Effect of SiO2/Al2O3 ratio on the whiteness of ceramic tile engobes with low zircon content

Varışli, S. Ö.; Taşkıran, F.; Öztürk, B.; Çiçek, B.

doi:10.1590/0366-69132023693913465

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Articles • Cerâmica 69 (391) • Jul-Sep 2023 • https://doi.org/10.1590/0366-69132023693913465 copy

Effect of SiO₂/Al₂O₃ ratio on the whiteness of ceramic tile engobes with low zircon content

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Micronized zircon (ZrSiO₄) is used as an opacifier in the production of engobes, opaque glazes, and floor tile bodies. Elevated price levels incentivize researchers to develop alternative engobe formulations with reduced zircon ratios. In this study, new engobes with low zircon content were developed with varying SiO₂-Al₂O₃ mixtures. The effect of the SiO₂/Al₂O₃ ratio on the performance and opacity of the wall and floor tile engobes was investigated. It has been observed that the amount of zircon in the sample compositions could be reduced up to 40% by optimizing the refractoriness-water absorption balance of the engobe with the SiO₂/Al₂O₃ ratio while keeping the opacity in the preferred levels. The color difference (∆E) value relative to the standard surface was below 1, which is acceptable for visual perception for all the samples. Other measurements such as water absorption and firing shrinkage of the floor tile samples were found to be compatible with the standard composition.

Keywords:
ceramic; engobe; opacifier; SiO₂/Al₂O₃ ratio; tile; zircon

Oxide	F-STD	F1	F2	F3	F4
SiO₂	9.48	9.59	9.53	9.48	9.57
Al₂O₃	1.15	1.18	1.21	1.24	1.21
K₂O	0.04	0.04	0.04	0.04	0.04
Na₂O	0.55	0.55	0.55	0.55	0.55
CaO	0.35	0.35	0.35	0.35	0.35
MgO	0.05	0.05	0.05	0.05	0.05
B₂O₃	0.10	0.10	0.10	0.10	0.10
ZrO₂	0.53	0.46	0.46	0.46	0.44
SiO₂/Al₂O₃	8.28	8.15	7.88	7.62	7.92

Raw material	F-STD	F1	F2	F3	F4
Total zircon	8.0	4.8	4.8	4.8	4.0
Total free SiO₂	36.0	38.4	37.6	36.8	38.4

Raw material	W-STD	W1	W2	W3	W4
Total zircon	12.0	7.2	7.2	7.2	6.0
Total free SiO₂	10.0	13.6	12.4	11.2	13.6

Oxide	W-STD	W1	W2	W3	W4
SiO₂	5.21	5.31	5.26	5.20	5.29
Al₂O₃	0.66	0.69	0.72	0.76	0.72
K₂O	0.04	0.04	0.04	0.04	0.04
Na₂O	0.28	0.28	0.28	0.28	0.28
CaO	0.63	0.63	0.63	0.63	0.63
MgO	0.05	0.05	0.05	0.05	0.05
B₂O₃	0.06	0.06	0.06	0.06	0.06
TiO₂	0.31	0.31	0.31	0.31	0.31
ZrO₂	0.36	0.29	0.29	0.29	0.28
SiO₂/Al₂O₃	7.85	7.67	7.25	6.88	7.32

Raw material	SiO₂	Al₂O₃	CaO	MgO	ZrO₂	K₂O	Na₂O	TiO₂	LOI
Kaolin	52.4	32.6	0.15	0.22	-	1.09	0.22	0.19	13.2
Clay	51.8	26.6	0.27	-	-	1.49	0.15	1.17	18.4
Na-feldspar	70.3	17.5	0.88	-	-	-	10.9	-	0.41
Zircon	34.7	2.48	-	-	62.6	-	0.24	-	-
Quartz	99.3	0.42	0.12	-	-	-	-	-	0.14
Alumina	0.07	99.2	-	-	-	-	0.64	-	0.06

Color value	F-STD	F1	F2	F3	F4
L*	88.00	87.64	87.84	87.78	87.74
a*	-0.35	-0.23	-0.27	-0.31	-0.26
b*	4.46	4.56	4.65	4.12	4.70
∆E	-	0.38	0.25	0.40	0.36

Color value	W-STD	W1	W2	W3	W4
L*	91.40	90.88	91.41	91.68	91.04
a*	-0.38	-0.36	-0.48	-0.40	-0.33
b*	3.35	3.00	3.66	3.76	2.99
∆E	-	0.63	0.33	0.50	0.51

	F-STD	F1	F2	F3	F4	Body
α 300 °C	61.60	65.46	64.73	62.65	64.46	66.68
α 400 °C	64.38	68.10	67.65	65.23	67.80	69.77
α 500 °C	67.32	71.75	70.50	68.87	71.15	72.15

	W-STD	W1	W2	W3	W4	Body
α 300 °C	59.57	61.22	59.52	59.33	59.85	62.15
α 400 °C	61.60	63.73	62.01	61.06	62.16	64.92
α 500 °C	63.90	66.31	64.54	63.17	64.63	67.58

Oxide	F-STD	F-2	W-STD	W-2
SiO₂	59.7	58.2	62.4	58.3
Al₂O₃	23.2	26.0	13.2	17.0
CaO	1.0	1.2	7.0	7.2
ZrO₂	8.6	7.0	6.8	6.2
Na₂O	6.1	6.2	4.6	4.8
K₂O	1.4	1.4	0.8	1.0
MgO	-	-	1.2	1.4
TiO₂	-	-	4.0	4.1

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