LaMgAl_(11)O_(19)(LMA),characterized by high melting point,low density and thermal conductivity as well as good infrared emissivity,is regarded as a potential candidate for the thermal protection of hypersonic vehicle...LaMgAl_(11)O_(19)(LMA),characterized by high melting point,low density and thermal conductivity as well as good infrared emissivity,is regarded as a potential candidate for the thermal protection of hypersonic vehicles.Nevertheless,the unsatisfied phase stability at high temperature results in declining of the emissivity below 6μm,which limits the extensive applications of LaMgAl_(11)O_(19).In order to overcome this obstacle,three dense bulk high-entropy ceramics,(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Pr_(0.2))MgAl_(11)O_(19)(HE LMA-1),(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Dy_(0.2))Mg Al_(11)O_(19)(HE LMA-2)and La(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2))Al_(11)O_(19)(HE LMA-3),were designed and successfully prepared through solid state reaction at 1700℃for 4 h in one step.XRD analyses show that the phase compositions of HE LMA-1,HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61%,95.49%and 94.31%,respectively.Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating,while second phase appears in other two samples.The stability of HE LMA-1 is attributed to small average size differenceδ(~4%)of constitute elements.Intriguingly,the average emissivity of HE LMA-1 in the range of 3-6μm reaches 0.9,which is significantly higher than that of LMA and other two HE LMA samples.The emissivity of all samples remains above 0.95 from 6 to 10μm.In the far infrared region(10-14μm),although the emissivity of these specimens decreases slightly,it still exceeds 0.85.The UV-Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band,which enhances the infrared emission of HE LMA-1 below 6μm.In a word,with improved phase stability and thermal emissivity in infrared range,high-entropy REMgAl_(11)O_(19),especially(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Pr_(0.2))MgAl_(11)O_(19)(HE LMA-1),is a promising candidate in thermal protection coatings of hypersonic vehicles.展开更多
NiCr2O4（NCO）spinel composites with different Mn/Ni atomic ratios（Mn/Ni=0.05,0.10,0.15,and 0.20）were synthesized via solid state reaction method.Phase compositions and microstructure of samples were characterized b...NiCr2O4（NCO）spinel composites with different Mn/Ni atomic ratios（Mn/Ni=0.05,0.10,0.15,and 0.20）were synthesized via solid state reaction method.Phase compositions and microstructure of samples were characterized by X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The TG-DSC curves showed that the appropriate baking temperature for Mn-doped NCO spinel preparation was approximately 1 320℃.X-ray diffraction patterns exhibited the formation of NCO spinel with Fd-3m space group.Valence state of the Mn ions was determined from 2p and 3s X-ray photoelectron spectra.Manganese ions were mostly in divalent and trivalent states,and the ratio of Mn^2＋/Mn^3＋was 0.78-0.98.Fourier transform infrared spectroscopy（FTIR）was used to analyze the spectral emissivity of Mn doped NCO spinel.It was revealed that the infrared emissivity of Mn-doped NCO spinel in 1.8-5μm could be significantly enhanced with increasing content of Mn^2＋,reaching as high as 0.9398.Mn-doped NCO spinel showed excellent radiation performance and good prospect in high emissivity applications in the temperature range of 800-1 200℃.展开更多
Transition metal disilicides are widely used as heating elements and infrared emission coatings.However,the limited intrinsic infrared emissivity and high thermal conductivity are the main limitations to their applica...Transition metal disilicides are widely used as heating elements and infrared emission coatings.However,the limited intrinsic infrared emissivity and high thermal conductivity are the main limitations to their applications as infrared emission coatings in the thermal protection system.To cope with these prob-lems,four medium and high-entropy transition metal disilicides,i.e.,(V_(0.25)Ta_(0.25)Mo_(0.25)W_(0.25))Si_(2)(ME-1),(Nb_(0.25)Ta_(0.25)Mo_(0.25)W_(0.25))Si_(2)(ME-2),(V_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-1),and(Cr_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-2),were designed and synthesized by spark plasma sintering method using transition metal binary disilicides as precursors.The introduction of multi-elements into transition metal disilicides not only im-proved the infrared emissivity but also reduced the electrical and thermal conductivity.Among them,(Cr_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-2)had the lowest electrical conductivity of 3789 S cm-1,which is over one order of magnitude lower than that of MoSi_(2)(50000 S cm^(-1)),and total infrared emissivity of 0.42 at room temperature,which is nearly double of that of TaSi_(2).Benefiting from low electrical conductivity and phonon scattering due to lattice distortion,the medium and high-entropy transition metal disilicides also demonstrated a significant decline in thermal conductivity compared to their binary counterparts.Of all samples,HE-2 exhibited the lowest thermal conductivity of 6.4 W m^(−1)K^(−1).The high-entropy tran-sition metal disilicides also present excellent oxidation resistance at high temperatures.The improved infrared emissivity,reduced thermal conductivity,excellent oxidation resistance,and lower densities of these medium and high-entropy transition metal disilicides portend that they are promising as infrared emission coating materials for applications in thermal protection systems.展开更多
