Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment
This study considers the limitations of cobalt violet orthophosphate, Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub>, in the ceramic industry due to its large amount of cobalt. Mg<sub>x</sub>Co<sub>3−x</sub>P<sub>2</sub>O<sub>8&...
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MDPI AG
2022-01-01
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| Online Access: | https://www.mdpi.com/1996-1944/15/3/1111 |
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| author | Mª Ángeles Tena Rafael Mendoza Camino Trobajo Santiago García-Granda |
| author_facet | Mª Ángeles Tena Rafael Mendoza Camino Trobajo Santiago García-Granda |
| author_sort | Mª Ángeles Tena |
| collection | DOAJ |
| description | This study considers the limitations of cobalt violet orthophosphate, Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub>, in the ceramic industry due to its large amount of cobalt. Mg<sub>x</sub>Co<sub>3−x</sub>P<sub>2</sub>O<sub>8</sub> (0 ≤ x ≤ 3) solid solutions with the stable Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> structure were synthesised via the chemical coprecipitation method. The formation of solid solutions between the isostructural Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> and Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub> compounds decreased the toxically large amount of cobalt in this inorganic pigment and increased the melting point to a temperature higher than 1200 °C when x ≥ 1.5. Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> melted at 1160 °C, and compositions with x ≥ 1.5 were stable between 800 and 1200 °C. The substitution of Co(II) with Mg(II) decreased the toxicity of these materials and decreased their price; hence, the interest of these materials for the ceramic industry is greater. An interesting purple colour with a* = 31.6 and b* = −24.2 was obtained from a powdered Mg<sub>2.5</sub>Co<sub>0.5</sub>P<sub>2</sub>O<sub>8</sub> composition fired at 1200 °C. It considerably reduced the amount of cobalt, thus improving the colour of the Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> pigment (a* = 16.2 and b* = −20.1 at 1000 °C). Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> is classified as an inorganic pigment (DCMA-8-11-1), and the solid solutions prepared were also inorganic pigments when unglazed. When introducing 3% of the sample (pigment) together with enamel, spreading the mixture on a ceramic support and calcining the whole in an electric oven, a colour change from violet to blue was observed due to the change in the local environment of Co(II), which could be seen in the UVV spectra of the glazed samples with the displacement of the bands towards higher wavelengths and with the appearance of a new band assigned to tetrahedral Co(II). This blue colour was also obtained with Co<sub>2</sub>SiO<sub>4</sub>, MgCoSiO<sub>4</sub> or Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> pigments containing a greater amount of cobalt. |
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| spelling | doaj.art-35eddf4a79054ae999ed567155b7b4812023-11-23T17:02:28ZengMDPI AGMaterials1996-19442022-01-01153111110.3390/ma15031111Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> PigmentMª Ángeles Tena0Rafael Mendoza1Camino Trobajo2Santiago García-Granda3Inorganic Chemistry Area, Inorganic and Organic Chemistry Department, Jaume I University, P.O. Box 224, 12006 Castellón, SpainPhysical Chemistry Area, Scientific and Technical Services, Oviedo University-CINN, 33006 Oviedo, SpainInorganic Chemistry Area, Organic and Inorganic Chemistry Department, Oviedo University-CINN, 33006 Oviedo, SpainPhysical Chemistry Area, Physical and Analytical Chemistry Department, Oviedo University-CINN, 33006 Oviedo, SpainThis study considers the limitations of cobalt violet orthophosphate, Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub>, in the ceramic industry due to its large amount of cobalt. Mg<sub>x</sub>Co<sub>3−x</sub>P<sub>2</sub>O<sub>8</sub> (0 ≤ x ≤ 3) solid solutions with the stable Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> structure were synthesised via the chemical coprecipitation method. The formation of solid solutions between the isostructural Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> and Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub> compounds decreased the toxically large amount of cobalt in this inorganic pigment and increased the melting point to a temperature higher than 1200 °C when x ≥ 1.5. Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> melted at 1160 °C, and compositions with x ≥ 1.5 were stable between 800 and 1200 °C. The substitution of Co(II) with Mg(II) decreased the toxicity of these materials and decreased their price; hence, the interest of these materials for the ceramic industry is greater. An interesting purple colour with a* = 31.6 and b* = −24.2 was obtained from a powdered Mg<sub>2.5</sub>Co<sub>0.5</sub>P<sub>2</sub>O<sub>8</sub> composition fired at 1200 °C. It considerably reduced the amount of cobalt, thus improving the colour of the Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> pigment (a* = 16.2 and b* = −20.1 at 1000 °C). Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> is classified as an inorganic pigment (DCMA-8-11-1), and the solid solutions prepared were also inorganic pigments when unglazed. When introducing 3% of the sample (pigment) together with enamel, spreading the mixture on a ceramic support and calcining the whole in an electric oven, a colour change from violet to blue was observed due to the change in the local environment of Co(II), which could be seen in the UVV spectra of the glazed samples with the displacement of the bands towards higher wavelengths and with the appearance of a new band assigned to tetrahedral Co(II). This blue colour was also obtained with Co<sub>2</sub>SiO<sub>4</sub>, MgCoSiO<sub>4</sub> or Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> pigments containing a greater amount of cobalt.https://www.mdpi.com/1996-1944/15/3/1111minimisation of toxicityCo<sub>3</sub>P<sub>2</sub>O<sub>8</sub>α-Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub>solid solutionspigments |
| spellingShingle | Mª Ángeles Tena Rafael Mendoza Camino Trobajo Santiago García-Granda Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment Materials minimisation of toxicity Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> α-Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub> solid solutions pigments |
| title | Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment |
| title_full | Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment |
| title_fullStr | Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment |
| title_full_unstemmed | Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment |
| title_short | Cobalt Minimisation in Violet Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> Pigment |
| title_sort | cobalt minimisation in violet co sub 3 sub p sub 2 sub o sub 8 sub pigment |
| topic | minimisation of toxicity Co<sub>3</sub>P<sub>2</sub>O<sub>8</sub> α-Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub> solid solutions pigments |
| url | https://www.mdpi.com/1996-1944/15/3/1111 |
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