Survey of boron nitride solubility in basic ammonothermal solutions containing alkali or alkaline-earth metals

• Ammonothermal solubility of boron nitride (BN) using alkali metal mineralizers Li 3 N, Na, K, and alkali earth metal mineralizers Mg, Ca, Sr, Ba is measured. • Solubility of BN is found to increase with increasing temperature with all studied alkali and alkali earth mineralizers. • NH 3 decomposition is estimated and solubility normalization is compared relative to the initial fill vs. final NH 3 concentration. • BN solubility is found to decrease at lower pressures when using a Na mineralizer. • Solubility levels are only slightly lower compared to solubility of GaN suggesting viability for crystal growth. The temperature-dependent solubility of boron nitride (BN) in sodium (Na) containing supercritical ammonia (NH 3 ) was previously demonstrated. This study explores the temperature–dependent solubility of BN with other basic mineralizers (alkali metals lithium (Li) and potassium (K), and alkaline-earth metals magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba)) over a pressure range of 156–202 MPa. Additionally, this study analyzes the temperature dependence of BN solubility with a Na mineralizer, at lower pressures (from 81—118 MPa). Solubility measurements were performed on a gravimetric basis and normalized to the initial fill amount of ammonia or the indirectly, experimentally measured concentration of ammonia in the autoclave at the end of the hot, dwell conditions. All investigated mineralizers exhibited normal solubility of BN with respect to temperature achieving solubilities close to but slightly below that of Na in all cases except Ba for which equal solubility was observed. Magnesium and Ca exhibited the lowest solubilities approximately an order of magnitude lower than Ba. For Na, a decrease in autoclave pressure yielded a decrease in the normalized BN solubility (for both fill and dwell ammonia).