Impact of synthesis method on the properties of near-infrared region-reflective SrSn0.9Mn0.1O3 brown pigment

Brown near-infrared region (NIR) reflective pigment of SrSn_0.9Mn_0.1O₃ was prepared using four different methods: the classical ceramic method, both wet and dry mechanochemical activation processes and the precipitation method. The pigments were characterised in terms of colour properties, NIR reflectivity, phase composition, particle size distribution and particle morphology. The prepared powders were applied to the organic matrix in mass tone, and their resulting colour hues shifted from copper brown via chocolate brown to dark brown. The NIR solar reflectance was calculated in the wavelength interval of 700–1650 nm following the ASTM 173-03 standard and their values of powder form were 25%–44%. The colour hue and NIR solar reflectance were dependent on the calcination temperature and the preparation method. The optimal condition for the preparation of the most NIR-reflective saturated brown pigment is the precipitation method and a temperature of 1050 °C (R_solar = 42%; C_{powder form} = 18.4), with an interesting matchstick shape of particles.     

Synthesis of black pigments containing chromium from leather sludge

The black ceramic pigments with spinel structure have been prepared by using Cr-rich leather sludge in this paper. The washed Cr-rich leather sludge calcined at 1100 °C for 1 h as chromium oxide precursor (named as CA) was mixed with an appropriate proportion of other industrial metallic oxides, followed synthesizing black ceramic pigment by sintering. Both non-washed and washed sludge fired at 1100 °C were characterized by X-ray fluorescence (XRF) in order to determine their chemical compositions and X-ray diffraction (XRD) analysis to confirm that CA mainly contains Cr₂O₃ crystal phase. The results show that CA could be used as a source of chromium to prepare black pigment. The crystalline phases of obtained pigments were characterized by XRD. Furthermore, the morphology as well as the composition of pigments was investigated by scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The color coordinates of pigments were examined and compared with the commercial pigments based on CIE-L* a* b* values measured using UV–vis spectroscopy. The obtained pigments sintered at 1200 °C with 35–55 wt% content of CA possess the excellent black spinel structure and color effect. Under optimized conditions, the pigment has low average spectral reflectance (7%).     

In situ synthesis of orange rutile ceramic pigments by non-conventional methods

Different precursor-mixtures of orange Cr,Sb-TiO₂ ceramic pigment have been obtained by non-conventional methods (heterogeneous ammonia coprecipitation, urea homogeneous coprecipitation, PECHINI polyester method and an original aqueous–organic coprecipitation method in water–diethylenglycol medium) in order to produce in situ the pigment through the ceramic body firing. The pigmenting performances of powders were appraised in two cases: (a) as ceramic pigment for glazed porcelain stoneware and (b) as ceramic inks for screen printing of porcelain stoneware. Samples were characterised by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV–vis-NIR spectroscopy by diffuse reflectance method, CIE-L*a*b* colour parameters, BET specific surface area and crystallite size measured by the Scherrer method. The colouring performance of raw powders obtained by non-conventional methods in glazed porcelain stoneware improves that of the ceramic samples fired at 1100 °C used as reference. TEM observations indicate nanostructured powders with pigmenting performance depending on factors such as their specific surface area (BET), the crystalline phases detected by XRD (e.g. anatase–rutile presence) and their crystallite size (Scherrer measurements). Ammonia coprecipitated samples, both in water and in water–diethylenglycol medium without surfactant addition, or modified by the addition of sodium dodecyl sulphate as surfactant, stand out by their colouring performance.     

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.     

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.     

Synthesis and characterization of novel nontoxic BiFe1−xAlxO3/mica-titania pigments with high NIR reflectance

