A Nonhazardous Alternative to Mercury in Liquid Intrusion Porosimetry: Systematic Study of Intrusion/Extrusion Behavior of a Gallium-Based Liquid Metal (eGaInSn) into Meso- and Macroporous Silica, Alumina, and Carbon Materials.

Mercury porosimetry is considered the standard method for the characterization of macroporous solids. However, health risks and environmental concerns make a replacement for mercury sought-after. Despite many advances in various techniques, so far, no alternative method is available. Here, we introduce a novel method using, instead of mercury, eGaInSn (Galinstan), a nonhazardous, eutectic gallium alloy, liquid at ambient temperatures, which is already widely used as a replacement for mercury (e.g., thermometers). We utilize a conventional porosimeter with only minor but necessary modifications in sample cell design and filling procedure. To evaluate its potential for pore characterization, we systematically studied the phase and wetting behavior of eGaInSn via intrusion/extrusion experiments in a series of well-defined meso- and macroporous silica (controlled pore glasses), alumina, and disordered carbon materials, including certified reference materials, exhibiting mode pore sizes from the narrow meso- (<20 nm) to the macropore range (1.7 μm). Our results suggest that the intrusion mechanism of eGaInSn represents, analogue to mercury, a confinement-induced shift of the vapor-liquid phase transition of a nonwetting fluid to pressures larger than the saturation vapor pressure. Comparing the pore size/volume distributions obtained by eGaInSn reveals excellent agreement with state-of-the-art mercury porosimetry. Furthermore, we systematically studied the effect of pretreatment conditions of the porous materials, e.g., degassing temperature, on the intrusion/extrusion behavior of eGaInSn and find that the degassing temperature has essentially no influence on the eGaInSn intrusion pressure and curve, but significantly affects the extrusion behavior. We demonstrate that, under certain, well-defined experimental conditions, the intrinsic eGaInSn intrusion-extrusion hysteresis loop is revealed, which contains important additional textural information. In conclusion, our work can be considered the first systematic study of the effect of confinement on the wetting and phase behavior of eGaInSn utilizing intrusion/extrusion measurements with a novel method offering potential to finally replace toxic mercury in the analysis of meso- and macroporous solids.