Evaluation of Ti-Doped Al-Si Phase Change Materials Composites for Effective Use in Thermal Energy Storage and Thermal Management Systems

The incessant world energy crisis, and the effects of global warming demand clean and sustainable energy alternatives to generate, store, and save energy for use when needed, curtailing the mismatch between energy demand and supply. Latent heat thermal energy storage (LHTES) using metal alloy-based phase change materials (PCMs) and their composites has attracted a lot of interest because of their ability to absorb, store and release large latent heat during the phase change phenomenon, thus making PCMs one of the important players in energy storage and utilization technologies. Al alloy-based PCMs such as Al-Si and their composites show great potential for LHTES and utilizations. However, efficient applications are constrained by possible liquid leakages, supercooling (SC), and phase change hysteresis (PCH) etc. Specifically, SC phenomenon and the consequent PCH are major drawbacks against efficient practical utilizations. While PCH is the difference between the melting and solidification temperature, supercooling refers to a condition where PCMs remain in liquid state at a temperature lower than their solidification temperature. It inhibits the crystallization process in PCMs, thereby impeding the PCM’s ability to transition from a liquid to a solid phase upon cooling, resulting not only in the non-release of stored heat within the expected temperature range, but also intensifies energy consumption and reduces the efficiency of TES systems. Previously, our group reported the fabrication of PCM composites. Characterized by high heat storage density and high thermal stability, the composite PCMs exhibited large supercooling and phase change hysteresis. So far, suppression of the SC and PCH of Al-Si PCMs and their composites are seldom reported despite the large heat storage density per unit volume, and exceptional thermal stability for practical TES applications. Moreover, Al-Si composite PCMs with enhanced thermal properties promise decarbonation to curb the effects of global warming. Therefore, mitigation of the supercooling phenomenon is highly essential for efficient use of not only PCMs but also their composites. Herein, we present the development of Ti-doped Al-Si MEPCM composites with suppressed SC and PCH.<br/>In the field of metal alloying, it is well known that Al intermetallic compounds such as ZrAl₃, B₂Al, and TiAl₃ etc. are probable nucleating agents for Al. Moreover, the use of additives as nucleation agents has been proposed to aid in mitigating supercooling. In the light of the foregoing, we first fabricated Ti-doped Al-Si MEPCMs by the adherence of TiO₂ nanoadditive and α-Al₂O₃ (shell material) to the microcapsules via high-speed impact blending, and heat oxidation treatment. Next, the composite material was fabricated using α-Al₂O₃ powder as sintering aids. Mixed powder of the MEPCM (80 vol%) and the binder (20 vol%) were wet-mixed and a small amount of the powder (0.5 g) was added to a die with a diameter of 1 cm and pressed for 1 min at 20 MPa and 25 °C. Cylindrical pellets with a height of approximately 4 mm obtained after pressing were heated from 25 °C to 1000 °C at a rate of 10 °C min⁻¹. Following heat treatment, structural and thermal properties of the MEPCMs composites were investigated. The pictorial and SEM images of the Ti-doped Al-Si MEPCM composites show successful fabrication of stable composite materials. Furthermore, using the same sintering aid, we observed approximately 57% and 91% reduction of the inherent SC and PCH of Al-Si MEPCM composites by an addition of 3wt.% TiO₂. This stems from enhanced crystallization due to heterogenous nucleation of the formed intermetallic compound, TiSi₂. The results demonstrate the development of Ti-doped Al-Si MEPCM composite of high latent heat capacity with suppressed supercooling and phase change hysteresis, paving way for effective practical use in thermal management and thermal energy storage systems.