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Journal ArticleDOI

A molecular dynamics study on oxidation of aluminum hydride (AlH3)/hydroxyl-terminated polybutadiene (HTPB) solid fuel

01 Jan 2021-Vol. 38, Iss: 3, pp 4469-4476
TL;DR: In this paper, a reactive molecular dynamics simulation method is employed to investigate the fundamental oxidation mechanisms of AlH3/HTPB solid fuel using a core-shell nanoparticle configuration.
Abstract: Aluminum hydride (AlH3) is a promising replacement for aluminum in hybrid and solid propellants, where hydroxyl-terminated polybutadiene (HTPB) is normally used as a binder. In this study, a reactive molecular dynamics simulation method is employed to investigate the fundamental oxidation mechanisms of AlH3/HTPB solid fuel using a core-shell nanoparticle configuration. The overall oxidation is found to proceed in three distinctive stages: (I) preheating, (II) acceleration and (III) oxidation. Furthermore, oxidation mechanisms of AlH3 and HTPB are separately studied to understand their different roles during the overall oxidation process. With respect to the oxidation of the AlH3 nanoparticle, the reaction is delayed compared with the oxidation of pure AlH3, due to the initial coverage of the nanoparticle surface by HTPB molecules. Additionally, decomposition of HTPB/HTPB intermediates is observed to occur on the nanoparticle surface and some of the decomposed products are integrated with the nanoparticle. In the meantime, the AlH3 nanoparticle facilitates the HTPB initiation by dehydroxylation or dehydrogenation. Moreover, the primary decomposition pathway of HTPB/HTPB intermediates is the continuous scission of carbon chain to form a large amount of C4 species, which are finally oxidized at a later stage of the reaction producing CO, CO2 and H2O. The new atomistic insights obtained from the present research could potentially benefit the design of AlH3/HTPB-based solid propellants.

Summary (3 min read)

1. Introduction

  • Aluminum hydride (AlH3) is a promising ingredient used in a wide range of propulsion systems [1, 2], which has been extensively studied in the past decades [3-6].
  • AlH3 has a high gravimetric (10.1 wt %) and volumetric (149 kg/m3) hydrogen capacity [7] and has been recognized as an excellent replacement for aluminum in hybrid and solid propellants [8].
  • Therefore, understanding of the oxidation of AlH3/HTPB composite is of great theoretical and practical importance.
  • While these studies have revealed the enhancement of HTPB combustion with the addition of AlH3, detailed 3 / 19 understanding of the whole oxidation process is lacking.

2.1. ReaxFF molecular dynamics

  • The reactive force-field molecular dynamics (ReaxFF MD) combines the advantages of quantum mechanics (QM) and the classic MD to form a powerful yet computationally affordable simulation approach for reactive systems.
  • It undercuts the prohibitive computational cost of QM while overcoming the inability of the classic MD for simulating chemical reactions [14, 15].
  • The ReaxFF MD is therefore an efficient method to study the long-time large-scale reactive systems that are impractical or impossible for either QM or classic MD methods.
  • The ReaxFF is based on the bondorder concept and the force field parameters are trained with QM calculations or/and experimental data to give it accuracy and fidelity.

2.2. Simulation details

  • The parameter set for Al/C/H/O interactions [22], which was extended from the original Al/H description [23] specifically parameterized for aluminium hydride is chosen as the force field used in this study.
  • After the upgrade from Al/H to Al/C/H/O, the force field incorporates hydrocarbons as well as oxidation reactions thereby allowing the investigation of mutual interaction between Al- and hydrocarbon-based materials during the oxidation process.
  • The proportion of a, b and c components of HTPB is about 1:1:3 [28], so a simplified HTPB molecule (C20H32O2) comprising one cis-, one vinyl-, and three trans-form butadiene units terminated with a hydroxyl group at each end is adopted.
  • After the equilibration, some core-shell nanoparticle exposed areas with random shape and size can be seen on the composite surface (Fig. 1c), which is reasonable as HTPB acts as the binder rather than the coating material for AlH3 in the solid propellant.
  • This simulation system constructed for oxidation reaction contains 23538 atoms in total and starts from 300 K under NVE ensemble.

3.1. Overall oxidation process

  • The oxidation reaction is found to proceed in three main stages, which can be characterised by the time evolution of temperature and the number of key species as shown in Fig.
  • The sublimation of HTPB around the nanoparticle is observed, which leads to the increase in its molecule number.
  • Stage II starts from 100 to 200 ps, where a significant change in both temperature and the number of key species occurs.
  • During this stage, the nanoparticle temperature gradually falls from its maximum and tends to be stable in the end but the temperature of the rest still goes up and approaches the system temperature.
  • This indicates that the HTPB reaction plays a dominant role at Stage III.

