Cooling rate of reactant solution in a flow-type supercritical hydrothermal reactor estimated using neutron radiography

Abstract Rapid cooling of reactants quenches the intermediate state of chemical reactions and enables the synthesis of novel materials that cannot be realized by thermodynamic equilibrium processes. In this study, we estimated the cooling rate of reactant solutions during the supercritical hydrothermal synthesis of metal oxide nanoparticles. Neutron radiography measurements were performed to visualize the profile of the average water density at a junction where a stream of heated water was mixed with another stream of cooling water. The cooling rate of the heated water that mimicked the reactant solution was estimated using the relationship between the density and temperature of water under constant pressure conditions. This result should provide vital information about the flow-type synthesis of novel metal oxide nanoparticles.