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SEM-EDX of an ASTM Level 3 face mask and a carbon veil (CV) sheet: (a) schematic of an ASTM Level 3 face mask with an electrically heatable CV layer; (b) CV layer; (c) top layer of the ASTM Level 3 face mask; (d) middle layer of the ASTM Level 3 face mask; (e) bottom layer of the ASTM Level 3 face mask; and (f) EDX analysis data of a CV layer.
