Titanate-based chemistry

Very good mixing on an atomic scale can be achieved by chemical methods [5], and in the context of electroceramics the production of high purity, sub-micron barium titanate-based powders for the manufacture of multilayer capacitors (see Section 5.4.3) is of paramount importance. Tight control over powder chemistry has a direct and significant influence over capacitor failure rates. Also, the strong... 

Generally, nomenclature systems use a base on which the name is constructed. This base can be derived from a parent compound name such as sil (from silane) in substitutive nomenclature (mainly used for organic compounds) or titan a central atom name such as cobalt in additive nomenclature (mainly used in coordination chemistry). 

Reductive amination is historically defined as the combination of a Brpnsted acid, a ketone, an amine, and a coexisting reductant. The recent evolution of titanium (IV) alkoxides, as mild Lewis acid replacements for Brpnsted acids, owes its genesis to a clever modification of titanium amide chemistry demonstrated by Mattson et al. in 1990. By prestirring a ketone, amine, and Ti(OiPr)4 (neat), followed by the addition of EtOH and NaBH3CN, the desired reductive amination product was afforded (Scheme 8.8). The same authors suggested that these reductive aminations proceeded through a hemiaminal titanate intermediate, based on IR spectroscopy before addition of the reductant. 

Dispersion aids and compatibiUzers based on reactive phosphato-titanate chemistries are also said to reduce viscosity of fiUed compounds. They are compatible with nonpolar polymers such as POs, and are available in masterbatch form (more is said about these compatibilizers in Chapter 14) [11-1]. 

In order to establish the model of intergranular impedance for doped barium titanate, it is important to notice that miorostructure properties of BaTiOj based materials, expressed in their grain boundary contacts, are of basic importance for electric properties of these materials. The barrier character of the grain boundaries is especially pronounced for doped BaTiOs materials which are used as PTC resistors. Basically two types of dopants can be introduced into BaTiOs large ions of valence 3+ and higher, can be incorporated into Ba positions, while the small ions of valence 5+ and higher, can be incorporated into the Ti sublattice [9-11], Usually, the extent of the solid solution of a dopant ion in a host structure depends on the site where the dopant ion is incorporated into the host structure, the compensation mechanism and the solid solubility limit [12], For the rare-earth-ion incorporation into the BaTiOs lattice, the BaTiOs defect chemistry mainly depends on the lattice site where the ion is incorporated [13], It has been shown that the three-valent ions incorporated at the Ba -sites act as donors, which extra donor charge is compensated by ionized Ti vacancies (V -), the three-valent ions... 

The most important factor is that, unlike the silicon to carbon bond, the titanium to carbon bond is very unstable and cannot be used to permanently attach organic groups for surface treatment applications. The organo-titanates are thus generally based on tetra-substimted titanium, where all the substituents are linked by titanimn-oxygen-carbon bonds, and their chemistry is dominated by the hydrolytic sensitivity of these. Alkoxy radicals are rapidly hydrolysed, with the rate in water decreasing as the chain length increases, due to reduced solubility. Acyloxy derivatives are also fairly readily hydrolysed. 

Sriprang N., Kaewchinda D., Kennedy J.D., MUne S.J. Processing and sol chemistry of a triol-based sol-gel route for preparing lead zirconate titanate thin films. J. Am. Ceram. Soc. 2000 83 1914-1920... 

The titanates are most often used as in situ coupling agents dissolved in a suitable vehicle. Because of the breadth of titanate chemistry commercially available, a water, solvent or oil based diluent can usually be conveniently found. For example, titanate can be added to an elastomer in the process oil before filler addition. The matrix itself can also serve as diluent, as in the case of polyolefins where a neoalkoxytitanate can be blended into the melt flux prior to filler addition. 

In some sense the actuators, which generate action on command (i.e. information) form the counterpart to sensors which collect information about the surroundings. Actuators which change the composition have been implicitly addressed by the text (cf. e.g. electrochemical piunps). Actuators in a narrower sense cause mechanical effects (e.g. transfer of electrical into mechanical energy) and rely especially on the phenomenon of electrostriction (cf. piezoelectricity). For details the reader is referred to Ref. [573]. Also in this context perovskites play a dominant role (in particular perovskites based on lead titanate zirconates), and defect chemistry, even though not decisive, is of considerable importance (cf. Section 2.2.7). 

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