Exploring float glass powder as corrosion resistant glass coating applied to concrete by flame spraying
- Untersuchung von Floatglas als korrosionsbeständige Glasbeschichtung aufgebracht auf Beton mittels Flammspritzen
Zhang, Li; Conradt, Reinhard (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2014)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2014
Float glass was chosen as precursor material to generate protective coatings on concrete structures against chemical attack. The method of application was flame spraying. The feedstock for flame spraying was in form of powders. The preparation methods (dry ball milling and spray drying) affected the morphology, the particle size distribution and the spray ability of the coating powders. Compared to as-sprayed coatings from dry ball milled powders, coatings from the spray dried powders had a more favorable performance. No obvious open pores existed and a better adhesive performance was obtained. Influences of the process parameters (spraying distance and preheating) were evaluated based on the morphology of the as-sprayed coatings, indicating that a combination of 50 mm spraying distance and 500°C preheating led to a dense coating and sufficient adhesion. The tensile bonding strength and the corrosion resistance of the coatings were investigated. Failures in the tensile strength test occurred in the upper part of the concrete, indicating sufficient bonding strengths between the as-sprayed coatings and the substrates. In corrosion tests, the as-sprayed coating from a powder SD33, spray dried powder from a water-based suspension having 33 wt.% glass content, completely inhibited the penetration of the H2SO4 solution going through the coating into the concrete. Furthermore, after 7 days of exposure to the acid solution, no corrosion phenomena were found in the samples, indicating the extraordinary corrosion resistance of this coating. Two mechanisms are responsible for pore formation in the flame sprayed glass coatings: Pores are formed from the entrapped gas. They are normally round and small, and the edges of those pores are smooth. Another mechanism is pore formation due to a lack of liquid from the molten deposits to fill the interstices between the overlapping splats; the interstitial pores are normally bigger (over 100 µm), and have an irregular or round shape with sharp edges. Porosity of the coatings is measured by image analysis, whereby an easy method has been developed to transfer the measured 2D images into 3D porosity. It is found that the coating from the powder SD33 possesses the lowest porosity.