Near-infrared Reflective Pigments Research Articles

Effects of NIR-reflective pigments on waterborne polyurethane coatings and their thermal insulation performance

Waterborne coatings have garnered much attention and gradually occupied the coating market recently due to the significant advantages in volatile organic compound emissions compared with solvent-borne coatings. Waterborne polyurethane coatings are a majority portion of waterborne coatings. Unlike solvent-borne coatings, the film formation of waterborne coatings occurs in an inhomogeneous phase, which brings a challenge for pigmentation in waterborne coatings. However, the influence of pigment on film formation and the property of waterborne polyurethane coating remain unclear. In this study, the different contents of commercial black near-infrared (NIR) reflective pigments were incorporated into both commercial and synthetic waterborne polyurethane systems. The film formation process was monitored by multispeckle diffusing wave spectroscopy. The impact of the pigment content on dry films was assessed through scanning electron microscope, color and gloss measurements, dynamical thermal analyzer, and tensile testing. Furthermore, the thermal insulation performance of the waterborne polyurethane coatings was evaluated to study the function of the NIR reflective pigments. Our findings reveal that the addition of black NIR reflective pigments yields a multifaceted effect on film formation and coating morphology and improves thermal insulating property. Elevated pigment content correlated with increased crosslinking density, tensile stress, and Young's modulus.

Low-temperature synthesis of bismuth and vanadium substituted LaPO4 near-infrared reflective pigment and its aging resistance nature on PMMA

Low-temperature synthesis of bismuth and vanadium substituted LaPO4 near-infrared reflective pigment and its aging resistance nature on PMMA

A black pigment that shows strong near-infrared reflectivity for solar heat control

Solar thermal energy regulation is important for sustainable development, comfortable housing, and living. Black compounds are usually considered as an absorber of solar heat. This work reports a series of black near-infrared reflective pigments, Ca2-yMgyMn(1)1-xMn(2)xO4 (x = 0–1, y = 0–0.5), which show strong near-infrared (NIR) reflectivity. Comprehensive analyses were carried out to characterize the obtained pigments including X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and UV–Vis–NIR spectrophotometry. Through the substitution of MnO2 with Mn2O3, NIR solar reflectance of the black pigment can be enhanced by 13%, which might be mainly attributed to differences in particle size and lattice parameters. Meanwhile, through Mg doping, the obtained pigment Ca1.8Mg0.2MnO4 shows excellent color performances (L* = 43, a* = 0.36, b* = −0.37) and NIR solar reflectance (R*, ∼60%). EnergyPlus simulation results show that for a warm city (Haikou), using the Ca1.8Mg0.2MnO4 coating (L* = 25, R* = 51%) can reduce annual cooling energy consumption by 21%.

Cu doped YInO3-ZnO green colored NIR reflective pigments: Synthesis and application in PMMA based cool-roof coatings

A series of Cu modified YInO3-ZnO green colored NIR reflective pigments was synthesized by sol-gel route. The dried gel precursor was calcined at different temperatures for 2 h (550 °C, 650 °C, 750 °C, 800 °C, and 850 °C), observing the formation of greenish pigments. The calcined pigments were characterized by thermogravimetry (TGA), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD) to investigate the physio-chemical and structural properties. The synthesized pigments showed near-infrared (NIR) reflectance ability and a green color attributed to the formation of Cu-substituted cubic and hexagonal YInO3 structures. The pigments were embedded in PMMA based to assess their potential to develop cool roofs coatings. The pigments demonstrated slightly reduced NIR reflectance when embedded in the polymeric paste. The thermal properties were assessed by exposing the coatings under a xenon arc lamp to measure the heating up of the coatings containing the various pigments.

Codoping Ti in low Co-containing hibonite achieving excellent optical properties for near-infrared reflective pigment applications

To reduce carcinogenic cobalt content in pigments, a series of near-infrared reflective pigments based on CaAl12-x-yCoxTiyO19 (x = 0–0.5 and y = 0-(x+0.3)) were prepared via solid state reactions. Although the cobalt content in the pigment CaAl11.7Co0.1Ti0.2O19 is only 0.87% by mass, the resulting pigment still has excellent color properties (64.89, 3.88, −40.30) and near-infrared reflectance (∼70%). The structural information of the obtained pigments were analyzed by XRD refinement, and the results revealed that the doping concentration of titanium relative to cobalt significantly affected the coordination structure of cobalt in hibonite, which in turn apparently influenced the optical properties of the obtained samples. The actual cooling effect of the CaAl11.7Co0.1Ti0.2O19 coating was tested using a model house and the annual energy consumption was simulated by using EnergyPlus software. For a warm city (Haikou), using this CaAl11.7Co0.1Ti0.2O19 coating can reduce energy consumption for cooling by 24.75%.

