#galvanization

Researchers create coating solution for safer food storage

In a collaborative effort to improve the food industry, Dr. Mustafa Akbulut, professor of chemical engineering, and Dr. Luis Cisneros-Zevallos, professor of horticultural science, have developed a two-step coating solution for galvanized steel that is more hygienic and reduces the risk of corrosion. Galvanized steel containers and surfaces are used for harvested produce because of their durability, strength and lower cost compared to stainless steel. However, bacteria residing in storage containers can cause corrosion. The new coating will reduce corrosion by at least 70%, Akbulut said. "This material is more durable and doesn't experience corrosion," Akbulut said. "The surface itself can repel the bacteria so it doesn't get germs stuck on it. Normal steel tends to collect pathogens and microorganisms, but the coated steel is overcoming that issue. These are the main benefits of this technology."

The key is in the coating: Multilayered coating to improve the corrosion resistance of steel

The strength of steel makes it one of the most robust materials known to humankind. When galvanized with zinc (Zn), it becomes more resistant to corrosion. This makes it an economical choice to use in construction and infrastructure.

In the last decade, Zn reserves have fallen appreciably, forcing us to switch to using Zn alloys. Magnesium (Mg) is the most commonly used alloy mineral, and when used in small amounts it can improve the corrosive resistance of Zn.

Now, Professor Myeong-Hoon Lee, Head of the Center of Surface Corrosion Control Engineering at Korea Maritime and Ocean University, and his colleagues have proposed a novel coating for steel that promises to increase its longevity. "During my time in the navy, I noticed a lot of machines that were rusting. So, I engaged in this research, hoping to produce better anti-corrosive steel," says Prof. Lee, explaining his motivation behind the study.

"To survive in harsh environments, high anti-corrosive materials need to be developed. Steel is one such material and increasing its life span makes the steel more sustainable," Prof. Lee explains. Their study was published in Corrosion Science.

Mini-spanglizer - Galvanizing - Coating defects

Defect name: Mini-spanglizer Record No.: 2002 Type of defect (Internal/Surface): Internal, surface Defect classification: Coating defects Steel name: Steel Steel composition in weight %: No data. Note:  Although the science and technology of continuous galvanizing have improved significantly over the years, it is still a challenge to produce defect-free coatings. Studies indicate that poor substrate surface quality, insufficient strip cleaning, mechanical damage to the substrate surface due to handling, and inadequate process control are the main causes of coating defects. The recent introduction of high strength steels makes the production of galvanized coatings for applications such as exposed autobody panels even more challenging. To produce high quality zinc-coated strip, galvanizers need to improve quality control of the incoming strip as well as the continuous galvanizing process. The operation of a mini-spanglizer may introduce coating defects. Shown in Figure 1 are circular dents apparently caused by the impingement of liquid droplets from the spanglizer. If spangles are minimized through the spray of zinc dust to the coating, residual zinc dust may accumulate on rolls down the stream, causing coating defects. 

Zn coating II - Coating defects

Defect name: Zn coating Record No.: 1680 Type of defect (Internal/Surface): Surface Defect classification: Coating defects Steel name: Steel Steel composition in weight %: No data. Note:  In fact, when the micrographs of wear tracks are observed it is possible to see that the Zn-Fe surface shows more debris particles when compared to galvanized surface, Figure 1. A spread structure is visualized on the wear track of Zn-Fe surface, Figure 1d. This fact could indicate plastic deformation of the coating or wear particles compacted. Plastic deformation could take off relatively large particles by an adhesive wear mechanism. On the contrary, at the galvanized surface defined grooves were observed on the wear tracks. Some sticking of fragmented abrasive particles could also been observed, Fig 1b. These remarks are indicative that the wear mechanism predominant to galvanized surface was abrasive wear. Actually, as illustrated in Figure 1a, at the surface of the wear track formed on the Zn-Fe sample, heterogeneous spherical-like agglomerates of wear/corrosion products are observed. These products were not seen on the wear tracks of zinc, which appeared almost free of wear debris. These observations have a two-fold relevance. First the presence of the wear/corrosion products appears to be responsible for the relatively low friction coefficient monitored during the test. But, on the other hand, it indicates that the formation of wear/corrosion debris becomes quite more important in the Zn-Fe samples.

A rough substrate surface - Galvanizing - Coating defects

Defect name: Rough substrate surface Record No.: 1992 Type of defect (Internal/Surface): Internal, surface Defect classification: Coating defects Steel name: Steel Steel composition in weight %: No data. Note:  Although the science and technology of continuous galvanizing have improved significantly over the years, it is still a challenge to produce defect-free coatings. Studies indicate that poor substrate surface quality, insufficient strip cleaning, mechanical damage to the substrate surface due to handling, and inadequate process control are the main causes of coating defects. The recent introduction of high strength steels makes the production of galvanized coatings for applications such as exposed autobody panels even more challenging. To produce high quality zinc-coated strip, galvanizers need to improve quality control of the incoming strip as well as the continuous galvanizing process. A rough substrate surface containing iron fines and slivers is prone to the development of outbursts in the coating. The resultant coating is rough with numerous areas of localized thick coatings. After being flattened in temper rolling, these areas reflect light differently, appearing as either dark or bright spots depending on the lighting condition. A typical sample is shown in Figure 1. Studies indicate that the density of this kind of defect decreases with increasing coating weight, suggesting that such a defect can be masked by a thick coating.

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