A series of novel nontoxic near-infrared (NIR) reflective pigments based on Al-doped BiFeO₃ coated mica-titania were synthesized by precipitation combined with sol-gel method. The pigments of the formula BiFe_1−xAl_xO₃/mica-titania (x = 0, 0.1, 0.2, 0.3, 0.4) were characterized by XRD, FE-SEM, TG-DTA, UV–vis–NIR spectrophotometer and CIE L^* a^* b^* color scales. The results illustrate that the BiFeO₃ nanoparticles are coated on the surface of mica-titania uniformly, and the doped BiFe_1−xAl_xO₃/mica-titania is similar to BiFeO₃/mica-titania composite in morphology. Furthermore, the absorption edge of composite pigments shift to shorter wavelength (533–495 nm) can be attributed to O_2p-Fe_3d charge transfer transitions and change the color of the pigments from brown to orange. Additionally, the NIR solar reflectance of the powdered pigments and pigmented coatings were measured. The results reveal that with the increase of progressive doping of Al³⁺ for Fe³⁺, the NIR solar reflectance of the pigments increase gradually and exhibit higher NIR solar reflectance (R* ≥ 47.8%) than the conventional pigment of similar color. Moreover, we also evaluated the thermal and chemical stability of the pigments. In conclusion, the pigments have the potential to be applied as “cool pigments”.     

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%).     

金红石型云母钛珠光颜料的合成研究

采用化学诱导法合成金红石型云母钛珠光颜料 ,以SnCl4及其复配物为金红石诱导促进剂 ,在 85 0℃、0 5h的焙烧条件下合成得到了完全金红石型的云母钛珠光颜料。由正交试验得到了金红石化学诱导促进剂最佳复合配方为 :m(云母 )∶m(SnCl4)∶m(ZnO)∶m(C助剂 ) =10 0∶3∶2∶4。此方法缩短了焙烧时间 ,并使颜料表面的TiO2 相转变温度降低了约 10 0℃ ,使制得的耐候性云母钛珠光颜料具有高的珠光光泽     

An overview of using solid wastes for pigment industry

This work reports the use of wastes (Al-rich anodizing sludge, Cr/Ni galvanizing sludge, foundry sand, tionite and marble sawing mud) to formulate distinct inorganic pigment structures that were synthesized by the solid state reaction method. One of the tested formulations is a novel pigment based on hibonite (CaO·6Al₂O₃), that was found a suitable hosting structure to accommodate cobalt or nickel chromophore ions in tetrahedral coordination, then giving strong blue or turquoise hues, respectively. The use of Cr as chromophore was tested in three distinct pigment structures: (i) red-wine Cr-CaSnSiO₅ and brown Cr-CaTiSiO₅; (ii) Cr-CaTiO₃; (iii) and Cr-TiO₂. Developed phases were determined, and the colouring mechanisms of the chromophore species were defined based on diffuse reflectance data. Then, the pigments were added to a standard transparent glaze, and the hues which developed were estimated from L*a*b* colorimetric measurements under the oxygen partial pressure in the atmosphere, to define stable workability window.     

Mica/polypyrrole (doped) composite containing coatings for the corrosion protection of cold rolled steel

Micas/polypyrroles (PPys) doped with molybdate, p-toluene sulfonate, dodecyl benzene sulfonate, and 2-naphthalene sulfonate composite pigments were synthesized by chemical oxidative polymerization and characterized in coatings for corrosion protection on cold rolled steel substrate by various electrochemical techniques. Synthesized composite pigments were characterized for morphology by scanning electron microscopy, which indicated physical formation of PPy on the surface of mica. Chemical composition of the composite pigments was analyzed by X-ray photoelectron spectroscopy which chemically confirmed doped PPy formation on the mica surface. Coatings were formulated at 20% pigment volume concentration (composite pigments or as-received mica pigment) and were applied on cold rolled steel substrate. Coatings were exposed to salt spray test conditions (ASTM B117) for 30 days and were periodically assessed for corrosion with electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and potentiodynamic polarization. EIS and circuit modeling results demonstrated higher coating resistance (R _c) for mica/PPy (doped) composite coatings as compared to as-received mica pigment containing coating after 30 days of salt spray exposure. Lower current density and more positive corrosion potential values were observed for mica/PPy (doped) composite coatings as compared to mica pigment-based coating in potentiodynamic polarization measurements, indicating improved corrosion protection for cold rolled steel substrate. OCP measurements revealed more positive values for mica/PPy (doped) composite coatings as compared to mica pigment-based coating suggesting superior corrosion protection for mica/PPy (doped) composites.     

