The effect of phosphorus on the formation of mullite whiskers from citric acid activated kaolin. Issue 15 (15th October 2018) - Zhang, Chenyang
Abstract: Mullite with an aspect ratio of 82.08 was prepared by adding 4.5 wt% Ca3 (PO4 )2 to citric acid activated kaolin. Phosphorus (P) has a significant role in the formation of well-developed mullite whiskers. The mechanisms were discussed based on X-ray diffraction, FTIR, SEM, EDS and 31 P MAS NMR. The addition of P decreases the quartz content, but increases the liquid phase content. When the Ca3 (PO4 )2 content is less than 4.5 wt%, the main types of P in glass phase are Q 1 and Q 2 ; with increasing P content, the aspect ratio of mullite increases. When the Ca3 (PO4 )2 content is higher than 4.5 wt%, a higher polymerization degree of P (Q 3 ) appears; however, the aspect ratio of mullite decreases. Therefore, the range of P contents enhancing the formation of mullite whiskers is narrow.