Infrared emissivity was studied in Zno.99Mo.olO （M is Mn, Fe or Ni） and Znl_xCoxO （x=0.01, 0.02, 0.03 and 0.04） powders synthesized by solid-state reaction at various temperatures. XRD patterns confirm the wurtzit...Infrared emissivity was studied in Zno.99Mo.olO （M is Mn, Fe or Ni） and Znl_xCoxO （x=0.01, 0.02, 0.03 and 0.04） powders synthesized by solid-state reaction at various temperatures. XRD patterns confirm the wurtzite structure of the prepared samples. No peaks of other phases arising from impurities are detected in Mn- and Co-doped ZnO, hut the peaks of ZnFe204 and NiO are observed in Zno.99Feo.010 and Zno.99Nio.o10. The SEM observations indicate that with larger grain sizes than those of Zn0.99Feo.010 and Zno.99Ni0.010, Co-doped ZnO exhibits smooth grain surfaces. The infrared absorption spectra show that infrared absorptions related to oxygen in Zn0.99M0.010 are much stronger than those in Co-doped ZnO. Co ions are dissolved into the ZnO lattice with Co2＋ state from XPS spectra analysis. The infrared emissivity results imply that the emissivity of Zno.99Ni0.010 is the highest （0.829） and that of Zno.99C00.010 is the lowest （0.784） at 1 200 ℃. The emissivity of Zno.99Co0.010 decreases to the minimum （0.752） at 1 150 ℃ and then increases with growing calcination temperature. As the Co doping content grows, the emissivity of Co-doped ZnO calcined at 1 200 ℃ falls to 0.758 in the molar fraction of 3% and then ascends.展开更多
Sn-doped ZnO particles were successfully synthesized by chemical co-precipitation method.Their morphology,phase,microstructure and infrared emissivity were characterized.The results show that the Sn-doped ZnO particle...Sn-doped ZnO particles were successfully synthesized by chemical co-precipitation method.Their morphology,phase,microstructure and infrared emissivity were characterized.The results show that the Sn-doped ZnO particles are of ellipsoid shape,their crystalline structure changed with thermal process temperature,the optimal thermal process temperature and Sn-doped proportion are 1000℃ and 15%,respectively,the minimum emissivity values are 0.42,0.28,0.46 and 0.48 corresponding to the infrared wavelengths of 0~∞,3~5,8~14 and 14~20 μm,which indicates that the Sn-doped ZnO particles have the application potential as low infrared emissivity material.展开更多
The microwave absorption property and infrared emissivity have been investigated for the single-layer coating made of the epoxy-polyurethane resin and carbonyl iron powders with variation of annealing treatment. Micro...The microwave absorption property and infrared emissivity have been investigated for the single-layer coating made of the epoxy-polyurethane resin and carbonyl iron powders with variation of annealing treatment. Microwave-absorbing property was investigated by measuring the complex permittivity and complex permeability of the absorber in the frequency range from 2 to 18 GHz. Infrared emissivity value was measured using IR-2 Infrared Emissometer in the wavelength range of 8-14 μm. After annealing, the Fe （110） peak became sharp, and the crystallization improved significantly. Annealing treatment could reduce the sttrface energy of powders, improve compatibility between fillers and adhesives, and result in increase of the density of the coating. The lowest value of infrared emissivity （0.419） was obtained from the coating made of the carbonyl iron powder annealed at 700℃ for 1 h. With the variation of the annealing temperature, the magnetic and dielectric properties of the carbonyl iron particle were changed. The maximum reflection loss decreased and the matching frequency shifted to lower frequency with increasing the annealing temperature of carbonyl iron particles, which coincided with the variation of the complex permeability and permittivity according to the annealing temperature. Magnetic loss factor and dielectric loss factor of carbonyl iron particles were improved with increasing the annealing temperature in the 2-18 GHz range.展开更多
A copper coating was deposited by electroless plating on the surfaces of urea-formaldehyde microcap- sules containing paraffin （UFP） particles. This composite microcapsule structure had low infrared OR） emissivity ...A copper coating was deposited by electroless plating on the surfaces of urea-formaldehyde microcap- sules containing paraffin （UFP） particles. This composite microcapsule structure had low infrared OR） emissivity and maintained a constant temperature, and could be used in IR stealth applications. The eiectroless copper layer formation and its micro-appearance, and the effect of the copper layer on the IR emissivity and thermal properties of the composite microcapsules were investigated. The IR emissivity of the composite microcapsules at wavelengths of 1-14 μm gradually decreased with increasing copper mass on the surface. After formation of an integrated copper layer, the rate of IR emissivity decrease was lower. This is because the copper coating improves the surface conductivity of the UFP; a high conductivity results in high reflectivity, which leads to a decrease in IR emissivity. The lowest IR emissivity achieved was 0.68. The phase-change enthalpy of the composite microcapsules decreased with increasing amount of copper coated on the surface because of the high density of copper. When the mass increase of the UFP after electroless copper plating was about 300%, the composite microcapsules had low IR emissivity （about 0.8） and a high phase-change enthalpy （80J/g）.展开更多
