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  • Author or Editor: J. Tseng x
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Abstract  

It was found that trace amount of various ions could be effectively adsorbed onto hydrous magnesium oxide from aqueous solution. Attempts were made to investigate the feasibility of using hydrous magnesium oxide as preconcentration agent for neutron activation analysis (NAA). The procedure was successfully applied for the measurements of trace amounts of elements in the surface water of a number of large rivers which play very important roles in the lives of local people. Some of them are polluted rather badly. In order to improve the living standards it is rather important to establish reliable analytical methods so that more effective surveillance may be enforced on pollution control problems. NAA is generally accepted as one of the most suitable methods for simultaneous and multielemental determination of trace amounts of elements. In this work polluted surface waters were investigated by NAA using Tsing Hua Open-pool Reactor (THOR).

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Abstract  

We have recently developed a new method of measuring the initial51Cr(III) produced from nuclear recoil of K2CrO4. In our method, K2CrO4 was mixed with MgO in the presence of a small amount of water, and the mixture was irradiated in a nuclear reactor. After irradiation, the mixture was dissolved in water, and MgO precipitate was separated from the solution. The yield of recoil51Cr(III) could be calculated from the51Cr activity in the precipitate measured. On the other hand, the yield of retention of51Cr as chromate could be calcualted from the activity found in the supernatant. The51Cr(III) yield thus obtained is almost a factor of 2 higher than observed in pure K2CrO4 without mixing with MgO, irradiated under the same condition. Another important observation is that the51Cr(III) yield is independent of irradiation time in the presence of MgO. Without MgO, the observed51Cr(III) yield decreases with increasing irradiation time, suggesting possible oxidation of Cr(III) to chromate during irradiation. This variation is not observed in the system of K2CrO4 containing MgO, indicating that the initial Cr(III) is adsorbed immediately after nuclear recoil by MgO and is protected from oxidation by gamma radiation.

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Abstract  

The radioactive tracer technique was used to investigate the adsorption behaviour of 47 ions onto hydrous magnesium oxide. Detailed studies on Co(II), Zn(II), La(III) and Ce(III) reveal that the adsorption isotherms of these ions obey Langmuir's law. Radiochemical separation using hydrous magnesium oxide was applied to the RNAA of NBS standard reference materials, and satisfactory results were obtained. Hydrous magnesium oxide was also used to adsorb various ions from aqueous solution for the purpose of preconcentration which was followed by NAA or ICP-AES analysis. Satisfactory results have been observed in both methods.

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Abstract  

Tert-butyl peroxybenzoate (TBPB) is one of the sensitive and hazardous chemicals which have been popularly employed in petrifaction industries in the past. This study attempted to elucidate its unsafe characteristics and thermally sensitive structure so as to help prevent runaway reactions, fires or explosions in the process environment. We employed differential scanning calorimetry (DSC) to assess the kinetic parameters (such as exothermic onset temperature (T 0), heat of reaction (ΔH), frequency factor (A)), and the other safety parameters using four different scanning rates (1, 2, 4 and 10°C min−1) combined with curve-fitting method. The results indicated that TBPB becomes very dangerous during decomposition reactions; the onset temperature and reaction heat were about 100°C and 1300 J g−1, respectively. Through this study, TBPB accidents could be reduced to an accepted level with safety parameters under control. According to the findings in the study and the concept of inherent safety, TBPB runaway reactions could be thoroughly prevented in the relevant plants.

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Abstract  

Organic peroxides have caused many serious explosions and fires that were promoted by thermal instability, chemical pollutants, and even mechanical shock. Cumene hydroperoxide (CHP) has been employed in polymerization and for producing phenol and dicumyl peroxide (DCPO). Differential scanning calorimetry (DSC) has been used to assess the thermal hazards associated with CHP contacting sodium hydroxide (NaOH). Thermokinetic parameters, such as exothermic onset temperature (T 0), peak temperature (T max), and enthalpy (ΔH) were obtained. Experimental data were obtained using DSC and curve fitting using thermal safety software (TSS) was employed to obtain the kinetic parameters. Isothermal microcalorimetry (thermal activity monitor, TAM) was used to investigate the thermal hazards associated with storing of CHP and CHP mixed with NaOH under isothermal conditions. TAM showed that in the temperature range from 70 to 90°C an autocatalytic reaction occurs. This was apparent in the thermal curves. Depending on the operating conditions, NaOH may be one of the chemicals or catalysts incompatible with CHP. When CHP was mixed with NaOH, the T 0 is lower and reactions become more complex than those associated with assessment of the decomposition of the pure peroxide. The data by curve fitting indicated that the activation energy (E a) for the induced decomposition is smaller than that for decomposition of CHP in the absence of hydroxide.

