During a routine detailed visual inspection of a MEMU, a “purple” compound was seen between the balls of the vertical auger bearing. After identification, the compound was confirmed to be TACN (Tetraamine Copper Nitrate).
The formation of this compound was mainly due to the presence of ammonium nitrate in the bearing after cleaning the vertical auger with water. The dissolved ammonium nitrate reacted with the copper of the separator (made of bronze) causing the generation of the explosive compound TACN inside the bearing.