Fabrication and Evaluation of β-SiAlON Nanoceramics

β-SiAlON nanoceramics were fabricated from β-SiAlON nano powder using the spark-plasma sintering (SPS) technique. The β-SiAlON nanopowder (Si4Al2O2N6) was synthesized from a mixture of SiO2 (QS-102, Tokuyama Co., Japan), AlOOH (Tomita, Japan) and C (Mitsubishi Chemical, Japan) using the carbothermal reduction nitridation (CRN) method. The heating rate for SPS was 50
/min. The β-SiAlON nanoceramics had high strength (500 MPa). TEM observation showed that the intergranular glassy phase was scarcely present at the grain boundary of the β-SiAlON nanoceramics. Aqueous corrosion resistance was evaluated by measuring the weight loss after soaking in 5 and 35 wt.% H2SO4aq. and 5 wt.% HNO3aq. at 80
for 100 h. It was found that β-SiAlON nanoceramics have much higher corrosion resistance than commercialized silicon nitride ceramics in acid solutions. Commercialized Si3N4 ceramics have an intergranular glassy phase created as a result of the sintering aids in them. Thus, they are easily corroded by acid solutions because the intergranular glassy phase is easily corroded under such conditions. The excellent corrosion resistance of the β-SiAlON nanoceramics stems from their glass-free grain boundaries, since the β-SiAlON nanoceramics were produced without using a sintering aid.