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Abstract  

An approach based on sequential extraction separation and the subsequent ICP-MS measurement was introduced to determine 99Tc in radioactive wastes. The radwastes were firstly alkaline-fused and the 99Tc was separated by a sequential solvent extraction prior to ICP-MS measurement. NaDDC was selected as a chelation reagent in the solvent extraction processes. The influence of HCl and matrix concentration on the recovery yield and the effectiveness of removing isobar and unwanted radionuclides, such as 137Cs, 54Mn, 60Co and 110mAg, were evaluated. The designed sequential extraction procedure was optimized by an extraction experiment. The proposed technique is proven to be a simple and practical alternative for 99Tc determination in low-level radioactive wastes; chemical separation of 99Tc can be simplified and preconcentration such as precipitation and/or ion exchange, before the solvent extraction, can be excluded.

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Abstract  

In this study, a mixture of methyl ethyl ketone peroxide (MEKPO) with various contaminants, such as H2SO4 and NaOH, was prepared in order to elucidate the cause of these accidents and the results of upset conditions. Thermokinetic parameters were acquired by both differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2). In addition, we simulated the thermokinetic parameters and created kinetic models for the specific contaminants. The results indicate that the thermal hazard of MEKPO is less than that of the mixed MEKPO with the above-mentioned contaminants. Consequently, the evaluated parameters could be used to prevent any unexpected exothermic runaway reaction or to alleviate hazards to an acceptable extent, if such a reaction occurs.

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Abstract  

Methyl ethyl ketone peroxide (MEKPO) possesses complex structures which have caused many incidents involving fires or explosions by mixing with incompatible substances, external fires, and others. In this study, reactivities or incompatibilities of MEKPO with inorganic acids (HCl, HNO3, H3PO4 and H2SO4) were assessed by differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2). Parameters obtained by the above-mentioned devices could be readily employed to discuss the runaway reaction, such as onset temperature (T 0), heat of reaction (ΔH d), time to maximum rate (TMR), maximum self heat rate (dT/dt)max, adiabatic temperature rise (ΔT ad), maximum pressure of decomposition (P max) and so on. Mixing MEKPO with hydrochloric acid resulted in the lowest T 0 among inorganic acids. Nitric acid not only lowered the T 0 but also delivered the highest heat releasing rate or self heat rate (dT/dt), which was concluded to be the worst case in terms of contamination hazards during storage or transportation of MEKPO.

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Abstract  

Styrene is an important chemical in the petrochemical industry. In recent years, there have been sporadic releases, runaway reactions, fires, and thermal explosion accidents incurred by styrene and its derivatives worldwide. The purpose of this study was to estimate the impact of styrene and its derivatives of α-methylstyrene (AMS) and trans-β-methylstyrene (TBMS) contacting with benzaldehyde. Experiments were carried out to evaluate the thermokinetic parameters estimated by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III). TAM III was used to determine the fundamental thermokinetics under various isothermal temperatures, 80, 90 and 100°C. This autocatalytic reaction was demonstrated in thermal curves. After styrene was contacted with benzaldehyde, the exothermic onset temperature (T 0) and the total heat of reaction (Q total) were altered by DSC tests. When benzaldehyde is mixed with AMS and TBMS, the reaction time will be shorter but the enthalpy reduced, as revealed by TAM III tests. As AMS and TBMS, respectively, were contacted with benzaldehyde, both exothermic phenomena were changed during the reaction excursion. According to the results of this research, an operator should dictate the oxygen concentration in order to avoid any potential hazards during handling and transportation.

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Abstract  

Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics regarding stability would represent potential hazards during the production or utilization stage and could be determined by calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate the thermokinetic parameters for MWNTs at various compositions. Thermoanalytical curves showed that the average heat of decomposition (ΔH d) of the MWNTs samples in a manufacturing process was about 31,723 J g−1, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence of sulfuric acid (H2SO4). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch addition with reactants of H2SO4. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation or accident.

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