태양광 폐모듈로부터 회수한 실리콘의 2단계 직접 질화 반응을 통한 Si₃N₄ 급속 합성
Rapid Synthesis of Si₃N₄ via a Two-Step Direct Nitridation Reaction Using Silicon Recycled from End-of-Life Photovoltaic (EoL PV) Modules
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In this study, recycled Si (r-Si) recovered from end-of-life photovoltaic (EoL PV) modules was used to synthesize Si₃N₄. The recovered r-Si powder was treated via ball milling to obtain an average particle size of approximately 1 µm, after which it was subjected to two-step direct nitridation under a N₂–H₂ atmosphere. Specifically, first-step nitridation (conducted at 1350℃), which promoted surface nitridation, was followed by second-step nitridation (performed at 1450℃), which enabled complete conversion within 10 min. The resulting Si₃N₄ predominantly comprised the α-phase (87-91%), and the minor β-phase fraction (9-13%) was attributed to local heat-concentration-induced melting. Additionally, volatile SiO species, generated via the reduction of SiO₂ or partial oxidation of Si, reacted with N₂ in the gas phase, further contributing to β-Si ₃N₄ formation. Analysis of particle sizes, along with scanning electron microscopy, confirmed grain coarsening at a prolonged holding time. The sample maintained at 1350℃ for 60 min, followed by 10 min at 1450℃ (#60-10), exhibited a smaller particle size with a short processing time, thus representing the optimal synthetic condition. In addition, the mechanism of phase formation was analyzed in terms of the overall two-step nitridation process and the reactions at each temperature. The findings experimentally validate the viability of utilizing r-Si derived from PV modules as a raw material for producing advanced ceramics, contributing to resource circulation and domestic material self-sufficiency.
Abstract
In this study, recycled Si (r-Si) recovered from end-of-life photovoltaic (EoL PV) modules was used to synthesize Si₃N₄. The recovered r-Si powder was treated via ball milling to obtain an average particle size of approximately 1 µm, after which it was subjected to two-step direct nitridation under a N₂–H₂ atmosphere. Specifically, first-step nitridation (conducted at 1350℃), which promoted surface nitridation, was followed by second-step nitridation (performed at 1450℃), which enabled complete conversion within 10 min. The resulting Si₃N₄ predominantly comprised the α-phase (87-91%), and the minor β-phase fraction (9-13%) was attributed to local heat-concentration-induced melting. Additionally, volatile SiO species, generated via the reduction of SiO₂ or partial oxidation of Si, reacted with N₂ in the gas phase, further contributing to β-Si ₃N₄ formation. Analysis of particle sizes, along with scanning electron microscopy, confirmed grain coarsening at a prolonged holding time. The sample maintained at 1350℃ for 60 min, followed by 10 min at 1450℃ (#60-10), exhibited a smaller particle size with a short processing time, thus representing the optimal synthetic condition. In addition, the mechanism of phase formation was analyzed in terms of the overall two-step nitridation process and the reactions at each temperature. The findings experimentally validate the viability of utilizing r-Si derived from PV modules as a raw material for producing advanced ceramics, contributing to resource circulation and domestic material self-sufficiency.