The process of metal surface state change makes it have the characteristics of low corrosion rate of precious metals and high positive electrode potential. Metal passivation caused by spontaneous chemical interaction between metal and surrounding medium is called chemical passivation or self-passivation. General strong oxidants (concentrated nitric acid, potassium permanganate, K2Cr2O7, HClO3, etc.). ) can passivate the metal. Passivated metals have lost some of their original properties. If the metal is passivated by electrochemical anodic polarization, it is called anodic passivation. For example, Fe is immersed in H2SO4 solution as anode, calomel electrode as cathode, and connected with an external power supply to form an electrolytic cell. The potential (j) of the anode electrode changes continuously, and the results obtained by observing the changes of current (i) and j are shown in the figure. Curve AB indicates that the metal dissolves according to the normal anode law, which is called the activation zone. In the CD segment, the value of I is very small and has nothing to do with J, which is called passivation region. At this time, a corrosion-resistant protective film is formed on the metal surface in a passive state. The DE part is an over-activated area, and some new anodic reactions may be under way. Keeping the anode electrode potential within the range of CD can prevent metal corrosion. The main theories of metal passivation are: ① adsorption theory. It is considered that the surface adsorption layer of oxygen or oxygen-containing ions is formed on the metal surface. ② Film-forming theory. It is considered that a dense oxide film with good coverage is formed on the metal surface, and its thickness is about10-10 ~10-9 meters. The adsorption layer or oxide film separates the metal from the solution, which reduces the corrosion rate of the metal and passivates the metal.

The sandblasting process is to locally sandblast the surface of metal jewelry according to the design requirements, so that the polished surface of metal jewelry is in sharp contrast and the artistic beauty of jewelry lines is enhanced. There are two kinds of blasting techniques: one is dry sand and the other is water sand.

First, the main tools needed for sandblasting

① sandblasting machine;

② air compressor;

③ emery (quartz sand);

④ Protective tape or wax

Second, the operation steps

1. Seal the parts of polished jewelry that don't need sandblasting with protective wax or protective tape for protection. When sticking protective tape or wax, the lines should be smooth and tidy.

2, according to the requirements, choose the appropriate thickness of emery, put it into the sandblasting machine. Then debug the required air pressure.

3. Hold the broken jewelry pieces, put the parts that need sandblasting into the sandblasting machine, aim at the sand outlet of the sandblasting machine, open the pneumatic valve, and spray emery on the metal jewelry pieces by air pressure until it meets the requirements. The sandblasting position should be complete and uniform to achieve the effect.

Just compare yourself.