**5. Acknowledgment**

296 Advances in Crystallization Processes

The change in composition of internal water is proposed as a method for approximate dating of agates (a variety of chalcedony) (Moxon, 2004). It has been demonstrated in geological environments that less stable silica polymorphs appear to have transformed over

time to chalcedony and microquartz (Nash & Hopkinson, 2004).

Fig. 10. Chalcedony formation. Krumbein, W.C., Garrels, R.M., (1952).

This research was partially supported by grants to María Prado Figueroa from Secretaría General de Ciencia y Técnica, Universidad Nacional del Sur (UNS), Bahía Blanca, Argentina. MPF is grateful to Dr. T. Moxon, 55 Common Lane, Auckley, Doncaster DN93HX, UK, for many interesting suggestions about chalcedony formation and isolation.

MPF is grateful to Prof. F.J. Barrantes, ex-Director of the Centro Científico Tecnológico Bahía Blanca, Argentina (CCT-BBca, CONICET - UNS) for his permanent interest in this study.

MPF appreciate Lic. E. Buzzi and Mr. M. Diestefano from the CCT-BBca, CONICET – UNS, for technical assistance. Finally, the author is very grateful to Lic. M. Salaberry, English Translator, for her excellent work.

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**Synthesis and Characterization of Crystalline** 

*1Center of Exact Science and Technology, University of Caxias do Sul, Caxias do Sul, RS, 2Laboratory of Ceramic Materials (LACER), Departament of Materials, Engineering School, Federal University of Rio Grande do Sul, Osvaldo Aranha, Porto Alegre, RS,* 

Zirconium titanate (ZT)-based ceramic materials, ZrTiO4, have many attractive properties: high resistivity, high dielectric constant, high permittivity at microwave frequencies and excellent temperature stability for microwave properties (Bianco *et al*, 1999; Leoni *et al*, 2001). These materials have an extremely wide range of technological application, such as in microwave telecommunications (as capacitors, dielectric resonators in filters, and oscillators) (Navio *et al*, 1993; Navio *et al*, 1994; Azough *et al* 1996), in the manufacture of hightemperature pigments (Hund and Anorg, 1985; Dondi *et al*, 2006) in catalysis (as effective acid-base bifunctional catalysts and photocatalysts) (Tanabe, 1970; Araka and Tanabe, 1980), as structural ceramics (Parker, 1990) and, more recently, as biomaterial coated on 316L SS for

The formation of ZrTiO4 has been studied by several authors (McHale *et al*, 1989; Christoffersen *et al*, 1992a; Bhattacharya *et al*, 1996; Hom *et al*, 2001; Ananta *et al*, 2003; Kim *et* 

Zirconium titanate is normally synthesized by solid-state reaction of oxide mixtures between ZrO2 and TiO2 at elevated temperatures (1200-1600°C) and long heating times and also requires post treatment such as energy-intensive grinding/milling procedures for powder formation and this process usually leads to inhomogeneous, coarse, and multiphase powders of poor purity (Lynch, 1972; Swartz, 1982; McHale *et al*, 1983; McHale *et al,* 1986; Parker, 1990; Christoffersen *et al*, 1992b; Park et al, 1996; Stubicar *et al*, 2001; Troitzsch *et al,* 2004; Dondi *et al,*  2006). ZrTiO4 ceramics have the orthorhombic structure of α-PbO2 (Blasse, 1966; Newnham, 1967) and belongs to the space group Pbcn. Above 1200 °C the Zr ion and Ti ion of the high temperature normal phase are randomly distributed on octahedral site in α-PbO2 type structure. (McHale *et al*, 1983; Christoffersen *et al*, 1992b; Azough *et al*, 1993; Ul'yanova *et al*, 1995). In contrast to the displaced transitions which take place at discrete temperature, ZrTiO4 ceramics undergoes a continuous phase transition of the normal to incommensurate over the

The chemical preparation of reactive precursors offers advantages over traditional processing techniques because of the higher purity and better homogeneity obtained the

*al*, 2004; Troitzsch *et al*, 2005; Vittayakorn *et al*, 2006; Licina *et al*, 2008).

temperatures of 1200°C to 1100°C by increasing order in the Zr-Ti distributions.

**1. Introduction** 

biomedical applications (Devi *et al*, 2011).

**Zirconium Titanate Obtained by Sol-Gel** 

Venina dos Santos1 and C.P. Bergmann2

*Brazil* 

Whittaker, V.P. (1977). The electromotor system of Torpedo as a model cholinergic system. *Naturwissenschaften* 64, 606-611. **12** 
