How to choose the raw material of polyurethane powder coating

2021-12-02   Pageview:227

Isocyanic polyurethane powder coating is made by mixing, melting, extruding and crushing with hydroxy polyester resin and closed isocyanate curing agent as the base material, plus catalyst, leveling agent and color filler. When the coating is baked, the isocyanate in a closed state is unsealed and released for curing.

 

 

 

 

 

 

 

 

 

 

 

 

Chromate, permanganate, vanadate, tungstate, and pincerate have good corrosion inhibition under certain conditions, but in a neutral medium, this type of corrosion inhibitor has a critical concentration. When the concentration is lower than this, not only will it not play a role in corrosion inhibition, but will cause local corrosion (such as pitting corrosion); only when the concentration of the corrosion inhibitor exceeds this critical value, the corrosion rate can be reduced and the concentration of the corrosion inhibitor will continue to be increased. The corrosion can be almost completely stopped. This kind of corrosion inhibitor is called “dangerous corrosion inhibitor” because of the existence of such a critical value. In actual use, the corrosion inhibition effect must be maintained at an appropriate concentration, with the exception of sodium benzoate. In addition, aggressive anions (such as chloride ions) can also affect the effectiveness of this type of corrosion inhibitor.

There are currently different opinions on the corrosion inhibition mechanism of nitrite, and there are mainly three opinions: one is that the formation of a protective film of Fez O on the surface of steel prevents the anodic dissolution of iron. The passivation film on the surface of iron is that the oxygen in the water oxidizes FeO to F egOs. The formed nitrite ions are adsorbed on the iron surface, reducing the free energy of the system and making passivation easier. The second is that nitrite ions are directly involved in the process of producing iron oxide. Third, it is believed that the nitrite ions adsorbed on the surface of the steel oxidize ptfe powder dispersion the divalent iron to the trivalent iron like a catalyst, without loss itself, and play a role in accelerating the formation of a dense passivation film on the steel.

The oxide film isolates the metal from the corrosive medium; ② inhibits the metal ionization process due to characteristic adsorption; ③ makes the metal electrode potential reach the passivation potential. This kind of corrosion inhibitor either directly inhibits the anode reaction in electrochemical corrosion, or at the same time increases the cathode effect, which increases the cathode current and causes metal passivation.

Cathode type corrosion inhibitor
The corrosion inhibition effect of cathodic corrosion inhibitors on metals in corrosive media is mainly to increase the cathodic polarization in electrochemical corrosion, hinder the progress of the cathodic process, move the corrosion potential in the negative direction, and reduce the corrosion rate.

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