Reflective Pigments Research Articles

Magnesium titanate as a new high solar reflectance pigment to fabricate cooling engineering composites for energy saving areas

Fresnel’s law and Maxwell’s equation indicate that the greater the dielectric constant of the material, the greater the refractive index of the material, which makes the material present higher solar reflectance. Magnesium titanate (MT) is an important dielectric ceramic material. It is necessary to investigate the solar reflectance effect of MT particles in practical application areas. In this work, the cooling engineering polymer-ceramic composites were prepared by MT particles and polypropylene (PP)/styrene-ethylene-butylene-styrene copolymer (SEBS)/processing oil matrix. The cooling efficiency of composites was analyzed by solar reflectance, IR thermography analysis, emissivity and solar simulation analysis. The results indicate that solar reflectance enhanced from 16.09% to 60.51% with the content of MT particles increased from 0 to 10 phr. Meanwhile, solar simulation result presents that the inner temperature decreased from 50.4 to 31.5 °C, meaning the fabricated polymer-ceramic composites has a cooling effect of 18.9 °C. Thus, MT dielectric ceramic material can be used as a solar reflectance filler to fabricate cooling engineering polymer-ceramic composites for energy saving application areas.

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.

Ce and Fe doped gahnite: Cost effective solar reflective pigment for cool coating applications

In the current investigation, a new series of Ce doped gahnites of the formula ZnAl2-xCexO4 (x = 0–0.04), Fe doped gahnites of the formula ZnAl2-yFeyO4 (y = 0–0.5) and Ce and Fe co-doped gahnites of the formula ZnAl2-x-yCexFeyO4 (x = 0–0.04; y = 0–0.5) with high near infrared (NIR) reflectance were fabricated to mitigate the heat island effect. All the designed pigments were characterized by powder X-ray diffraction (PXRD), Fourier transformed infra red spectroscopy (FT-IR), Ultraviolet-Diffuse reflectance spectroscopy (UV-DRS). Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and CIE-L*a*b* colour values. Band gap of the white gahnite of the formula ZnAl2O4 (Eg = 3.8 eV) shifted to 2.70 eV and 2.15 eV for the pigments ZnAl1.96Ce0.04O4 and ZnAl1.5Fe0.5O4 respectively. Ce doped gahnites broadened the absorption centre from 250 nm to 350 nm in the UV spectrum and resulted in yellow colour. Whereas Fe doping introduced additional electronic transition between 440 nm and 490 nm and exhibited reddish yellow colour. NIR reflectance of ZnAl1.96Ce0.04O4, ZnAl1.5Fe0.5O4 and ZnAl1.78Fe0.2Ce0.02O4 was found to be 86%, 65%, 80% respectively between 700 and 2500 nm regions. Good thermal and chemical stability along with high NIR reflectance made the prepared pigments as a potential candidate to design cool roofing materials.

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.

Study on Preparation and thermal reflective properties of energy saving pigments with selective solar reflection

Currently, the color of common reflective insulation coating is mainly white, but the white color coating is monotonous and its resistance is poor, moreover, the reflective performance tends to drop after pollution. In addition, color coating has the advantages of anti-dirty and beautiful appearance, so study on colored paint is of great significance. Based on the principle of three-tone color, the effect of thermal reflective pigments on the near-infrared reflectance of color reflective heat-insulating coatings was studied by blending three kinds of color reflective heat-insulating coatings of orange, green and purple with composite inorganic heat-reflective pigments as raw materials. The results show that the thermal insulation effect of heat-reflective pigments is significantly improved, and the near-infrared reflectance of green pigments can be increased by about 25%. The thermal reflection thermal insulation coating of the green system is 2.78 times higher than that of the same color common thermal insulating coating.

