... . 2. 1. Bring about yellowing problem: 4. How to use TR-121 correctly metal impurity. dragged in for treatment uncompleted zinc ... nitric acid, especially for Hint: practice operation. condense solution of TR-121,about 12000-14000dm2/l, the customer can adjust additive ... ) ? water zinc plating ? nine ? immersed HNO3(0.5%) ? nine ? immersed TR-121 ? cold water 2. Process flow: F. According with American ...