8/11/2019 ME 774 group 03

1/44

ME-774

Term paper Presentation

Group-03

Modelling of High-reactivity of CuO/Alnanothermite composites using Density

functional theory Calculations

Manish Kumar

S. Vignesh

Ankit Kumar Chouksey

Devendra Arya

8/11/2019 ME 774 group 03

2/44

Density functional theory

DFT allows to get information about the energy, the structure and the molecularproperties of molecules

based on the wavefunction use.

DFT depends on two H-K (HohenbergKohn) theorem :

First theorem: The first HK theorem demonstrates that the ground state properties of amany-electron system are uniquely determined by an electron densitythat depends on only 3

spatial coordinates.

Second theorem: The second HK theorem defines an energy functional for the system andproves that the correct ground state electron density minimizes this energy functional.

density functional theory finds increasingly broad application in the chemical and material

sciences for the interpretation and prediction of complex system behavior at an atomic scale.

All the periodic Density Functional Theory (DFT) calculations arecarried out using the PerdewBurkeErnzerhof [3] implementationof the generalized gradient approximation in VASP 5.2 (Vienna Ab initioSimulation Package)

http://en.wikipedia.org/wiki/Walter_Kohnhttp://en.wikipedia.org/wiki/Stationary_statehttp://en.wikipedia.org/wiki/Electronic_densityhttp://en.wikipedia.org/wiki/Electronic_densityhttp://en.wikipedia.org/wiki/Electronic_densityhttp://en.wikipedia.org/wiki/Electronic_densityhttp://en.wikipedia.org/wiki/Stationary_statehttp://en.wikipedia.org/wiki/Stationary_statehttp://en.wikipedia.org/wiki/Stationary_statehttp://en.wikipedia.org/wiki/Walter_Kohn

8/11/2019 ME 774 group 03

3/44

Nanothermites - Introduction

Nanoassembled thermite composites aremetastable intermolecular compositescomprising a nanoscale metallic fuel and

oxidizer (CuO, Fe2O3, Bi2O3, MoO3, etc).

These materials, when ignited, produce rapidrelease of heat and pressure by self-

propagating combustion reaction throughoutthe whole material

8/11/2019 ME 774 group 03

4/44

CuOAl Nanothermites

Reasons for choosing CuO - CuO (p-type semiconductor with band gap of 1.2 eV) is of

great interest owing to its wide applications in Heterogeneous catalysis

Gas sensing Lithium electrode material Solar cells Reactive oxidizers in nanothermite composites

CuO has also been recognized as attractive oxygen carrier

for capturing and separation of CO2 with little energy lossin chemical looping combustion of fossil fuels and waste toreduce the greenhouse gas emissions.

8/11/2019 ME 774 group 03

5/44

CuOAl Nanothermites

The intimacy of both reactants (Al and CuO)reduces the diffusion widths and thereforeaccelerates the oxido-reduction reaction that

can be expressed as:

Al+CuOAl2O3+Cu+H,

with H being the heat of reaction equaltheoretically to 21 kJ/cm3.

8/11/2019 ME 774 group 03

6/44

CuOAl Nanothermites

Reasons for choosing Aluminum Aluminum nanopowder is widely used as a fuel

element in these composites due to its- Low cost Availability Ease of manufacturing and Favorable physical properties such as

high reaction enthalpy, low vapor pressure, low melting temperature and high thermal conductivity

8/11/2019 ME 774 group 03

7/44

Advantages of Nanothermites

The nano scale self assembly of such materials increasesthe surface contact between atomic clusters. Such highinterfacial area leads to a decreased diffusion distance,reduced atomic length scale for heat and mass transfer, andso forth, leading to high ignition sensitivity and fastreaction/propagation rate with minimum heat loss

The high speed of combustion coupled with highpressure/shock waves have found several defense andcivilian applications like

micro thrusters safe arm and fire devices MEMS-based molecular delivery actuators

8/11/2019 ME 774 group 03

8/44

Fabrication of CuO nanorods

Conventional methods of making CuO solid-state reaction methods, sonoemulsion methods, hydrothermal methods,

electrochemical methods, and thermal oxidation of copper in air.

