Sodium as densification aid in MgAl2O4 nanoceramics

Abstract

• Na + reduces the pressures needed for densification of MgAl 2 O 4 nanoceramics. • Fully dense Na-doped MgAl 2 O 4 with grain sizes below 15 nm were produced. • The samples showed toughness of 5.2 MPa/m 1/2 and hardness > 24 GPa. Magnesium aluminate nanoceramics show superior hardness due to an extension of the Hall-Petch relationship down to grain sizes below 10 nm. However, the manufacturing of nanoceramics with such exceedingly small grains constitutes a significant challenge. This work proposes sodium as an effective dopant to reduce the processing requirements to achieve full densification with inhibited coarsening. Using Spark Plasma Sintering, we produced fully dense transparent Na-doped MgAl 2 O 4 under 400 MPa at 1000 °C with grain sizes below 15 nm. Na-doped samples achieved indentation fracture toughness (K 1C ) as high as 5.23 MPa/m 1/2 , surpassing values characteristic of undoped MgAl 2 O 4 with a similar grain size, 3.57 MPa/m 1/2 . The role of Na + as a sintering aid is briefly discussed.