Blue Ceramic Pigments Research Articles

Precipitation synthesis of Zn2-xCoxSiO4 blue ceramic pigments: Color performance and application

A simplified precipitation route based on using silica hydrogel derived from serpentine minerals as a source of silica SiO2 has been first applied for producing blue cobalt-doped willemite pigments. The relevant variations of cobalt ions concentrations in SiO2–NaOH–ZnCl2–CoCl2–H2O system adequate with Zn2-xCoxSiO4 compositions where 0<x ≤ 0.92 and heat-treatment at 900 °C have yielded the pigments demonstrating a wide spectrum of blue tints. The optical characteristics of these pigments have revealed that Zn1·5Co0·5SiO4 pigment is distinguished by the highest absorption responsible for deepest blue hue similar to ultramarine. The comparison of their chromatic parameters with those of the identical ones produced by sol-gel routes has shown that the synthesized pigments with the compositions where x = 0.2 ÷ 0.5 manifest competitive color performances. The synthesis optimization has reduced calcination temperature up to 800 °C and stirring time up to 60 min. The homogeneity achieved in the intermediates by the suggested synthesis has yielded the pigments having uniform crystalline structure with controlled particle size. 120-minutes stirring has reduced the pigment particle size to dimensions less than 66 nm. Zn1.5Co0.5SiO4 pigment exhibits excellent color performances and tinting on heating up to 1200 °C and in wall tile glaze.

Study of the Synthesis Variables in the Preparation of CoAl2O4 Pigment Using Microwaves to Reduce Energetic Consumption

Due to the importance of optimizing the manufacture of ceramic pigments, motivated by the increase in prices of both raw materials and energy, and the need to control manufacturing parameters to obtain optimal conditions for the preparation of ceramic inks, two synthesis routes (traditional route and coprecipitation) and two calcination methods (traditional oven and microwave oven) are proposed to obtain the blue ceramic pigment CoAl2O4 with the aim of minimizing the use of mineralizers or flux agents and reducing energy consumption in its manufacturing. The pigments prepared were characterized by thermal analysis and structurally by XRD and SEM, with particle sizes below 300 nm observed. Finally, the colorimetric coordinates of glazed tiles with the pigments obtained were characterized. In all cases, the microwave-assisted synthesis increased the color intensity, considerably decreasing the temperature and calcination time, obtaining a particle size under 300 nm with a very narrow size distribution, and substantially improving the energy cost of its preparation and the color development of the final product. The viability of the combination of synthesis by coprecipitation and microwave calcination as a method of industrial preparation of ceramic pigments has been demonstrated.

Effects of Coloration of Spinel CoAl2O4 Cobalt Blue Pigments: Composition, Structure, and Cation Distribution

Cobalt blue ceramic pigments mainly consisting of CoAl2O4 are subject to the difficulty of color control. Here, a perspective is reported regarding research on the reasons for color change based on the control of the heat treatment and ratio of components. Macroscopically, the composition of pigment powders determines the color. Microscopically, the crystallite characters including size, cation distribution, and structure have an important effect on the color. The ingredient, structural, and color properties of the pigment powders are analyzed using thermo gravimetry–differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD) measurement, Rietveld refinement, energy dispersive spectrometer (EDS), and colorimetry analysis. The color is proven to be associated with cation distribution, such as that of Co2+ and Co3+. It is indicated that high heating temperature, long heating time, and a large proportion of Al3+ can, respectively, induce the Co2+ and Al3+ in tetrahedral and octahedral sites.