Many of the assemblers, or surfactants as they are morecommonly known, that are used for sustenance ofdirectional growth of nanomaterials are toxic in nature orotherwise some industrial processes that are used in theirmanufacture involve highly carcinogenic and toxicchemicals or reagents for polymerization.

8/11/2019 ME 774 group 03

9/44

Fabrication of CuO rods using Aloe-Vera gel

Medicinal plant extracts such as Aloe vera havebeen recently explored in the synthesis of metaloxides such as CuO, ZnO, In2O3,FexOy and tinoxide nanoparticles.

Two methodsSonoemulsion Biosynthesis of CuO Nanorods. Sonoemulsion biosynthesis is a process similar to the

standard sonoemulsion methodwherein a nonionic

surfactant like poly-(ethylene glycol) of molecularweight 8000 (PEG8000) is being replaced by Aloe veragel.

8/11/2019 ME 774 group 03

10/44

Fabrication of CuO rods using Aloe-Vera gel (cont.)

Solid-State Biosynthesis of CuO Nanorods CuO nanorods are synthesized by solid-state

mixing of CuCl22H2O and NaOH in the presence ofaloe vera gel.

Conventional Process - Solid-State ReactionSynthesis of CuO Nanorods. (bio hazardous)

the synthesis of CuO nanorods is prepared byfollowing the one-sep reaction process using theionic surfactant PEG400

8/11/2019 ME 774 group 03

11/44

Combustion Performance of CuONanorods/nAl Nanothermites-

The combustion process of biosynthesizedCuO nanorods/nAl nanothermites shows thespecific characteristics of excess gas

generation. The combustion wave speed isfound to be maximum at equivalence ratio of1.6.

8/11/2019 ME 774 group 03

12/44

8/11/2019 ME 774 group 03

13/44

Conclusions in differences between conventional methods toprepare CuO nano rods and using Aloe Vera gel

Aloe vera gel as bio templating/capping agent for green synthesis of CuOnanorods in both solid and emulsion phase reaction process which alsoserved as catalyst enhancing the reactivity of CuO oxidizers via excess gasrelease during the exothermic reaction with nano aluminum

The typical gas generating role of Aloe vera that adheres as surfacefunctional groups on CuO nanostructures leads to marked improvements

in the combustion and pressure generation properties of the composites. The biosynthesized CuO nanorods have the outstanding ability of

abundant gas generation which delivered 2.3 times higher pressuremagnitude and 4 times higher pressurization rate of PEG400 assisted CuOnanorods/nAl nanothermites.

The quantity of surface functional groups from Aloe vera has been found

to be responsible for governing the dynamic pressure characteristics ofnanothermites.

8/11/2019 ME 774 group 03

14/44

8/11/2019 ME 774 group 03

15/44

Introduction to Formation of Al/CuO

bilayerfilms: Basic mechanisms through

density functionaltheory calculations

We carry out Density Functional Theory calculations of the initial steps of CuOdeposition onto Al surface and Al deposition onto CuO surface to investigate the

basic mechanisms responsible for the growth of Al/CuO interface.

Our aim is to understand how Al atoms can react on a CuO surface on one hand,and in turn how CuO molecules dissociate and react on an Al surface.

8/11/2019 ME 774 group 03

16/44

Aluminium (111) surface is modelled by a six-layer slab containing 96atoms with 14 of vacuum to mimic a real surface, in an orthorhombicsimulation box. The bottom layer is fixed during geometry optimization toreproduce the bulk behaviour, and the Cu and O ad atoms are depositedonly on one side of the slab

The super cell for CuO(111) is monoclinic, it contains 192 atoms, withplanes of 16 Cu atoms alternated with two semi-planes of 8 O atoms.Again, during optimization the bottom layer is fixed and Al atoms areadded on one side of the slab.