Al2O3/SnO2 co-nanoparticles were prepared with a modified sol-gel technique followed by a thermal treatment process. With these co-nanoparticles the grafted collagen-Al2O3/SnO2 nanocomposites were obtained using a sup...Al2O3/SnO2 co-nanoparticles were prepared with a modified sol-gel technique followed by a thermal treatment process. With these co-nanoparticles the grafted collagen-Al2O3/SnO2 nanocomposites were obtained using a supersonic dispersion method. X-ray diffraction, FT-IR analysis, transmission electron microscopy, TGA/DTA and infrared emissivity test were performed to characterize the resulting nanoparticles and nanocomposites, respectively. The Al2O3/SnO2 co-nanoparticles showed a narrow distribution of size between 20-40 nm and could be uniformly absorbed on the tri-helix scaffolds of the grafted collagen without any aggregation. The nanocomposites possessed better thermal stability and substantially lower infrared emissivity than the grafted collagen and Al2O3/SnO2 co-nanoparticles with an increase of degradation temperature from 39 to 210 ℃ and a decrease of infrared emissivity from 0.850 of the grafted collagen and 0.708 of the Al2O3/SnO2 co-nanoparticles to 0.424, which provided a potential application of the nanocomposites to areas such as photoelectronics.展开更多
A thin radar-infrared stealth-compatible structure with reflectivity below -10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8μm-14 μm is reported. The designed st...A thin radar-infrared stealth-compatible structure with reflectivity below -10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8μm-14 μm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface （MFSS）, resistive frequency selective surface （RFSS）, and metal backing from the top down, and it is only 2. l-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.展开更多
A kind of far infrared radiation ceramics was prepared by using silicate minerals, calcium carbonate and silicon dioxide as main raw materials, and cerium nitrate as additive. The structure of the ceramics and far inf...A kind of far infrared radiation ceramics was prepared by using silicate minerals, calcium carbonate and silicon dioxide as main raw materials, and cerium nitrate as additive. The structure of the ceramics and far infrared radiation properties on the surface tension of water were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and a tensiometer, respectively. It was showed that, after being sintered at 1160 ℃, the solid solution was formed by CeO2 and Fe2O3, thus the crystal parameters （c/a axis ratio） and interplanar spacing of Fe2O3 increased. The addition of cerium was regarded to improve the far infrared radiation of ceramics, and the maximum emissivity value in the range of 5-20 μm was 0.94. The surface tension of water gradually decreased with increasing radiation time.展开更多
Lightweight infrared stealth and absorption-dominant electromagnetic interference(EMI)shielding materials are highly desirable in areas of aerospace,weapons,military and wearable electronics.Herein,lightweight and hig...Lightweight infrared stealth and absorption-dominant electromagnetic interference(EMI)shielding materials are highly desirable in areas of aerospace,weapons,military and wearable electronics.Herein,lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO_(2)(SC-CO_(2))foaming combined with hydrogen bonding assembly and compression molding strategy.The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity,and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures.Particularly,the segregated nanocomposite foams present a large radiation temperature reduction of 70.2℃ at the object temperature of 100℃,and a significantly improved EM wave absorptivity/reflectivity(A/R)ratio of 2.15 at an ultralow Ti_(3)C_(2)T_(x) content of 1.7 vol%.Moreover,the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles.The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace,weapons,military and wearable electronics.展开更多
Platinum films were sputter-deposited on two groups of nickel alloy substrates, in which the first group was the samples with rough surface, and the other group with polished surface. The platinum thin-films were appl...Platinum films were sputter-deposited on two groups of nickel alloy substrates, in which the first group was the samples with rough surface, and the other group with polished surface. The platinum thin-films were applied to serve as the low-emissivity layers to reflect thermal radiation. Then, the platinum-coated samples were heated in air at 600 ℃ for 200 h to explore the effect of high-temperature environment on the emissivity of coated platinum film. After annealing, the average IR emissivity （at the wavelength of 3-14 μm） of the platinum film was only about 0.1 for polished sample and 0.45 for rough sample. The diffusion between platinum and the nickelalloy elements at 600 ℃ had been also discussed.展开更多
Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were i...Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were investigated. The structure and surface morphologies of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The UV-Vis absorption and infrared emissivities were investigated by a UV-Vis spectrophotometer and an infrared emissometer, respectively. XRD patterns confirm the wurtzite structure of the as prepared samples with single phase. Smooth grain surfaces are detected in all doped ZnO samples, while ZnO:Li and ZnO:Na present the aggregation of grains. The redshifts in the optical band-gap are observed in K-, Na-, and Li-doped ZnO with the values 3.150, 3.144, and 3.142 eV. Due to better crystalline quality, ZnO:K shows a lower emissivity than others. The emissivity of K-doped ZnO decreases to the minimum value(0.804), at 1200 °C and holding 2 h. Compared with KNO3 as K source, K2CO3 doped ZnO has lower emissivities.展开更多
Infrared emissivities of Zn0.99-xMn0.01CoxO （x = 0.00, 0.01, 0.03, 0.05） powders synthesized at different calcination temperatures by solid-state reaction are investigated. Their phases, morphologies, UV absorption ...Infrared emissivities of Zn0.99-xMn0.01CoxO （x = 0.00, 0.01, 0.03, 0.05） powders synthesized at different calcination temperatures by solid-state reaction are investigated. Their phases, morphologies, UV absorption spectra, and infrared emissivities are studied by XRD, SEM, UV spectrophotometer, and an IR-2 dual-band infrared emissometer in a range of 8 μm-14 μm. Doped ZnO still has a wurtzite structure, and no peaks of other phases originating from impurities are detected. The optical band-gap decreases as the Co content and calcination temperature ascend, and of which the smallest optical band gap is 2.19 eV. The lowest infrared emissivity, 0.754, is observed in Zn0.98Mn0.01Co0.01O with the increase in Co concentration. The infrared emissivity experiences fluctuations as the calcination temperature increases, and its minimum value is 0.762 at 1100 ℃.展开更多