Allochroic effect of praseodymium doped neodymium molybdate pigment synthesized by solid-state reaction

This paper was to synthesize praseodymium-doped neodymium molybdate allochroic pigments with different molar ratios of molybdenum (Mo), neodymium (Nd) and praseodymium (Pr) through solid-state reactions. The pigments synthesized were investigated by X-ray diffraction (XRD), selected area electron diffraction (SAED), thermogravimetry and differential thermal analysis (TG-DSC), diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS) and colorimeter. The results show that a pure neodymium molybdate (i.e., Nd₂MoO₆) can be formed after sintering at 1000 °C for 3 h, and praseodymium-doped neodymium molybdate can be synthesized after sintering at 1000 °C for 3 h due to praseodymium ions entering in the lattice of Nd₂MoO₆. The crystal structure in the pigment synthesized can transform from cubic to tetragonal depending on the molar ratio of neodymium/molybdenum and sintering procedure. The color properties of pigments were measured in color space CIEL*a*b* under different standard illuminants (i.e., solar-light (D65), incandescent light (A), cool white fluorescent lamp (F2), and three-band fluorescent lamp (F11)). The results show that the colors of the pigments vary under different illuminants. According to the color difference (ΔE) analysis, neodymium molybdate pigment exhibits a maximum color difference of 10.69, and the maximum color difference of praseodymium-doped neodymium molybdate pigment with doping content of 0.2 increases to 17.63 due to the Pr³⁺ ions substitution for Nd³⁺ ions in the lattice. In addition, the color difference of the pigments with allochroic effect was discussed based on the colorimetry. The color difference of the pigments is due to a high reflectance region at 540–550 nm and a low reflectance region at 380–500 nm.     

Environmental-friendly yellow pigment based on Tb and M (M = Ca or Ba) co-doped Y2O3

A yellow inorganic ceramic pigment with general formula Y_1.86?xM_xTb_0.14O_3?x/2 (M = Ca and/or Zn) with x = 0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300 °C when x = 0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y_1.86Tb_0.14O₃ samples. The intensity of the yellow colour in the samples is related to the presence of Tb⁴⁺ ions. Samples with higher concentration of Tb⁴⁺ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x = 0.06 and 0.32 fired at 1300 °C were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers.     

Silica-silicon composites for near-infrared reflection: A comprehensive computational and experimental study

Compact layers containing embedded semiconductor particles consolidated using pulsed electric current sintering exhibit intense, broadband near-infrared reflectance. The composites consolidated from nano- or micro-silica powder have a different porous microstructure which causes scattering at the air-matrix interface and larger reflectance primarily in the visible region. The 3 mm thick composite compacts reflect up to 72% of the incident radiation in the near-infrared region with a semiconductor microinclusion volume fraction of 1% which closely matches predictions from multiscale Monte Carlo modeling and Kubelka-Munk theory. Further, the calculated spectra predict a reddish tan compact with improved reflectance can be obtained by decreasing the average particle size or broadening the standard deviation. The high reflectance is achieved with minimal dissipative losses and facile manufacturing, and the composites described herein are well-suited to control the radiative transfer of heat in devices at high temperature and under harsh conditions.     

Low temperature synthesis of green submicro Cr-ZrSiO4 ceramic pigments by solid-state method

A green submicro Cr-ZrSiO₄ pigment was successfully synthesized with Li₂CO₃ used as mineralizer by a simple solid-state method at low temperature. The formations of the samples with and without mineralizer were investigated by X-ray diffraction, scanning electron microscope, and thermogravimetry differential thermal analysis, respectively. The reflectance spectrum and color properties of the Cr-ZrSiO₄ pigments were characterized and analyzed. The XRD results show that Li₂CO₃ as a mineralizer can significantly promote the formation of ZrSiO₄ and decrease the synthesis temperature to 900°C, which is 500°C lower than without mineralizer. The SEM revealed that the Li₂CO₃ containing ceramic powders are more homogeneous than undoped samples and have uniform particle size between 100 and 500 nm. It is indicated that Li₂CO₃ as a mineralizer can effectively destroy the Si-O bond of random network structure, reduce the viscosity and accelerate the formation of ZrSiO₄ at low temperature. The results from CIE L*a*b* characterization indicate that the samples exhibit high doping limitation (x = 0.06) and green hue (a* = −10.13) at 900°C. In addition, the method used in this work has the advantages of simple process, low cost, and large-scale production, and is expected to synthesize other types of high-temperature ceramic pigments.     

