Effect of particle size and shape of NTO on micromeritic characteristics and its explosive formulations

doi:10.1016/j.powtec.2013.11.029

Powder Technology

Volume 253, February 2014, Pages 276-283

https://doi.org/10.1016/j.powtec.2013.11.029 Get rights and content

Highlights

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Prepared spherical NTO of specific particle size viz., 150,100,25,15, 10 & < 5 μm
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Micromeritic properties of NTO were determined and correlated with size & shape.
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Bimodal mixture was identified based on packability & flowability parameters.
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Paste explosive formulations were made and their flow behavior studied.
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Spherical NTO brought down the viscosity by about 75% compared with non-spherical.

Abstract

Particles with spherical shape and specific size distribution are major considerations in achieving high performance, solid loading and mix fluidity in processing of energetic materials for high explosive/rocket propellant applications. Spherical 3-Nitro-1, 2, 4-triazol-5-one (NTO) of specific particle size distribution (PSD) was prepared by a proprietary process and the powders were characterized by X-ray powder diffraction, thermal and spectral methods. Present study explores the spherical-NTO of specific particle size D (4, 3) of 150, 100, 25, 15, 10, and less than 5 μm and their bi/trimodal mixtures for their micromeritic properties. From the packability and flowability constants, bimodal mixture of coarse (150 μm) to fine (25 μm) ratio of 70:30 is found to be optimum for processing in explosive formulations. Paste explosive formulations were made based on identified bimodal mixture and their flow behavior studied by viscosity studies. The study inferred that spherical particles of NTO bring down the viscosity by about 75% for the same explosive content to binder ratio in comparison with non-spherical-NTO. Porosity data also supports the same for improvement in explosive loading by 10% by the usage of spherical-NTO over non-spherical particles for the given explosive to binder ratio.

Graphical abstract

Micromeritic characterization of 3-Nitro-1, 2, 4-triazol-5-one (NTO) powder is very much essential before it is realized in the explosive formulations. Effects of particle size and shape on various micromeritic properties of NTO powders were studied. A bimodal distribution comprising of 150 and 25 μm spherical NTO particles in 70:30 ratio has been identified by considering density and flowability. Paste explosive formulations were made with the bimodal mixture and viscosity studies ensured the improvement in mix-fluidity of these compositions based on spherical-NTO compared with non-spherical-NTO. Porosity data also supports the same improvement in explosive loading by 10% by the usage of spherical-NTO over non-spherical one, for the given explosive to binder ratio. Overall the study concludes that the spherical NTO powders are vital in realizing the HE/propellant formulations with increased explosive content that can lead to enhanced performance.

Introduction

Powder technology applications demand particular size and shape of solids which are very crucial to achieve high packing density arrangements thereby enhancing the amount of solids per unit volume [1]. The specific particle size distribution with spherical shape is an important criterion in industries like nano-materials, pharmaceuticals and especially high energy materials. The particle size significantly influences many properties of particulate materials and offers valuable indication for quality control and performance. A coarse spherical particle flows more easily and leads to obtaining high bulk density [2]. Fine particles with desired shape are always required to improve the ballistic parameters; further the maximum energy output obtained from detonation wave in the case of solid explosives and propellants due to high surface area [3], [4]. Hence, it is very important to measure and control the particle size and its distribution. Mixture of two or more distributions (bi/tri/multi-modal) is also used to achieve theoretical maximum density and thus, performance [5].

In explosive formulations, shape of the particles also plays a key role in realizing better packability and processability. It is reported that spherical particles of explosives improve the mix-fluidity of formulations and have great impact on scale to alter the performance and insensitivity towards a sudden shock than non-spherical crystals [6].

Globally, insensitive munition (IM) class of formulations is being developed over the conventional munitions. 3-Nitro-1, 2, 4-triazol-5-one (NTO) is proven to be one of the promising insensitive candidates in high explosive formulations [7], [8]. NTO is being prepared from semicarbazide-hydrochloride in two steps and the resulting NTO of this process is jagged and rod type crystals which are non-spherical in nature. Few researchers were successful in developing spherical-NTO by cooling crystallization, while, recently, a proprietary process has been developed to prepare spherical-NTO having specific particle size distribution at bench scale [5], [6]. Recently, a proprietary process has been developed to prepare spherical-NTO having specific particle size distribution at bench scale. Characterization of these spherical particles in comparison with non-spherical particles is of great interest to the explosive industry. Micromeritic characterization includes bulk density, tapped bulk density, compressibility index (Carr's index, CI), Hausner ratio (HR) and also the various particle densities and porosities. The CI and HR can give indication about the flowability of the powders which is necessarily to ensure before being used in HE formulations. Further, S.V. Patil et al. reported that flow properties such as compactibility, packability and wettability properties were enhanced to a great extent with spherical particles [9], [10], [11], [12].

