Pr 2 NiO (4+δ) coatings of rare earth nickelate oxide were prepared through RF magnetron co-sputtering, combined with an appropriate heat treatment. The study focused on optimizing the growth conditions to enhance the thermal emittance of the coatings, taking into account the influence of thickness and roughness. The research findings revealed interesting insights. Firstly, by analyzing room temperature infrared reflectivity and studying the temperature dependence of the normal spectral emittance in the range of 500 cm −1 to 5500 cm −1 , it was observed that the total emittance increased as the coating thickness increased. However, this increase tended to approach a saturation value at higher thicknesses. Additionally, the study demonstrated that a coating thickness of 2.8 μm was sufficient to effectively shield the substrate's infrared thermal response. This suggests the potential application of these coatings for thermal management purposes. Furthermore, the influence of roughness on the emittance was predominantly observed in the spectral range of 1200 cm −1 to 3600 cm −1 . This finding highlights the importance of considering surface roughness when designing coatings for optimal thermal properties. In summary, the research provided valuable insights into the growth conditions and the impact of thickness and roughness on the thermal emittance of Pr 2 NiO 4+δ coatings. These findings contribute to the development of improved materials for thermal management and related applications.

The rheology and thermodynamical evolution of magma, either in reservoirs, conduits, or at the surface, are governed by temperature. To determine the field temperature, remote-sensing methods based on measuring the infrared radiance are widely applied, but they are subject to assumptions and caveats that can propagate into large uncertainties. This is related to the poor knowledge of one of the most critical parameters, namely the spectral emissivity. In this work, we aim at filling this gap through in situ spectral emissivity measurements performed over wide temperature (700–1600 K) and spectral ranges (1.25– $25~\mu \text{m}$ ) on two representative phonolitic compositions from Erebus (Antartica) and Teide (Spain) volcanoes. The laboratory spectra allow to determine precisely spectral emissivity in the thermal infrared (TIR), middle infrared (MIR), and shortwave infrared (SWIR) ranges. The results reveal the complexity and contrasted behavior of the radiative properties of the two rocks melts, despite their broadly similar composition. The spectral emissivity varies significantly as a function of temperature, composition, crystallinity, thickness, and thermal history. Altogether, the data reveal that emissivity cannot be considered as a constant value and question previous arguments that active lava always has lower emissivity than frozen lava. Finally, the laboratory-measured values of spectral emissivity were used to refine the temperature of Erebus lava lake gathered from previous remote-sensing methods.

CSP (Concentrated Solar Power) plants technologies use the concentration of solar energy on a receiver to produce heat and then electricity by a thermodynamical process. A solar absorber material is used to convert the energy carried by light into heat. This type of material works at high temperatures (up to 1000 degrees C) under a highly concentrated solar flux (up to x1000 or more). Optical properties determine the performance of absorbers and it is thus necessary to measure their spectral absorptance and emittance. Solar absorptance is directly linked to the capacity of the absorber material to convert the solar flux into heat. Emittance drives the radiative thermal losses for the heated absorber and depends on the absorber temperature. The characterization of a material in operational conditions at high temperatures requires advanced apparatuses, and different measurement methods exist for the characterization of these two quantities of relevance regarding an absorber. A Round Robin Test (RRT) was conducted with the objective of comparing different new optical apparatuses and methods for measuring the emittance or luminance of various solar absorbers in air. Measurements were carried out directly at temperatures up to 560 degrees C while heating the samples, and also indirectly by hemispherical reflectance measurements at room temperature. In this paper, the Round Robin Test procedure to compare apparatuses is described, as well as the corresponding reflectance and emittance results on four types of materials. In addition, a discussion of some factors of influence over high temperature measurements in air and of the observed discrepancies among results from the evaluators is presented. The reliability of reflectance/emittance measurements is also demonstrated and statistics of deviations from the mean value are analysed. These allow us to infer information about measurement reproducibility. The reflectance spectra of all samples after high temperature measurements in air (up to 500 degrees C) do not show any significant changes.

We report on the high-temperature evolution of far- and mid-infrared reflectivity and emissivity spectra of ambient orthorhombic ErMnO3 from 12 K to sample decomposition above 1800 K. At low temperatures the number of phonons agrees with the predictions for orthorhombic space group D-2h(16)-Pbnm (Z = 4) and coexists with a paramagnon spin resonance and rare-earth crystal-field transitions. Increasing the temperature, a number of vibrational bands undergo profile broadening and softening approaching the orbital disordered phase where the orthorhombic O' lower-temperature cooperative phase coexists with cubic-orthorhombic O. O-ErMnO3 undergoes a first-order order-disorder transition into the perovskite cubic phase at T-cubic similar to 1329 K +/- 20 K where the three triple degenerate phonons allowed by the space group Pm-3m (Z = 1) are identified. At about 800 K, a quantitative small polaron analysis of the orthorhombic midinfrared real part optical conductivity shows that antisymmetric and symmetric breathing modes sustain the strongest electron-phonon interactions. Above T-cubic the bipolaron fingerprint profile is the midinfrared dominant and only feature. Its appearance correlates with the localized screening of the highest vibrational mode reststrahlen band. We propose that the longitudinal optical mode macroscopic field screening is a consequence of dynamically sharing S disproportioned e(g) electrons hovering over the Jahn-Teller distorted octahedral dimer {Mn(Q(JT))(3+delta)[Mn(Q(JT))[3](-)(delta)]O-6/2}(2). A thermal driven insulator-metal transition is detected with onset similar to 1600 K. We also address the occurrence of an inhomogeneity induced terahertz band result of heating the samples in dry air, triggering Mn3+ Mn4+ double exchange, under the presence of Mn4+ smaller ions stabilizing the orthorhombic lattice.

