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Cobalt Minimisation in Violet Co3P2O8 Pigment
Mª Ángeles Tena1, Rafael Mendoza2, Camino Trobajo3
1Inorganic Chemistry Area, Inorganic and Organic Chemistry Department, Jaume I University, P.O. Box 224, 12006 Castellón, Spain.
Materials (Basel, Switzerland)
|February 15, 2022
Summary
This study developed new inorganic pigments by substituting cobalt with magnesium in cobalt violet orthophosphate. These Mg-Co-P solid solutions offer reduced toxicity, lower cost, and improved thermal stability for ceramic applications.
Area of Science:
- Materials Science
- Inorganic Chemistry
- Ceramic Pigments
Background:
- Cobalt violet orthophosphate (Co3P2O8) is a valuable ceramic pigment but has limitations due to high cobalt content.
- High cobalt levels in pigments can lead to toxicity concerns and affect material properties.
- The ceramic industry requires pigments with enhanced thermal stability and reduced environmental impact.
Purpose of the Study:
- To synthesize MgxCo3-xP2O8 solid solutions to mitigate the limitations of Co3P2O8.
- To investigate the impact of magnesium substitution on the pigment's properties, including toxicity, thermal stability, and color.
- To evaluate the potential of these novel solid solutions as inorganic pigments in the ceramic industry.
Main Methods:
- Solid solutions of MgxCo3-xP2O8 (0 ≤ x ≤ 3) were synthesized using the chemical coprecipitation method.
- Characterization involved analyzing the crystal structure, thermal stability (melting point), and color properties (a* and b* values).
- The synthesized pigments were tested in ceramic applications by mixing with enamel and calcining.
Main Results:
- The formation of MgxCo3-xP2O8 solid solutions successfully reduced the cobalt content and increased the melting point above 1200 °C for x ≥ 1.5.
- Compositions with x ≥ 1.5 exhibited stability between 800 °C and 1200 °C, offering a wider processing window.
- Magnesium substitution decreased toxicity and cost, while improving color properties, with Mg2.5Co0.5P2O8 yielding a desirable purple hue.
- Glazed samples showed a color shift from violet to blue, attributed to changes in the cobalt(II) local environment, confirmed by UV-Vis spectroscopy.
Conclusions:
- MgxCo3-xP2O8 solid solutions represent a promising alternative to pure cobalt violet orthophosphate for the ceramic industry.
- These materials offer a favorable balance of reduced toxicity, enhanced thermal stability, improved color characteristics, and lower production costs.
- The observed color transformation upon glazing opens possibilities for novel blue ceramic pigments derived from these magnesium-cobalt phosphate systems.
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