Design,fabrication, and magnetic properties of novel (Ni,Cr,Zr)-co-doped M-type barium ferrite ceramics

Multicomponent co-doping is an effective method to balance the counteracting magnetic properties of ferrite ceramics. In this work, novel (Ni,Cr,Zr)-co-doped M-type barium hexaferrites (BaFe_12-3xNi_xCr_xZr_xO₁₉, x = 0–0.8) were designed and synthesized by traditional solid-state reaction. Thermogravimetric analysis indicated that NiO would participate in the formation of secondary phase NiFe₂O₄ in the as-synthesized powder. Through traditional solid-state sintering, by using the synthesized pure-phase magnetic powders, almost full-dense ceramics were fabricated. Visual high-temperature deformation analysis revealed that there was no obvious difference in the sintering behavior and densification temperature of the ceramics with different compositional x, due to the low sintering activity of the as-synthesized magnetic powders. And X-ray diffraction analysis indicated that all the fabricated ceramics are of pure-phase M-type barium ferrite, and the lattice parameter c/a firstly increased as x raised up to 0.4 and then remained almost unchanged with further increased x, even if the lattice distortion became heavier. Microstructure examination revealed that the grain size monotonously decreased as the quantity of the substituent ions increased. The remnant magnetization and coercivity of the fabricated ceramics decreased monotonously as x increased, while the saturated magnetization could be maintained till the samples with x ≤ 0.4. Taking all the parameters into consideration, the samples with x = 0.4 might be a good candidate for transformer cores.     

TiO2@CoTiO3 complex green pigments with low cobalt content and tunable color properties

Green complex pigments with TiO₂@CoTiO₃ core–shell structure were prepared through calcination of precursors obtained from the precipitation of Co²⁺ on TiO₂ particles. The synthesized pigments were characterized by colorimetry, near-infrared diffuse reflectance spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet–visible (UV–vis) spectroscopy. The pigments were found to consist of a rutile TiO₂ core and outer ilmenite CoTiO₃ shell. The green pigments with good color properties could be obtained via calcination of the precursors at 800 °C. The pigments with Co/Ti ratio of 0.4 had the highest green component value and exhibited good color properties (L*=49.51, a*=−34.58, b*=5.53). The color properties could be tuned by just changing the Co/Ti ratio. The as-prepared complex pigments exhibited an enhanced near-infrared reflectance compared with pure CoTiO₃ pigments and also exhibited better color properties than the mixed pigments of TiO₂ and CoTiO₃. Further, the complex pigments had much lower consumption of cobalt compared to pure CoTiO₃ and Co₂TiO₄ pigments. The special core–shell structure was found to be responsible for the enhanced near-infrared reflectance and good color properties.     

Solution combustion synthesis of FeCr2O4:Zn,Al pigment powders

FeCr₂O₄:Zn,Al pigment powders were prepared via a solution combustion synthesis method. Effects of Zn and Al dopants and less/extra Fe content on the structure, molecular bonds, and optical properties of powders were studied. Results showed that addition of dopants as well as extra/less content of Fe led to weaker combustion and consequently lower X-ray diffraction peak intensities, lattice parameters, and differential thermal analysis peak intensities. Moreover, Fourier transform infrared analysis illustrated that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies with moving away from stoichiometry. In addition, scanning electron micrographs showed that in all samples, porous spongy microstructures were formed with highly flake-like agglomerated particles. Furthermore, there was a significant difference between the powder samples and the tiles colored with in glaze powders due to the partial dissolution of pigments in contact with the molten glaze of tiles. In comparison to the tile colored with the stoichiometric FeCr₂O₄ pigments without dopants, the color difference (ΔE) in the tiles colored by the iron chromite pigments doped with Zn and Al dopants and less/extra Fe content reached the high values as large as ΔE = 36.19. The solar reflectance values (R_s) in near-infrared region were above 50% in all samples. Near 80% R_s in the tile colored by the iron chromite pigment doped with 3 mol% Zn and the yellowish brown appearance (L* = 43.44, a* = 6.77, b* = 18.38, c* = 19.59, h = 69.79) showed that the sample was a good candidate for cool building materials such as roof tiles.     

