Strengthening of hollow glass microspheres via a new K2CO3-KOH-activated ion-exchange strategy

Abstract

Hollow glass microspheres (HGMs) are lightweight fillers with potential applications in construction materials, but their limited compressive strength hinders widespread use. This study proposes a new strengthening strategy for HGMs by ion exchange treatment of K⁺ with Na⁺. HGMs were treated in different molten salts at 520–600 °C for 1–6 h, and their compressive strength, density, moisture content, buoyancy, and microstructure were systematically studied. The compressive strength of HGMs in a mixed melt of KNO₃-0.5 wt% KOH-3 wt% K₂CO₃ reached a high value of 112 MPa after heating at 580 °C for only 3 h, compared to 80 MPa in pure KNO₃ after 24 h. Extended treatment caused some HGMs to fracture, reducing floatation and increasing density. Elemental analysis, including surface phase composition and cross-sectional distribution, confirmed the successful ion exchange of Na⁺ and K⁺. Increased densification of the HGMs formed a compressive stress layer on their thin walls, inhibiting crack extension and enhancing compressive strength. Overall, adjusting ion exchange parameters improved the compressive strength of HGMs, making them suitable for high-performance applications in aerospace, automotive, and marine engineering. Future efforts will aim to reduce costs or incorporate acid etching to improve surface stability and minimize material loss during strengthening.