AbstractThe apparent activation energy for the following reactions has been determined by measuring the amount of carbon removed from samples of powder heated to various temperatures in an atmosphere of either dry or wet hydrogen:Dry Hydrogen“As-carburized”tungsten carbide: no reaction up to 900°C.Water–milled tungsten carbide: 8·38 kcal/mole over the range 600–900°C.Water–milled tungsten carbide+ 6% cobalt: complex reaction over the range 600–900°C.Wet Hydrogen“As-carburized”tungsten carbide: 58·1 kcal/mole over the range 800–900°C.Water–milled tungsten carbide: 34·8 kcal/mole over the range 700–900°C.Water–milled tungsten carbide+ 6% cobalt: 38·4 kcal/mole over the range 825–900°C; 7·38 kcal/mole over the range 600–800°C.It has been shown that ball-milling in water changes both the physical and chemical properties of tungsten carbide powder. These changes are discussed in relation to the marked differences in reaction rates. A number of possible reasons for these differences are given.