Microstructural improvement of solar salt based MgO composites through surface tension/wettability modification with SiO2 nanoparticles

Argyrios Anagnostopoulos*, M. Elena Navarro, Yulong Ding

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Composite phase change materials (CPMCs) are of particular interest in high-temperature thermal energy storage and waste heat utilization applications. To further enhance their thermal conductivity, CPCMs are often doped with nanosized particles (NPs). However, NP's influence the PCM's viscosity and wettability, significantly contributing to the CPCM's microstructure. Their effects on the PCM's viscosity have been extensively documented, but little has been done on its effect on wettability. To this end, we investigated, using a custom maximum bubble pressure tensiometer, the surface tension of the solar salt, as well as its contact angle on an MgO {1 0 0} surface with various concentrations of α-SiO2 NPs. At 0.5 wt%, an increase of 2.45% on the surface tension is observed, scaling up to 11.8% at 2.5 wt%. Contrary to the pure salt, in the presence of SiO2 the surface tension increases up to 400 °C followed by rapid decay, which is found to be related to NP agglomeration and subsequent sedimentation. In terms of contact angle NP addition leads to an increase at the melting point, but fully wetting conditions are attained at 390 °C independent of α-SiO2 content. To capitalize on this effect, MgO-Solar salt CPCMs without and with 1.0 wt % SiO2 are kept at 390 °C for 5 h. Silica addition leads to smaller leakage (mass loss), improved density (by 8.9%), improved porosity (by 18.9%), mean pore size reduction (by 100%) and enhanced thermal diffusivity (by 6.5%). This is suggested to be indirectly related to the surface tension/wettability modification through doping with polar NPs.

Original languageEnglish
Article number111577
Number of pages10
JournalSolar Energy Materials and Solar Cells
Early online date16 Feb 2022
Publication statusPublished - May 2022

Bibliographical note

Funding Information:
The authors would like to acknowledge partial financial support from UK EPSRC under grants EP/S016627/1 , EP/V012053/1 , EP/S032622/1 , EP/P004709/1 and EP/T022981/1 .

Publisher Copyright:
© 2022 Elsevier B.V.


  • Composite materials
  • Nanoparticle
  • Solar salt
  • Surface tension
  • Thermal energy storage

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films


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