Synthesis and characterization of sol-gel derived alumina–cobalt composite by in–situ reduction

In an effort to explore the potential of alumina composite particularly as structural material, gas sensors and microwave absorber, a 15 weight% cobalt–reinforced alumina composite was synthesized. The composite was produced via a novel in–situ reduction method, in which hexa–hydrated cobalt chloride was reduced by non toxic dextrose within the pores of alumina gel. This gel was derived through sol–gel process using aluminum isopropxide as precursor. The reduction was carried at various temperatures—850°C, 950°C, 1000°C, 1100°C, and 1150°C. Notably, perceptible metallic cobalt formation occurred only at temperatures of 950°C and above. The sample reduced at 1150°C consisted of stable alpha alumina, reinforced with nano–sized metallic cobalt particles (~ 30 nm), which were finer than those (~ 50 nm) obtained at 950°C. This refinement in particle size at high temperature is a novel observation confirmed through XRD, DLS, FESEM and TEM analysis.