Multilayer passive radiative selective cooling coating based on Al/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering

A multilayer passive radiative selective cooling coating based on Al/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering is presented. The design was first theoretically optimized using the optical constants, refractive index and extinction coefficient, of thin single layers. The spectral optical constants in the wavelength range from 0.3 to 27 µm were calculated from the transmittance and reflectance data of thin single layers deposited on silicon and glass substrates. The samples were characterized by Scanning Electron Microscopy, X-ray diffraction, Fourier-transform Infrared Spectroscopy and UV–VIS–NIR spectroscopy. It is shown that the TiO2 layer presents a partially rutile phase polycrystalline structure and a higher refractive index than amorphous SiO2 and SiNx layers in the spectral range from 0.3 to 2.5 μm. The cooling device was deposited on copper substrates and a thin low-density polyethylene foil with high transmittance in the 8 to 13 µm spectral range was used as convection cover material. The device is characterized by both low reflectance (high emittance) in the sky atmospheric window (wavelength range from 8 to 13 µm) and high hemispherical reflectance elsewhere, allowing for temperature drops of average 7.4 °C at night-time in winter, which corresponds to a net cooling power of ~43 W m−2. Further, a temperature drop of 2.5 °C was obtained during winter daytime.FCT in the framework of the Strategic Funding UID/FIS/04650/2013 and the financial support of FCT, POCI and PORL operational programs through the project POCI-01-0145-FEDER-016907 (PTDC/CTM-ENE/2892/2014), co-financed by European community fund FEDE

High Si multilayered TiSiN/TiN(Ag) films with superior oxidation resistance

In this work, the effect of Ag content on the morphology, structure, mechanical properties, thermal stability, and oxidation resistance of multilayered TiSiN/TiN(Ag) films, with Si concentration in the range of 6.3e7.0 at.%, is investigated. The coatings are deposited by DC reactive magnetron sputtering, with increasing Ag content from 0 to 13.9 at.%. All coatings exhibit a face-centered cubic structure (f.c.c NaCl type) and the Ag diffraction peaks progressively increase with increasing Ag content. The hardness and the reduced elastic modulus of the as-deposited films decrease with increasing Ag; these mechanical properties are higher after annealing at 800 C in protective atmosphere due to the improvement of the crystallinity of the films. The multilayered architecture of the coatings promotes a good barrier against Ag diffusion towards the surface in protective atmosphere. Ag addition does not influence the onset point of oxidation of the films, but it degrades the oxidation resistance due to the Ag diffusion during the oxidation process, which promotes extra paths for ions diffusion

Influence of Ag additions on the structure, mechanical properties and oxidation behaviour of CrAlNAg coatings deposited by sputtering

In this work, the influence of Ag additions into CrAlN coatings on the surface morphology, chemical composition, structure, hardness and oxidation behaviour was studied. Increasing the Ag content decreased the size of the morphological features and produced a more compact coatings. All coatings displayed a fcc structure typical of transition metal nitrides; the silver phase was indexed for the coatings with Ag concentration ≥8.6 at.%. XPS results confirmed that Ag existed as nanoclusters within the coating structure. A maximum hardness of around 23 GPa was observed for the 8.6 at.% of Ag. The decrease of the hardness with further increase in the Ag content was ascribed to the much softer character of this phase. The reference CrAlN coating displayed the best oxidation resistance and the lowest onset point of oxidation. The good oxidation resistance of this coating was attributed to the formation of a continuous and protective thin Cr2O3 layer on the top of the oxide layer. Ag additions degraded the oxidation resistance of the coatings, since the diffusion of Ag to the top surface of the oxide scale created extra paths for ions diffusion in the protective Cr-O layer. The formation of AgCrO2 phase in CrAlNAg9 coating, for the particular temperature of at 800 °C, was responsible for the low oxidation resistance of the coating as compared to the same coating oxidized at 900 °C. © 202

The effect of increasing Si content in the absorber layers (CrAlSiNx /CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability

In this work, the effect of increasing Si content in the absorber layers (CrAlSiNx /CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability are studied. The two optical stacks presented consist of four magnetron sputtered layers on stainless steel substrates. In both cases, tungsten is used as back-reflector, CrAlSixN/CrAlSiOyNx as absorber layers with different Si/(Cr+Al+Si) atomic ratio (0.15 and 0.30, respectively) and finally the SiAlOx antireflection layer. The structures were theoretically designed by SCOUT software depended on experimental transmittance (T) and reflectance (R) of thin single layers deposited on glass substrates. It is observed that optical stack coatings with higher silicon content show better selectivity values, high solar absorptance, α= 95.9%, and low emissivity, ε= 9.7 % (calculated for 400 ºC), with higher thermal stability at 600 ºC in vacuum, for 650 h. Additionally, with the annealing at 600 ºC an increase of surface roughness was found, which was smaller for sample with higher Si content.The authors acknowledge the support of FCT in the framework of the Strategic Funding UID/FIS/04650/2013 and the financial support of FCT, POCI and PORL operational programs through the project POCI-01-0145-FEDER-016907 (PTDC/CTM-ENE/2892/2014), co-financed by European community fund FEDER

The adjustments of stock prices to information about inflation: evidence from MENA countries

This study extends the empirical evidence by analysing the reaction of monthly stock returns to the unexpected portion of CPI inflation rate and by capturing the asymmetric shocks to volatility of unexpected inflation in five MENA countries. Both Threshold GARCH and Exponential GARCH are used to catch the news affect that unexpected inflation may have on stock returns. Results document a negative and strongly significant relationship between unexpected inflation and stock returns in MENA countries. Results also indicate that the stock markets of the listed MENA countries do not feel the high up and down movements in the markets and as such the volatilities. The asymmetric news effect is absent.