ZnO nanostructures decorated hollow glass microspheres as near infrared reflective pigment

Hollow glass microsphere/ZnO composite pigments were successfully prepared by a facile sol-gel method. ZnO coating layers composed of nanosheets, nanoplates, or nanoparticles were anchored at the surface of hollow glass microspheres by formation of Zn-O-Si bond. A reasonable growth mechanism for elucidating the formation of ZnO nanocoating was proposed. The results indicated that the near-infrared reflectance property of the composite pigments was strongly affected by the morphology of ZnO nanostructures. The nanoparticles structures exhibited higher near-infrared reflectance than that of nanosheets and nanoplates structures. The near-infrared solar reflectance of hollow glass microsphere/ZnO composite pigments was 95.7%, while the total solar reflectance of the composite pigment was as high as 97.2%. An approximately 11.1 °C decrease in outer surface temperature was obtained for the heat box coated with composite pigments. Therefore, hollow glass microsphere/ZnO composites are excellent near infrared reflective pigments for efficient solar reflective coatings designed for building facades and roofs.     

Near-infrared reflective properties of perylene derivatives

Dyes and pigments with high reflectance in the near-infrared (NIR) region can extensively control the heat buildup. Perylene-based pigments exhibit considerable reflectance in the NIR region. The reflectance of a material depends upon a number of factors, such as particle size, concentration of the reflective material, the distribution of particles within the material and the material’s refractive index. The refractive index, in turn, depends on the electronic structure of the material. Therefore,differently substituted perylene compounds are expected to exhibit different reflectance in the NIR region. To elaborate this point, different perylene bisimide derivatives have been synthesized, and their ability to reflect in the NIR region has been determined and compared to the results for commercially available pigments. Significant variation in the relative reflectance is observed in the NIR region for differently substituted perylene bisimide compounds. The NIR reflectance of different perylene tetracarboxy diimide derivatives (PCIs) was also compared to the reflectance of 3,4:9,10-perylenetetracarboxylic dianhydride (PTCA), the precursor from which the PCIs are commonly synthesized. PTCA exhibits significantly higher relative reflectance in the given region than any of the diimide derivatives synthesized from it in this study.     

Crystal structure and near-infrared reflective properties of Fe3+ doped AlPO4 pigments

Novel non-toxic orange yellow inorganic pigments Al_1−xFe_xPO₄(x=0.00, 0.03, 0.05, 0.08) with high near-infrared reflectance (NIR) have been synthesized by a coprecipitation method. The structures of samples were investigated by XRD and Raman spectroscopy, and the reflective properties were tested by UV–vis–NIR spectrophotometer. Results demonstrated that with more Fe³⁺ added, the color of the powder samples changed from white to orange yellow and the near-infrared reflectance decreased from 98.03% to 72.56%, which is higher than the commercial orange yellow pigment (61.99%). The near-infrared reflectance of corresponding coatings decreased from 69.35% to 59.10%, which is higher than the commercial coating with the similar color (51.88%). From the XRD diffraction spectrogram, we can see the peaks did not change with more Fe³⁺ added. However, because of ionic radius of Fe³⁺(0.63 Å) is a little larger than Al³⁺(0.53 Å), the cell volume increases a little when more Fe³⁺ is added. Furthermore, from the Raman spectrogram, we can see that doping with Fe³⁺, there is a new Raman peak which is assigned to the asymmetric [FeO₄] stretch. In addition, replacing Fe³⁺ for Al³⁺ in AlPO₄ caused the band gap decreased from 5.98eV to 3.60 eV, which can cause the absorption of more near-infrared radiation and that is the reason of the decrease of near-infrared reflectance.     

