Impact of alumina powder bed on hardness and fracture toughness in the sintering process of NiO-GDC-Bi2O3 composite prepared by sol-gel method

This study explores the sintering process of NiO-Ce0.9Gd0.1O1.95 + 35 wt% Bi2O3 ceramic composites synthesized via the sol-gel method, with a focus on the influence of an alumina powder bed during sintering. Uniaxially pressed disks were sintered at 890 degrees C for varying durations (0, 12, 24, and 61 h), with an additional disc sintered at 1450 degrees C for 6 h for comparative analysis. Sintering processes employed alumina as a powder bed, and subsequent evaluation included hardness and fracture toughness assessments. Relative densities of 53% and 48% were achieved for composites sintered at 890 and 1450 degrees C, respectively. The maximum hardness of 4.13 +/- 0.13 GPa was attained by the composite sintered at 890 degrees C for 61 h, while the highest fracture toughness (2.98 +/- 0.35 MPa.m(1/2)) was observed in the composite sintered at 1450 degrees C for 6 h. Evidence indicates that an interaction between Bi2O3 and the alumina bed occurred, adversely affecting the mechanical properties by promoting the depletion of Bi2O3, especially at elevated sintering temperatures. [GRAPHICS] .