In situ monitoring technologies for ammonthermal reactors

We developed an optical cell which can be operated at real ammonthermal reaction conditions under high pressure (200MPa, 300MPa optional) and temperatures up to 650 °C. First video optical and spectroscopical studies were made to demonstrate the feasibility of in situ monitoring of the ammonothermal growth process of GaN with the optical cell. So far unknown parameters like e.g. flow velocity of the fluid could be investigated by simple imaging of particle movement. The in situ optical cell offers access to spectroscopic investigations or direct temperature measurements. First measurements show light absorption of chemical species in the reaction fluid in the UV to near IR range which changes with temperature and pressure implying that more than one intermediate species is present. The application of this optical cell is not restricted to a particular ammonothermal route but can be applied to either ammonothermal variant. An additional development was a reactor with fiv e type K thermocouples to measure the temperature distribution directly in the reaction chamber up to 650 °C and 300 MPa. The flexibility of the thermocouples allows the measurements at nearly any point in the fluid.