Porous Silicon Nitride Ceramics with High Performance for Diesel Exhaust After-Treatment System

Diesel Particulate Filter (DPF) has become a standard after treatment device to remove particulate matter (PM) exhausted from diesel engines. Cordierite and Silicon Carbide are commonly used materials for construction of DPF. Customers, however, require further improvement concerning the performance of DPF. Cordierite has low limitation of PM loading capacity due to its lower thermal shock resistance, while silicon carbide has higher back-pressure due to its larger grain size. Generally, silicon nitride which is one of the typical thermal resistant ceramics has high mechanical strength and thermal shock resistance. Kubota's development of porous silicon nitride is structured with controlled small grain crystals of elongated hexagonal systems. This enables high PM filtration efficiency with low back pressure increase and higher filtering efficiencies for smaller PM. Also, due to its unique micro-structure, a larger amount of wash-coating of catalysts can be applied with lower back pressure increase than conventional materials. A higher capacity of wash-coating of a catalyst support provides the possibility of superior catalyst efficiency with a lower amount of precious metals used as active components of the catalyst. Concerning the manufacturing cost, silicon nitride provides another advantage, as a one body design DPF can be manufactured. According to its physical properties, the thermal stress level during operation is the same level as cordierite. In conclusion, this paper indicates the high performance of silicon nitride ceramics for the application of DPF substrate and its exceptional commercial value.