A high-temperature high-pressure small-angle neutron scattering cell for studying hydro­thermal reactions in supercritical water

A high-temperature high-pressure cell equipped with a metallic window was developed for small-angle neutron scattering (SANS). The feasibility of a Ti alloy (Ti–6Al–4V) as a candidate window material was assessed, considering its mechanical strength and neutron characteristics. SANS experiments should be conducted using safe and reliable materials without risk of window damage or leakage of the activated samples due to window breakage. SANS profiles measured for supercritical heavy water showed maximum scattering intensity at temperatures and pressures near the critical density. Additionally, the utility of the cell for observations of the decomposition of plastic in supercritical water is presented. The cell facilitates analysis of reaction mechanisms under sub- and supercritical conditions, which could provide detailed information to aid efficient decomposition and recycling, contributing to a sustainable society.