Nanothermites are a new realm of nano-energetic materials and are used in systems that need a fast energy release rate at low ignition temperature. However, conventional ignition methods are based on hot spots, posing the risk of unwanted ignition.
Study: Doping of Al/CuO with Microwave Absorbing Ti3C2 MXene for Improved Ignition and Combustion Performance. Image Credit: taffpixture/Shutterstock.com
Although microwave (MW)-based igniting systems interact with thermite (ignitable material), the presence of protective alumina (Al2O3) on aluminum (Al) restricts the susceptibility of thermites to MW and requires MW radiation with high ignition power and extended ignition delay times.
In a recent study published in Chemical Engineering Journal, titanium carbide (Ti3C2) MXene was introduced into Al/copper oxide (CuO) energetic nanocomposites as MW susceptors. The integration of MXene into Al/CuO nanocomposites reduced the required power for MW ignition and shortened the ignition delay compared to the parent Al/CuO nanothermite.
Moreover, the introduction of MXene controlled the gas production, heat release, and Al/CuO/MXene composite’s combustion performance extending the safety, adaptability, and flexibility of Al/CuO/MXene nanothermites.
Nanothermites and MXene
Metastable intermolecular composites (MICs) have favorable combustion properties and high energy density. MICs are nanothermites with low ignition temperatures and a fast rate of energy release. These properties are important for the applications of MICs in explosive charges, energetic micro-electro-mechanical systems, propellants, and many others.
Nanothermites are ignited by the formation of a hot spot (laser irradiation or electrostatic discharge), and the low energy requirement for activating the nanothermites poses the risk of undesirable or accidental activation of the systems. To this end, MW radiation allows safe, selective, and noncontact activation of the nanothermites. The main advantage of MW radiation is the safe activation of nanothermites by interacting with the whole surface instead of specific points or hot spots. Additionally, adjusting the MW radiation can modulate the energy output.
MXene is a two-dimensional (2D) material obtained by selective etching of ‘A’ element from the MAX phase with the general formula Mn+1AXn, where M is ascribed to early transition metals, A is essentially a group of 13 or 14 elements, and X represents either/both carbon and nitrogen.
The combination of metallic conductivity of transition metal carbides with the hydrophilic nature of oxygen or hydroxyl-terminated surface in MXene results in unique properties and morphologies. Moreover, the number of layered structures of MXene are controllable, which enables the scattering of electromagnetic waves and multiple reflections of materials on MW radiation.
MXene has a high conducting property that permits polarization and dielectric loss. Furthermore, the generation of functional groups or surface defects during the etching process generates dipoles in MXene in an electromagnetic field, increasing the dielectric loss capacity.
Integration of Ti3C2 MXene into Nanothermites for Improved Ignition and Combustion Performance
In the present work, Ti3C2 MXene were presented as MW susceptor material for the first time by integrating them into Al/CuO nanothermites to enhance the MW absorption capacity of the resulting Al/CuO/MXene composite material.
Composite materials with different Ti3C2 MXene content were measured for their respective MW ignition delay and minimum MW power requirement using a customized MW probe ignition device. Furthermore, analytical methods like field emission electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray micro-computed tomography (μCT), and X-ray diffractometer (XRD) were employed to analyze the distribution and morphology of Al/CuO/MXene composites.
The FESEM images of Ti3C2 MXene revealed the uniform distribution of the three components and appeared as an accordion-type structure. The outermost alumina shell of aluminum nanoparticles in Al/CuO/MXene composites was about 4 nanometers thick, as observed in FESEM images.
EDS spectra showed that the most abundant elements in Ti3C2 MXene were titanium (Ti), and carbon (C), and the presence of fluorine (F) and chlorine (Cl) residues were due to the etching of the MAX phase with hydrochloric (HCl) and hydrofluoric (HF) acids. TEM images of Al/CuO/MXene composites revealed that Al and CuO nanoparticles were uniformly distributed around and between the layers of Ti3C2 MXene.
Furthermore, investigating the ignition temperature, ignition delay times, heat release, and the combustion performance of the prepared nanocomposites revealed the effect of Ti3C2 MXene on the novel Al/CuO/MXene composite’s ignition and combustion.
Overall, the concept of introducing Ti3C2 MXene as MW susceptor into Al/CuO nanothermites was demonstrated for the first time in the present work. The ignition delay time and power of Al/CuO nanothermites with different Ti3C2 MXene content were investigated under MW stimulation. TEM images revealed the uniform distribution of Ti3C2 MXene in the Al/CuO nanothermites, achieved by magnetic stirring and ultrasonic dispersion.
The optimized content of Ti3C2 MXene in Al/CuO/MXene composite was 2.5 weight %, while the ignition delay time and MW power for this optimized content were 3.87 seconds and 13 watts, respectively. Moreover, the optimum effect was achieved at 1 weight % of Ti3C2 MXene doping. The Al/CuO/MXene composite’s differential scanning calorimetry (DSC) thermogram revealed that the presence of Ti3C2 MXene significantly altered the thermal behavior of Al/CuO nanothermites.
Cheng, J., Zhang, Z., Wang, Y., Li, F., Cao, J., Gozin, M., Ye, Y et al. (2022) Doping of Al/CuO with Microwave Absorbing Ti3C2 MXene for Improved Ignition and Combustion Performance. Chemical Engineering Journal. https://www.sciencedirect.com/science/article/pii/S138589472203858X?via%3Dihub