The stoichiometric vanadium（IV） oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 n...The stoichiometric vanadium（IV） oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 ℃ for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.展开更多
Unidentified Infrared emission bands (UIBs) are infrared discrete emissions from circumstellar regions, interstellar media (ISM), star-forming regions, and extragalactic objects for which the identity of the emitting ...Unidentified Infrared emission bands (UIBs) are infrared discrete emissions from circumstellar regions, interstellar media (ISM), star-forming regions, and extragalactic objects for which the identity of the emitting materials is unknown. The main infrared features occur around peaks at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with the photon’s rest energy at the peaks 0.376, 0.200, 0.161, 0.144, 0.111, and 0.098 eV, respectively. The UIB emission phenomenon has been studied for about forty five years. The prevailing hypothesis is that the materials responsible for UIB are polycyclic aromatic hydrocarbon (PAH) molecules. PAHs are thought to be one of the main forms in which carbon exists in space. And yet, not a single member of this group of compounds had been identified in space definitively until now [1]. In frames of Hypersphere World-Universe Model (WUM), we introduced Dark Matter (DM) particles, named DIONs, with the rest energy 0.199 eV and an energy density of 68.8% of the total energy density of the World. DIONs compose Outer shells of DM Supercluster’s Cores—the main objects of the World [2]. In this paper, we give an explanation of UIB emission based on the self-annihilation of DM particles DIONs and biDIONs (DIONs pairs) with a rest energy about 0.38 eV that depends on the binding energy. To the best of our knowledge, WUM is the only cosmological model in existence that is consistent with UIB emission phenomenon.展开更多
Nowadays,it is a great challenge to reduce energy consumption and exhaust emission for human activities,in particular,high temperature industries.Among many efforts made to realize energy savings for high temperature ...Nowadays,it is a great challenge to reduce energy consumption and exhaust emission for human activities,in particular,high temperature industries.Among many efforts made to realize energy savings for high temperature furnaces and kilns,the use of high emissivity materials is considered to be an effective route to increase their thermal efficiency by enhancing heat transfer.Most materials with high refractoriness and superior chemical stability have weak infrared absorption and radiation properties;however,their emissivity in infrared regions（1 —25 μm） could be effectively increased by ion doping.This is attributed to three main mechanisms：1） distortion of the crystal lattice;2） increase of free carrier absorption; 3） formation of impurity energy level.In this paper,the development and advancement of various material systems with high emissivity including non-oxides and oxide based ceramics were reviewed.It is also suggested that the establishment of evaluation models or instruments for energy savings would be beneficial to design and application of high emissivity materials in various high-temperature environment.Furthermore,more efforts should be made on durability of high emissivity materials at high service temperatures and on the standardization of testing methods for emissivity.展开更多
1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of glo...1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of global energy expenditure[1,2],necessitating urgent development of sustainable cooling alter-natives.Radiative cooling emerges as a passive thermal regu-lation strategy,operating without external energy input via direct infrared emission from materials to the environment[3].展开更多
To adapt to the complex environment where low infrared emissivity and high infrared emissivity coexist,a radar stealth-infrared camouflage compatibility metasurface requires meta-atoms with customized infrared emissiv...To adapt to the complex environment where low infrared emissivity and high infrared emissivity coexist,a radar stealth-infrared camouflage compatibility metasurface requires meta-atoms with customized infrared emissivity.Generally,the infrared emissivity is determined by the occupation ratio.However,the high occupation ratio will interfere with the scattering reduction function due to the Lorentz resonance from the metal patch.To address the problem,a method for decoupling Lorentz resonance is proposed in this paper.By shifting the resonant frequency of the metal patch to a high frequency,the Lorentz resonance is suppressed in the frequency band of scattering reduction.To verify the method,a single functional layer metasurface with microwave scattering reduction and customized infrared emissivity is designed.The scattering reduction at 3.5–5.5 GHz is realized through the polarization conversion.Meanwhile,the infrared emissivity of the metasurface can be gradient-designed by changing the occupation ratios of the meta-atoms.Compared with the initial design,the improved metasurface expands the infrared emissivity range from 0.60–0.80 to 0.51–0.80,and the scattering reduction effect remains unchanged.The experimental results agree with the simulated results.The work enriches the infrared emissivity function,which can be applied to camouflage in complex spectrum backgrounds.展开更多
