Porous Si3N4 and producing method thereof

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A producing method of a porous Si3N4 having high porosity and formed of Si3N4 particles having a high aspect ratio includes the following steps. A compound of a rare earth element as a first sintering agent is mixed in an amount of 7.5-45 parts by mass, in terms of an oxide of the element, with respect to 100 parts by mass of Si powder to obtain mixed powder. A binder is added to the mixed powder, which is then molded into a molded body. The molded body is heated in a nitrogen atmosphere to 300-500°C to remove the binder. The binder-removed body is heated in a nitrogen atmosphere to 1350-1500°C for nitriding. The nitrided body is then sintered at 1750-1900°C at a nitrogen pressure of 0.1-1 atmosphere.