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  • Author or Editor: M. Rajić x
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Abstract  

The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method. From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic phase, the mean value of the activation energy of 146.3 kJ mol–1, and the pre-exponential factor of 3.43⋅1014 min–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation energy of153.3 kJ mol–1, and the pre-exponential factor of 4.11⋅1014 min–1 are obtained.

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Abstract  

The paper deals with results of thermal analysis of low-alloyed chromium-molybdenum steel. The methods of analysis were dilatometry, differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The Ac1 and Ac3 temperatures of the steel samples measured by dilatometry and DTA during the heating period were in good agreement. Generated by cooling a martensitic structure first became apparent at 503 K. Tempering of the as-quenched samples showed the presence of the second tempering stage in the region between 473 and 573 K. At that stage heat capacity decreased from 0.48 to 0.32 J g-1 K-1, as a result of conversion of transition carbide due to heat consumption. After normalization of the as-quenched samples the heat capacity values were restored to between 0.42 and 0.47 J g-1 K-1 in the temperature range from 373 to 673 K.

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Abstract  

This article aims to modify conventional epoxy resin by blending with four different Mannich base oligomers. These oligomers are similar to phenolic resin matrix and simultaneously function as amino curing agent for epoxy matrix. In this context, Mannich base oligomers were prepared, respectively, by Mannich polycondensation reaction of four phenols namely phenol, m-cresol, resorcinol and 1,5-dihydroxy naphthalene, respectively, with formaldehyde and piperazine in presence of acid catalyst. The resulting oligomers were characterized by elemental analysis, spectral studies (IR and NMR), number average molecular mass

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estimated by non-aqueous conductometric titration and thermal stability by thermogravimetric analysis (TG). Each of these oligomers was used in resin matrix as a blending component for the modification of commercial epoxy resin for fabricating glass fibre reinforced laminates. Finally, these laminates were evaluated for their synergetic thermal stability, mechanical properties and chemical resistance to different reagents.

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Abstract  

Heat treatment of pipes was performed under industrial conditions at 580C in a dry protective gas containing a CO2–CO–H2–N2 mixture. A commercial adsorbent (733 kg) used for production ofthe gas removed 52.7 l of water in five h and 22.5 min. During the annealing of pipesoxidation and decarburization were not observed. The results were confirmed bymetallographic analysis. The values of enthalpy of water desorption (36.4–40.5 kJ mol–1) obtained by DSC and TG measurements were close to those of water evaporation(44.1 kJ mol–1). This suggests that the bonds between the water molecules andadsorbents were not of chemical but of physical nature.

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A three-year field trial was conducted to study the effect of plant population and harvesting dates on the yield of cleaned 2.0-6.0 mm seed and the seed yield (g) per plant. The highest seed yield was obtained with a spacing of 50 × 12 cm, or 160,000 plants/ha. A decrease in the plant-to-plant spacing to 9 cm decreased the yield by an average of 70 kg/ha over the three study years. The seed yield decreased to an even greater extent when the plant-to-plant spacing was 16 or 24 cm. The seed yields increased the most between the first and second harvesting dates: 400 kg/ha, or 50 kg/ha a day. On the last harvesting date, the seed yield was as low as 5-8 kg/ha. The yield loss was somewhat higher in the most densely sown treatment. The effect of spacing and harvesting date on seed yield per plant was similar to that on total seed yield.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: N. Sonar, Vaishali De, V. Pardeshi, Y. Raghvendra, T. Valsala, M. Sonavane, Y. Kulkarni and Raj Kanwar

Abstract  

99Tc is one of the long lived fission product with high fission yield. From radioactive waste management point of view it is very much essential to evaluate the concentration of technetium in the radioactive liquid waste in order to finalise the treatment process to extract/isolate it from the stream which is discharged to the environment. For the estimation of 99Tc in the radioactive liquid waste stream, extraction of the stable complex of technetium-tetraphenyl arsonium chloride (TPAC) into chloroform followed by beta counting was studied. Various parameters like pH, time of equilibration, concentration of TPAC in chloroform, use of other solvent for extraction as well as interference of various other radionuclides present in the waste were also studied. The radioactive liquid waste being handled in plant contains high concentrations of salts in the form of sodium nitrate. Hence effect of salt concentration on the percentage extraction was also evaluated. The extraction behavior does not dependent on change in the pH of the solution. Almost 99.5% extraction was observed in the pH range of 1–13.0. High concentration of salt is affecting the extraction. However, this can be taken care by diluting the radioactive waste. It takes almost 90 min time for maximum extraction. Presence of radionuclides like 137Cs, 90Sr are not interfering the extraction of 99Tc. However, 106Ru is getting slightly extracted along with 99Tc. The error due to 106Ru can be eliminated by taking gamma spectrum and deducting the activity from the total beta activity to get 99Tc activity. Nitrobenzene can be used for extraction of Tc–TPAC complex in place of chloroform.

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Abstract  

Diffusion of sodium in Mn and Ti bearing sodium borosilicate glass used for the immobilization of the high level waste at the Waste Immobilization Plant, Tarapur has been studied by heterogeneous isotopic exchange using 24Na as the radiotracer for sodium. The temperature dependence of the self-diffusion coefficient of sodium in the glass was found to follow Arrhenius equation below the glass transition temperature.

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