Real-Time Measurement on the Heat Release Property of Titanium Blended with Different Carbon Allotropes, under Externally Constant Heat Flux

Abstract

Ti/C blended powder is commonly employed as an initiating combustion agent for preparing calcium aluminate; a dedicated test system is exploited for real-time examining of the heat release of Ti/C blended powder during combustion under atmosphere conditions with an externally constant heat flux of 973 K, which is comprised of cone calorimeter, thermal-gravimetry/differential scanning calorimetry, X-ray diffraction (XRD), scanning electron microscope/energy dispersive spectrometer, and a theoretical thermal calculation, with the aim of quantitatively illuminating its combustion mechanism in depth. Furthermore, a comparison of the heat release property of titanium powder blended with different carbon allotropes, including natural flaky graphite (FG), carbon black (CB), expandable graphite (EG), and vermicular graphite (VG) is preliminarily investigated, to clarify the effect of different carbon allotropes on the heat release property of Ti/C blended powder. It reveals that the oxidation reaction between Ti and O 2 initiates the subsequent combination of TiC through a thermal explosion reaction, using graphite (FG, VG, or EG) and Ti powder as the starting materials, respectively. Moreover, EG facilitates an accelerated (fire growth index of 0.42 kW·m −2 ·s −1 ) and enhanced peak heat release rate (pHRR) of 30.7 kW·m −2 at 73 s, while VG suppresses the heat release with the pHRR of 5.2 kW·m −2 at 64 s and fire growth index of 0.08 kW·m −2 ·s −1 , and FG favors the formation of TiC with a higher crystallinity from XRD. Additively, the prior NaOH-impregnation is favorable for the formation of TiC for Ti/CB blended powder, although the TiO 2 predominates final combustion production. It reveals the chemical evolution and mechanisms evolved in the formation of TiC during ignition.Metals 2019, 9, 981 2 of 16 contains expandable graphite (EG), vermicular graphite (VG), or expanded graphite after instantaneous expansion of EG, and natural flaky graphite (FG), which hold obviously different micro-structures and properties. Therefore, the various carbon sources affect the productions formed by SHS reaction [11]. It has been reported that the carbon nanotube and graphene as carbon sources impart enhanced tribological properties [12]; CB favors the formation of nano-metric TiC-carbon composite with a smaller particle size, as the most effective carbon allotrope for hindering the sintering of TiC under high temperature [13]. However, there is an interesting phenomenon-that the explosive reaction between graphite and titanium powder occurs under atmospheric pressure at 973 K with a transiently glaring flame, which inspired us to excavate its reaction mechanism, in order to explain the curious phenomenon.Consequently, the real-time measurement of heat release property involved in titanium blended with different carbon allotropes is preliminarily investigated, which is detected and recorded by cone calorimeter (CC) and thermal-gravimetry/differential scanning calorimetry (TG/DSC), respectively, using FG, CB, EG, and VG as different ...