Investigation of dissolution- and crystrallization equilibria as a basis for the ammonothermal crystalgrowth of nitrides

了解氮化镓在氨热合成中的溶解度是理解和控制氨热合成过程以及优化操作条件的重要前提。为了生成溶解度数据并获得氨热工艺的最佳条件，在第二个资助期提供了四种不同的系统：(i)在第一阶段，建立了一个实验装置，其中有六个高压灭菌器，可能有高压灭菌器加注站和三个加热炉，三个区域用于不同的合成功能。有了这个实验装置，在均匀加热条件下的溶解度测量和沿高压灭菌器长度的温度梯度的结晶实验正在与TP 3、6和z合作进行。（ii）设计了一个由两个高压灭菌器组成的原型双反应器，以了解采样技术并改进过程的优化。在项目的第二阶段，将通过从双反应器中收集样品并通过非原位表征方法进行综合溶解度测量。（iii）项目二期将上述双反应器升级为多反应器，整合更多取样反应器，了解结晶动力学。氨热过程的质量平衡和产物的表征将分别通过这种多反应器采样和非原位表征方法进行。（iv）据我们所知，我们将首次利用超声速度的原位测量来确定氮化镓的溶解度和超临界氨的密度。此外，通过这种原位超声方法可以获得结晶动力学方面的知识。

The knowledge on the solubility of GaN in ammonothermal synthesis is a crucial prerequisite to understand and control the process as well as to optimize the operating conditions. In order to generate the solubility data and to obtain the optimal conditions for the ammonothermal process four different systems available in the second funding period: (i) In the first phase, an experimental set-up was built with six autoclaves having a possibility of autoclave filling station and three heating ovens with three zones for different synthesis functions. With this experimental set-up, solubility measurements under uniform heating conditions and the crystallization experiments with a temperature gradient along the length of autoclave are being performed in collaboration with TP 3, 6 and Z. (ii) A prototype double reactor consists of two autoclaves was designed to understand the sampling technique and to improve the optimization of the process. In the second period of the project, com-prehensive solubility measurements will be performed by collecting the samples from the double reactor and analyzing through ex situ characterization methods. (iii) In the second period of the project, the above-mentioned double reactor will be upgraded to multiple reactors with the integration of more sampling reactors to understand the crystallization kinetics. Mass balance of the ammonothermal process and the characterization of the products will be performed through this multiple reactor sampling and ex situ characterization methods, respectively. (iv) To the best of our knowledge, for the first time we will determine the solubility of GaN and the density of the supercritical ammonia using in situ measurement of ultrasonic velocity. In addition, knowledge on the crystallization kinetics will be obtained through this in situ ultrasonic method.