Terahertz dielectric properties of plasma-sprayed thermal-barrier coatings

Watanabe, Makoto; Katayama, Seiji; Yamawaki, Hisashi; Shiwa, Mitsuharu

doi:10.1016/j.surfcoat.2011.03.144

Cited by 31 publications

(31 citation statements)

References 27 publications

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“…The refractive index of YSZ obtained by Equation (2) was 5.20. Given the variability of the refractive index with the thermal spray condition, the above refractive index cannot be used directly [34].…”

Section: Thz-tds System and The Inspection Methodsmentioning

confidence: 99%

Nondestructive Interface Morphology Characterization of Thermal Barrier Coatings Using Terahertz Time-Domain Spectroscopy

Wang

Huang

et al. 2019

Coatings

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In this work, a terahertz time-domain spectroscopy (THz-TDS) system was used to measure the thickness of thermal barrier coatings (TBCs) and characterize the interface morphology of TBCs after erosion. Reflection mode, with an angle of incidence of 0, was used for inspection before and after erosion. The refractive index, thickness, and internal structure evolution tendency of the yttria-stabilized zirconia (YSZ) top coat were estimated under consideration of the interaction between the pulsed THz waves and the TBCs. The surface roughness of the top coat surface was considered for the errors analysis in the refractive index and thickness measurement. To reduce the errors introduced by the refractive index change after erosion, two mathematical models were built to assess the thickness loss. Then, the thickness loss was compared with results estimated by the micrometer inspection method. Finally, the basic erosion sample profile with Ra roughness was obtained, and the broadening of THz pulses were suggested as a possible measure for the top coat porosity change, showing that THz waves can be a novel online non-destructive and non-contact evaluation method that can be widely utilized to evaluate the integrity of TBCs applied to gas turbine blades.

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Section: Thz-tds System and The Inspection Methodsmentioning

confidence: 99%

Nondestructive Interface Morphology Characterization of Thermal Barrier Coatings Using Terahertz Time-Domain Spectroscopy

Wang

Huang

et al. 2019

Coatings

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“…Figure 1 displays typical transmission-type THz-TDS setup [28,29]. In this optical arrangement, the modulated femtosecond laser pulse of about 10 fs duration at a wavelength of 780 nm is split into the pump and probe beams.…”

Section: Terahertz Time-domain Spectroscopymentioning

confidence: 99%

“…From the spectrum and phase delay data of specimen and reference, IR-spectra software calculates the complex refractive indexes (ñ = n - iκ) of the EP specimens in THz range. The mathematical algorithm is described in detail elsewhere [28,29]. Since the transmittance of electromagnetic waves through a 2 mm thick epoxy specimen rapidly decreases with increasing frequency above 1 THz, the effective frequency range is limited up to 1 THz.…”

Section: Terahertz Time-domain Spectroscopymentioning

confidence: 99%

“…The main advantages of THz-TDS for NDT studies are the high penetration of THz electromagnetic waves into polymers [13][14][15][16][17][18], high sensitivity to the inter/intra molecular vibrations (especially for water) [18][19][20][21][22][23][24][25][26], and ability to estimate the materials dielectric properties without direct contact [27][28][29]. The THz spectra of various thermoplastics [13][14][15] and thermosets [16,17] measured by THz-TDS were reported.…”

mentioning

confidence: 99%

“…Although free and bound water was experimentally studied by FT-IR [10,30,31], NMR [32], thermomechanical analysis [31,32] etc., it is still a highly controversial subject. Since the interactions of the bound water and free water show slightly different dielectric properties [14,20,[22][23][24][25]29], THz-TDS could have an advantage to distinguish these two states of water. In fact, the THz dielectric spectra of bulk water is composed of several spectral peaks related to the different relaxation times and intermolecular stretching vibration of water [23,24].…”

mentioning

confidence: 99%

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Non-destructive evaluation by terahertz spectroscopy for penetration of acid solutions into epoxy resin

Kusano¹,

Kubouchi²,

Bulgarevich³

et al. 2016

Express Polym. Lett.

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Abstract. Epoxy resins are used as high-performance thermosetting linings to protect substrates under corrosive environments. However, in a severe corrosive chemical solution, such protective layers may degrade with long time due to penetrations of solvent and solute molecules into resin network. In this regard, the terahertz time-domain spectroscopy (THz-TDS) is a promising tool for non-destructive evaluation of the penetrant amounts due to high transparency of such plastic materials and high sensitivity to the molecular vibrations in terahertz spectral range. In this work, the complex refractive indexes n and κ of epoxy specimens were measured after immersion into sulfuric acid solutions and compared with penetrated mass fractions of water and acid ions. It was found that n and κ depended linearly with water and sulfuric acid mass fraction in specimens, and κ of sulfuric acid immersed specimens was lager at higher frequency. While the calculated Δκ agreed well with THz-TDS measurement by THz-TDS, the calculated Δn was higher than the measurement. The difference may be attributed to the water and sulfuric states in the specimen.

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Thermal Spray Coatings for Electromagnetic Wave Absorption and Interference Shielding: A Review and Future Challenges

et al. 2022

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This review aims to consolidate scattered literature on thermally sprayed coatings with nonionizing electromagnetic (EM) wave absorption and shielding over specific wavelengths potentially useful in diverse applications (e.g., microwave to millimeter wave, solar selective, photocatalytic, interference shielding, thermal barrier‐heat/emissivity). Materials EM properties such as electric permittivity, magnetic permeability, electrical conductivity, and dielectric loss are critical due to which a material can respond to absorbed, reflected, transmitted, or may excite surface electromagnetic waves at frequencies typical of electromagnetic radiations. Thermal spraying is a standard industrial practice used for depositing coatings where the sprayed layer is formed by successive impact of fully or partially molten droplets/particles of a material exposed to high or moderate temperatures and velocities. However, as an emerging novel application of an existing thermal spray techniques, some special considerations are warranted for targeted development involving relevant characterization. Key potential research areas of development relating to material selection and coating fabrication strategies and their impact on existing practices in the field are identified. The study shows a research gap in the feedstock materials design and doping, and their complex selection covered by thermally sprayed coatings that can be critical to advancing applications exploiting their electromagnetic properties.

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Terahertz dielectric properties of plasma-sprayed thermal-barrier coatings

Cited by 31 publications

References 27 publications

Nondestructive Interface Morphology Characterization of Thermal Barrier Coatings Using Terahertz Time-Domain Spectroscopy

Nondestructive Interface Morphology Characterization of Thermal Barrier Coatings Using Terahertz Time-Domain Spectroscopy

Non-destructive evaluation by terahertz spectroscopy for penetration of acid solutions into epoxy resin

Thermal Spray Coatings for Electromagnetic Wave Absorption and Interference Shielding: A Review and Future Challenges

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