Pure Magnéli Ti 4 O 7 nanotube arrays (NTA) were successfully fabricated by reducing TiO 2 NTA with hydrogen at 850 °C for 30 minutes. The microstructure, composition and electrochemical behavior of the prepared Ti 4 O 7 NTA were characterized by means of X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy , X-ray Photoelectron Spectroscopy, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy . The as-prepared Ti 4 O 7 NTA had a highly-ordered tubular structure with high crystallinity , large electrochemical window of water electrolysis (2.4 V vs. Ag/AgCl, pH = 6.0) and low interfacial charge transfer resistance when they were employed as anode for electro-oxidation. Phenol was electro-oxidized on Ti 4 O 7 particles and Ti 4 O 7 NTA with the latter giving 20% more Chemical Oxygen Demand (COD) removal. Pure Ti 4 O 7 NTA also displayed larger degradation coefficient as well as higher COD removal and current efficiency than Boron-doped Diamond and other types of Magnéli NTAs. Cathodic polarization was found to be an effective way of restoring the electrochemical performance of oxidized Ti 4 O 7 NTA as an anode.
Magnéli phases are an important class of transition metal oxides widely utilized in fields such as batteries, electrocatalysis , and photocatalysis . However, there are no reports on the use of Magnéli phases as additives in ceramic sintering. In order to explore the impact of the Magnéli phase as an additive on the sintering process, self-made Magnéli phase Ti 4 O 7 powder was added to the graded mixture of titanium dioxide (TiO 2 ) coarse powder and nanopowder , and sintered under atmospheric conditions in this study. The sintering characteristics, microstructure, and mechanical properties of TiO 2 ceramics with different content of Ti 4 O 7 were characterized. The results revealed that the addition of Ti 4 O 7 contributed to the reduction of the densification temperature of TiO 2 ceramics. Compared to the undoped sample, the addition of 1 wt% Ti 4 O 7 powder significantly improved the flexural strength and Vickers hardness of TiO 2 ceramics by 13.5% and 24.8%. According to the results of thermal analysis, UV–Vis–NIR, and XPS, the mechanism of Ti 4 O 7 in the sintering process of TiO 2 ceramics under atmospheric conditions was systematically discussed. This work not only obtained TiO 2 ceramics with improved performance but also showed the tremendous potential of Magnéli phases in the field of ceramic sintering.
Magnéli phase ceramics have gained extensive attention in a variety of fields, including batteries, electrocatalysis , and wastewater treatment, due to their distinctive properties. In this study, high-performance Magnéli phase Ti 4 O 7 ceramics were synthesized by in-situ hot-pressed sintering of titanium (Ti) and titanium dioxide (TiO 2 ) in a single step. The effects of the sintering temperature and Ti content on the phase transformation and morphology of ceramics were investigated. Moreover, the mechanical properties and electrical conductivity of the samples were systematically characterized. Results show that the sample with the Ti/TiO 2 weight ratio of 0.09 sintered at 1000 °C has impressive comprehensive properties, including a high bulk density of 4.281 g·cm −1 , a mean value of flexural strength of 125.58 MPa, and an excellent conductivity of 1129 S·cm −1 . Furthermore, an evolution mechanism of the in-situ sintering for Ti/TiO 2 was discussed based on the experimental data, and the pattern of variation observed by samples can be reasonably explained.
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