Metal alkoxide crosslinking agentMany metal alkoxides can act as crosslinking agents during hydrolysis and condensation processes. For example, tetrabutyl titanate, tetrabutyl zirconate and other metal alkoxides will first undergo hydrolysis reaction under the preparation conditions of the sol gel method to generate corresponding metal hydroxyl compounds, which will further undergo polycondensation reaction to form a gel with three-dimensional network structure to play the role of cross-linking. The reaction process is roughly as follows:
Hydrolysis reaction (taking tetrabutyl titanate as an example):
Condensation reaction:
Through such hydrolysis and polycondensation, metal alkoxides build a cross-linking network, which makes the gel and subsequent coatings more stable, and can give the coatings good performance such as high temperature resistance and chemical corrosion resistance.
Organic multifunctional compounds
Polyols: Polyols such as propylene glycol and pentaerythritol contain multiple hydroxyl functional groups in their molecules. In the sol gel system, these hydroxyl groups can be condensed with the hydroxyl groups generated by the hydrolysis of metal alkoxides or other hydroxyl containing substances, thus connecting different gel segments to form a cross-linked structure. For example, the hydroxyl group of glycerol can be condensed with the hydroxyl group of ethyl silicate after hydrolysis to form a more complex network, enhance the stability of gel, improve the flexibility of the coating and other properties.
Polyamines: such as ethylenediamine, diethylenetriamine and other polyamine compounds, whose amino groups have high reactivity and can react chemically with reactive groups (such as epoxy groups, carboxyl groups, etc.) contained in the sol system to achieve cross-linking. For example, in the organic modified sol system containing epoxy group, the amino groups of polyamine compounds can undergo ring opening addition reaction with epoxy group, "bind" different gel segments together, improve the cross-linking density of gel network, and improve the strength and toughness of the coating.
Inorganic acids or inorganic acid salts
Inorganic acids (such as nitric acid, hydrochloric acid, etc.): In the sol gel method, an appropriate amount of inorganic acids can be used as a catalyst to promote the hydrolysis of metal alkoxides and other precursors. At the same time, acid radical ions can also participate in the formation of the gel network, playing a certain role in cross-linking. For example, in the preparation of silica gel coating, the presence of hydrochloric acid not only accelerates the hydrolysis of ethyl silicate, but its chloride ion may also participate in the construction of gel network through certain coordination and other interaction modes with the silicon hydroxyl generated by hydrolysis, so as to improve the cross-linking structure of gel and improve the compactness of the coating.
Inorganic acid salts (such as sodium aluminate, sodium silicate, etc.): they can provide additional metal ions and acid radical ions in the sol gel system. These ions can interact with the original hydrolysates in the system to form new chemical bonds, and then participate in cross-linking. For example, aluminum ions in sodium aluminate can polymerize with hydroxyl compounds generated by hydrolysis of other metal alkoxides, integrate into the gel network, enhance the cross-linking degree of gel, and improve the thermal stability and mechanical properties of the coating.
Organic polymer
Organic polymers with reactive functional groups can also be used for crosslinking. For example, acrylic resins containing carboxyl groups and epoxy resins containing epoxy groups can undergo chemical reactions with corresponding active groups (such as amino groups, hydroxyl groups, etc.) in the sol system to achieve cross-linking. When epoxy resin is introduced into the sol gel system, its epoxy group can react with the hydroxyl group generated by the hydrolysis of metal alkoxides or the amino group of the added polyamine crosslinker, combine the chain segments of organic polymers with the inorganic gel network, create a cross-linking structure with both inorganic and organic characteristics, and improve the comprehensive performance of the coating, such as adhesion, wear resistance, etc.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150K. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.