phonetic alphabet. A list of standard words used for each letter in the alphabet. The use of a standard phonetic alphabet assures that the letters are not misunderstood during radio transmission. See International phonetic alphabet.
phosgene gas. A highly toxic, colorless gas, with an unpleasant odor. Phosgene is formed when certain halogen compounds, such as Freon or carbon tetrachloride, are passed through a flame.
phosphate-ester hydraulic fluid. A synthetic hydraulic fluid used in many high-performance aircraft hydraulic systems. Phosphate-ester hydraulic fluid is fire-resistant and is used in place of petroleum-base hydraulic fluid. It is identified by the military specifications number MIL-H-8446.
phosphate film (corrosion protection). A dense, airtight film formed on the surface of aluminum or magnesium alloy to prevent oxygen or electrolyte reaching the surface and causing oxidation or corrosion.
phosphorescent paint. Paint that absorbs energy from natural or ultraviolet light and radiates visible light. Phosphorescent paint continues to glow for some time after the excitation is removed, and for this reason it is used on dials and hands of clocks, watches, and aircraft instruments so they can be seen in the dark. Phosphorescent paint has replaced radium paint for instrument marking because of the poisonous nature of radium.
phosphorus. A highly reactive, poisonous, nonmetallic chemical element. The symbol for phosphorus is P, its atomic number is 15, and its atomic weight is 30.98. Phosphorus is used in the manufacture of matches, explosives, and fertilizer.