The disclosed technology relates to methods of inhibiting corrosion in reaction chambers configured for hydrothermal reaction of feeds containing a heteroatom. An embodiment of such a method comprises providing a feed stream comprising a phosphorus-containing material, an alkali metal compound, water, and a corrosion-inhibitor. The embodiment additionally includes introducing the feed stream and oxidant into a reactor chamber and oxidizing the phosphorus-containing material at an oxidation temperature greater than about 374° C. and an oxidation pressure exceeding about 25 bar, wherein the reactor chamber has inner surfaces comprising a material that corrodes when in contact with a phosphorus compound within the reactor. The embodiment additionally includes selectively reacting the corrosion-inhibitor with phosphorus within the reactor, thereby precipitating in the reactor chamber a phosphorus-containing solid inorganic compound. The embodiment further includes forming in the reactor chamber an alkali salt melt and carrying away from the reactor chamber a mixture comprising the solid phosphorus-containing inorganic compound and the alkali salt melt.