We report on THz absorption spectroscopy combined with high magnetic fields of polycrystalline RCrO3 (R= Pr, Sm, Er) aiming understanding spin wave resonances at their low temperature magnetic phases. Our measurements show that the temperature, and the implicit anisotropies at which the Cr3+ spin reorientation at TSR takes place, are determinant on the ferromagnetic-like (FM) and the antiferromagnetic-like (AFM) spin modes being optically active. It is found that they are dependent on Rare Earth 4f moment and ion size. We also studied temperature and field dependence of crystal field levels in the same spectroscopic region. Pr3+ non-Kramers emerges at 100 K and Zeeman splits. An observed absence of spin wave resonances in PrCrO3 is attributed to Pr3+ remaining paramagnetic. In SmCrO3 near cancelation of the spin and orbital moments is proposed as the possible reason for not detecting Sm3+ ground state transitions. Here, the FM and AFM resonant modes harden when the temperature decreases and split linearly on applied fields at 5 K and below. In ErCrO3 the Er3+ Kramers doublet becomes active at about the TSR onset. Each line further experiences Zeeman splitting under magnetic fields while an spin reversal induced by a 2.5 T field, back to the Gamma4 (Fz) from the Gamma1 phase at 2 K, produces a secondary splitting. The 5 K AFM and FM excitations in ErCrO3 have a concerted frequency-intensity temperature dependence and a shoulder pointing to the Er3+ smaller ion size also disrupting the two magnetic sublattice approximation . Both resonances reduce to one when the temperature is lowered to 2 K in the Gamma1 representation.

The enameling is a technique of decoration whereby objects or flat surfaces are covered by a vitreous glaze that is fused by intense heat to create a brilliantly colored decorative effect. It is an art form noted for its brilliant, glossy surface, which is hard and long-lasting. It is known that the firing method used to produce enamels plays a very important role in the color rendering. The objective of this work was to compare enamel decors obtained with two kinds of firing systems: a conventional furnace and infrared emitters, in order to gain better understanding and control the development of new colors. The results highlighted a deep impact of the heating technique on the final color due to the formation of layers having very different chemical phases and textural properties. The obtained materials have been characterized by different physico-chemical techniques such as infrared spectroscopy, XRD, SEM and EDS. Infrared heating allowed the production of nearly pure red enamel decor with a shiny aspect which was not the case with conventional furnace firing. The paper also showed that color design of different color shades would be possible by using hybrid systems allowing a fine tuning of thermal gradients during the heat treatment. (C) 2017 Elsevier B.V. All rights reserved.

Thermal emission has been the historic paradigm to understand quantization of energy, for light and matter. However, the universal far field blackbody radiation is not sufficient to account for the near field effects of the thermal emission. When matter is heated up, surface polaritons at its boundary become thermally excited, and intense electromagnetic fields evanescently decay away from the surface. For a given material, with a well-defined shape, the population of these surface modes obeys a thermodynamic distribution, according to the local density of states in vacuum near the interface. In addition, rising up the temperature is susceptible to induce phenomenological changes of the surface mode resonances, such as broadening or shift.

Concentrating Solar Power (CSP) technologies in arid areas suffer of a too high water consumption at the condenser of their power-block. The different alternative dry cooling technologies previously proposed to overcome this weakness lead to a decrease of 3-7% in whole efficiency of the power plant and a corresponding increase of 10% in the cost of the produced electricity. The new dry cooling approach proposed in the present study is based on using the solar field (SF) as a macro heat exchanger. Nightly, the extended available surface area of the SF allows convective thermal exchange with the surrounding environment and additional radiative heat transfer with the 3 K extra atmospheric space through the atmospheric window in between 8 and 14 pm. The exchanged radiative heat flow density depends directly on the optical properties of the exposed materials. In the present paper, performances of conventional and innovating reflective materials are presented through the assessment of their spectral emissivity. Aluminum film (innovating material) appears to be the most efficient one with a mean spectral emissivity around 95%, while glass mirrors (conventional materials) area round 86%. Moreover, within the spectral range of the atmospheric window 8-14 mu m, aluminum film is more stable than the glass mirror with a respective standard deviation of 3 and 7.8 respectively. The results confirm that radiative heat transfer can contribute to the cooling needs of linear Fresnel and parabolic trough CSP plant power block at a level of 95% and 53% respectively. (C) 2017 Elsevier Ltd. All rights reserved.