This paper reports that indium tin oxide （ITO） crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, ...This paper reports that indium tin oxide （ITO） crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, microstructure, infrared emissivity c and powder resistivity of indium tin oxides by means of x-ray diffraction, Fourier transform infrared, and transmission electron microscope. The optimum sintering temperature of 1350℃ and Sn doping content 6～8wt% are determined. The application of ITO in the military camouflage field is proposed.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.51772027 and 51972089。
文摘LaMgAl_(11)O_(19)(LMA),characterized by high melting point,low density and thermal conductivity as well as good infrared emissivity,is regarded as a potential candidate for the thermal protection of hypersonic vehicles.Nevertheless,the unsatisfied phase stability at high temperature results in declining of the emissivity below 6μm,which limits the extensive applications of LaMgAl_(11)O_(19).In order to overcome this obstacle,three dense bulk high-entropy ceramics,(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Pr_(0.2))MgAl_(11)O_(19)(HE LMA-1),(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Dy_(0.2))Mg Al_(11)O_(19)(HE LMA-2)and La(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2))Al_(11)O_(19)(HE LMA-3),were designed and successfully prepared through solid state reaction at 1700℃for 4 h in one step.XRD analyses show that the phase compositions of HE LMA-1,HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61%,95.49%and 94.31%,respectively.Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating,while second phase appears in other two samples.The stability of HE LMA-1 is attributed to small average size differenceδ(~4%)of constitute elements.Intriguingly,the average emissivity of HE LMA-1 in the range of 3-6μm reaches 0.9,which is significantly higher than that of LMA and other two HE LMA samples.The emissivity of all samples remains above 0.95 from 6 to 10μm.In the far infrared region(10-14μm),although the emissivity of these specimens decreases slightly,it still exceeds 0.85.The UV-Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band,which enhances the infrared emission of HE LMA-1 below 6μm.In a word,with improved phase stability and thermal emissivity in infrared range,high-entropy REMgAl_(11)O_(19),especially(La_(0.2)Nd_(0.2)Gd_(0.2)Sm_(0.2)Pr_(0.2))MgAl_(11)O_(19)(HE LMA-1),is a promising candidate in thermal protection coatings of hypersonic vehicles.
基金Funded by the Scientific and Technological Research Projects for Education Department of Hubei Province(Q20161407)
文摘NiCr2O4（NCO）spinel composites with different Mn/Ni atomic ratios（Mn/Ni=0.05,0.10,0.15,and 0.20）were synthesized via solid state reaction method.Phase compositions and microstructure of samples were characterized by X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The TG-DSC curves showed that the appropriate baking temperature for Mn-doped NCO spinel preparation was approximately 1 320℃.X-ray diffraction patterns exhibited the formation of NCO spinel with Fd-3m space group.Valence state of the Mn ions was determined from 2p and 3s X-ray photoelectron spectra.Manganese ions were mostly in divalent and trivalent states,and the ratio of Mn^2＋/Mn^3＋was 0.78-0.98.Fourier transform infrared spectroscopy（FTIR）was used to analyze the spectral emissivity of Mn doped NCO spinel.It was revealed that the infrared emissivity of Mn-doped NCO spinel in 1.8-5μm could be significantly enhanced with increasing content of Mn^2＋,reaching as high as 0.9398.Mn-doped NCO spinel showed excellent radiation performance and good prospect in high emissivity applications in the temperature range of 800-1 200℃.
基金This work was financially supported by the National Natu-ral Science Foundation of China(Nos.51972082,51972089,and 52172041)the Key Program of National Natural Science Foun-dation of China(No.52032003).
文摘Transition metal disilicides are widely used as heating elements and infrared emission coatings.However,the limited intrinsic infrared emissivity and high thermal conductivity are the main limitations to their applications as infrared emission coatings in the thermal protection system.To cope with these prob-lems,four medium and high-entropy transition metal disilicides,i.e.,(V_(0.25)Ta_(0.25)Mo_(0.25)W_(0.25))Si_(2)(ME-1),(Nb_(0.25)Ta_(0.25)Mo_(0.25)W_(0.25))Si_(2)(ME-2),(V_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-1),and(Cr_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-2),were designed and synthesized by spark plasma sintering method using transition metal binary disilicides as precursors.The introduction of multi-elements into transition metal disilicides not only im-proved the infrared emissivity but also reduced the electrical and thermal conductivity.Among them,(Cr_(0.2)Nb_(0.2)Ta_(0.2)Mo_(0.2)W_(0.2))Si_(2)(HE-2)had the lowest electrical conductivity of 3789 S cm-1,which is over one order of magnitude lower than that of MoSi_(2)(50000 S cm^(-1)),and total infrared emissivity of 0.42 at room temperature,which is nearly double of that of TaSi_(2).Benefiting from low electrical conductivity and phonon scattering due to lattice distortion,the medium and high-entropy transition metal disilicides also demonstrated a significant decline in thermal conductivity compared to their binary counterparts.Of all samples,HE-2 exhibited the lowest thermal conductivity of 6.4 W m^(−1)K^(−1).The high-entropy tran-sition metal disilicides also present excellent oxidation resistance at high temperatures.The improved infrared emissivity,reduced thermal conductivity,excellent oxidation resistance,and lower densities of these medium and high-entropy transition metal disilicides portend that they are promising as infrared emission coating materials for applications in thermal protection systems.
