Activated magnetite (Fe3O4-δ) was applied to reducing CO2 gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a CO2 removal process. One of the typical dry methods is CO2 decomposition using activated magnetite (Fe3O4-δ). Generally, Fe3O4-δ is manufactured by reduction of Fe3O4 by H2 gas. This process has an explosion risk. Therefore, a non-explosive process to make Fe3O4-δ was studied using FeC2O4·2H2O and N2. FeSO4·7H2O and (NH4)2C2O4·H2O were used as starting materials. So, α-FeC2O4·2H2O was synthesized by precipitation method. During the calcination process, FeC2O4·2H2O was decomposed to Fe3O4, CO, and CO2. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 m2/g to 9.32 m2/g. The densities of FeC2O4·2H2O and Fe3O4 were 2.28 g/cm3 and 5.2 g/cm3, respectively. Also, the Fe3O4 was reduced to Fe3O4-δ by CO. From the TGA results in air of the specimen that was calcined at 450˚C for three hours in N2 atmosphere, the δ-value of Fe3O4-δ was estimated. The δ-value of Fe3O4-δ was 0.3170 when the sample was heat treated at 400˚C for 3 hours and 0.6583 when the sample was heat treated at 450˚C for 3 hours. Fe3O4-δ was oxidized to Fe3O4 when Fe3O4-δ was reacted with CO2 because CO2 is decomposed to C and O2.

The effect of the precipitator (NaOH, NH4OH) and the amount of the precipitator (150, 200, 250, 300 ml) on the formation of Fe3(PO4)2, which is the precursor used for cathode material LiFePO4 in Li-ion rechargeable batteries was investigated by the co-precipitation method. A pure precursor of olivine LiFePO4 was successfully prepared with coprecipitation from an aqueous solution containing trivalent iron ions. The acid solution was prepared by mixing 150 ml FeSO4(1M) and 100 ml H3PO4(1M). The concentration of the NaOH and NH4OH solution was 1 M. The reaction temperature (25˚C) and reaction time (30 min) were fixed. Nitrogen gas (500 ml/min) was flowed during the reaction to prevent oxidation of Fe2+. Single phase Fe3(PO4)2 was formed when 150, 200, 250 and 300 ml NaOH solutions were added and 150, 200 ml NH4OH solutions were added. However, Fe3(PO4)2 and NH4FePO4 were formed when 250 and 300 ml NH4OH was added. The morphology of the Fe3(PO4)2 changed according to the pH. Plate-like lenticular shaped Fe3(PO4)2 formed in the acidic solution below pH 5 and plate-like rhombus shaped Fe3(PO4)2 formed around pH 9. For the NH4OH, the pH value after 30 min reaction was higher with the same amount of additions of NaOH and NH4OH. It is believed that the formation mechanism of Fe3(PO4)2 is quite different between NaOH and NH4OH. Further investigation on this mechanism is needed. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the pH value was measured by pH-Meter.

The effect of ferrous/ferric molar ratio on the formation of nano-sized magnetite particles was investigated by a co-precipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide was used as a precipitant. In this experiment, the variables were the ferrous/ferric molar ratio (1.0, 1.25, 2.5 and 5.0) and the equivalent ratio (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0), while the reaction temperature (25˚C) and reaction time (30 min.) were fixed. Argon gas was flowed during the reactions to prevent the Fe2+ from oxidizing in the air. Single-phase magnetite was synthesized when the equivalent ratio was above 2.0 with the ferrous/ferric molar ratios. However, goethite and magnetite were synthesized when the equivalent ratio was 1.0. The crystallinity of magnetite increased as the equivalent ratio increased up to 3.0. The crystallite size (5.6 to 11.6 nm), median particle size (15.4 to 19.5 nm), and saturation magnetization (43 to 71 emu.g-1) changed depending on the ferrous/ferric molar ratio. The highest saturation magnetization (71 emu.g-1) was obtained when the equivalent ratio was 3.0 and the ferrous/ferric molar ratio was 2.5.