Processing Optimization and Toxicological Evaluation of “Lead-Free” Piezoceramics: A KNN-Based Case Study

Abstract

Due to the ever-increasing limitations of the use of lead-based materials, the manufacturing of lead-free piezoceramics with competitive piezoelectric properties and established nontoxicity is considered a priority for the scientific and industrial community. In this work, a lead-free system based on sodium potassium niobate (KNN), opportunely modified with MgNb2O6 (MN), was prepared through a combination of a mechanochemical activation method and air sintering, and its toxicity was evaluated. The effect of the mechanical processing on the microstructure refinement of the processed powders was established by X-ray diffraction and the average crystallite size content of the Nb2O5 species was evaluated. The experimental evidence was rationalized using a phenomenological model which permitted us to obtain the amount of powder processed at each collision and to optimize the activation step of the pre-calcined reagents. This influenced the final density and piezoresponse of the as-sintered pellets, which showed optimal properties compared with other KNN systems. Their toxicological potential was evaluated through exposure experiments to the pulverized KNN-based pellets, employing two widely used human and environmental cellular models. The in vitro assays proved, under the selected conditions, the absence of cytotoxicity of KNN-bases systems here studied.

Processing, microstructure, electrical properties and cytotoxic behaviour of lead-free 0.99K0.5Na0.5NbO3-0.01BiFeO3 piezoceramics prepared using Spark Plasma Sintering (SPS)

“…[35] Regarding the safety of their powder forms, recently our group evaluated the toxicity of different KNNs with increasing amounts of MgNb2O6 ternary oxide in the same model organisms applied in this work. [15] The results described here using the A549 cells are in line with those obtained on the work cited above, since no effect on their viability was observed.…”

“…[13,14] The toxicological potential of the prepared samples was determined by in vitro screening employing two model organisms that were selected as representatives of human (A549 cell line) and environmental exposures (Saccharomyces cerevisiae), as described in detail elsewhere. [15] The materials under study (SA1, SA2, SA3, SA4 and SA5) and the PZT (commercial reference sample, Meggit Ferroperm PZ26) were smashed in a mortar and sieved (0.125 mm mesh size) to obtain a uniform powder. Stocks of the powder materials resuspended in water at 10 g/L were prepared to carry out the experiments.…”

Low-temperature processing of screen-printed piezoelectric KNbO3 with integration onto biodegradable paper substrates

“…This work shows the first successful fabrication of fully eco-friendly KNbO 3 -based printed piezoelectric devices on green substrates 24,25 . Through careful material selection and the utilisation of printing technologies, the core challenges associated with conventional high-temperature processed Pb-based piezoelectrics are overcome.…”

Sodium Potassium Niobate-Based Piezoelectrics Sintered in Humid Air

“…One of the most common issues with KNN is the lack of reproducibility in the manufacturing at industrial scale [4,9,10]. It is well known that alkali oxides are volatile and prone to evaporate during sintering, limiting the densification and causing formation of secondary phases [4,11].…”