基金Project(2009K06_03) supported by the Scientific and Technological Program of Shaanxi Province,China
文摘Infrared emissivity was studied in Zno.99Mo.olO （M is Mn, Fe or Ni） and Znl_xCoxO （x=0.01, 0.02, 0.03 and 0.04） powders synthesized by solid-state reaction at various temperatures. XRD patterns confirm the wurtzite structure of the prepared samples. No peaks of other phases arising from impurities are detected in Mn- and Co-doped ZnO, hut the peaks of ZnFe204 and NiO are observed in Zno.99Feo.010 and Zno.99Nio.o10. The SEM observations indicate that with larger grain sizes than those of Zn0.99Feo.010 and Zno.99Ni0.010, Co-doped ZnO exhibits smooth grain surfaces. The infrared absorption spectra show that infrared absorptions related to oxygen in Zn0.99M0.010 are much stronger than those in Co-doped ZnO. Co ions are dissolved into the ZnO lattice with Co2＋ state from XPS spectra analysis. The infrared emissivity results imply that the emissivity of Zno.99Ni0.010 is the highest （0.829） and that of Zno.99C00.010 is the lowest （0.784） at 1 200 ℃. The emissivity of Zno.99Co0.010 decreases to the minimum （0.752） at 1 150 ℃ and then increases with growing calcination temperature. As the Co doping content grows, the emissivity of Co-doped ZnO calcined at 1 200 ℃ falls to 0.758 in the molar fraction of 3% and then ascends.
文摘Sn-doped ZnO particles were successfully synthesized by chemical co-precipitation method.Their morphology,phase,microstructure and infrared emissivity were characterized.The results show that the Sn-doped ZnO particles are of ellipsoid shape,their crystalline structure changed with thermal process temperature,the optimal thermal process temperature and Sn-doped proportion are 1000℃ and 15%,respectively,the minimum emissivity values are 0.42,0.28,0.46 and 0.48 corresponding to the infrared wavelengths of 0~∞,3~5,8~14 and 14~20 μm,which indicates that the Sn-doped ZnO particles have the application potential as low infrared emissivity material.
基金supported by the National Natural Science Foundation of China (Grant No. 90505008)the Weaponry Equipment Preresearch Foundation of China (Grant No. 51410040305HK0214)
文摘The microwave absorption property and infrared emissivity have been investigated for the single-layer coating made of the epoxy-polyurethane resin and carbonyl iron powders with variation of annealing treatment. Microwave-absorbing property was investigated by measuring the complex permittivity and complex permeability of the absorber in the frequency range from 2 to 18 GHz. Infrared emissivity value was measured using IR-2 Infrared Emissometer in the wavelength range of 8-14 μm. After annealing, the Fe （110） peak became sharp, and the crystallization improved significantly. Annealing treatment could reduce the sttrface energy of powders, improve compatibility between fillers and adhesives, and result in increase of the density of the coating. The lowest value of infrared emissivity （0.419） was obtained from the coating made of the carbonyl iron powder annealed at 700℃ for 1 h. With the variation of the annealing temperature, the magnetic and dielectric properties of the carbonyl iron particle were changed. The maximum reflection loss decreased and the matching frequency shifted to lower frequency with increasing the annealing temperature of carbonyl iron particles, which coincided with the variation of the complex permeability and permittivity according to the annealing temperature. Magnetic loss factor and dielectric loss factor of carbonyl iron particles were improved with increasing the annealing temperature in the 2-18 GHz range.
文摘A copper coating was deposited by electroless plating on the surfaces of urea-formaldehyde microcap- sules containing paraffin （UFP） particles. This composite microcapsule structure had low infrared OR） emissivity and maintained a constant temperature, and could be used in IR stealth applications. The eiectroless copper layer formation and its micro-appearance, and the effect of the copper layer on the IR emissivity and thermal properties of the composite microcapsules were investigated. The IR emissivity of the composite microcapsules at wavelengths of 1-14 μm gradually decreased with increasing copper mass on the surface. After formation of an integrated copper layer, the rate of IR emissivity decrease was lower. This is because the copper coating improves the surface conductivity of the UFP; a high conductivity results in high reflectivity, which leads to a decrease in IR emissivity. The lowest IR emissivity achieved was 0.68. The phase-change enthalpy of the composite microcapsules decreased with increasing amount of copper coated on the surface because of the high density of copper. When the mass increase of the UFP after electroless copper plating was about 300%, the composite microcapsules had low IR emissivity （about 0.8） and a high phase-change enthalpy （80J/g）.
基金Project supported by the National Natural Science Foundation of China for Distinguished Young Scholar （No. 20325518）, Creative Research Groups （No. 20521503） and a key program （No. 20535010） to JHX, the Program for New Century Excellent Talents in Universities of Education Ministry of China to ZYM （No. NCET-04-0482）, and the Postdoctoral Foundation of China to CY （No. 2005038234）.
