An Improved Thermodynamic Model for Phosphorus Smoke

摘要

Orthophosphoric acid is commonly employed to represent the solution thermodynamics of phosphorus smoke droplets. However, transmission measurements in the 8- to 12-micrometer region demonstrate significant disparities between phosphorus smoke and comparable orthophosphoric acid mists. Since the transmission characteristics in the 8- to 12-micrometer region are primarily due to absorption by specific molecular species, it may be concluded the acid species of a phosphorus smoke is not solely orthophosphoric acid. It is the intent of this study to delineate the expected range of error resulting from the use of an orthophosphoric acid thermodynamic model for the prediction of the physicochemical properties of a phosphorus smoke under tactical conditions. Results show the orthophosphoric acid model underestimates phosphorus smoke acid fractions by as much as 25% for relative humidities less than 90%. The water activity of an arbitrary mixture of condensed phosphoric acids is derived from the orthophosphoric acid water activity model through a solute number reduction scheme. Asserting the acid mixture is 75% pyrophosphoric acid and 25% orthophosphoric acid, phosphorus smoke data are accurately predicted by mixture model calculations.