Presence Of Zirconium Research Articles

Effect of zirconia additions on the reaction sintering of aluminium titanate

Yttria-stabilized zirconia was added to a chemically prepared mixture of alumina and titania. The effect of the zirconia on the microstructure and resultant properties was studied following reaction sintering to form aluminium titanate. An increase in mechanical strength was observed with little effect on the excellent thermal properties of the aluminium titanate. This was attributed to generation of extra microcracks by the transformation of the zirconia phase and the unusual microstructure produced by the presence of zirconia.

Estimate of the Activation Energies for Boundary Diffusion from Rate‐Controlled Sintering of Pure Alumina, and Alumina Doped with Zirconia or Titania

Sintering experiments at constant heating rates were employed to estimate the activation energy for sintering in alumina and in alumina containing 5 vol% zirconia or 5 vol% titania. Grain growth, which can complicate the analysis of sintering kinetics data, was suppressed by using uniformly and densely packed grain compacts prepared by colloidal processing. Grain‐boundary diffusion is believed to have been the dominant sintering mechanism. The activation energies were 440 ± 40 kJ/mol for pure alumina, 585 ± 40 kJ/mol for alumina (titania), and 730 ± 60 kJ/mol for alumina (zirconia). The alumina and alumina (titania) results are in agreement with the values reported in the literature. The possibility that the higher activation energies for doped alumina reflect a stronger bonding at alumina interfaces in the presence of zirconium and titanium is discussed.

Analysis of mixtures of hafnium and zirconium by the methylthymol blue—hydrogen peroxide method

The reaction of hydrogen peroxide with the zirconium(IV) and hafnium(IV) Methylthymol Blue complexes (MeMTB) has been investigated. The conditional stability constants of the Zr(IV) and Hf(IV) complexes with hydrogen peroxide [ K′ Me(H 2O 2) ] were determined spectrophotometrically. The K′ Me(H 2O 2) values found, which depend on the acidity, are 3.91 × 10 2 3.24 × 10 2, 2.63 × 10 2 at [HCl] = 0.2, 0.3, 1.0 M respectively for Me = Zr(IV) and 0.828, 0.523, 0.319 for Me = Hf(IV). The ratios of the conditional stability constants, K′ Me(H 2O 2) / K′ MeMTB, are: 5.52 × 10 −4, 5.79 × 10 −4, 8.23 × 10 −4 for Me = Zr(IV) and 2.08 × 10 −6, 2.74 × 10 −6, 1.48 × 10 −5 for Me = Hf(IV) at the three acidities. The maximum of the ratio of the relative conditional stability constants is obtained in 0.2 M hydrochloric acid. The conditions which should be complied with for the determination of hafnium in the presence of zirconium are discussed. The results were compared with those obtained by the Xylenol Orange—hydrochloric acid method. They are superior for samples containing less than 20 mole% of hafnium in admixture with zirconium.

Si 3N 4-Al 2O 3-ZrO 3 hot pressed composites

Development of microstructure, thermal expansion behaviour and room temperature MOR, Vickers microhardness and toughness have been studied for 83wt%Si 3N 4-5wt%Al 2O 3-12wt%ZrO 2 composites hot pressed at 34.4MPa for various times and temperatures. The deleterious presence of Zr-O-N phases is avoided in these materials. Microcracking has been observed because of the mismatch between thermal expansion coefficients. A phenomenological model is suggested to account for the variation of cell parameters of the β'-phase with the progress of the α→β' conversion. No detectable improvement in hardness and toughness results from the presence of zirconia. The substantial MOR increase, from ~370 MPa for a Si 3N 4-Al 2O 3 reference material to~630 MPa for the ZrO 2 composite has been ascribed more properly to a grain boundary phase effect, than to specific ZrO 2-induced microcrack strengthening.

ChemInform Abstract: The Polarographic Reduction of Nitrate Ion in the Presence of Zirconium(IV) has been studied by dc and phase‐selective ac polarography.

Chemischer InformationsdienstVolume 17, Issue 42 Physical Inorganic Chemistry ChemInform Abstract: The Polarographic Reduction of Nitrate Ion in the Presence of Zirconium(IV) has been studied by dc and phase-selective ac polarography. N. OGAWA, N. OGAWASearch for more papers by this authorH. KODAIKU, H. KODAIKUSearch for more papers by this authorS. IKEDA, S. IKEDASearch for more papers by this author N. OGAWA, N. OGAWASearch for more papers by this authorH. KODAIKU, H. KODAIKUSearch for more papers by this authorS. IKEDA, S. IKEDASearch for more papers by this author First published: October 21, 1986 https://doi.org/10.1002/chin.198642027AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue42October 21, 1986 RelatedInformation

On the polarographic reduction of nitrate ion in the presence of zirconium(IV)

The polarographic reduction of nitrate ion in the presence of zirconium(IV) is studied by dc and phase-selective ac polarography. The total reduction process was proved by means of controlled-potential electrolysis and chemical analysis to conform to NO − 3+8H +6 e −→NH 2OHH +=2 H 2O. Using a measurement of differential capacity, a large part of the difference between the reduction transfer to the vicinity of the electrode but to a charge transfer step and/or a chemical reaction step. The zirconium(IV) is concluded to act as an intermediary for the charge transfer from the electrode to the nitrate ion.

