Zirconia Zirconium-titanium

Zinc oxide (ZnO) is widely used as an active filler in rubber and as a weatherability improver in polyolefins and polyesters. Titanium dioxide (TiOj) is widely used as a white pigment and as a weatherability improver in many polymers. Ground barites (BaS04) yield x-ray-opaque plastics with controlled densities. The addition of finely divided calcined alumina or silicon carbide produces abrasive composites. Zirconia, zirconium silicate, and iron oxide, which have specific gravities greater than 4.5, are used to produce plastics with controlled high densities. 

For pressing as well as extrusion, the solid electrolyte precursor particles (e.g., zirconia) are often mixed or reacted with an inorganic cementing substance. It is preferred that such adhesive materials also have ion permselective properties as the precursor particles. Phosphates of zirconium, titanium and zinc are examples of such cements although other materials such as calcium aluminate and calcium aluminosilicates are candidates as well [Arrance et al., 1969]. For these cementing materials to be effective, the metal oxides must be only partially hydrated so that they are reactive with the bonding compounds. 

Zirconium oxide (ZrO ) is the most common compound of zirconium found in nature. It has many uses, including the production of heat-resistant fabrics and high-temperature electrodes and tools, as well as in the treatment of skin diseases. The mineral baddeleyite (known as zirconia or ZrO ) is the natural form of zirconium oxide and is used to produce metallic zirconium by the use of the Kroll process. The KroU process is used to produce titanium metal as well as zirconium. The metals, in the form of metaUic tetrachlorides, are reduced with magnesium metal and then heated to red-hot under normal pressure in the presence of a blanket of inert gas such as helium or argon. 

At higher temperatures, zirconium dioxide and titanium dioxide supports gave much greater stability along with polymer-based supports [100,101] based on polystyrene-divinyl benzene (PS-DVB) such as PLRP-S noted in Table 9.5. PS-DVB supports have been reported to give a serious column bleed at 250°C [66]. Polybutadiene (PBD) modified zirconia columns have been used at temperatures up to 300°C and carbon-coated zirconia has been used at temperatures up to 370°C [66]. Applications have included the separation of steroids [73] and herbicides [102].The specific order of column bleed varied depending on the detection method as shown in Table 9.5. 

Merck in Japan has recently patented [16] a process for the production of water and weather-resistant pearlescent pigments produced by coating mica with hydrous zirconia. This is in many ways similar to processes operated in the titanium oxide industry and mentioned previously. The zirconium hydroxide aids dispersion and gives better compatibility with the polymer matrix that it is incorporated in. 

Inorganic precursors are much cheaper and easier to handle than metal alkoxides. Therefore the industrial production of oxide powders for ceramics and catalysts is mainly based on the precipitation or coprecipitation of inorganic salts from aqueous solutions. Gibbsite, Al(OH)3, (see Aluminum Inorganic Chemistry) is precipitated from aluminate solutions. Ti02 powders are made via the controlled hydrolysis of titanium salts. Stabilized zirconia is coprecipitated from aqueous solutions of zirconium oxychloride, ZrOC, and yttrium nitrate, YlKOsjs. 

Similarly, impervious yttria-stabilized zirconia membranes doped with titania have been prepared by the electrochemical vapor deposition method [Hazbun, 1988]. Zirconium, yttrium and titanium chlorides in vapor form react with oxygen on the heated surface of a porous support tube in a reaction chamber at 1,100 to 1,300 C under controlled conditions. Membranes with a thickness of 2 to 60 pm have been made this way. The dopant, titania, is added to increase electron How of the resultant membrane and can be tailored to achieve the desired balance between ionic and electronic conductivity. Brinkman and Burggraaf [1995] also used electrochemical vapor deposition to grow thin, dense layers of zirconia/yttria/terbia membranes on porous ceramic supports. Depending on the deposition temperature, the growth of the membrane layer is limited by the bulk electrochemical transport or pore diffusion. 

Titania and Zirconia Membranes Prepared by the Polymeric Route Titanium and zirconium propoxides can be used as precursors for the preparation of nanoporous titania and zirconia membranes. To avoid the precipitation of inhomogeneous hydroxide particles during the hydrolysis step, the alkoxide reactivity can be modified with acetylacetone (acacH). This chelating agent reacts readily with transition metal alkoxides, as follows [34] ... 

As the first example, we mention the organomodified zirconia-titania [3] obtained using 1,12-diaminedodecane, zirconium, and titanium butoxides as precursors. That organofunctionahzed compound exhibits a hexagonal nanostructure and particles with spherical morphology, as shown in Fig. 4.1. 

Zirconia, which is stable as well as titania, especially, in alkali solution, is also one of the promising materials for separation membranes. Several manufacturers have commercialized zirconia UF membranes, but not NF membranes. Zirconium propoxide [30] or butoxide [31], which are mainly used as precursors of zirconia sols, are highly sensitive to water to form suspensions (the reaction rate with water is much faster than titanium alkoxide), the preparation of nanosized sols is difficult. Therefore, very few reports have appeared on the successful preparation of zirconia nanofiltration membranes. Vacassy et al. [30] added acetylacetone to zirconia propoxide to prevent hydrolysis, and reported a successful preparation of porous zirconia membranes showing a water permeability of 3.4 X 10 ms Pa and a rejection of 55% towards saccharose (MW = 342). 

Corrosion resistance. Zirconium exhibits abetter chemical resistance than titanium when in contact with corrosive attack in harsh conditions. The corrosion resistance of zirconium is due to the formation of a dense, tenaciously adherent, chemically inert oxide film of zirconia... 

Another catalyst system found in the patent literature involves the deposition of halides such as zirconium tetrachloride, vanadium tetrachloride, titanium tetraiodide, or oxyhalides such as chromium oxychloride or vanadium oxychloride on a finely divided particulate inorganic substrate having surface hydroxyl groups. Among such solids are alumina, zirconia, silica (particularly a pyrogenic silica such as Cab-O-SiF ), or a carbon black such as channel black or furnace black. A toluene slurry of this material is added, under dry nitrogen, to a toluene solution of A -vinyl-pyrrolidone containing a small amount of triisobutylaluminum. After 24 hr at 80°C, a 25% yield of polymer is produced [73]. 

Zirconia monoliths can be prepared from alkoxy precursors however, obtaining mechanically stable zirconia monolithic materials is a challenging task [8]. Zirconium alkoxides have faster hydrolysis rates compared with aluminiun or titanium alkoxides. This is due to larger positive partial charge of the zirconium atom, which enhances nucleophilic attacks on the zirconium atoms [52]. 

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