# Demonstrating a Quartz Crystal Microbalance with Dissipation (QCMD) to Enhance the Monitoring and Mechanistic Understanding of Iron Carbonate Crystalline Films

## TL;DR

This paper shows how a QCMD device can track the formation of iron carbonate films in real time, improving understanding of their structure and mechanical properties.

## Contribution

A new framework for using QCMD with viscoelastic modeling to better analyze crystal deposition and film mechanics.

## Key findings

- Siderite particles form a layered film on QCMD surfaces, with distinct size distributions.
- Viscoelastic modeling of the film improves accuracy in determining elastic and storage moduli.
- A composite model of hard particles and water enhances the interpretation of QCMD data.

## Abstract

This paper reports the real time monitoring of siderite
deposition,
on both Au- and Fe-coated surfaces, using the changes in frequency
and dissipation of quartz crystal microbalance with dissipation (QCMD).
In an iron chloride solution saturated with carbon dioxide, buffered
with sodium bicarbonate to pH 6.8, roughly spherical particles of
siderite formed within 15 min, which subsequently deposited on the
QCMD crystal surface. Imaging of the surface showed a layer formed
from particles ca. < 0.5 μm in diameter. Larger particles
are clearly deposited on top of the lower layer; these larger particles
are >1 μm in diameter. Monitoring of the frequency clearly
differentiates
the formation of the lower layer from the larger crystals deposited
on top at later times. The elastic moduli calculated from QCMD data
showed a progressive dissipation increase; the modeling of the solid–liquid
interface using a flat approximation resulted in a poor estimation
of elastic and storage moduli. Rather, the impedance modeled as a
viscoelastic layer in contact with a semi-infinite liquid, where a
random bumpy surface with a Gaussian correlator is used, is much more
accurate in determining the elastic and storage moduli as losses from
the uneven interface are considered. A further step considers that
the film is in fact a composite consisting of hard spherical particles
of siderite with water in the vacant spaces. This is treated by considering
the individual contributions of the phases to the losses measured,
thereby further improving the accuracy of the description of the film
and the QCMD data. Collectively, this work presents a new framework
for the use of QCMD, paired with traditional approaches, to enhance
the understanding of crystal deposition and film formation as well
as quantify the often evolving mechanical properties.