Dielectric relaxations above room temperature in DMPU derived polyaniline film

Dielectric measurements carried out on drop casted from solution of emeraldine base form of polyaniline films in the temperature range 30–300 °C revealed occurrence of two maxima in the loss tangent as a function of temperature. The activation energies corresponding to these two relaxation processes were found to be ∼0.5 eV and ∼1.5 eV. The occurrence of one relaxation peak in the dispersion curve of the imaginary part of the electric modulus suggests the absence of microphase separation in the film. Thermogravimetric analysis and infrared spectroscopic measurements showed that the films retained its integrity up to 300 °C. The dielectric relaxation at higher temperatures with large activation energy of 1.5 eV is attributed to increase in the barrier potential due to decrease in the polymer conjugation as a result of wide amplitude motion of the chain segments well above the glass transition temperature.     

Economic Batch Quantities for Manufactured Parts

The fundamental assumption in the classical Economic Batch Quantity model is that the products which are manufactured by a company have demands which are independent of each other. In an assembly operation, the demand for the components is mainly due to the demand for the parent assembly and hence the classical model is not applicable. In such a situation, requirements planning methodology may be successfully employed. A case study is described in this paper in which a number of factors besides set-up and stock-holding costs are considered. The results have proved to be of considerable benefit to the company.     

Regioselective Synthesis of Nitrofuran Containing Novel Spiropyrrolidine Library through 1,3‐Dipolar Cycloaddition Reactions

A novel series of nitrofuran containing spiropyrrolidines has been synthesized with high regioselectivity in moderate to excellent yields via 1,3‐dipolar cycloaddition reaction of azomethine ylides with various substituted chalcones.     

Differential thermal analysis of potassium perchlorate

A study has been made of the differential thermal analysis of (i) potassium perchlorate in powdered form, (ii) potassium perchlorate in pelletized form, (iii) potassium perchlorate recrystallized from liquid NH₃, and (iv) potassium perchlorate preheated for 24 hours at 375°. Pretreatment of potassium perchlorate leads to a desensitization of both endothermic and exothermic processes. Additionally, the pretreatment tends to convert the symmetric exotherm into an asymmetric exotherm due to merging of the two exotherms. An analysis of the factors causing asymmetry in the exotherm has thrown fresh light on the mechanism of thermal decomposition of potassium perchlorate.

---

Zusammenfassung Eine differentialthermoanalytische Untersuchung wurde an, (i) Kaliumperchlorat in Pulverform, (ii) Kaliumperchlorat in pelletisierter Form, (iii) Kaliumperchlorat, umkristallisiert aus flüssigem Ammoniak und (iv) Kaliumperchlorat, 24 Stunden bei 375° vorgeheizt, durchgeführt. Die Vorbehandlung von Kaliumperchlorat führt zu einer Verdichtung sowohl der endothermen als auch der exotherman Vorgänge. Ausserdem führt die Vorbehandlung zur Umwandlung der symmetrischen Exotherme in eine asymmetrische Exotherme durch Vereinigung der zwei Exothermen. Die Analyse der die Asymetrie der Exothermen verursachenden Faktoren zeigte den Mechanismus der thermischen Zersetzung des Kaliumperchlorats unter neuen Gesichtspunkten.

---

Résumé On a effectué l'étude par analyse thermique différentielle du perchlorate de potassium: (i) en poudre, (ii) sous forme comprimée, (iii) recristallisé dans NH₃ liquide, (iv) préchauffé à 375° pendant 24 heures. Le traitement préalable du perchlorate de potassium entraîne la désensibilisation des processus endothermiques et exothermiques. De plus, le traitement préalable tend à convertir l'exotherme symétrique en un exotherme asymétrique, du fait de la fusion des deux exothermes. Une analyse des facteurs causant l'asymétrie de l'exotherme a donné une vue nouvelle du mécanisme de la décomposition thermique du perchlorate de potassium.

---

, , , 375° 24 . . , , . , , .

---

---

This work has been supported by a grant from the Indian Space Research Organization (I.S.R.O). It also includes financial support to one of the authors (D. S.). This support is gratefully acknowledged.     

Kinetics of low temperature hydrogen reduction of the metastable spinels

The kinetics of reduction at relatively low temperatures with hydrogen of pure and doped metastable non-stoichiometric magnetite with 1 at% Mn, Co, Ni and Cu and also with 5 at % Ni and Cu have been investigated by using isothermal thermogravimetry in the temperature range 300–400°C. With increase in the concentration of the dopant (5 at% Ni and Cu), the reactivity increases. The activation energies for pure magnetite varies from 7 to 9 kcal/mole with the preparation temperature of precursorf Fe₂O₃ (250–400°C), being the lowest for those prepared at the lowest temperatures. The corresponding activation energies for the reduction of doped samples (Fe, M)_3?zO₄, it depends, apart from their porosity and surface areas, on the nature of the solute atom, amount of disorder, whether it occupies the tetrahedral (A) or octahedral (B) sites in the non-stoichiometric spinel and possibly on hydrogen ‘Spill over’ effects.