17. Special Equipment for Ammonothermal Processes

As the ammonothermal method often requires technically challenging conditions such as high temperature, high pressure and reaction media that are rather corrosive towards most metals (see Chap. 11), the further development of ammonothermal process equipment is of vital importance for tapping the full potential of the ammonothermal method. Suitable high-pressure/high-temperature autoclaves are therefore the basic requirement for a successful process. Ammonothermal syntheses are conventionally carried out in autoclaves, which do not allow monitoring of the physical and chemical processes during the experiments. Therefore, in situ measurement techniques at process conditions are crucial for obtaining a holistic understanding of ammonothermal processes. The following chapter presents optical cells for in situ monitoring enabling UV/Vis and Raman spectroscopy, X-ray imaging and X-ray diffraction as well as ultrasonic measurements. Additionally, special equipment like a rotatable feedthrough and a ceramic-crucible-based systems for minimization of corrosion and contamination are described.