Thermomechanical properties and oxidation resistance of zirconia CVI-matrix composites: 1—Mechanical behavior

The mechanical behavior of various zirconia-based fibrous composites has been studied at ambient and high temperatures. The composites were prepared by ZrO₂-CVI densification, from preforms made of alumina or carbon fibers consolidated with a small amount of alumina, pyrocarbon or hex-BN. When loaded under compression at room temperature, 2D-C-C/ZrO₂ composites exhibit mechanical behavior similar to that already reported for the related 2D-C-C/SiC, 2D-C-C/B₄C, 2D-C-C/TiC or 2D-C-C/BN materials with: (i) a linear elastic domain, (ii) a damaging domain prior to failure and (iii) an anisotropy which decreases as V(ZrO₂) is raised. Under three-point bending, the alumina-zirconia composites behave, at room temperature, in a non-brittle manner when the preform has been consolidated by BN, with crack deviation and pull-out phenomena. The variations of the stiffness and strength versus V(ZrO₂) obey exponential laws at room temperature. Finally, the alumina-zirconia composites keep their strength and rigidity up to about 1000°C under an atmosphere of argon/hydrogen.     

Electrically conductive porous alumina/graphite composite synthesized by starch consolidation with reductive sintering

This paper reports a facile and environment-friendly process to synthesize electrically conductive porous alumina/graphite composites by starch consolidation technique followed by reductive sintering. Green ceramic composites were consolidated with different starches and sintered at different temperatures in an argon atmosphere. Electrical measurements, carbon contents and Raman analyses of carbon structures determined an optimal sintering temperature of 1700 °C, which lead to a uniform formation of conductive graphitic networks at an optimal concentration of about 3.8 vol% in the porous composites. These carbon networks resulted into porous composites having high electrical conductivities measured in the range from 3 to 7 S/cm, which depended on the starch types and their porous properties. Correspondingly, the bulk porosities of the sintered composites were measured from 42 to 46%, with rounded micropores having diameters ranging from 14 to 39 μm. These porous properties of the sintered composites offer promising applications for conductive membrane and porous electrode.     

Cellulosic nanocomposites. I. Thermally deformable cellulose hexanoates from heterogeneous reaction

Partially derivatized cellulose esters were prepared from dissolving‐grade wood pulp fibers by reaction with a mixed p‐toluene sulfonic/hexanoic anhydride system in a nonswelling (cyclohexane‐based) reaction medium. The partially derivatized pulp fibers, which failed to undergo a significant change in shape or appearance during the modification, proved to be resistant to swelling (in water), were thermally deformable, and retained their biodegradability. Because X‐ray diffractometry provided evidence for the presence of unsubstituted, ordered cellulose with cellulose I morphology, the thermally reshaped and consolidated sheets were found to consist of commingled mixtures of cellulose esters and cellulose I. The transparent or semitransparent consolidated sheets (depending on the degree of substitution) were found to represent composites in which cellulose I serves as a discontinuous inclusion that reinforces a continuous, partially ordered cellulose ester matrix. The composites, which revealed cohesive or adhesive failure at rupture, depending on the degree of substitution, had modulus values and tensile strengths as high as 1.3 GPa and 25 MPa, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2242–2253, 2000     

Solid state bonding of graphite/thermoset composites via interchain transesterification reaction (ITR)

Thick section composite laminates are expensive and difficult to manufacture because of problems with porosity, large reaction exotherms from epoxies and residual strains. The copolyester thermosets described here can eliminate these problems. Through interchain transesterification reactions, individually cured prepreg plies of graphite reinforced copolyester can be bonded with each other in the solid state. ITR bonding is shown to produce well‐consolidated laminates with less than 2% void volume and mechanical properties comparable to those of current high‐end polymer matrix composites. DMA testing showed the glass transition to begin at 190°C for a 45% fiber volume fraction composite. Tensile testing of 55% fiber volume composites at room temperature showed modulus, strength and elongation to failure averages of 105.4 GPa, 1.02 GPa and 1.0% respectively.     

An S-scheme heterojunction of Bi2WO6/AgIO3 nanocomposites that enhances photocatalytic degradation of Rhodamine B and antifouling properties

Bi₂WO₆/AgIO₃ (BWO/AIO) nanosheet composites were constructed by a two-step hydrothermal method. The structure, morphology and photoelectrochemical properties of the composites were characterized by X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-DRS), transmission electron microscopy (TEM), impedance, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The constructed photocatalyst composites exhibited the best photocatalytic performance at a molar ratio of BWO/AIO-0.8. In addition, there was complete degradation of RhB by the BWO/AIO-0.8 in 180 min under illumination, and the bactericidal rates were 99.10%, 97.32% and 96.3% for P. aeruginosa, S. aureus and E. coli, respectively, in 60 min. Based on the energy band structure of the semiconductor and radical trapping experiments, the S-scheme heterojunction was associated with the enhanced photocatalytic properties.     

