A high-quality conversion coating is essential for the durability of painted metal goods. The process of applying an inorganic conversion coating to a metallic surface involves removing any surface contaminants, then chemically converting the clean surface into a non-conductive, inorganic conversion coating. Conversion coatings increase the overall surface area and promote adhesion of the subsequently applied organic film. In addition, conversion coatings change the chemical nature of the surface, which increases corrosion resistance. It is these two functions, increasing surface area and changing the surface chemistry, that serve as a base for preparing the substrate material for paint finishes.
There are a number of driving forces in the pretreatment industry today with quality, cost and the environment being the most predominant. While these aren’t new issues, the pretreatment industry has responded to the needs of finishers by creating technology to address each of these requirements. In understanding the complete manufacturing process, including paint formulations, application equipment and regulatory impacts, it’s possible to address each driver simultaneously.
The conversion coating chemistries predominately used today are either zinc or iron phosphate. There is movement to replace these technologies with new types of phosphate-free or very-low-phosphate metal pretreatments. The new-generation technologies have been commercialized by many vendors over the past several years and are rapidly becoming industry standards. Regardless of the chemistry, conversion coatings are used to promote adhesion and improve corrosion resistance. Depending on the conversion coating and the desired performance, the conversion coating can be applied at a number of points in the process.
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The hybridized matrix membrane developed in the study presents a unique design strategy for highly hydrophobic coatings showing great long-term corrosion resistance.
Addressing the Corrosion Problem of Magnesium Alloy
Thanks to their low weight, high specific strength, and recyclability, magnesium (Mg) alloys are employed across many industries, including the automotive and aeronautical sectors and electronic equipment.
Despite this, magnesium alloys can easily suffer from corrosion in aqueous conditions because of their strong chemical activity, restricting their widespread applicability.
Multifarious techniques, including electrodeposition, ionic implants, and surface coatings, have been used to improve the corrosion resistance of magnesium alloys.
Surface coatings, particularly organic surface coatings, offer great corrosion resistance with the advantages of being facile and inexpensive.
PDMS Coatings for Better Corrosion Resistance
Compared to traditional organic coatings, PDMS is a unique polymeric material having low surface energy, high chain flexibility, superior thermal oxidation resistance, and chemical corrosion resistance thanks to the robust silicon-oxygen-silicon backbones.
PDMS is extensively used in flexible electronic devices and microfluidics. Moreover, due to its strong water-repellent nature, PDMS is a preferred material for corrosion resistant coatings.
While PDMS polymer coatings exhibit strong corrosion resistance and barrier function, their protective powers become weaker when they absorb water after extended contact with a corrosive medium.
Meanwhile, doping or hybridization can lead to the formation of microcracks and microspores in organic coatings, which ultimately causes poor corrosion resistance durability.