Structure And Performance Research Of The Mullite Fiber Network Used As The Diesel Engineer Gas Filter

Ceramic fiber web has been widely used as the diesel particulate filter because of their mechanical,thermal and chemical stability.With the time increasing the diesel exhaust particles accumulated in the filters,which seriously affected the property of diesel engineer.The common method was to load catalyst on the filter material,which can make soot particles oxidative decomposition at lower temperature in order to make the filter regeneration.However,the catalyst particles agglomerated on the surface of fibers easily which would reduce the soot-catalyst contact surface area and largely reduce the catalytic activity.In order to load the catalyst on the surface of fiber homogeneously,herein three fiber webs(N-mullite,P-mullite and W-mullite)with different hierarchical structures were prepared by pump filtration method.The filtration efficiency,mechnical stability and soot oxidation activity were measured.The secondary structures assembled on the mullite fiber changed the pores structures insider the fiber filters,which increased the filtration efficiency of the ultrafine particles.(As for 0.1~0.3um particles,the filtration efficiency increased from 23.35%(N-mullite fiber web)to64.94%(P-mullite fiber web)and 91.59%(W-mullite fiber web))?Moreover,the hierarchical structures also increased a lot of new specific surface areas inside the filter,which not only increased the dosage of catalyst greatly(increased from 9.49%(N-mullite fiber web)to 12.22%(P-mullite fiber web)and 13.48%(W-mullite fiber web)),but also increased the number of catalyst-soot contact points which improve the soot oxidation activity(the soot oxidation begins temperature in W-mullite fiber web was 434~oC similar with 443~oC in P-mullite fiber web and both lower than 473~oC in N-mullite fiber web in large extent).In the room temperature,the limit deformation of the whisker/fiber network was 2 times than the N-mullite fiber network and increased to 2.5 times at elevated temperature.The plastic deformation of the fiber network assembled with secondary structures made the network integrity when the stress reached to the limit,which made the structures hold mechanical stability.In this article the principle of the secondary sturcture growth were also discussed.the mullite grains on the fibers surface acted as the nucleation seeds,that`s why the mullite whisker preferred to grow on the surface of the mullte fiber.Moreover,the fluorinion accelerated the process of reaction.The growth of the secondary structures follow the gas-phase reaction mechanism,the saturated vapor pressure of the active gas can influence the crystal morphology in large extent.Increasing the reaction temperature and changing the ratios of active powder and mullite fiber could increase the pressure of the reactive gas which changed the structure of whisker and produced the corundum plates.