Ceramic pigments on the base of technogenic silica-containing material—waste vanadium catalyst were obtained in this work. Corundum is identified along with the predominant mullite phase in the composition of pigments. The ions of nickel, chromium, and iron are embedded in the structure if the concentration of the corresponding oxide in the initial mixture does not exceed 10 wt.%. In this case, the oxide is not identified in a free form according to the results of X-ray diffraction analysis. Spinel CoAl2O4 is formed in cobalt pigments. The developed pigments keep the firing temperature up to 1200°C. The obtained pigments may be recommended for ceramic paints and colored glazes for building materials.
At the present, the construction industry needs decorative building materials, which are produced with the applying of ceramic pigments, dyes, and decorative glaze. There has been a great interest within the ceramic industry in the development of high-stability pigments, which show intense tonality and satisfy both technological and environmental requirements [
The requirements to raw materials for ceramic pigment production are constant chemical composition, purity (no coloring impurities), and the ability to form stable crystalline structure. Ceramic pigments with the structure of the potassium feldspar were obtained in [
The crystal structure of mullite (3Al2O3 · 2SiO2) is similar to the sillimanite one, despite some differences in their compositions. A characteristic feature of the mullite structure is the presence of two types of the Al3+ ions; a half of them enter into the crystal lattice with the coordination number 6, the other half with the coordination number 4 [
The purpose of this work was the production and investigation of heat-resistant ceramic pigments with mullite structure by using industrial waste vanadium catalyst.
The raw material used in the study was a waste vanadium catalyst (WVC), which is used for the manufacture of sulfuric acid in the plant “Nitrogen” (Kemerovo, Russia) in the work.
Raw materials for WVC are natural diatomite, vanadium oxide (V2O5), potassium oxide (K2O), and sulfur oxide (SO3) in the form of potassium vanadium sulfate (K2S2O7
The chemical composition of WVC was determined by X-ray fluorescence analysis (XRF, Philips X′UNIQUE II) (Table
Chemical composition of the waste vanadium catalyst.
Raw material | Oxide content, wt.% |
|
|||
---|---|---|---|---|---|
SiO2 | Al2O3 | V2O5 | K2O | ||
Waste vanadium catalyst | 64.90 | 5.20 | 6.20 | 9.10 | 14.60 |
The XRD data of vanadium catalysts initial and
The WVC comprised the structure-forming oxides—SiO2, and Al2O3. Aluminum oxide (Al2O3) was added to the catalyst to provide mullite structure formation. Al2O3 was 99.9% of purity and particle size of 20–30
Waste vanadium catalyst was milled up to particle size less than 20–30 microns. Aluminum oxide is included in the catalyst composition but in a small concentration (up to 5 wt.%), which is not enough to form mullite. So additional alumina was added to WVC to obtain stoichiometric mullite by the following reaction:
Firstly, WVC of 42 wt.% and alumina of 58 wt.% were mixed without any chromophore by dry method in a ball mill for 3 h. This mixture was named as “check sample” (CS) and used to determine structure formation. The prepared composition mixture was sintered in corundum pots at
The initial compositions to obtain mullite pigments.
Sample number | The content of main components, wt.% | |||||
---|---|---|---|---|---|---|
WVC | Al2O3 | CoO | NiO | Cr2O3 | Fe2O3 | |
CS2 | 42 | 58 | — | — | — | — |
M1 | 38 | 57 | 5 | — | — | — |
M3 | 34 | 51 | 15 | — | — | — |
M4 | 38 | 57 | — | 5 | — | — |
M6 | 34 | 51 | — | 15 | — | — |
M7 | 38 | 57 | — | — | 5 | — |
M8 | 36 | 54 | — | — | 10 | — |
M9 | 38 | 54 | — | — | — | 5 |
M10 | 36 | 57 | — | — | — | 10 |
A preliminary characterisation of pigments involved the identification by X-ray diffraction (XRD-7000S Shimadzu) of the main crystalline phases formed, upon firing, and measurements of the CIE Lab colour parameters. The reflectance data in the visible region were used to obtain the three relevant parameters,
Polyphase structure was obtained at the firing of the samples without chromophores at the
Radiograms of the check sample and the pigments of mullite composition, (
SEM images of the pigments of mullite composition: (a) check sample; (b) chromium-containing pigment. The areas on the images are 1—mullite, and 2—corundum (
Some amorphization of the pigment structure was observed with the increase in the firing temperature up to 1200°C. It was associated with the presence of fusible potassium oxide K2O in the WVC (9.1 wt.%) (see Table
The intensity of the all reflections decreased when the chromophore was added (see Figure
The spinel CoAl2O4 (
The color of the pigments and some overgraze dyes.
Sample |
The color of overglaze dyes | ||
---|---|---|---|
1100°C3 | 1200°C3 | 850°C3 | |
M1 (Co2+) | Sky blue | Greenish blue | Sky blue |
M3 (Co2+) | Blue | Blue | Blue |
M4 (Ni2+) | Light green | Light olive | Light green |
M6 (Ni2+) | Turquoise | Turquoise (darker) | Turquoise |
M8 (Cr3+) | Dark olive | Dark olive | Brownish pink |
M9 (Fe3+) | Light brown | Reddish brown | Brown |
M10 (Fe3+) | Brown | Reddish brown | Brown |
The color of the obtained pigments (a), overglaze dyes (b) and glazes (c).
The pigments of mullite composition were tested as overglaze colors (see Table
The color coordinates
Color characteristics of the obtained ceramic pigments and dyes (
Sample number | Pigment colour parameters | Dye colour parameters | ||||
---|---|---|---|---|---|---|
|
|
|
|
|
| |
M1 (Co2+) | 48.0 | 0.0 | −16.0 | 58.0 | 0.0 | −15.0 |
M3 (Co2+) | 38.0 | 0.0 | −19.0 | 44.0 | 0.0 | −10.0 |
M4 (Ni2+) | 53.0 | −6.0 | 6.1 | 66.0 | −1.0 | 11.0 |
M6 (Ni2+) | 46.0 | −6.0 | 4.7 | 56.0 | −4.0 | 9.4 |
M8 (Cr3+) | 44.0 | 2.4 | 2.8 | 54.0 | 10.0 | 19.0 |
M9 (Fe3+) | 47.0 | 4.3 | 9.9 | 57.0 | 11.0 | 15.0 |
M10 (Fe3+) | 38.0 | 7.6 | 7.1 | 54.0 | 5.2 | 18.0 |
Spectral reflectance curves of the obtained pigments (
The ceramic pigments were produced using technogenic silica-containing raw material—waste vanadium catalyst in the work. Corundum phase along with the predominant mullite is identified in the composition of the obtained pigments and dyes. The ions of nickel, chromium, and iron are embedded in the structure up to the concentration of the corresponding oxide 10 wt.%; in this case, the oxide is not identified in a free form on XRD pattern. The spinel CoAl2O4 forms in the cobalt-containing pigments. Cobalt pigments are characterized by the highest color saturation. The developed pigments keep a firing temperature up to 1200°C.
The research results show that the usage of vanadium catalyst is promising and economically expedient because the pigments synthesized on its basis are not inferior industrial pigments by color properties and heat resistance, and they exceed the pigments described in [
X-ray fluorescence
X-ray diffraction
Scanning electron microscopy
Waste vanadium catalyst
Sintering temperature, °C
Commission Internationale I’Eclairage—international commission on illumination of the standard colorimetric coordinates
The work was supported by the Ministry of Education and Science of Russian Federation. The state task is “Science” no. 3.3055.2011.