Synthesis and spectral characterization of CoxMg1-xAl2O4 as new nano-coloring agent of ceramic pigment

Control of Optical Reflection in Ca2MgWO6 by Co and Mo Doping

To develop novel inorganic red pigments without harmful elements, we focused on the band structure of Ca2(Mg, Co)WO6 and attempted to narrow its bandgap by replacing the W6+ sites in the host structure of Mo6+. Ca2Mg1-xCoxW1-yMoyO6 (0.10 ≤ x ≤ 0.30; 0.45 ≤ y ≤ 0.60) samples were synthesized by a sol-gel method using citric acids, and the crystal structure, optical properties, and color of the samples were characterized. The Ca2Mg1-xCoxW1-yMoyO6 solid solution was successfully formed, which absorbed visible light at wavelengths below 600 nm. In addition, the absorption wavelength shifted to longer wavelengths with increasing Mo6+ content. This is because a new conduction band composed of a Co3d-W5d-Mo4d hybrid orbital was formed by Mo6+ doping to reduce the bandgap energy. Thus, the color of the samples gradually changed from pale orange to dark red, with a hue angle (h°) of less than 35°. Based on the above results, the optical absorption wavelength of the Ca2Mg1-xCoxW1-yMoyO6 system can be controlled to change the color by adjusting the bandgap energy.

Synthesis and characterisation of Ba(Zn1−xCox)2Si2O7 (0 ≤ x ≤ 0.50) for blue-violet inorganic pigments

Ba(Zn_1−xCo_x)₂Si₂O₇ (0 ≤ x ≤ 0.50) solid solutions were synthesized as novel blue-violet inorganic pigments by a conventional solid-state reaction method. The crystal structure, optical properties, and colour of the pigments were characterized. All the pigments were obtained in a single-phase form. The pigments strongly absorbed visible light at wavelengths from 550 to 650 nm, corresponding to the range of green to orange light. This optical absorption was caused by the d–d transition of the tetrahedrally coordinated Co²⁺ (⁴A₂(F) → ⁴T₁(P)), which was the origin of the blue-violet colour of the pigments. The most intense colour was obtained for Ba(Zn_0.85Co_0.15)₂Si₂O₇, where a* = +52.2 and b* = −65.5 in the CIE (Commission Internationale de l'Éclairage) L*a*b* system. These absolute values were significantly larger than those of commercial violet pigments such as Co₃(PO₄)₂ (a* = +33 and b* = −32) and NH₄MnP₂O₇ (a* = +39 and b* = −21). Therefore, the Ba(Zn_0.85Co_0.15)₂Si₂O₇ pigment could be a novel blue-violet inorganic pigment.

Ba(Zn_1−xCo_x)₂Si₂O₇ (0 ≤ x ≤ 0.50) solid solutions were synthesized as blue-violet inorganic pigments and the colour gradually changed from pale blue-violet to deep blue-violet with increasing the Co²⁺ concentration.

A novel method for the clean synthesis of nano-sized cobalt based blue pigments

The nano-sized modified composition can effectively improve chromatic performance to produce thenard's blue colour in decoration of ceramics.

Simple and Efficient Rout for Synthesis of Spinel Nanopigments

Nano-sized CoxMg1−xAl2O4(x= 0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1) inorganic pigments were synthesized via combustion method usingβ-alanine, as a single and novel fuel, at 800°C in open furnace. The obtained powders were characterized by means of X-ray diffraction (XRD), energy dispersive X-ray (EDX) elemental analysis, diffuse reflectance spectrum (DRS), CIEL*a*b* color measurements, and scanning electron microscope (SEM). XRD patterns show that all calcined powders have single phase cubic spinel structure. EDX analysis revealed the composition of desired spinels. The diffuse reflectance spectra of the CoxMg1−xAl2O4(x> 0) pigments confirmed the presence of tetrahedrally coordinated Co2+ions in the spinel lattice. The colorimetric data pointed out the formation of blue pigments (forx> 0), corresponding to highly negative values ofb*, and the bluest color was produced forx= 0.8 and 1. SEM images showed nanoparticles with less than 30 nm crystallite size and flakes-like appearance of all synthesized powders.

Synthesis, thermal and spectral characterization of nanosized Ni(x)Mg(1-x)Al2O4 powders as new ceramic pigments via combustion route using 3-methylpyrozole-5-one as fuel

New Ni(x)Mg(1-x)Al(2)O(4) nanosized in different composition (0.1≤x≤0.8) powders have been synthesized successively for first time by using low temperature combustion reaction (LTCR) of corresponding metal chlorides, carbonates and nitrates as salts with 3-methylpyrozole-5-one (3MP5O) as fuel at 300°C in open air furnace. Magnesium aluminate spinel (MgAl(2)O(4)) was used as crystalline host network for the synthesis of nickel-based nano ceramic pigments. The structure of prepared samples was characterized by using different techniques such as thermal analysis (TG-DTG/DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). UV/Visible and Diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameters methods have been used for color measurements. The obtained results reveal that Ni(x)Mg(1-x)Al(2)O(4) powder of samples is formed in the single crystalline and pure phase with average particle size of 6.35-33.11 nm in the temperature range 500-1200°C. The density, particle size, shape and color are determined for all prepared samples with different calcination time and temperature.

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy

Co(x)Zn(1-x)Al(2)O(4) (x = 0.01-0.6) nanoparticles were synthesized by the citrate sol-gel method and were characterized by X-ray powder diffraction and transmission electron microscopy to identify the crystalline phase and determine the particle size. X-ray photoelectron spectroscopy and (27)Al solid-state NMR spectroscopy were used to study the distribution of the cations in the tetrahedral and octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles as a function of particle size and composition. The results show that all of the as-synthesized samples exhibit spinel-type single phase; the crystallite size of the samples is about 20-50 nm and increases with increasing annealing temperature and decreases with Co-enrichment. Zn(2+) ions are located in large proportions in the tetrahedral sites and in small proportions in the octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles. The fraction of octahedral Zn(2+) increases with increasing Co concentration and decreases with increasing particle size. Besides the tetrahedral and octahedral coordinations, the presence of the second octahedrally coordinated Al(3+) ions is observed in the nanoparticles. The change of the inversion parameter (2 times the fraction of Al(3+) ions in tetrahedral sites) with Co concentration and particle size is consistent with that of the Zn fraction in octahedral sites. Analysis of the absorption properties indicates that Co(2+) ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The inversion degree of Co(2+) decreases with increasing particle size.