SrTiO3 as a new solar reflective pigment on the cooling property of PMMA-ceramic composites

Abstract Polymer-ceramic hybridization is an important method for preparing functional materials. Strontium titanate (SrTiO3, ST), a typical perovskite ceramic, has been widely applied in the electronics industry and photocatalytic fields. However, ST was barely reported to be utilized in cool materials. Herein, ST ceramic, as a solar reflective pigment, was introduced into a polymer matrix to prepare cool material. Specifically, the influences of both weight contents and surface grafting modification about ST on the properties of poly(methyl methacrylate) (PMMA)/ST composites were investigated, which include cooling performance, surface roughness, thermal emissivity, dispersion of particles and mechanical strength. The obtained composites containing 20 wt% unmodified ST possess excellent cooling property due to high thermal emissivity (86.8%, in 8–13 μm) and high solar reflectance (70.7%, in the whole solar band) which increased by 142% than that of pure PMMA resin. Temperature test highlighted that the composites containing 20 wt% unmodified ST was only 26.6 °C, 11.4 °C lower than that of PMMA resin and only 2 °C higher than initial temperature. Moreover, the surface grafting modification of ST by the silane coupling agent was proved to improve the dispersibility of ST in PMMA resin. Both the cooling and mechanical properties of composites containing modified ST particles were further improved. Though the solar reflectance of PMMA/ST composites was lower than that of PMMA/TiO2 composites, temperature tests showed that the PMMA/ST composites had a similar cooling performance with the PMMA/TiO2 composites when the content of the ceramic particles were 5.8 v%. This work not only prepared the polymer-ceramic hybrid materials with excellent cooling performance but also expanded the application of ST ceramic in the field of composites.

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

The mechanism of photocatalyst and the effects of co-doping CeO2 on refractive index and reflectivity from DFT calculation

In this paper, the structural, electronic and optical properties of (N, P), (N, S), (C, P) and (C, S) co-doped CeO2 are studied by using the method of density functional theory (DFT) + U method. The calculated lattice constant, the charge, the bond order, the cell volume and the bond length of CeO2 are consistent with previous experimental and theoretical results. For co-doped CeO2 systems, the calculated results show that the lattice constants, the bond order of CeO as well as the cell volume increase, while the charge of Ce decrease. Due to co-doping, the energy gap (Eg) between valence band and conduction band becomes narrower than that of pure CeO2. Meanwhile, the electron structures of the co-doped CeO2 are changed, which may lead to transformation of optical properties. Nonmetallic atomic orbital (C 2p, N 2p, P 3p, S 3p) and metal atomic orbital (Ce 4f and 5d) are hybridized, except for the hybridization between Ce (4f and 5d) and O (2p). Compared with CeO2, Eg between Ce 4f and Ce 5d becomes smaller. Further, the optical absorption, refractive index and reflectivity of them are investigated. The calculated results reveal that their absorption edges have a red shift. Co-doping enhances visible light photocatalytic activity, which is related to the transition of valence band → conduction band, and Ce 4f → Ce 5d. The co-doped CeO2 has high refractive index and reflectivity. Therefore they may be becoming an important materials in single (or multilayered) optical coatings and optical reflective pigments.

Preparation of Colorful, Infrared-Reflective, and Superhydrophobic Polymer Films with Obvious Resistance to Dust Deposition.

In recent years, polymer films containing deep color and near-infrared (NIR)-reflective pigments have received much attention for their potential applications in energy-saving fields. However, in practical environments, dust present in the air is easily adsorbed and adheres to the surface of these films, thus gradually reducing their NIR reflectance. In this work, black or deep-red infrared-reflective pigments were firstly mixed with melted low-density polyethylene (LDPE) and then the resulting composite was thermally pressed on to a metal template possessing micro- and nanostructure surface roughness. After being cooled to a suitable temperature, the LDPE composite film was peeled from the template. Ultraviolet-visible-near-infrared spectroscopy and an indoor infrared lamp irradiation test both confirmed that the prepared films exhibit high NIR reflectance and high heat reflectance. Moreover, due to the stretching-controlled micromolding process, the films all exhibited a superhydrophobic (SH) property. After incubation in outdoor conditions for 1 month, the NIR reflectance of the SH films remained almost consistent; however, the films that did not possess SH property showed a marked decrease in their ability to reflect NIR radiation. By a combination of scanning electron microscopy imaging, we conclude that our films are able to resist dust deposition and thus avoid deterioration of their infrared-reflective properties. We believe that these colorful, infrared-reflective, SH, and cost-effective films have potential application for reducing energy consumption where minimal solar irradiation is required.

