Comment on “In situ imaging of ultra-fast loss of nanostructure in nanoparticle aggregates” [J. Appl. Phys. 115, 084903 (2014)]

Abstract

Response to "Comment on 'In situ imaging of ultra-fast loss of nanostructure in nanoparticle aggregates'" [J.

Spallation of Isolated Aluminum Nanoparticles by Rapid Photothermal Heating

“…In other words, larger-diameter particles are expected to be activated by the MDM at lower temperatures than smaller diameter particles that have the same oxide thickness. Assuming a 3 nm shell thickness, an 80-nm-diameter Al NP would fracture at 1107 K, while a 35-nm-diameter Al NP would fracture at 1805 K based on previously published data . For the particle assembly in Figure a, all particles reach between 937 and 1500 K (full melting) within the duration of the laser rise time of 7 μs, with a heating rate of ∼(1–2) × 10 8 K/s.…”

“…Assuming a 3 nm shell thickness, an 80-nm-diameter Al NP would fracture at 1107 K, while a 35-nm-diameter Al NP would fracture at 1805 K based on previously published data. 43 For the particle assembly in Figure 3a, all particles reach between 937 and 1500 K (full melting) within the duration of the laser rise time of 7 μs, with a heating rate of ∼(1−2) × 10 8 K/s. For the particle assembly in Figure 3b, all Al NPs that spalled reached a simulated temperature greater than 1035 K, while the Al NP that did not spall experienced incomplete melting at a temperature of 934 K. On the basis of simulation and experimental observations, the Al particle diameter, shell thickness, heating rate, and core Al temperatures of spalled Al NPs exceed the threshold values predicted by the MDM.…”

“…The estimated heating rates of the Al NPs ranged between 10 6 and 10 11 K/s; however, the potential underestimation of the alumina shell thickness and insufficient temperature to induce the MDM may explain the observed sintering mechanism rather than the MDM. 25 A similar experiment using a thin-film MEMS-based heater that generated a 10 6 K/s heating rate failed to produce Al NP spallation even in the presence of WO 3 oxide NPs. 28 A clear set of experiments that examine isolated Al NPs without an oxidizer and clearly meet and exceed the MDM threshold heating parameters are needed to conclusively validate the proposed spallation mechanism.…”

“…23 Shells with preexisting defects, including nanovoids, impurities, and heterogeneous shell thickness, may hinder the occurrence of MDM. 24,25 Promoting the rapid spallation and ejection of molten Al fuel, as proposed by the MDM model, could drastically Several different heating schemes have been attempted to observe MDM. One such experiment used photothermal heating of nanoscale Al disks fabricated using electron-beam lithography and Al evaporation.…”

Stress relaxation in pre-stressed aluminum core–shell particles: X-ray diffraction study, modeling, and improved reactivity

“…However, qualitatively, it is now clear that if annealing at are sufficient for almost complete stress relaxation, then annealing time at higher temperatures should be much shorter. This also will reduce probability of sintering of particles, which may lead to local stress concentration in a shell and suppress MDM [20]. The main focus of the experimental research will be on more precise determination of the creep parameters in the temperature range, determination of the minimum required annealing time and cooling rate in order to avoid stress relaxation during cooling.…”