Microstructure evolution and simulation of copolymerization reaction using a percolation kinetic gelation model

A new kinetic gelation model that incorporates the kinetics of non-linear free radical copolymerization is presented. Copolymerization of bi- and tetrafunctional monomer mixtures is simulated to characterize kinetic effects on polymerization statistics and microstructures. An algorithm for random next step selection in a self-avoiding random walk and efficient mechanisms of component's mobility are introduced to improve the universality of the predictions by removing commonly occurring simulation deficiencies due to early trapping of radicals. The model has the capability to predict the onset of the sol-gel transition, and the effect of chemical composition on the transition point. It is shown that a better understanding of microstructure evolution during polymerization and chemical gelation is attained. Lastly, one important benefit of the simulation method is the ability to simulate very highly packed random chains or microgels within a polymer network.     

酸化改善油层渗流状况的地质研究：以百口泉油田为例

油井井底和近井地带地层结垢，油层内部粘土质点的迁移、堆积、膨胀导致油层渗流条件变差，这是造成克拉玛依百口泉油田产液量大幅度下降的主要原因。采用酸化工艺改善油层渗流条件，使产液量和产油量都有大幅度提高。采取酸化措施前应先找水、堵水。实践表明，采用胶束酸酸化效果最佳。     

Conductive Materials for Proton Exchange Membrane Fuel Cell Bipolar Plates Made from PVDF,PET and Co‐continuous PVDF/PET Filled with Carbon Additives

The aim of this work was to develop and characterise electrically conductive materials for proton exchange membrane fuel cells and bipolar plates (BPPs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black (CB) powder and, in some cases, graphite synthetic flakes mixed with pure PET, PVDF or with PVDF/PET systems. They were first developed by twin‐screw extrusion process then compression‐molded to give BPP final shape. As the developed blends have to meet properties suitable for BPP applications, they were characterised for their rheological properties, electrical through‐plane resistivity (the inverse of conductivity), oxygen permeability, flexural and impact properties. Results showed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. It was also observed that the lowest resistivity values were obtained with mixing PVDF and PET at controlled compositions to ensure PVDF/PET co‐continuous morphology. Also, slow cooling rates helped to attain the lowest values of through‐plane resistivity for all studied blends. This behaviour was related to the higher crystallinity obtained with low cooling rates leading to smaller amorphous regions in which carbon particles are much more concentrated.     

Experimental and Theoretical Investigation of Degradation Mechanisms by Particle Coarsening in SOFC Electrodes

Performance degradation data obtained from single solid oxide fuel cells, tested at 850 °C with air and humidified H₂ and using Ni‐YSZ anode supported cells, are presented here. Microscopic investigation is carried out on both anode and cathode to quantify variations in the morphology at different operation times. The comparison between the measurements on the cells and the SEM image analysis allows to conclude that there is no relationship between the initial cell activation and microstructural modifications of the electrodes. On the other hand, it was found that cell degradation is strictly related to the coarsening of Ni particles occurring in the anode. A theoretical analysis based on an electrode micromodel has been performed in order to compare the variation in performance, expected from particle size change, with the observed data. The model confirmed the conclusions of the experimental results.     

应用表面活性剂改善非牛顿原油的渗流流变性

通过大量的室内研究 ,筛选研制出了价格低廉、耐矿化度、硬度好 ,对稠油具有强乳化降粘 ,改善非牛顿原油渗流流变性效果显著的表面活性剂体系JHSS - 0 1。室内模拟试验表明JHSS - 0 1吞吐后采油速度提高 2 0 %～ 5 0 %。同时在八面河及江汉王场油田进行了现场试验 ,7口井累计增油 12 83t,投入产出比 1∶5 2 ,经济效益明显。     

Effect of percolation frequency on biohydrogen production from fruit and vegetable wastes by dry fermentation

Organic solid wastes are the most abundant sources for biohydrogen production. Dry fermentation system has many advantages over continuously fed reactor systems for treatment of organic solid wastes. In this study the effect of percolation frequency on yield of biohydrogen production from fruit and vegetable wastes using dry fermentation system was examined. For this purpose 2 times percolation per day, 1 time percolation per day and 1 time percolation per 2 days frequency were compared and the hydrogen yields were observed as; 57 mL H₂/gVS_removed, 53 mL H₂/gVS_removed and 68 mL H₂/gVS_removed respectively. The percolation frequency didn't affect the overall yield but significantly affected the biohydrogen producing reactor of the dry fermentation system. 80% of the hydrogen was produced in percolation tank during 1 time per 2 days feeding and almost all hydrogen production was conducted in dry fermenter during 2 times per day percolation. Therefore the percolation frequency is found to be very important for system operation characteristics.     

