Enhanced mechanical properties of lightweight Al2O3-C refractories reinforced by combined one-dimensional ceramic phases

We prepared a new lightweight Al₂O₃-C refractory material with a higher strength by using microporous corundum aggregates instead of dense tabular corundum aggregates, which was reinforced by in situ formed SiC whiskers, multi-walled carbon nanotubes (MWCNTs), and mullite rods. A comparative study of the microstructure, mechanical properties, and fracture behavior was carried out for dense and lightweight Al₂O₃-C refractories coked at 1200°C and 1400°C, respectively. By using the microporous corundum aggregates, a better aggregate/matrix interface bonding and an optimized distribution of SiC whiskers were obtained. The SiC whiskers formed inside the microporous corundum aggregates and simultaneously in the matrix by a vapor-solid reaction mechanism, resulting in an enhancement at the microporous aggregate/matrix interface. Furthermore, the in situ formed MWCNTs and well-developed mullite rods at 1200°C in the matrix also contributed to the better interface structure. Thus, due to the improved microporous aggregate/matrix interface, the crack propagation along the aggregate/matrix interface was suppressed, resulting in an increased crack propagation within the aggregates. Consequently, the synergy between microporous corundum aggregates and combined one-dimensional ceramic phases caused a lower bulk density but a markedly higher strength, a higher fracture energy, and a higher toughness of lightweight Al₂O₃-C refractories compared to the dense ones. Overall, our study allows to overcome the traditional concept that a higher strength of refractories is reached by a higher density.     

Enhanced Analog Performance and High-Frequency Applications of Dielectric Engineered High-K Schottky Nanowire FET

Silicon - In this paper, Gallium Nitride (GaN) based Dielectric Engineered High-K GaN Schottky Nanowire Field Effect Transistor (DE-HK-GaN-SNWFET) is examined for enhancing analog performance for...     

Heat transfer prediction for radiant floor heating/cooling systems using artificial neural network (ANN)

Radiant floor cooling and heating systems (RHC) are gaining popularity as compared with conventional space conditioning systems. An understanding of the heat transfer capacity of the radiant system is desirable to design a space conditioning system using RHC technology. In the present work, a simplified heat flux model for RHC is developed for both cooling and heating modes of operation. The Artificial Neural Network (ANN) technique is used for the development of the simplified model. Experimental data from literature covering a wide operating range of the RHC is considered for model development and validation. Operating parameters such as mass flow rate (m_f), heat resistance (R_s), mean temperature of water flowing through the pipe (T_m), and operative temperature (T_op) are considered independent variables influencing the heat flux (q_t). The neural network consists of four input layers, one output layer, and one hidden layer with a feed-forward-back-propagation algorithm. A study on the selection of the optimum number of neurons in the range of 1–9 for the hidden layer is also performed. On the basis of the performance parameters, namely, average-absolute-relative-deviation (AARD = 0.11283) percentage, mean-square-error (MSE = 0.00055), and the coefficient of determination (R² = 0.9984), a hidden layer is modeled with five neurons.     

Nexuses Between the Chemical Design and Performance of Small Molecule Dopant-Free Hole Transporting Materials in Perovskite Solar Cells

Perovskite solar cells (PSCs) have grabbed much attention of researchers owing to their quick rise in power conversion efficiency (PCE). However, long-term stability remains a hurdle in commercialization, partly due to the inclusion of necessary hygroscopic dopants in hole transporting materials, enhancing the complexity and total cost. Generally, the efforts in designing dopant-free hole transporting materials (HTMs) are devoted toward small molecule and polymeric HTMs, where small molecule based HTMs (SM-HTMs) are dominant due to their reproducibility, facile synthesis, and low cost. Still, the state-of-art dopant-free SM-HTM has not been achieved yet, mainly because of the knowledge gap between device engineering and molecular designs. From a molecular engineering perspective, this article reviews dopant-free SM-HTMs for PSCs, outlining analyses of chemical structures with promising properties toward achieving effective, low-cost, and scalable materials for devices with higher stability. Finally, an outlook of dopant-free SM-HTMs toward commercial application and insight into the development of long-term stability PSCs devices is provided.     

Detection of Nontrivial Topology Driven by Charge Density Wave in a Semi-Dirac Metal

The presence of electron correlations in a system with topological order can lead to exotic ground states. Considering single crystals of LaAgSb₂ which has a square net crystal structure, one finds multiple charge density wave transitions (CDW) as the temperature is lowered. Large planar Hall (PHE) signals are found in the CDW phase, which are still finite in the high-temperature phase though they change sign. Optimizing the structure within first-principles calculations, one finds an unusual chiral metallic phase. This is because as the temperature is lowered, the separation between the Ag/Sb atoms on different layers decreases, leading to stronger repulsions between electrons associated with atoms on different layers. This leads to successive layers sliding with respect to each other, thereby stabilizing a chiral structure in which inversion symmetry is also broken. The large Berry curvature associated with the low-temperature structure explains the low-temperature PHE. At high temperature, the PHE arises from the changes induced in the anisotropic Dirac cone in presence of a magnetic field. This work represents a route toward detecting and understanding the mechanism in a correlation-driven topological transition through electron transport measurements, complemented by ab-initio electronic structure calculations.     

Oxidation behaviors of low carbon MgO-C refractories: Roles of Ti2AlC and Ti2AlN

In this study, Ti₂AlC/Ti₂AlN powders were first incorporated to fabricate low-carbon MgO-C refractories, and their oxidation behaviors were investigated. Computed tomography (CT) results indicated that stress cracks only occurred in the Ti₂AlC-added sample after exposure to 1100°C, and the anomalous oxidation behavior of Ti₂AlC powder at 578°C worsened the oxidation result at 1100°C for MgO-C refractories with Ti₂AlC. At 1500°C, the oxidation behaviors of MgO-Ti₂AlC/Ti₂AlN-C samples revealed a slight mass gain due to the disintegration of Ti₂AlC/Ti₂AlN, and their oxidation resistances increased by 18% as compared to their counterparts. In addition, the role of Ti₂AlC/Ti₂AlN was elucidated. The oxidation process was comprehensive and was mainly determined by the deterioration of carbon and MAX phases. The obtained results indicated that Ti₂AlN was more suitable for fabricating low-carbon MgO-C refractories as compared with Ti₂AlC.