Color hue controlling of blue ceramic pigments with low cobalt contents via crystal field engineering

Color hue controlling of blue ceramic pigments with low cobalt contents via crystal field engineering

Microwave-assisted polyol synthesis of V–ZrSiO4 nanoparticles and its use as a blue ceramic pigment

Microwave-assisted polyol synthesis of V–ZrSiO4 nanoparticles and its use as a blue ceramic pigment

제강분진을 활용한 고온발색 청색무기안료 합성 및 특성에 관한 연구

Electric arc furnace dust (EAFD) is a solid waste generated by the steel-scrap recycling process. It mainly consists of zinc oxides(ZnO), alumina (Al₂O₃), iron oxides (Fe₂O₃), and silica (SiO₂). Here we report the preparation and characterization of blue ceramic pigments using EAFD powder as a starting material. (Zn(EAFD),Co)Al₂O₄ blue ceramic pigment was prepared by the solid-state reaction method. The color characteristics of the pigment obtained were compared with those of pure CoAl2O4. The new pigment was characterized using XRD, CIE-L * a * b * color-measurements, SEM, and EDX. The XRD analysis revealed that the (Zn(EAFD), Co)Al₂O₄ pigment was composed of mainly the spinel phase of (Zn,Co)Al₂O₄. The Zn(EAFD) 0.25 ,Co 0.75 Al₂O₄ pigments showed a vivid blue color with a b * value of -28.64 and a good glaze stability with a transparent glaze.

Co-Doped Willemite 파란색 안료의 합성과 생성기구

Turquoise blue pigment of Vanadium-zircon blue (DCMA number 14-42-2), which was already commercialized, was stable to be reproduced but insufficient to give strong blue. However, it possible to obtain more intense blue by partially substituting cobalt ions into the willemite(Zn₂SiO₄) lattice classified into DCMA number 7-10-2 for blue ceramic pigment. By the composition of willemite Co x Zn 2-x SiO₄(X=0.01, 0.03, 0.05, 0.07, 0.09 mole), this study used reagent grade zinc oxide, cobalt oxide and silicon dioxide as starting materials, carrying out the synthesis with solid reaction method by adding H₃BO₃ as a mineralizer. The firing temperature was between 1200℃ and 1400℃. The characteristics of synthesized pigment were analyzed by X-ray diffraction, Raman spectroscopy and SEM and the characteristics of color tones were analyzed by UV-Vis spectroscopy and CIE-L * a * b * measurement. As a result, the optimal composition was Zn 1.95 Co 0.05 with 1wt% of H₃BO₃ as a mineralizer and firing condition was 1350℃/3 h. L * a * b * value was 29.25, 41.03, -59.93 for on glaze pigment and 37.03, 36.41, -60.03 for under glaze pigment.

Co-doped willemite ceramic pigments: Technological behaviour, crystal structure and optical properties

Cobalt-doped willemite is a promising blue ceramic pigment, but some important aspects concerning crystal structure, optical properties and technological behaviour are still undisclosed. In order to get new insight on these features, willemite pigments (Zn 2− x Co x SiO 4, 0 < x < 0.3) were synthesized by the ceramic route and characterized from the structural (XRPD with Rietveld refinement), optical (DRS and colorimetry), microstructural (SEM, STEM, TEM, EDX, EELS) and technological (simulation of the ceramic process) viewpoints. The incorporation of cobalt in the willemite lattice, taking preferentially place in the Zn1 tetrahedral site, induces an increase of unit-cell parameters, metal–oxygen distances, and inter-tetrahedral tilting. It causes shifting and enhanced splitting of spin-allowed bands of Co 2+ in tetrahedral coordination, implying slight changes of crystal field strength Dq and Racah B parameter, but increasing spin-orbit coupling parameter λ. Willemite pigments impart deep blue hue to ceramic glazes and glassy coatings with a colouring performance better than commercial Co-bearing colorants in the 800–1200 °C range. Detailed SEM-TEM investigation and microanalysis proved that no diffusion phenomena occur at the pigment–glassy coating interface and that willemite pigments are chemically inert during firing at 1050 °C.

