Soft Processing of Hard Ceramics: Viscoelastic h-BN Doughs for Complex Functional Modules

Processing hard ceramic materials into complex three-dimensional architectures generally requires high-temperature sintering, prolonged shaping, or low-throughput additive manufacturing. Here, we present a soft-processing strategy based on highly viscoelastic hexagonal boron nitride (h-BN) doughs that enables rapid, scalable fabrication of complex functional ceramic modules under ambient conditions. The doughs are formulated by combining h-BN platelets, bimodally sized Al2O3 particles, a small amount of polymeric binder, and a percolated p-aramid fiber network. Bimodal particle packing increases the maximum ceramic loading, while the physically interlocked fiber network markedly enhances viscoelasticity, structural recovery, and shape retention with minimal binder content. As a result, the doughs exhibit pronounced deformability under applied stress and solid-like stability after relaxation, allowing precise cold stamping of complex three-dimensional geometries within seconds. The resulting structures show improved dimensional accuracy, mechanical durability, fatigue resistance, and thermal stability over a wide temperature range. They also exhibit high thermal conductivity in both in-plane and through-plane directions and can function as conformal heat-dissipating blocks or predesigned thermally conductive frameworks embedded in polymer matrices. This work demonstrates how colloidal packing and fiber-network assembly can transform hard ceramic particles into processable soft matter, providing a versatile route to large-area, structurally complex, and thermally functional ceramic modules.