The effect of preliminary heat treatment on the durability of reaction bonded silicon nitride crucibles for solar cells applications

• Published in: Journal of crystal growth 2020-07, Vol.542, p.125670, Article 125670
• Main Authors: Hendawi, Rania, Ciftja, Arjan, Stokkan, Gaute, Arnberg, Lars, Di Sabatino, Marisa
• Format: Article
• Language: English
• Subjects: A1. Characterization; A1. Crucible cracking; A1. Heat treatment; B1. Nitrides; Crucibles; Crystallization; Differential thermal analysis; Differential thermogravimetric analysis; Durability; Heat treating; Heat treatment; Internal oxidation; Oxidation; Phase distribution; Photovoltaic cells; Porosity; Silicon dioxide; Silicon nitride; Solar cells; Thermal stress; Thermogravimetry; Wall thickness; Wetting
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2020.125670

•The crucibles’ lifetime is limited by the heat treatment step that lead to fracture.•Determination of number of heat treatment cycles to failure at different temperatures.•Investigation of failure’s mechanism and main influence factors.•The effect of phase and porosity distribution on the crucibles’ behavior. Silicon nitride crucibles have the potential to replace silica crucibles and reduce the cost of silicon crystallization because of their reusability potential. Till date, crucibles’ heat treatment before each use is a prerequisite to achieve non-wetting conditions that is needed to facilitate the ingot release and hence enable reusability. Yet, no studies have examined the heat treatment influence on the crucibles’ durability. The present investigation focuses on the crucibles’ heat treatment and its impact on the crucibles’ lifetime. Repeated heat-treatments of silicon nitride crucibles in the air at above 1100 °C leads to crucible fracture. Therefore, this study identifies the cause and the mechanism of such failures by applying different heat treatment procedures in the air. The mass gain and the oxidation rates of the crucibles at different temperatures are measured via Thermogravimetry (TG) and Differential Thermal Analyzer (DTA). The results show that the porosity and phase distribution along the crucible wall thickness, play a key role in the crucible’s behavior during oxidation. Moreover, excessive internal oxidation in the tested crucibles results in severe thermal stresses which cause cracking during cooling.