Synthesis and characterization of a new high near-infrared reflectance yellow pigment: Bi2-xErxMoO6

A series of environmentally friendly near-infrared reflective pigments Bi2-xErxMoO6 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized by high temperature solid-state method. The optical and structural characteristics of the synthesized pigment were characterized by ultraviolet–visible–near infrared diffuse reflection spectrum (UV–Vis–NIR spectrum), X-ray diffractometer (XRD), scanning electron microscopy (SEM). The color of the samples changed from milky white to yellow with increasing Er3+ doping concentration. Importantly, the Er3+-doped Bi2MoO6 pigments exhibit high NIR reflectance (ranging from 90.5% to 106.1%) in 700–2500 nm region and which is higher than the NIR reflectance of commercially available bismuth vanadate pigment (80%). Compared with BaSO4, Bi2-0.6Er0.6MoO6 exhibits 106.1% NIR reflectance and 99.6% NIR solar reflectance. The thermal insulation experiments show that the bottom temperature of the aluminum plate coated with Bi2MoO6: Er coating decreases by 3 °C compared with that of the TiO2 coating. Meanwhile, acid and alkali resistance tests show that these pigments may have a well chemically stable in the natural environment. We believe that the samples may have important applications in antisolar irradiation, energy saving and environmental protection.

Development and performance evaluation of cool black surface on thermoplastic polyolefins via incorporation of non‐near infrared absorptive pigments

Absorption of the near-infrared (NIR) region of solar irradiance spectrum of the sunlight causes increase of the temperature of black inner parts of vehicles. The surface temperature of these parts can be decreased by reflecting or transmitting the NIR region of sunlight. This study intends to decrease the temperature of black surfaces that are exposed to sunlight and create cool black surfaces by preventing the absorption of the NIR region of the solar irradiance spectrum. Incorporation of cool black pigments having NIR reflective or NIR transparent properties into thermoplastic olefins (TPOs) was studied. A series of compounds were generated containing only NIR reflective pigment (REF), only NIR transparent pigment (TRANS) and the mixture of these two pigments in specific loading levels. The surface temperature of black TPO compounds were compared to the TPO compounds containing conventional pigments. Results showed that an optimum TPO compound having cool black surface was obtained with the sample MIX-5 (2% REF + 0.4% TRANS) which demonstrated 28.2% cooling compared to samples with carbon black, 9.04 MPa tensile strength, 1200% elongation at break and mold shrinkage values of 0.61% and 0.11% at directions parallel and perpendicular to flow respectively.

Solution combustion synthesis of gray-blue Mn-doped YBO3 pigments with high NIR reflectance for energy-saving buildings

High near-infrared (NIR) reflective pigments have broad application prospects in alleviating urban heat island effect. But in fact, an easy and efficient method of preparing non-toxic and high near-infrared reflective pigments remains a desired choice for energy-saving coatings. In this research, several Mn doped YBO3 pigments, possessing gray-blue and high near-infrared reflectance, were effectively prepared by solution combustion method. Relevant techniques were used to characterize the crystalline structure, morphology feature, optical properties, chemical tolerance, and heat insulation effect of the prepared pigments. The results presented that the color of powders varied from white to gray-blue due to the Mn doping. The band gap energy increased from 2.03 eV to 2.14 eV as the doping amount raised, and it could be assigned to the charge transfer transition between O 2p valence bands and Mn 3d conduction bands. The typical YB0.97Mn0.03O3 pigment stated the excellent near-infrared reflectance of 66.18% and significant color properties (L* = 69.75, a* = −5.46, and b* = −6.36). Notably, the surface temperature of YB0.97Mn0.03O3 coating is 39.5 °C lower than the gray-blue commercial pigmented coating. This work demonstrated that the prepared pigments with rather high reflectance possessed potential application in energy-saving materials for buildings.

