Study On The Surface Modification And Filtration Properties Of DPF Based On Cordierite

Particulate matter filter of diesel engine?DPF?has a high filter efficiency of particulate matter?PM?,which is recognized as the most effective and simple method of diesel particulate matter.But the back pressure in DPF application is still a problem that cannot be ignored.It comes down to an irreconcilable contradiction between the permeability and the filtration precision of the filter,especially the filtration of nano-particles.Therefore,it is still a challenge to achieve efficient and precise filtration of particulate matter in exhaust without sacrificing the permeability of engine exhaust.In this paper,mullite whiskers,aluminum borate whiskers and mullite micron tubes were grown on the surface of cordierite honeycomb ceramic under the influence of respiratory ciliary structure,which aims to improve the filtration performance of cordiera-based DPF on particulate matter.The concrete research contents are as follows:?1?Using TEOS and Al?NO₃?₃·9H₂O as raw materials,mullite whiskers were grown on the surface of cordierite by sol-gel combined with molten salt method,and the effects of different reaction conditions on the whiskers growth were investigated.We found that the optimal growth conditions are as follows:using Na₂SO₄ as the molten salt,the ratio of dry gel powder and molten salt is 1:2,the reaction temperature is 1000?and holding time is 3 h.The cordierite before and after modification was analyzed by XRD,EDS,XPS and specific surface area respectively.The results showed that:The element composition of cordierite is different from that of whiskers and the whisker component is mullite,the ratio of atomic number of Al,Si and O is 3:1:6.7,which happens to be the ratio of mullite?3Al₂O₃·2SiO₂?.The total pore volume and specific surface area of cordierite increased by 10times and 34 times respectively.?2?Using borax and ammonium aluminum sulfate as raw materials,aluminum borate whiskers were grown on the surface of cordierite by co-precipitation combined with molten salt method,and the effects of different reaction conditions on the whiskers growth were investigated.We found that the optimal growth conditions are as follows:using Na₂SO₄ as the molten salt,the ratio of powders and molten salt is 1:6,the reaction temperature is 1050?and holding time is 3 h.The cordierite grown with whiskers was analyzed by XRD,EDS,XPS and specific surface area respectively.The results showed that the element composition of cordierite and whiskers were different.The whisker composition was aluminum borate?9Al₂O₃·2B₂O₃?,and the atomic ratio of Al,B and O was 19.5:4:34.The total pore volume and specific surface area of cordierite increased by 9 times and 27 times respectively.?3?Using TEOS,crystal aluminium chloride,ether as raw material,mullite micron tube were grown on the surface of cordierite by sol-gel combined with molten salt method.The cordierite grown with micron tube was analyzed by XRD,EDS,XPS and specific surface area respectively.The results showed that:the micron tube component is mullite,the ratio of atomic number of Al,Si and O is 3:1:6.6,which happens to be the ratio of mullite?3Al₂O₃·2SiO₂?.The total pore volume and specific surface area of cordierite increased by 22times and 57 times respectively.We found that ether plays an important role on the hollow structure of micron tube,and the infrared analysis for the intermediate product verified this conjecture.Thus,the growth mechanism of the hollow structure of the micron tube on cordierite was revealed:diethyl ether may have an influence on the diffusion path of the raw material in the mass transfer droplets.The raw materials SiO₂ and Al₂O₃ start to separate out when they diffuse to the contact angle between the droplet and the matrix,and then grow to form a hollow structure.?4?A flue gas filtration performance test platform was set up in order to investigate the PM filtration performance of cordierite ceramic which before and after modification.Results show that the filter efficiency of modified cordierite honeycomb ceramics has increased significantly than unmodified cordierite when the carbon concentration at 0.10mol/L,0.15mol/L,0.20mol/L.The filtration efficiency of cordierite honeycomb ceramics was about70%.The filtration efficiency of cordierite grown with mullite whiskers was similar to that grown with aluminum borate whiskers but the former was slightly higher,and the filtration efficiency were both around 80%.The filtration efficiency of cordierite grown with mullite micron tubes was much higher,around 90%.