“…To determine the compounds of deposits, XRD analysis was adopted and the results are shown in Figures – . We can see that the major compounds in the outer layer of deposits were ammonium fluoroborate (NH 4 BF 4 , 2θ = 23.087°, 24.451°, 25.096°, 27.974°, 31.485°, 35.314°, 35.823°, 37.320°, 39.408°, 40.388°, and 41.676°), ammonium fluoride (NH 4 F, 2θ = 26.265°, 32.542°, and 64.059°), ammonium fluorosilicate [(NH 4 ) 2 SiF 6 , 2θ = 30.074°, 37.067°, 43.070°, and 53.611], and boric acid (H 3 BO 3 , 2θ = 30.781°), which are white or transparent crystals at steady room temperature. − In addition, the outer layer contained some silicon dioxide (SiO 2 , 2θ = 27.031° and 50.470°), aluminum silicate (Al 2 SiO 5 , 2θ = 38.601° and 50.060°), and aluminum oxide (Al 2 O 3 , 2θ = 46.720° and 56.970°), which are components of coal ash . The major compounds in the inner layer of deposits were ferric oxide (F 2 O 3 , 2θ = 20.692°, 31.890°, 33.151°, and 68.218°), ferrous sulfate (FeSO 4 , 2θ = 21.090°, 41.308°, and 49.695°), ferric oxyhydroxide (FeOOH, 2θ = 26.875°, 39.308°, and 39.963°), ferric chloride (FeCl 3 , 2θ = 35.534° and 46.281°), ferrous fluoride (FeF 2 , 2θ = 38.341° and 55.542°), and ferrous chloride (FeCl 2 , 2θ = 50.658° and 53.172°), which are ferrous products of dew point corrosion .…”