Utilization of ferrochromium fly ash as a pigment raw material in stoneware glaze and underglaze decoration: Munevver Caki, Nuran Ay and Selvin Yesilay Kaya detail their research on pigment raw material.
Calcination temperatures can be between 700-1400[degrees]C depending on the system. (1,2) Pigments can be classified differently (natural metallic oxides, complex inorganic colour pigments and different non-oxide pigments and so forth) depending on their chemical properties, production methods and utilization areas. (3) In many compositions, the colour obtained by using chrome is the characteristic chrome green. By mixing CoO, [Fe.sub.2][O.sub.3] and [Cr.sub.2][O.sub.3] in appropriate proportions, black and grey colours can be obtained. (4,5) There is much research on chrome-based colourants.6-10 In order to obtain appropriate coloured powder as high temperature grey pigment, Bondioli, Barbieri and Manfredini (11) were mixed with (Fe, Zn)[Cr.sub.2][O.sub.4], ferrochromium fly ash having spinel that is rich in terms of iron by adding two different chrome precursors, [Cr.sub.2][O.sub.3] and Cr[(OH).sub.3]. (11) Without transforming into pigment form, between four and 25 percent ratios in weight, ferrochromium fly ash is used directly as a chrome oxide source in colouring glazes.12 In the present research, the pigments are produced by using ferrochromium fly ash instead of [Cr.sub.2][O.sub.3]. The pigments obtained are used as in-glaze colourants in stoneware glazes and as underglaze decoration components on white earthenware bodies. Moreover, the effect of using ferrochromium fly ash on colouring is here investigated.
In order to obtain pigment, [Cr.sub.2][O.sub.3], CoO, [Al.sub.2][O.sub.3] and ferrochromium fly ash (Table 1) provided by the Ferrochromium Plant located in Antalya, Turkey, are used.
Pigment recipes were prepared according to [Cr.sub.2][O.sub.3]-CoO-[Al.sub.2][O.sub.3] triaxial system (Figure 1) and compositions which are coded as 1 and 4 were chosen.
[FIGURE 1 OMITTED]
First, pigment recipes were composed by using [Cr.sub.2][O.sub.3], CoO and [Al.sub.2][O.sub.3] raw materials, and then they were composed by using CoO, [Al.sub.2][O.sub.3] and ferrochromium fly ash instead of [Cr.sub.2][O.sub.3]. The standart pigment recipies were coded as STD-P1 and STD-P4. Pigment compositions prepared by using ferrochromium fly ash instead of [Cr.sub.2][O.sub.3] in the ratio of 80 percent and 60 percent coded as P1FA and P4FA.
Weighed pigment raw materials were wet-ground in a ball-mill for 20 minutes; slips obtained were sieved through 100 mesh sieves and then dried at 105[degrees]C. Each mixture was calcined at 1100[degrees]C. Wet-grinding, sieving and drying processes were conducted again.
Calcined pigments were added in the weight ratio of three, five and 10 percent into the transparent stoneware glaze coded as STG. The Seger Formula of this glaze, containing alkali oxide and boron oxide is seen in Table 3. Prepared glazes were applied onto stoneware bisques by pouring and then they were fired at 1160[degrees]C.
Besides using STD-P1, P1FA, STD-P4 and P4FA coded pigments in stoneware glazes, they were also used for underglaze decoration. In this respect, Kutahya Tiles were decorated by using each pigment. After being glazed with transparent glaze decorated products, they were fired at 930[degrees]C.
RESULTS AND DISCUSSION
When the STD-P1 coded pigment containing 80 percent [Cr.sub.2][O.sub.3], 10 percent CoO and 10 percent [Al.sub.2][O.sub.3] was added into the alkali-boron stoneware glaze in the ratio of three, five and 10 percent, typical chrome greens were achieved at 1160[degrees]C (Figure 2; STD-P1-3 percent, STD-P1-5 percent, STDP1-10 percent). It was observed that when the P1FA coded pigment obtained by using ferrochromium fly ash instead of [Cr.sub.2][O.sub.3] (80 percent ferrochromium fly ash, 10 percent CoO, 10 percent [Al.sub.2][O.sub.3]) was used in the ratio of 3 percent, 5 percent and 10 percent in the glaze, the colour was changed from light greenish blue to dark blue (Figure 2; P1FA-3 percent, P1FA-5 percent, P1FA-10 percent.
