What role does phosphorus play in copper anodes

The results show that the anodic dissolution of copper in sulfuric acid is a step reaction. Copper first loses an electron to form copper e+, which is a fast reaction, and then loses an electron to form copper, which is a slow step. It can be seen that univalent copper ions are inevitably formed in the process of copper dissolution at the anode. This has been confirmed by experiments with rotating ring - disk electrodes. The monovalent copper in solution is very unstable and can be decomposed into metallic copper and divalent copper ions by disproportionation reaction.

Since the space of the double zone near the electrode is very small, the concentration of the monovalent copper in the double zone space will be quite large. Under such conditions, the disproportionation reaction of copper ions will be very easy to carry out. Therefore, univalent copper generated in the process of copper anode dissolution is the main source of copper powder.

With the increase of temperature, the copper powder generation rate increases, that is, the percentage of the copper powder generated in the dissolved copper volume increases. The dissolution current of copper electrode is much larger than that of pure copper. In a certain phosphorus range, the higher the phosphorus content in copper, the better the dissolution performance of anode.

Why does anodic dissolution occur uniformly on the crystal plane? After adding phosphorus to pure copper, thermodynamically stable polycrystalline structure is formed, with small grain boundaries and low energy. Moreover, phosphorus preferentially accumulates at grain boundaries. Surface tension measurements show that phosphorus is a surface active element for copper in the melt, which reduces the surface tension of the melt. As the energy of grain boundaries decreases, selective grain boundary dissolution is difficult to occur. So the anodic dissolution occurs uniformly on the crystal plane. Right?

The increase of copper oxide will improve the increase of copper mud grain boundary more soluble than other parts of the crystal. If there is Cu20 impurity in the middle of the crystal, the preferential dissolution will be faster and more grains will be peeled off from the metal body. At the same time, Cu20 is dissolved in sulfuric acid, which increases the monovalent copper in the solution. Therefore, the presence of Cu20 in the anode will aggravate the formation of anode mud, and the elimination of copper powder depends on the removal of Cu20 in copper.