Flow fouling and static scaling characterisation of micro/nanostructure enchanced metal alloys

Abstract

This final-year project aims to investigate fouling and scaling characteristics on metal alloy surfaces and develop effective anti-fouling/scaling strategies. The research involves utilizing existing methods and techniques to prevent scaling by applying superhydrophobic (SHP) coatings and slippery liquid-infused porous surfaces (SLIPSs) on metal alloy substrates.

This study conducted static scaling tests at three different temperatures (55°C, 65°C and 75°C) for samples with varying microstructure development timings (5, 10 and 15 mins). The effect of surface orientation on foulant/scale formation was also investigated. In addition, a flow fouling test setup was also designed, installed, and commissioned for the characterization of flow fouling performance.

The major findings involve a slight degradation in hydrophobicity across all SHP-coated samples. The SHP samples which underwent 10 minutes of oxidation, exposed to scaling temperatures of 55°C and 75°C, and positioned in a tilted orientation, showed the most significant decline in hydrophobicity. Additionally, the sample that underwent 15 minutes of oxidation showed a considerable decline in contact angle of 35° when scaling tests were performed at a temperature of 65°C and positioned horizontally upright. On the other hand, all SLIPs coated samples showed no change in contact angle measurements, indicating the full retention of hydrophobicity.

Upon measurements using the ImageJ software, it was determined that SLIPs samples scaled less than SHP samples. The orientation of the samples during scaling tests also played a significant role in the amount of scale growth. As observed in the study, the 70° tilted samples exhibited significantly less scale growth compared to the horizontally oriented samples.

The combined effects of temperature and sample orientation also influence the magnitude of scale formation. Samples placed horizontally and subjected to a scaling temperature of 75°C tend to scale more than those of the same orientation but are subjected to lower scaling temperatures and those tilted at an angle. Moreover, samples placed horizontally and subjected to 55°C and 65°C scaling temperatures attracted bubbles on their surface, which provided protection against scaling.

During the scaling test, samples scaled at 65°C and placed at a tilted angle, experienced degradation of their respective microstructures and SHP or SLIPs coatings. It was speculated that thermal degradation occurred because of certain critical conditions (temperature and orientation of samples) being met.