New routes to the preparation of pillared montmorillonite catalysts

Clay catalysts have been prepared using reagents different from the aluminum chlorhydrate solution usually employed to pillar smectite minerals. Colloidal alumina, alumina-coated silica and solutions containing chlorhydrated complexes of zirconium and aluminum produced pillared bentonites which, upon calcination at 400 °C, formed microporous two-dimensional structures with 200 – 500 m 2 g −1 Langmuir surface area and basal spacing between 17 and 18 Å. These pillared clays contain both Bronsted and Lewis acid sites; above 300 °C, pyridine is retained predominantly on Lewis centers. The presence of zirconia seems to enhance Brönsted acidity, whereas pillaring with colloidal alumina particles increases the catalyst Lewis acidity. Cracking activity for gas oil conversion depends mainly on the surface area generated by pillaring. Pillared bentonites are more active but less selective than similarly prepared pillared hectorite catalysts.

Sr 2Mn 2O 5, an oxygen-defect perovskite with Mn(III) in square pyramidal coordination

An oxygen-defect perovskite Sr 2Mn 2O 5 was isolated by reduction of SrMnO 3−x perovskites in the presence of zirconium. Its structure, similar to that of Ca 2Mn 2O 5, has been determined by X-ray powder diffraction and HREM. The orthorhombic cell has the parameters : a = 5.523(1) A ̊ , b = 10.761(5) A ̊ , c = 3.811(1) A ̊ . The possible space groups are Pbam and Pba2. The framework is built up from corner-sharing MnO 4 pyramids forming pseudo-hexagonal tunne l s running along 〈001〉 and perovskite tunnels running along 〈110〉 and 〈110〉. This oxide is antiferromagnetic with T N ⋍ 380 ± 10 K and θ P ⋍ 300 ± 10 K .

Modification of steel surfaces by thermal treatment in the presence of ZrB 2 and KBF 4

The preparation of coatings on some tool and carbon steels by treatment with ZrB 2 and various activators was investigated. The phase composition and layer structure were studied. It was shown that increases in the amounts of carbon and some alloying elements in the steel hinder the diffusion of the transition metal into the matrix. The presence of zirconium in the surface zone results in the formation of phases with an enhanced hardness compared with that of iron borides. The treatment of steel surfaces with zirconium diboride and some activators by the contact method was shown to lead to complex boronization-zirconization.

Zirconium cocatalysis of the cobalt-catalyzed autoxidation of alkylaromatic hydrocarbons

Zirconium (and hafnium) compounds are remarkably effective cocatalysts for the cobalt-catalyzed autoxidation of alkyl aromatics in acetic acid. The autoxidation of p-xylene to terephthalic acid in the presence of zirconium and other metal salts has been studied at 100 °C, 1 atm O 2. Only Zr and Hf salts are very effective, increasing yields from 40 to 90% and decreasing induction times from 325 to 135 min. Th shows moderate activity. Zr and Hf salts are unique in (a) their ability to attain greater than sixfold coordination in solution and (b) their high stability toward reduction to lower oxidation states. A kinetic investigation of the zirconium acetate-cocatalyzed autoxidation of toluene at 87 °C suggests that Zr favors Co (III) acetate monomer formation by formation of a weak ZrCo complex.

Influence of zirconium on the extraction of niobium from nitric acid by phosphate esters

Using stable niobium solutions in nitric acid, the extraction of tracer niobium into di-n-butyl butyl phosphonate has been studied over the 2–9M HNO3 range in the prescence of varying concentrations of zirconium up to 0.4 M. The large synergic effect on niobium extraction produced by the presence of macro zirconium has been studied in detail using 8 M HNO3, and the formation of double zirconium/niobium complexes is suggested. Similar but less marked synergic effects in the extraction of niobium into tri-n-butyl phosphate in the presence of zirconium are also reported.

Nb3Sn diffusion layers. An experimental study of their superconducting properties as related to the Zr content and cold-work amount of the Nb base ribbons

In the present work the results of a systematic experimental analysis on current-carrying properties of superconducting Nb3Sn diffusion layers are presented. The influence of the Zr content (up to a maximum of 7%) and of cold-work of Nb base ribbons on the critical current (at 64 kG) is discussed. It is shown that, while the presence of zirconium leads to a higher critical current density, at the same time it affects the diffusion coefficients, so that the thickness of diffusion layer is decreased. Results concerning pinning mechanism are also presented and discussed.

Effect of zirconium(IV) on the extraction of strontium by some acidic organophosphorus extractants

The effect of zirconium(IV) has been studied on the extraction of strontium by di- n-butyl, di- n-amyl, di- n-octyl and di(2-ethylexyl) phosphoric acids as well as n-octyl hydrogen phenylphosphonate and n-octyl hydrogen n-octylphosphonate. The presence of zirconium(IV) in the extraction system causes an enhancement of the distribution ratio of strontium with all the extractants studied, but the enhancements vary in magnitude with the different extractants. The effect of the zirconium concentration, the acidity of the aqueous phase, the extractant concentration as well as the diluent nature on the enhancement of the strontium extraction has been examined.

