Doped Pigments Research Articles

Ce doped (Y, Yb)3Al5O12 yellow cool pigment with high solar reflectance and enhanced colour performance

The high solar reflectance and good colour performance are requisite for the practical application of the colour-cool pigment. In this work, Ce-doped Yb3Al5O12 and (Y, Yb)3Al5O12 ceramic pigments were prepared by the sol-gel method. Both Ce3+ and Ce4+ ions coexist in the doped pigments. Due to the 4f→5d electron transition of Ce3+, the Ce-doped pigments have a selective absorption at around 400–520 nm, which is responsible for the yellow hue. The content of the Ce3+ ion determines the colour performance of the pigment. The size effect from the smaller Yb3+ ion results in an increased content of Ce3+ in the Ce-doped pigments, leading to an improved colour performance. The incorporation of Y3+ ion can effectively decrease the absorption at 975 nm, thereby enhancing the solar reflectance to 80.6 %, while maintaining good colour performance (Yb0.7Y2.1Ce0.2Al5O12, L* = 91.40, a* = -4.89, b* = 45.33). In a simulation experiment, the ceramic glaze coating based on the prepared pigment showed a temperature reduction of 5.2 °C compared to the commercial yellow pigment ceramic coating.

Influence of metal and nonmetal doping on wetting and dispersing characteristics of TiO2 pigment for coating applications

BackgroundDispersing of pigment particles in paint medium is the hardest stage in paint and coating production. Pigment agglomerates must be wetted, separated, and dispersed in paint matrix with a suitable distance from each other. MethodsIn the present work, we have studied the effect of doping of TiO2 pigment with metallic and nonmetallic elements on its wetting and dispersing properties. For this reason, TiO2 pigment was doped with Cu as a metallic and N as a nonmetallic element. Doped pigments were characterized by XRD, SEM, and FTIR and then wetting properties of the obtained pigments were tested by contact angle measurement with water. Also dispersing properties of pigments were studied by grinding time (dispersing time) in the ball mill apparatus. Significant findingsThe results showed that doping of TiO2 pigment with metallic element Cu reduced the contact angle whereas doping with non-metal element N caused to increase in the contact angle. Also, a complete test series of coatings prepared with these two doped pigments in comparison to unmodified pigments showed that the final properties of the paint film weren't affected by utilizing doped pigments.

Estimating thermal insulation performance and weather resistance of acrylonitrile-styrene-acrylate modified with high solar reflective pigments: Pr3+/Cr3+ doped BaTiO3

This paper is conducted to evaluate the thermal insulation potential and weather resistance of modified acrylonitrile-styrene-acrylate (ASA) resin as building materials. The synthesized Pr3+/Cr3+ doped BaTiO3 pigments were served as additives. The Ba1-xPrxTiO3 (x = 0.03, 0.04, 0.05) and Ba1-xPrxTi1-yCryO3 (x/y = 0.03/0.03, 0.03/0.05, 0.05/0.05) pigments are the tetragonal replacement solid solution. The sample particles display approximately spherical and the powders all have a yellow tone. Ba1-xPrxTiO3 and Ba1-xPrxTi1-yCryO3 pigments both exhibit distinctly high NIR solar reflectance of 94.39%-96.39% and 66.89%-91.50%, respectively. The variations of the NIR solar reflectance values are mainly attributed to the difference in free charge carrier concentration in the doped pigments. The NIR solar reflectance of ASA modified with 10 wt% pigments can reach 58.85%-81.68%. After performing near-infrared radiation, the inner surface temperature of the modified ASA can be reduced by 6.4 °C at a maximum than that of unmodified ASA, and the modified ASA provides saving up to 18% of heat. Moreover, the addition of NIR reflectance pigments can further improve the weather resistance of ASA materials. In short, the modified ASA can be effectively applied to building materials to maximize the heat-insulating effect and service life.

Synthesis and characterization of a new high NIR reflective ytterbium molybdenum oxide and related doped pigments

A novel yellow NIR reflecting pigment with the formula Yb6Mo2O15 crystallizing in a trigonal structure with the color coordinates L* = 88.7, a* = −6.6, b* = 55.0, C* = 55.4, and h° = 96.8 is described. Color variation from pale yellow to brick-red was realized by partial substitution of Yb3+ or Mo6+ with various metal ions. The novel pigments of the formula Yb6−xDxMo2O15±δ (D = Na, Ca, Ti, Bi) and Yb6Mo2−xMxO15−δ (M = Na, Fe, Co, Nb, Bi) were characterized by powder XRD and UV–Vis-NIR diffuse reflectance spectroscopy. The high NIR solar reflectance of Yb6Mo2O15 of 93.7% (PTFE used as reference) was further improved with Yb5.4Ti0.6Mo2O15+δ and Yb6NbMoO15−δ reaching values of 99.4%, and 99.7%, respectively. Finally, the potential of the new rare earth molybdenum oxides for use as cool pigments in rooftop applications was demonstrated by the developed brick-red compound Yb6Mo1.6Fe0.4O15−δ having an enlarged band gap of 2.46 eV in comparison to 2.3 eV for Yb6Mo2O15. Furthermore, Yb6Mo1.6Fe0.4O15−δ exhibits an impressive NIR reflectivity of 90.4%.

