Phase Transformations In The Process Of Aluminothermic Reduction And Nitridation Reaction Of Micro-crystal Muscovites At High Temperture

In this paper, the transformation mechanism of the aluminothermic reduction & nitridation on the micro-crystal muscovites at high temperature, and the composition and content of phases in the product affected by the addition of aluminum powder under different thermal reduction and nitridation reaction were studied. XRD, SEM and X-ray energy dispersive spectroscopy were applied to analyze the composition and morphology in the different phases of the samples. The results showed that between 1350℃to 1450℃, the major phases of the samples were corundum and Sialon phase. When the aluminum dosage was 25 and 35 (wt %), the major phases wereβ-Sialon.When the aluminum dosage was 45 (wt %), the major phases wereβ-Sialon and Si-Al-ON. Through the calcination at 1550℃, the major phases of samples were corundum, AlON, and Sialon. With the 25 and 35 (wt %) dosage of aluminum, there wasβ-Sialon, and with 45 (wt %) dosage of aluminum, there were Si3Al7O3N9 and SiAl8O2N8.Calcination temperature and aluminum content had significant impact on the Z value ofβ-Sialon. The results showed that along with the calcination temperature from 1350℃to 1450℃, and then to 1550℃, when the dosage of aluminum was fixed at 25 (wt %), the Z values ofβ-Sialon were 2.3126, 2.5455, 2.8325. When the dosage was 35 (wt. %), the Z values ofβ-Sialon were 2.8659, 3.1654, 3.3041, but when the dosage was 45 (wt. %), the Z values ofβ-Sialon were 3.8387, 4.1243. While the calcining temperature was 1550℃, theβ-Sialon phase changed to AlN. Along with the addition of aluminum powder increasing from 25 (wt. %) to 35 (wt. %), and then to 45 (wt. %), at 1350℃, the Z values ofβ-Sialon were 2.3126, 2.8659, 3.3041, at 1450℃, the Z values ofβ-Sialon were 2.5455, 3.1654, 3.8387, but at 1550℃, from 25 (wt%) to 35 (wt%), the Z values ofβ-Sialon increased from 2.8325 to 3.3041, while at 45 (wt. %) dosage of aluminum powder, theβ-Sialon phase had transformed to AlN. This showed that the Si and N atoms in muscoviteβ-Sialon phase were replaced by Al and O atoms in the transformation,.as the calcination temperature and the amount of aluminum powder increased. The calcination temperature and aluminum content in the aluminothermic reduction nitridation reaction process influenced the muscovite composition and content. The results showed that: fixed 25 (wt %) dosage of aluminum, as the calcination temperature increased from 1350℃to 1450℃, the content ofβ-Sialon and corundum phase decreased, at 1550℃, the content ofβ-Sialon and corundum phase increased.Fixed 35 (wt.%) dosage of aluminum, as the calcination temperature increased from 1350℃to 1450℃, the content ofβ-Sialon phase increased, and the content of corundum phase decreased, at 1550℃, the content ofβ-Sialon phase reduced and the content of corundum phase growed. Fixed 45 (wt.%) dosage of aluminum, as the calcination temperature increased from 1350℃to 1450℃, the content ofβ-Sialon, corundum and Si-Al-ON decreased. If the temperature rose to 1550℃,β-Sialon, corundum and Si-Al-ON phase completely disappeared, while Si₃Al₇O₃N₉ and SiAl₈O₂N₈ phase appeared in large content.The addition of 35 (wt %) amount of aluminum powder helped to form the highest content ofβ-Sialon, which indicated that the right amount of aluminum powder is conducive for the content ofβ-Sialon. But when the amount of aluminum powder was added to 45 (wt %), the excess of aluminum powder would promoteβ-Sialon to transform to the AlN.