Search

Polyethylene glycol (PEG) is widely used as a phase change material (PCM) in thermal energy storage systems due to its high latent heat and chemical stability. However, practical application has been hindered by its low thermal conductivity and leakage issues. Therefore, developing shape-stable high thermal conductivity PCM is of great importance. In this study, new shape-stable composite PCM with high thermal conductivity and leak-prevention capabilities were designed. The porous carbon skeleton of diamond foam (DF) and dual-3D carbon nanotube-diamond foam (CDF) were prepared using the microwave plasma chemical vapor deposition method. The composite materials (DF/PEG and CDF/PEG) were produced by vacuum impregnation with PEG and skeletons. The results showed that CDF/PEG had the highest thermal conductivity, measuring 2.30 W·m−1·K−1, which is 707% higher than that of pure PEG. The employing of 3D networks of CNTs, which can improve the phonon mean free path in DF/PEG (1.79 W·m−1·K−1) while reducing phonon dispersion.The phonon vibration of dual-3D CDF plays an important role in heat transfer. PEG was physically absorbed and well-distributed in CDF, alleviating leakage of liquid PEG. The weight loss of CDF/PEG was only 25% at 70 °C for 120 s. Using CDF is an attractive and efficient strategy to increase the heat transfer of PEG and improve heat storage efficiency, alleviate the problem of poor shape-stability. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method for growing carbon nanotubes (CNTs) via microwave plasma chemical vapor deposition (MPCVD) on diamond and silicon substrates. Scanning electron microscopy (SEM) and Raman spectroscopy analyses revealed dense, multi-walled carbon nanotubes growing on the diamond substrate. Optical Emission Spectroscopy (OES) showed that in the process of growing carbon nanotubes with the MPCVD method, the CH4 introduced into the system is excited by microwaves and dissociated to form active radicals such as C2 and CH, which are considered the C source of the synthesized carbon nanotube. Observation with high-resolution transmission electron microscopy (HRTEM) showed that most Ni catalyst nanoparticles that catalyze the growth of carbon nanotubes are located close to the diamond surface. In contrast, on the Si substrate, Ni catalyst nanoparticles were randomly distributed. A unique transition layer was observed between the diamond and carbon nanotubes, with the Ni particles being immersed into this transition layer and acting as anchors to fix the carbon nanotubes, resulting in a robust connection between the diamond and the CNT coating. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) and diamonds are allotropes of carbon, exhibiting excellent thermal, mechanical, optical, and electrical properties. Integrating CNTs with diamonds could advance the thermal management of high-heat-flux devices, light absorption, and novel semiconductor devices. This study reports the synthesis of vertical CNTs on a diamond substrate using microwave plasma chemical vapor deposition (MPCVD). Enhanced interfacial adhesion between the CNTs and diamond was confirmed by subjecting the CNT/diamond composite to ultrasonic vibrations and analyzing the morphology via scanning electron microscopy. The growth mechanism of CNTs on the diamond and the CNT/diamond interface bonding behavior were investigated using scanning transmission electron microscopy, electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and optical emission spectroscopy. The results indicate that the carbon supplied from two different sources drove the growth of CNTs primarily through the root-growth mechanism and, to a lesser extent, through the tip-growth mechanism. The tip-growth mechanism may involve the formation of a covalent connection at the CNT/diamond interface. For the root-growth mechanism, two interfaces emerged in the CNT/diamond composite, namely Fe/diamond and CNT/Fe. Additionally, mixed cementite phases connected the CNTs to the diamond substrate. Elucidating the bonding mechanism between the CNTs and diamond can provide insights into the dynamics of the carbon atoms in the catalyst and offer a deeper understanding of the growth mechanism of CNTs on the diamond substrate. [Display omitted] • Vertical carbon nanotubes were prepared on a diamond substrate using MPCVD. • Carbon nanotubes exhibited excellent adhesion responses on the diamond substrate. • The growth of vertical carbon nanotubes was driven by a dual-carbon source supply. • The robust connection of the carbon nanotubes and diamond substrate strongly relied on a cementite mixture. [ABSTRACT FROM AUTHOR]