We systematically calculate the heat of reaction, or binding energy, as thedifference between the energies of the initial and the final states:

8/11/2019 ME 774 group 03

17/44

The energy diagram is constructed as follows the energy for eachconfiguration is calculated by placing an Al atom near a known site andrunning an optimization. Then, either the atom stays in this site and we

obtain the total energy of this final state, or it moves away and the site issaid unstable. In this latter case, it simply does not appear on the graph.The binding energies are reported on this diagram, which is readable fromthe left to the right to follow the penetration path.

1. Al on CuO

8/11/2019 ME 774 group 03

18/44

Adsorption process releases enough energy to overcome the energybarriers of 0.6 eV, so that the Al atom penetrates into the first Cu layer. Asshown in fig this substitutional position is the most stable. It is due to anincrease of the coordination number, and that it leads to an amorphization

of the surface.

8/11/2019 ME 774 group 03

19/44

2. CuO on AlAlthough this reaction is also exothermic but it shows a completely differentbehaviour. We observe the spontaneous barrierless dissociation of the CuOmolecule on the Al(111) surface.

2.1 Cu on AlBoth the adsorption and insertion in the first layer, leading to a so-called

dumbbell-like structure,are exothermic and seem to be almost equiprobable:Eb=2.8 and 2.9 eV. These numbers are not useful for our deposition process,since Cu is only deposited in its molecular form. But it shows that the adsorptionsite may be fcc or hcp with equal probabilities.The activation barrier for the formation of this dumbbell-like structure is

calculated with NEB method and is equal to 0.5 eV. We can say that this lowbarrier will be passed at RT, allowing the system to stabilize in the dumbbellconfiguration, for one isolated copper atom. Indeed, further penetration of Cuatom is again unfavourable, even in the second subsurface layer.

8/11/2019 ME 774 group 03

20/44

8/11/2019 ME 774 group 03

21/44

2.1 Cu on Al

The activation barrier for the fcc to hcp transition is 0.68 eV, but is only 0.27 eV forthe hcp to fcc transition. This leads to high migration rates towards fccconfiguration. Contrary to the two previous cases ,the oxygen penetration into thesubsurface, even in the first layer, is energetically unfavourable with 0.75 eVenergy loss. Moreover, the high activation energy of 1.73 eV for this penetrationmakes it kinetically impossible to occur at low deposition temperatures.

8/11/2019 ME 774 group 03

22/44

8/11/2019 ME 774 group 03

23/44

Discussion:

We demonstrate that Al does penetrate the CuO surface with subsequentamorphization of the CuO upper layer. In turn, CuO undergoes a dissociative

adsorption onto Al, leading to isolated Cu and O atoms of which furtherpenetration in the Al surface is detailed. While Cu pathway for subsurfacepenetration is characterized by a low activation barrier (0.5 eV), O interaction withthe Al surface is much more complex; aluminium oxidation is shown to occur at anominal oxygen coverage through a drastic rearrangement of the Al surface atoms.

8/11/2019 ME 774 group 03

24/44

Al lattice

8/11/2019 ME 774 group 03

25/44

Al lattice Band Gap = -13.6 eV

8/11/2019 ME 774 group 03

26/44

Density of state of Al lattice

density of states (DOS) of a system describes the number of states per interval ofenergy at each energy level that are available to be occupied by electrons.