Vanadium and bismuth doped FePO4 as Near Infra Red (NIR) reflective pigment for energy saving application

In the current investigation a series of NIR reflective pigments were synthesised using naturally abundant iron based phosphates. FePO4, Vanadium (V) doped FePO4 of composition FeP1-xVxO4 (x = 0, 0.05, 0.1, 0.15, 0.2), Bismuth (Bi) doped FePO4 of composition BiyFe1-yPO4 (0.03, 0.05, 0.15) and Bi and V co-doped FePO4 of composition Bi0.03Fe0.97P0.8V0.2O4 were prepared by following co-precipitation method. All the tailored materials were characterized using Powder X-ray Diffraction Analysis (PXRD), Fourier Transformed Infra Red (FT-IR), X-ray Photo electron spectroscopy (XPS), Ultra visible Diffuse Reflectance Spectra (UV-DRS), Scanning Electron Microscopy (SEM) techniques and Commission Internationale de l’Eclairage (CIE-LAB) colour parameters. Strain in lattice was observed by the substitution of comparatively bigger V5+ ion into P5+ hence shift in high intense peak was observed. Doping of small amount of Bi3+(x = 0.03) into Fe3+ lattice leads to the introduction of Bi2O3 as secondary phase and the intensity of bismuth oxide phase was increased as the doping concentration increases. Existence of Fe2+ along with Fe3+ was noticed in Bi0.03Fe0.97P0.8V0.2O4 which was confirmed through XPS technique. Reddish brown FePO4 (b* = 17.49) has changed into mustard yellow (b* = 40.47) as the V5+concentration increases from 0 to 0.2. Bi0.03Fe0.97PO4 has turned into reddish orange. 60% reflectance was observed in the NIR region as a result of co-doping of bismuth (Bi) and vanadium (V) into FePO4. Hence V and Bi doped FePO4 materials can serve as potential cool pigments.

Synthesis and characterization of novel yellow-green Al-doped Y3Fe5O12 nano-pigments with high NIR reflectance

The pigments with high near-infrared (NIR) reflectance hold great promise toward both fundamental types of researches and applications for the realization of comfortable indoor-temperature by mitigating urban heat island effect. However, the facile yet simple method for the NIR reflective pigments with bright color and non-toxic feature remains a huge challenge, limiting their practical application. Herein, we proposed a mild and universal method of solution combustion for constructing the non-toxic and NIR reflective yellow-green pigments of Al-doped Y3Fe5O12. The Y3Fe4AlO12 pigment presented a high NIR reflectance of 87.66%, and an outstanding acid/alkali resistance. Moreover, the pigment had an impressive color performance (L* = 78.72, a* = − 4.05, b* = 40.04). Besides, the practical near-infrared reflection performance revealed that the transient surface temperature of the Y3Fe4AlO12 pigment was 7.6 °C lower than that of the pigment with similar color on the market. This research supplied high NIR reflecting pigments of Y3Fe5−xAlxO12 as promising coatings for roofs and exterior walls of buildings, acting as a favorable solution for urban heat island effect.

High Near-Infrared Reflectance Orange Pigments of Fe-Doped La2W2O9: Preparation, Characterization, and Energy Consumption Simulation

A new series of orange highly near-infrared reflective pigments based on Fe-doped La2W2O9 were effectively fabricated via solution combustion synthesis. The acquired pigment powders were characteri...

Impact of Incorporating NIR Reflective Pigments in Finishing Coatings of ETICS

Near-infrared (NIR) reflective materials are being developed for mitigating building cooling needs. Their use contributes to broadening the range of colours, responding to the urban aesthetic demand without compromising the building performance. Despite the increase in NIR reflective pigments investigation, there is still a knowledge gap in their applicability, impact, and durability in multilayer finishing coatings of External Thermal Insulation Composite Systems (ETICS). Hence, the main goal of this work consists of evaluating the impact of incorporating NIR reflective pigments (NRP) in the solar reflectance of the surface layer of ETICS, without affecting the colour perception, as well as their influence on the colour durability and surface temperature. As such, colour, solar reflectance, and surface temperature were monitored for 2 years in dark-coloured specimens of ETICS, with and without NRP and a primer layer. It was confirmed that the main contribution of NRP is the increase of solar reflectance and, consequently, the decrease in surface temperature, especially for high exterior temperatures (around 30 ºC). Moreover, these pigments highly increase the NIR reflectance without affecting the visible colour. In addition, they contribute to maintaining the colour characteristics. The application of primer increased the surface temperature, especially for higher exterior temperatures. However, it contributes to a lower colour difference and solar reflectance variation, which is an important achievement for durability purposes.

