Zirconia phosphate

Note 20 mg/1 of copper feirocyanide and 10 mg/1 of zirconia phosphate are added to the wastes [Gumming and Turner, 1988]... 

Schafer et al. used several spectroscopic techniques to characterize the surface species on phosphate-modified zirconia particles. Their results show that phosphate merely adsorbs on the surface of zirconia under the mildest phosphate concentration, i.e., neutral pH, room temperature, and short contact times. However, at acidic pH and higher temperarnres, esterification of the phosphate with surface hydroxyls takes place as the kinetic barriers are overcome. The solid NMR studies clearly show the presence of covalently bound phosphate. This phosphate modification effectively blocks the sites responsible for the strong interaction of certain Lewis bases with the zirconia surface, resulting in a more biocompatible stationary phase. Unlike fluoride-modified zirconia, phosphate-modified zirconia behaves as a classic cation exchanger and not as a mixed-mode medium analogous to hydroxyapatite, despite spectroscopic evidence of zirconium phosphate formation on the surface. This limits the applicability of the supports, as most proteins and enzymes are anionic at neutral pH. Nevertheless, its ability to separate proteins with high p/ values still deserves much attention. The preparative-scale separation of murine IgGs from a fermentation broth demonstrates the utiUty of the supports for solutes that are retained. 

Phosphate ions were also used to increase acidity on the surface of zirconia aerogel. Boyse et al. [40] prepared zirconia-phosphate aerogels by two methods a one-step sol-gel synthesis followed by SCD and an incipient wetness impregnation synthesis of a calcined zirconia aerogel. They reported that zirconia-phosphate aerogels possess Bronsted acid sites, and the phosphate species were claimed to be responsible of their generation. 

Boyse R A (1996) Preparation and characterization of zirconia-phosphate aerogels. Catal letters 38 225-230... 

It has been proposed that hybrid membranes are more proton conductive at low humidity than the parent polymer membranes. For example, zirconia phosphate (ZrP) was formed in the sulfonated poly(arylene ether sulfone). Nanoparticles of zirconia phosphate were homogeneously distributed in the membranes as crystalline ot-zirconium hydrogen phosphate hydrate [96]. The composite membrane (with ZrP up to 50 wt%) showed 3.7 x 10 S/cm of the proton conductivity at 90" C, 30% RH, which was ca. 5 times higher than that of the parent polymer membrane under the same conditions. It is claimed that the composite effect depends upon interfacial contact between the polymer matrix and additives, and inappropriate preparation procedure could result in opposite effects. 

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

Mesoporous zirconia has been prepared using anionic surfactants containing reactive oxygens that could bind Zr2+ (224-226). Mesoporous zirconia was obtained using alkyl phosphate amphiphiles but they were not stable to template removal. 

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

The hosts for ACT and REE immobilization are phases with a fluorite-derived structure (cubic zirconia-based solid solutions, pyrochlore, zirco-nolite, murataite), and zircon. The REEs and minor ACTs may be incorporated in perovskite, monazite, apatite-britholite, and titanite. Perovskite and titanite are also hosts for Sr, whereas hollandite is a host phase for Cs and corrosion products. None of these ceramics is truly a single-phase material, and other phases such as silicates (pyroxene, nepheliiie, plagioclase), oxides (spinel, hibonite/loveringite, crichtonite), or phosphates may be present and incorporate some radionuclides and process contaminants. A brief description of the most important phases suitable for immobilization of ACTs and REEs is given below. 

Mansur, C., M. Pope, M. R. Pascucci, and S. Shivkumar, Zirconia-calcium phosphate composite for bone replacement, Ceram. Int., 24, 77 (1998). 

It has been reported (4,5) that solid electrolyte sensors using stabilized zirconia can detect reducible gases in ambient atmosphere by making use of an anomalous EMF which is unusually larger than is expected from the Nernst equation. However, these sensors should be operated in a temperature range above ca. 300°C mainly because the ionic conductivity of stabilized zirconia is too small at lower temperatures. On the other hand, solid state proton conductors such as antimonic acid (6,1), zirconium phosphate (8), and dodecamolybdo-phosphoric acid (9) are known to exhibit relatively high protonic conductivities at room temperature. We recently found that the electrochemical cell using these proton conductors could detect... 

The acid function of the catalyst is supplied by the support. Among the supports mentioned in the literature are silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, silica-titania, acid-treated clays, acidic metal phosphates, alumina, and other such solid acids. The acidic properties of these amorphous catalysts can be further activated by the addition of small proportions of acidic halides such as HF, BF3, SiFit, and the like (3.). Zeolites such as the faujasites and mordenites are also important supports for hydrocracking catalysts (2). 

Both aluminum oxide and zirconium oxide are catalytically interesting materials. Pure zirconium oxide is a weak acid catalyst and to increase its acid strength and thermal stability it is usually modified with anions such as phosphates. In the context of mesoporous zirconia prepared from zirconium sulfate using the S+X I+ synthesis route it was found that by ion exchanging sulfate counter-anions in the product with phosphates, thermally stable microporous zirconium oxo-phosphates could be obtained [30-32]. Thermally stable mesoporous zirconium phosphate, zirconium oxo-phosphate and sulfate were synthesized in a similar way [33, 34], The often-encountered thermal instability of transition metal oxide mesoporous materials was circumvented in these studies by delayed crystallization caused by the presence of phosphate or sulfate anions. 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

Ceisla U., Froba M., Stucky G., Schiith F., Flighly ordered porous zirconias from surfactant-controlled syntheses Zirconium oxide-sulfate and zirconium oxo phosphate, Chem. Mater. 11 (1999), 227-234. 

In a detailed study, mesostructured zirconia has been prepared by using various amphiphilic surfactants with different headgroups (anionic and nonionic) and different tail lengths (1-18 carbons) as templates. Removal of snrfactants leads to the loss of structural order and a decrease ofthe siuface area. However, the presence of phosphates and snlfates in the walls may improve the stability. 

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. 

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