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The gel casting method was used for the production of Si3N4 porous ceramics with 25 vol% solid loading, and the effect ofadding 1 and 3 wt.% of BN whisker-like (synthesized in the laboratory) on the flexural strength of the composites wasinvestigated. The gel-cast samples were prepared using an AM-MBAM monomer system and deionized water solvent. The gelcast bodies were dried at ambient temperature and humidity for 48hrs. The burnout process was carried out at 600 oC for14hrs in the air. The samples were then subjected to heat treatment at 1650 oC for 2 hrs in a bed of 50% Si3N4-50% BN. Resultsshowed that BN whisker-like were agglomerated in deionized water. To solve this problem and to properly disperse thewhisker-like in the slurry, active surface agent groups were employed. Adding BN whisker-like to ceramic bodies, increasedthe porosity from 33% in samples without BN to 46% in samples containing 3 wt% BN whisker-like, resulting in a decreasein the density from 1.8 g/cm3 to about1.61 g/cm3. Since the Si3N4 ceramics require aids for the sintering, SiO2 and Y2O3additives were used with a ratio of 1 to 2, respectively, which led to the formation of Si2N2O phase. Si2N2O is similar to theSi3N4 phase in terms of the thermal expansion coefficient and chemical properties. Because of its rod shaped morphology, ithas a similar function to β-Si3N4 phase in improving the mechanical properties of the ceramic. Although porosity in theceramics containing 3 wt.% BN whisker-like was higher than those containing 1 wt.%, the porosity created vacant spaces forfurther growth of Si2N2O-rod shaped grains and in spite of higher porosity, better flexural strength was achieved for bodieswith 3 wt.% BN whisker-like. Also, in bodies without BN whisker-like, the flexural strength was 88 MPa, due to the lowporosity and the presence of stretched Si2N2O grains.