3.2. Mechanisms of AlH3/Al2O3 core-shell nanoparticle oxidation

  • The reaction mechanisms of the nanoparticle during the overall oxidation process are investigated.
  • Until 150 ps, most of the core H atoms are released with the core area complemented by shell O atoms.
  • In the meantime, the ambient O atoms continuously flow into the nanoparticle.
  • At Stage I, the slow drop in H/Al is caused by the departure of HTPB molecules from the nanoparticle surface rather than the generation of any product.
  • The obtained reaction mechanisms in the present research is consistent with the simplified model that Al oxidation takes place after the dehydrogenation of AlH3 from the experimental study of [4].

3.3. Mechanisms of HTPB oxidation

  • Figure 5 describes the time evolution of the number of key species related to HTPB reaction during the overall oxidation process and the major mechanisms of HTPB oxidation are studied.
  • Instead of the scission of carbon chain, the nanoparticle facilitates the HTPB initiation by dehydroxylation or 13 / 19 dehydrogenation.
  • The production of C20H31O2 continues to increase at Stage II but the contribution mainly comes from the dehydrogenation of HTPB by ambient O2 molecules.
  • Meanwhile, the C-C bond at either end of HTPB or its intermediates is broken producing C4H6, C4H6O and C4H6OH.
  • It is observed that after the cleavage of terminal C4 units, the scission of the remaining carbon chain still begins with its terminal C4 parts, resulting in the significant production of C4H6.

3.4. Discussion on the simplification of HTPB model

  • The solid HTPB in reality may have a relative molecular mass of several million terminated with a hydroxyl group at each end.
  • A simplified HTPB model of C20H32O2 is adopted in the present research because it is impractical to employ a realistic HTPB model together with the corresponding micronsize AlH3/Al2O3 particle in ReaxFF MD simulations considering the current computational capability.
  • This simplification leads to relatively excessive number of hydroxyl groups in the simulation system.
  • Similarly, the dihydroxylation and dehydrogenation of HTPB described in Section 3.3 would be less evident.
  • Nevertheless, the major decomposition products of HTPB obtained from the simulation including C2H4, C4H6 and C5H6 are in good agreement with experimental results [29].

4. Conclusions

  • The fundamental oxidation mechanisms of AlH3/HTPB solid fuel are investigated using ReaxFF MD simulations.
  • The duration of Stage (I) is approximately the same as that of Stage (II) and Stage (III) would be much longer until the end of the reaction.
  • Finally, the C4 species are further oxidized to produce CO, CO2 and H2O.
  • The findings from the present research could potentially benefit the design of AlH3/HTPB-based solid propellants.

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Figures (5)

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1 / 19
A molecular dynamics study on oxidation of aluminum hydride (AlH
3
)/hydroxyl-
terminated polybutadiene (HTPB) solid fuel
Muye Feng
a
, Heping Li
b,c
, Kai H. Luo
b,
a
Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,
Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
b
Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE, UK
c
School of Science, Hangzhou Dianzi University, Hangzhou 310018, China
Abstract
Aluminum hydride (AlH
3
) is a promising replacement for aluminum in hybrid and solid
propellants, where hydroxyl-terminated polybutadiene (HTPB) is normally used as a binder. In this
study, a reactive molecular dynamics simulation method is employed to investigate the fundamental
oxidation mechanisms of AlH
3
/HTPB solid fuel using a core-shell nanoparticle configuration. The
overall oxidation is found to proceed in three distinctive stages: (I) preheating, (II) acceleration and
(III) oxidation. Furthermore, oxidation mechanisms of AlH
3
and HTPB are separately studied to
understand their different roles during the overall oxidation process. With respect to the oxidation of
the AlH
3
nanoparticle, the reaction is delayed compared with the oxidation of pure AlH
3
, due to the
initial coverage of the nanoparticle surface by HTPB molecules. Additionally, decomposition of
HTPB/HTPB intermediates is observed to occur on the nanoparticle surface and some of the
decomposed products are integrated with the nanoparticle. In the meantime, the AlH
3
nanoparticle
facilitates the HTPB initiation by dehydroxylation or dehydrogenation. Moreover, the primary
decomposition pathway of HTPB/HTPB intermediates is the continuous scission of carbon chain to
form a large amount of C
4
species, which are finally oxidized at a later stage of the reaction producing
Corresponding author at: Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE,
UK. Tel: +44 (0)20 7679 3916. E-mail address: k.luo@ucl.ac.uk (Kai H. Luo)