Preparation of high near-infrared reflectance mica/(Ni,Sb)-co-doped rutile yellow composite pigment via mechanochemical pretreatment and sintering

Mica/(Ni, Sb)-co-doped rutile yellow composite pigment with a high near-infrared reflectance was prepared via mechanochemical pretreatment and subsequent sintering. (Ni, Sb)-co-doped rutile yellow pigment was synthesized by a solid-phase method in the presence of sodium fluoride (NaF) as a mineralizer, and mica was peeled by ultrafine grinding. The pigment, mica and mica/pigment composite were characterized by X-ray diffraction, laser diffraction particle size analysis, nitrogen gas adsorption method, scanning electron microscopy, energy dispersive spectroscopy, ultraviolet–visible–near-infrared spectroscopy, CIEL*a*b* color scales, and infrared irradiation image, respectively. The results show that the temperature of synthesizing a pure rutile pigment in solid-phase reaction is reduced by 100°C due to the addition of mineralizer NaF. (Ni, Sb)-co-doped rutile pigment has better color rendering performance and near-infrared (NIR) reflectance. Ultrafine grinding produces the finer flatty mica particles with fresh reflective surfaces, thus improving NIR reflectance of peeled mica. In mica/pigment composite prepared via mechanochemical pretreatment and subsequent sintering, peeled mica has a synergistic effect on (Ni, Sb)-co-doped rutile pigment particles to further scatter near-infrared radiation through the multiple layer reflections, leading to a better heat insulation. The high near-infrared reflectance of composite pigment increases to 97.72%, and the b* value of the pigment synthesized with 1 wt% NaF is 37.77. For the irradiation infrared lamp, the surface temperature of aluminum plate coated with mica/(Ni, Sb)-co-doped rutile yellow composite pigment is 40.1 ± 0.2°C, which is lower than that of aluminum plate uncoated determined by thermal camera and thermocouple. When aluminum plate coated with mica/(Ni, Sb)-co-doped rutile yellow composite pigment is under sunshine, its surface temperature is 38.6 ± 0.2°C. In addition, the mechanism of preparing the composite pigment via mechanochemical pretreatment and subsequent sintering and the multiple structure reflection effect on peeled mica surface coated with (Ni, Sb)-co-doped rutile yellow pigment particles were also discussed.     

Preparation of near-infrared absorbing composites comprised of conjugated macroligands on the surface of PbS nanoparticles

We report a facile macroligand strategy towards the synthesis of low-bandgap inorganic-organic composites comprised of semiconductor PbS nanoparticles and functional copolymers. For this, thiol-functional thiophene-based macroligands have been used as coligands for PbS nanoparticles. Thus, solution processable organic-inorganic hybrid materials with absorption in the near-infrared have been obtained. The resulting nanoparticle-polymer composites were characterized in detail by optical and FT-IR spectroscopy as well as TEM showing their potential as novel functional inorganic-organic hybrid materials when applied in initial proof-of-concept hybrid photovoltaic devices.     

Improved coloristic properties and high NIR reflectance of environment-friendly yellow pigments based on bismuth vanadate

Herein, fine powders of yellow pigments based on BiVO₄ were successfully prepared in two crystalline forms, tetragonal zircon-structured and monoclinic scheelite-structured, through a ethylene glycol-assisted method subjected to a thermal treatment at two different temperatures. The obtained materials were brightly colored with different hues of yellow, exhibited high reflection in the near-infrared region and showed visible luminescence under excitation by UV light. The new preparation method had a considerable effect on chromatic properties of the prepared scheelite-structured BiVO₄ pigments. The sample with the most vivid and bright shade of yellow was found to have the L^*a^*b^* and L^*C^*_ab h^*_ab color coordinates of (87.28, 0.37, 91.53) and (87.28, 91.53, 89.79), which are indicative of exceptionally good chromatic properties superior and/or comparable to those of other inorganic yellow pigments, both commercially available and recently described. In addition, the NIR reflectance of this powder was very high (≥?80%).     

