Cold Sintering Process: A Novel Technique for Low‐Temperature Ceramic Processing of Ferroelectrics

Abstract

Research on sintering of dense ceramic materials has been very active in the past decades and still keeps gaining in popularity. Although a number of new techniques have been developed, the sintering process is still performed at high temperatures. Very recently we established a novel protocol, the “Cold Sintering Process (CSP)”, to achieve dense ceramic solids at extraordinarily low temperatures of <300°C. A wide variety of chemistries and composites were successfully densified using this technique. In this article, a comprehensive CSP tutorial will be delivered by employing three classic ferroelectric materials (KH2PO4, NaNO2, and BaTiO3) as examples. Together with detailed experimental demonstrations, fundamental mechanisms, as well as the underlying physics from a thermodynamics perspective, are collaboratively outlined. Such an impactful technique opens up a new way for cost‐effective and energy‐saving ceramic processing. We hope that this article will provide a promising route to guide future studies on ultralow temperature ceramic sintering or ceramic materials related integration.

Unveiling the mechanisms of cold sintering of ZnO at 250 °C by varying applied stress and characterizing grain boundaries by Kelvin Probe Force Microscopy

“…However, CSP was carried out under larger contents of water (4 -30 wt.%) and the related mechanisms were hypothesized as solution-precipitation liquid-phase assisted sintering. Due to the low temperature and the precipitation phenomena of an amorphous phase, CSP often requires a further annealing treatment at higher temperature (~ 700 -900 °C) to crystallize the ceramic compound [19]. Nevertheless, this further thermal treatment was not required for the ZnO [20].…”

“…According to the low sintering temperature used in the present FAST/SPS experiments and the recently proposed CSP [19], the same compositions were consolidated under similar conditions using a warm-press hand pressing with a heater holder. The uniaxial pressure was kept at 150…”

“…The moistened ceramics pellets were obtained either by mixing the power with water (typically 4-25 wt.%, i.e. even higher volume content) or storing the powder into a humidity chamber [19], as in [13]. The drastically reduced temperatures enable to use simple warm hand press equipment with a heater holder, which is for sure an advantage.…”

“…CSP is thought to be based on liquid phase sintering mechanisms -particle rearrangement and dissolutionprecipitation stages -, which creates a supersaturated environment and enables a fast precipitation process on the particle surfaces to reach the final densification. Nevertheless, for some materials like zirconia, CSP is more a compaction process than sintering, and a further thermal treatment at higher temperature is required to fully crystallize the material [19] [21].…”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…Two‐dimensional ceramics possess characteristics that make them scientifically interesting and potentially useful. For example, enhanced transport properties in two‐dimensional ceramics can enable energy storage devices and may play a role in cold sintering . The rich catalytic properties of two‐dimensional ceramics enable reactions that are important for the production and utilization of solar fuels .…”