Preparation and characterization of SnO2 nanoparticles in aqueous solution of [EMIM][EtSO4] as a low cost ionic liquid using ultrasonic irradiation

A facile, template-free, room temperature and environmentally benign green route for the preparation of SnO₂ nanoparticles in aqueous solution of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO₄], room-temperature ionic liquid (RTIL), via ultrasonic irradiation is proposed. The X-ray diffraction (XRD) studies display that the products are excellently crystallized in the form of tetragonal rutile structure. Energy dispersive X-ray spectroscopy (EDX) investigations reveal the products are pure. The morphology of as-prepared nanoparticles was characterized by scanning electron microscopy (SEM). Diffuse reflectance spectra (DRS) of the products exhibit band gap energy of about 3.98 eV which shows blue shift of 0.38 eV that can be attributed to quantum confinement effect of SnO₂ nanoparticles. A possible formation mechanism of the SnO₂ nanoparticles using ultrasonic irradiation in aqueous solution of the RTIL is presented.     

Cool and photocatalytic yellow ceramic pigments; from lead-tin to Cr doped scheelite pigments

The historical lead based pigments (XVII-XVIII century), the modern Ni,Sb-rutile (1939) and Pr-zircon (1961) yellow pigments as well as the novel yellow pigments based on Cr-scheelite and Mo-yttrium cerate pigments were synthesized and compared as semiconductors of high NIR reflectance (cool pigments) and with photocatalytic activity. All powders are wide band gap semiconductors (E_g=2.1–3.1?eV) with high NIR reflectance, ranging from 80% for Cr-Scheelite to 86% of Naples yellow, except Ni,Sb-rutile pigment that shows 55%. The low color performance of lead based pigments in alkyd paint and lead-free glazes along with its toxicity, discard these pigments as cool eco-friendly pigments. The Pr-zircon, Cr-scheelite and Mo-yttrium cerate pigments exhibit high NIR reflectance (R_NIR =?80–83%) and yellow coloration (b*?=?57.6–45.3) but only Pr-zircon and Cr-scheelite show color stability in alkyd paint and lead free glaze applications. Regarding to results of Orange II photodegradation test, lead based and Ni,Sb-rutile pigments inhibits the photolysis of the UV irradiation, acting as protecting agents from irradiation. The Mo-cerate shows a slight photocatalytic activity (t_1/2 =?301?min) and both Cr-scheelite and Pr-zircon pigments show a moderate activity (t_1/2 =?198 and 184?min respectively). Looking at a possible industrial application, the leaching test shows that the fluorides released by Pr-zircon (16.8?mg/g) as well as the Cr(VI) of Cr-scheelite (6?mg/g) should be treated and controlled. The Cr-scheelite solid solution Ca(Cr_xW_1-x)O₄ is stable to x?=?0.2 but its pigmenting capacity saturates at x?=?0.1.     

Synthesis and characterization of multi-colored pigments of LiRE(MoO4+δ)2 (RE = Ce,Pr, Nd,Er) with high near-infrared reflectance

Multi-colored pigments based on rare earth (RE) with the formula of LiRE(MoO_4+δ)₂ (RE = Ce, Pr, Nd, Er) were developed via the solid-state reaction method. Related characterization techniques were used for investigating the crystal structure, morphology characteristic, reflecting property, and color performance of the synthesized pigment. The prepared pigment of LiRE(MoO_4+δ)₂ (RE = Ce, Pr, Nd, Er) shows four colors, namely orange-yellow (Ce), bright green (Pr), lavender (Nd) and pink (Er). Moreover, all of the pigments possess high NIR reflectance in the range of 95–98% at 1100 nm. Remarkably, the average NIR reflectance of LiCe(MoO_4+δ)₂ pigment reaches up to 95.28%, and the NIR solar reflectance is also up to 95.02%. Besides, the pigment of LiCe(MoO_4+δ)₂ exhibits good yellow hue (b* = 75.08). The application practical of LiCe(MoO_4+δ)₂ coated on galvanized sheet exhibits excellent coloring performance. The designed pigments show chemical stabilities in the acid/alkali testing. All of above, the superior performances of color and reflectance from LiRE(MoO_4+δ)₂ provide visual enjoyment for people and exhibit potential for energy savings.