The effect of Mg2+ doping on the infrared emissivity of LaCrO3 perovskites

The infrared high emissivity ceramic material plays an important role in thermal protection of hypersonic vehicles. LaCrO₃, characterized by excellent thermal stability and high emissivity, can be applied as infrared high emissivity material. LaCrO₃ and Mg²⁺ doped LaCrO₃ were prepared via solid state reaction method. XRD analyses showed that LaCr_1-xMg_xO₃ (x = 0, 0.1, 0.2, 0.25, 0.3) were single-phase solid solutions. The doping-effect of Mg²⁺ on the infrared emissivity was investigated. In the range of 2.5–8 μm, the infrared emissivity of all doped materials had significant improvement, the average emissivity of materials increased from 0.66 to 0.83. In the range above 8 μm, the emissivity of all materials had a similar trend and compared to LaCrO₃, the emissivity of Mg²⁺ doped LaCrO₃ had little decrease.     

Synergetic enhancement of electrical conductivity and infrared emissivity of SiC-MoSi2 ceramics via N doping

N-doped SiC-MoSi₂ ceramics were successfully fabricated by hot pressing in N₂ using Y(NO₃)₃.6 H₂O as both sintering aids and additional N sources. The impact of Y(NO₃)₃.6 H₂O content on the densification, electrical properties, and infrared emission performance of the resulting ceramics were investigated. The distribution of Y-based sintering aid is improved by melting of Y(NO₃)₃.6 H₂O during slurry drying, enabling the relative density to increase up to 97.4%. Y(NO₃)₃.6 H₂O subsequently decomposes during sintering and allows the substitution of atomic N for the C sites in SiC lattice and production of the N-derived donor level. A larger amount of N dopant elevates the carrier density up to 1.90 × 10¹⁶ cm^-3. Remarkably, The SiC ? 10 wt% MoSi₂ ceramics sintered with 16.9 wt% Y(NO₃)₃.6 H₂O exhibits the lowest electrical resistivity (0.791 Ω·cm at room temperature) and highest infrared emissivity (0.913 at 800 ℃), the latter of which may also be attributed to lattice distortion induced by N doping. This work demonstrates N doping as a prospective strategy for synergistically optimizing the electrical conduction and infrared emission performance of SiC-based ceramics for infrared source applications.     

High infrared emissivity energy-saving coatings based on LaMnO3 perovskite ceramics

In this preliminary work, a series of LaCr_xMn_1-xO₃ (x = 0, 0.25, 0.5, 0.75, 1) ceramic powders were initially synthesized by a facile solid-state reaction method. In the next step, high emissivity coatings were successfully papered by air-spraying using LaMnO₃ powder as the filler material (with the highest emissivity ε_{3–5μm, 600 °C} = 0.922) and phosphate as the binder phase. The morphology, structure, and infra-red emissivity of the samples were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and infra-red emissometery. High-temperature cyclic heat treatment results showed that the prepared coating has very good adhesion and excellent high-temperature resistance. A simulated furnace heating test revealed that the prepared coating can save input energy as high as 13.2%.     

Ca-Mn co-doping LaCrO3 coating with high emissivity and good mechanical property for enhancing high-temperature radiant heat dissipation

Two techniques, including spray drying and electrostatic spray, were applied to produce feedstocks for preparing Ca-Mn co-doping LaCrO₃ ceramic coatings with two different structures on Ni-based alloy by the atmospheric plasma spraying method. The results show that coating from feedstocks produced by spray drying exhibits lower roughness and porosity than the coating from feedstocks produced by electrostatic spray due to the full melting of smaller feedstocks. Higher proportion of melting zones is beneficial to enhance the ratio of hardness to modulus to improve wear resistance. The emissivity of the coatings with roughness from 0.65 µm to 4.6 µm is all above 0.9 in the waveband of 1–14 µm at room temperature. What’s more, structure-dependent emissivity is affected by surface roughness and pore size due to the infrared scattering. The temperature-dependent thermal infrared emissivity at 1–14 µm decreases with the increasing temperature, and is still above 0.67 at 1200 °C.     

