Engineering Research Equipment Grant: Acquisition of a Pore Structure Characterization System

固体产物的气固反应在许多化学过程工业中都遇到过，应用范围从陶瓷材料制造到污染控制的气体洗涤。由于固体产物的形成，在研究这类反应时，除了质量和热传递以及化学反应外，还必须考虑许多其他过程。这些过程大多与固体形态的演变有关，因为固体产物的形成和反应物质通过形成的固体产物层的扩散。如果固体产物在化学计量上比它产生的固体反应物占据更多的体积，则可能出现孔堵塞现象，从而导致不完全转化。由于不同大小的孔隙在不同的时间被堵塞——孔隙越小，越早被堵塞——反应颗粒的瞬态行为通常不仅取决于多孔煅烧固体的平均结构特性(即，内表面积和孔隙率)，但孔径分布的形式，以及，即使在反应条件下的特点是可以忽略不计的颗粒内浓度梯度。在存在显著的颗粒内扩散限制的情况下，具有孔闭合行为的气固反应的总体情况变得相当复杂。如果颗粒外表面的反应速率远远高于内部的反应速率，则可能在颗粒外表面完全关闭孔隙，而内部仍有开放空间。这种情况会导致最终转化率远远低于完全堵塞内部空间的化学计量学所预测的转化率。基于这些观察，pi正在实验研究与固体产物气固反应。此设备拨款用于能够确定任何固体材料的物理微观结构的自动化实验室系统。它是用来阐明加工条件对固体产物和反应物微观结构性质的影响及其对气固反应体系行为的影响。具体来说，该设备是一个自动化的汞孔隙度计，配有适当的硬件和软件，用于数据采集和分析。该系统将用于分析一些涉及粉末和多孔介质的实验项目的固体样品，包括：(1)金属氧化物与硫化氢和二氧化硫的反应，用于控制煤炭利用系统的污染物排放；(2)化学蒸汽渗透制备陶瓷基复合材料时多孔预制品的致密化；(3)使用粉末材料技术制造金属和陶瓷复合材料所涉及的粉末和粉末压块（新鲜或部分烧结）的表征。

Gas-solid reactions with solid product are encountered in a number of chemical process industries with applications ranging from ceramic material manufacture to gas scrubbing for pollution control. Because of the formation of the solid product, a number of other processes must be considered in the study of this type of reactions in addition to mass and heat transport and chemical reaction. Most of these processes are related to the evolution of the morphology of the solid because of the formation of the solid product and the diffusion of the reactive species through the formed layer of solid product. If the solid product occupies stoichiometrically more volume than the solid reactant from which it results, phenomena of pore plugging and, as a result, incomplete conversion may arise. Since pores of different size are expected to be plugged at different times - the smaller the pores, the earlier they will be plugged - the transient behavior of the reacting particles should in general depend not only on the average structural properties of the porous calcined solid (i.e, internal surface area and porosity) but on the form of the pore size distribution as well, even under reaction conditions characterized by negligible intraparticle concentration gradients. In the presence of significant intraparticle diffusion limitations, the overall picture of a gas-solid reaction with pore closure behavior becomes considerably more complex. If the reaction rate at the external surface of the particles is much higher than that in the interior, complete pore closure may take place at the external surface while there is still open space left in the interior. Such an event can lead to ultimate conversions much lower than those predicted by the stoichiometry of the reaction for complete plugging of the internal space. Based on these observations, the PIs are experimentally studying gas-solid reactions with solid product. This equipment grant is for an automated laboratory system capable of determining the physical microstructure of any solid material. It is to be used to elucidate the effects of processing conditions on the microstructural properties of solid products and reactants and their effects on the behavior of gas-solid reaction systems. Specifically the equipment is an automated mercury porosimeter with appropriate hardware and software for data acquisition and analysis. The system will be used to analyze solid samples for a number of experimental projects involving powders and porous media including: (1) reactions of metal oxides with hydrogen sulfide and sulfur dioxide employed to control pollutant emissions from coal utilization systems, (2) densification of porous preforms in manufacturing ceramic matrix composites by chemical vapor infiltration, and (3) characterization of powders and powder compacts (fresh or partially sintered) involved in the fabrication of metal and ceramic composites using powdered material techniques.