文摘Al2O3/SnO2 co-nanoparticles were prepared with a modified sol-gel technique followed by a thermal treatment process. With these co-nanoparticles the grafted collagen-Al2O3/SnO2 nanocomposites were obtained using a supersonic dispersion method. X-ray diffraction, FT-IR analysis, transmission electron microscopy, TGA/DTA and infrared emissivity test were performed to characterize the resulting nanoparticles and nanocomposites, respectively. The Al2O3/SnO2 co-nanoparticles showed a narrow distribution of size between 20-40 nm and could be uniformly absorbed on the tri-helix scaffolds of the grafted collagen without any aggregation. The nanocomposites possessed better thermal stability and substantially lower infrared emissivity than the grafted collagen and Al2O3/SnO2 co-nanoparticles with an increase of degradation temperature from 39 to 210 ℃ and a decrease of infrared emissivity from 0.850 of the grafted collagen and 0.708 of the Al2O3/SnO2 co-nanoparticles to 0.424, which provided a potential application of the nanocomposites to areas such as photoelectronics.
基金Project supported by the National Natural Science Foundation of China (Grant No.51202291)
文摘A thin radar-infrared stealth-compatible structure with reflectivity below -10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8μm-14 μm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface （MFSS）, resistive frequency selective surface （RFSS）, and metal backing from the top down, and it is only 2. l-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.
基金Project supported by the National Key Technology R&D Program(2011BAE30B04)University Innovation Team Leader Training Program in Hebei Province(LJRC020)
文摘A kind of far infrared radiation ceramics was prepared by using silicate minerals, calcium carbonate and silicon dioxide as main raw materials, and cerium nitrate as additive. The structure of the ceramics and far infrared radiation properties on the surface tension of water were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and a tensiometer, respectively. It was showed that, after being sintered at 1160 ℃, the solid solution was formed by CeO2 and Fe2O3, thus the crystal parameters （c/a axis ratio） and interplanar spacing of Fe2O3 increased. The addition of cerium was regarded to improve the far infrared radiation of ceramics, and the maximum emissivity value in the range of 5-20 μm was 0.94. The surface tension of water gradually decreased with increasing radiation time.
基金the National Natural Science Foundation of China (52273083, 51903145)Key Research and Development Project of Shaanxi Province (2023-YBGY-476)+1 种基金Natural Science Foundation of Chongqing,China (CSTB2023NSCQ-MSX0691)National College Students Innovation and Entrepreneurship Training Program (202310699172)
文摘Lightweight infrared stealth and absorption-dominant electromagnetic interference(EMI)shielding materials are highly desirable in areas of aerospace,weapons,military and wearable electronics.Herein,lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO_(2)(SC-CO_(2))foaming combined with hydrogen bonding assembly and compression molding strategy.The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity,and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures.Particularly,the segregated nanocomposite foams present a large radiation temperature reduction of 70.2℃ at the object temperature of 100℃,and a significantly improved EM wave absorptivity/reflectivity(A/R)ratio of 2.15 at an ultralow Ti_(3)C_(2)T_(x) content of 1.7 vol%.Moreover,the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles.The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace,weapons,military and wearable electronics.
基金supported by the fund of the State Key Laboratory of Solidification Processing in NWPU, NoKP200901
文摘Platinum films were sputter-deposited on two groups of nickel alloy substrates, in which the first group was the samples with rough surface, and the other group with polished surface. The platinum thin-films were applied to serve as the low-emissivity layers to reflect thermal radiation. Then, the platinum-coated samples were heated in air at 600 ℃ for 200 h to explore the effect of high-temperature environment on the emissivity of coated platinum film. After annealing, the average IR emissivity （at the wavelength of 3-14 μm） of the platinum film was only about 0.1 for polished sample and 0.45 for rough sample. The diffusion between platinum and the nickelalloy elements at 600 ℃ had been also discussed.
基金Project(JB141405)supported by the Fundamental Research Funds for the Central Universities of China
文摘Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were investigated. The structure and surface morphologies of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The UV-Vis absorption and infrared emissivities were investigated by a UV-Vis spectrophotometer and an infrared emissometer, respectively. XRD patterns confirm the wurtzite structure of the as prepared samples with single phase. Smooth grain surfaces are detected in all doped ZnO samples, while ZnO:Li and ZnO:Na present the aggregation of grains. The redshifts in the optical band-gap are observed in K-, Na-, and Li-doped ZnO with the values 3.150, 3.144, and 3.142 eV. Due to better crystalline quality, ZnO:K shows a lower emissivity than others. The emissivity of K-doped ZnO decreases to the minimum value(0.804), at 1200 °C and holding 2 h. Compared with KNO3 as K source, K2CO3 doped ZnO has lower emissivities.
文摘Infrared emissivities of Zn0.99-xMn0.01CoxO （x = 0.00, 0.01, 0.03, 0.05） powders synthesized at different calcination temperatures by solid-state reaction are investigated. Their phases, morphologies, UV absorption spectra, and infrared emissivities are studied by XRD, SEM, UV spectrophotometer, and an IR-2 dual-band infrared emissometer in a range of 8 μm-14 μm. Doped ZnO still has a wurtzite structure, and no peaks of other phases originating from impurities are detected. The optical band-gap decreases as the Co content and calcination temperature ascend, and of which the smallest optical band gap is 2.19 eV. The lowest infrared emissivity, 0.754, is observed in Zn0.98Mn0.01Co0.01O with the increase in Co concentration. The infrared emissivity experiences fluctuations as the calcination temperature increases, and its minimum value is 0.762 at 1100 ℃.
