Silicate Rings in Woody Biomass Ash Melts Based on Molecular Dynamics Simulations

TL;DR

This study uses simulations to explore how silicate rings in molten biomass ash change with different cation contents.

Contribution

The paper introduces a new method to characterize ring interconnectivity and cation clustering in silicate melts.

Findings

Increasing basic cation content reduces overall ring numbers but increases larger rings (>10-membered).

Compositions with more K cations produce rings with weaker Si–O bonds and wider Si–O–Si angles.

Small rings tend to interconnect with specific larger rings, with cation clusters near Si-rich regions.

Abstract

The medium-range ordering of the molten CaO–K2O–SiO2 system was investigated by studying
the
primitive silicate rings extracted from molecular dynamics simulations.
Variations in the ring size distribution and the interconnectivity
between the rings due to the different contents of the basic cations
(Ca2+ and K+) were identified. With increasing
basic cation content, i.e., depolymerization, the overall number of
rings decreased, but increasingly larger rings (>10-membered) occurred
while small-sized rings (4- to 7-membered) remained the most common.
The share of 5-membered rings increased with depolymerization, particularly
with K content. In terms of ring structure, compositions with more
K cations also tended to produce rings with longer Si–O bonds
and wider Si–O–Si angles; i.e., rings that were weaker
and more stretched. A method was introduced to characterize the interconnectivity
between rings, which indicated that the most common small-sized rings
have a tendency to be interconnected to rings of specific larger sizes,
depending on the composition. Visualization and counting of the basic
cations inside of these rings showed that they were cation clusters.
It suggests that these basic cation clusters tend to be located adjacent
to Si-rich regions where small-sized rings interconnect with each
other.

Figures