Influence of chelating agent and reaction time on the swelling process for preparation of porous TiO2 particles

This study aimed to describe the preparation and characterization of porous titanium oxide particles of narrow particle size distribution by a single-step swelling process of polystyrene template microspheres. In this research, different specific surface areas, porous structures and densities of porous titanium oxide particles had been synthesized with various experimental parameters. Two main parameters were tested and discussed: (1) acetylacetone amount (from 0 to 1 ml) and (2) reaction time (from 2 to 32 h). Polystyrene template particles were polymerized by emulsifier free-emulsion polymerization (a kind of polymerization method). For the swelling process to be successful, a chelating agent (acetylacetone) was added to delay the aqueous hydrolysis of titanium (IV) isopropoxide in the water phase. The influences of various reaction parameters on size, morphology, composition, specific surface area, porous structure and density of particles were investigated. The properties of particles were analyzed by scanning electron microscope, Brunauer–Emmett–Teller, Fourier transform infrared analysis, thermogravimetric analysis, powder X-ray diffraction, and specific gravity meter.     

Experimental and theoretical determination of the particle size of hydrotreating catalysts of different shapes

Equations for calculating the total geometric volume and external area of lobe-shaped catalytic particles as a function of easy-to-determine geometric parameters are presented in this work. Particle density was experimentally determined by the ASTM C-128 standard method, which, together with the average weight of various particles, was used to estimate the total external volume. The calculated total geometric volume was then compared with that obtained by the proposed equations for the purpose of validation. A variety of porous and non-porous particles with different shapes and sizes were employed for validation of both the experimental method and the proposed equations. In the absence of an experimental approach to determine external area, the corresponding equations were validated indirectly by comparing bulk densities determined by the ASTM C-29 experimental method with those calculated with particle density and bed void fraction. Calculated values of external volume and surface were in good agreement with experimental data.     

Modeling on lithium insertion of porous carbon electrodes

MCMBs with different crystal structure were tested for an anode of lithium ion batteries (LIB) and the model describing the behavior of porous anodes was simulated numerically by using orthogonal collocation method (OCM). Kinetic parameters such as diffusion coefficients, exchange current densities, and transfer coefficient, describing electrochemical intercalation system of lithium ions, were estimated by fitting the experimental cyclic voltametry (CV) results with the theoretical ones. It was investigated that the theoretical cyclic voltamograms obtained using above parameters fitted well with the experimental curves for the various scan rates from 1 mV s⁻¹ to 5 μV s⁻¹. The parameters were then evaluated on their extended application in various C-rate-charge/discharge cycling tests with showing good agreements between experiments and simulations. As the results show, it was found that numerical simulations based on both potentiometry and galvanometry experimental data resulted in more accurate parameters of electrochemical system. Simulations indicate there exist the optimum design conditions of electrode and separator to obtain the good performance of lithium ion batteries.     

Strength Degradation of Nonrandom Porous Ceramic Structures under Uniaxial Compressive Loading

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three-dimensional nonrandom porous ceramics.     

Porous materials from crystallizable polyolefins produced by gel technology

A new method for obtaining porous and porous fiber polymers is presented. This method is based on using gel-type technology (without previously preparing polymer solutions) for crystallizable polymers, preparing polyethylenes, and including polyethylenes of very high molecular mass and isotactic polypropylene. The method consists in swelling crystalline polymer films at elevated temperatures in a proper solvent with subsequent precipitation with a non-solvent at different conditions. In this case, simultaneous or consecutive processes of phase separation of amorphous or/and crystalline type occurs; stretching the sample can also accompany this process. Complete phase diagrams of two- and three-component systems (polymer-solvent and polymer-solvent precipitator) were constructed. Temperature-concentration boundaries of amorphous separartion (binodal) and crystallization (liquidus) are reported for the system polyethylene? o-xylene? dimethyl formamide. Phase transitions of both types influence characteristics of the resultant porous structure. They were prepared by simultaneous (precipitation of a gel by dimethyl formamide at 25°C) or consecutive (precipitation with a hot non-solvent at 138°C and following cooling) phase separation. Studied were the effect of experimental conditions (temperature, times for solvation and precipitation, polymer molecular mass, the thermodynamic quality of solvents and parameters of film stretching) on peculiarities of the structure and quantitative characteristics of final porous and fiber-porous polyolefins. It has been demonstrated that the method proposed allows us to obtain a crystalline and highly porous polymer with open poros, a bimodal size distribution and with a highly developed inner surface. Further high strength and small shrinkage are characteristic of the fiber-porous materials. The method under discussion appears to be universal, it does not require a preliminary preparation of polymer solutions and can be realized within a general technology of polymer films and sheet processing. Highly porous polymers obtained by this technology, primarily based on polyethylenes of very high molecular mass, can be used as neutral supports for multi-functional membranes, polymeric covers, frame systems for implants and other applications.     

