Naoto Tsubouchi

Chemical characterization of dust particles recovered from bag filters of electric arc furnaces for steelmaking: Some factors influencing the formation of hexachlorobenzene

To make clear some factors controlling the formation of hexachlorobenzene (HCB) in the process of electric arc furnace (EAF) steelmaking, six dust samples recovered from different bag filters in commercial EAF steelmaking plants have been characterized with XRD, SEM-EPMA, XPS and temperature-programmed desorption (TPD) techniques. These dust samples contain 1.9-8.0 mass% of chlorine element, and the XPS and TPD measurements exhibit that the Cl is enriched at the dust surface and composed of the inorganic and organic functionalities, part of the Cl being evolved as HCl in the temperature region of flue gas treatment. All of the samples also include 2.1-6.4 mass% of carbon element, and some of the C can release CO(2) in the TPD up to 300°C to form active carbon sites. The number is related closely to HCB concentration of each dust. Further, it is suggested that the Zn present in the samples consists of ZnFe(2)O(4), ZnO and surface ZnCO(3), and the dust with a larger content of the ZnCO(3) has a higher concentration of HCB. It is possible that HCB formation occurs via gas-solid-solid interactions among gaseous Cl-containing compounds in flue gas, active carbon sites and surface Zn-species produced in exhaust ducts and bag filters.

Synthesis of BaTiO3 nanoparticles from TiO2-coated BaCO3 particles derived using a wet-chemical method

Abstract BaCO3 particles coated with amorphous TiO2 precursor are prepared by a wet chemical method to produce BaTiO3 nanoparticles at low temperatures. Subsequently, we investigate the formation behavior of BaTiO3 particles and the particle growth behavior when the precursor is subjected to heat treatment. The state of the amorphous TiO2 coating on the surface of BaCO3 particles depends on the concentration of NH4HCO3, and the optimum concentration is found to be in the range 0.5–1.0 M. Thermogravimetric curves of the BaCO3 particles coated with the TiO2 precursor, prepared from BaCO3 particles of various sizes, show BaTiO3 formation occurring mainly at 550–650 °C in the case of fine BaCO3 particles. However, as evidenced from the curves, the temperature of formation of BaTiO3 shifts to higher values with an increase in the size of the BaCO3 particles. The average particle size of single phase BaTiO3 at heat-treatment temperature of 650–900 °C is observed to be in the range 60–250 nm.

Chemical characterization of unburned carbon in coal fly ashes by use of TPD/TPO and LRS methods.

Functional forms of the unburned carbon present in six kinds of coal fly ashes have been examined mainly by the temperature-programmed desorption (TPD)/temperature-programmed oxidation (TPO) and laser Raman spectroscopy (LRS) methods. The carbon contents of the ash samples range from 0.4 to 4.1 mass%. The LRS analysis shows that the C consists of both amorphous and crystallized forms, and the proportion of the former is as large as 50-65 C%. Further, the TPD measurement exhibits that the C contains several types of surface oxygen species, such as carboxyl and lactone/acid anhydride groups, which can readily be decomposed into CO2 up to 700 °C to provide active carbon sites. The results of the TPD also indicate that the ashes have surface CaCO3, and most of this species can be converted to CaO and CO2 around 600-700 °C. Interestingly, there is a significant correlation between organic fluorine concentrations and carboxyl/lactone/acid anhydride groups or surface CaCO3 contents in the ash samples. It might thus be possible that the formation of organic F forms proceeds through gas-solid-solid interactions among HF (and/or F2) in flue gas, active carbon sites and surface Ca species produced around 600-700 °C downstream of coal-fired boilers.