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We propose a facile and combined methodology to develop magnetron sputtered various metals and alloy (e.g. tungsten, tin and nichrome), and metal oxide (indium tin oxide) thin film-based micro-patt...

This study has dual objectives, one to develop single layer ZrB2-SiC-based ceramic absorber coating on stainless substrate, and another aim is to explore the degradation of ZrB2- SiC bulk ceramic in molten solar salt. In particular, we report the molten salt corrosion behavior of earlier developed ZrB2-SiC ceramic composite at 400 °C for 100 h. The corrosion rate in solar salt was determined to be 0.73 ± 0.09 mg h-1/cm2by gravimetric analysis. Binary and ternary oxide phases were formed due to electrochemical corrosion. The hot-pressed bulk ZrB2-SiC ceramic exhibits a high solar absorptance of 0.848 and also a high thermal emissivity of 0.66. A one-layer solar selective absorber coating without antireflection layer was developed using the ceramic disk as a sputtering target. When deposited using radio frequency (RF) magnetron sputtering technique on stainless steel substrate, a solar absorptance of 0.769 and thermal emissivity of 0.15 was obtained for an amorphous coating of thickness ~90 nm, without antireflection coating. The composition, determined by electron probe microanalyzer and X-ray photoelectron spectroscopy techniques, revealed nonstoichiometric phases in the layer with a relatively higher concentration of the lighter elements. The implication of the present work for concentrated solar power application is discussed. © 2021 American Chemical Society. All rights reserved.

Plasma electrolytic oxidation (PEO) or microarc oxidation process has been carried out on Ti6Al4V substrate in electrolytic bath containing sodium silicate and sodium hypophosphate. The phase composition, microstructure and roughness of the PEO coating are examined by x-ray diffraction, scanning electron microscopy and profilometry techniques, respectively. Wavelength-dependent thermo-optical properties viz. solar absorptance ( $$\alpha_{s}$$ ) and IR emittance (eir) are recorded by UV-VIS-NIR and FTIR spectrophotometer, respectively. Nanomechanical properties such as nanohardness (H) and Young’s modulus (E) are evaluated by well-established nanoindentation technique. The PEO coating is found to be hydrophobic (contact angle ~108°) and possesses low thickness of 5-9 $$\upmu$$ m. Average eir is obtained to be 85% while average $$\alpha_{s}$$ is recorded as 76%. The characteristics H and E values are 2.59 GPa and 81.45 GPa, respectively. The PEO coating is also characterized with respect to potentiodynamic polarization and impedance spectroscopy to evaluate corrosion resistance. The total impedance and corrosion current density (icorr) are in the order of 1 MΩ and 10-8 µA.cm-2, respectively. The results indicate superior corrosion resistance of the present PEO coating compared to similar coatings reported in the literature.

Nano-scale load (P) dependency of fracture toughness (K1C) of indium tin oxide (ITO) coating on silicon (Si) substrate is evaluated by nanoindentation based direct and energy methods. A Berkovich triangular diamond nanoindenter is used with nine different P values e.g., 10, 15, 20, 30, 40, 50, 100, 150 and 200 mN. Extensive utilization of both optical microscopy (OM) and field emission scanning electron microscopy (FESEM) techniques reveal that up to P ≤ 40 mN only the sharp radial cracks form from three corners of the nanoindent. However, for P > 40 mN, multiple cracks occur over and above the radial cracks. Finally, at P: 150–200 mN coating gets chipped off from the substrate. The K1C values of the ITO coating are calculated on the basis of both the conventional radial crack length measurement based method and the strain energy release based method. The K1C values are strongly sensitive to variations in P. Further, the strain energy method results in higher magnitudes of the K1C values.

We have fabricated VO2 nano-columns (NCs) on the aluminized quartz glass substrates using glancing angle deposition (GLAD) technique inside the electron beam (e-beam) evaporator chamber. An e-beam deposited TiO2 thin cap-layer has been introduced on the top of the VO2 NCs to protect VO2 phase which is usually unstable and turns to stable higher oxidation state, i.e., V2O5. The X-ray diffraction (XRD) analysis of TiO2 thin film (TF) coated VO2 NCs shows the presence of VO2 phases along with the other oxidation states. The Fourier-Transform-Infrared-Spectroscopy (FTIR) confirms the presence of Ti–O–V, V–O vibrations bands in VO2 NCs/TiO2 TF samples. The VO2 NCs/TiO2 TF sample possesses a sharp drop (~103 order) in resistance at the transition temperature (Tc) ~66 °C. This sample also shows a stable semiconducting to metallic phase (vice versa as well) transition temperature (PTT) hysteresis even after one month which ensures the stable performance in terms of phase transition characteristic. Small-radius polaron model (SRPM) is used to calculate the sheet resistance of the VO2 NCs, where we consider the effect of thermal lattice vibrations on the overlap integral of the crystal atoms. The temperature dependency of constants A and e have been observed uniquely. The Fermi-Dirac (F-D), Migdal distribution (MD) model have been taken into account for the first time to calculate the conduction band carrier density of VO2 NCs and ratio of the resistance in the semiconducting (RS), metallic phase (RM) is also calculated. The calculated electron concentration ( n c ) is 3.1 × 1019 cm-3 at the point of PTT (66 °C).

