Effect of Silicon Addition on High-Temperature Solid Particle Erosion-Wear Behaviour of Mullite-SiC Composite Refractories Prepared by Nitriding Reactive

Solid particle erosion-wear experiments on as-prepared mullite-SiC composite refractories by nitriding reactive sintering were performed at elevated temperatures, using sharp black SiC abrasive particles at an impact speed of 50 m/s and the impact angle of 90° in the air atmosphere. The effects of silicon powder addition and erosion temperature on the erosion-wear resistance of mullite-SiC composite refractories were studied. The test results reveal that Si powders caused nitriding reaction to form β-sialon whiskers in the matrix of mullite-SiC composite refractories. The erosion-wear resistance of mullite-SiC composite refractories was improved with the increase of silicon powder addition and erosion temperature, and the minimum volume erosion rate was under the condition of 12% silicon added and a temperature of 1400°C. The major erosion-wear mechanisms of mullite-SiC composite refractories were brittle erosion at the erosion temperature from room temperature to 1000°C and then plastic deformation from 1200°C to 1400°C

Si 3

Si3N4-SiCp composites reinforced by in situ catalytic formed nanofibers were prepared at a relatively low sintering temperature. The effects of catalyst Co on the phase compositions, microstructures, and physicochemical-mechanical properties of samples sintered at 1350°C–1450°C were investigated. The results showed that the catalyst Co enhanced the nitridation of Si. With the increase of Co addition (from 0 wt% to 2.0 wt.%), the apparent porosity of as-prepared refractories was initially decreased and subsequently increased, while the bulk density and the bending strength exhibited an opposite trend. The Si3N4-SiCp composites sintered at 1400°C had the highest strength of 60.2 MPa when the Co content was 0.5 wt.%. The catalyst Co facilitated the sintering of Si3N4-SiCp composites as well as the formation of Si3N4 nanofibers which exhibited network connection and could improve their strength

An investigation on the speed dependence of ice resistance using an advanced CFD+DEM approach based on pre-sawn ice tests

Over the past decades, the underlying mechanism of level ice resistance changing with ship speed has not been fully understood, particularly the resistance component due to ship interactions with broken ice pieces. Pre-sawn ice test can negate icebreaking component from the whole resistance of a ship in level ice, providing an effective approach to decompose ship-ice interactions and investigate the speed-dependent resistance from broken ice pieces. This work has built a computational model that can realistically simulate a ship advancing in a pre-sawn ice channel. The model applies Computational Fluid Dynamics (CFD) to solve the flow around an advancing ship, which is coupled with an enhanced Discrete Element Method (DEM) to model pre-sawn ice pieces. Model-scale experiments have also been conducted at the Aalto Ice Tank to validate the simulations, which shows the computational model can provide a reasonable estimation of the pre-sawn ice's resistance and movement around the ship. Upon validation, the dependence of ice resistance on ship speed was analysed. The simulations enable underwater monitoring of the ice motions, indicating that the speed dependence results from the mass of ice submerged underneath the ship and the displacement of broken ice induced by the ship. The identified relationships are more complex than the widely-used assumption that ice resistance linearly changes with ship speed in all cases, which provides a deeper understanding of ice resistance. As such, the findings from this study can potentially facilitate improvements in relevant empirical equations, useful for ship design, operational strategies and maritime management in polar regions

Pressure-tailored lithium deposition and dissolution in lithium metal batteries

A porous electrode resulting from unregulated Li growth is the major cause of the low Coulombic efficiency and potential safety hazards of rechargeable Li metal batteries. Strategies aiming to achieve large granular Li deposits have been extensively explored; yet, the ideal Li deposits, which consist of large Li particles that are seamlessly packed on the electrode and can be reversibly deposited and stripped, have never been achieved. Here, by controlling the uniaxial stack pressure during battery operation, a dense Li deposition (99.49% electrode density) with an ideal columnar structure has been achieved. Using multi-scale characterization and simulation, we elucidated the critical role of stack pressure on Li nucleation, growth and dissolution processes, and developed innovative strategies to maintain the ideal Li morphology during extended cycling. The precision manipulation of Li deposition and dissolution is a critical step to enable fast charging and low temperature operation for Li metal batteries