Effects of compaction pressure and shrinkage anisotropy on crystallization in SiO₂ nanoparticle-processed fused silica: Experiments and molecular dynamics insights

K s  =  ε axial / ε radial is an experimental index of post-sintering shrinkage anisotropy. • Among the tested pressures, 120 MPa gives near-isotropic shrinkage and the lowest relative crystallinity index. • Larger deviations of K s from unity are associated with greater cristobalite formation. • Seed-assisted MD links stress-component ratio to interfacial ordering near a crystalline seed. Fused silica combines transparency and thermal stability, but conventional melt processing restricts complex shaping. Pressure-assisted near-net shaping of SiO₂ nanoparticles enables high surface quality and geometric complexity, although nonuniform compaction may influence densification and cristobalite formation. In this study, uniaxial thermal imprinting and sintering experiments were combined with seed-assisted enhanced-sampling molecular dynamics (MD). The axial-to-radial shrinkage ratio, Kₛ , quantified shrinkage anisotropy. At 120 MPa, Kₛ  = 0.99 ± 0.01, with near-theoretical density and the lowest relative crystallinity index, whereas larger deviations from unity corresponded to higher crystallinity. Differential scanning calorimetry (DSC) showed a cooling event attributable to the β -to- α cristobalite transition in the 30 MPa specimen. Seed-assisted MD further linked the imposed stress-component ratio to interfacial ordering around the crystalline seed, although direct stress and pore-resolved measurements are required to establish causality. Overall, 120 MPa provided the most favorable overall response among the tested conditions, indicating that shrinkage anisotropy can guide compaction-pressure selection in fused-silica forming. Download: Download high-res image (171KB) Download: Download full-size image