Preparation And Properties Of Filtering Ceramics For High Temperature Exhaust Gas

The objective of this dissertation is to study the preparation and properties of filtering ceramics for high temperature exhaust gas, the effects of gel-cast-foaming method and space-holder method on the properties were systematically examined for the filtering ceramics. The low linear expansion of SiO₂-Al₂O₃-K₂O-Li₂O system as combination agent andβ-cordierite as base material were determined to prepare the filtering ceramics.The effects of the solid loading, dispersant kind, dispersant content, pH value, milling time and gelling agent content on the suspension rheological properties were researched in detail. The experimental results indicate that the STTP (sodium tripolyphosphate) dispersant is better than PAAS (polyacrylate sodium) on the dispersion effect, and its optimal content is 1.2wt%. The slurry with the high solid loading of 58wt% can be prepared, and can satisfy with the gel-cast-foaming requests through the recipe optimizing. The effects of firing process on the properties were examined for the filtering ceramics. It was found that the filtering ceramics of high combination properties was obtained at the firing temperature 1235℃for 30 min.The gel-cast-foaming method is difficult to realize large-scale industrial production due to its complex process and high cost, the space-holder method was mainly discussed in this dissertation. The effects of the foaming agent and combination agent on the apparent porosity and compressive strength were quantitatively examined for the filtering ceramics by space-holder method. The experimental results indicate that the apparent porosity for filtering ceramics will increase with the increasing of porous agent, but will decrease with more combination agent; the compressive strength for filtering ceramics will decrease with the increasing of foaming agent, but will increase with more combination agent. The basic recipe for the space-holder-method was established as following: cordierite 75 wt%, combination agent 25 wt%, pore-forming agent 50wt %.The processing parameters such as milling time, molding pressure, sintering temperature and sintering time were optimized with the orthogonal experiments, the optimized condition were the molding pressure 6 MPa, sintering temperature 1250℃, sintering time 15 minutes. The high compressive strength and apparent porosity of filtering ceramics were prepared in these optimized conditions, the compressive strength 15.9MPa, apparent porosity 57.9% and thermal shock resistance (1000-25℃) can reach up to 10 times with no crack.The filtration properties of filtering ceramics made by gel-casting-foam method and space-holder method were also compared in this thesis. The results showed that the relationship between filter resistance and wind velocity for filtering was in positive linear correlation; the filter resistance and gas permeability of filtering ceramics made by gel-casting-foam method were better than the one that made by space-holder-method, but the efficiency for filtering bug dust from thermal power plant both can reach 99%.