A novel high reflective glass-ceramic ink with Bi2Ti2O7 nanocrystals used for the photovoltaic glass backplane

Photovoltaic glass ink is a kind of ink used for the photovoltaic glass backplane to enhance the photoelectric conversion efficiency of solar cells. In this work, a novel kind of photovoltaic glass-ceramic ink, with Bi₂Ti₂O₇ nanocrystals precipitated from the low-melting glass for the first time in the short sintering process, was successfully designed and prepared to further improve the reflectance of near-infrared light. Bi₂Ti₂O₇ nanocrystals fill the gap between TiO₂ color pigments to a certain extent, which reduce the diffraction of light and greatly improve the reflectivity of the photovoltaic glass backplane to near-infrared light. In the near-infrared wavelength range (780–2500 nm), the average reflectance of photovoltaic glass ink with Bi₂Ti₂O₇ nanocrystals is 20.6% higher than that without Bi₂Ti₂O₇ nanocrystals. The maximum reflectance of photovoltaic glass-ceramic ink is 86.18%. Our research and findings have provided an important reference point for future development of photovoltaic glass inks.     

Structure and properties of talc-filled polypropylene: Effect of phosphate coating

Talc surface treatment was carried out using a series of phosphate coating levels. The coated talc was characterized using quantitative diffuse reflectance FTIR analysis, which revealed a saturation of surface coverage at around 6 wt % phosphate. Coated and uncoated talc had a nucleation effect; and the degree of crystallinity of composites increased initially, then gradually decreased with increasing phosphate coating level. The talc dispersion was improved as coating level increased; however, the platelet alignment was reduced. The addition of 0.5 wt % phosphate to talc resulted in a maximum increase in tensile strength and a significant drop in flexural modulus. Improvement of falling weight impact properties of the composites were achieved at high coating levels. © 1996 John Wiley & Sons, Inc.     

Facile fabrication of cool yellow pigment with enhanced NIR reflectance by tailoring oxygen defects and its application in energy-saving building

Intensity of absorption tail at long wavelength side of absorption edge is affected by concentration of oxygen vacancy (O_v), which determines chromaticity, near-infrared (NIR) reflectance and application value of cool pigments. In this work, a feasible strategy is proposed to restrain the generation of O_v by lattice distortion to enhance color and NIR reflectance. Compression lattice is formed by introducing smaller ions of Ti⁴⁺ or Zr⁴⁺ into Tb site in SrTbO₃ host. This results in significant reduction of concentration of O_v. Compared to SrTbO₃, color component L* of SrTb_0.6Zr_0.4O₃ increases from 69.09 to 87.30. Moreover, NIR and solar reflectance are remarkably enhanced, reaching 18.3% and 19.3%, respectively. In addition, 11.6 °C and 5.6 °C decreases in temperature were observed for inner surface of roof and indoor room of simulation house. The strategy proposed in this work will contribute to developing color-cool pigments with suitable properties and high solar regulation ability.     

Mixing of carbon nanotubes (CNTs) and aluminum powder for powder metallurgy use

In recent years, carbon nanotubes (CNTs) reinforced aluminum matrix composites (AMCs) have attracted increasing attention. The quality of dispersion, however, is a crucial factor which determines the homogeneity and final mechanical properties of these composites. This work studied the mechanical mixing methods, viz. high energy and low energy ball millings, and compared them to a novel polyester binder-assisted (PBA) mixing method. Experimental results showed that the high energy and low energy ball-milled CNTs disintegrated and there were residual stresses, unlike the PBA-CNTs. The CNT dispersion conditions by these three methods were discussed. The Al-CNTs mixture was subsequently consolidated by powder metallurgy (PM) technique. Small addition of CNTs (0.5 wt.%) evidently improved the tensile strength and hardness of the composite by comparing with the pure matrix. Mechanical property enhancements of the Al-0.5CNT composites from PBA and high energy ball milling were superior to that mixed by low energy ball milling. This showed good dispersion effect in PBA and high energy ball milling technique.     

