| 
         Trade mark  | 
      
         Added impurity  | 
      
         Impurity quantity %  | 
      
         Other impurity  | 
      
         Electric discharged power  | 
      
         Color sign  | 
    
| 
         WC20  | 
      
         CeO2  | 
      
         1.8~2.2%  | 
      
         <0.2%  | 
      
         2.7~2.8  | 
      
         grey  |