Effects of size, shape and floatage of Cu particles on the low infrared emissivity coatings

Low infrared emissivity coating was prepared by the copper (Cu) particles and ethylene–propylene–diene monomer (EPDM) binder. The effect of size, shape and floatage of Cu particles on infrared emissivity of the coatings was systematically investigated. The results indicated that the optimized Cu particles with the minimum coating emissivity are several micron-sized, flaky and high-leafing, exhibiting 0.78, 0.72 and 0.10 emissivity value, respectively. The formation of low infrared emissivity coatings depends strongly on the floatage of Cu particles, not the size or shape, and the results obtained by leafing aluminum (Al) and bismuth oxide (Bi₂O₃) pigment are in good agreement with this standpoint. A theoretical model was proposed to account for the mechanism, which indicated that the low porosity of the coatings with leafing pigments plays an important role in the formation of low emissivity coatings.     

CdZnS半导体颜料涂层红外发射率的研究

以Cd(CH_3COO)_2,Zn(CH_3COO)_2,Na_2S等为原料,通过共沉淀法制备CdZnS半导体颜料,用XRD,EDS,SEM等手段对颜料结构、成分、形貌进行了表征。研究了烧结温度和掺杂含量对CdZnS半导体颜料涂层红外发射率的影响。结果表明,烧结温度和掺杂含量对半导体颜料涂层光学性能有决定性作用,通过调配工艺条件可以获得较低的颜料涂层红外发射率。     

Effects of rare-earth oxide doping on the thermal radiation performance of HfO2 coating

In this study, the REO-HfO₂ (REO = Tb₄O₇, Gd₂O₃ and Sm₂O₃) coatings and pure HfO₂ coatings were prepared by atmospheric plasma spraying. The chemical compositions, morphologies, infrared radiation performance and thermal resistances of the coatings were systematically investigated. The experimental results showed that the Tb₄O₇-HfO₂, Gd₂O₃-HfO₂, Sm₂O₃-HfO₂ and pure HfO₂ coatings had infrared emissivity values of 0.863, 0.852, 0.854 and 0.621, respectively, at room temperature. Based on the phase analysis, the higher infrared emissivity of the REO-HfO₂ coatings could be attributed to the fact that the newly formed RE₂Hf₂O₇ (RE = Tb, Gd and Sm) phase, which had a defective fluorite-type structure, and the RE³⁺ ions enhanced the lattice absorption and electron absorption. Additionally, the Tb₄O₇-HfO₂ coating exhibited a relatively higher infrared emissivity than those of the Gd₂O₃-HfO₂ and Sm₂O₃-HfO₂ coating over the wavelength range of 1–15 μm, which was due to the relatively higher vibrational frequency of the TbO bond in RE₂Hf₂O₇ (RE = Tb, Gd and Sm) and the transformation of Tb³⁺ into Tb⁴⁺ in the Tb₄O₇-HfO₂ system. In addition, the REO-HfO₂ ceramic coatings exhibited excellent thermal resistance, which could withstand high-temperature treatment at 1600 °C for at least 50 h without undergoing a phase change and exfoliation, and the infrared emissivity at different temperatures hardly changed after thermal treatment.     

Corrosion resistance and infrared emissivity properties of EPDM (EPDM-g-MAH) film on low infrared emissivity PU/Cu coating

In order to improve the corrosion resistance of low infrared emissivity polyurethane (PU)/Cu coating, ethylene-propylene-diene monomer (EPDM) and maleic anhydride grafted EPDM (EPDM-g-MAH) were deposited on PU/Cu coating by spin coating, respectively. The ability of EPDM and EPDM-g-MAH to serve as corrosion protective films for PU/Cu coating was examined by evolved emissivity immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. And the chemical composition and surface morphology of PU/Cu coating before and after corrosion were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that all of the coated samples present a better corrosion resistance than bare PU/Cu coating due to indissolubility of Cu by aggressive ions, and the effect of EPDM-g-MAH is better than that of EPDM.     

Temperature-dependent infrared emissivity property of Ce-doped ZnO nanoparticles

The low infrared emissivity materials with good high-temperature properties remain a challenge for the infrared stealth of hot targets in 3–5 μm waveband. To further decrease the infrared emissivity of ZnO, the Ce-doped ZnO nanoparticles were prepared by a facile sol-gel method and the infrared emissivity properties in 3~5 μm waveband in high temperature conditions were deeply investigated by doping different concentration of Ce in ZnO. The influences of Ce dopant concentration on the microstructure, morphology, conductivity, lattice vibration and high-temperature infrared emissivity properties of Ce-doped ZnO were systematically studied, as well as the detailed analysis of temperature-dependent infrared emissivity properties through the conductivity and lattice vibration based on the theory of solid state physics. When the Ce dopant concentration is 3%, the infrared emissivity of Ce-doped ZnO decreases dramatically from room temperature to 800 °C in comparison with undoped ZnO and reaches the lowest value of 0.329 at 500 °C. It is indicated that the excess doping of Ce would produce an impurity phase of CeO₂ in the crystal, therefore decreases the conductivity, and causes extra lattice vibration in infrared region, and results in the increase of infrared emissivity. The infrared emissivity versus temperature exhibits a “U” type curve, which is caused by the competition effects of the conductivity and lattice vibration at elevated temperature.     

