In recent years, wind energy has gained widespread attention and has been regarded as one of the renewable energy resources for the future. However, surface erosion of wind turbine blades, which are key components of wind turbines, can degrade the aerodynamic properties of blades, thereby, reducing the energy efficiency and service life. It has been estimated that wind turbine blade erosion can reduce annual energy production by 20–25% with severe erosion. In this sense, understanding and mitigating of leading edge erosion of wind turbine blades caused by rain and solid particles are critical to develop efficient technologies for wind turbine blades. To protect the wind turbine blades, various types of polymer-based coatings have been developed. In general, polymer composites offer excellent strength, durability, flexibility, ease of fabrication, and low cost. This comprehensive review is aimed to provide broad information and recent developments about the characteristics of leading edge erosion by rain and solid particles, their mechanisms, testing methods and associated standards, and development of erosion protection coatings for wind turbines. Updated advances in characteristics of polymeric protective coatings, process of coating development, coating materials, coating types, and simulation for the coating development against rain and solid particle erosions have also been addressed in this review.
The role of quantum dots (QDs) of SnO2 in detecting low concentrations of methane (CH4) at a relatively low temperature of ∼150 °C with high response (S ∼ 3.5%) and response time below 1 min is reported. A simple room temperature single step chemical process was adopted for the growth of SnO2 nanoparticles of a size around 2.4 nm. These nanoparticles were subsequently annealed at 800 °C to increase the grain size to 25 nm. The as-prepared SnO2 nanoparticles, being smaller than the corresponding Bohr radius (2.7 nm), showed a strong quantum confinement effect with a blue shift in the band gap energy from 3.6 eV for the bulk SnO2 to 4.37 eV for the QDs. These QDs exhibited a strong sensing response to CH4 in comparison to the annealed sample. A low activation energy of 90 meV, as estimated from the temperature dependent S plot for SnO2 QDs, was found to be the driving force for such unusual high sensitivity at a low operating temperature. X-ray diffraction, transmission electron microscopy, along with Raman spectroscopy measurements are used for the detailed structural studies. The critical role of the chemisorbed oxygen species present at different operating temperatures on the surface of the off-stoichiometric quantum sized SnO2 and bulk-like annealed samples are discussed in light of the adsorption kinetics.
Pressure-induced phase transition studies in nanomaterials are important to comprehend thermodynamics at the nanoscale. Raman spectroscopic studies at high pressure in a diamond anvil cell were performed up to 40 GPa on rutile tetragonal phase of SnO2 nanoparticles (NPs) of sizes ∼2, 4, and 25 nm to investigate their phase stability and phonon anharmonicity. In 25 nm NPs, evidence of phase transitions was observed at ∼11 and ∼24 GPa, 4 nm NPs indicated a cubic phase transition ∼21 GPa, and the 2.4 nm quasi-nanocrystals were found to stable up to 30 GPa. Raman spectra down to 90 K indicated that phonons of 2.4 nm NPs were more anharmonic. The analysis of total Raman intensity with increasing pressure suggested propagation of disorder from the surface to the central core of the NPs under pressure. Pressure-induced effects on 25, 4, and 2.4 nm NPs reduced their average diameters to 6.4 ± 2.6, 4.04 ± 1.36, and 3.85 ± 0.9 nm, respectively. Using Raman mode Grüneisen parameters γj, the thermal expansion coefficient α of the 25, 4, and 2.4 nm SnO2 NPs at 300 K was estimated as 1.674 × 10–6, 1.178 × 10–6, and 1.690 × 10–6 K–1, respectively.
Wind energy is considered a clean energy source and is predicted to be one of the primary sources of electricity. However, leading-edge erosion of wind turbine blades due to impacts from rain drops, solid particles, hailstones, bird fouling, ice, etc., is a major concern for the wind energy sector that reduces annual energy production. Therefore, leading-edge protection of turbine blades has been an important topic of research and development in the last 20 years. Further, there are critical issues related to the amount of waste produced, including glass fiber, carbon fiber, and various harmful volatile organic compounds in turbine fabrication and their end-of-life phases. Hence, it is vital to use eco-friendly, solvent-free materials and to extend blade life to make wind energy a perfect clean energy source. In this study, cellulose microparticles (CMP) and cellulose microfibers (CMF) have been used as fillers to reinforce water-based polyurethane (PU) coatings developed on glass fiber reinforced polymer (GFRP) substrates by a simple spray method for the first time. Field emission scanning electron microscopy images show the agglomerated particles of CMP and fiber-like morphology of CMF. Fourier transform infrared spectra of CMP, CMF, and related coatings exhibit associated C–H, C=O, and N–H absorption bands of cellulose and polyurethane. Thermal gravimetric analysis shows that CMP is stable up to 285 °C, whereas CMF degradation is observed at 243 °C. X-ray photoelectron spectroscopy of C 1s and O 1s core levels of CMP, CMF and related coatings show C–C/C–H, C–O, C–OH, and O–C=O bonds associated with cellulose structure. The solid particle erosion resistance properties of the coatings have been evaluated with different concentrations of CMP and CMF at impact angles of 30° and 90°, and all of the coatings are observed to outperform the PU and bare GFRP substrates. Three-dimensional (3D) profiles of erosion scans confirm the shape of erosion scars, and 2D profiles have been used to calculate volume loss due to erosion. CMP-reinforced PU coating with 5 wt.% filler concentration and CMF-reinforced PU coating with 2 wt.% concentration are found to be the best-performing coatings against solid particle erosion. Nanoindentation studies have been performed to establish a relation between H3/E2 and the average erosion rate of the coatings.
Because of higher energy absorbing capacity of porous metals, these materials are used in car crash protection, armours, etc. However, to the best of our knowledge the porous metals are not used in solid particle erosion (SPE) resistant coatings. Nanotechnology allowed development of effective erosion resistant coatings by reducing the grain size of coatings to ≤ 10 nm. As a further development to it, here the porous metal layers, sandwiched between blocks of Ti/TiN multilayers to develop the next generation SPE resistant coatings. Two different ultra-thin Ti/TiN (bi-layer ~7.5 nm, 373 bilayers) multi-layered coatings (each ~9 μm) with dense (Ti/TIN-D) and porous (Ti/TIN-P) Ti layers (320 nm) were deposited on Ti6Al4V substrates using magnetron sputtering system. The erosion tests were conducted with respect to erodent speed (30 to 100 m/s), angle (30 to 90°), and temperature (25 to 700 °C). The average erosion resistance performance of Ti/TIN-P coating is 44 times better than Ti6Al4V substrate and 3.3 times better than Ti/TIN-D coating for 100 m/s erodent speed. Finite element simulations were used to understand the superior performance of Ti/TIN-P over Ti/TIN-D coating for different speeds (20 to 100 m/s). The simulation results are in agreement with the experimental results.
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