suited to describe the drying of dense particle aggregates at the pore scale.