LaMn1-xTixO3-NiMn2O4(0≤x≤0.7): A composite NTC ceramic with controllable electrical property and high stability

A series of NTC thermistor ceramics based on LaMn_1-xTi_xO₃-NiMn₂O₄(0≤x≤0.7) composite system have been fabricated by solid-state method. X-ray diffraction analysis indicates the composite ceramics mainly consisting of a rhombohedral perovskite LaMn_1-xTi_xO₃ phase and a cubic spinel NiMn₂O₄ phase. SEM images show high density of the as-prepared composite ceramics. The effects of the Ti doping and the weight ratio of LaMn_1-xTi_xO₃/NiMn₂O₄ on electrical property have been studied. The electrical resistivity ρ increases significantly with Ti addition increasing and decreases obviously with LaMn_1-xTi_xO₃ concentration increasing. The ρ_25°C and B values are in the range of 3.2–53,200.0Ω·cm and 1300–4008 K, respectively, and could be adjusted to desired values and applied in various fields. The conductive mechanism may be related to the ion migration and the percolation theory. After annealing at 125°C for 1000h, the resistance shifts are less than 0.52%, suggesting good stability of the composite and high potential for NTC thermistor applications.     

A numerical investigation of the connection between state of dispersion and percolation and its effect on the elastic properties of 2D random microstructures

The present work is dedicated to a numerical investigation of the connection between state of dispersion and percolation and its effect on the elastic properties of 2D random microstructures. The main objective consists in checking out the link between percolation and mechanical response in the context of a heterogeneous medium the reinforcements of which are not homogeneously dispersed. Besides, the influence of the stiffness of inclusions is also investigated since this could impact on the percolation effects. For these purposes, large samples of volume elements are generated according to the Monte Carlo method. We consider the low cost framework of 2D random grids which enables large and in-depth investigations. Besides, the spatial distribution of heterogeneities is simulated with the help of the 2-scale Boolean scheme of disks which is a powerful tool for modelling and studying several states of dispersion. The numerical results highlight beneficial mechanical reinforcements for a heterogeneous dispersion when the percolation phenomenon is enhanced. This improvement is highly sensitive to the stiffness of heterogeneities.     

Investigation of Ce0.9Gd0.1O2-δ dispersed Sm1.5Sr0.5NiO4+δ: Cathode for intermediate temperature solid oxide fuel cell applications

Dispersion of nanocrystalline (94–350 nm) Ce_0.9Gd_0.1O_2-δ in superfine (260–312 nm) Sm_1.5Sr_0.5NiO_4+δ using modified precipitation technique is established using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. Presence of Ce_0.9Gd_0.1O_2-δ grains inhibits grain growth of Sm_1.5Sr_0.5NiO_4+δ, which provides morphological stability (up to 1100 °C). Ce_0.9Gd_0.1O_2-δ concentration dependent behaviours of ionic conductivity, surface exchange rate and electrode polarization resistance (R_p) of composites (determined using electrochemical impedance spectroscopy) are comprehended using percolation model. Three oxygen reduction reaction mechanisms are considered to understand electrochemical performance. Minimum R_p (0.81 Ω cm² at 700 °C) for 70Sm_1.5Sr_0.5NiO_4+δ:30Ce_0.9Gd_0.1O_2-δ is correlated to percolation threshold (optimum (i) electrochemically active sites (ii) oxygen reduction reaction kinetics, (iii) O^2- conductivity and (iv) charge transfer rate). Nano crystallite size of Ce_0.9Gd_0.1O_2-δ is crucial for enhancement in electrochemical performance. Oxygen partial pressure dependent electrochemical impedance spectroscopy studies reveal dominance of coexisting non-charge transfer oxygen adsorption/desorption and bulk O^2- diffusion.     

Self-limited growth of nanocrystals in phosphosilicate melts during cooling

In this Letter, we demonstrate that the spontaneous nanophase-separation can greatly enhance the heterogeneous nucleation in the investigated phosphosilicate melts. The two separated phases are found to be the phosphate-rich phase as the floppy domain and the silicate-rich phases as rigid phase. We found that sodium phosphate nanocrystals form in the phosphate-rich phase during melt cooling. The growth of these nanocrystals are self-limited, i.e., limited by the surrounding silicate-rich phase with higher viscosity, and hence lower ionic diffusion compared to the phosphate-rich phase. Our results show that the substitution of B₂O₃ or Al₂O₃ for partial Na₂O enhances the spontaneous nucleation, although the viscosity of silicate-rich matrix phase is increased by such substitution. This implies that the compositional substitution enhances nanophase separation and thereby lowers the activation energy for non-isothermal crystallization. This work indicates that nanophase separation is crucial for fabrication of transparent glass-ceramics from phosphosilicate melts.