Degradation of sulfamethazine in coastal aquaculture tailwater by Na2S2O4@iron-electrode electrooxidation combined with ceramic membrane process.

Offshore aquaculture's explosive growth improves the public food chain while also unavoidably adding new pollutants to the environment. Consequently, the protection of coastal marine eco-systems depends on the efficient treatment of wastewater from marine aquaculture. For the sulfamethazine (SMZ) of representative sulfonamides and total organic pollutants removal utilizing in-situ high salinity, this work has established an inventive and systematic treatment process coupled with iron-electrode electrochemical and ultrafiltration. Additionally, the activated dithionite (DTN) was being used in the electrochemical and ultrafiltration processes with electricity/varivalent iron (FeII/FeIII) and ceramic membrane (CM), respectively, indicated by the notations DTN@iron-electrode/EO-CM. Quenching experiments and ESR detection have identified plenty of reactive species including SO4·-, ·OH, 1O2, and O2·-, for the advanced treatment. In addition, the mass spectrometry (MS) and the Gaussian simulation calculation for these primary reaction sites revealed the dominate SMZ degradation mechanisms, including cleavage of S-N bond, hydroxylation, and Smile-type rearrangement in DTN@iron-electrode/EO process. The DTN@iron-electrode/EO effluent also demonstrated superior membrane fouling mitigation in terms of the CM process, owing to its higher specific flux. XPS and SEM confirmed the reducing membrane fouling, which showed the formation of a loose and porous cake layer. This work clarified diverse reactive species formation and detoxification with DTN@iron-electrode/EO system and offers a sustainable and efficient process for treating tailwater from coastal aquaculture.

The effects of the formation of a multi-scale reinforcing phase on the microstructure evolution and mechanical properties of a Ti2AlC/TiAl alloy.

In order to acquire TiAl composites with a multi-scale reinforcing phase, and to improve the microstructure and tensile properties at elevated temperatures, TiAl alloys have been prepared with different added carbon content levels via vacuum arc melting. The results show that when the carbon content is greater than or equal to 1.0 at%, then Ti2AlC forms and the microstructure changes from having a dendrite morphology to an equiaxed crystal morphology. The B2 phase disappears in the Ti2AlC-containing alloys. As the carbon content increases from 0 to 3.0 at%, the lamellar colony size decreases from 148.4 to 32.8 µm and the lamellar width decreases from 441.2 to 117.6 nm. More nanoscale Ti2AlC particles form in the α2 lamellae at a higher carbon content, and there are a lot of dislocations around them. As the carbon content, the Ti2AlC content increases from 0 to 16.8 vol% and the length-diameter ratio decreases from 9.2 to 1.8. The reason for the microstructure refinement is that carbon and carbide act as heterogeneous particles during solidification, and carbide dissolves some alloy elements, improving the microstructure uniformity. Compressive testing shows that the maximum compressive strength is 2324.3 MPa at a carbon content of 1.5%. At a carbon content of 2.5%, the compression strain is higher (28.1%). Tensile testing at elevated temperatures shows that upon increasing the temperature from 750 to 850 °C, the tensile strength increases from 398 to 541 MPa, and the strain increases from 6.1 to 12.2% with a temperature increase from 750 to 950 °C. The increase in the mechanical properties is attributed to the refined lamellar colonies and lamellar width, the solid solution of elements, and the formation of nanoprecipitates.

Effects of Tantalum on Microstructure Evolution and Mechanical Properties of High-Nb TiAl Alloys Reinforced by Ti2AlC.

Experiments have been carried out to study the relationship between the addition of tantalum and microstructure, especially the formation of the B2 phase in lamellar colonies. The mechanical properties, with different contents of Ta, were also measured. Ti46Al8Nb2.6CxTa alloys were prepared by casting with the content of Ta varying from zero to 1.0 at.%. Experimental results show that the B2 phase forms in lamellar colonies with the addition of Ta, and its content increases when the content of Ta increases. Meanwhile, the γ phase decreases and the lattice parameter of the α 2 phase increases. The size of the lamellar colony decreased from 29.9 to 21.6 µm. Ta dissolves into Ti2AlC by substitution, and its solubility is more than 1.1% tested by EDS. Nb, which is necessary for the formation of the B2 phase, comes from two aspects. The first is that Ta dissolves into the Ti2AlC and partly replaces the Nb atom and the second is the decrease in the γ phase because it has higher solid solubility for Nb. The increase in Nb in the liquid phase increases the composition supercooling and heteronucleation at the solidification front, which accounts for refining the lamellar colony. Room temperature compressive testing showed that the compressive strength and the strain increased when the Ta content increased up to 0.8% and then decreased. Improvement of the compressive properties resulted from the grain boundary strengthening and their decrease induced by more content of the B2 phase. Tensile properties, at elevated temperature, were improved with testing temperature increasing from 750 to 950°C, because solid solution strengthening is a major influence factor.