EFFECTS OF BORIC ACID DOSAGE AND REACTION TEMPERATURE ON THE PHASE COMPOSITION AND MICROSTRUCTURE OF Si C-B₄C COMPOSITE POWDERS SYNTHESISED BY THE CARBOTHERMAL REDUCTION METHOD

Abstract

SiC-B 4 C composite powders were synthesised by the carbothermal reduction method under argon atmosphere by using boric acid, silica sol, and flake graphite as the raw materials. The effects of the boric acid dosage and reaction temperature on the phase composition and microstructure of the synthesised SiC-B 4 C composite powders were studied, and the synthesis mechanism of these powders were discussed. The results show that the suitable reaction conditions for synthesising the SiC-B 4 C composite powders were kept at 1500 °C and 1550 °C for 2 h when the amounts of excess boric acid were 0 wt. % -20 wt. % and 30 wt. %, respectively. The microscopic morphology of the SiC-B 4 C powder samples with a 0 wt. % -20 wt. % excess of boric acid calcined at 1500 °C for 2 h was mainly composed of flake particles, short rod-shaped particles, and a small amount of approximately spherical particles. The powder samples calcined at 1500 °C for 2 h generated not only irregular polygonal structure particles, but also a small amount of long rod-shaped particles and fibrous whiskers when the amount of excess boric acid was 30 wt. %.

SYNTHESIS AND MECHANISM OF SiC-ZrC COMPOSITE POWDERS BY CARBOTHERMAL REDUCTION METHOD

“…The starch in the used raw material will decompose to form elemental carbon under the condition of low temperature (above 200 °C) [27]. The main synthesis reactions between zirconium dioxide (ZrO 2 ), silica sol (mSiO 2 •nH 2 O), and starch (C 6 H 10 O 5 ) n in the system at high temperature are shown in Equations 1 and 2 [28][29][30]. The value of ΔG can be calculated using Equation 3.…”