Catalysts – Homogeneous Catalysts

Homogeneous catalysts and the reactants they catalyze are in the same state of matter (solid, liquid, or gaseous). For example, if the reactant is a gas, then the catalyst will also be a gas. Laughing gas (dinitrogen tetroxide) is an inert gas and is used as an anesthetic. However, when it reacts with chlorine and sunlight, it decomposes into nitrogen and oxygen. At this point, chlorine is a homogeneous catalyst that breaks down the otherwise stable laughing gas into its constituent elements.

In addition, the same silicone defoamer product is used in the coating system, because of the different compatibility with different paint bases, the tendency of shrinkage caused is also different. If several paint bases are used in combination, it can sometimes be improved. For example, the combination of alkyd modified polyester/melamine coatings can eliminate the drawbacks of shrinkage caused by silicone defoamers.

Phenyl-modified silicone oil as a defoaming agent can avoid some drawbacks such as shrinkage, but its defoaming ability is greatly reduced. Polyether-modified silicone oil is the main component of self-emulsifying defoamers and is easy to emulsify in water. When polyether modified silicone oil is used above its cloud point temperature, it loses its solubility in water and shows defoaming properties; if it is used below the cloud point temperature, wax emulsion ceramics its solubility in the system increases, and its defoaming effect will be lost. The defoamer formulated with polyether modified silicone oil has good heat resistance and mechanical stability, and it does not produce the negative effects of shrinkage and recoatability caused by methyl silicone oil as a defoamer.

Silicone oils containing carbon functional groups (such as carboxyl groups, amido groups, amino groups, epoxy groups, etc.) are all reactive silicone oils. It can chemically react with the coating resin, can cure the resin, form a network with the resin, and improve the strength of the paint base; it can also wet the filler, increase the compatibility of the filler and the resin, and improve the leveling of the coating. Some of these silicone oils have some special functions. For example, silicone oils containing organotin groups (-SnR a) have anti-fouling properties such as sterilization and killing marine organisms. Therefore, these silicone oils are used in coatings in China. More and more attention has been paid to foreigners.