DC magnetron co-sputtering technique is utilised to develop reflective Ag- and Al-based metal films co-sputtered with Ni deposited on quartz glass substrates. The sputtered films are characterised ...

Transparent super-hydrophobic monolithic silica aerogels are prepared by the cost-effective ambient pressure drying. The drying of aerogel is performed at various temperatures ranging from 25 to 200°C. Oxidation states of different silica aerogels are investigated by XPS which shows the presence of both SiO and SiO2 phases. Thermal stability of hydrophobic aerogel is found as ~320°C investigated by TGA and DSC. The chemical bonds (i.e., –CH3) responsible for the hydrophobic (WCA > 170°) nature of synthesized silica aerogels are identified by FTIR. Further, out-gassing properties of the silica aerogels have been investigated and they are found in limit for the space application. The highest hardness and Young’s modulus are measured by the nanoindentation technique for the aerogel dried at 120°C which has higher density, while density decreases for the aerogel dried at 200°C and the corresponding nanomechanical properties are found to be lowest as expected.

The present pandemic coronavirus disease 2019 (COVID-19) becomes a serious concern of global health threat which is elicited by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). This pa...

Present work reports thermal conductivity measurement in a commercial soda–lime–silica glass substrate by the transient 3$$\omega$$ method using a unique, custom-built in-house setup. Most importantly, a micro-heater (MH) cum temperature sensor is fabricated for this purpose. At first the MH-patterned mask is developed by CO2 laser cutting technique on quartz glass. The MH (L-5 mm, W-65–70 μm, t-140 nm) is fabricated by sputtered Au thin film on the commercial soda–lime–silica glass substrate. Following evaluations of the thermo-electrical properties, microstructure and surface morphology of the Au thin film, the TCR of the MH is noted to be 0.001469 K−1. Finally, the thermal conductivity of the soda–lime–silica glass substrate is measured as 1.46 W·m−1·K−1. The error in measurement calculated by the Kline–McClintock method is

The feasibility of utilizing commercially available silica aerogel-based flexible composite blankets as passive thermal control element in applications such as extraterrestrial environments is investigated. Differential scanning calorimetry showed that aerogel blanket was thermally stable over – 150 to 126 °C. The outgassing behavior, e.g., total mass loss, collected volatile condensable materials, water vapor regained and recovered mass loss, was within acceptable range recommended for the space applications. ASTM tension and tear tests confirmed the material’s mechanical integrity. The thermo-optical properties remained nearly unaltered in simulated space environmental tests such as relative humidity, thermal cycling and thermo-vacuum tests and confirmed the space worthiness of the aerogel. Aluminized Kapton stitched or anchored to the blanket could be used to control the optical transparency of the aerogel. These outcomes highlight the potential of commercial aerogel composite blankets as passive thermal control element in spacecraft. Structural and chemical characterization of the material was also done using scanning electron microscopy, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy.

Micro heaters are important part in miniaturized heating applications. These applications required precise control of temperature over the applied surface that need to be heated. This present work is the computational study of the micro heater performance under various design criteria. Three different models of the heaters were studied for multi-physical phenomena, viz. the temperature uniformity and the mechanical stability. Effect of various parameters of the heaters, viz. pattern design, applied voltage and layer thickness, for nichrome (NiCr) based micro-heaters have been studied using COMSOL Multiphysics. Finally, conclusions are made by comparison of design parameters to reach best solution among nichrome micro-heaters.

Silica aerogel is a unique ultra light weight nano porous material which offers superior thermal insulation property as compared to the conventional thermal insulating materials. It can be applied not only for ground and aerospace applications but also in low and high temperatures and pressure regimes. Aerogel granules and monolith are synthesized by the sol–gel route while aerogel based composites are fabricated by the reinforcement of fibers, particle and opacifiers. Due to the characteristic brittleness (i.e., poor mechanical properties) of monolith or bulk aerogel, it is restricted in several applications. To improve the mechanical integrity and flexibility, usually different fibers are reinforced with aerogel and hence it can be used as flexible thermal insulation blankets. Further, to achieve effective thermal insulation behaviour particularly at high temperature, often opacifiers are doped with silica aerogel. In the present brief review, the prospects of bulk aerogel and aerogel based composites are discussed for the application of thermal insulation and thermal stability.