The Effects of Porous Structure on the Burning Characteristics of Foamed NC‐Based Gun Propellants

The effects of porous structure on the burning characteristics of foamed NC‐based (nitrocellulose‐based) gun propellants were investigated by closed vessel and quenched combustion experiments. The foamed NC‐based TEGDN (triethylene glycol dinitrate) gun propellants with different porous structures were prepared by adjusting the process parameters in the foaming process. SEM (scanning electron microscopy) was used to observe the morphologies of foamed TEGDN propellants, and the densities of the foamed propellants were also measured to evaluate the porosities of foamed propellants. The experimental results showed that the burning characteristics of the novel foamed propellants are totally different from combustion characteristics of parallel‐layer. Further investigations revealed that the burning characteristics of the foamed NC‐based propellants largely depend on the porous structure, larger pores and higher porosity would lead to higher burning rate of the foamed TEGDN propellants.     

Piezoelectric response of porous ceramic and composite materials based on Pb(Zr,Ti)O3: experiment and modelling

Abstract

The present paper presents experimental and theoretical studies of the effective piezoelectric properties of porous Pb(Zr,Ti)O₃ based ceramics and composites. The experimental dependence of piezoelectric coefficients and dielectric permittivity on relative density is determined for porous materials containing different piezopassive components. The piezoelectric response of these materials in a wide range of volume concentrations of the piezopassive components are analysed in the framework of a model of a modified laminated composite with 2–2 and 1–3 connectivity elements. The role of these elements in forming different concentration dependences of the effective parameters of the porous piezoceramic and piezocomposite materials is discussed.     

碳多孔体中碳化硅晶须原位生长条件的实验与模型研究

根据碳化硅晶须生长的特定驱动力要求，通过实验和建立气相传输模型研究了碳多孔体中碳化硅晶须原位生长的条件。模型和实验研究均表明：温度和多孔体表面气相组成对多孔体内的晶须原位生长起决定作用；体内附加反应可以改变晶须生长所要求的温度和表面气相条件。     

均匀多孔介质下乙醇溶液的过冷度

为了研究多孔介质对乙醇溶液过冷度的影响,实验搭建了不同孔隙率和不同热导率的多孔介质的实验系统,通过改变乙醇溶液浓度探究了浓度对过冷度的影响,通过改变孔隙率和热导率探究强化换热方法。数据的处理采用统计学的方法,每种工况下实验32次。结果表明：多孔介质的孔隙率和热导率对乙醇溶液过冷度有影响;随着孔隙率的减小和热导率的增加,平均过冷度值减小,过冷度稳定性增强;高浓度对减小过冷度作用明显,浓度越高,过冷度平均值和最大值越小,而浓度的变化对稳定性影响较小。     

Modified Pressure-Decay Technique for Evaluating the Permeability of Highly Dense Refractories

The experimental evaluation of permeability parameters encounters different difficulties, depending on the features of the materials. Traditional steady-state techniques for refractory castables and other highly dense ceramics demand arduous work and require reliable measurements at high pressure and for extremely low flow rates. In this paper, a recent and promising technique known as vacuum-decay permeametry is modified to consider the effect of gas compressibility and fluid inertia. Darcy's law is replaced by Forchheimer's equation, which has been proved to better represent the interactions between fluid and a castable porous medium. The modified method is modeled and applied experimentally to refractory samples with different permeability levels. Results that have been compared to a well-established steady-state permeametry method confirm the validity of the model.     