High infrared emissivity of SiC-AlN ceramics at room temperature

SiC-AlN ceramics were fabricated by pressureless sintering with B₄C-C as sintering additives. The effects of AlN contents on infrared emissivity, thermal conductivity and electrical properties of SiC ceramics were investigated. The improvement of total emissivity is slight before 3 wt%AlN, but impressive after 3 wt%AlN. The significant increase of the emissivity for AlN content higher than 3 wt% could be explained via DFT calculation, that the impurity energy level formed by N atom doping into 4H-SiC and the lattice distortion are mainly responsible for it. Besides, the highest total emissivity is 0.775 when the content of AlN is 5 wt%. Additionally, more AlN solid solution results in a decrease in thermal conductivity and an enhancement in electrical resistivity. There is always a compromise among the three properties of SiC-AlN ceramics.     

Al0.97Y0.03PO4 thermal radiation material with enhanced infrared emissivity

Al_0.97Y_0.03PO₄ thermal radiation material was prepared by homogeneous precipitation method. The influences of Y-doping on crystallization behavior, infrared vibration absorption, surface chemical elemental composition, chemical environment, grain size and infrared emissivity property were analysed in detail by X-ray diffraction, X-ray photoelectron spectroscopy, Solid state NMR, Scanning electron micrograph and infrared emissivity spectrometer, respectively. It is found that the doping of Y greatly improves the infrared radiation property and reduces the grain size. Compared with non-doped AlPO₄, Al_0.97Y_0.03PO₄ thermal radiation material possesses a higher infrared emissivity of 0.931 ± 0.002, which suggests that it will have a promising application in the field of infrared heating and drying.     

An elevated temperature infrared emissivity ceramic coating formed on 2024 aluminium alloy by microarc oxidation

An infrared emissivity coating material containing γ-Al₂O₃ was prepared on 2024 aluminium alloy surface by the microarc oxidation (MAO) method. The microstructure of the coatings was analysed by SEM, XRD and EDS techniques. The infrared emissivity properties tested at 500 °C were investigated by an infrared radiometer based on a Fourier transform infrared spectrometer. The results show that the infrared emissivity values of coated Al samples depend on the phase composition and surface roughness of the coatings. Corresponding to increasing coatings thickness, the gradually increasing γ-Al₂O₃ content and some oxide compounds containing Si and P contribute to the higher infrared emissivity value (about 0.85) in the wavelength range of 8–20 μm. The increasing surface roughness leads to an obvious increase in emissivity from 0.2 to 0.4 at wavelength 3–5 μm.     

Preparation,dielectric property and infrared emissivity of Fe-doped ZnO powder by coprecipitation method at various reaction time

Fe-doped ZnO powders have been synthesized by the coprecipitation method at 600 °C with various reaction time, using zinc nitrate as the staring material, urea as the precipitator, and ferric nitrate as the doping source, respectively. The phase and morphology of the prepared powders have been characterized by X-ray diffraction and scanning electron microscopy, respectively. It was found that the prepared product synthesized for 1 h had a pure ZnO wurtzite structure and was a ZnO(Fe) solid solution powder. The real part, imaginary part, and dielectric loss of complex permittivity of prepared powders in the frequency range of 8.2–12.4 GHz decreased with increasing reaction time. The average infrared emissivities of prepared powders at the waveband range of 8–14 μm increased with extending reaction time.     

