Role of Strain-Induced Microscale Compositional Pulling on Optical Properties of High Al Content AlGaN Quantum Wells for Deep-Ultraviolet LED

A systematic study was carried out for strain-induced microscale compositional pulling effect on the structural and optical properties of high Al content AlGaN multiple quantum wells (MQWs). Investigations reveal that a large tensile strain is introduced during the epitaxial growth of AlGaN MQWs, due to the grain boundary formation, coalescence and growth. The presence of this tensile strain results in the microscale inhomogeneous compositional pulling and Ga segregation, which is further confirmed by the lower formation enthalpy of Ga atom than Al atom on AlGaN slab using first principle simulations. The strain-induced microscale compositional pulling leads to an asymmetrical feature of emission spectra and local variation in emission energy of AlGaN MQWs. Because of a stronger three-dimensional carrier localization, the area of Ga segregation shows a higher emission efficiency compared with the intrinsic area of MQWs, which is benefit for fabricating efficient AlGaN-based deep-ultraviolet light-emitting diode.

Effect of Exhausted Olive Cake Contamination on Fly and Bottom Ash in Power Plants

With the aim to prevent possible power plant malfunction due to the feedstock properties and suggest possible ash applications, feedstock samples and bottom and fly ash samples collected along more than a year in a 16 MW suspension-fired boiler power plant, fed mainly with pulverized exhausted olive cake (orujillo), were studied. A detailed characterization of fly and bottom ash has been done, as well as a seasonal evolution study. Altogether in order to find any trend on the ash composition changes and to study the relationship between ash (both fly and bottom fractions) and, on the one hand, the feedstock composition, and on the other hand, the troublesome deposit formation. A relationship between deposit growth and higher Cl and Na content in the feedstock has been noticed, showing the need for some control on these feedstock’s components. The high Cl and Na content is attributed to external contamination. Furthermore, the high Al content in the feedstock and the strong relationship between Al, Fe and Si (indicating a common origin) suggest some biomass soil contamination. However, no relationship was observed between troublesome deposit formation and the hypothesized biomass soil contamination. Graphic Abstract

Use of CO2 to Cure Steel Slag and Gypsum-Based Material

To improve the utilization of steel slag (SS) in CO2 capture and making building materials, the paper mainly discussed the effects of desulphurization gypsum (DG) and w/s ratio on strength development and CO2 capture capability of high Al content SS. It showed that 10 wt% DG enhanced the strength of hydration-curing SS by 262% at 28 days. Similarly, adding 6 wt% DG in carbonation-curing SS contributed to increases in strength and CO2 uptake by 283% and 33.54%, reaching 42.68 MPa and 19.12%, respectively. Strength decreases and CO2 uptake increases with w/s. Microanalysis (QXRD, SEM-EDS, TG-DTG, FTIR, XPS, and MIP) revealed that the main hydration products of SS were C-S-H gel and C4AH13, which transformed to ettringite with DG addition. The carbonation products were mainly calcite and aragonite. Additionally, the amount of aragonite, mechanically weaker than calcite, decreased and calcite increased significantly when DG was added in carbonation-curing samples, providing a denser structure and higher strength than those without DG. Furthermore, high Al 2p binding energies revealed the formation of monocarboaluminate in the DG-added carbonation samples, corresponding to higher CO2 uptake. This study provides guidance for the preparation of SS-DG carbide building materials.

Non-metallic Inclusions in Different Ferroalloys and Their Effect on the Steel Quality: A Review

Ferroalloys have become increasingly important due to their indispensable role in steelmaking. In addition, the demand for improved steel qualities has increased considerably, which in turn highlights the quality of ferroalloys. This is due to the fact that the impurities in ferroalloys directly and significantly influence the quality of steel products. To gain a better understanding of the main trace elements and inclusions in ferroalloys (such as FeSi, FeMn, SiMn, FeTi, FeCr, FeMo, FeNb, FeV, FeB, some complex ferroalloys) and their behaviours in steel melt after the additions of these ferroalloys, information from a large number of previous results on this topic was extensively reviewed in this work. The applications of different ferroalloys and their production trends were discussed. In addition, the effects of some trace element impurities from ferroalloys on the inclusion characteristics in steel were also discussed. The possible harmful inclusions in different ferroalloys were identified. Overall, the results showed that the inclusions present in ferroalloys had the following influence on the final steel cleanliness: (1) MnO, MnS and MnO–SiO2–MnS inclusions from FeMn and SiMn alloys have a temporary influence on the steel quality; (2) the effect of large size SiO2 inclusions (up to 200 μm) in FeSi and FeMo alloys on the steel cleanliness is not fully understood. The effect of Al, Ca contents should be considered before the addition of FeSi alloys. In addition, Al2O3 inclusions and relatively high Al content are commonly found in FeTi, FeNb and FeV alloys due to their production process. This information should be paid more attention to when these ferroalloys are added to steel; (3) except for the existing inclusions in these alloys, the Ti-rich, Nb-rich, V-rich carbides and nitrides, which have important effects on the steel properties also should be studied further; and (4) specific alloys containing REM oxides, Cr–C–N, Cr–Mn–O, Al2O3, Al–Ti–O, TiS and Ti(C, N) have not been studied enough to enable a judgement on their influence on the steel cleanliness. Finally, some suggestions were given for further studies for the development of ferroalloy productions.