Transparent luminescent bulk nanocomposites of polysiloxane embedded with CdS nanocrystallines by a direct dispersion process

Transparent luminescent bulk nanocomposites of polysiloxane (PSO) embedded with semiconductor nanocrystals (NCs) have been fabricated by the direct dispersion of CdS NCs in alkyl-(poly)siloxane (APS) followed by co-polymerization. The non-polar characteristics of the APS precursor are compatible with the CdS NC surface (oleylamine), which allows the direct dispersion of the CdS NCs without the need of any surfactant exchange. Chemical crosslinking of the NC-APS dispersion via hydrosilylation between Si-H and the vinyl group in APS immobilizes the CdS NCs in the polysiloxane network. Net-shaped three-dimensional bulk transparent polysiloxane/CdS NC composites were obtained by liquid casting of the NC-precursor dispersion and chemical crosslinking. The PSO/CdS NC composites show visible luminescence under ultraviolet excitation and the luminescent color is tunable from blue to red by controlling the NC concentration in the composite. Photoluminescence spectral analyses reveal the origin of the luminescence as being from the defect emission of the CdS NCs (550-900 nm) and an emission from the PSO matrix (380-550 nm). The luminescent spectra covered a wide range from the ultraviolet to the near-infrared region. The luminescence of the PSO/CdS NC nanocomposites was stable without any apparent degradation after exposure to air for a long time. This simple direct dispersion process is feasible for the fabrication of luminescent nanocomposites with useful optical properties for potential applications in optics and photoelectron devices.     

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

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.     

Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide Fibers

A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200°C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7–0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200°C for 100 h. Heat treatment at 1300°C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature.     

Investigation of microstructure and thermoelectric properties of p‐type BiSbTe/ZnO composites

In this research work, p‐type BiSbTe/ZnO (2 wt%) nanocomposite powders were fabricated by high‐energy ball milling at different milling times, and subsequently, powders were consolidated by spark plasma sintering at 673 K temperature. The existence of nanoinclusions was confirmed by SEM‐EDS mapping. Vickers hardness values greatly improved due to reduction in grain size which prevents the crack propagation and dispersion strengthening mechanism. The decrease in carrier density, which plays a critical role in thermoelectrics, dramatically increases the Seebeck coefficient, and subsequently, decreases the electrical conductivity upon the dispersion of ZnO nanorods into the BiSbTe matrix. The thermal conductivity was noticeably reduced by ~13% in BiSbTe/ZnO composites for 5‐minute samples due to blocking of carriers/phonons at interfaces, and/or grain boundaries. The peak ZT of 0.92 was obtained for BiSbTe matrix, and 0.91 for BiSbTe/ZnO (5 minutes) composites at room temperatures.     

Surface topography and cooling effects in poly(vinyl chloride) (PVC)/titanium dioxide (TiO<Subscript>2</Subscript>) composites exposed to UV-irradiation

Rutile titanium dioxide (TiO₂), at different amounts (0, 1, 3, 5, 8 and 10 phr), was used to prepare PVC/TiO₂ composites as cool materials. Exposure to the ultraviolet (UV)-irradiation at 65 °C (black-panel thermometers) with a xenon arc as the light source (0.51 W/(m² nm), 340 nm) for 200, 400 and 600 h resulted in the formation of polyene structure in PVC and causing discoloration. Besides, atomic force microscopy and roughness measurements were used to examine the changes in surface topography and roughness before and after UV-irradiation. Ethylenic index was used to characterize the aging degree of composites. The contact angle value of composites became smaller and their polarity increased after exposing to UV-irradiation, but the presence of TiO₂ effectively prevented this process. In addition, exposure to UV-irradiation had little effect on the reflectance of PVC/TiO₂ composites over the whole solar wavelength range (200–2500 nm), especially in near infrared (NIR) region (700–2500 nm). This allowed the TiO₂-loaded samples to display an excellent cooling property whether indoors or outdoors. The addition of higher quantities of TiO₂ led to higher efficiency of the cooling effect. In general, this study provides strong support for the property of long-term outdoor use of PVC/TiO₂ composites with high solar reflectance and excellent cooling performance.