Capa de Transacciones

The Al and CuO nanoparticles were dispersed in ethanol, with a loading of 1 % and 3 %

by weight, respectively, and sonicated for 30 min. The loading ratio was chosen to produce

a composite with the Al and CuO layers that have a comparable thickness after vacuum

filtration. To avoid the accumulation of nanoparticles at the bottom of the container, the

suspension was kept under sonication until used for vacuum filtration. The solution

containing the nanoparticle suspension was added to a funnel and it was temporarily held

above the filter paper. The system was then vacuumed using the vacuum pump and the

nanoparticles were deposited on the filter. To produce the Al/CuO composite, the Al

nanoparticle suspension was added into the glass funnel to form the first layer. As the solvent

was removed by the vacuum pump, an Al thin film was formed with a porosity that allows

solvent to pass through. Then the CuO suspension was added and the CuO nanoparticles were

deposited on the surface of the Al thin film to form the second layer. The same procedure

was repeated to fabricate a composite with multiple layers. The layered thin film was dried

Vacuum pump Vacuum pump

Filter paper Glass funnel

Nanoparticles solution

Thin film

film. To avoid this, a pressure of 500 psi was applied to the thin film as it was dried. The thin

film was then detached from the filter paper entirely. Acetone was chosen as the solvent to

disperse the NiO nanoparticles for the fabrication of the Al and NiO multi-layer composite.

The NiO nanoparticles were dispersed with a 3 % weight loading, and sonicated for 30 min.

The main procedure for producing the Al and NiO composite was similar to that of the Al

and CuO multi-layer composite, as described above.

The dispersion quality of the nanoparticles was evaluated in different solvents using the

following criteria: 1) the nanoparticles should be well dispersed to eliminate agglomeration

of these particles, and 2) the solution should provide an air-free environment that allows the

dispersed nanoparticles to be stored for a few days. In addition, it was important to choose a

solvent that has no reaction with the Al and oxidizer nanoparticles, which is why ethanol and

acetone were considered. However, the difference in the viscosity of these two solvents was

found to impact the sample preparation times and various microstructures. Because ethanol

has a higher viscosity, it was found to cause a long vacuum filtration time for the NiO

nanoparticles. Therefore, it was replaced by acetone during the deposition of the NiO

nanoparticles.

4.3.3 Characterization

To quantify the fuel content, Al nanoparticles were heated in TGA/DSC (NETZSCH STA

model 449F3A-0918-M Jupiter) under an oxygen atmosphere. The heating rate was set to

about this process may be found in the reference [149]. The initiation temperature and

produced energy of the layered composites were characterized with TGA/DSC. Furthermore,

The TGA/DSC measurements were conducted in an argon atmosphere for characterizing the

energetic properties of the Al/CuO and Al/NiO composites.

To fabricate a multi-layer composite with controllable thicknesses of the individual layers

for different types of nanoparticles, the densities (g/cm3) of these individual layers should be

controlled. More specifically, the density of a layer with the same type of nanoparticles

should be kept as constant. In order to achieve this goal, a two-step procedure was developed.

At this first step, a single layer containing a specified type of nanoparticles was fabricated

using vacuum filtration with a variable thickness. The solution with a fixed nanoparticle

loading (in mg/ml) was added into the glass funnel and the derived thickness of the layer is

dependent on the amount of the solution (in ml). The following equation was used to calculate

the density of the single layer film

𝜌 = 4𝑉×𝐶

𝜋𝐷^2𝑇 (Eq. 4.1)

where V and C are the volume of solution added into the funnel (ml), and the nanoparticle

loading of the solution (mg/ml), respectively. D and T denote the diameter and the thickness

of the thin film, respectively. Due to the brittle nature of the produced multi-layer composites,

it was difficult to measure the film thickness using calipers. The film was placed between

two glass discs with the same diameter of the film and the distance between the surfaces of

these glass discs was measured as the thickness of the film. At the second step when these

process, based on the desired thickness of the corresponding layer and the calculated density

values of single layer nanoparticle films.

The energetic properties of layered Al/CuO and Al/NiO composites were investigated

with TGA/DSC. The detailed procedure and conditions can be found in our previous

publication.[149] In short, the layered composite samples were placed into a crucible, and were

then loaded into the TGA/DSC reactor. The reactor was then vacuumed to remove air, and

then it was filled with argon with 1 bar. The microstructures of the produced composites were

investigated with SEM (Zeiss Merlin). These samples were coated with gold to provide a

needed electrical conductivity. The elemental mapping and EDAX tasks were performed on

the same SEM.