Self propagating high temperature synthesis of BaFe12−xCrxO19 and Li0.5Fe2.5−xCrxO4

Abstract

Thermal initiation of a mix of BaO 2 , Fe 2 O 3 , Cr 2 O 3 and iron powder in air induces a self propagating reaction with velocity 1-2 mm s –1 and the formation of predominantly BaFe 12–x Cr x O 19 . Thermal initiation of a mixture of Li 2 O 2 , Fe 2 O 3 , Cr 2 O 3 and iron powder in air also induces a propagation wave with formation of predominantly Li 0.5 Fe 2.5–x Cr x O4. Heating either product mixture to 1150-1200 °C for 2 h produces phase pure crystalline powders of BaFe 12–x Cr x O 19 and Li 0.5 Fe 2.5–x Cr x O 4 . An external 1.1 T magnetic field increased the SHS synthesis wave velocity and temperature for both hard (BaFe 12–x Cr x O 19 ) and soft ferrites (Li 0.5 Fe 2.5–x Cr x O 4 ). Materials synthesised in a magnetic field showed significant changes in H c , σ max and σ r compared to those synthesized in zero field. All the samples were characterised by X-ray powder diffraction, FTIR, VSM, EDAX/SEM and Mossbauer spectroscopy.