Cold Sintering Process of Composites: Bridging the Processing Temperature Gap of Ceramic and Polymer Materials

Abstract

Co‐sintering ceramic and thermoplastic polymer composites in a single step with very high volume fractions of ceramics seems unlikely, given the vast differences in the typical sintering temperatures of ceramics versus polymers. These processing limitations are overcome with the introduction of a new sintering approach, namely “cold sintering process” (CSP). CSP utilizes a transient low temperature solvent, such as water or water with dissolved solutes in stoichiometric ratios consistent with the ceramic composition, to control the dissolution and precipitation of ceramics and effect densification between room temperature and ≈200 °C. Under these conditions, thermoplastic polymers and ceramic materials can be jointly formed into dense composites. Three diphasic composite examples are demonstrated to show the overall diversity of composite material design between organic and inorganic oxides, including the microwave dielectric Li2MoO4–(C2F4 ) n , electrolyte Li1.5Al0.5Ge1.5(PO4)3–(CH2CF2 ) x [CF2CF(CF3)] y , and semiconductor V2O5–poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate composites. Cold sintering is more general and shall have a major impact on the processing of composite materials for many different applications, mechanical, thermal, and electronic, to mention a few possibilities. CSP concepts open up new composite material design and device integration schemes, impacting a wide variety of applications.

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

“…Large reduction of the sintering temperature using water as sintering aid has also been reported by the recently labelled "cold sintering process" [17][16] [18]. 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.…”

“…All these studies suggest that the presence of water can, under given conditions, strongly reduce the sintering temperature of oxide powder compacts, by partial dissolution of the particles and subsequent precipitation, synthesis reaction or the diffusion of ions from the water molecules into the crystal structure [17][14] [24]. Nevertheless, more fundamental investigations are required that is also the scope of the present paper.…”

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

“…35,36 However, this mechanism is not applicable for the densification of ceramics owing to the brittle nature of these materials. 37,38 Furthermore, it should be pointed out that our facility to perform the Cold Sintering Process is extremely simple, compared to other sintering techniques that are built upon sophisticated components, such as MVS, FS, SPS, and HPS. We have successfully demonstrated its feasibility to sinter over 50 inorganic compounds in our laboratory at incredibly low temperatures of 25°C-300°C within a short time period of 1-60 min.…”

Ceramic–Salt Composite Electrolytes from Cold Sintering

“…[9,12,[14][15][16][17] Such a sintering process has obvious limitations, including Li loss, impurity phase formation, incompatibility with organic materials, difficulties in integrating all-solid-state batteries with composite cathodes, and high processing cost. [18,[20][21][22][23] As a consequence, ceramics such as alkali molybdates, BaTiO 3 , and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) can be sintered at a temperature that is an order of magnitude lower than through conventional means. [18,[20][21][22][23] As a consequence, ceramics such as alkali molybdates, BaTiO 3 , and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) can be sintered at a temperature that is an order of magnitude lower than through conventional means.…”

“…[18,[20][21][22][23] As a consequence, ceramics such as alkali molybdates, BaTiO 3 , and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) can be sintered at a temperature that is an order of magnitude lower than through conventional means. [21] Although densification of LAGP and LAGP composites is achieved at 120 °C to densities of 85% using water as a transient solvent, cold sintered solid electrolytes have low [21] Although densification of LAGP and LAGP composites is achieved at 120 °C to densities of 85% using water as a transient solvent, cold sintered solid electrolytes have low…”