Adsorption Characteristics of SF6 and its Main Over-Thermal Decomposition Components on Ag (1 1 1) Surface

Poor contact is one of the main causes of the internal fault of SF₆ gas insulated equipment. Taking the most common over-thermal decomposition process of SF₆ caused by poor silver-plated copper contacts as an example, this article combines with density functional theory (DFT) and establishes the gas–solid contact interface adsorption model of SF₆ and its main decomposition characteristic products (SO₂F₂, SO₂, SOF₂, HF, and H₂S) with solid silver. Adsorption energy, charge transfer, and density of electronic state were used to analyze the reaction activity of SF₆ and its main decomposition products with the Ag surface. It is found that SF₆ and SO₂ are chemically adsorbed on the Ag surface, and the reaction activity is relatively strong. When chemical adsorption occurs, SF₆ bonds with the metal surface by the 2p orbitals of F atoms, and SO₂ is bonded to the metal surface by the 2p orbitals of O atoms. There is also a strong reaction trend between HF and Ag (1 1 1), while SO₂F₂, SOF₂, and H₂S only physically absorbed with the Ag (1 1 1) surface. This indicates that under the local overheating failure caused by metal contacts, SF₆ will first undergo chemical adsorption in the SF₆/Ag (1 1 1) system and then undergo a decomposition reaction near the metal surface rather than in free space. The participation of Ag reduces the difficulty of the decomposition reaction to some extent. The results lay a foundation for finally revealing the interfacial reaction process of SF₆-Ag.