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

TLDR

Co‑sintering high‑ceramic‑volume composites is difficult because ceramics and polymers require vastly different sintering temperatures. The study introduces the cold sintering process (CSP) to overcome these processing limitations. CSP uses a transient low‑temperature solvent to dissolve and precipitate ceramics, enabling densification of ceramics and polymers between room temperature and about 200 °C into dense composites. The authors demonstrate CSP on three diphasic composites—Li₂MoO₄–(C₂F₄)n, Li₁.₅Al₀.₅Ge₁.₅(PO₄)₃–(CH₂CF₂)x[CF₂CF(CF₃)]+y, and V₂O₅–poly(3,4‑ethylenedioxythiophene) polystyrene sulfonate—showing its versatility and potential to transform mechanical, thermal, and electronic composite processing.

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 Li 2 MoO 4 –(C 2 F 4 ) n , electrolyte Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 –(CH 2 CF 2 ) x [CF 2 CF(CF 3 )] y , and semiconductor V 2 O 5 –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.