Reactivity passivation of red phosphorus with thin plasma-deposited carbon coating

[Display omitted] •Plasma-deposited carbon coating provides thin, non-reactive surface on red phosphorus.•Carbon coating suppresses toxic byproducts from red phosphorus break down by H2O and O2.•XPS and IR data elucidate mechanism of PH3 and POx production by carbon coating.•Carbon coating provides stability of red phosphorus in humid, ambient environments. Red phosphorus, when exposed to humid environments in air, breaks down into toxic phosphine gas and acidic phosphorus species, presenting a challenge for many applications, such as flame retardants or pyrotechnic obscurants. We have developed and characterized a method of plasma-deposited carbon to form a nanometer-thick, chemically stable carbon layer on red phosphorus particles to suppress phosphine and acidic phosphorus production. Using a combination of XPS surface analysis and a novel IR headspace analysis method, we developed and quantified an understanding of the reaction of red phosphorus with water vapor and the suppression of decomposition products using plasma-deposited carbon coatings. Phosphine production, quantified by IR, was accompanied by the formation of surface POx species produced as the particles react with water vapor. Increasing plasma deposition time increased thickness and uniformity of graphitic carbon coating, corresponding to a marked decrease in phosphine generation and formation of surface POx species.