硅灰石合成高比表面积二氧化硅的工艺研究

一系列硅灰石酸处理实验表明,产物物理性质与反应速度、反应时间、中和最终ｐＨ值等工艺条件有关。同时发现,如果工艺条件恰当,可以制得４００～６００ｍ＾２／ｇ的高比表面积二氧化硅。     

Interfacial area and volumetric mass transfer coefficient in a bubble reactor at elevated pressures

The present study deals with the pressure effects on mass transfer parameters within a bubble reactor operating at pressures up to . The gas-liquid systems are N₂/CO₂-aqueous solution of Na₂CO₃-NaHCO₃ and N₂/CO₂-aqueous solution of NaOH. A sintered powder plate is used as a gas distributor. Three parameters characterizing the mass transfer are identified and investigated with respect to pressure: the gas-liquid interfacial area a, the volumetric liquid side mass transfer coefficient k_La and the volumetric gas side mass transfer coefficient k_Ga. The gas-liquid absorption with chemical reaction is used and the mass transfer parameters are determined by using the model reaction between CO₂ and the aqueous solutions of Na₂CO₃-NaHCO₃ and NaOH. For a given gas mass flow rate, the interfacial area as well as the volumetric liquid mass transfer coefficient decrease with increasing operating pressure. However, for a given pressure, a and k_La increase with increasing gas mass flow rates. The mass transfer coefficient k_L is independent of pressure. Furthermore, the pressure increase results in a decrease of k_G and k_Ga for a given gas mass flow rate. The values of the interfacial area, which are obtained from both chemical systems are found to be different. These discrepancies are attributed to the choice of the liquid system in the absorption reaction model.     

Preparation of porous carbons from thermoplastic precursors and their performance for electric double layer capacitors

Porous carbons with high surface area were successfully prepared from thermoplastic precursors, such as poly(vinyl alcohol) (PVA), hydroxyl propyl cellulose and poly(ethylene terephthalate), by the carbonization of a mixture with MgO at 900 °C in an inert atmosphere. After carbonization the MgO was dissolved out using a diluted sulfuric acid and the carbons formed were isolated. The mixing of the PVA carbon precursor with the MgO precursors (reagent grade MgO, magnesium acetate or citrate) was done either in powder form or in an aqueous solution. The BET surface area of the carbons obtained via solution mixing could reach a very high value, such as 2000 m²/g, without any activation process. The pore structure of the resultant carbons was found to depend strongly on the mixing method; the carbons prepared via solution mixing were rich in mesopores, but those produced via powder mixing were rich in micropores. The size of mesopores was found to be almost the same as that of the MgO particles, suggesting a way of controlling the mesopore size in the resultant carbons. Measurement of capacitance was carried out in 1 mol/L H₂SO₄ electrolyte. The porous carbon with a BET surface area of 1900 m²/g prepared at 900 °C through solution mixing of Mg acetate with PVA showed a fairly high EDLC capacitance, about 250 F/g with a current density of 20 mA/g and 210 F/g with 1000 mA/g. The rate performance was closely related to the mesoporous surface area.     

Simultaneous measurement of flow pattern and mass transfer coefficient in bubble columns

Mass transfer studies were carried out in a bubble column using the chemical method. Catalytic oxidation of sodium sulfite was chosen for the studies and the corresponding specific rates of oxidation were obtained using a stirred cell. Laser Doppler anemometer (LDA) was used to measure the instantaneous velocities in the same stirred cell as well as in bubble columns (100 and i.d.). An efficient algorithm based on the multiresolution analysis of the velocity-time data using wavelets was used for the isolation of data belonging to the gas and liquid phases. Eddy isolation model was used for the characterization of the eddy motion including the estimation of the energy dissipation rate. Using the knowledge of eddy motion, a methodology was developed for the prediction of true mass transfer coefficient (k_L) in a stirred cell as well as in bubble columns. The predicted values of k_L have been compared with the experimental values obtained by the chemical method.     

On the importance of some surface and interface characteristics in the formation of the properties of adhesive joints

The importance of some relative surface characteristics which determines the strength of adhesive joints: specific surface of substrate , relative contact area β and specific contact area β in the adhesion interaction process were emphasised. Existing and potential methods of experimental evaluation of these characteristics were shortly analysed. The durability of the adhesive joints in water media significantly increases with growth of specific surface ^* of chemically treated substrate evaluated from the SEM micrographs. Specific surface calculated from the experimental data of hexane adsorption measurements for iron particles (particulate model of steel substrate) is more then ten times greater than respective ^* values. The relative contact area β of the Al₂O₃ particles (in wide range of ) with PE melt was in a roundabout way evaluated by experimental determination of the affect of on kinetic of peel strength formation of adhesive joints: Al₂O₃ filled PE-steel. The speculation was based on the ability of Al₂O₃ to adsorb low-molecular products of contact oxidation of PE which takes place in the process of formation of adhesive joints and determines their strength. The ability of sorption in its turn is proportional to efficient value of β. The availability of the Al₂O₃ surface was evaluated.     

粉煤灰吸附特性研究

在粉煤灰理化特性分析的基础上,对粉煤灰进行了物理激发和化学激发.研究结果表明：物理激发和化学激发均能提高粉煤灰的吸附活性.化学激发方法在反应温度为90℃、反应时间为12h、灰钙比为5、水固比为15时,粉煤灰的吸附活性提高最大.     

磁西勘查区主采煤层煤层气赋存特征

据勘探研究磁西勘查区主采煤层既是煤层气源岩,又是其储集层,煤层有机显微组分以镜质组为主,煤的变质程度为中~高变质的烟煤~无烟煤,生气量较高,为高瓦斯矿区。本区以正断层为主,断层使煤层与泥质岩层接触,具有一定的封闭性。煤层埋深较大,主采2号煤层直接顶板为泥岩、粉砂岩,岩性致密,透气性较差,有利于煤层气资源的保存,从而使煤层气含量升高。     

Analysis of junction temperatures in high-power GaN-based LEDs

We presented the analysis of the incomplete conduction in bonding medium in high power GaN-based light-emitting diode (LED) packages. A numerical study was carried out with parametric model to understand the junction temperature variation due to bonding medium defects. Transient thermal measurement was performed to evaluate LED’s junction temperature. Thermal resistance from chip to lead frame was 20 K/W in our sample LED. It was suggested that only 60% of the surface area of the bonding medium was involved...     

基于多级搜索区域的协同进化遗传算法*

针对传统多种群协同进化算法仍然存在收敛速度慢、计算复杂性不能随进化过程有效降低等问题,提出了一种基于多级搜索区域的协同进化遗传算法,给出了一种衡量种群进化停滞的标准。通过聚类分析将搜索区域划为三个等级,对于较高等级的区域加强搜索粒度,逐步缩小搜索范围,提高了收敛速度并降低了算法复杂度。实验结果表明,该算法是求解最优化问题的一种有效方法。     

高密度电阻率法在采空区探测中的应用

简述了高密度电阻率法的基本原理和资料解释分析的方法.高密度电阻率法是一种具有成本低、效率高、采集信息丰富并且探测精度高的地球物理探测技术.采用高密度电阻率法,结合全站仪测量空间坐标数据进行地形校正,针对采空区的复杂状况,选用不同的极距,在复杂的采空区地表布设了5条测线,完成了3 679个测点的测量.结合测区地质状况和异常的特殊形态,通过数据处理,确定了采空区的分布位置,取得了良好的探测效果,证明了高密度电阻率法在当今工程地质勘察中具有很大的优势.