8/11/2019 ME 774 group 03

27/44

CuO lattice

8/11/2019 ME 774 group 03

28/44

CuO lattice Band Gap = -0.815 eV

8/11/2019 ME 774 group 03

29/44

Density of state of CuO lattice

8/11/2019 ME 774 group 03

30/44

Copper latticeAnd

DOS of cu lattice

8/11/2019 ME 774 group 03

31/44

Copper lattice Band structure

8/11/2019 ME 774 group 03

32/44

8/11/2019 ME 774 group 03

33/44

Aluminum oxide band structure

8/11/2019 ME 774 group 03

34/44

Simulation result for cu lattice

Simulation result for aluminum oxide

8/11/2019 ME 774 group 03

35/44

Aluminum lattice simulation result

Copper oxide simulation result

8/11/2019 ME 774 group 03

36/44

Thermite Reaction

2 Al(s) + 3 CuO(s) AlO(s) + 3 Cu(s)In order to calculate heat of reaction rH, We need

enthalpy of formation of reactants and products

rH = fH(AlO) + 3fH(Cu) - 3fH(CuO) - 2fH(Al)From the geometry optimisation simulation

fH(AlO) = -624.58 kcal/mol

fH(Cu) = -111.52 kcal/mol

fH(CuO) = -164.5 kcal/molfH(Al) = -73.13 kcal/mol

8/11/2019 ME 774 group 03

37/44

Heat of Reaction rH

rH = -624.58 -3(111.52) +3(164.5) + 2(73.13) kcal/mol

rH = -319.38 kcal/mol

The actual heat of reaction (rH) is = -288.75 kcal/mol

% error in obtained value = 9.59%

8/11/2019 ME 774 group 03

38/44

Today, the fundamental issue that limits the control of all reactive nano-materials and nano-composites is the lack of understanding of the interface chemistry and associated reactionmechanisms.

In case of nano-thermites the interface layer between the metal and oxide controls the onsetreaction temperature, reaction kinetics, and stability at low temperature.

Spectroscopy, differential scanning calorimetry, and high resolution transmission electronmicroscopy, in conjunction with first-principles calculations to identify the stable configurationsthat can occur at the interface and determine the kinetic barriers for their formation.

An interface layer formed during physical deposition of aluminum is composed of a mixture of Cu,O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., withspurious exothermic reactions at lower temperature).

Atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA)Produces aconformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (0.5nm), resulting in better stability at low temperature and reduced reactivity.

Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO toform an amorphous interfacial layer that is an important component for superior protectionProperties of the interface and is responsible for the high system stability.

8/11/2019 ME 774 group 03

39/44

nature of the monolayer interface between CuO and alumina/Al rather than the thickness ofthe alumina layer that controls the kinetics of Al diffusion, underscoring the importance of thechemical bonding at the interface in these energetic materials.

Nano-composites, Al/CuO bilayer nano-foils represent a good model system to study reactiveinterfaces: they are composed of a nano-layer of Al (fuel) and a nanolayer of CuO (oxidizer)deposited by physical deposition methods providing a good control over thickness and purity.The Al + CuO reaction is among the most exothermic thermite reactions with a maximumtheoretical heat of reaction of 3.9 kJ/g that can be released within a fraction of a second.

An understanding of the chemistry that controls the interface formation between the tworeactive materials, which is still missing, would represent a step forward to control theresponse of reactive nano-composites. This includes the characterization of the formation ofthe interface as a function of deposition conditions, associated atomic arrangements, andsubsequent effects on the material properties.

We assess how the chemical nature of the interface impacts the exothermic response, by

varying the deposition techniques by using DFT.

Adsorption and Decomposition reactions on CuO are calculated using frame of densityfunctional theory DFT. DFT calculations of the adsorption and reaction mechanism on CuO areexplored theoretically.

8/11/2019 ME 774 group 03

40/44

Nature of the Sputter-Deposited Copper Oxide

Thin Film.

After CuO sputter deposition, the resultingcopper oxide layer is analyzed by XRD (Figure1a) and IR absorption.

spectroscopy (Figure 1b). Cupric oxide, CuO,diffraction lines can clearly be seen in the XRD

pattern. The infrared absorbance spectrum inFigure 1b also confirms copper(II) oxide asevidenced by modes at 507, 517, and 590cm1characteristic of CuO. There is notably noevidence for copper(I) oxide (cuprous oxide,Cu2O), characterized by an absorption band at

623 cm1.

