Titanate synthesis

MacLaren, I., Ponton, C.B. A TEM and HREM study of particle formation during barium titanate synthesis in aqueous solution. J. Eun Ceram. Soc. 20, 1267-1275 (2000)... 

In the next few paragraphs, we will discuss the processes involved in synthesis ofbarium titanate. This is an extremely important material for electronic industry due to its outstanding ferroelectric, piezoelectric and dielectric properties. Chemistry ofBa and Ti and crystal structure of BaTiOg are relatively simple. Phase transformations of barium titanate have been deeply studied and well documented. Thus, it may be considered as a convenient model oxide material. It is not surprising that a lot of information about application of Pechini method is available for this compound. Here we will attempt to create the complete scenario of barium titanate synthesis by PC method, and then we will expand this knowledge to discuss synthesis of other important multicomponent oxide materials. 

XRD patterns, 86 polymeric precursors, 59 polymeric siloxanes, 401 polymerizable complex (PC) method for barium titanate synthesis, 82 for photocatalysts synthesis, 93 use of, 77... 

K. Osseo-Asare, F. J. Arriagada, and J. H. Adair, "Solubility Relationships in the Coprecipitation Synthesis of Barium Titanate Heterogeneous Equihbria in the Ba—Ti—C2O4—H2O System," in G. L. Messing, E. R. Fuller, Jr., and Hans Hausin, eds.. Ceramic Powder Science Vol. 2,1987, pp. 47-53. 

D. Miller, J. H. Adair, W. Huebner, and R. E. Newnham, "A Comparative Assessment of Chemical Synthesis Techniques for Barium Titanate," Paper, 88th Annual Meeting of the American Ceramic Society, Pittsburgh, Pa., April 27—30, 1987. 

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. 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

TYZOR TPT and the tetraethyl titanate, TYZOR ET [3087-36-3], have also been prepared by direct electrochemical synthesis. The reaction involves anode dissolution of titanium in the presence of the appropriate alcohol and a conductive admixture (3). 

Allylic titanates having an electrofugal leaving group, e.g., trimethylsilyl68 75 - 77, at the 3-position are powerful reagents for the highly stereoselective synthesis of 1-hetero-substituted 3-alkadienes. For the carbonyl addition of the appropriate titanated allyl sulfides ( ) or carbamates ( and ), reliable y-selectivity and anti diastereoselectivity are reported. The... 

The addition of titanated 2-methylpropenamides to 2-(ter/-butoxycarbonylamino)a]dehydes was investigated during the synthesis of dipeptide isosteres and was shown to exhibit low selectivity only93,94. 

Many ester-forming reactions reported in the literature cannot be applied to the synthesis of polyesters due to side reactions, incomplete conversions, or non-quantitative yields. Some examples of nonconventional polyester syntheses are listed below. Most of them lead to oligomers rather titan polymers and require expensive reactants or special reaction conditions, which make them of little practical interest. 

The nucleophilic aromatic substitution reaction for the synthesis of poly(arylene ether ketone)s is similar to that of polysulfone, involving aromatic dihalides and aromatic diphenolates. Since carbonyl is a weaker electron-withdrawing group titan sulfonyl, in most cases, difluorides need to be used to afford high-molecular-weight polymers. Typically potassium carbonate is used as a base to avoid the... 

Miyazaki, T., Akita, H., Ishida, E., Ashizuka, M. and Ohtsuki, C. (2006) Synthesis of bioactive organic-inorganic hybrids from tetraisopropyl titanate and hydroxyethylmethacrylate. Journal of the Ceramic Society ofJapan, 114, 87-91. 

Outside of catalyst preparation, reaction of sucrose with metal nitrates has been used to prepare nanocomposite mixed oxide materials. Wu et al. [46] reported the synthesis of Mg0-Al203 and Y203-Zr02 mixed oxides by reaction of nitrate precursors with sucrose. The resulting powders had smaller particles than those prepared without sucrose. Das [47] used a similar method in the presence of poly vinylalcohol to produce nanocrystalline lead zirconium titanate and metal ferrierites (MFe204, M = Co, Ni, or Zn). The materials prepared using sucrose had smaller crystallites than those made without. Both authors observed an exothermic decomposition of the precursors during calcination. 

These reactions have been studied in detail for materials such as silica, and understanding of reaction mechanisms, as well as of the role of the precursor and catalyst (acid or base), has been well documented.63,64 Similar studies have been carried out in other material systems, most notably, lead zirconate titanate [Pb(Zr,Ti)03 PZT].52,65-68 For multicomponent (mixed-metal) systems such as those noted, prehydrolysis of less reactive alkoxides is sometimes employed to improve solution compositional uniformity. Other synthetic strategies to achieve molecular level mixing of reagents have also been employed. Here, synthesis of mixed-metal alkoxides has been a focus of investigators.40-42 A key point is to restrict the amount of water and to control how it is added to form solubalizable precursor species, rather than to induce precipitation.1,52,69,70... 

Ihlefeld, J. F. Borland, W. Maria, J. P. 2005. Synthesis and properties of barium titanate thin film on copper substrates. In Ferroelectric Thin Films XIII, edited by Ramesh, R. Maria, J. P. Alexe, M. Joshi, V. Mat. Res. Soc. Symp. Proc. 902 7-14. 

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

Characterization of the surface impurities on the catalyst is also essential, and photoreactivity data should be analyzed in terms of active and accessible surface area. The defect state of the surface and nanostructure are also important aspects to understand. Current advances in the synthesis allow preparing Titania or titanate nanorods with different diameter and aspect ratio, and different surface nanostructure as well. Limiting the discussion here to only preparations by hydrothermal treatment (for reasons of conciseness), various mechanisms of growing of the nanorods has been reported. The differences in the mechanism of formation would imply differences in the surface characteristics of the nanorods, but there is no literature available on this topic. 

Fig. 6 Schematic representation of the morphology evolution and the formation process of sodium and hydrogen-titanate nanostructures during hydrothermal synthesis in the presence of alkali medium. Elaborated from the picture and schemes reported by Wu et al.219...

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