非热平衡多孔介质内反应与传热传质耦合过程

采用局部热不平衡假设,对发生强吸热化学反应的多孔介质体系建立了反应与传热、传质耦合问题的数学模型,采用Ergun-Forchheimer-Brinkman方程描述多孔介质中的流体流动.运用交替方向隐式(ADI)方法对模型离散求解,并采用文献中的实验数据对模型进行验证.计算了不同条件下颗粒物料层内气体和固体骨架的温度场、产物气体浓度场以及固体转化率分布,以得到多孔介质体系内固有化学反应时的传热、传质规律.结果表明,不能忽略固体骨架与流体间的温度差.入口渗流速度、入口气体温度以及固体颗粒尺寸是影响系统反应特性的重要参数.研究结果对具有强吸热反应的固定床反应器的设计和运行具有一定的参考作用.     

Modelling electrochemical impedance data for semi-bipolar lead acid batteries

Electrochemical impedance spectroscopy offers an alternative method of performing nondestructive characterisation of electrodes and batteries in stationary power stations compared to the more conventional discharge tests. A model for porous electrodes is used to analyse impedance data in such a way that physical parameters can be evaluated. It is also suggested that these parameters can be used as a way of determining the state of health of a battery during float charging. A method for the calculation of the steady-state current of porous electrodes is also presented, based on the impedance model. The combined d.c. and a.c. analysis confirm more concisely the validity of the theoretical assumptions used to explain the experimental data.     

Modeling and Stress Analysis During Drying of a Deformable and Saturated Porous Medium

This article addresses how to express the behaviors that develop stresses within a porous media during convective drying processes. The work is focused on the coupling of the thermal (temperature distribution), hygroscopic (moisture, humidity), and mechanical (strains and stresses) aspects shown during the drying process of a saturated porous medium. Natural clay plate samples were used as a model material. Using two different mechanical behaviors (elastic and viscoelastic), the strain–stress equations were studied and discussed through the simulation results. Obtaining almost the same parameters of the main modeling variables (temperature, liquid pressure, and moisture content), a significant difference was observed between the results obtained for the stresses assuming the two behaviors, particularly depending on the viscoelastic parameters deduced from an experimental study. The simulation highlights a response of the medium supposed viscoelastic different to that of elastic case in intensity and response time.     

定向凝固干燥法制备取向多孔聚乙烯醇材料研究

文章利用定向凝固干燥法制备了取向多孔聚乙烯醇(PVA)材料。研究并探讨了PVA溶液的浓度、PVA溶液浸入液氮速度等工艺参数对制备的样品微观结构的影响规律。研究结果表明:以水溶性聚合物PVA为原料、利用定向凝固干燥法制备取向多孔材料是可行的。这为聚合物基多孔材料的发展提供了新的思路和方法。     

Fabrication of porous polylactic acid films assisted by dip‐coating and template leaching techniques

A new simple method was developed to fabricate porous polylactic acid (PLA) films coated directly on substrates. The PLA films with a controllable thickness were realized using a dip‐coating technique. The pore structure of the resulting porous PLA films was tailored by utilizing phase inversion process and template leaching techniques. The experimental results show that the resulting PLA films became thicker when using the coating solution with a higher viscosity or applying a faster withdrawal speed. The porous structures (pore size and void density) of the resulting PLA films are significantly influenced by the polymer concentration, the nonsolvents, and the addition of poly(ethylene glycol) templates. The analyses of solubility parameters was utilized to explain the porous structures of the resulting PLA films in details. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Simulation study and kinetic parameter estimation of underground coal gasification in Alberta reservoirs

A new method is developed for the estimation of chemical reaction kinetics at high-pressure underground coal gasification from the field produced gas composition. This method combines a developed numerical forward model and field data to investigate uncertain parameters. The forward model is developed on the basis of a unique porous media approach that combines the effects of heat, mass transport, and chemical reactions to simulate the underground coal gasification in three-dimensional basis. The chemical reaction kinetics, that is limited to low pressure, is upscaled based on the available experimental data. A comprehensive sensitivity analysis is carried out to estimate the reaction kinetics and investigate the effect of various parameters, such as pressure, temperature, and reaction environment, on the produced gas composition. The novelty of the developed method is in its applicability as well as its ability to generate the chemical reaction kinetics that corresponds to the field under study. The advantage of the proposed technique is that the sensitivity of the model to different kinetic parameters can be investigated by a graphical method.