Wenbo Zhou

Direct Deposit Laminate Nanocomposites with Enhanced Propellent Properties

One of the challenges in the use of energetic nanoparticles within a polymer matrix for propellant applications is obtaining high particle loading (high energy density) while maintaining mechanical integrity and reactivity. In this study, we explore a new strategy that utilizes laminate structures. Here, a laminate of alternating layers of aluminum nanoparticle (Al-NPs)/copper oxide nanoparticle (CuO-NPs) thermites in a polyvinylidene fluoride (PVDF) reactive binder, with a spacer layer of PVDF was fabricated by a electrospray layer-by-layer deposition method. The deposited layers containing up to 60 wt % Al-NPs/CuO-NPs thermite are found to be uniform and mechanically flexible. Both the reactive and mechanical properties of laminate significantly outperformed the single-layer structure with the same material composition. These results suggest that deploying a multilayer laminate structure enables the incorporation of high loadings of energetic materials and, in some cases, enhances the reactive properties over the corresponding homogeneous structure. These results imply that an additive manufacturing approach may yield significant advantages in developing a tailored architecture for advanced propulsion systems.

Persulfate salt as an oxidizer for biocidal energetic nano-thermites

Nanoscale potassium persulfate (K2S2O8) was evaluated as an alternative to other peroxy salts, such as periodates (KIO4), in aluminum-fueled energetic nano-composite formulations. High speed imaging coupled with temperature jump (T-jump) ignition found the nano-Al/K2S2O8 reaction to have an ignition temperature of 600 °C which is comparable to nano-Al/KIO4 and lower than nano-Al/K2SO4. The results from constant-volume pressure cell experiments further show that nano-Al/K2S2O8 releases more gas and has a longer burn time than nano-Al/KIO4. Thermal analyses at low heating rates (10 °C min−1) by coupled differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and mass spectrometry (MS) show that there are three main steps of thermal decomposition for nano-K2S2O8, with initial exothermic decomposition to release O2 at 270 °C, and following endothermic decomposition to release both O2 and SO2 at higher temperatures. The heat of formation of K2S2O8 was measured to be −1844.5 kJ mol−1 based on the DSC results. Experiments performed at ultrafast heating rates (∼105 °C s−1) using temperature-jump time-of-flight (T-jump/TOF) MS show that the low O2 generation temperature of nano-K2S2O8 contributes to its high reactivity in nano-thermite compositions. An ignition mechanism involving gaseous oxygen was proposed for nano-thermite compositions containing reactive oxysalts such as nano-K2S2O8. In contrast, a condense phase ignition mechanism was proposed for nano-thermites involving less reactive oxysalts such as nano-K2SO4. Given that the nano-Al/K2S2O8 system is highly exothermic in addition to generating a considerable amount of SO2, it may be a candidate for use in energetic biocidal applications.

Ultra-fast self-assembly and stabilization of reactive nanoparticles in reduced graphene oxide films

Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material.

Evaluating free vs bound oxygen on ignition of nano-aluminum based energetics leads to a critical reaction rate criterion

This study investigates the ignition of nano-aluminum (n-Al) and n-Al based energetic materials (nanothermites) at varying O2 pressures (1–18 atm), aiming to differentiate the effects of free and bound oxygen on ignition and to assess if it is possible to identify a critical reaction condition for ignition independent of oxygen source. Ignition experiments were conducted by rapidly heating the samples on a fine Pt wire at a heating rate of ∼105 °C s−1 to determine the ignition time and temperature. The ignition temperature of n-Al was found to reduce as the O2 pressure increased, whereas the ignition temperatures of nanothermites (n-Al/Fe2O3, n-Al/Bi2O3, n-Al/K2SO4, and n-Al/K2S2O8) had different sensitivities to O2 pressure depending on the formulations. A phenomenological kinetic/transport model was evaluated to correlate the concentrations of oxygen both in condensed and gaseous phases, with the initiation rate of Al-O at ignition temperature. We found that a constant critical reaction rate (5 × 10−2 m...

Quantitative attachment and detachment of bacterial spores from fine wires through continuous and pulsed DC electrophoretic deposition.

We demonstrate the uniform attachment of bacterial spores electrophoretically onto fine wires in liquids and subsequently quantitatively detached back into suspension. It was found that the use of a pulsed voltage method resulted in a uniform coverage of spores and prevented visible bubble formation resulting from water electrolysis which tended to dislodge the spores from the wires. By monitoring the electrophoretically derived current, this method could also be used to quantitatively measure the surface charges on spores and the deposition rate. The method is generic and should be applicable to the deposition of any charged biological material (e.g., spores, bacteria, viruses) onto metal surfaces.