Synthesis of Mg 1−xCo xAl 2O 4 blue pigments via combustion route

MgAl 2O 4 was successfully used as crystalline host network for the synthesis of cobalt-based blue ceramic pigments. Different compositions of Mg 1− x Co x Al 2O 4 ( x = 0.1–0.3) powders have been prepared by the combustion reaction of corresponding metal nitrates with mixtures of urea and β-alanine. The resultant powders were characterized by means of XRD, TG-DTA, EDAX, SEM, BET surface area, diffuse reflectance spectrometry and CIEL∗ a∗ b∗ color measurement. For x = 0.2, thermal analysis investigations evidenced that combustion reaction occurs at 276 °C. XRD analysis certified the formation of the designed solid solution, no additional thermal treatment being required. EDAX elemental analysis confirmed the purity of the as-prepared compound. The resulted powders had large surface areas, which varied from 8.7 to 62.6 m 2/g. The crystallite size of Mg 1− x Co x Al 2O 4 powders was less than 15 nm. Experimental results evidenced that as the proportion of Co 2+ increased, the crystallite size decreased and the specific surface area increased. The diffuse reflectance spectra of the Mg 1− x Co x Al 2O 4 pigments confirmed the presence of tetrahedrally coordinated Co 2+. CIEL∗ a∗ b∗ chromatic coordinates indicated that the bluest color was obtained for x = 0.2.

Blue-violet ceramic pigments based on Co and Mg Co 2− xMg xP 2O 7 diphosphates

Solid solutions of Co and Mg diphosphates with compositions Co 2− x Mg x P 2O 7 ( x = 0, 0.1, 0.2, 0.3, 0.5, 0.7, 1.0, 1.5 and 1.8) have been prepared and characterized for the first time as alternative low-toxicity blue ceramic pigments. The compositions were prepared through the conventional coprecipitation route and calcined up to 1000 °C/2 h. Samples were characterized by thermal analysis, XRD, SEM/EDX, UV–vis-NIR spectroscopy and colour measurements (CIE- L * a * b *). Isostructural Co 2− x Mg x P 2O 7 diphosphate solid solutions (monoclinic system and P21/ c spatial group) formed successfully within the studied range of compositions, accompanied only by a minor quantity of residual Co or Mg orthophosphates (M 3(PO 4) 2). Interestingly, the obtained solid solutions developed nice blue-violet colourations even with high Mg doping after enamelling within double-firing ( x = 1.5–1.8) and single-firing ( x = 1.0–1.5) ceramic glasses. These optimal compositions containing a minimized Co amount (measured values around 7–16 wt%) could be therefore less toxic alternatives to the conventional Co 3(PO 4) 2 blue ceramic pigment.

Ni-doped hibonite (CaAl 12O 19): A new turquoise blue ceramic pigment

A new structure for ceramic pigments was synthesized by a conventional solid state reaction process. It is based on Ni-doped hibonite, CaAl 12O 19, which assumes a turquoise-like blue colour similar to that of V-doped zircon. Hibonite is associated with anorthite, CaAl 2Si 2O 8, acting like a fluxing agent in order to lower the synthesis temperature, and with cassiterite, SnO 2, acting as a tin buffer to promote coupled Ni 2+ + Sn 4+ → Al 3+ + Al 3+ substitutions, in order to ensure the electric neutrality of the hibonite lattice. Since relatively low chromophore contents are required, this new system constitutes an interesting alternative to the common blue ceramic pigments based on cobalt aluminate spinel or vanadium-doped zircon, implying lower cost and environmental advantages. The pigments characterization was performed by X-ray powder diffraction, diffuse reflectance spectroscopy, CIELAB colorimetric analysis, and testing in ceramic glazes and bodies. The substitution of Al 3+ by bigger ions, like Ni 2+ and Sn 4+, increases the cell volume compared to undoped hibonite and is responsible for the turquoise blue colour, as verified by UV–vis analysis. The chromatic mechanism is due to incorporation of Ni 2+ in tetrahedral coordination, likely occurring at the site M3 of the hibonite lattice, where it partially substitutes the Al 3+ ion. While this product shows a strong hue as a pigment, it is not stable after severe testing in glazes and attempts to improve its colouring performance are now under development.