Spectrophotometric study of a hafnium-hematein chelate

A spectrophotometric study of an analytically useful hafnium chelate of hematein is presented. The stoichiometry, the formation constant, the optimal pH range and the free energy of formation of the chelate are described. Beer's law is obtained in the range 3–25 μg of hafnium(IV). The red-brown chelate, of probable formula HfO[hematein] 2, can be used for the colorimetric determination of hafnium in the presence of zirconium, if the molar concentrations of both metals are the same. The molar absorptivity of the hafnium chelate is 5.8·10 4 1 mole -1 cm -1 at 520 nm and pH 2.0 at room temperature.

Determination of Sulfaquinoxaline in Feeds: Collaborative Study

Abstract In the method developed, sulfaquinoxaline is extracted from the feed sample with dimethylformamide and separated from interfering substances by chromatography on alumina. The isolated sulfaquinoxaline is diazotized and coupled in the presence of zirconium. The color complex is then extracted with butanol and measured at 550 nm. Recoveries of sulfaquinoxaline from feeds reported by 13 collaborators ranged from 96 to 101%, with a coefficient of variation of 5%. This assay method is suitable for determining sulfaquinoxaline at all levels and has been adopted as official first action, to replace methods 38.139 and 38.140–38.141.

Studies on the analytical chemistry of hafnium and zirconium. Part III. Spectrofluorimetric determination of hafnium in the presence of zirconium by using quercetin

Hafnium at concentrations of 0·2 per cent. m/m and above in hafnium-zirconium mixtures can be determined spectrofluorimetrically via its complex with quercetin in 55 per cent. perchloric acid. There is no interference from zirconium.

The determination of hafnium in ores and ore-processing products by a (?, ??) reaction

presence of zirconium by thermal-neutron activation for Hf ta~ {TI/2 = 5.5 h) or Hf 181 (]71/2 = 46 days) requires very long periods of time [2, 3]. The results of the analysis are also affected by elements accompanying the hafnium, and this reduces the accuracy and reliability of the results. The sensitivity of analysis for the isotope Hf 179m when the neutron flux density is 1012-10 la neatrons/cm 2 �9 sec is no better than 0.03-0.04% [2-4], although a sensitivity of 5 �9 10-4% was achieved in [5] by the analysis of zirconium concentrates. The presence of zirconium (Zr 89m, Tt/2 = 4.4 min), silicon (Si 28 (n, p)A128, Ti/2 = 2.3 rain), and other elements [6] interferes with analysis using 14 MeV neutrons by the Hf 1~~ (n, 2n)Hf 179m reaction. The threshold sensitivity for the determination of hafnium at a flux of 1 �9 109 neutrons/era 2 �9 sec for a 0.1 g specimen is only 50/~g in the absence of interfering elements. The proposed activation method for determining hafnium from the (y, y') reaction is extreraely rapid, selective, and highly sensitive. One circumstance favoring the use of this interaction for determining the hafnium content of ores and ore-processing products is that when the bremsstrahlung boundary energy (Eymax) is below the thresholds for thermonuclear reactions, there is no possibility of activating any of the light elements up to arsenic. T hese elements are the principal rock-forming components of ore specimens. Moreover, there are only 21 nuclei, of 18 elements from selenium to mercury, which display ~someric activity in connection with the (y, 7') reaction with T1/2 ranging from seconds to days [7-9]. Zirconium, always found in association with hafnium, is not excited in this reaction. This substantially improves the selectivity of the analysis and considerably simplifies the interpretation of the Y-spectra. Another fact in favor of using this method is that there is practically no self-shielding effect, so that it is possible to analyze samples which are more representative than in the case of neutron-activati on analysis. The inelastic scattering of y-quanta by nuclei of the isotope Hf 179 leads to the formation of the rectastable state Hf 179m, with TI/2 = 19 see and Ey = 215 keV. The excitation of ttf 17ore was carried out by means of bremsstrahlung from a linear accelerator with an electron energy of 5 MeV.

Studies on the analytical chemistry of hafnium and zirconium. Part II. Fluorimetric determination of hafnium in the presence of zirconium by using quercetin

Hafnium at concentrations of 0·2 per cent. m/m and above in hafnium-zirconium mixtures can be determined spectrofluorimetrically via its complex with quercetin in 55 per cent. perchloric acid. There is no interference from zirconium.

Fluorimetric determination of hafnium in the presence of zirconium

Fluorimetric determination of hafnium in the presence of zirconium

Spectrophotometric studies of titanium (IV) complex with 3-benzyl 4,5-dihydroxycoumarin

3-Benzyl-4, 5-d’hydroxycoumarin has been used for the spectrophotometric determination of titanium (IV). It forms a deep orange red complex with titanium (IV) and the complex is stable at pH 1·8–2·5. The system obeys Lambert-Beer’s law at 380 mµ, within this pH range, up to 6·2 p.p.m. of titanium. The presence of zirconium and thorium up to twofold and fourfold concentrations respectively of titanium does not cause any interference.