YIn0.9Mn0.1O3–ZnO NIR reflective nano-pigment exhibiting three different colors: Ochre, cyan blue, and deep blue

A set of NIR reflective nano-pigments displaying YIn0.9Mn0.1O3–ZnO stoichiometry was synthesized by sol-gel route. The dried gel precursor was calcined at different temperatures for 2h (550 ​°C, 650 ​°C, 750 ​°C, 800 ​°C, and 850 ​°C), observing the formation of three ochre pigments and two different blue shades. Precursors and final calcined pigments were characterized by thermogravimetry (TGA) and differential scanning calorimetry (DSC) analysis to monitor the NIR reflective pigments production and their thermal resistance. Fourier transform infrared (FT-IR) spectra were collected to know chemical changes obtained by calcination process. Crystalline phases and morphology of nano-pigments were studied using X-ray diffraction (XRD) and scanning transmission electron microscope (STEM) observation, respectively. The synthesized pigments showed near infrared (NIR) reflectance ability. The final color was evaluated according to CIE-1976L∗a∗b∗ method obtaining a standard identification of each color.

Near infrared reflective pigments based on Bi3YO6 for heat insulation

In this paper, a series of high performance near-infrared reflective pigments based on Bi3YO6 doped with Fe2O3 and Tb4O7 were prepared by high-temperature calcination method. The pigments were characterized by some analytic techniques, such as XRD, Particle size analyzer, SEM, EDS, UV–vis–NIR spectrophotometer, CIE L*a*b* (1976) color space and infrared thermal imaging. Experimental results showed that the Fe2O3 doping in Bi3YO6 could change the color from bright yellow to ochre red. The substitution of Tb (IV)-doped pigments changed the color to dark orange. The doping of Fe (III) and Tb (IV) contributed to enriching the color diversities of pigments. Among the synthesized pigments, Bi3-xFexYO6 and Bi3Y1-xTbxO6+δ displayed a disordered defective fluorite-type structure. The effect of doping Fe (III) and Tb (IV) reduced the near-infrared reflectance of the pigment. Excepting for Bi3-xFexYO6 (x = 0.8), the near infrared reflectance of some other pigments were higher than the China National standard (CNs). Chemical resistance tests showed that the pigments had excellent acid and alkali resistance. Finally, the application practical of traditional iron oxide yellow pigment and three prepared pigments, i.e., Bi3YO6, Bi3-xFexYO6 (x = 0.4) and Bi3Y1-xTbxO6+δ (x = 0.05) were studied and compared by infrared thermal imaging. The test results showed that Bi3YO6 still had a strong near-infrared reflection effect after being painted. Compared with traditional iron yellow pigment, Bi3YO6 could reduce the surface temperature of galvanized sheet by 20 °C under the illumination of infrared light. The series of Fe (III) and Tb (IV) doped pigments prepared in this paper have revealed some promising application values.

NIR reflective pigments to mitigate the urban heat islands effect (UHIE)

For building applications, coatings are needed in order to obtain an attractive appearance and protection against the outdoor environments. Buildings are responsible for consumption of cooling energy. Cool coatings applied over buildings surface provide an effective solution for passive cooling of building indoors and influencing local outdoor microclimate, mitigating urban heat islands effect (UHIE). Cool coatings have to resistant to weathering and ageing. For this reason, we developed near infrared (NIR) reflective pigments with the aim to add in binder and obtaining a cool coating. A series of pigments displaying YIn0.9Mn0.1O3–ZnO stoichiometry was synthesized by sol-gel route. The dried gel precursor was calcined at different temperatures for 2h (650°C, 800°C and 850°C) to observe the formation of a light brown pigment and two different blue shades. Precursors and calcined final pigments were characterized by using physicochemical analyses. The colour of pigments was studied using CIE-2004 L*a*b* colorimetric method. The cooling effect of pigments and their thermal stability were confirmed by NIR reflectance measurements and TGA respectively.

Coprecipitation synthesis of a green Co-doped wurtzite structure high near-infrared reflective pigments using ammonia as precipitant

A low content cobalt of green pigments have been synthesized by coprecipitation method. The pigments were characterized by XRD, SEM, TG-DSC, UV–vis and CIE L*a*b*C*h* colorimetric. The results show that the calcination temperature for the prepared pigments are only 1000 °C and all pigments maintain the basic ZnO crystal structure. The coprecipitation method and the ammonia as a precipitant can obtain fine and uniform particles, good colorimetric performance (a* = −17.25) and high near infrared reflectance value. Finally, the synthesized pigments were applied to the roof surface of a self-made experimental device for application testing, the results showed that the room temperature at which the roof was coated with the sample was nearly 10 °C lower than which the ordinary pigments were applied. So, the synthesized pigments have good thermal stability, chemical stability, high near infrared reflectance, and low cobalt nitrate content (1.92 wt%). Also, they are the excellent candidates for cool pigments.