Optically active amino acid-based polyacetylenes: Effect of tunable helical conformation on infrared emissivity property

Chiral amino acid-based monosubstituted acetylene monomers [N-tert-butoxy-carbonyl-l-phenylalanine-N′-propargylamide (LP), and N-tert-butoxycarbonyl-l-serine-N′-propargylamide (LS)] were (co)polymerized with rhodium zwitterion catalyst in THF to afford helical polyacetylenes (PAs) with moderate molecular weights (4400–14,800) in good yields. The optically active PA copolymers were soluble in common organic solvents and proven to adopt predominately single-handed helical conformations according to their intense Cotton effect and large specific rotations. Various contents of amino acid units in side chains facilitated controllable helical secondary structure while the helix was primarily stabilized by hydrogen bonding and steric repulsion between the substituents. Intramolecular hydrogen bonds constructed between hydroxyl and amide groups, in particular, played a significant role in adjusting the helicity and orderliness of the helix. The infrared emissivity values of the PAs at wavelength of 8–14 μm were measured and the correlation between helical conformations and their effect on infrared emission were systematically investigated. The results showed that more well-ordered and compact screw-sense could enhance the performance of organic polymers in lowering their infrared emissivity. Among all the as-prepared PAs, poly(LP₅₀-co-LS₅₀) exhibited the lowest infrared emissivity value (ε₂₅ = 0.632) and possessed excellent resistance against heat.     

The influence of Ca2+ and Zn2+ doping on the development of sustainable pigments based on GdFeO3 perovskite: From a reddish colour towards a pure black

Black pigments are very commonly used and arouse widespread interest in the ceramic industry. Nevertheless, these pigments contain toxic elements that are detrimental to human health. In view of this, the present work is focused on the development of sustainable black pigments prepared by a coprecipitation method at 1200 °C. Samples with the nominal formula (Gd_1–xCa_x)(Fe_0.95Zn_0.05)O_2.975–x/2 (x = 0.00, 0.05, 0.10) showed single-phase orthorhombic perovskite. The presence of dopants played an important role in the reduction of Fe³⁺ to Fe²⁺ and caused different local distortions in the structure which explained the final black colouration of these pigments in comparison with the red GdFeO₃ sample. The loss of symmetry and the increase in the number of d-d transitions of iron may explain the aforementioned changes. Co-doped pigments reached low C* values, improving on the purest black colour obtained in a commercial black ceramic pigment, which contains toxic elements. In addition to presenting good NIR solar reflectance values of up to 8%, the final colours of these pigments were also stable after their application in a commercial transparent glaze at 1080 °C that could be used for tiles.     

Inverted pyramid Er3+ and Yb3+ Co-doped TiO2 nanorod arrays based perovskite solar cell: Infrared response and improved current density

In this study, a Yb³⁺, Er³⁺ co-doped TiO₂ inverted pyramid nanorod (NR) array and a compact TiO₂ film are simultaneously fabricated as the mesoporous support layer and electron-blocking layer, respectively, by a one-pot hydrothermal method. The scanning electron microscopy results show that the incorporation of Er³⁺ and Yb³⁺ causes changes not only in the growth rate of the NRs, but also in the TiO₂ NR morphology. The Er³⁺, Yb³⁺ co-doped TiO₂ NRs exhibit an inverted pyramidal morphology, which is beneficial for perovskite permeation and light utilization. Notably, the Er³⁺, Yb³⁺ co-doping causes changes in the band gap of TiO₂ and leads to 25% increase in the current density. The electrochemical impedance spectroscopy results show that the device based on the doped TiO₂ NRs has a higher recombination resistance and a lower transfer resistance than those of the undoped device, and thereby, the doped device exhibits a lower electron recombination rate. In addition, the upconversion Er and Yb co-doped device exhibits 25% higher current density and 17% higher photon-to-electron conversion efficiency, as revealed by the J-V test results. Moreover, the optimized efficiency of the TiO₂ NR array-based perovskite solar cell is determined to be 10.02%. Furthermore, the Er and Yb co-doped device exhibits a near-infrared response, an efficiency of 0.1% is achieved under infrared light (800–1100 nm) irradiation. This upconversion material can widen the photovoltaic responses of solar cells into the near-infrared region and improve the utilization of sunlight.     

