Starvation-Induced Hollowing: Formation of Magnesium Sulfate Microtubes via a Surface-Limited Growth Mechanism

For many years, research and application of magnesium sulfate have focused on its chemical properties, but the microstructure of its core structure has never been broken through. This study accidentally observed the spontaneous formation of a novel magnesium sulfate hollow microtube (MgSO4·6H2O) in a metastable supersaturated solution. This structure has a dense outer shell and a single hole channel that communicates internally. Research on the formation mechanism and regulatory laws shows that high supersaturation triggers rapid nonequilibrium deposition of the outer shell, leading to limited internal ion diffusion and local phase separation, which is the key to the formation of hollow structures. In addition, ethanol molecules can weaken the hydrogen-bonding network of the solvent by entering the Mg+2 coordination layer, promoting ion migration and structural recombination, and enhancing the formation of hollow structures. Further investigation revealed that selective adsorption of impurity ions on crystal surfaces can cause surface electron density rearrangement, reduce crystal surface stability, and induce directional evolution of the hollow morphology. The hollow microtube structure has unique application potential in heat absorption dehydration, water vapor release, flame retardancy, and other aspects. This study has theoretical implications for understanding the interface behavior and structural evolution during the crystallization process.