2 / 19
CO, CO
2
and H
2
O. The new atomistic insights obtained from the present research could potentially
benefit the design of AlH
3
/HTPB-based solid propellants.
Keywords: AlH
3
/HTPB solid fuel; Oxidation; Molecular dynamics; Reactive force field
1. Introduction
Aluminum hydride (AlH
3
) is a promising ingredient used in a wide range of propulsion systems
[1, 2], which has been extensively studied in the past decades [3-6]. AlH
3
has a high gravimetric
(10.1 wt %) and volumetric (149 kg/m
3
) hydrogen capacity [7] and has been recognized as an excellent
replacement for aluminum in hybrid and solid propellants [8]. Replacing Al with AlH
3
can result in
more than 10% increase in specific impulse over currently used rocket propellants [9]. Additionally,
the flame temperature and average molecular mass of the combustion products can be reduced in the
presence of AlH
3
[8]. Despite these advantages, the practical use of AlH
3
in propellants suffers from
some issues including strong sensitivity to oxidation and hydration, and low thermal stability [10].
Hydroxyl-terminated polybutadiene (HTPB) is an oligomer of butadiene terminated with a hydroxyl
group at each end, which is a standard binder formulated in Al or AlH
3
-based solid propellants [8, 11].
The nature and composition of HTPB make it also a fuel that is involved in the combustion process.
Therefore, understanding of the oxidation of AlH
3
/HTPB composite is of great theoretical and practical
importance.
However, compared with pure AlH
3
, the decomposition and oxidation of AlH
3
/HTPB composite
system are rarely investigated. Among the few previous studies, Young et al. [12] compared the
combustion characteristics of Al/HTPB and AlH
3
/HTPB solid fuels using nitrous oxide as the oxidizer
and found that the regression rate of HTPB was increased by approximately 20% with a 40 wt % AlH
3
loading, whereas the addition of Al at all loadings (10-40%) decreased the regression rate of HTPB.
Chen et al. [13] also observed the improvement (up to 57.2%) in the HTPB regression rate with AlH
3
and attributed it to the rapid H
2
release from AlH
3
dehydrogenation forming a porous layer. While
these studies have revealed the enhancement of HTPB combustion with the addition of AlH
3
, detailed

3 / 19
understanding of the whole oxidation process is lacking. In this study, reactive molecular dynamics
(MD) simulations are employed to investigate the fundamental oxidation mechanisms of AlH
3
/HTPB
solid fuel. In addition, the oxidation mechanisms of AlH
3
and HTPB are also separately scrutinized to
gain deeper insights into their different roles and mutual interactions during the overall oxidation
process.
2. Methods
2.1. ReaxFF molecular dynamics
The reactive force-field molecular dynamics (ReaxFF MD) combines the advantages of quantum
mechanics (QM) and the classic MD to form a powerful yet computationally affordable simulation
approach for reactive systems. It undercuts the prohibitive computational cost of QM while
overcoming the inability of the classic MD for simulating chemical reactions [14, 15]. The ReaxFF
MD is therefore an efficient method to study the long-time large-scale reactive systems that are
impractical or impossible for either QM or classic MD methods. The ReaxFF is based on the bond-
order concept and the force field parameters are trained with QM calculations or/and experimental
data to give it accuracy and fidelity. To describe the dissociation, transition and formation of chemical
bonds, ReaxFF bond orders are calculated directly from interatomic distances as shown in Eq. (1) [15]:
( ) ( ) ( )
bo2 bo4 bo6
bo1 bo3 bo5
BO BO BO BO
exp / exp / exp /
ij ij ij ij
pp p
ij o ij o ij o
p rr p rr p rr
σ π ππ
σ π ππ
=++
 
=++
 
 
(1)
where BO is the bond order between atoms i and j, r
ij
is interatomic distance, r
o
terms are equilibrium
bond lengths, and p
bo
terms are empirical parameters. The general expression of the ReaxFF potential
consisting of different energy contributions is given in Eq. (2) [16]:
system bond over under lp val tor vdWaals Coulomb
E E E E EE E E E= + + ++ + + +
(2)

4 / 19
where E
system
, E
bond
, E
over
, E
under
, E
lp
, E
val
, E
tor
, E
vdWaals
and E
Coulomb
represent total energy, bond energy,
overcoordination energy penalty, undercoordination stability, lone pair energy, valence angle energy,
torsion angle energy, van der Waals energy and Coulomb energy, respectively.
The ReaxFF MD methodology has been successfully applied in a broad range of reactive systems
[17-21]. Detailed information on ReaxFF including its development and exhaustive formulation can
be found in references [15, 16].
2.2. Simulation details
The parameter set for Al/C/H/O interactions [22], which was extended from the original Al/H
description [23] specifically parameterized for aluminium hydride is chosen as the force field used in
this study. The original Al/H force field is capable of describing the reaction of AlH
3
clusters and their
dehydrogenation process. After the upgrade from Al/H to Al/C/H/O, the force field incorporates
hydrocarbons as well as oxidation reactions thereby allowing the investigation of mutual interaction
between Al- and hydrocarbon-based materials during the oxidation process. Hence, this Al/C/H/O
force field covers all of the chemical reactions that may occur in the research. The present simulations
consist of two main parts: (1) system construction and equilibration under the canonical (NVT) and
isothermal-isobaric (NPT) ensembles, and (2) oxidation reaction under the microcanonical (NVE)
ensemble. Three independent runs are conducted for the final oxidation system, and the results are
averaged for analysis. Error bars (color filling around the curve) shown in the present study are
determined by the standard error of the mean. The time step used is 0.2 fs and the simulation data are
outputted at an interval of 0.2 ps. A commonly used 0.3 bond order cutoff is employed to analyse the
species formed. All of the ReaxFF MD simulations are performed using the LAMMPS package [24]
and the visualization of simulation data is conducted through OVITO [25].
2.3. System construction