True density is an intrinsic characteristic of a material which depends on its chemical nature and crystalline structure [13]. The presence of interstitial voids, cracks and inclusion of solvents contribute towards the lowering the true density of the material, that effects the performance of the material in the formulation. In addition, porosity of a material affects the compressibility properties as well the performance parameters in the formulations to a large extent. Porosity is the simplest and most accessible parameter for characterizing the particle packing [14]. Several studies revealed that the presence of porosity in an explosive formulation sensitizes the material to shock phenomenon. Factors such as void volumes and particle size will alter shock sensitivity [15], [16]. True and skeletal volume measurements can also give an insight about inter and intra-particle porosity. In the present study the porosities are derived from volume measurements and are correlated to the binder to explosive ratio.

Particle shape and size of explosive greatly affect the viscosity and flow behavior of compositions made out of these powders [17], [18]. Further, it is well-understood that an increase in mix-fluidity of composite explosives results in improved solid explosive powder loading in liquid binder matrix [5]. Hence, the present study attempts to develop paste explosive compositions based on the developed spherical-NTO having specific particle size distribution and study the flow behavior of the compositions in comparison with non-spherical particles.

The present investigation aims to study the complete micromeritic properties of spherical-NTO having specific particle size distribution. Flow and compressibility behavior of the powders are correlated and used for achieving the mixtures having optimal packing density with reasonably good flow behavior. Various density measurements and derived porosity are attempted to correlate with the percentage solid loading of paste explosives. Viscosity studies were performed to find out the extent of improvement in mix-fluidity of spherical-NTO compared with non-spherical-NTO compositions.

Section snippets

Materials

All the reagents and chemicals used in the present study were of AR grade and used as such. Hydroxy terminated polybutadiene (HTPB) having number average molecular weight (M_n) of 2500 g/mol and dioctyl adipate (DOA) were procured by commercial sources. Spherical-NTO of specific particle size distribution was prepared from in-house non-spherical-NTO [5]. Spheroidization process of NTO was carried out by dissolving non-spherical NTO in N-methyl pyrrolidone and the solution is cooled to − 10 °C at

Results and discussion

Micromeritic properties of an energetic material play a vital role in achieving explosive formulations with optimal performance that decides the realization of high theoretical maximum density (TMD) and mix-fluidity during their processing. Flow parameters of the material depend on a number of other variables which include micromeritic properties such as particle size & its distribution, shape & surface texture and also the kind of surface forces. This study addresses the role of various

Conclusions

Micromeritic characterization of particulate powders is very much essential before they realized in the explosive formulations. Effects of particle size and shape on various micromeritic properties of NTO powders were studied. Considering density and flowability, a bimodal distribution comprising of 150 and 25 μm spherical particles in 70:30 ratio has been identified. Paste explosive formulations were made with the identified bimodal mixture and viscosity studies ensured the improvement in

References (24)

K.J. Kim
Spherulitic crystallization of 3-nitro-1, 2, 4-triazole-5-one in water and N-methyl-2-pyrrolidone
J. Cryst. Growth
(2000)
H. Ostmark et al.
The chemistry of 3-Nitro-1, 2, 4- triazol-5-one (NTO)
Thermochem. Acta
(1993)
M. Viana et al.
About pycnometric density measurements
Talanta
(2002)
J.Q. Xu et al.
Quantification of the mechanisms governing the packing of iron ore fines
Powder Technol.
(2006)
G. Lumay et al.
Measuring the flowing properties of powders and grains
Powder Technol.
(2012)
K. Kawakita et al.
Some considerations on powder compression equations
Powder Technol.
(1971)
M. Yamashiro et al.
An experimental study on the relationship between compressibility, fluidity and cohesion of powder solids at small tapping numbers
Powder Technol.
(1983)
J.F. Thomas et al.
Effect of seggregation on the packing of spherical and non-spherical particles
Powder technol.
(1994)
B. Yadollah et al.
Control of the particle size of submicron HMX explosive by spraying in non-solvent
J. Energetic Mater.
(2010)
T. Jung et al.
Particle design using supercritical fluids
J. Supercrit. Fluids
(2001)

S.M. Pourmortazavi et al.

Low temperature micronization and particle size control of energetic materials using super critical carbon dioxide

R. Vijayalakshmi et al.

Particle size management studies on spherical 3-Nitro-1, 2, 4-triazol-5-one

Part. Part. Syst. Charact.

(2011)

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View full text

Effect of particle size and shape of NTO on micromeritic characteristics and its explosive formulations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Results and discussion

Conclusions

J. Cryst. Growth

Thermochem. Acta

Talanta

Powder Technol.

Powder Technol.

Powder Technol.

Powder Technol.

Effect of seggregation on the packing of spherical and non-spherical particles

Powder technol.

Control of the particle size of submicron HMX explosive by spraying in non-solvent

J. Energetic Mater.

Particle design using supercritical fluids

J. Supercrit. Fluids

Low temperature micronization and particle size control of energetic materials using super critical carbon dioxide

Particle size management studies on spherical 3-Nitro-1, 2, 4-triazol-5-one

Part. Part. Syst. Charact.