A New Approach of Improving Rain Erosion Resistance of Nanocomposite Sol-Gel Coatings by Optimization Process Factors
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THE coatings that are applied in different systems with regard to service conditions should be able to withstand mechanical damage and abrasion for a long time. The issue of economic losses caused by wear and erosion of metallic structures is very important. Great efforts are made on the development of protection systems from liquid impact in the last decades.[1–6] Two different types of coatings were developed for the purpose of wear and erosion protection in the past: hard inorganic coatings and pliant, rubber-like organic coatings.[2,7,8] A new generation of organic–inorganic coatings is very interesting because they combine properties of the polymeric material (flexibility) and properties of the ceramic (hardness). The advantage of the organically modified sol-gel system is the possibility to prepare thick, crack-free coatings that increased resistance to rain erosion.[9–11] The organic–inorganic hybrid network provides sufficient mechanical stability to avoid the cracks’ cause of the rain droplet impact, and it is flexible enough to absorb the kinetic energy of droplets. The liquid AKBAR HOJJATI NAJAFABADI and HAMED RAHIMI, Researchers and Ph.D. Students, and REZA SHOJA RAZAVI and REZA MOZAFFARINIA, Associate Professors, are with the Department of Materials Engineering, Malek Ashtar University of Technology, Shahin Shahr, 83145-115 Isfahan, Iran. Contact e-mails: [email protected]; [email protected] Manuscript submitted April 4, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
impact of a water drop caused the failure that divided into two regimes. In the first level, deformation and first cracks initiate in the surface, which occurs when the water droplet impacts the surface (water droplet impact). In the second level, high-velocity lateral water jets can tear away any unevenness in the surface material greater than 100 nm (lateral jets). A detailed description can be found elsewhere.[2,12] As is well known, the sol-gel organic–inorganic hybrid coatings resistant to rain erosion depend on a number of compositional and processing factors, including the 3-glycidoxypropyltrimethoxisilane (GPTMS)/tetraethylorthosilicate (TEOS) molar ratio, hydrolysis water content, drying and curing temperatures, and curing time. A few studies focus on the optimization of compositional and process factors for different goals.[13–15] This study focuses on the optimization of compositional and process factors of new protection systems that are resistant to rain erosion, using a combination of hard and pliant compounds by using statistical design of experiment (DoE) methodology based on Taguchi orthogonal design. Process optimization has been done using the multifactor analysis of variance (ANOVA) analysis method. II.
EXPERIMENTAL
A. Statistical DoE Methodology Sol-gel hybrid coatings are sufficiently affected by process conditions such as water hydrolysis content,
organic/inorganic ratio, pH, synthesis temperature, drying and curing times and temperatures, etc. To study the effect of the key parameters as a function of erosion rate,
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