Optical and durability performance of near-infrared reflective coatings for cool pavement: Laboratorial investigation

Coating with high reflectance applied on pavement is an effective way of cool pavement to improve the outdoor thermal comfort and mitigate the urban heat island effect. Cool coating with high near-infrared reflectance is potential to improve the reflectance without affecting the visual environment or causing glare issue. Limited research focused on the near-infrared reflective coatings for pavement and its comprehensive pavement durability performance. This study applied pavement coatings with near-infrared fillers and pigments to obtain high near-infrared reflectance. The orthogonal experimental design method combining the multi-index integrated evaluation method (MIEM) and the single index balanced evaluation method (SBEM) were applied to optimize the formula of coatings with superior comprehensive performance. The optical performance and durability performance including the skid-resistance, anti-abrasion, and film hardness were investigated. The results showed that the near-infrared TiO2 is one type of near-infrared reflective pigment with the bigger particle size and greater bandgap than the energy of near-infrared solar radiation. The near-infrared reflectance of coatings increased first and then decreased with the increase of near-infrared titanium oxide. The optimal proportion of red iron oxide, R–TiO2 and NIR-TiO2 is 5:25:8, which has the superior comprehensive performance of optical properties and pavement durability performance. The near-infrared reflectance could reach 60% and the pavement performance all meet the requirement in practical application. This study will provide useful insights for the development of cool pavement in dark color with high reflection to mitigate the urban heat island effect.

Synthesis and coloration of highly dispersive SiO2/BiVO4 hybrid pigments with low cost and high NIR reflectance

Highly dispersed SiO2/BiVO4 hybrid pigments with a spherical structure and high near-infrared (NIR) reflectance have been successfully fabricated by a facile sol–gel method followed by calcination. The dispersed and uniformly spherical particles of the hybrid pigments were caused by the support provided by SiO2 microspheres, and their color was adjusted via the band-gap energy, which was changed with the incorporation of SiO2 microspheres. The SiO2/BiVO4-3 hybrid pigment presented higher yellow hues (b* = 91.42) and more dispersed spherical particles than other as-prepared hybrid pigments and commercially available BiVO4-based yellow pigment. This strategy could save 72 wt% resource of BiVO4 while yielding the same amount of yellow pigment with high color performance. Therefore, the prepared hybrid pigments not only dramatically decreased the cost of expensive pigments, but also saved scarce resources and reduced environmental pollution. In addition, the SiO2/BiVO4-3 hybrid pigment also presented high NIR reflective performance, which demonstrated that it would be a favorable candidate for colorful NIR reflective pigments with wide applications in heat insulation.

Near-infrared Reflective Pigments Based on Cu 2+ and Tb 3+ Codoped BaZrO3: Preparation and Performance

Near-infrared Reflective Pigments Based on Cu 2+ and Tb 3+ Codoped BaZrO3: Preparation and Performance

Preparation, characterization and thermal performance evaluation of coating colored with NIR reflective pigments: BiVO4 coated mica-titanium oxide

A series of environmentally nontoxic near-infrared reflective pigments of BiVO4 coated mica-titanium oxide were synthesized. The pigments were characterized by XRD, FE-SEM, UV–vis-NIR spectrophotometer and CIE L∗ a∗ b∗ color scales. The results illustrated that the BiVO4 particles with a size of ∼500 nm were firmly adhered to mica-titanium oxide substrate. Additionally, the composite pigments change the color from white to bright yellow with the increase of the BiVO4 loadings. All the pigments had higher NIR reflectance than conventional yellow pigment (≥70.0%). In the simulated experiment, the temperature difference of the inner surface temperature of coatings and the interior air temperature of boxes reached 4.5 °C and 2.3 °C, respectively, indicating that the good thermal insulation performance of the sample coating (30% BiVO4) could be used as building roof material to reduce the heat buildup and decrease the indoor temperature. Furthermore, we also evaluated aging resistance of the pigments. In conclusion, BiVO4 coated mica-titanium oxide composite pigments have great potential in serving as cool materials for building coatings and they also meet energy-saving and environmentally friendly requirements.