Zhongping Zhu

Thermodynamics of Reactions Among Al2O3, CaO, SiO2 and Fe2O3 During Roasting Processes

The thermodynamic of the chemical reactions among Al2O3, CaO, SiO2 and Fe2O3 in the roasting processes was investigated in this chapter. The chemical reactions are classified into SiO2-Al2O3 system, Fe2O3-Al2O3 system, SiO2-Fe2O3 system, CaO-Al2O3 system, SiO2-CaO system, SiO2-calcium aluminates system, CaO-Fe2O3 system, Al2O3-calcium ferrites system and Al2O3-CaO-SiO2-Fe2O3 system. When the roasting temperature is over 1100K, 3Al2O3·2SiO2 is preferentially formed in SiO2-Al2O3 system; FeO·Al2O3 can be formed in Fe2O3-Al2O3 system; ferric oxide and SiO2 could not generate iron silicate; 12CaO·7Al2O3 is preferentially formed in CaO-Al2O3 system when one mole Al2O3 reacts with CaO; 2CaO·SiO2 is preferentially formed in SiO2-CaO system; except for CaO·2Al2O3 and CaO·Al2O3, the other calcium aluminates can transform into calcium silicate by reacting with SiO2 in SiO2-calcium aluminates system; 2CaO·Fe2O3 is preferentially formed in CaOFe2O3 system; alumina is unable to form 3CaO·Al2O3 with calcium ferrites(2CaO·Fe2O3 and CaO·Fe2O3), but able to form 12CaO·7Al2O3 with 2CaO·Fe2O3; when CaO, Fe2O3, Al2O3,SiO2 coexist, they are more likely to form ternary compound 2CaO·Al2O3·SiO2 and 4CaO·Al2O3·Fe2O3.

Microwave Synthesis of Co–Ni Ferrite/Graphene Nanocomposite for Microwave Absorption

As the absorbing material composed of sole carbon is difficult to meet the comprehensive requirements of microwave applications, preparation of carbonaceous nanocomposite materials becomes an effective method to increase microwave absorption properties. In this study, a novel nanocomposite composed of Co–Ni ferrite and graphene was synthesized via a simple and rapid microwave hydrothermal method in just a few minutes. It was demonstrated that the minimum microwave reflection loss of the composite of 3 mm thickness with a low filling ratio (20 wt%) reached −13.1 dB at 17.2 GHz with an effective absorption bandwidth of 3.1 GHz. The good performance of the composite was believed to be a result of high dielectric loss of graphene associated with a multi-dielectric relaxation process and magnetic loss of the ferrite mainly originated from natural ferromagnetic resonance.