5 / 19
In order to approximate the realistic experimental condition, the following procedure for system
construction is carried out:
Due to the existence of an oxide layer on AlH
3
, the core-shell AlH
3
/Al
2
O
3
structure is first built
following these steps: (1a) cut a 5 nm diameter α-AlH
3
nanoparticle from the crystal structure and
relax it for 100 ps; (1b) cut the 3.5 nm diameter core from the relaxed AlH
3
nanoparticle; (2a) cut a 6
nm diameter α-Al
2
O
3
nanoparticle from the crystal structure and relax it for 100 ps; (2b) create the
amorphous Al
2
O
3
by annealing [26] the relaxed Al
2
O
3
nanoparticle for 100 ps (experimental results
reported that the surface oxide layer covering the AlH
3
is amorphous Al
2
O
3
[27]); (2c) cut a 0.5 nm
thickness shell from the annealed Al
2
O
3
nanoparticle (radius from 1.75 to 2.25 nm); (3) combine the
AlH
3
core and Al
2
O
3
shell together and then relax the core-shell structure for 100 ps. The core-shell
nanoparticle contains 5670 atoms (801 core Al, 954 shell Al, 2525 H, and 1390 shell O atoms,
respectively). After the relaxation, a small amount of core H atoms have diffused into the oxide shell
and to the nanoparticle surface as seen in Fig. 1a. All of the relaxation processes are performed at 300
K and the temperature during annealing is heated up to 2500 K under the NVT ensemble.

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References
More filters
Journal ArticleDOI
TL;DR: In this article, three parallel algorithms for classical molecular dynamics are presented, which can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors.

32,670 citations

01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

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Abstract: The Open Visualization Tool (OVITO) is a new 3D visualization software designed for post-processing atomistic data obtained from molecular dynamics or Monte Carlo simulations. Unique analysis, editing and animations functions are integrated into its easy-to-use graphical user interface. The software is written in object-oriented C++, controllable via Python scripts and easily extendable through a plug-in interface. It is distributed as open-source software and can be downloaded from the website http://ovito.sourceforge.net/.

8,956 citations

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Abstract: The reactive force-field (ReaxFF) interatomic potential is a powerful computational tool for exploring, developing and optimizing material properties. Methods based on the principles of quantum mechanics (QM), while offering valuable theoretical guidance at the electronic level, are often too computationally intense for simulations that consider the full dynamic evolution of a system. Alternatively, empirical interatomic potentials that are based on classical principles require significantly fewer computational resources, which enables simulations to better describe dynamic processes over longer timeframes and on larger scales. Such methods, however, typically require a predefined connectivity between atoms, precluding simulations that involve reactive events. The ReaxFF method was developed to help bridge this gap. Approaching the gap from the classical side, ReaxFF casts the empirical interatomic potential within a bond-order formalism, thus implicitly describing chemical bonding without expensive QM calculations. This article provides an overview of the development, application, and future directions of the ReaxFF method.

1,239 citations

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Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "A molecular dynamics study on oxidation of aluminum hydride (alh3)/hydroxyl- terminated polybutadiene (htpb) solid fuel" ?

In this study, a reactive molecular dynamics simulation method is employed to investigate the fundamental oxidation mechanisms of AlH3/HTPB solid fuel using a core-shell nanoparticle configuration. Furthermore, oxidation mechanisms of AlH3 and HTPB are separately studied to understand their different roles during the overall oxidation process. With respect to the oxidation of the AlH3 nanoparticle, the reaction is delayed compared with the oxidation of pure AlH3, due to the initial coverage of the nanoparticle surface by HTPB molecules. Additionally, decomposition of HTPB/HTPB intermediates is observed to occur on the nanoparticle surface and some of the decomposed products are integrated with the nanoparticle. In the meantime, the AlH3 nanoparticle facilitates the HTPB initiation by dehydroxylation or dehydrogenation.