Nowadays there is an intense research for developing alternative thermal energies storage materials, able to work at the 800–1000°C temperature range, for concentrated solar plants. The challenge is wide and extends from different ceramics to natural rocks. In the present work, the aim is first to select representative basaltic rocks from different localities over the Mediterranean basin and close volcanic sites, these going from Tenerife Island up to Egypt. Second, to evaluate the effect of mineralogy, composition and texture of such natural materials on thermal properties during heating process (up to 1000°C). All analyzed basalts are stable over a wide range of temperatures and especially those containing high amounts of MgO and FeO*, since they present valuable physical and chemical potential as being used as thermal storage material in concentrated solar plant operating until 1000°C.

A simple and robust analytical model is used to finely predict the spectral emittance under air up to 1300 K of α-SiC open-cell foams constituted of optically thick struts. The model integrates both the chemical composition and the macro-porosity and is valid only if foams have volumes higher than their Representative Elementary Volumes required for determining their emittance. Infrared emission spectroscopy carried out on a doped silicon carbide single crystal associated to homemade numerical tools based on 3D meshed images (Monte Carlo Ray Tracing code, foam generator) make possible to understand the exact role of the cell network in emittance. Finally, one can tune the spectral emittance of α-SiC foams up to 1300 K by simply changing their porosity.

Polycrystalline Pr2NiO4+δ coatings have been deposited on alumina substrates at room temperature by RF magnetron co-sputtering from Pr and Ni metallic composite target. The mixed target's area and the sputtering conditions were optimized to reach an atomic ratio Pr/Ni of 2. A subsequent annealing, at 1050–1100°C, allowed obtaining Pr2NiO4+δ phase after in situ high temperature x-ray diffraction study performed on as-deposited film. Microstructural analyses (SEM and AFM) revealed dense and rough microstructure. Normal spectral emittance measurements performed at 794 °C in the spectral range 400–5000cm-1 showed an emissivity of ε≈0.8.

Semitransparent materials, like silica or alumina, are highly used by high-temperature industries as refractory materials in blast or glass-making furnaces, first for their good mechanical properties. The knowledge of their radiative properties is also essential to improve thermal transfers. However, characterizing experimentally the high temperature dependence of radiative properties of semitransparent ceramic materials remains nowadays a difficult task. This paper reports a hybrid methodology to address this problem. The approach relies on two or more experimental emittance measurements, performed by infrared spectroscopy on samples of increasing thicknesses, and application of emittance models. The efficiency of the method is illustrated by using experimental data obtained on Jargal M samples, an industrial electrofused ceramic, and a virtual media built from X-ray computed tomography images. Two emittance models, a model from the literature and a new model proposed in this work, are selected to be a part of the hybrid methodology, since they allow retrieving complementary information on the optical and scattering properties of the materials. Both models show a good efficiency to reproduce emittance behavior of the industrial and virtual samples. Parameters are extracted from these models to improve our knowledge of the characteristic thickness of radiative transfer into semitransparent materials and the emittance value of semi-infinite media.

Absorption and scattering properties of pyrolytic boron nitride (pBN) have been characterized by infrared spectroscopy. The strong dielectric anisotropy predicted by first principles calculations is confirmed by measurements performed on a highly oriented pBN sample. Optical properties of textured samples elaborated by chemical vapor deposition were identified from normal hemispherical reflectance and transmittance spectra by applying modified two-flux and four-flux transport models. It is also shown that coating carbon–carbon composites used to build solar shields with a pBN layer having an optimal thickness could improve the protection performance.

Graphene has emerged as a promising material for infrared (IR) photodetectors and plasmonics. In this context, wafer scale epitaxial graphene on SiC is of great interest in a variety of applications in optics and nanoelectronics. Here we present IR reflectance spectroscopy of graphene grown epitaxially on the C-face of 6H-SiC over a broad optical range, from terahertz (THz) to mid-infrared (MIR). Contrary to the transmittance, reflectance measurements are not hampered by the transmission window of the substrate, and in particular by the SiC Reststrahlen band in the MIR. This allows us to present IR reflectance data exhibiting a continuous evolution from the regime of intraband to interband charge carrier transitions. A consistent and simultaneous analysis of the contributions from both transitions to the optical response yields precise information on the carrier dynamics and the number of layers. The properties of the graphene layers derived from IR reflection spectroscopy are corroborated by other techniques (micro-Raman and X-ray photoelectron spectroscopies, transport measurements). Moreover, we also present MIR microscopy mapping, showing that spatially-resolved information can be gathered, giving indications on the sample homogeneity. Our work paves the way for a still scarcely explored field of epitaxial graphene-based THz and MIR optical devices.