Date: Thursday, Nov 28, 2019
Time: 12:00 p.m.
Title: Development of Robust Scale Resistant Surfaces Made of Rare Earth Oxides
Presenter: Runqian Zhang (PhD Candidate)
Supervisor: G. Azimi
Scaling – also called precipitation fouling – is a major unresolved problem in various industries from power generation and desalination to oil and gas and hydrometallurgy. It is estimated that the energy loss related to scale deposition on heat exchangers accounts for 2% of the total world energy production, and the capital loss associated with heat exchangers scaling is about 0.25% of the gross domestic product (GDP) of industrialized countries. Many studies have focused on developing scale resistant surfaces by coating substrates with low surface energy materials, most of which are polymeric; thus, they deteriorate under harsh environments that are generally encountered during scale formation in various industries.
Ceramics are robust materials with excellent high temperature and wear resistance properties. In this study, we present a new generation of ceramics made of lanthanide rare earth oxides (REO) with low tendency for scale nucleation and growth. Specifically, CeO2, Gd2O3 and Er2O3 films are sputter-deposited on glass substrates, and exposed to a saturated aqueous solution of calcium sulfate dihydrate (or gypsum) together with non-treated glass and stainless steel substrates for 60 h. The solution reached supersaturation due to evaporation of the aqueous phase over time, resulting in gypsum scale formation on the test substrates. Scale formation on different substrate surfaces was characterized qualitatively using scanning electron microscopy (SEM) and quantitatively (mass gain). The results show that the REO surfaces reduced scale formation by 55% compared with glass, and by 77% compared with stainless steel. This scale mitigation tendency is due to the low surface energy feature of REOs, which is measured to be as low as ~24 mJ/m2. The nano-scale smoothness and the topography of prepared REO surfaces were confirmed using atomic force microscopy (AFM). Furthermore, research is underway to measure the adhesion force between gypsum crystals and the test surfaces (REO, glass and stainless steel) using AFM with customized gypsum AFM tip.