Synthesis and characterization of new nano-particles as blue ceramic pigment

The synthesis of a new nano-blue ceramic pigment Co x Mg 1− x Al 2O 4 (0 ≤ x ≤ 0.1) using the combination between co-precipitation and combustion synthesis (CS) method. The structure of pigments is assigned based on thermogravimetric and differential thermogravimetric analysis (TG-DTGA), X-ray diffractions (XRD), and UV–vis spectroscopy. Also, diffuse reflectance spectroscopy (DRS) using CIE L* a* b* parameter measurement method, infrared spectroscopy (IR) and transmission electron microscopy (TEM) is used. The result revealed that the nano-size particle pigment was obtained in range 24–35 nm by using 3-methyl-pyrozole-5-one (3MP5O) as a fuel at 400 °C in open furnace. Also, results show the varying colors and particles’ size as a result of different calcination temperatures from 500 to 1200 °C for 2 h.

Structure and colour of cobalt ceramic pigments from phosphates

Co 3− x Fe x P 2O 8+ x/2 (0 ≤ x ≤ 2.0) and Fe 1− x Co x PO 4− x/2 (0 ≤ x ≤ 0.5) compositions were synthetized by the chemical coprecipitation method and characterized by differential thermal analysis and thermogravimetric analysis, X-ray diffraction, UV–vis–NIR spectroscopy, CIE L* a* b* parameters measurements and electronic microscopy. At 1000 °C, Co 3(PO 4) 2 solid solutions (Co 3− x Fe x P 2O 8+ x/2 ; 0 ≤ x ≤ 0.3) and FePO 4 solid solutions (Fe 1− x Co x PO 4− x/2 ; 0 ≤ x ≤ 0.02) were obtained. From enamelled samples, the blue colouration is detected when an appreciable amount of Co 3(PO 4) 2 (Co 3− x Fe x P 2O 8+ x/2 samples) or Co 2P 2O 7 (Fe 1− x Co x PO 4− x/2 samples) is present in powdered samples. These materials develop blue colourations in enamelled samples when 0 ≤ x ≤ 1.0 in Co 3− x Fe x P 2O 8+ x/2 (between 48 and 32 wt.% Co) compositions and when x ≥ 0.30 in Fe 1− x Co x PO 4− x/2 (≥12 wt.% Co) compositions. Fe 1− x Co x PO 4− x/2 (0.3 ≤ x ≤ 0.5) compositions can be considered to minimize the Co content in blue ceramic pigments.

Cobalt minimisation in willemite (CoxZn2−xSiO4) ceramic pigments

Industrially available blue ceramic pigments, with the exception of vanadium–zircon blue, (Zr,V)SiO4, contain Co. To minimise the use of toxic and scarce cobalt, while also maintaining an intense blue colour, the performance as blue ceramic pigments of both Co2+–Zn2SiO4 (willemite) and Zn2+–Co2SiO4 (olivine) solid solutions was studied. The addition of cobalt in the willemite lattice was minimised. A wide range of compositions, CoxZn2−xSiO4 (x = 2, 1.95, 1.5, 1, 0.9, 0.5, 0.05 and 0), were prepared and characterised by X-ray diffraction, lattice parameter measurements, UV–VIS–NIR spectroscopy, CIE-L*a*b* colour measurements and electronic microscopy (SEM/EDAX). The results show that an intense and more blue ceramic pigment is obtained based on the willemite lattice, with an optimised, low Co content, ranging from 25 mol% Co (Co0.5Zn1.5SiO4) to 2.5 mol% Co (Co0.05Zn1.95SiO4). This last composition (with only 2.5 mol% Co) exhibits the best blue hue once enamelled (b* = −39), though it is also considerably lighter (L* = 57).