Hydrolysis of Organosilane Coupling Agents in Protective Coatings for Metal Surface Treatment Industry

Silane coupling agents are directly coated on metal surfaces to form chemical bonding structures with the metal substrate, thereby changing the properties of the metal surface. This has remarkable and unique advantages over other organic coating surface treatment technologies for metal surface corrosion prevention; At the same time, due to its characteristics of no pollution, good corrosion resistance of treated parts, and strong bonding with coatings, if it can be industrialized, it is expected to replace phosphating and passivation treatment on metal surfaces.

The mechanism of action of organosilane coupling agents as a new type of coating on metal surfaces is that they first undergo hydrolysis reaction to generate silanol. The silanol hydroxyl groups form hydrogen bonds on the inorganic surface, and further undergo dehydration reaction to form Si-O-M (M is the inorganic surface) covalent bonds, and form a coating on the inorganic surface.

At the same time, the hydrolysis product of silane, silanol molecules, can also condense and aggregate with each other to form a network structure film covering the surface of the substrate. This film has the characteristic of resisting corrosion from external acids, alkalis, salts, etc. The hydrolysis process of coupling agents is a prerequisite for the realization of the above process, which plays an important role in the synthesis of chemical bonds between silane and inorganic substrates. Different organic silicon coupling agents have different hydrolysis rates, and the selection of system solvents and pH is important.

Due to the low conductivity of the reactants organosilicon and water, while the conductivity of the products silanol and alcohol is high, even if ethanol is used as the solvent, the conductivity of the system remains unchanged before and after the reaction. Therefore, the conductivity of the silane system gradually increases during hydrolysis, and after a certain period of time, the reaction reaches equilibrium, and the corresponding conductivity value stabilizes at a certain value. This indicates that hydrolysis has reached equilibrium, and the amount of silanol is the maximum amount under this hydrolysis condition.

Directly using silane coating to solve the protection of iron-based surfaces, the hydrolysis status of silane and the amount of silanol generated have a significant impact on the final film-forming effect of the process.