Abstract
The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated. Cr dramatically improved the conversation of Si to silicon nitride (Si3N4). The complete conversion was achieved at 1350 °C upon addition of 1.25 wt% Cr. This temperature was much lower than that required in the case without using a catalyst. Meanwhile, Cr played an important role in the in-situ growth of one-dimensional (1-D) α-Si3N4 nanostructures. α-Si3N4 nanowires and nanobelts became the primary product phases when 5 wt% Cr was used as the catalyst. The growth processes of the 1-D α-Si3N4 nanostructures were governed by the vapor-solid mechanism. First-principle calculations suggest that electrons can be transferred from Cr atoms to N atoms, facilitating the Si nitridation.
Highlights
The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated
The direct nitridation of Si powder is regarded as a low-cost and straightforward route for the large scale production of Si3N4 powder and bulk Si3N4 based materials. With this technique, much unreacted Si often remains in the final products, due to partial Si melting caused by the high nitridation temperature used and additional heat released from the strong exothermic reaction between Si and nitrogen
Upon further increasing the temperature to 1350 °C, the overall conversion (OC) in the reference sample increased to 91% whereas most of the Si had been nitrided in the sample containing 1.25 wt% Cr
Summary
The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated. The direct nitridation of Si powder is regarded as a low-cost and straightforward route for the large scale production of Si3N4 powder and bulk Si3N4 based materials With this technique, much unreacted Si often remains in the final products, due to partial Si melting caused by the high nitridation temperature used and additional heat released from the strong exothermic reaction between Si and nitrogen. Among the transition metals, cobalt (Co) was found to show significant accelerating effects on the Si nitridation and in-situ growth of α-Si3N4 nanorods or nanowires[21] When it is used as a catalyst, low melting Co and/or Co-Si alloy phases will remain after the nitridation, which could potentially deteriorate high-temperature properties of the final product materials[22,23]. On the other hand, according to Pavarjarn et al.[15], Cr had no obvious effect on the Si nitridation even at 1300 °C
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