Melting and freezing of argon in a granular packing of linear mesopore arrays

TL;DR

This study investigates the melting and freezing behaviors of argon confined in linear mesopore arrays, revealing complex mechanisms influenced by pore filling, adsorption sites, and pressure effects, through specific heat measurements.

Contribution

It provides a detailed analysis of phase transitions of argon in mesoporous structures, highlighting the roles of adsorption sites and pressure effects, which were not fully understood before.

Findings

Interfacial melting causes a single melting peak.

Freezing involves homogeneous, heterogeneous, and delayering transitions.

Pressure release explains temperature shifts during overfilling.

Abstract

Freezing and melting of Ar condensed in a granular packing of template-grown arrays of linear mesopores (SBA-15, mean pore diameter 8 nanometer) has been studied by specific heat measurements C as a function of fractional filling of the pores. While interfacial melting leads to a single melting peak in C, homogeneous and heterogeneous freezing along with a delayering transition for partial fillings of the pores result in a complex freezing mechanism explainable only by a consideration of regular adsorption sites (in the cylindrical mesopores) and irregular adsorption sites (in niches of the rough external surfaces of the grains, and at points of mutual contact of the powder grains). The tensile pressure release upon reaching bulk liquid/vapor coexistence quantitatively accounts for an upward shift of the melting/freeezing temperature observed while overfilling the mesopores.