Steel slag-KNO3 phase change composites for thermal storage at medium-high temperature and solid waste recycling

Phase change composites (PCCs) have broad applications in thermal energy storage systems. In this work, we fabricated a series of steel slag-KNO3 PCCs by mixed sintering, which can be used in the medium-high tem-perature TES system and have the advantages of solid waste resource utilization. The composite's properties were characterized by determining their compressive strength, Young's modulus, latent heat, thermogravimetric performance, thermal conductivity, and cyclic thermal stability. The results suggested that the steel slag-KNO3 PCCs possessed good mechanical and thermal properties. When the KNO3 contents ranged from 38 wt% to 50 wt %, the composites maintained high compressive strength (30-35 MPa) and Young's modulus (1600-1700 MPa). The composites with 50 wt% KNO3 exhibited a latent heat of 43 J/g in 300-350 degrees C and a thermal conductivity of about 0.68 W m-1 K- 1. The steel slag-KNO3 PCCs also presented excellent cyclic thermal stability. After 48 thermal cycles, the composite's latent heat decreased slightly by 2.5-3.7 J/g, and the thermal conductivity increased by 16%-25% compared with that of composites before thermal cycling. This study has important guiding significance for developing medium-high temperature PCCs with low cost and high performance used in TES systems, and may provide a new path for the utilization of solid waste resources.