Dielectric behavior of FLASH sintered KNN

The market for lead-based piezoceramics, mainly (Pb1-x ZrxTiO3, PZT) - based materials, is higher than $100 billion per year. Due to lead-toxicity, the demand for lead-free piezoceramics is increasing. Potassium Sodium Niobate solid solutions, namely K0.5Na0.5NbO3, KNN, is currently one of the most promising materials for electromechanical applications. However, monophasic conventionally sintered KNN is hard to obtain, due to alkali evaporation during sintering (T\u3e 1100 ºC, t \u3e 2h). Within this context, there is an increasing interest in sustainable sintering techniques, as FLASH, to decrease both sintering time and temperature, avoiding alkali vaporization. However, FLASH applied to bulk ceramics, frequently produces inhomogeneous specimens. Figure 1 – Variation of length with temperature of FLASH sintered KNN, after a 2 h isothermal step. SEM micrograph showing the uniformly dense microstructure. In this work, we propose an experimental approach that allows the production of homogeneous, highly dense, KNN. In this method, the use of FLASH sintering contributed to reduce KNN sintering temperature for more than 200 ºC and the cycle time in ~3h. Uniform densification was achieved by using an isothermal step before the application of the electric field. Scanning Electron Microscopy (SEM) and Specific Surface Area (SSA) measurements were performed to characterize the pre-FLASH sintering microstructure. Please click Additional Files below to see the full abstract

Modeling of Joule heating in KNN FLASH sintering

In this work, we propose the use of FLASH sintering as an alternative technique to densify Potassium Sodium Niobate, K0.5Na0.5NbO3, KNN, a piezoceramic with relevant promising applications and a possible viable substitute of lead zirconate titanate based compositions (Pb1-x ZrxTiO3, PZT). We aim to increase this material performance by densifying KNN ceramics without secondary phase segregation. Furthermore, FLASH will contribute to a more sustainable processing of piezoelectrics as lead-free ceramics at reduced sintering temperature and time. Please click Additional Files below to see the full abstract

Exploitation of industrial application of FLASH to sinter ceramics

FLASH is an electric field-assisted sintering technique recently proposed to densify materials in a more sustainable, energy reductive and cost-effective way than conventional sintering (CS). FLASH sintering promotes the densification of materials by using a combination of temperature and electric field. The use of electric field allows a decrease in the sintering temperature, and as important as well, in the sintering cycle duration. The advantages of FLASH, when compared with other field-assisted techniques, are: low investment, no need for specific atmosphere and dies, and specimen shape versatility. Please click Additional Files below to see the full abstract