8/11/2019 ME 774 group 03

41/44

Formation, Chemistry, and Structure of InterfaceGenerated upon TMA Surface Reactions with CuO

during ALD of Al2O3.

DFT calculations of the adsorption and reaction mechanism of TMA on CuO are exploredtheoretically.

First, TMA preferably adsorbs on top of a three- coordinated oxygen atom in Figure with anenergy gain of 1.38 eV.

This results in the formation of AlO bond (dAlO = 1.86 ). This adsorption considerablyaffects the initial TMA symmetry, giving rise to an umbrella structure attached to the surface

via a CH3Cu bond (dCuC = 2.19 ). Furthermore, migration of the methyl group on the surface is expected since its lower energy

state is found when C is attached to surface oxygen atoms .

0.87 eV of energy gain compared to CH3 attached to Cu, the migration activation energybeing as low as 0.46 eV.

8/11/2019 ME 774 group 03

42/44

Further dissociation of the TMA surface complex on CuO is found to be endothermic by 0.31and 1.90 eV for the loss of the second and third TMA methyl groups respectively.

The methoxy formation through O extraction is largely exothermic (0.92 eV).

The infrared absorption spectra observed in assigned usingDFT calculations, highlighting the consistency between thesurface chemistry described by DFT and the experimentaldata. The mechanisms of interface formation are furtherderived through experimental data that are consistent with

DFT.

The deposition of isolated Al atoms on CuO surfaces leads toan amorphization of the surface/interface via the insertion ofAl atoms into substitutional Cu sites, resulting in a mixedinterface composed of Al, Cu, and O. The massiverearrangement of oxygen atoms around aluminum atomsconfirms the CuO reduction observed experimentally.

8/11/2019 ME 774 group 03

43/44

nature of the monolayer interface between CuO and alumina/Al rather than the thickness ofthe alumina layer that controls the kinetics of Al diffusion, underscoring the importance of thechemical bonding at the interface in these energetic materials.

Nano-composites, Al/CuO bilayer nano-foils represent a good model system to study reactiveinterfaces: they are composed of a nano-layer of Al (fuel) and a nanolayer of CuO (oxidizer)deposited by physical deposition methods providing a good control over thickness and purity.The Al + CuO reaction is among the most exothermic thermite reactions with a maximumtheoretical heat of reaction of 3.9 kJ/g that can be released within a fraction of a second.

An understanding of the chemistry that controls the interface formation between the tworeactive materials, which is still missing, would represent a step forward to control theresponse of reactive nano-composites. This includes the characterization of the formation ofthe interface as a function of deposition conditions, associated atomic arrangements, andsubsequent effects on the material properties.

We assess how the chemical nature of the interface impacts the exothermic response, by

varying the deposition techniques by using DFT.

Adsorption and Decomposition reactions on CuO are calculated using frame of densityfunctional theory DFT. DFT calculations of the adsorption and reaction mechanism on CuO areexplored theoretically.

8/11/2019 ME 774 group 03

44/44

References:-1. Patel V. K. and Bhattacharya S., dx.doi.org/10.1021/am404308s| ACS Appl.

Mater. Interfaces2013, 5, 13364133742. Kwon, Jinhee and Ducr, Jean Marie and Alphonse, Pierre and

Bahrami, Mehdi and Petrantoni, Marine and Veyan, Jean-Francois andTenailleau, Christophe and Estve, Alain and Rossi, Carole and Chabal,Yves J. Interfacial Chemistry in Al/CuO Reactive Nanomaterial and ItsRole in Exothermic Reaction. (2013) ACS Applied Materials & Interfaces,vol. 5 (n 3). pp. 605-613. ISSN 1944-8244

3. Clo Lanthony, Jean-Marie Ducr, Alain Estve, Carole Rossi, MehdiDjafari-Rouhani, Thin Solid Films 520 (2012) 47684771