Cold sintering of α‐alumina using functionalized boehmite: A cost‐effective approach to reduce sintering temperature

A novel cold-assisted sintering process using a combination of functionalized boehmite and α-alumina particles is demonstrated. Functionalized boehmite and α-alumina composites were initially densified using a cold sintering process at <300°C followed by heat treatment at 1400°C‒1450°C (∼200°C‒300°C lower than conventionally sintered α-alumina). Highest relative densities (99%) were achieved using meso-scale α-alumina (D50 = 720 nm) in a 50:50 wt% mixture with boehmite, functionalized in 2 M acetic acid. The high densities at low temperature were attributed to easy propagation of the transformation to α phase within the dense boehmite matrix, accompanied by enhanced nucleation on the surface of the alumina particles. Critical aspects of the transformation sequence from functionalized boehmite to α-alumina were characterized using Raman and Fourier transform infrared spectroscopy. Preliminary hardness measurements were comparable with conventional alumina sintered at ∼1650°C and initial microwave measurements showed promise for the fabrication of high-temperature co-fired ceramic substrates in electronics.