[Show abstract][Hide abstract] ABSTRACT: Nanostructures of single crystallites of spinel LiMn2O4 (LMO) were prepared by the simple pyrolysis of aqueous solution of LiNO3 and Mn(NO3)2 in a confined space such as either droplets or mesopores. When the mixed nitrate solution was spray pyrolyzed at temperatures below 700 °C, 1-μm LMO spheres were obtained consisting of ~20-nm single crystallites randomly packed. Such LMO phase, once obtained, would sustain for further heat-treatment. Next, new spraying solution was prepared by adding the precursor for mesoporous silica (MPS) to the nitrates solution. By spray pyrolyzing such solution, LMO was impregnated inside pores of the MPS being structured. The silica could be removed by subsequent NaOH treatment to leave spherical LMO mesophase. The nitrates was also able to soak into the existing MPS having cylindrical pores and form short isolated LMO chains in the mesopores by the subsequent heating. After the same NaOH treatment, the LMO phase turned into bundles of very ‘long’, and often straight, chains, consisting of 8-nm LMO nanoparticles. This will be elucidated through further study.
No preview · Article · Sep 2013 · Journal of Sol-Gel Science and Technology
[Show abstract][Hide abstract] ABSTRACT: High-temperature CO2 sorbents were prepared by leaching and recrystallizing of calcium resources such as steel slag, tail-wollastonite, waste cement and fly ash. Alumina and small amount of silica in the sorbents were useful to maintain the CO2 sorption for more than 30 cycles. However, the silica, if included more than 10 mol% with respect to CaO, had negative effect on the sorption by more than its mole fraction. Thus, it was necessary to control Si dissolution for the resources composed of calcium silicate such as steel slag. The highest sorption of the sorbents from steel slag was 49% with 66% calcium utilization. On the other hand, if silica is in ‘free’ state, such as in waste cement, it hardly dissolves in the acid. Therefore, the sorbent could be prepared in core(SiO2)–shell(CaO) type by restructuring waste cement to show 100% utilization of the calcium in the shell.
No preview · Article · Jul 2012 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: Industrial wastes that have calcium silicates as main ingredients include steelmaking slag, wasted cement, fly ashes and so on. We separated and/or re-crystallized calcium oxide and silica from these wastes. The concentration of acetic acid as an extract, extraction time, and extraction temperature had significant influence on the composition of the extract or the raffinate. We found that more silica was extracted with lower temperature, higher concentration of acetic acid and shorter extraction time. Under the same conditions of extraction, silica in the slag was more extractable than that in waste cement. In the former, extracted silica was gelated out of the extract while the recrystallized solids on the gel showed very low CO2 absorptivity. On the other hand, porous solids recrystallized from the latter was more active for the absorption. The absorptivity was kept almost constant in their repeated use.