Dioxide zirconium

The source for zirconium dioxide (Zr02, zirconia) is zircon (ZrSi04), which occurs in igneous rocks. A secondary source of zircon is from beach sands. In these sands, it is mixed with ilmenite, rutile, and monazite. 

One way of producing zirconia from zircon is by dissociating it above 1750°C. The dissociation reaction is given in Equation 12.7. 

A similar double microemulsion method for zirconia particle preparation was also reported by Wang etal. [255], where 53 wt% cyclohexane and 35 wt% NP-5/ NP-9 (wt ratio 1 1) were used as the oil (continuous) phase and the surfactant respectively. The water (dispersed) phases in the two microemulsions were 12 wt% of Q.75M zirconyl nitrate and 2.0M ammonia solutions. 

Herrig and Hempelmann [256] proposed a general single microemulsion scheme for the synthesis of various single and multiple oxides. In all such cases, microemulsions were first prepared by mixing cyclohexane (continuous phase), water (dispersed phase) and the surfactant Brij 30. This was then poured into an 

Yang and Chen [257] exploited the well-used AOT/isooctane/water system for producing Y-stabilized zirconia particles. Two methods were used  

The particles were gathered by centrifugation, washed with ethanol and calcined at 600 C/3h. The doped zirconia particles were tetragonal in structure and varied in size from 6.6 nm to 26.7 nm (average size 13 nm). 

The system CTAB/l-hexanol/water was utilized by Fang and Yang [258] for preparation of Zr02-Y203 nanoparticles. In one (reverse) microemulsion, aqueous ammonium hydroxide was introduced as precipitant while the other contained Zr-oxychloride and Y-nitrate (ZrA = 94/6) the two were mixed under stirring. The precipitate obtained by centrifugation was ultrasonically washed in pure ethanol, dried at 85 C under vacuum and calcined at 600 C/2h. The particle size distribution was wide, from about 10 nm to 70 nm. 

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Exposure limits for siHcon carbide and powders of zirconium compounds (including zirconium dioxide) have been estabHshed by ACGIH. TLV—TWA s are 10 mg/m and 5 mg/m, respectively. OSHA guidelines for zirconium compounds call for a PEL of 5 mg/m. There are no exposure limits for siHcon nitride powder, but pmdent practice suggests a TLV—TWA of 0.1 mg/m. The soHd ceramics present no apparent health hazard. In machining such ceramics, however, care should be taken to prevent inhalation of respirable particles in amounts in excess of estabHshed limits. Disposal should be in approved landfills the materials are inert and should pose no danger to the environment. 

Zirconium carbide is inert to most reagents but is dissolved by hydrofluoric acid solutions which also contain nitrate or peroxide ions, and by hot concentrated sulfuric acid. Zirconium carbide reacts exothermically with halogens above 250°C to form zirconium tetrahaHdes, and with oxidizers to zirconium dioxide in ak above 700°C. Zirconium carbide forms soHd solutions with other transition-metal carbides and most of the transition-metal... 

B. R. Rossing, L. H. Cadoff, and T. K. Gupta, "The Fabrication and Properties of Electrodes Based on Zirconium Dioxide," Vol. 2, 6th International Conference onMHD Electrical Power Generation, Washington, D.C., June 1975, pp. 105—117. 

Ethyl Acetate. Catalysts proposed for the vapor-phase production of ethyl acetate include siUca gel, zirconium dioxide, activated charcoal, and potassium hydrogen sulfate. More recendy, phosphoric-acid-treated coal (65) and calcium phosphate (66) catalysts have been described. 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

Titanium dioxide used for adhesive applications should contain an inorganic coating to control polarity, improve its ease of dispersion, and improve its weather resistance. The inorganic coating (zirconium dioxide, silica, alumina) is applied in the aqueous sluny by precipitation of one or more hydrated metal oxides and by neutralization of acidic and alkaline compounds. 

Conceptually elegant, the SOFC nonetheless contains inherently expensive materials, such as an electrolyte made from zirconium dioxide stabilized with yttrium oxide, a strontium-doped lanthanum man-gaiiite cathode, and a nickel-doped stabilized zirconia anode. Moreover, no low-cost fabrication methods have yet been devised. 

High-temperature solid-oxide fuel cells (SOFCs). The working electrolyte is a solid electrolyte based on zirconium dioxide doped with oxides of yttrium and other metals the working temperatures are 800 to 1000°C. Experimental plants with a power of up to lOOkW have been built with such systems in the United States and Japan. 

The high temperatures attainable in a plasma furnace, with no restrictions with regard to factors such as the furnace atmosphere or the crucible material, has made processing by thermal decomposition a practicable and useful method. A good example is the thermal decomposition of low-cost zircon (ZrSi04) to produce zirconium dioxide (Zr02). The fur-... 

Doped zirconium dioxide is the solid electrolyte in lambda sensors (oxygen sensors used in the field of environmental protection). 

Another study on the preparation of supported oxides illustrates how SIMS can be used to follow the decomposition of catalyst precursors during calcination. We discuss the formation of zirconium dioxide from zirconium ethoxide on a silica support [15], Zr02 is catalytically active for a number of reactions such as isosynthesis, methanol synthesis, and catalytic cracking, but is also of considerable interest as a barrier against diffusion of catalytically active metals such as rhodium or cobalt into alumina supports at elevated temperatures. 

Two catalyst systems were developed by Standard Oil and Philips petroleum. Standard Oil process uses metal catalyst such as molybdenum trioxide on supports like alumina or titanium or zirconium dioxide. The process is carried out at 200-300°C at Organisation and Qualities... 

The phthalic anhydride/urea process may also be employed to convert tetra-chloro phthalic anhydride to green copper hexadecachloro phthalocyanine by condensation. In this case, titanium or zirconium dioxides, particularly in the form of hydrated gels, are used instead of the molybdenum salts which are used in the phthalic anhydride process [23]. There is a certain disadvantage to the fact that the products lack brilliance and require additional purification. 

Synonyms Zirconium dioxide zirconium silicate zirconium tetrachloride... 

In rats, the oral LDso of several zirconium compounds ranged from 1.7 to lOg/kg. Animals acutely poisoned by zirconium compounds show progressive depression and decrease in activity until death. Repeated inhalation of zirconium tetrachloride mist by dogs for 2 months at 6 mg zirconium/m caused slight decreases in hemoglobin and in erythrocyte counts, with some increased mortality over that of controls. These effects may have been due to the liberation of hydrogen chloride. Animals exposed to zirconium dioxide dust for... 

Interfacial properties of zirconium dioxide and magnetite in water. J. Colloid Interface Sci. 91 560-570... 

Synonyms zirconia zirconium dioxide zirconic anhydride... 

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. 

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