Here is a working example:
\documentclass[preprint, 12pt, 3p, twocolumn, sort&compress]{elsarticle}
\usepackage{siunitx}
\usepackage{booktabs}
\usepackage{graphicx}
\usepackage{threeparttable}
\usepackage{caption}
\usepackage{subcaption}
\begin{document}
\begin{table}[]
\begin{threeparttable}
\resizebox{\columnwidth}{!}{%
\begin{tabular}{@{}ccc@{}}
\toprule
\begin{tabular}[c]{@{}c@{}}Heating rate\ (\si[per-mode=symbol]{\degreeCelsius\per\minute})\end{tabular} &
\begin{tabular}[c]{@{}c@{}}Final temperature\ (\si{\degreeCelsius})\end{tabular} &
\begin{tabular}[c]{@{}c@{}}Carbonisation time\ (\si{\minute})\end{tabular} \ \midrule
1.4\tnote{$a$} & 1000 & 708 \
3.0 & 600 & 192 \
3.0 & 800 & 258 \
3.0 & 1000 & 325 \
3.0 & 1200 & 392 \
3.0 & 1400 & 458 \
3.0 & 1600 & 525 \
10.0 & 1000 & 98 \
20.0 & 1000 & 49 \
40.0 & 1000 & 24 \ \bottomrule
\end{tabular}%
}
\begin{tablenotes}
\footnotesize
\item[$a$]{\SI[per-mode=symbol]{1}{\degreeCelsius\per\minute} to \SI{600}{\degreeCelsius} and then \SI[per-mode=symbol]{3}{\degreeCelsius\per\minute} to \SI{1000}{\degreeCelsius}}
\end{tablenotes}
\caption{Investigated carbonisation conditions \cite{bengtssonCarbonFibersLignin2020}}
\label{tab:conditions}
\end{threeparttable}
\end{table}
\end{document}
My code produces this output (see image):
Any idea how I might stop the footnote overhanging the column?
Much appreciated.



\resizeboxin general; in this particular case,threeparttableis not able to guess the table width. – egreg Apr 10 '21 at 12:28