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October 19th and 20th, 2011 · EUROGRESS, Aachen, Germany

MOLTEN GLASS ATTACK ON AZS REFRACTORIES PRODUCED WITH ALTERNATIVE RAW MATERIALS

G.A. Castillo Rodríguez, T.K. Das Roy, L. I. García-Ortiz, A.M. Guzmán, E.A. Rodríguez Castellanos, Jaime. E. Valadez*,Programa Doctoral en Ingeniería de Materiales, FIME – UANL; Nuevo León, México

Table 2: Samples formulations.

Sample Alumina Mullite Bauxite Zirconia Zircon Silica

BZS – – 48.35 – 30.96 1.62

AZS 43 – – 20 – 37

MZA 11 60.38 – – 31 –

Samples of each combination with a fi ne particle size (45 µ) were prepared, they were pressed at 193.40 MPa and sintered in an electric furnace in a heating rate of 5 ºC/min reaching 1600 ºC in a laps of 5 hours and a low cooling as follow inside the furnace; these samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectrosco-py (SEM-EDS). By other hand, molten glass attack was carried out by a penetration test (Norma ASTM C621 – 09), placing 5g of soda-lime glass, with the composition showed in Table 3, on the sample, the sample was placed inside of an electric furnace to a temperature of 1450 ºC at a heating rate of 10 ºC/min, keeping this temperature in a lapse of 4 hours, subsequent a slow cooling inside the furnace. Samples attacked were cut across and prepared for their observation by SEM.

Table 3: Soda-Lime Glass chemical analysis.

Soda-Lime Glass

SiO2 Na2O MgO CaO Al2O3 K2O

71.16 7.80 0.16 7.14 0.92 0.226

RESULTSX-ray diffraction (XRD)X-ray diffraction (Fig. 1) indicates the presence of phases as mul-lite (M) in the 2� angles of 26.2, 26 and 16.5 in descending order of intensity), zircon (ZS) in the 2� angles of 26.98, 35.6 and 53.4, and corundum (C) at 2� angles of 43.5, 35.2 and 57.3, phases through the refractory does its function, since their presence im-ply more stability to the contact with molten materials[10], as well as volumetric changes having free zirconia as baddeleyite (B) (2� angles of 28, 31.5 and 50) or silica (Q) as quartz (2� angles of 26.6, 20.8 and 50.1) in the refractory matrix.

SEM ResultsThe fi gure 2 corresponds to the BZS refractory formulation wich indicates the presence of mullite and zirconia.

INTRODUCTIONVariety of applications of ceramic materials in industry has moti-vated the scientifi c community to develop high performance ma-terials in each area, it has been reached by optimization of the materials properties, by incorporating some agents to the compo-sitions, modifying manufacture processes, an strictly raw mate-rials selection and/or refi nement of them; great advantages have gotten over recent years thanks to new technology, which plays an important role in the components characterization; nowadays, we have materials for specifi c applications.In many cases of materials development, we seek to optimize their performance; in other cases is projected to effi cient energy use and determine a new process with the same results[1-2]. The eco-nomic blow which is not only affecting industry but the world as whole, request low cost materials, by modifying process param-eters, particle sizes distributions, concentrations, and some oth-er parameters.[3-4]

Glass industry has advanced in this lapse of time and also tech-nology has evolved, starting a research line that is updating devel-oping variety of glasses for different purpose, process and mate-rials involved in the production of this transparent materials, ones of this materials involved in glass production, are the AZS refrac-tories, which are used as a coating for glass melting furnaces due to their high resistance to corrosive attack of alkalis from glass[5-6], those refractories are composed of mullite, corundum, zircon and a glassy phase[7], which contributes in resistance to corrosion, in the recent research people have reduced the content of zirconia due to how expensive it is[8], keeping the material performance, reducing particle sizes and new shaping techniques as well as the use of alternative raw materials in order to reduce the production costs[4-5]. For this reason, the aim of this research is focused in the production of AZS refractories with low zirconia content using al-ternative raw materials in order to reduce cost and obtain materi-als with a performance similar to commercial refractories.

EXPERIMENTAL PROCEDUREThis research consisted in the preparation of samples produced with different raw materials, as alumina, mullite, bauxite, zirco-nia, zircon and silica[9], which chemical analysis is shown in ta-ble 1; with these raw materials were pressed pills of the refractory formulations, BZS (Bauxite-Zircon-Silica), AZS (Alumina-Zir-conia-Silica) and MZA (Mullite-Zircon-Alumina) according to presented in Table 2.

Table 1: Raw materials chemical composition

Raw Materials Al2O3 ZrO2 SiO2 Otros

Bauxite 88.93 – 5.08 5.99

Mullite 53.2 – 43.3 3.5

Zircon – 64.6 35.0 0.4

Alumina 99 – – 1

Zirconia – 99 – 1

Sílica – – 99 1

* Corresponding author Jaime Elihezer Valadez Ramos, jaimevaladezramos@gmail.com Fig. 1: X-ray diffraction of BZS, AZS and MZA formulations

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54th International Colloquium on Refractories 2011 – Refractories for Industrial

Figure 3 corresponds to the MZA refractory formulation wich in-dicates the presence of zircon and alumina as corundum.Figure 4 shows SEM images of the microstructure of samples with some porosity and random distribution of different phases in AZS refractory formulations. The microanalysis by EDS indicates the presence of zirconia (white phase in fi gure 2a), mullite (black phase in fi gure 2b) and zircon (gray phase in fi gure 2c), which corroborate the presevnce of phases detected by X–ray diffraction.Its important to mention that the presence of these phases, mul-lite and zircon, contributes in the corrosion resistance of this type of refractory material, mullite presents high resistance to the ero-sion and chemical attack. However, zircon contributes to the di-mensional stability because it does not have volumetric changes associated with changes of the monoclinic to tetragonal zirconia around 1170°C.

