Microwave catalyzed carbothermic reduction of zinc oxide and zinc ferrite: effect of microwave energy on the reaction activation energy.

Mamdouh Omran,Tero Vuolio,Yilmaz Kacar,Timo Fabritius,Yaowei Yu,Eetu-Pekka Heikkinen,Guo Chen

doi:10.1039/d0ra04574h

Abstract

Recently, more attention has been paid to the use of microwave (MW) energy in accelerating chemical reactions. The effect of microwave energy on the reduction of zinc oxide and zinc ferrite was investigated. The results indicated that the temperatures required to initiate zinc oxide and zinc ferrite reduction under MW heating were 550 and 450 °C, respectively, while under conventional thermal (CT) heating, were 950 and 850 °C, respectively. Apparently, the MW reaction had a negative standard Gibbs free energy (ΔG) at a lower temperature (∼400 °C) when compared to the CT reaction. Additionally, the activation energy (Ea) substantially decreased from 223.7 and 221.1 kJ mol−1 under CT heating to 64.8 and 32.9 kJ mol−1 under MW heating for Zn oxide and zinc ferrite, respectively. The enhancement in zinc reduction under MW energy was due to the rapid and bulk heating phenomena of MWs as well as the interactions occurring between the electromagnetic MW pattern and the molecules of heated materials.

Highlights

Attention in different elds of chemistry and metallurgy has been increasingly paid to using microwave (MW) energy to increase the reaction rates and improve the recovery of valuable metals
TG–differential scanning calorimetry (DSC) The TG and DSC curves of zinc oxide and zinc ferrite are revealed in Fig. 5A and Fig. 5B, respectively
At a high temperature of about $1200 C, there is a deep slop in the DSC curve owing to the sintering of both zinc oxide and zinc ferrite (Fig. 5B)

Summary

Introduction

Attention in different elds of chemistry and metallurgy has been increasingly paid to using microwave (MW) energy to increase the reaction rates and improve the recovery of valuable metals. Recent studies have shown that the use of MW energy results in a substantial improvement in the rate of reaction when compared to conventional thermal heating.[1,2,3] Microwave energy is a novel type of electromagnetic wave, with 300 MHz to 300 GHz frequencies.[4,5] Microwave heating is generated by interaction between the dielectric material and the MW eld.[6,7] This contrasts with conventional thermal heating, which heats the sample from the outside-in through heat transfer mechanisms.[8,9].

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Conclusion