[FIGURE 2 OMITTED]
It is known that colouring material and chemical composition of glaze used are basic factors affecting the surface colour and structural properties of a ceramic product. It is thought that a concentration of [Cr.sub.2][O.sub.3] in ferrochromium fly ash (28-33 percent) is lower compared to chrome oxide with technical purity (99 percent) and it includes components such as [Fe.sub.2][O.sub.3], CaO and MgO. This situation causes cobalt oxide's dominance in a pigment recipe and the colour of a glazed surface turns to light greenish blue from chrome green. With the increase of pigment ratio in the glaze with alkali oxide and boron oxide it turns to dark blue. It is confirmed that using STD-P4 coded pigment containing 60 percent [Cr.sub.2][O.sub.3], 30 percent CoO and 10 percent [Al.sub.2][O.sub.3] and P4FA coded pigment containing 60 percent ferrochromium fly ash, 30 percent CoO and 10 percent [Al.sub.2][O.sub.3] give colour tones of green and blue respectively (Figure 3).
[FIGURE 3 OMITTED]
It was observed that in under-glaze decoration applications of pigments on white earthenware bodies, the under-glaze color of STD-P1 coded pigment produced with 80 % pure chrome oxide gave characteristic chrome green and the P1FA coded pigments produced by using ferrochromium fly ash instead of pure chrome oxide in the same ratio indicated greenish black color. When the amount of [Cr.sub.2][O.sub.3] was decreased from 80 % to 60 %, the pigment (STD-P4) produced by pure chrome oxide gave bluish green color. Moreover, when ferrochromium fly ash was used (P4FA) instead of pure chrome oxide in the pigment system it gave bluish black color (Figure 4).
[FIGURE 4 OMITTED]
It was determined that ferrochromium fly ash can be used as an alternative raw material source in ceramics pigment production, especially being evaluated in stoneware glazes and under-glaze decorations studies of white earthenware products. The colours of fly ash based pigments change from light greenish blue to dark blue. It is thought that new pigments can be synthesized in different systems (two materials testing by the line blend method or quadraxial blends) by using ferrochromium fly ash and metal oxides except CoO and [Al.sub.2][O.sub.3] or by changing composition and calcination temperatures. By this means different glazed surfaces with rich visual effect can be obtained.
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Munevver Caki , Nuran Ay  and Selvin Yesilay Kaya  detail their research on pigment raw material
 Anadolu University, Faculty of Fine Arts, Department of Ceramics, Eskisehir, Turkey.  Anadolu University, Faculty of Engineering and Architecture, Department of Materials Science and Engineering, Iki Eylul Campus, Eskisehir, Turkey.  Anadolu University, Faculty of Fine Arts, Department of Glass, Eskisehir, Turkey.
TABLE 1: CHEMICAL ANALYSIS OF FERROCHROMIUM FLY ASH (WT. PERCENTAGE) [Fe.sub.2][O.sub.3] Si[O.sub.2] [A1.sub.2][O.sub.3] CaO 9-12 4-6 6-8 26-31 [Fe.sub.2][O.sub.3] MgO Carbon Sulphur * L.O.I 9-12 11-14 0.2-0.4 0.2-0.7 1-4 * L.O.I: Losses on Ignition. TABLE 2: PIGMENT RECIPES (WT. PERCENT) Pigment [Cr.sub.2][O.sub.3] Ferrochromium CoO [Al.sub.2] Code Fly Ash [O.sub.3] STD-P1 80 - 10 10 P1FA - 80 10 10 STD-P4 60 - 30 10 P4FA - 60 30 10 TABLE 3: SEGER FORMULA OF TRANSPARENT STONEWARE GLAZE Glaze Number Seger Formula 0.402 [Na.sub.2]O 4.396 Si[O.sub.2] STG 0.186 [K.sub.2]O 0.500 [Al.sub.2][O.sub.3] 1.031 [B.sub.2][O.sub.3] 0.412 CaO TABLE 4. CHEMICAL ANALYSIS OF RAW MATERIALS USED IN THE STANDARD STONEWARE GLAZE (WT. PERCENTAGE) Raw material Si[O.sub.2] [Al.sub.2][O.sub.3] Sodium feldspar 68.87 17.46 Potassium feldspar 67.06 17.15 Ulexite 2.87 - Kaolin 69.12 18.98 Quartz 99.50 - Raw material [Fe.sub.2][O.sub.3] CaO MgO [Na.sub.2]O Sodium feldspar 0.06 0.58 0.03 12.08 Potassium feldspar 0.16 0.14 - 2.64 Ulexite 0.20 15.45 1.54 6.48 Kaolin 0.80 1.30 1.51 0.25 Quartz - - - - Raw material [K.sub.2]O Ti[O.sub.2] [B.sub.2][O.sub.3] Sodium feldspar 0.25 0.27 - Potassium feldspar 12.65 - - Ulexite 0.18 0.04 38.67 Kaolin 2.93 0.80 Quartz - 0.07 - Raw material * L.O.I Sodium feldspar 0.40 Potassium feldspar 0.20 Ulexite 34.57 Kaolin 4.31 Quartz 0.43 * L.O.I: Losses on Ignition.
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|Author:||Caki, Munevver; Ay, Nuran; Kaya, Selvin Yesilay|
|Date:||Nov 1, 2010|
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