Silicon nitride honeycomb filter and method for its production

Abstract

A method for producing a silicon nitride honeycomb filter, which comprises heat-treating in a nitrogen atmosphere a green body comprising from 50 to 85 mass % of metal silicon particles having an average particle diameter of from 5 to 50 μm, from 5 to 30 mass % of glass hollow particles having a softening temperature of from 400 to 1000° C. and from 10 to 20 mass % of an organic binder to convert metal silicon substantially to silicon nitride.

1 . A method for producing a silicon nitride honeycomb filter, which comprises heat-treating in a nitrogen atmosphere a green body comprising from 50 to 85 mass % of metal silicon particles having an average particle diameter of from 5 to 50 μm, from 5 to 30 mass % of glass hollow particles having a softening temperature of from 400 to 1000° C. and from 10 to 20 mass % of an organic binder to convert metal silicon substantially to silicon nitride.  
     
     
         2 . The method for producing a silicon nitride honeycomb filter according to  claim 1 , wherein as the glass hollow particles, glass hollow particles having an average diameter of from 20 to 60 μm are used.  
     
     
         3 . The method for producing a silicon nitride honeycomb filter according to  claim 2 , wherein as the glass hollow particles, glass hollow particles having an apparent specific gravity of from 0.2 to 0.8 are used.  
     
     
         4 . The method for producing a silicon nitride honeycomb filter according to  claim 2 , wherein glass of the glass hollow particles is soda lime borosilicate glass, soda lime glass or borosilicate glass.  
     
     
         5 . The method for producing a silicon nitride honeycomb filter according to  claim 2 , wherein the heat-treating conditions are such that heat treatment of a first stage is carried out by maintaining the green body in a nitrogen atmosphere at a temperature of from 1200 to 1400° C. for from 3 to 24 hours, and then, heat treatment of a second stage is further carried out by maintaining it at a temperature within a range of from 1500 to 1800° C. for from 1 to 12 hours.  
     
     
         6 . The method for producing a silicon nitride honeycomb filter according to  claim 5 , wherein as the glass hollow particles, glass hollow particles having an apparent specific gravity of from 0.2 to 0.8 are used.  
     
     
         7 . The method for producing a silicon nitride honeycomb filter according to  claim 5 , wherein glass of the glass hollow particles is soda lime borosilicate glass, soda lime glass or borosilicate glass.  
     
     
         8 . The method for producing a silicon nitride honeycomb filter according to  claim 5 , wherein the temperature raising rate during the heat treatment is from 50 to 600° C./hr.  
     
     
         9 . The method for producing a silicon nitride honeycomb filter according to  claim 5 , wherein the nitrogen partial pressure in the nitrogen atmosphere is at least 50 kPa.  
     
     
         10 . The method for producing a silicon nitride honeycomb filter according to  claim 1 , wherein the volume blend ratio of the metal silicon particles and the glass hollow particles is such that the metal silicon particles are from 40 to 65 vol % and the glass hollow particles are from 35 to 60 vol %.  
     
     
         11 . A silicon nitride honeycomb filter wherein the average pore diameter is from 10 to 30 μm as measured by a mercury immersion method, the sum of pore volumes of pores having pore diameters of at least 5 μm is at least 70% of the sum of pore volumes of all pores, and the porosity is from 60 to 80%.