Effect of Y‐α‐Sialon Seeding and Holding Time on the Formation of Elongated (Ca,Dy)‐α‐Sialon Crystals Prepared via Carbothermal Reduction and Nitridation

Abstract

Single‐phase (Ca,Dy)‐α‐Sialon with elongated crystals and high aspect ratios was prepared at 1700°C by carbothermal reduction and nitridation (CRN) with Y‐α‐Sialon seed crystals. Effects of Y‐α‐Sialon seeding and holding time on the phase assemblage and crystal morphology of CRN products were discussed. The results showed that adding seed crystals and prolonging holding time could facilitate not only phase transformation, but also crystal refinement. Moreover, they resulted in the increase of the aspect ratios of α‐Sialon crystals, due to the decreasing range in the crystal width exceeding that in the length. In addition, a highly unusual phenomenon of crystal size reduction during reaction was observed in the seeded samples with the holding time extending from 2 to 4 h. Crystallization from liquid phase and growth followed by nucleation based on the surface of existing large crystals were the growth modes of elongated α‐Sialon crystals.

Phase transformation of high aluminium fly ash in carbothermal reduction–nitridation at high temperatures

“…Ca-a-Sialon has a range of attractive properties, such as high hardness, good corrosion resistance and excellent thermal shock resistance. 18,19 Previously, some literatures reported the synthesis of Ca-a-Sialon by using fly ash as raw material. 16,20 When the temperature reached 1700uC, a phase with a plate-like morphology formed with obvious differences from to the Sialon grains prepared at others temperatures.…”

Si3N4‐SiCp Composites Reinforced by In Situ Co‐Catalyzed Generated Si3N4 Nanofibers

“…In past few years, controlling microstructural development to optimize materials' mechanical properties has been the focus of intensive research [5][6][7][8][9]. The previous studies show that single or mixed additives such as Y 2 O 3 , MgO, Al 2 O 3 + Y 2 O 3 , and Al 2 O 3 + ZrO 2 are useful for enhancing the mechanical properties of Si 3 N 4 -SiC p composite refractories [10][11][12][13].…”