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- Author or Editor: J.-S. Lee x
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Abstract
The new polycyclic nitramine 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) has been focused as a considerable amount of research recently on investigating its polymorphs, relative stability, and respective reaction chemistry. It is known as CL-20 popularly, CL-20 is a very high-energy and relatively high oxygen balance value crystalline compound whose method of synthesis and detailed performance data are still classified. 5-oxo-3-nitro-1,2,4-triazole (NTO, or nitrotriazolone) was an insensitive molecule comparison general explosives, and the NTO based polymer bonded explosives (PBX) was a low vulnerability explosive. Both energetic materials are all very important high explosives, which is used in a variety of military formulations widely owing to the properties of high energy and desensitization of PBX, many researchers have demonstrated the usefulness of above two energetic materials in explosive component. In this work, the thermal decomposition characteristics of explosives CL-20 and NTO were studied using thermal analytical techniques (TG, DSC), then the compatibility of above two explosives with silicone rubber, and the decomposition kinetic parameters such as activation energies of decomposition, the frequency factor of the decompose reaction are also evaluated by non-isothermal DSC techniques.
Abstract
A procedure is presented to provide sequential determination of isotopic strontium, thorium, plutonium, uranium, and americium in a single biological sample. The method begins with digestion and dissolution of the sample. Tracers and/or carriers are added to the sample for the purpose of chemical yield monitoring. Strontium is first separated from the actinides and from most of the interfering constituents of the sample by precipitation as carbonates. Strontium isotopes are purified, and 89Sr and 90Sr are measured by gas proportional counting. Actinides are separated and purified by ion exchange chromatography, co-precipitated with neodymium fluoride, filtered, and counted by alpha-particle spectrometry.
Abstract
Sorption experiments for radionuclides such as 14C, 99Tc, 137Cs, 90Sr, 63Ni, and 241Am were conducted using two different groundwaters (GM-1 and SS-5) and solid materials (granodiorite and fracture-filling material) sampled from the Wolsong low- and intermediate-level radioactive waste (LILW) repository, Gyeongju, Korea. The distribution coefficients of the radionuclides, K d’s, were obtained and their sorption properties were discussed for each radionuclide. For all sorbing radionuclides, the K d values for the fracture-filling material were observed to be higher than those for granodiorite regardless of the groundwater. The K d values were increased in the sequence 99Tc < 14C < 90Sr < 137Cs < 63Ni < 241Am regardless of sorbent types implying that the sorption of radionuclides onto geological media is affected by their chemical behavior in accordance with geochemical environments. Anionic radionuclides such as 14C and 99Tc showed very low K d values both for the granodiorite and fracture-filling material. The mineralogical composition of the geological media and groundwater conditions was also observed to be important in the sorption of sorbing radionuclides, especially in the case of strongly sorbing radionuclides.
Summary
Some stability and convergence theorems of the modified Ishikawa iterative sequences with errors for asymptotically nonexpansive mapping in the intermediate sense and asymptotically pseudo contractive and uniformly Lipschitzian mappings in Banach spaces are obtained.
Abstract
The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural composite materials.
This study aimed to develop a chromatographic method to quantitatively determine phenol in fish tissues. This method involves solvent extraction of acidified samples, followed by derivatization to phenyl acetate and analysis with gas chromatography coupled with mass spectrometry (GC–MS). Phenol in a representative tissue sample (belly, gill, or renal tubules), which was homogenized with 2 N sulfuric acid, was extracted with ethyl acetate and derivatized to phenyl acetate using acetic anhydride and K2CO3 in water. An n-butyl acetate extract was injected into the GC–MS. The linearity (r 2) of the calibration curve was greater than 0.996. The analytical repeatability, which is expressed as the relative standard deviation, was less than 6.14%, and the recovery was greater than 96.3%. The method detection limit and the limit of quantitation were 8.0 μg/kg and 26 μg/kg, respectively. The proposed method is also applicable to the analysis of other biological tissues for phenol and its analogs, such as pentachlorophenol.
Abstract
Radiation treatment with gamma-rays was used to improve the biodegradability of EDTA that is known to be a non-biodegradable substance. The effect of metal ions and catalysts on the treatment of EDTA was studied first. The removal of EDTA was definitely decreased in the presence of metal ions such as Cr(III), Cd(II), Pb(II) and Cu(II) at doses greater than 3 kGy. The addition of a TiO2
Summary
New, quantitative methods for the determination of actinides have been developed for application to marine environmental samples (e.g., sediment and fish). The procedures include aggressive dissolution, separation by anion-exchange resin, separation and purification by extraction chromatography (e.g., TRU, TEVA and UTEVA resins) with measurement of the radionuclides by semiconductor alpha-spectrometry (SAS). Anion-exchange has proved to be a strong tool to treat large volume samples, and extraction chromatography shows an excellent selectivity and reduction of the amounts of acids. The results of the analysis of uranium, thorium, plutonium and americium isotopes by this method in marine samples (IAEA-384, -385 and -414) provided excellent agreement with the recommended values with good chemical recoveries.
Abstract
Most elemental concentrations in crops should be related to those in soil and other circumferential environments. In the present study, more than thirty minor and trace elements in soils and crops were determined by the use of ICP, XRF and NAA. Soil and crop samples were collected at eleven abandoned mine regions in Chungnam province located in the middle part of Korea. The elemental concentrations in soils were compared to the crustal mean concentrations in both Chungnam area and worldwide. The concentration ratios of the elements in soils and crop compartments were calculated and the distribution characteristics of each element were investigated between soil and crop compartments.
Summary In this study, the thermal properties of agro-flour-filled polybutylene succinate (PBS) bio-composites were investigated. PBS is one of the biodegradable polymers made from the condensation reaction of glycols and dicarboxylic acid and is naturally degraded by natural soil burial system. The thermal properties of the bio-composites were analyzed according to the agro-flour content and mesh size. On increasing agro-flour content, the thermal stability, degradation temperature and derivative thermogravimetric curve (DTGmax) temperature of the bio-composites decreased while the ash content increased. The thermal degradation of the bio-composites was not affected by agro-flour mesh size. The glass transition (T g) and melting (T m) temperatures of the bio-composites were not significantly changed. The storage modulus (E’) of the bio-composites was higher than that of neat PBS, because the incorporation of agro-flour increased the stiffness of the bio-composites. At higher temperatures, E’ of the bio-composites decreased due to the increasing viscosity and chain mobility of neat PBS. The thermal properties of bio-composites have an important effect on the manufacturing system and application methods.
