The sub-group element, which is the same family as chromium, is a silver-white metal, hard and tough, so it is commonly used as a wear-resistant, corrosion-resistant, heat-resistant layer. The chemical properties of molybdenum are not chrome-active, are not corroded by air at normal temperatures, and do not interact with acids or bases. At present, there is no electroplating molybdenum process in the production process, and the characteristics of molybdenum (such as wear resistance) are only based on the chemical properties of molybdenum, and the molybdenum is melted under high temperature and high pressure with special equipment, and then sprayed. Apply a layer of molybdenum to the surface of the workpiece.
The chemical and physical properties of molybdenum exclude the use of chemical methods to remove molybdenum, so only the breakthrough is sought from electrochemical methods. The determination of the molybdenum working solution was determined by theoretical analysis to determine the use of electrochemical method to remove molybdenum. Thereby causing corrosion to the base of the gear. According to the theoretical electrode potential value, metal molybdenum and copper and chromium belong to the same non-active metal. For the iron matrix, copper, chromium and molybdenum belong to the cathodic protective layer. According to the theory, the removal of the molybdenum layer can refer to the method of removing copper and chrome plating. Therefore, the molybdenum layer removal process was tested by the copper plating removal process. As an oxidizing agent of metal molybdenum, it has an oxidation effect on the molybdenum layer Discharging on the anode facilitates the dissolution and stripping of the plating metal, thereby achieving the purpose of removing the molybdenum layer, and, in the stripping solution, acts as a conductive salt, which can effectively improve the conductivity of the molybdenum-removing electrolyte.
Sodium nitrite has a dual role in the electrochemical anti-molybdenum solution. First, as an anodic corrosion inhibitor, after removing the molybdenum layer of the molybdenum-removing gear, the base metal of the protection gear is not corroded; on the other hand, it can be used as a conductive The salt effectively increases the conductivity of the molybdenum solution. The complexing agent forms a complex with the molybdenum ion formed by electrochemical dissolution of the anode in the solution, effectively maintaining the stability of the electrochemical molybdenum solution, ensuring the smooth progress of the molybdenum retreating, and the complexing agent also helps to maintain the gear The smoothness of the base metal. When the molybdenum layer is removed by this process, the above can be retired, and when molybdenum is removed, a large amount of gas escapes from the anode, which greatly promotes the electrolytic stripping of the molybdenum layer on the anode, but at the same time The anode escaped. Therefore, this formulation is not suitable for the removal of the molybdenum layer. The function of the complexing agent is basically the same as that of the process recipe. Discharge and release oxygen on the anode. Oxygen acts to strip the metal molybdenum without causing other contamination, and the final product is oxygen and water. A dense protective film is formed on the iron matrix to prevent iron from participating in the reaction. After the process is completed, the process can be completed and the effect of molybdenum removal is good. The study of the developer shows that when the molybdenum-dispensing transmission gear is removed from the molybdenum layer in the molybdenum-removing liquid, it is impossible to judge whether the molybdenum layer is completely removed or not, and only by extending the time. When the molybdenum layer is removed, the gear must be taken out of the tank and examined by copper sulfate titration.
Using this method to test fast and agile is a traditional multi-purpose method, but the method has the following shortcomings: if the molybdenum layer is intact, no voids, no copper spots will appear; but if the molybdenum layer itself has voids or molybdenum If the layer is not partially removed, the displayed result is inaccurate; "The dead angle and corner portion cannot be inspected; the method is troublesome to operate, and the gear is taken out at regular intervals, washed, dried, and inspected. If it is not qualified, re-hang it. With the re-entry slot to continue to retreat molybdenum, so repeated until the inspection is qualified. Based on the above reasons, it is desirable to find a fast, accurate and convenient method. When the gear is taken out from the trough, it can be judged at a glance without cleaning or drying. Whether there is a molybdenum layer. It is necessary to add a compound to the molybdenum solution as a color developer. If a molybdenum layer is present, it can show different colors, which are different from the color of the iron matrix and the color of the molybdenum layer. Differently, it can be seen from the theoretical analysis that the activity of metal molybdenum is not strong, so it must be made to react with other compounds. Very strong oxidizing. Many strong oxidants such as potassium permanganate, potassium dichromate (sodium) and perchlorate have been tested in the molybdenum solution. It is hoped that a strong oxidant will react with metal molybdenum to produce a redox reaction. A layer oxide film is used to achieve the purpose of exhibiting the presence of a molybdenum layer.
Through data query and theoretical discussion, it is believed that in an alkaline solution, and under the action of electrochemical reaction, the oxidant can undergo redox reaction with metal molybdenum to form black molybdenum oxide, thereby achieving the purpose of color development. Therefore, an oxidizing agent was added to the molybdenum-removing solution, and when the molybdenum was removed to half, the gear was taken out from the tank to observe, and it was observed that there was a very strong black film in the place where the molybdenum was sprayed, and the black film and the iron matrix and the molybdenum layer were observed. The appearance is significantly different. Re-set the gear into the molybdenum solution and continue to remove the molybdenum. After the gear is taken out from the solution, the molybdenum layer is removed. The appearance of the iron matrix after sandblasting is revealed, and there is no retreat. The black color of the oxide film is still present. This shows the superiority of the oxidant.
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