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%).     

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.     

Preparation and thermal reflectivity of nickel antimony titanium yellow rutile coated hollow glass microspheres composite pigment

In order to reduce the urban heat island effect, nonwhite lightweight pigments with high near infrared reflectance were studied. Nickel Antimony Titanium Yellow Rutile pigments (TiNiY) coated hollow glass microspheres (HGM@TiNiY) with core-shell structure were prepared by a novel mixing slurry-sintering method. The Reflective property of HGM@TiNiY/SR composite coating prepared by mixing HGM@TiNiY with silicone resin (SR) was investigated by an UV–Vis–NIR spectrum analyzer. The results showed that the size distribution of TiNiY particles was from 150 to 450?nm with an average size of 230?nm, and the binding mode of TiNiY particles with HGM and the formation mechanism of TiNiY Shell were discussed. The UV–Vis–NIR reflectance of HGM@TiNiY/SR coating was not only better than that of others filled with HGM powders or TiNiY powders alone but also higher than that of the coating filled with the mixture of HGM and TiNiY powders at the same volume ratio. A possible mechanism of HGM@TiNiY/SR coating on thermal reflection was discussed. This clearly indicates that the pigment of HGM@TiNiY with core-shell structure could be applied as a good colour cool pigment.     

Preparation of nanoscale azo pigment yellow 13/poly(styrene–maleic acid) composite dispersions via free‐radical precipitation polymerization

Nanoscale azo pigment yellow 13 (PY13) was coated by poly(styrene–maleic acid) (PSMA) with a free‐radical precipitation polymerization, followed by the preparation of the dispersion. The effects of the PSMA structure on the particle size and centrifugal stability were investigated. The experimental results revealed that the particle size was large, and the stability of the PY13/PSMA dispersions was high when the molar ratio of the feeding maleic acid to styrene, the weight ratio of the feeding initiator to monomer, and the weight ratio of the feeding monomer to pigment were about 1.0, 0.6, and 20%, respectively. Fourier transform infrared spectroscopy, dynamic light scattering, and transmission electron microscopy indicated that PY13 was coated by PSMA. The PY13/PSMA dispersion was stable in the pH range 5.6–10.5. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of alumina-based sintering aid on the microstructure,selected mechanical properties,and coefficient of friction of Cf/SiC composite prepared via spark plasma sintering (SPS) method

C_f-SiC air brake discs are being developed due to their high-temperature oxidation resistance compared to conventional C_f/C discs. The C_f-SiC air brake discs should have a coefficient of friction (COF) close to 0.4, a low wear rate, a density higher than 95% of the theoretical density, and flexural strength of more than 200 MPa. To reach the properties of C_f-SiC composite to the required characteristics of the air brake disc, different amounts of alumina-based sintering aid were used. For this purpose, first silicon carbide nanoparticles, sintering aids Al₂O₃–MgO, MgAl₂O₄, Al₂O₃–Y₂O₃, Al₂O₃–SiO₂–MgO, and carbon fiber (20 wt%) with a 5-mm length were prepared. Next, the final composite bulk was created via the SPS method at 1900 °C under a pressure of 50 MPa. The density of the sample sintered with the Al₂O₃–SiO₂–MgO sintering aid was higher than that of other sintering aids. The density value was obtained at 98% and 100% at 8 wt% and 4 wt% respectively. It was also found that the use of 4 wt% of Al₂O₃–SiO₂–MgO offered better mechanical properties compared to 8 wt%, due to the absence of Al₈Si₄O₂₀ phase at 4 wt%. The examination of mechanical properties showed that the hardness (3564 Vickers) and flexural strength (479 MPa) of the sample with the Al₂O₃–SiO₂–MgO sintering aid were higher than those of other sintering aids. The samples with the Al₂O₃–SiO₂–MgO sintering aid with 4 wt% revealed a COF of 0.41, showing the closest feature to the desired indices of aircraft brake discs.     

Preparation,microstructure and electrical property of GdSmZr2O7-(Li0.52Na0.48)2CO3 composite electrolyte via carbonate infiltration

Porous GdSmZr₂O₇ (GSZ) with different porosities has been prepared by the solid state reaction, and GSZ-carbonates composites have been prepared by infiltrating (Li_0·52Na_0.48)₂CO₃ (LNC) molten carbonates. Phase structure, microstructure and electrical property have been analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). SEM results show that the voids in porous GSZ are uniformly distributed. The relative density of GSZ-LNC composites obtained by molten salt infiltration is above 93%. The electrical conductivity of the GSZ-LNC composites obtained by molten salt infiltration reaches the highest value of 0.50 S cm⁻¹ at 600 °C, which is much higher than that of GSZ-LNC composites prepared by traditional mechanical mixing method. This excellent electrical property strongly indicates that the GSZ-LNC composite obtained by molten salt infiltration is a promising ionic conductor.