… (NF 3 ). HFCs are mainly used in closed systems (e.g. as refrigerants), in open systems (e.g. as propellants), and as process gas e.g. for semiconductor … (NF 3 ). HFCs are mainly used in closed systems (e.g. as refrigerants), in open systems (e.g. as propellants), and as process gas e.g. for semiconductor …