About the Dominance of Mesopores in Physisorption in Amorphous Materials.

Christoph Strangfeld,Philipp Wiehle,Sarah Mandy Munsch

doi:10.3390/molecules26237190

Christoph Strangfeld, Philipp Wiehle + Show 1 more

Open Access

https://doi.org/10.3390/molecules26237190

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Abstract

Amorphous, porous materials represent by far the largest proportion of natural and men-made materials. Their pore networks consists of a wide range of pore sizes, including meso- and macropores. Within such a pore network, material moisture plays a crucial role in almost all transport processes. In the hygroscopic range, the pores are partially saturated and liquid water is only located at the pore fringe due to physisorption. Therefore, material parameters such as porosity or median pore diameter are inadequate to predict material moisture and moisture transport. To quantify the spatial distribution of material moisture, Hillerborg’s adsorption theory is used to predict the water layer thickness for different pore geometries. This is done for all pore sizes, including those in the lower nanometre range. Based on this approach, it is shown that the material moisture is almost completely located in mesopores, although the pore network is highly dominated by macropores. Thus, mesopores are mainly responsible for the moisture storage capacity, while macropores determine the moisture transport capacity, of an amorphous material. Finally, an electrical analogical circuit is used as a model to predict the diffusion coefficient based on the pore-size distribution, including physisorption.

Highlights

There is a wide variety of natural and man-made porous materials
The chosen pore geometry is validated by means of experimentally measured sorption isotherms
It was shown that most of the material moisture is located in mesopores

Summary

Introduction

There is a wide variety of natural and man-made porous materials. Amorphous porous materials represent the largest share of porous materials. Concrete accounts for the largest share at ∼40%, followed by aggregates at ∼35%, bricks at ∼10%, and asphalt at ∼5% [2]. Manufacturing building materials causes about 11% of global CO2 emissions [4], with the cement industry accounting for the largest share at around 8% of global CO2 emissions [5]. In Germany, approximately 9 billion euros in repair costs are generated by mass transfer within the amorphous, porous cement matrix. Extrapolated to the EU, the figure is approximately 36 billion euros. This trend is reflected in the waste industry: 36.4% of all waste of the EU comes directly from the building industry and a further 25.3% from mining and aggregates production [8].

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