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Abstract  

Pooling lauroyl peroxide (LPO) with nitric acid, we used differential scanning calorimetry (DSC) to assess the thermokinetic parameters, such as exothermic onset temperature (T 0), heat of decomposition (ΔH d), frequency factor (A), and the other safety parameters. When LPO was contaminated with nitric acid (HNO3), we found the exploder 1-nitrododecane. Obvious products were sensitive and hazardous chemicals. Concentration reaching 1–12 N HNO3 emitted a large amount of heat. This study combined with curve-fitting method to elucidate its unsafe characteristics and thermally sensitive structure to help prevent runaway reactions, fires and explosions in the process environment. According to the findings and the concept of inherently safer design, LPO runaway reactions could be adequately prevented in the relevant plants.

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Abstract

With two active O–O peroxide groups, 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC) has a certain degree of thermal instability. It is usually used as an initiator in chemical processes, and therefore reckless operation may result in serious thermal accidents. This study focused on the runaway reactions of BTBPC alone and mixed with various concentrations of nitric acid (1, 2, 4, and 8 N). The essential thermokinetic parameters, such as exothermic onset temperature (T o), activation energy (E a), frequency factor (A), time to maximum rate under adiabatic condition (TMRad) and time to conversion limit (TCL), were evaluated by differential scanning calorimetry at the heating rate of 4 °C min−1, and a kinetics-based curve fitting method was used to assess the thermokinetic parameters. All the results indicated that BTBPC mixed with one more than 4 N nitric acid dramatically increased the degree of thermal hazard in the exothermic peak and became more dangerous. However, it was relatively safe for BTBPC mixed with less than 1 N nitric acid under 34.5 °C.

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Abstract  

We have developed a laser flash apparatus for simultaneous measurements of thermal diffusivity and specific heat capacity of solid materials by introducing recent technical progress: uniform heating by a homogenized laser beam using an optical fiber with a mode mixer, measuring transient temperature of a specimen with a calibrated radiation thermometer, analyzing a transient temperature curve with a curve fitting method, to achieve differential laser flash calorimetry. Thermal diffusivity, specific heat capacity and thermal conductivity of glassy carbon and molybdenum were measured in the temperature range from 300 to 1100 K.

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Summary Relaxation behavior of GeySe100-y (y=8 and 10) glasses related to the viscosity behavior was studied by dilatometry. The method of two consecutive temperature jumps was applied to study the volume relaxation. The relaxation response can be described by Tool-Narayanaswamy-Moynihan model and the parameters of this model ?h*, ß, x, A were determined using curve fitting method and characteristic times method. Viscosities of studied materials in the range of 108-1013 Pas were measured by penetration method. The calculated values of activation energies of viscous flow E? are close to the values of effective activation energies of relaxation ?h* for studied chalcogenide materials.

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Summary  

A new acquisition and evaluation procedure has been introduced for the measurement of time-dependent processes in gamma-ray spectrometry, in order to extract more information, including half-lives, from the data recorded during acquisition and to enable a more comprehensive analysis of the results. These advanced, off-line data evaluation techniques improve the selectivity and the background subtraction and make it possible to estimate the important analytical parameters (e.g., half-lives) more accurately than with the usual decay curve fitting method.

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Abstract  

A new and simple method for selective spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol (PAR) and N-octylacetamide into benzene over pH 7.0–9.0 is described. The molar absorptivity of the complex with 9 different amides is in the range of (0.40–3.2)·104 1·mol–1·cm–1 at the absorption maximum. Out of these, the most sensitive compound N-octylacetamide (OAA) was chosen for detailed studies in the present investigation. The detection limit of the method is 0.008 g U·ml–1. The system obeys Beer's law in the range of 0–5 g U·ml–1. The method is free from interferences of most of the common metal ions except vanadium(V) and copper(II), which are masked by proper masking agents. The composition of the complex is determined by curve-fitting method. The method has been applied for the recovery of the metal from rock samples and synthetic mixtures.

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Abstract  

Humic substances (HSs) occur throughout the ecosphere in soils, waters and underground systems. The strong complexation of HSs is of importance in the migration of radionuclies in geological media. Renewed interest in stability constants of complexes of radioelements and radionuclides with humic and fulvic acids has been generated by problems associated with the nuclide migration in the environment. Use of the ion exchange method for the determination of conditional stability constants of metal-HS complexes was examined and reviewed. The complexation of HS to metal ions cannot be described in rigorous mathematical terms because of the ill-defined nature of HSs in contrast with the complexation of single ligands. Furthermore, the advantages and disadvantages of Schubert's and, Ardakani-Stevenson's, curve fitting methods were discussed. The great stabilities of HS complexes to rare earths (Yb(III), Tb(III), Eu(III), Gd(III)), americium(III), cobalt(II), uranyl(VI) and thorium(IV) were revealed.

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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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Kinetic analysis of thermogravimetric data

XIV. Three integral methods and their computer programs

Journal of Thermal Analysis and Calorimetry
Authors: J. Zsakó and J. Zsakó

Computer programs are given in Fortran language for three integral methods of deriving kinetic parameters from TG curves. Method 1 is a computerized variant of Doyle's curve-fitting method and performs the calculation of the exponential integralp(x) by means of author's empirical formula. Methods 2 and 3 are variants of the Coats-Redfern linearization method. Testing of the methods on both theoretical and experimental TG curves shows them to be almost equivalent as far as the results obtained are concerned, but Method 1 needs a ten-fold higher computer time.

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A complex investigation was performed for a polluted area using both experi-mental and computer modelling methods. Among the experimental methods the adsorption and desorption isotherms were measured to estimate the concentration dependent equilibrium in the soil-groundwater system. A new calculation method was worked out for determining the transport para-meters from results of laboratory tests. Heavy metal solution was leached through a soil column continuously. The effluent fluidum was collected, and the heavy metal concentration of the collected fractions was measured by atomic absorption spectrophotometer. As the result of the analytic process breakthrough curves were measured in laboratory scale. Due to the applied initial and boundary conditions the transport equation can be solved analytically. Using the Ogata and Banks (1961) solution of the transport equation a new curve fitting method was introduced. After several transformations of the equation a theoretical function was fitted to the measured concentration vs. time and to the concentration vs. effluent volume data. The parameters of the fitted curve could be used as the dispersion and retardation parameters of a transport model.  The water chemistry of the system controls the rate of adsorption and desorption of metals to and from sediment. Adsorption removes the metal from the water column and stores the metal in the substrate. Desorption returns the metal to the water column, where recirculation and bioassimilation may occur. Metals are probably desorbed from the soil if the salt concentration of the water increases, and in case of some metals decreases with the redox potential and with pH.  Parallel to determining the basic transport parameters of the system using the column study, the maximal equilibrium concentration of chromium-containing compounds with different oxidation states were calculated with the MINTEQ model with two variable functions (pH and redox potential). As a result of the calculations a non-liner relation was established, as at specific points the maximal equilibrium concentration of chromium increases with a high gradient. This means that there are combinations of pH and redox potential values in the case of which chromium has a high solubility. It is advisable to avoid these points in the pH-E h field if we want to stabilize the contaminant. This state is to be reached when the goal is the mobilization of the pollutant to make the soil cleaning process possible. With the introduced calculation method areas on the pH-redox potential field (at high pH and E h values) are found in which the concentration of pollutants may reach a critical value. The introduced calculation method is quick and gives results accurate enough for a pilot test.

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