This technical information has been contributed by
DCHN
Click here to find suppliers

Corrosion-Resistant Coating Technology Enhances Applications in Medical and Beyond

Rebecca Carnes
Design-2-Part Magazine

Medical customers came to DCHN with a problem. Their aluminum products for instruments, trays, and devices were being degraded by the pre-cleaners used for sterilization, leading to corrosion. This is a dangerous side effect in the medical industry where instruments need to be absolutely clean to help prevent the spread of disease.

Aluminum is a highly desired material in medical and other industries because it's less expensive, easier to machine, and lighter than other metals. But aluminum products with conventional coating processes were being attacked and degraded by higher pH pre-cleaners, resulting in an attack on the dyes and corrosion of the substrate metal. Medical customers were coming to DCHN with major concerns.

"So we worked on this project well over a year, developing a coating called Micralox® that earned the first USPTO patent for an anodic coating in 20 years," said David DiBiasio, director of sales and marketing for DCHN. "We actually found a way to partially convert the amorphous structure of a standard Type III hardcoat and turn it into a partial microcrystalline composition."

Because a crystalline structure is very tight and stable at the molecular level, it does not like to change. Thus, the aluminum part is protected from chemical dissolution, and therefore corrosion, by a minimum power of ten. This means that an item with a traditional coating would last only a year, whereas Micralox allows for ten years of protection, DiBiasio explained.

The Micralox technology is reported to be well suited not just for medical applications, but for any industry—such as marine and oil—where a part is in danger of corrosion. It is said to be beneficial anywhere that there is exposure of aluminum to sulfur, acidic environments, and high pollution. "Any corrosive environment that any kind of aluminum oxide has difficulty withstanding, Micralox will enhance," he said.

Conventional anodic coatings are degraded by both high and low pH cleaners, but the Micralox hard coating process changes anodic molecules into partially crystalline structures for maximum chemical and corrosion resistance, DiBiasio explained. Citing a YouTube video on the Micralox process, DiBiasio further explained how an aluminum part with a conventional hard coat comes in contact with a stripping agent of 13.9 pH, and within five minutes the hard coat disappears and the aluminum substrate is degraded. "You can see it. It actually bubbles like champagne, yet on the other side, the Micralox is completely intact," he said.

The Micralox process also allows for the avoidance of trying to coat an aluminum with something like a nylon to make it last longer. Plastic coatings can lead to something called "wetting" where the coating doesn't dry and establishes an environment where pathogens can grow—very undesirable for medical instruments, dental instruments, and surgical instruments. Because Micralox has a high thermal conductivity, the surface dries very quickly. Unlike plastic coatings that can become brittle, chip, and delaminate, anodic coatings develop from and are integral with the substrate and therefore last much longer.

"It's the conversion of the oxide itself," DiBiasio said. "So we're not trying to cover the aluminum oxide; it's actually a fundamental change in the aluminum oxide itself. That's the crystalline structure." Aluminum oxide contains a porous structure, which allows for pathways where corrosion ions can get into the pores and create a breakdown. "This Micralox coating significantly reduces these pathways and therefore the risk of corrosion," he added.

Micralox also allows for vibrant colors because it builds a clear hardcoat rather than a dark grey or brown finish as with the traditional aluminum coatings. "It's a proprietary process, so we're the only ones that can build this clear, dense hardcoat that meets Mil-A-8625 Type III. So now when you add dye to this (Micralox) hardcoat, you still get the bright vivid colors of the dyes. You're not mixing it with that dark brown color you get with a normal hardcoat. You have the best of both worlds—you have a Type II cosmetic finish with the corrosion resistance and the durability of a Type III hardcoat," DiBiasio explained.

Micralox is part of DCHN's proprietary Sanford Process® technologies, which comprise a number of hard coat anodizing processes. The Sanford Process can be applied to a wide variety of parts and enables the company to hard coat virtually all aluminum alloys, including 2000 series and cast. It offers numerous advantages over traditional hard coat anodizing techniques, DiBiasio said, including better abrasion and corrosion resistance, greater coating hardness and uniformity, higher thermal conductivity, and the ability to add bright, vivid colors to the resulting hard anodized aluminum.

DCHN (www.d-chn.com), a part of Katahdin Industries, Inc., handles the company's metal finishing and anodizing, with a focus on technical aluminum anodizing, electropolishing, and passivation. Sanford Process Corp, which licenses the Micralox technology, is also a division of Katahdin Industries.