Insights on decomposition process of c-C4F8 and c-C4F8/N2 mixture as substitutes for SF6

Topotactic fluorination of intermetallics as an efficient route towards quantum materials

Intermetallics represent an important family of compounds, in which insertion of light elements (H, B, C, N) has been widely explored for decades to synthesize novel phases and promote functional materials such as permanent magnets or magnetocalorics. Fluorine insertion, however, has remained elusive so far since the strong reactivity of this atypical element, the most electronegative one, tends to produce the chemical decomposition of these systems. Here, we introduce a topochemical method to intercalate fluorine atoms into intermetallics, using perfluorocarbon reactant with covalent C-F bonds. We demonstrate the potential of this approach with the synthesis of non-stoichiometric mixed anion (Si-F) LaFeSiF_x single-crystals, which are further shown to host FeSi-based superconductivity. Fluorine topochemistry on intermetallics is thus proven to be an effective route to provide functional materials where the coexistence of ionic and metallo-covalent blocks, and their interactions through inductive effects, is at the root of their functional properties.

Insertion of light elements in intermetallics has been explored to synthesize functional materials. Here the authors report topotactic intercalation of fluorine atoms into intermetallics using a perfluorocarbon reactant with covalent C-F bonds to obtain quantum materials.

Application of plasma catalysis system for C4F8 removal

Octafluorocyclobutane (C₄F₈) with a GWP₁₀₀ (global warming potential) of 10,000 times of CO₂ is listed as potent greenhouse gas. Therefore, development of effective control technologies for reducing C₄F₈ emissions has become an emerging issue to be addressed. In this study, decomposition of C₄F₈ was investigated via three systems including catalytic hydrolysis, non-thermal plasma, and plasma catalysis, respectively. Decomposition of C₄F₈ achieved with catalytic hydrolysis reaches the highest efficiency of 20.1%, being obtained with γ-Al₂O₃ as catalyst in the presence of 10% H₂O_(g) and operating temperature of 800 °C. For plasma-based system, the highest C₄F₈ conversion obtained with non-thermal plasma is 62% at a voltage of 23 kV. As for the plasma catalysis system, 100% C₄F₈ conversion efficiency can be achieved at an applied voltage of 22-23 kV. The effects of various parameters such as gas flow rate and C₄F₈ concentration on plasma-based system show that the plasma catalysis also has better resistivity for the high gas flow rate. The highest energy efficiency of 0.75 g/kWh is obtained for the gas flow rate of 500 mL/min, with the C₄F₈ conversion of 41%. The highest conversion 89% was achieved with the O₂ content of 0.5%. Addition of Ar improves the performance of plasma-based system. When Ar is controlled at 20%, C₄F₈ conversions obtained with plasma catalysis reach 100% at applied voltage of 22-23 kV even in the presence of 5% O₂. The main products of the C₄F₈ conversion include CO₂, NO_x, and COF₂ when O₂ is added into the system. As water vapor is added, HF is also formed. This study has confirmed that combined non-thermal plasma with catalyst system to convert C₄F₈ is indeed feasible and has good potential for further development.

Alternative Environmentally Friendly Insulating Gases for SF6

Sulfur hexafluoride (SF6) shows excellent insulation performance as an insulating gas. It is suitable for various climate conditions due to its low boiling point (−64 °C). Therefore, it has been widely used in power grid equipment. However, its global warming potential (GWP) is 23,500 times higher than that of CO2. Thus, it is imperative to find an environmentally friendly insulating gas with excellent insulation performance, lower GWP, and which is harmless to equipment and workers to replace SF6. In this review, four possible alternatives, including perfluorocarbons, trifluoroiodomethane, perfluorinated ketones, and fluoronitrile are reviewed in terms of basic physicochemical properties, insulation properties, decomposition properties, and compatibility with metals. The influences of trace H2O or O2 on their insulation performances are also discussed. The insulation strengths of these insulating gases were comparable to or higher than that of SF6. The GWPs of these insulating gases were lower than that of SF6. Due to their relatively high boiling point, they should be used as a mixture with buffering gases with low boiling points. Based on these four characteristics, perfluorinated ketones (C5F10O and C6F12O) and fluoronitrile (C4F7N) could partially substitute SF6 in some electrical equipment. Finally, some future needs and perspectives of environmentally friendly insulating gases are addressed for further studies.