Experiment and simulation of infrared emissivity properties of doped LaAlO3

In this study, LaAlO₃ doped with Sr/Co/Mn was prepared by sol-gel method, with its infrared (IR) radiative properties and variation mechanism investigated by X-ray powder diffraction, X-ray photoelectron spectroscopy, IR, scanning electron microscopy. Meanwhile, the electronic band structure was simulated by Cambridge Serial Total Energy Package. The conclusions are as follows: the order of emissivity in the near-IR band is La_0.67Sr_0.33Al_0.67Mn_0.33O₃> La_0.67Sr_0.33Al_0.67Co_0.33O₃> LaAl_0.67Mn_0.33O₃> LaAl_0.67Co_0.33O₃> LaAlO₃. In 0–2.5 μm at room temperature, the emissivity of La_0.67Sr_0.33Al_0.67Mn_0.33O₃ can reach 0.9504. The emissivity increase mechanism lies in the further free carrier absorption caused by numerous small polarons formed by the Sr-Mn co-doping and increased concentration of electron-oxygen vacancies. Meanwhile, the Sr-Mn co-doping causes lattice distortion and strengthens the lattice vibration absorption. The band gap of La_0.67Sr_0.33Al_0.67Mn_0.33O₃ is 0.910 eV, much smaller than 3.445 eV of LaAlO₃, favorable to the valence band electron transition, generating more electron-oxygen vacancy pairs and promoting free carrier absorption. La_0.67Sr_0.33Al_0.67Mn_0.33O₃ conduction band migrates to the lower energy region, while Mn3d impurity energy level appears. Thanks to the band gap reduction, dielectric function imaginary peaks, and absorption coefficient peaks are red-shifted. Due to its high emissivity, La_0.67Sr_0.33Al_0.67Mn_0.33O₃ has a high utilization value and broad potential application.     

Effect of doping graphene oxide on the structure and properties of SiO2 based high emissivity coatings

High emissivity coatings have received a great attention due to their energy saving capability for using in spacecraft and industrial furnaces applications. In this study, a feasible spray deposition method was employed to prepare a high emissivity coating on Kovar alloy substrate with porous structure after heat treatment. Graphene oxide was used to dope coating to improve its emissivity. The emissivity enhancement mechanisms of the graphene oxide doped SiO₂ coatings have been investigated. Results show that coating emissivity can be significantly improved (6.41 and 9.64% of coating emissivity at 500 and 800°C, respectively) by doping graphene oxide. Thus, this study proposed a feasible and effective method to prepare high emissivity coatings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48794.     

Preparation and characterization of a greenish yellow lackluster coating with low infrared emissivity based on Prussian blue modified aluminum

Greenish yellow lackluster coatings with low infrared emissivity were prepared by Prussian blue (PB) surface modified Al powders and polyurethanes. The morphology and component of PB/Al powder were characterized by scanning electron microscopy and X-ray diffractometer. The infrared emissivity, surface gloss and visible light color of PB/Al composite coating were investigated by an infrared emissometer, a glossmeter and a colorimeter, respectively. Mechanical properties of PB/Al composite coatings were studied by using adhesion test and impact strength test. The results indicate that PB/Al powder decreases not only the gloss of the coating, but also its emissivity within the wavelength range of 8–14 μm. The composite coatings have good adherence and impact strength at PB/Al content below 50 wt.%, and then the mechanical properties decrease in the PB/Al content range from 50 wt.% to 60 wt.%. By comparing PB/Al composite coating and Al powder tinting coating with the same color and surface gloss, PB/Al composite coating exhibits significant lower infrared emissivity, which is attributed to closer inter-powder distances of metallic fillers and higher electrical conductivity in the coating.     

Sol-gel construction of honeycomb-like CuMn2O4 spinels with high infrared emissivity

Spinel materials are gradually becoming high infrared radiation materials with the most potential because of their special crystal structure. However, it is still difficult to design the microstructure reasonably and synthesize it at low temperature. In this paper, the honeycomb-like CuMn₂O₄ spinels were prepared via a facile sol-gel method with a subsequent low-temperature sintering treatment. Therefore, the CMO samples with numerous pores are conducive to improving absorptivity and emissivity. Moreover, the optimum experimental conditions for high infrared emissivity were acquired by detailed investigation of the synthesis parameters including the molar ratio of trimonium citrate to metal ions, the molar ratio of urea to metal ions and the sintering temperature. Under the synergistic effect of internal factors such as, a suitable amount of impurities, abundant oxygen vacancy, small band gap, and good crystallinity, the obtained sample CMO-800 achieved excellent infrared radiation performance. Its infrared emissivity values at the test temperature of 30 °C and 600 °C separately reached 0.801 and 0.965 in the wavelength range of 3–5 μm. More significantly, this work provides significant guidance for the design and preparation of spinel materials with excellent infrared emissivity.