Preparation and Properties of Polyamide/Polyethylene/Near Infrared Reflective Pigment Composites

The effect of the addition of NIR (near infrared reflective pigment filler, nickel antimony titanium yellow rutile) into the polyamide/metallocene-based polyethylene elastomer (mPE) blends on increasing the infrared reflection of PA6 (Polyamide 6) and limiting the thermal heat accumulation in light of environmental and energy conservation concerns was examined. The NIR was included in mPE or mPE-g-MA (maleic anhydride) to form NmPE or NmPE-g-MA masterbatches, respectively, which were used in combination with polyamide 6 (PA6) to prepare PA6/NmPE or PA6/NmPE-g-MA composites. The dispersed domains of mPE modifier were larger in dimension in comparison with those of the corresponding counterparts using mPE-g-MA as the NIR carrier due to the increased interfacial interactions of the anhydride groups of the MA and the amine groups in PA6. NIR tended to increase the crystallization temperature of PA6 of up to 3°C through the nucleation role of the NIR for the NmPE-filled samples. However, this increment was diminished at higher mPE-g-MA content for the NmPE-g-MA-filled samples, suggested to be due to the interaction of mPE-g-MA and PA6 impeding the chain mobility for crystallization growth, offsetting the nucleation role of NIR. The NmPE-g-MA modified samples resulted in the highest improvement in Young’s modulus compared with the NmPE modified samples. An increase of 2 times in the impact strength occurred for PA6/NmPE(60 phr) sample, which increased to a value of 80 ± 5 (J/m). However, a non-break behavior was observed for the PA6/NmPE-g-MA samples at higher modifier contents. The values of infrared reflection increased significantly, indicating the effectiveness of NIR to improve the reflection properties of the prepared composite systems.

Case Study: Mitigation of heat stress in feedlot cattle by applying reflective pigments to the dorsal body surface

ABSTRACT Heat stress in feedlot cattle has serious animal welfare and economic implications. The objective of this experiment was to determine whether a titanium dioxide coating applied to the dorsal midline of cattle would reflect solar radiation and mitigate heat stress. Feedlot heifers (n = 30; 269 ± 27.6 kg) were randomly assigned to a noncoated (control) or titanium dioxide–coated treatment. Coating was applied to the dorsal midline except for a control area over the dorsal anterior midline. Reflectance was measured with a suspended modified digital camera in a blue band, a green band, and a near-infrared band. Skin surface temperature was measured with a suspended infrared thermal imaging sensor. Vaginal thermometers recorded the internal body temperature of heifers. Reflectance in the blue, green, and red edge to near infrared bands were found to be 5.7, 8.8, and 10.3 times greater (P

Novel Bi3+ doped and Bi3+/Tb3+ co-doped LaYO3 pigments with high near-infrared reflectances

A series of environmentally benign and high NIR reflective pigments based on Bi3+ doped and Bi3+/Tb3+ co-doped LaYO3 are synthesized via the sol-gel method. The resulting powders were characterized by X-ray diffraction, UV–vis–NIR spectrophotometer and CIE L*a*b* (1976) color space. The doping of Bi3+ for La3+ in LaYO3 results in the color changes from light yellow to dark yellow and Bi3+/Tb3+ for La3+ in LaYO3 varies from soft orange to dark orange. Meanwhile, the band gaps of pigments decrease from 4.52 eV to 2.95 (Bi-doped) and 2.15 eV (Bi/Tb co-doped). Interestingly, the Bi-doped pigments possess high NIR solar reflectance (>95%) in the range of 700–2500 nm. In contrast, the Bi/Tb co-doped pigments decrease the NIR solar reflectance from 98.28% to 78.77%. The applicability studies of La0.5Bi0.5YO3 and La0.5Bi0.25Tb0.25YO3 pigments with TiO2 base coat on galvanized sheet reveal good coloring performance with high NIR reflectance. Acid/alkaline tests indicates good chemical stabilities of the pigments under the extreme weather conditions. The superior performances of developed pigments have revealed potentials to be employed in cool coatings.

Dark, Infrared Reflective, and Superhydrophobic Coatings by Waterborne Resins.

Recently, infrared reflective pigments possessing deep colors have attracted much attention. However, in polluted air, the coatings consisting of such pigments are easily contaminated which abates infrared reflectivity. In this work, black and infrared reflective pigments, fluorine silicon sol and a small number of SiO2 nanoparticles were introduced into waterborne epoxy resin emulsion and then coated on an aluminum plate. After drying, black coatings with infrared reflective and superhydrophobic (SH) properties were obtained. The average near-infrared (NIR) reflectivity of the coating over wavelength range of 780-2600 nm can reach 68%, which is much larger than that of carbon black coatings and even approaches that of white nano SiO2 coatings. Under the irradiation of a 275-W infrared lamp (with height 40 cm), the surface temperature of the coating is 63 °C, which is much lower than that of the carbon black coating (90 °C) and only 7 °C higher than that of the white nano SiO2 coating. Furthermore, the NIR reflective coating exhibited a typical SH property due to its low surface energy and high surface roughness, which may allow for self-cleaning performance in a practical environment, maintaining the coating's NIR reflective property.

