In order to understand the sensitivity of volatile-char interactions to mild temperatures (600-800 degrees C), in-situ rice husk char was prepared from fast pyrolysis (>10(3) K s (1)) on a fixed-bed reactor. Retention of K in char, changes in char structure and char reactivity were determined. The results showed that volatile-char interactions did not cause obvious effect on the char yield but showed an inhibitory effect on char reactivity. The inhibition began only above 650 degrees C and intensified with temperature rise, but kept almost unchanged at 700-800 degrees C. Char structure and retention of K have a combined effect on char reactivity. The decreased reactivity was caused by additional volatilization of K from char matrix and transformation of relatively smaller aromatic ring systems to large ring systems (>6 benzene rings) above 650 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.