Zirconium and Titanium Phosphates

Most of the reported inorganic fillers used to modify Nafion are composite where the inorganic particles (usually nanoparticles) are located in the membrane bulk. Most of them are prepared using the recast method, where the filler nanoparticles dispersed in a solvent are mixed with Nafion ionomer dispersion in the same solvent or a compatible one. The solution is cast on a Petri dish or a plane surface at high temperature to form the recast composite membrane. An alternative method adopted to prepare Nafion composites with silica [31, 32, 41, 95], functionalized silica [35], and zirconium and titanium phosphate [41], is the in situ sol-gel reaction method, schematized in Fig. 6.5. 

Bauer F, Willert-Porada M (2005) Characterization of zirconium and titanium phosphates and direct methanol fuel cell (DMFC) performance of functionally graded Nafion composite membranes prepared out of them. J Power Sources 145 101-107... 

Table 12-1. Surface areas of pillared zirconium and titanium phosphates. ...

The rare earths (see table II) have a marked geochemical affinity for fluorine, calcium, titanium, niobium, zirconium, and the phosphate and carbonate ions. The most important, from an economic viewpoint, are the carbonatites and the phosphates. 

If both Tiand Zr are present, the precipitate of zirconium phosphate may be filtered off (best in the presence of a little macerated filter paper, or a Whatman filtration accelerator), and the filtrate treated with Na2S03 or with Na2S203 solution and warmed. The peroxotitanic acid is reduced and titanium phosphate precipitates. It may be necessary to reduce the acidity of the solution somewhat to precipitate the titanium completely. Zr may also be identified by the alizarin-S reaction. 

Sant and Varma (183) found that low concentrations of zirconium lowered the temperature required to reach the maximum yield. Various interpretations of this observation have been put forward either the increase in surface area or the increase in oxygen transport rates can be sufficiently altered by the zirconium to result in high yields of MA at lower temperatures. The studies generally agree that aroimd 1.5% zirconium has the most beneficial effect on the activity, and good catalytic performance could be achieved at lower temperatures (172). One of the reasons for this that has been proposed is that zirconium and titanium both create acidic surface sites on the vanadium phosphate surface. These sites prevent the desorption of reaction intermediates (butene, butadiene, and furan) while facilitating the desorption of the acidic MA. 

In alpha zirconium or titanium phosphate, the aluminum Keggin ion can be intercalated after a previous treatment with butylamine (5) interlayer distances ranging from 13.6 to 16.1 A for the ne materials has been reported. -TiP can also be pillared with the aluminum Keggin ion and the surface area of the material ( 170 mV ) is retained by up to 70% after heating at 4(X) C. 

The most commonly used types of conversion coatings are phosphates and chromates or a process based upon a combination of these two. More recent developments have been in zirconium- and titanium-based chemistry along with cerium-based processes. The impetus behind the more modem conversion coatings is the replacement of hexavalent chromium, which is used in many conventional processes. Conversion coatings have been applied to most metals the most amenable metals along with a number of applications are given in Tables 1 and 2. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Bauer and Willert-Porada (2005) tested membranes containing phosphates of zirconium and titanium in DMFC-type cells. They found that adding the filler produced a certain decrease in protonic conductivity, but also an almost twofold decrease in methanol permeation through the membrane, so that the overall efficiency of cells with the composite membrane was somewhat higher than that of cells without fillers in the membrane. The authors also pointed out that a considerable improvement in the mechanical stability of the membrane was produced by the filler. 

Kapoor, M.P., Inagaki, S.,and Yoshida, H. (2005) Novel zirconium-titanium phosphates mesoporous materials for hydrogen production by photoinduced water splitting. Journal of Physical Chemistry B, 109 (19), 9231-9238. 

Most previous adsorption studies employing calorimetry have investigated cation exchange phenomena on zirconium phosphates (17-21), titanium phosphate (22) and clay minerals (23,24). 

Precipitation of the coating from aqueous solutions onto the suspended Ti02 particles. Batch processes in stirred tanks are preferred various compounds are deposited one after the other under optimum conditions. There is a very extensive patent literature on this subject. Continuous precipitation is sometimes used in mixing lines or cascades of stirred tanks. Coatings of widely differing compounds are produced in a variety of sequences. The most common are oxides, oxide hydrates, silicates, and/or phosphates of titanium, zirconium, silicon, and aluminum. For special applications, boron, tin, zinc, cerium, manganese, antimony, or vanadium compounds can be used [2.40], [2.41],... 

Lightfast pigments with dense surface coatings for the paper industry that have a stabilized lattice and a surface coating based on silicates or phosphates of titanium, zirconium, and aluminum ca. 90% TiOz... 

Recent research has explored a wide variety of filler-matrix combinations for ceramic composites. For example, scientists at the Japan Atomic Energy Research Institute have been studying a composite made of silicon carbide fibers embedded in a silicon carbide matrix for use in high-temperature applications, such as spacecraft components and nuclear fusion facilities. Other composites that have been tested include silicon nitride reinforcements embedded in silicon carbide matrix, carbon fibers in boron nitride matrix, silicon nitride in boron nitride, and silicon nitride in titanium nitride. Researchers are also testing other, less common filler and matrix materials in the development of new composites. These include titanium carbide (TiC), titanium boride (TiB2), chromium boride (CrB), zirconium oxide (Zr02), and lanthanum phosphate (LaP04). 

Wool Wool, though not as flammable as cotton, still needs flame retardation for specific applications, e.g., carpets, upholstered furniture in transport, etc. Ammonium phosphates and polyphosphate, boric acid-borax, and ammonium bromide can be successfully used in nondurable FR finishes for wool. Various commercial products have been reviewed by Horrocks.3 The most successful durable treatment for wool is Zirpro, developed by Benisek, which involves exhaustion of negatively charged complexes of zirconium or titanium onto positively charged wool fibers under acidic conditions at 60°C. The treatment can be applied to wool at any processing stage from loose fiber to fabric using exhaustion techniques. 

There are only a few minerals where thorium occurs as a significant constituent. The commercially important ore is the golden-brown, lanthanide phosphate, monazite [13064-1 -8/, LnPO where Ln = Ce, La, or Nd, in which thorium is generally present in a 1—15% elemental composition (7,8). Monazite is widely distributed around the world. Some deposits are quite large. Beach sands from Australia and India contain monazite from which concentrates of lanthanides, titanium, zirconium, and thorium are produced (7). The Travancore deposits in India are the most famous, and have been perhaps one of the most significant sources of commercial thorium. Additional information on the occurrence of thorium in minerals can be found in the literature (7). A review of the mineralogy of thorium is also available (9). 

Appreciable ionic conductivity is found in open framework or layered materials containing mobile cations (see Ionic Conductors). Several phosphates have been found to be good ionic conductors and are described above NASICON (Section 5.2.1), a-zirconium phosphates (Section 5.3.1), HUP (Section 5.3.3), and phosphate glasses (Section 5.4). Current interest in lithium ion-conducting electrolytes for battery apphcations has led to many lithium-containing phosphate glasses and crystalline solids such as NASICON type titanium phosphate being studied. ... 

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