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Thin, organo-ceramic coating improves corrosion and fouling resistance of metal components

By Gerald Ondrey |

CVDA chemical vapor deposition (CVD) process that bonds a silicon-oxide film to metal surfaces of any shape is being scaled up by Wicoatec GmbH (Ulm, Germany; www.wicoatec.com). Serial production started in 2017 with pilot-scale equipment, and capacities will be tripled by December 2018. As the next step, parent company Wieland Group (Ulm; www.wieland.com), decided to invest another €6 million in next-generation cleaning and coating equipment.

The Wicoatec process is a patented CVD process that operates at atmospheric pressure. Alkosiloxane precursors [tetramethyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS)] and some minor additives are vaporized and introduced into the coating chamber, which contains the cleaned substrate to be coated. There, the methoxy groups of TMOS (or ethoxy groups of TEOS) are hydrolyzed into silanols, which are unstable and condense as SiO2 on the metal surface, explains managing director Till Merkel. The SiO2 layers form chemical bonds to the metal oxides on the surface — as metal silicates do in nature, says Merkel.

“Atmospheric CVD is nothing new or revolutionary. However, we have found a way to transform the well-known single-pass vacuum-based CVD process into a multi-pass atmospheric process by backmixing of the gas phase. At the same time, process temperatures decreased from 900°C to 300°C,” says Merkel.

Because WiCoat organo-ceramic coatings are chemically bonded to the metal, they provide improved corrosion and fouling resistance by modifying physico-chemical surface properties. Also, Wicoat layers are ultrathin (0.05–5 µm), so the dimensions of the component are essentially unchanged.

“We can provide a homogeneous coating where other processes fail to provide any coating at all — for example, inside surfaces of plate heat exchangers (photo), distillation columns and 3-D printed parts,” says Merkel. “We believe — and ongoing projects with the process industries underline this — that this feature is really exciting to the industry.”

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