Silicon-Boron Alloys as New Ultra-High Temperature Phase-Change Materials: Solid/Liquid State Interaction with the h-BN Composite

Abstract

Silicon-boron alloys have been recently pointed out as novel ultra-high temperature phase change materials for applications in Latent Heat Thermal Energy Storage (LHTES) and conversion systems. One of the emerging challenges related to the development of such devices is a selection of refractories applicable to build a vessel for storing molten Si-B alloys at high temperatures and under consecutive melting/solidification conditions. Previously, it has been documented that hexagonal boron nitride (h-BN) is the only one ceramic showing a non-wettability and limited reactivity with Si-B alloys at temperatures up to 1750 • C, what makes it a good candidate of the first selection for the predicted application. Nevertheless, pure h-BN shows a rather low mechanical strength that could affect a durability of the LHTES vessel. Therefore, the main purpose of this work was to examine high temperature behavior of commercial high strength h-BN composite having a nominal composition of h-BN-24ZrO 2 -6SiC (vol.%) in contact with a solid/liquid eutectic Si-3.2B alloy. Two types of sessile drop experiments were carried out: a step-contact heating up to 1750 • C, and a thermocycling at 1300 − 1450 • C composed of 15 cycles of the alloy melting/solidification. The obtained results showed a lack of wettability in the examined system at temperatures up to 1750 • C. The Si-3.2B alloy presented good repeatability of melting/solidification temperatures in consecutive thermal cycles, which was not affected by the interaction with the h-BN composite. However, due to reactions taking place between the composite's components leading to structural degradation, it is not recommended to increase operational temperature of this material above 1450 • C. Keywords Silicon-boron alloys • Hexagonal boron nitride • Sessile drop method • Latent heat thermal energy storage • AMADEUS project Electronic supplementary material The online version of this article (

Conformal and Stoichiometric Chemical Vapor Deposition of Silicon Carbide onto Ultradeep Heterogeneous Micropores by Controlling the Initial Nucleation Stage

“…Although the exact value of θ of β-SiC on t-BN is not clear due to the sublimability of SiC, β-SiC is likely to exhibit a higher θ on t-BN (i.e., higher γ int and/or lower γ and ) compared to that on Si(100). This assumption is consistent with existing reports that Si wettability − is superior on β-SiC (8°) compared to t-BN (145°) …”

“…Although the exact value of θ of β-SiC on t-BN is not clear due to the sublimability of SiC, β-SiC is likely to exhibit a higher θ on t-BN (i.e., higher γ int and/or lower γ and ) compared to that on Si(100). This assumption is consistent with existing reports that Si wettability − is superior on β-SiC (8°) compared to t-BN (145°) The higher θ leads to lower nucleate density ( N ) of CVD at the initial nucleation stage, based on heterogeneous nucleation theory. , Here, N can be expressed as where n s is the total density of surface nucleation sites, Δ G * is the critical value of the total change in the Gibbs free energy associated with nucleation (Δ G ), k is Boltzmann’s constant, and Δ g v is the change in chemical free energy associated with condensation of atoms from vapor to solid.…”

“…To confirm this, the incubation period dependence on underlayer materials with different θ was studied. The θ of SiC deduced from the θ of molten Si − was confirmed to decrease in the order of t-BN, a-SiO 2 , and Si(100): 8° on β-SiC, 85° on a-SiO 2 , and 145° on t-BN . The incubation periods were longer in the order Si(100), a-SiO 2 , and t-BN, as shown in Figure (b).…”

“…Furthermore, the results of the present study were consistent with previous literature; t-BN exhibited the longest incubation periods (i.e., the poorest nucleation behavior) for SiC-CVD among Si(100), a-SiO 2 , and t-BN underlayers. Meanwhile, SiC has been suggested to exhibit the poorest wettability with h-BN among Si, a-SiO 2 , and h-BN, as deduced from wettability tests of molten-Si on β-SiC, a-SiO 2 , and h-BN underlayers. − …”

Simultaneous Differential Thermal Analysis and Thermogravimetric Analysis of Si-30B Alloy

“…Among others, good physicochemical compatibility between the container material and its holder is also required. For example, in the Netzsch STA 449 F3 Jupiter Ò device used in this study, the W-Re holder is suitable for graphite containers but it is not recommended for h-BN containers that show negligible reactivity with Si-B alloys up to 1760°C ( Ref 1,10).…”