SEM results after glass molten attack.After the penetration test by molten glass, samples were evaluated by SEM-EDS. In fi gures 5, 6 and 7 are shown analyzed samples after attack, in which the dendrites formation is detected and cor-respond to a high alkalis content coming from glass composition (see table 3). On the other hand can be seen that as we move away from attacked zone to refractory the presence of alkali decrease.

Fig. 2: EDS analysis on different phases of BZS; a) Mullite b). Zirconia

Fig. 3: EDS analysis on different phases of MZA; a) Zircon b) Alumina

Fig. 4: EDS analysis on different phases of AZS; a) Zirconia b) Mullite c) Zircon.

Fig. 5: BZS, formation of zirconia (white phase) by decomposi-tion of Zircon

Fig. 6: AZS, degradation caused by alkali.

BAD QUALTITY

BAD QUALTITY

BAD QUALTITY

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October 19th and 20th, 2011 · EUROGRESS, Aachen, Germany

The alkalis attack causes the defragmentation of refractories and the majority of those particles fall into the molten glass polluting the fi nal product [4].According to the above suggests that the presence of impurities in raw materials favors the penetration of glass, because they act as a fl ux, allowing penetration and corrosion of refractories which fall into the glass resulting in damage to the quality of the fi nal product [4].The highest glass penetration was presented by BZS (Figure 8), forming a dense layer diffi cult to penetrate by molten glass.In fi gure 8, we can see the complete dissolution in refractory, forming a dense layer almost impossible to penetrate but weak,

a layer such as this one, could provoke a deep penetration affect-ing furnace walls, in addition to release fragments of the layer to the product.Figure 9 show a no-dense layer formed over AZS which is easy to break, the layer is not totally marked, it is weak due to the porosity.Sample MZA shown in fi gure 10, presents a dense layer, due to dendrite formation structure turn out to get a highest strength in comparison with the others, not easy to break and diffi cult to re-move.

CONCLUSIONSThe formation of phases in our refractory is comparable to com-mercial refractory according to research published in the past, and corrosion resistance is consider to be comparable to commer-cial refractories.The formation of the dendrite interphase analyzed by SEM in at-tacked samples, indicates that they can behave as commercial products in presence of alkali from molten glass, because its acts as a barrier that stop penetration of molten glass, lit could be cor-roborated by data obtained by optical microscope.Finally, we conclude that AZS refractories can be produce with al-ternative raw materials (bauxites y zircon) using alternative raw materials of high purity avoiding refi nement can produce low cost refractories.

REFERENCES[1] Dávila Del Toro F; “Formulación optimizada del refractario

AZS/43-20-37”; Rev. Ingenierías, Vol. IX, No. 33, Octubre 2006.

[2] Aguilar Garib J. A; “Procesamiento de Materiales por medio de Microondas en la FIME”; Rev. Ingenierías, Vol. IV, No. 13, Octubre 2001.

[3] Pierre K, Nicolle J, “Glass and Slag Resistant Refractories and Process of Making Same”; Societe Generele Des Pro-duits Refractaires, France, 1966

[4] Guzmán A. M. Rodríguez P. and Sereno E; “Development of AZS Refractories for the Glass Industry”;

[5] Thomas E. A; Patel D. G. and Brandt W. F; “Bonded AZS Re-fractories for Glass Processing”; Dider Taylor Refractories Corporation, Journal of the Canadian Ceramic Society, Vol. 53, 1984.

[6] Velez M; Smith J; Moore R. E; “Refractory Degradation in Glass Tank Melters. A Survey of Testing Methods”; Univer-sity of Missouri-Rolla, USA, 1997

[7] Zanelli C; Dondi M; Raimondo M. and Guarini G; “Phase Composition of Alumina–Mullite-Zironia Refractory Mate-rials”; CNR-ISTEC, Journal of the European Ceramic Soci-ety, Vol. 30, Italy, 2010

[8] Velez M; Karakus M; Moore R. E; “UMR Digital Library: High Zirconia AZS Refractories”, 7[6] 36–37 (2002)

[9] Amaro Cortez C. E; “Desarrollo de Refractarios AZS Uti-lizando Bauxita y Zircón como Materias Primas”, Tesis UANL, 2004

[10] Kaisera A; Loberta M. and Telle R; “Thermal Stability of Zir-con (ZrSiO4)”, Journal of the European Ceramic Society, 28, 2008.

Fig. 7: MZA, dendrites formation caused by alkalis. In this case, it can observe decomposition of mullite forming the interphase.

Fig. 8: Sample BZS a) Calcium penetration b) Sodium penetra-tion.

Fig. 9: Sample AZS a) Calcium penetration b) Sodium penetration

Fig. 10: Sample MZA a) Calcium penetration b) Sodium and Po-tassium penetration