Zirconia alkoxide synthesis

Historically, stabilized (and partially stabilized) zirconia ceramics were prepared from powders in which the component oxides are mechanically blended prior to forming and sintering. Because solid state diffusion is sluggish, firing temperatures in excess of 1800°C are normally required. Furthermore, the dopant was nonuniformly distributed, leading to inferior electrical properties. Trace impurities in the raw materials can also lead to enhancement of electronic conductivity in certain temperature ranges, which is also undesirable. To overcome these problems, several procedures have been developed to prepare reactive (small particle size) and chemically pure and homogeneous precursor powders for both fully stabilized and partially stabilized material. Two of these are alkoxide synthesis and hydroxide coprecipitation. 

Two classes of precursor have been demonstrated to prepare such zirconia colloids salts [4-7] and alkoxides [8-10]. Given the constraints above, the hydrothermal synthesis from zirconium salts [4,7] is especially attractive. The salt is easier to protect and handle than alkoxide precursors, and the product colloid does not require the removal of organics or dispersing agents before further aqueous processing. Bleier and Cannon [7] showed that one can easily make 80 nm monodisperse aqueous sols with no dispersing agents. 

There are three generic routes to sulfated zirconia (sulfation of the oxide/ hydroxide, sol-gel synthesis with Zr alkoxides and sulfuric acid and, much less studied, the thermal decomposition of zirconium sulfate). Furthermore, many potential structures have been suggested on the basis of various studies (Figure Whether one is correct or there are several... 

The synthesis of zirconia nanomaterials by a one-step sol-gel route under supercritical C02(l) drying using zirconium alkoxides and acetic acid was reported by Sui et al. [24]. Their materials exhibited high surface areas (up to 399 m /g) and porosity, while the calcined materials demonstrated tetragonal and/or monoclinic nanocrystallites. Either a translucent or opaque monolith was obtained. Investigation by electron microscopy showed that the translucent monolithic Z1O2 exhibited a well-defined mesoporous structure, while the opaque monolith, formed using added alcohol as a co-solvent, was composed of loosely compacted nanospherical particles with a diameter of approximately 20 nm. 

The effects of different synthesis parameters on the properties of zirconia aerogels prepared by sol-gel process have been investigated by many research groups. In fact, taking into account that the hydrolysis of zirconium alkoxides is very fast, it has been noted that the rate of the condensation process can be influenced by the concentration of an acid catalyst leading to zirconia aerogels with different textural properties. The amount of added water... 

Chervin C N, Clapsaddle B J, Chiu H W, Gash A E, Satcher Jr J H, Kauziarich S M (2006) Role of cyclic ether and solvent in a non-alkoxide sol-gel synthesis of yttria-stabilized zirconia nanoparticles. Chem Mater 18 4865 874... 

Chervin CN, Clapsaddle BJ, Chiu HW, Gash AE, Sateher JH, Kauzlarich SM (2005) Aerogel synthesis of yttria-stabilized zirconia by a non-alkoxide sol-gel route. Chem Mater 17 3345 3351. 

Wu, J. C., and Cheng, L. (2000). An improved synthesis of ultrafiltration zirconia membranes via the sol-gel route using alkoxide precursor./. Membr. Sci. 167 253-261. 

The application of UV photoirradiation can also be extended when the film is not purely inorganic, which means that some of the organic precursors used in the synthesis have not been completely removed by postdeposition thermal treatment. This is in feet the case for titania and zirconia films whose synthesis requires control of the high reactivity of the transition metal alkoxides. Chelating agents or stabilizers have been used to control the reactivity of the precursors, such as acetylacetone, glycols [29], and alkanolamines [30], Just to name a few. 

On the other hand, zirconia is an interesting material to be used as catalyst support due to its thermal stability in different atmospheres. The most common methods that can be used to obtain zirconia are the sol-gel method, the micellar technique or the mechanochemical synthesis [3]. Zirconia is frequently prepared by micellar method, while the sol-gel method from an alkoxide is less used [4]. Its acid properties can be modified by addition of cationic or anionic substances, such as sulfate or tungstate [5]. 

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