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1

Optimization of Ammonium Sulfamate Nitration for the Preparation of Ammonium Dinitramide

Mandal A. K., Kunjir G. M., Singh J., Adhav S. S., Singh S. K., Pandey R. K., Bhattacharya B., Lakshmi Kantam M.

Central European Journal of Energetic Materials

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2014

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Vol. 11, no. 1

83--97

EN

The reaction kinetics for the preparation of ammonium dinitramide (ADN) is described. ADN is the ammonium salt of the dinitramide anion, and belongs to the group of inorganic oxidizers, mainly useful for energetic rocket propellant formulations, particularly for underwater applications. It is also a potential candidate to replace ammonium perchlorate (AP), in order to develop chlorine-free, green propellants. At HEMRL, ADN is prepared by the nitration of ammonium sulfamate (AS) using mixed acid, followed by hydrolysis, neutralization with ammonia (g) and rectification using solvent. The nitration of ammonium sulfamate (AS) is carried out at a subzero temperature of -40 ±1 °C. The yield of ADN is reliant on the formation of dinitramidic acid, an intermediate product formed during the hydrolysis step, and its stability is predominantly dependent upon the level of acidity and temperature of the reaction medium. Prior to these kinetics studies, process optimization of the nitration of ammonium sulfamate (AS) was performed and gave the final mole ratio of AS:HNO3:H2SO4. Since the nitration of AS is sensitive to temperature, the rate of reaction was studied at fixed temperatures with variation of time, keeping all of the other parameters, such as vessel volume, agitator speed, feed rate etc., constant. During these studies, predetermined quantities of ammonium sulfamate (AS) and mixed acid were allowed to react at a fixed temperature (-40 ±1 °C) for different reaction periods to generate the concentration profile of AS. Using this concentration profile, the reaction order and reaction rate constant were evaluated. In order to find the effect of temperature on the reaction rate and yield, experiments were conducted at other temperatures such as -30 and -50 °C. In the present studies, it was found that the optimum temperature of nitration is -40 ±1 °C and that the rate of reaction follows a pseudo second order process with rate constant 0.01113 (min-1)•(mol/L)-1. The reaction time evaluated for 55 to 60% conversion is about 70-80 minutes at -40 ±1 °C, based on this kinetics. The activation energy of AS nitration was found to be -4.6 kcal/mol, using the reaction kinetic data based on the temperature dependent rate equation derived from Arrhenius’s law.

2

Static, vibration and buckling analysis of skew composite and sandwich plates under thermo mechanical loading

Singh S. K., Chakrabarti A.

International Journal of Applied Mechanics and Engineering

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2013

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Vol. 18, no. 3

887--898

EN

Static, vibration and buckling behavior of laminated composite and sandwich skew plates is studied using an efficient C0 FE model developed based on refined higher order zigzag theory. The C0 FE model satisfies the interlaminar shear stress continuity at the interfaces and zero transverse shear stress conditions at plate top and bottom. In this model, the first derivatives of transverse displacement have been treated as independent variables to overcome the problem of C1 continuity associated with the plate theory. The C0 continuity of the present element is compensated in the stiffness matrix formulation by adding a suitable term. In order to avoid stress oscillations observed in the displacement based finite element, the stress field derived from temperature is made consistent with the total strain field by using field consistent approach. Numerical results are presented for different static, vibration and buckling problems by applying the FE model under thermo mechanical loading, where a nine noded C0 continuous isoparametric element is used. It is observed that there are very few results available in the literature on laminated composite and sandwich skew plates based on refined theories. As such many new results are also generated for future reference.

3

Assay of the Insensitive High Explosive 3-Nitro-1,2,4-triazol-5-one (NTO) by Acid-Base Titration

Nandi A. K., Singh S. K., Kunjir G. M., Singh J., Mandal A. K., Pandey R. K.

Central European Journal of Energetic Materials

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2013

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Vol. 10, no. 1

113--122

EN

The insensitive high explosive 3-nitro-1,2,4-triazol-5-one (NTO) is a weak acid (pKa 3.76) due to the labile N–H bond. The weakly acidic character of this compound is exploited for its assay by aqueous acid-base titration. The NTO sample was dissolved in water and the resultant solution was titrated against 0.07 N NaOH solution using phenolphthalein as indicator. Regular batch samples were assayed by this method and the results were compared with those obtained by the HPLC method. The aqueous acid-base titration method was found to be suitable for the quality control of the product.

4

Assay of the Insensitive High Explosive FOX-7 by Non-Aqueous Titration

Nandi A. K., Paramasivan P., Singh S. K., Mandal A. K., Pandey R. K.

Central European Journal of Energetic Materials

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2012

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Vol. 9, nr 4

343-352

EN

A non-aqueous titration method was developed to assay the insensitive high explosive 1,1-diamino-2, 2-dinitroethene (FOX-7). The weak acidic nature of FOX-7 (pKa 10.6) was exploited in the assay method. The sample was dissolved in the protophilic solvent N, N-dimethylformamide and titrated against sodium methoxide solution in benzene/methanol using azo violet as indicator. FOX-7 samples obtained from regular batch operations were assayed by this method and the results were compared with that of a recrystallized sample. The method is simple, rapid and has good accuracy and precision.

5

Relationship between deep levels and R₀A product in HgCdTe diodes

Singh S. K., Gopal V., Mehra R. M.

Opto-Electronics Review

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2001

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Vol. 9, No. 4

385-390

EN

This paper presents an analysis of the recently reported data of Yoshino et. al. [1,2] on p+ -n HgCdTe diodes with a view to verify quantitatively the previously reported relationship between deep levels and R₀A product of the diodes. The result of this analysis suggests that the trap level, located below 6 meV from the bottom of the conduction band edge, contributes to the trap assisted tunnelling currents in the medium reverse bias region. also there is evidence that zero bias resistance aera product is limited by the ohmic surface leakage and generation-recombination contributions. The observed current-voltage (I-V) characteristic and dynamic resistance-voltage (Rd-V) characteristics have been shown to excellently fit the theory by taking into account the contributions due to: (i) thermal diffusion of minority carrier from the neutral regions, (II) generation-recombination (g-r) current in the depletion region, (III) assisted tunnelling (TAT) currents due to a trap level located at 6 meV below the bottom of the conduction band edge, (iv) band to band tunnelling (BTB) currents, and (v) ohmic component of surface leakage currents. Though the R₀A product of the diodes is shown to be limited by g-r and surface concentrations, the variation in R₀A product of the diodes is interpreted as arsing due to the variation in planar area of the diodes accompanied with the varying surface contributions, since g-r contribution should remain constant for all diodes.