Barium titanate hydrothermal

The most significant commercial product is barium titanate, BaTiO, used to produce the ceramic capacitors found in almost all electronic products. As electronic circuitry has been rniniaturized, demand has increased for capacitors that can store a high amount of charge in a relatively small volume. This demand led to the development of highly efficient multilayer ceramic capacitors. In these devices, several layers of ceramic, from 25—50 ]lni in thickness, are separated by even thinner layers of electrode metal. Each layer must be dense, free of pin-holes and flaws, and ideally consist of several uniform grains of fired ceramic. Manufacturers are trying to reduce the layer thickness to 10—12 ]lni. Conventionally prepared ceramic powders cannot meet the rigorous demands of these appHcations, therefore an emphasis has been placed on production of advanced powders by hydrothermal synthesis and other methods. 

Table 2. Commercial Hydrothermal Barium Titanate Powders ...

Hennings, D. Rosenstein, G. Schreinemacher, H. 1991. Hydrothermal preparation of barium titanate from barium-titanium acetate gel precursors. J. Euro. Ceram. Soc. 8 107-115. 

This is a relatively low-temperature, water-based route capable of producing submicron, spherical and uniform sized particles of either high purity or chemically modified BT. Essentially barium, titanium and dopant compounds are reacted in a basic aqueous medium to form hydroxides. Under the hydrothermal conditions, typically in the temperature and pressure ranges 100-250 °C and 100kPa-3MPa ( —30 atm) respectively, sub-micron particles of either pure or modified barium titanate are precipitated. There are many variables which need careful control, especially the reactive areas of the precursors and the degrees of supersaturation of the various species. 

It is also possible to retain the hydrothermally produced barium titanate particles in aqueous suspension to form the basis of a tape-casting slurry capable of producing < 3 /mi dielectric layers. This route avoids the risk of the formation of hard agglomerates on drying the precipitates. 

Hydrothermal synthesis is being increasingly adopted for the commercial production of compositionally tailored barium titanates for MLCCs. 

Blanco-Lopez, M.C., Rand, B., and Riley, RL., J. Ear. Ceram. Soc., 17, 281,1997. Lu, S., Lee, B.I., and Wang, Z., Synthesis of redispersible nano-sized barium titanate powders by hydrothermal method, in Ceramic Transactions, vol. 106, Dielectric Materials Devices, edited by K.M. Narr and A.R. Bhalla, American Ceramic Society, Westerville, OH, 2000. 

With the exceptions of quartz and emerald, the typical crystals grown hydrothermally are small. There is no inherent reason for this. Hydrothermal synthesis of fine powders of barium titanate and similar dielectric materials is of importance in capacitor manufacture. 

Hydrothermal Barium Titanate (barium titanate of small particle size obtained by a hydrothermal method)... 

Ozen M, Mertens M, Luyten J, Snijkers F, D Hondt H, Cool P (2012) Hydrothermal S3mthesis of carbonate-free submicron-sized barium titanate from an amtnphous precursor S3mthesis and characterization. Ceram Int 38 619-625... 

Eckert JO, HungHouston CC, Gersten BL, Lencka MM, Riman RE (1996) Kinetics and mechanisms of hydrothermal synthesis of barium titanate. J Am Ceram Soc 79 2929-2939... 

Kumazawa, H., Annen, S., Sada, E. Hydrothermal synthesis of barium titanate fine particles from amorphous and crystalline titania. J. Mater. Sci. 30, 4740-4744 (1995)... 

Shi, E.-W., Xia, C.-T., Zhong, W.-Z., Wang, B.-G., Feng, C.-D. Crystallographic properties of hydrothermal barium titanate crystallites. 1. Am. Ceram. Soc. 80, 1567-1572 (1W7) Wada, S., Chikamori, H., Noma, T, Suzuki, T Hydrothermal synthesis of barium titanate crystallites using new stable titanium chelated complex in aqueous solution. J. Mater. Sd. Lett. 19, 245-247 (2000)... 

Wvekanandan, R., Kutty, T.R.N. Characterization of barium titanate fine powders formed from hydrothermal crystallization. Powder Technol. 57,181-192 (1989)... 

Chien, A.T., Speck, J.S., Lange, F.F., Daykin, A.C., Levi, C.G. Low temperature/low pressure hydrothermal synthesis of barium titanate powder and heteroepitaxial thin films. J. Mater. Res. 10, 1784-1789 (1995)... 

Dutta, P.K., Gregg, J.R. Hydrothermal synthesis of tetragonal barium titanate. Chem. Mater. 4, 843-846 (1992)... 

Wu, M., Long, J., Wang, G., Huang, A., Luo, Y. Hydrothermal synthesis of tetragonal barium titanate from barium hydroxide and titanium dioxide under moderate conditions. J. Am. Ceram. Soc. 82, 3254-3256 (1999)... 

Nyutu, E.K., Chen, C.H., Dutta, P.K., and Suib, S.L. (2008) Effect of microwave frequency on hydrothermal synthesis of nanocrystalline tetragonal barium titanate. /. Phys. Chem. C, 112, 9659-9667. 

Komarneni, S. and Katsuki, H. (2010) Microwave-hydrothermal synthesis of barium titanate under stirring condition. Ceram. Int., 36,1165-1169. 

Nucleation and Formation Mechanisms of Hydrothermally Derived Barium Titanate... 

Barium titanate powders were produced using either an amorphous hydrous Ti gel or anatase precursor in a barium hydroxide (Ba(OH)2) solution via a hydrothermal technique in order to discern the nucleation and formation mechanisms of BaTi03 as a function of Ti precursor characteristics. Isothermal reaction of the amorphous Ti hydrous gel and Ba(OH)2 suspension is believed to be limited by a phase boundary chemicd interaction. In contrast, the proposed BaTi03 formation mechanism from the anatase and Ba(OH>2 mixture entails a dissolution and recrystallization process. BaTi03 crystallite nucleation, studied using high resolution transmission electron microscopy, was observed at relatively low temperatures (38°C) in the amorphous hydrous Ti gel and Ba(OH)2 mixture. Additional solution conditions required to form phase pure crystallites include a C02-free environment, temperature >70°C and solution pH >13.4. Analysis of reaction kinetics at 75°C was performed using Hancock and Sharp s modification of the Johnson-Mehl-Avrami approach to compare observed microstructural evolution by transmission electron microscopy (7). 

Anatase Precursor Reaction. The earliest BaTi03 nucleation from the hydrothermally treated Ti precursor could not be visually discerned from the aggregated anatase. However, electron diffraction patterns suggest the presence of barium titanate. The HRTEM photomicrograph of a sample extract on ramping prior to attainment of the isothermal temperature illustrates lOnm nuclei in Figure 6. Due to the overlap and (approximately 10°) misorientation of the nuclei (observed by the split diffraction spots... 

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