Preparation of Near-Infrared (NIR) Reflective Pigment by Solid State Reaction between Fe<sub>2</sub>O<sub>3</sub> and Al<sub>2</sub>O<sub>3</sub>

Reflective pigment was prepared by using Fe2O3 and Al2O3 as starting materials. Fe2O3 and Al2O3 powders were mixed at 0.8:2, 1:2 and 1.2:2 mole ratio using ball milling. The mixed powders were dried and calcined at temperature of 1500°C, 1600°C and 1700°C for various soaking time at 2, 8 and 20 h. Phase data were analyzed by x-ray diffractometry. It was found that (Al1-x, Fex)2O3 presented as a new phase in calcined powders at temperature of 1500°C to 1700°C for 2 h. The other new phase such as FeAl2O4 was detected in calcined powders at temperature of 1700°C for 8 and 20 h. From the experimental results indicated that complete reaction was occurred when higher calcination temperature and longer soaking time were used, resulting in spinel structure (FeAl2O4) generated. Then, the synthesized powders were mixed with exterior paint by mass ratio of 0:100, 10:90, 20:80, 30:70 and 40:60, respectively. The mixed paints were sprayed on metal sheets. Then the coated metal sheets were exposed under 200 watts lamb and measured the temperature difference between the exposed side and opposite side. The result showed that at the ratio of 30:70 exhibited the highest temperature difference of 14°C approximately. From the result, we concluded that spinel structure (FeAl2O4) is a candidate for near-infrared (NIR) reflective pigment of exterior paint.

Novel near infrared reflective pigments based on hollow glass microsphere/BiOCl1-xIx composites: Optical property and superhydrophobicity

In this work, BiOCl1-xIx coated hollow glass microsphere was synthesized as a novel near infrared reflective pigment for superhydrophobic cool roof coatings. BiOCl1-xIx microflowers or microspheres were deposited on hollow glass microspheres using a simple chemical liquid deposition method. The morphologies of BiOCl1-xIx were found to differ drastically by varying the molar ratio of Cl to I. The color of the composite pigments changed from white to red and the band gap decreased from 3.16 eV to 1.87 eV as the increased content of I. The near infrared solar reflectance of the composite pigment was as high as 0.947. An approximately 8 °C decrease in outer surface temperature was obtained for the heat box coated with the composite pigments. With the help of the micro/nano-scale surface roughness of hollow glass microsphere/ BiOCl1-xIx composites, a superhydrophobic coating with a contact angle of 156.1° could be obtained. The superhydrophobic cool coating showed good antifouling property when they were fouled by the slurry solution containing montmorillonite and Rhodamine B. Moreover, the prepared superhydrophobic coatings exhibited long term stability and ultraviolet durability. Therefore, such superhydrophobic cool coatings with antifouling property is able to work for a longer time by preventing the contamination for building thermal insulation.

Optical property and thermal performance of hollow glass microsphere/BiOBr1-xIx composites as a novel colored near infrared reflective pigment

In this work, hollow glass microsphere/BiOBr1-xIx composites was synthesized as a series of novel colored near infrared reflective pigments. BiOBr1-xIx microflowers or microspheres were deposited on hollow glass microspheres using a simple chemical liquid deposition method. The morphologies and optical properties of the composite pigments were found to differ drastically by varying the molar ratio of I to Br. The color of the composite pigments was observed to turn from white to yellow, and then to red as the increased content of I. The band gap of the composites decreased from 2.87 to 1.87 eV with increasing I content. The near infrared solar reflectance of hollow glass microsphere/BiOBr1-xIx composite pigments was as high as 0.952. An approximately 9.4 °C decrease in outer surface temperature was obtained for the heat box coated with the composite pigments. Therefore, the synthesized composite pigments with tunable colors and high NIR reflectance have the potential to be applied as cool pigments in cool coatings to reduce the heat build-up.

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.