Fabrication of in-situ self-reinforced Si3N4 ceramic foams for high-temperature thermal insulation by protein foaming method

Abstract

To meet demand for lightweight and high-strength ceramic foams, in-situ self-reinforced Si3N4 ceramic foams, with compressive strength of 13.2–45.9 MPa, were fabricated by protein foaming method combined with sintered reaction-bonded method. For comparison, ordinary protein foamed ceramics with irregular block microstructure were fabricated via reaction-bonded method, which had compressive strength of 3.6–20.5 MPa. Physical properties of these two types of samples were systematically compared. When open porosity was about 80%, both types of Si3N4 ceramic foams had excellent thermal insulation properties (<0.15 W m−1 K−1), while compressive strength of in-situ self-reinforced samples increased by more than 158% compared with ordinary samples. Under high-temperature oxidation conditions, microstructures of both types of samples were deformed with increase in oxidation temperature. Moreover, after oxidation temperature was increased to 1400 °C, oxidation weight gain decreased from 18.07% for ordinary samples to only 2.18% for self-reinforced samples. Thus, high-temperature oxidation resistance of Si3N4 ceramic foams was greatly improved.