Titanate crystallization

Fig. 5. A 90° polished cross section of a production white titania enamel, with the microstructure showing the interface between steel and direct-on enamel as observed by reflected light micrography at 3500 x magnification using Nomarski Interface Contrast (oil immersion). A is a steel substrate B, complex interface phases including an iron—nickel alloy C, iron titanate crystals D, glassy matrix E, anatase, Ti02, crystals and F, quart2 particle.

In 1955, Aerojet-General Corporation issued a report (Higgins, 1955) that described a few experiments in which molten aJuminum (and other metals) were poured into water. The water vessel was a vertical 30-cm-diameter, 25-cm-long pipe with a steel bottom plate. The water depth was 23 cm. Metal was dropped from an overhead crucible, usually with a free fall of 51 cm before contacting the water. A barium titanate crystal pressure transducer was located in the side of the water vessel about 13 cm below the water surface. 

Barium titanate crystals rank high among those solids on which electronic research has been focused during the last two decades, because this compound and its derivatives belong to a promising group of ferroelectrics. The properties of single crystals of BaTiOs reveal that the crystals are not uniform they respond to an electrical field as if they have a skin which covers the bulk of the crystal. 

The rare earth titanates crystallize in an orthorhombically distorted form of the perovskite structure, commonly known as the GdFeOs type, found widely for other LnT03 materials and described in Pnma (Pbnm in earlier literature) (Figure 16). As the Ln + ions are too small for 12-fold coordination, the TOe octahedral tilt to accommodate a lower coordination number, which is near 9-fold. 

Typical values for k are 2.3 pCN for quartz and 140 pCN for barium titanate. For a 1 cm area and 1 mm thickness piezoelectric sensor with an applied force of 0.1 N, the output voltage v is 0.23 mV and 14 mV for the quartz and barium titanate crystals, respectively. Piezoelectric constants are given in the literature [1,2]. 

Szostak et al 52 have made calculations of the /Miyperpolarizability of 2-nitroaniline and 2 nitrophenol and for their radical ions and suggest that the latter might have a role in the nonlinear optical response. A localized orbital model of the response of the barium titanate crystal has been developed by Khatib et al 253 Lacroix et al.254 have performed INDO calculations on crystal structures for a highly polarizable zwitterionic merocyanine dye. 

Y.-S. Her, E. Matijevic, and M.C. Chon Preparation of Well Defined Colloidal Barium Titanate Crystals by the Controlled Double Jet Precipitation. J. Mater. Res., 10, 3106-3114 (1995). Controlled Double-Jet Precipitation of Uniform Colloidal CiystalUne Sr-and Zr-Doped Barium Titanates. J. Mater. Res., 11, 3121-3127 (1996). 

Smaller (e.g., 30 nm at 180 °C), better dispersed, and more uniform titanate crystals were obtained under stirring, while static conditions yielded aggregated and larger crystals at each temperature (e.g., 60-100 nm at 180 C)... 

The aUcoxide-salt method has been successfully used in the synthesis of compounds of complex stoichiometries as well. One example (Shen et al., 2002) is the synthesis of nanocrystalline Li4TisOi2. The two cation-sources were tetrabutyl titanate and lithium acetate with solvents like 2-propanol, acetic acid and water. Aging of the mixed solution led to the formation of a white gel that was dried and calcined to obtain the crystalline target product. The titanate crystallized as the single phase at 800°C the average size of the particles was 100 nm. 

Figure 22-6. Dielectric constant of barium titanate crystal change with temperature. and are the dielectric constants measured along the a-axis and c-axis, respectively. (Merz, 1949, with permission).

Type Piezoelectric—PZH —lead zirctmate titanate crystals. Diameter 2 /i6in (71mm). Length 6V2in (165 mm). Wa it 21b (900 g). Cable length 10 in (3 m). 

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