Structural analysis and characterization of doped spinel Co2−xMxTiO4 (M=Mg2+, Mn2+, Ni2+, Cu2+ and Zn2+) coated mica composite pigments

A new kind of composite mica pigments were prepared by coating Co2−xMxTiO4 composite oxide nanoparticles onto mica, to investigate the effects of doping ions Mg2+, Mn2+, Ni2+, Cu2+ and Zn2+ on the properties of the doped composite pearlescent pigments, such as the crystal structure, color and shading power. The structure, morphology, color and shading power of the coated pigments were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer and CIE L*a*b* methods. SEM images of coated pigments showed that mica were coated uniformly with a single layer of dispersed nanoparticles. Research of the doped composite pigments showed that the doping ions had entered into the spinel crystal structure, forming a new kind of composite mica pearlescent pigments coated with Co2−xMxTiO4. For the analysis of color and shading power of the pigments, doping of Ni2+ and Zn2+ can improve the color and shading power of the doped pigments, but the larger dosage of Zn2+ doping can weaken the color and shading power of the doped pigments. Doping of Mg2+, Mn2+ and Cu2+ metal ions can also weaken the color and shading power of the doped pigments.

Estimating thermal performance of cool coatings colored with high near-infrared reflective inorganic pigments: Iron doped La2Mo2O7 compounds

The paper estimates the thermal performance of cool coatings colored with a series of novel, environmentally benign and high near-infrared reflective inorganic pigments. Nanocrystalline La2Mo2−xFexO9 (x=0, 0.03, 0.05, 0.08, 0.10) pigments were synthesized with acrylamide gel technique. The substitution of Fe3+ for Mo6+ in La2Mo2O7 results in the color change from white to brilliant yellow. Fe3+ doped pigments have high near-infrared spectral reflectance of 71–93%. The thermal performance of corresponding pigmented coatings was estimated. Results demonstrate that the designed colored coatings possess high spectral reflectance close to that of corresponding pigments in the short near-infrared spectral range, and high solar reflectance of 61–75%, far superior to traditionally available building roofing materials of the same color. The indoor air temperature difference reaches more than 4.5°C in the simulated experiment, in which the boxes were covered with designed cool coating and traditional coating on their tops, exhibiting its pronounced thermal performance.

Synthesis of Sr4Al14O25:Eu2+ green emitting luminescent nano-pigment by solution combustion method

Luminescent nano-pigments based on strontium aluminates doped with various amounts of europium rare earth ion (Sr4Al14O25:Eu2+) were synthesized by solution combustion method which involves the exothermic reaction of an oxidizer and an organic fuel. It is a suitable method for producing chemically homogenous and pure powders with very fine particle size. Phases studies by X-ray diffractometer indicated formation of pure phase Sr4Al14O25 with crystallite sizes about 52.46 nm and peak shift of about 2θ = 0.26° due to Eu2+ doping. scanning electron microscope micrographs also revealed that the particles have irregular morphology and wide particle size distribution. The emission spectrum showed main emission peak at about 480 nm. Energy transfer mechanism between the two emission centers and the effect of Eu2+ ion concentration on emission spectrum was studied and it was deduced that the maximum emission intensity occurred at 4 at% of Eu2+. Absorption spectrum of the samples were lower than 0.5 %, especially in emission region of the doped pigments.

Inorganic pigments doped with tris(pyrazol-1-yl)borate lanthanide complexes: A photoluminescence study

The inorganic pigments malachite, Egyptian blue, Ercolano blue and chrome yellow have been doped with the neutral homoleptic Ln(III) complex Ln(Tp)3 (Ln=Eu, Tb; Tp=hydrotris(pyrazol-1-yl)borate) in the presence of arabic gum or acrylic emulsion as binders, in order to obtain photoluminescent materials of interest for cultural heritage restoration. The doped pigments have shown emissions associated to f–f transitions in the visible range upon excitation with UV light. Thermal and UV-light ageings have been carried out. In all the cases the photoluminescent behaviour is maintained, but in the cases of acrylic-based paints emission spectra and lifetimes are strongly influenced by thermal treatments. The choice of binder and pigments influences the photoluminescent behaviour of the corresponding film paints.

Transition metal-doped titanium(IV) dioxide: Characterisation and influence on photodegradation of poly(vinyl chloride)

The effects of transition metal dopants (V(IV), V(V), Mn(II), Cr(III), Mo(V), and W(V)), introduced into TiO 2, upon the rate of photodegradation of poly(vinyl chloride) (PVC) films containing TiO 2 have been measured. The rates were determined mainly by monitoring carbonyl group formation. In another set of experiments, the rates of chloride ion release from irradiated PVC particles suspended in water undergoing agitation with air or O 2 in the presence of particles of doped TiO 2 were measured electrochemically. The doping of TiO 2 (rutile) with Cr(III), V(V) or Mn(II) reduces the photoactivity of the pigment, while doping by Mo(V) or W(V) enhances its photoactivity; the results obtained from carbonyl index measurements are paralleled closely by those from chloride ion release. Even the most aggressive doped pigments were less reactive than Degussa P25 pigment, while the greatest protection to PVC film was offered by TiO 2 particles coated with Al 2O 3 or SiO 2. Overall, the photoactivity of doped TiO 2 is a complex function of dopant concentration, the energy levels of the dopants in the TiO 2 lattice, their d electronic configuration and their local distribution. Photoactivity is also linked to other factors such as crystal type, particle size distribution and surface area. There is a clear relationship between the tendency of the dopant to induce the rutile-to-anatase transition and its effect in enhancing the photoactivity of the pigment. The characterisation of the doped pigments was achieved using X-ray powder diffraction, EPR spectroscopy, diffuse reflectance UV–vis spectrophotometry, scanning optical and electron microscopy and particle size analysis using LALLS.