Electrical Porcelain Containing Ornamental Rock Waste: Microstructural Development

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1 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil Electrical Porcelain Containing Ornamental Rock Waste: icrostructural Development.. Silva 1,a, J.N.F. Holanda 1,b UENF- LV/GCer, v. lberto Lamego 2000, CEP: Campos dos Goytacazes - RJ. a myrianketos@hotmail.com, b holanda@uenf.br Keywords: rock waste, porcelain, microstructure, XRD bstract luminous electrical porcelains are used in the production of materials of high voltage insulators. The microstructure plays an important role in the performance of electrical porcelain. On the other hand, the porcelain materials undergo a series of physical and chemical transformations during firing. This makes the understanding of their microstructures rather complex. In this work was studied the microstructural development of electrical porcelain containing up to 35 wt.% of ornamental rock waste. The pieces ceramics were pressed at 50 Pa and sintered at 1300 ºC. The porcelain pieces were characterized via X-ray diffraction and scanning electron microscopy. The results indicate that the presence of the ornamental rock waste influenced the microstructural development of the pieces of electrical aluminous porcelain. Introduction Porcelains are vitrified ceramic materials. They are widely used for technical purposes. The electrical porcelains are used as insulators in electrical power transmission systems [1]. Porcelains are primarily composed of clay, feldspar, and quartz [2]. The clay gives plasticity to ceramic formulation, quartz maintains the shape of the porcelain piece during firing, and feldspar acts as flux [3]. In aluminous porcelain, however, the quartz is substituted by alumina. This type of porcelain is used in the manufacture of electric insulators high-voltage, for possessing adequate dielectric properties and superior mechanical properties the porcelains that use the quartz. 802

2 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil The ornamental rock industry generates huge amounts of wastes that have be discarded. These wastes are rich in flux materials. Thus, the ornamental rock wastes are attractive to be incorporated into electrical porcelain wares [4]. The microstructure plays an important role in the electric porcelain performance. The microstructure of the triaxial porcelain after the sintering consists of coarse alumina grains mixed fine together kept crystals of mullite for a glassy matrix [4]. This work has as objective to analyze the microstructure of aluminous electric porcelain sintered at 1300 ºC. The porcelain pieces were characterized in terms of scanning electron microscopy and X-ray diffraction. aterials and methods luminous porcelain compositions were formulated (Table 1) using mixtures of kaolin, Na-feldspar, quartz, and ornamental rock-cutting waste. The waste additions were up to 35 wt-% gradual replacement of Na-feldspar. Commercial kaolin, Nafeldspar, and quartz were used. The waste material was collected as dry powder from an ornamental rock-cutting plant located in the State of Rio de Janeiro, Brazil. Table 1 - The proportions of the blends for the formulations (wt.%) Formulation Kaolin Plastic Clay lumina Na-Feldspar Waste The raw materials were dry-ground and mixed using a laboratory mill, and then passed through a 325 mesh (45 µm ST) sieve. The porcelain compositions were mixed, homogenized, and granulated via the dry process. The moisture content (moisture mass/dry mass) was adjusted to 7 %. 803

3 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil The ceramic pastes prepared by dry process were pressed at 50 Pa, and then sintered in air at 1300 ºC during 1 h. icrostructure characterization of fractured surfaces was carried out by scanning electron microscopy (model SSX-550, Shimadzu) via secondary electron images (SEI), at 15 kv, after gold coating. The fired specimens were analyzed for mineralogical characterization by X-ray diffraction (model XRD-700, Shimadzu) using monochromatic Cu-Kα radiation at a scanning speed of 1.5º (2θ) per minute. Results and discussion XRD patterns for the 0, 20 and 35 samples fired at 1300 ºC are presented in Figs. 1-3, respectively. The results show that the crystalline phases found in the samples were primary mullite (3l 2 O 3.2SiO 2 ), α-alumina, and quartz. However, the intensities of the diffraction peaks are differentiate due the addition of the ornamental rock-cutting waste Intensidade (u.a) Ângulo 2 θ Fig. 1 XRD pattern of the sample 0 fired at 1300 ºC: alumina; quartz; and mullite. 804

4 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil Intensidade (u.a) Ângulo 2 θ Fig. 2 XRD pattern of the sample 20 fired at 1300 ºC: alumina; quartz; and mullite Intensidade (u.a) Ângulo 2 θ Fig. 3 XRD pattern of the sample 35 fired at 1300 ºC: alumina; quartz; and mullite. Figs. 4-6 are SEI of the fractured surfaces of the 0, 20 and 35 samples STD0 fired at 1300 ºC. They show the typical sequence of enhanced densification with waste addition. 805

5 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil (a) (b) Fig. 4 icrostructure of 0 fired at 1300 ºC: (a) 200 X; and (b) 1000 X. (a) (b) Fig. 5 icrostructure of 20 fired at 1300 ºC: (a) 200 X; and (b) 1000 X. (a) (b) Fig. 6 icrostructure of 35 fired at 1300 ºC: (a) 200 X; and (b) 1000 X. 806

6 Seventh International Latin merican Conference on Powder Technology, November 08-10, tibaia, SP, Brazil The effect of the waste addition on the microstructure of the tile pieces is evident. In general, the waste-added pieces are much more vitrified and characterized by few and small isolated pores. This result in lower open porosity. The presence of isolated rounded pores suggests that the material reached the final sintering stage. Thus, the use of ornamental rock-cutting waste in aluminous porcelain formulation brought about a relevant variation in microstructure, resulting in significantly denser structures. Conclusions The results showed that after firing at 1300 ºC the microstructure of ornamental rock-cutting waste containing aluminous porcelain mainly consists of α-alumina, quartz, and mullite. The grains held in a glassy matrix. The waste-added pieces are denser and with smooth fractured surfaces. cknowledgements The authors would like to thank CNPq, FPERJ and CPES for financial support and the LCO by the supply of the alumina powder. References [1].L. Chinelatto, D.P.F. Souza: Cerâmica Vol. 50, Nº 313 (2004), p [2].L. Chinelatto, D.P.F. Souza: Cerâmica Vol. 50, Nº 315 (2004), p [3] P.W. Olupot, Thesis (Licentiate in aterial Science), Royal Institute of Technology, Stockholm, Sweden, (2006). [4] B.C.. Pinheiro, aster Thesis, UENF-PPGEC, Campos dos Goytacazes, Brazil, (2005). 807