Preparation of Si3N4 foams by DCC method via dispersant reaction combined with protein-gelling

A novel forming method for preparing Si3N4 foams by DCC method via dispersant reaction combined with protein-gelling was proposed. Si3N4 foams were fabricated through temperature-induced hydrolysis of sodium tripolyphosphate (STPP) dispersant and simultaneous thermal gelling of ovalbumin binder at elevated temperature above 75 degrees C, with subsequent pressureless sintering at 1700 degrees C for 2 h. Stable Si3N4 suspension of 35 vol% solid loading with 0.5-2.0 wt% ovalbumin addition was obtained by adding 0.2 wt% STPP at alkaline region and room temperature. The controlled coagulation of the suspension could be realized after treating at 75 degrees C for around 1 h. Homogeneous composition distribution of Y and Al elements in EDS result indicated the uniform dispersion of sintering additives in green bodies, which was beneficial for the liquid phase sintering at high temperature. Typical spherical pore structure ranging from 110 to 320 mu m formed due to the ovalbumin foaming capability and elongated beta-Si3N4 crystalline grains generally over 3 mu m were observed in sintered Si3N4 ceramic foams. Finally, Si3N4 ceramic foams with porosities ranging from 65.5 +/- 1.5% to 80.8 +/- 1.0% and compressive strength from 9.7 +/- 0.9 MPa to 17.5 +/- 1.2 MPa were obtained. The result indicated that the novel preparation approach in combination with DCC method and protein-gelling could be a convenient and environmentally friendly route to prepare various ceramic foams with high porosity and excellent material homogeneity. (C) 2018 Elsevier B.V. All rights reserved.