Degradation mechanism of the superconducting performance of a Bi2212 cable under magnetic fields

In magnetic confinement fusion reactors, superconducting magnet systems are essential for generating and controlling high magnetic fields. To increase the magnetic field, new superconducting materials such as Bi2212 (Bi2Sr2CaCu2O8+x) have been selected in the design of magnet systems. However, the stability of the Bi2212 superconductor under magnetic fields must be studied for the routine and safe operation of magnet systems. In this work, the stability and degradation mechanism of a Bi2212 cable under magnetic fields were investigated. With a magnetic field of 5.8 T, the cable carrying 29 kA was exerted with a force of ~168.2 kN per meter. In the core area of the cable, moved wires were detected by computed tomography (CT). The macroscopic movement of the wires would vary with the axial position, which could be related to the twist structure. Then, the cable was decomposed, and the acquired wires were tested under 12 T at 4.2 K by four-probe method. The results indicated that the inner wires had relatively lower critical currents, which should be the reason for the degradation of cable performance. Scanning electron microscope (SEM) images of the superconducting phase within the wires confirmed that cracks existed in the superconducting phase of the inner wires, while intact crystals were found in that of the outer wires. The variation in microstructures gave rise to changes in the wire performance.

Degradation mechanism and life prediction of tailings and waste rock aggregate geopolymer concrete under freeze-thaw corrosion

To study the durability of tailings and waste rock aggregate geopolymer concrete (TWGPC), a large number of tailings and waste rock were used to replace natural sand and stone as aggregates, and a fly ash geopolymer was used to replace cement as cementing material to prepare TWGPC. The slow freezing method was used to carry out single freeze-thaw and freeze-thaw corrosion tests. Scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS) were used to analyse the microstructure and reaction products of TWGPC. The degradation mechanism of TWGPC was studied, and the life of TWGPC was predicted. The results show that the higher the concentration of corrosion solution was, the more significant the change trend of the mechanical properties test results. In the early stage of the cycle, acinar gypsum and short columnar ettringite were generated to fill the pores and improve the compactness and frost resistance of TWGPC. In the late stage of the cycle: calcium-silicate-hydrate (C-S-H) was decomposed and gradually replaced by magnesium-silicate-hydrate (M-S-H). The cohesion between mortar and aggregate was reduced, and a large number of products were generated. Cl- inhibited the transmission rate of SO42- and reduced the erosion effect of SO42- on TWGPC. The single freezing-thawing life prediction model had high accuracy, and the life prediction conclusion based on reliability was consistent with the appearance damage analysis, mechanical property testing and microscopic morphology analysis.

High Temperature Degradation Mechanism of Concrete with Plastering Layer

At present, the research on the high temperature degradation of concrete usually focuses on only the degradation of concrete itself without considering the effect of the plastering layer. It is necessary to take into account the influence of the plastering layer on the high temperature degradation of concrete. With an increase in the water/cement ratio, the explosion of concrete disappeared. Although increasing the water/cement ratio can alleviate the cracking of concrete due to lower pressure, it leads to a decrease in the mechanical properties of concrete after heating. It is proved that besides the water/cement ratio, the apparent phenomena and mechanical properties of concrete at high temperature can be affected by the plastering layer. The plastering layer can relieve the high temperature cracking of concrete, and even inhibit the high temperature explosion of concrete with 0.30 water/cement ratio. By means of an XRD test, scanning electron microscope test and thermogravimetric analysis, it is found that the plastering layer can promote the rehydration of unhydrated cement particles of 0.30 water/cement ratio concrete at high temperature and then promote the mechanical properties of concrete at 400 °C. However, the plastering layer accelerated the thermal decomposition of C-S-H gel of concrete with a water/cement ratio of 0.40 at high temperature, and finally accelerate the decline of mechanical property of concrete. To conclude, the low water/cement ratio and plastering layer can delay the deterioration of concrete at high temperature.

Photocatalytic Degradation of 4,4′-Isopropylidenebis(2,6-Dibromophenol) on Sulfur-Doped Nano TiO2

In present work, we examine the photocatalytic properties of S-doped TiO2 (S1, S2) compared to bare TiO2 (S0) in present work. The photocatalytic tests were performed in alkaline aqueous solutions (pH = 10) of three differently substituted phenols (phenol (I), 4,4′-isopropylidenebisphenol (II), and 4,4′-isopropylidenebis(2,6-dibromophenol) (III)). The activity of the catalysts was evaluated by monitoring I, II, III degradation in the reaction mixture. The physicochemical properties (particle size, ζ-potential, Ebg, Eu, E0cb, E0vb, σo, KL) of the catalysts were established, and we demonstrated their influence on degradation reaction kinetics. Substrate degradation rates are consistent with first-order kinetics. The apparent conversion constants of the tested compounds (kapp) in all cases reveal the sulfur-loaded catalyst S2 to show the best photocatalytic activity (for compound I and II S1 and S2 are similarly effective). The different efficiency of photocatalytic degradation I, II and III can be explained by the interactions between the catalyst and the substrate solution. The presence of bromine substituents in the benzene ring additionally allows reduction reactions. The yield of bromide ion release in the degradation reaction III corresponds to the Langmuir constant. The mixed oxidation-reduction degradation mechanism results in higher degradation efficiency. In general, the presence of sulfur atoms in the catalyst network improves the degradation efficiency, but too much sulfur is not desired for the reduction pathway.