Flame stand-off effects on propagation of 3D printed 94 wt% nanosized pyrolants loading composites

Abstract

Understanding the relationship between heat transport mechanisms, particularly given the new opportunities to microstructure architecture through additive manufacturing to adjust heat flux (energy release rate per area, unit W/m2), is highly desirable. In this study, we directly write free-standing iodized pyrolant sticks (94 wt% pre-assembled Ti/Ca(IO3)2 nanocomposites) with only 6 wt% binder addition. Compared to the substrate-supported pyrolant composites without using polymer (100 wt% Ti/Ca(IO3)2), we saw a > 4X reduction on the heat release rate with only 6 wt% polymer. Additionally the physically mixed case (94 wt% physically mixed Ti/Ca(IO3)2 has another 4X lower heat release rate than the above pre-assembled case. To explore heat feedback we observed the flame stand-off particularly in the samples with 6 wt% polymer via a microscopic imaging system with pyrometry. We found that with the pre-assembled and physically mixed pyrolants, the flame stand-off distances are ∼ 0.7 mm and ∼ 1.2 mm, respectively, which provides low heat feedback to the burning surface leading to partial ignition of nanocomposites on the burning surface. A simple thermal calculation was used to explain the relative role of the different modes of heat feedback and their relationship to stand-off and ignition.