Sang-Do Park

Influence of stoichiometry and alkalinity on barium hexaferrite formation via the supercritical water crystallization method

Fine particles of barium hexaferrite were prepared from aqueous solutions of iron nitrate, barium nitrate and potassium hydroxide by utilizing a continuous flow type supercritical water crystallization method. The influence of stoichiometry (Fe/Ba mole ratio) and alkalinity (R) on the product composition and morphology was studied under fixed temperature, pressure and residence time. Experiments were performed with varying Fe/Ba mole ratios and alkali mole ratio (R). Within mole ratio ranges of 0.5< Fe/Ba< 5, BaO-6Fe2O3 single phase was produced; and as the Fe/Ba mole ratio increased, α-Fe2O3 was also formed and its quantity increased with increasing mole ratio. At an Fe/Ba ratio of 12, stoichiometric mole ratio of BaO-6Fe2O3, the only product formed was α-Fe2O3 fine particles. In the case of the influence of alkalinity, single phase α-Fe2O3 was detected at R of 0.5 and if R exceeded 2, a single phase BaO-6Fe2O3 was detected. According to the results of the experiment and the study of reaction mechanisms, the formation of BaO-6Fe2O3 proceeds via a non-stoichiometric reaction and the product composition and morphology can be controlled by adjusting the reaction parameters to obtain optimum conditions for Ba(OH)2 precipitate formation.

Adsorptive separation of carbon dioxide by polyethyleneimine modified adsorbents

Utilization of carbon dioxide (CO2) has become an important global issue due to significant and continuous rise in atmospheric CO2 concentrations. To find a potential solution, two types of mesoporous materials, MCM-41 and MCM-48, were synthesized and impregnated with 30, 50 and 70 wt% of polyethyleneimine (PEI) in methanol to evaluate the performance of the materials in terms of CO2 adsorption. The materials were characterized by XRD, TGA, FTIR, TEM, SEM, N2-physisorption and BET techniques. All the PEI-loaded materials exhibited substantially higher reversible CO2 adsorption-desorption behaviors with >99% recovery. The above study proved that MCM-48 is a better material as compared to MCM-41 for loading of PEI. The material with 50 wt% loading of PEI on MCM-48, showed maximum adsorption of 248 mg/g-PEI at 80 °C which is about 30 times higher than that of MCM-48 and about 2.3 times that of pure PEI.