文摘The stoichiometric vanadium（IV） oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 ℃ for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.
文摘Unidentified Infrared emission bands (UIBs) are infrared discrete emissions from circumstellar regions, interstellar media (ISM), star-forming regions, and extragalactic objects for which the identity of the emitting materials is unknown. The main infrared features occur around peaks at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with the photon’s rest energy at the peaks 0.376, 0.200, 0.161, 0.144, 0.111, and 0.098 eV, respectively. The UIB emission phenomenon has been studied for about forty five years. The prevailing hypothesis is that the materials responsible for UIB are polycyclic aromatic hydrocarbon (PAH) molecules. PAHs are thought to be one of the main forms in which carbon exists in space. And yet, not a single member of this group of compounds had been identified in space definitively until now [1]. In frames of Hypersphere World-Universe Model (WUM), we introduced Dark Matter (DM) particles, named DIONs, with the rest energy 0.199 eV and an energy density of 68.8% of the total energy density of the World. DIONs compose Outer shells of DM Supercluster’s Cores—the main objects of the World [2]. In this paper, we give an explanation of UIB emission based on the self-annihilation of DM particles DIONs and biDIONs (DIONs pairs) with a rest energy about 0.38 eV that depends on the binding energy. To the best of our knowledge, WUM is the only cosmological model in existence that is consistent with UIB emission phenomenon.
基金Natural Science Foundation of China ( NSFC,Grant no. 51372255 )Beijing Natural Science Foundation ( BNSF,Grant no. 2131006 )+2 种基金International Science and Technology Cooperation Program of China ( Grant no. 2014DFR51010)External Cooperation Program of Chinese Academy of Sciences ( Grant no. GJHZ201310 )Open Foundation of State Key Laboratory of Advanced Refractories ( Grant no. 201401,Sinosteel Luoyang Institute of Refractories Research Co. ,Ltd. ) for the financial support
文摘Nowadays,it is a great challenge to reduce energy consumption and exhaust emission for human activities,in particular,high temperature industries.Among many efforts made to realize energy savings for high temperature furnaces and kilns,the use of high emissivity materials is considered to be an effective route to increase their thermal efficiency by enhancing heat transfer.Most materials with high refractoriness and superior chemical stability have weak infrared absorption and radiation properties;however,their emissivity in infrared regions（1 —25 μm） could be effectively increased by ion doping.This is attributed to three main mechanisms：1） distortion of the crystal lattice;2） increase of free carrier absorption; 3） formation of impurity energy level.In this paper,the development and advancement of various material systems with high emissivity including non-oxides and oxide based ceramics were reviewed.It is also suggested that the establishment of evaluation models or instruments for energy savings would be beneficial to design and application of high emissivity materials in various high-temperature environment.Furthermore,more efforts should be made on durability of high emissivity materials at high service temperatures and on the standardization of testing methods for emissivity.
基金the financial support from the National Key R&D Program of China(No.2020YFA0711500)the National Natural Science Foundation of China(Nos.52473215 and 52273248).
文摘1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of global energy expenditure[1,2],necessitating urgent development of sustainable cooling alter-natives.Radiative cooling emerges as a passive thermal regu-lation strategy,operating without external energy input via direct infrared emission from materials to the environment[3].
基金National Key Research and Development Program of China(2022YFB3806200)Natural Science Foundation of Shaanxi Province(2024JC-YBMS-504,2024JC-YBQN-0617)+1 种基金China Postdoctoral Science Foundation(2023M744291)Key Scientific and Technological Innovation Team of Shaanxi Province(2023-CX-TD-48)。
文摘To adapt to the complex environment where low infrared emissivity and high infrared emissivity coexist,a radar stealth-infrared camouflage compatibility metasurface requires meta-atoms with customized infrared emissivity.Generally,the infrared emissivity is determined by the occupation ratio.However,the high occupation ratio will interfere with the scattering reduction function due to the Lorentz resonance from the metal patch.To address the problem,a method for decoupling Lorentz resonance is proposed in this paper.By shifting the resonant frequency of the metal patch to a high frequency,the Lorentz resonance is suppressed in the frequency band of scattering reduction.To verify the method,a single functional layer metasurface with microwave scattering reduction and customized infrared emissivity is designed.The scattering reduction at 3.5–5.5 GHz is realized through the polarization conversion.Meanwhile,the infrared emissivity of the metasurface can be gradient-designed by changing the occupation ratios of the meta-atoms.Compared with the initial design,the improved metasurface expands the infrared emissivity range from 0.60–0.80 to 0.51–0.80,and the scattering reduction effect remains unchanged.The experimental results agree with the simulated results.The work enriches the infrared emissivity function,which can be applied to camouflage in complex spectrum backgrounds.
文摘This paper reports that indium tin oxide （ITO） crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, microstructure, infrared emissivity c and powder resistivity of indium tin oxides by means of x-ray diffraction, Fourier transform infrared, and transmission electron microscope. The optimum sintering temperature of 1350℃ and Sn doping content 6～8wt% are determined. The application of ITO in the military camouflage field is proposed.
