Synthesis of nanoparticulate yttrium aluminum garnet in supercritical water–ethanol mixtures

Single-phase YAG nanoparticles have been produced by the rapid hydrolysis and dehydration of Al3+ and Y3+ salts in EtOH–H2O mixtures using continuous supercritical water hydrothermal synthesis. The effects of the nature of the starting solution, the metal concentration, the EtOH content, the flow rate and the temperature on the particle size were studied. EtOH promotes crystallization and highly crystalline materials are obtained at relatively low temperatures. Furthermore the critical temperature of EtOH–H2O mixtures is lower than that of pure H2O, reducing the operating temperature. From the variables studied, the most important parameter seems to be the temperature and much smaller particles have been obtained when experiments are conducted under supercritical conditions (average 50 nm), in comparison to near critical or subcritical conditions (average 150 nm). The method is simple and clean and requires neither addition of a base to the system nor the use of very high reaction temperatures and potentially allows the continuous production of large quantities of material.