Zirconium Concentrations Research Articles

The influence of electronic and steric effects and the importance of polymerization conditions in the ethylene polymerization with zirconocene/MAO catalysts

A series of Cp′(C 5H 5)ZrCl 12 and Cp 2 ′ZrCl 12 precatalysts (Cp′ = C 5Me4H, C 4Me 4P, C 5Me 5) together with (C 5H 5) 2ZrCl 12 has been investigated in terms of steric and electronic variations and their catalytic activities in combination with methylalumoxane (MAO) towards the polymerization of ethylene are compared. The changes in the steric environment were evaluated on the basis of the structural data available and supplemented by theoretical structural studies on the semiempirical (ZINDO, EHMO) and density functional (DF) level. The X-ray structures of (C 5Me 4H) 2ZrCl 2 ( 3) and (C 4Me 4P)(C 5H 5)ZrCl 2 ( 4) have been determined ( 3: orthorhombic, Cmcm, a = 6.714(4), b = 17.275(4) c = 15.643(5) A ̊ , Z = 4 ; 4: monoclinic, P2 1/ c, a = 8.8791(5), b = 7.8051(8), c = 20.9215(10) A ̊ β = 94.422(4)° , Z = 4. 91Zr NMR data for the above series has been measured and is correlated to changes in the HOMO-LUMO gap available from electronic structure calculations. Under mostly homogeneous polymerization conditions, at very low zirconium concentrations the order of the catalytic activity found for ethylene polymerizations is (C 5H 5) 2ZrCl 2 > (C 5Me 4H)(C 5H 5)ZrCl 2 > (C 5Me 5)(C 5H 5)ZrCl 2 > (C 4Me 4P)(C 5H 5)ZrCl 2 > (C 5Me 4H) 2ZrCl 2 > (C 5Me 5) 2ZrCl 2 > (C 4Me 4P) 2ZrCl 2, which for the most part is inversely proportional to the steric demand of the ring ligands in the metallocene precatalysts except for the phospholyl systems. The lower activities of the phospholyl vs. the tetra- and penta-methylcyclopentadienyl compounds might imply an electronic effect such that the electron withdrawing phosphorus substituent decreases the activity, although further studies are needed to clarify this situation. Emphasis is placed on the control of the polymerization conditions and evaluation of the time-activity profiles. At higher zirconium concentrations an increased precipitation of polyethylene takes place during the course of polymerization and results in a transfer to the heterogeneous phase with a diffusion controlled reaction rate thereby invalidating any activity-comparing studies.

Reduction of bis(η5‐cyclopentadienyl)zirconium dichloride in the presence of methylalumoxane

AbstractThe reaction occurring between bis(η5‐C5H5)ZrCl2 (C5H5 = cyclopentadienyl) and methylalumoxane (MAO) has been studied by means of electron paramagnetic resonance (EPR) spectroscopy at different zirconium concentrations and Al/Zr mole ratios. The toluene solution of bis(η5‐C5H5)ZrCl2/methylalumoxane, in the absence of ethylene, was verified to be more stable than the catalytic system based on bis(η5‐C5H5)TiCl2/AIR3 (R = alkyl). Zr(IV) was reduced to Zr(III) in small amounts with a Landé factor g = 1,998 and a hyperfine interaction splitting constant α (91Zr) = 7 G. The presence of ethylene strongly increased the efficiency of the Zr(IV) to Zr(III) reduction. Simultaneously it modified the chemical electronic surrounding of the Zr nucleus as revealed by the sharp increase of α(91Zr) = 12 G.

The mobility of zirconium and other “immobile” elements during hydrothermal alteration

Development of zircon and other Zr phases in hydrothermal deposits indicates that Zr can be highly mobile in these systems. Mobility is most common in, but not restricted to, F-rich hydrothermal systems related to alkalic, F-rich igneous suites; these suites can range from peralkaline through metaluminous to peraluminous. A few examples are neither alkalic nor F rich. Three locations in the Trans-Pecos Magmatic Province, Texas, U.S.A., demonstrate this hydrothermal Zr mobility. All three igneous systems are alkalic and F rich but vary in alkali/Al ratios. Peralkaline rhyolites and trachytes in the Christmas Mountains contain as much as 2100 ppm Zr, mostly in aegirine or arfvedsonite; zircon is rare or absent. Fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38,000 ppm Zr, occurring as small, disseminated zircons. The deposits also are enriched in a variety of incompatible elements, including Be, rare-earth elements (REE), Y, Nb, Mo, Hf, Pb, Th and U. The Sierra Blanca intrusions, a series of mildly peraluminous, F-rich rhyolite laccoliths, contain as much as 1000 ppm Zr, mostly as zircon. Hydrothermal zircon occurs as overgrowths on magmatic grains, as veinlets connected to overgrowths, and in fluorspar replacement bodies in adjacent limestone. The highest Zr concentrations in fluorspar are ∼200 ppm. Metaluminous quartz monzonite from the Infiernito caldera contains 400–600 ppm Zr, mostly as zircon. Euhedral zircon in quartz-fluorite veins in the quartz monzonite indicates mobility of Zr. Zirconium concentrations in the veins are unknown, but the paucity of zircon suggests little Zr enrichment relative to the host. Zircon and, more rarely, zirconolite, occur in skarn in the Ertsberg District of Irian Jaya, Indonesia. Unlike in Texas, related igneous rocks are metaluminous, and the hydrothermal system was F poor. Worldwide, hydrothermal zircon, other Zr phases, and Ti- and Al-bearing phases occur in skarn, epithermal precious metal veins, volcanogenic massive-sulfide deposits and mylonites. We propose that differences in Zr mineralogy of igneous source rocks is an important factor in determining the availability of Zr to hydrothermal fluids. Although Zr concentrations in the Sierra Blanca and Christmas Mountains rhyolites are similar, Zr enrichment in fluorspar was much greater in the Christmas Mountains. We suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release Zr, but that zircon was only moderately attacked. Therefore, far more Zr was available for transport and subsequent deposition in the Christmas Mountains than at Sierra Blanca. Availability of other trace elements probably is also governed by their mineral host. Although Zr mobility is most common in F-rich hydrothermal systems related to alkalic and F-rich igneous systems, mobility at Ertsberg may have been promoted by sulfate complexing.

Preparation of fine zirconium hydrous oxide particles for dynamic ultrafiltration membrane

Fine and uniform zirconium hydrous oxide particles about 0.03–0.3 μm in diameter could be prepared by Matijevićs method in the presence of sulfuric acid. It is possible to control the size of particles by the use of zirconium concentrations in the approximate range (5·10 −4 −5·10 −3 kmol m −3) and molar ratios of zirconium to sulfate from about 1.0/0.7 to about 1.0/7.0. The particles are completely amorphous, and the surfaces consist of zirconium, oxygen and SO 2− 4, as shown by X-ray powder diffractometry and X-ray photoelectron spectroscopy respectively.

Processing and electrical properties of Pb (ZrxTi1−x)O3 (x=0.2–0.75) films: Comparison of metallo-organic decomposition and sol-gel processes

The deposition of thin Pb(ZrxTi1−x)O3 films by sol-gel and by metallo-organic decomposition (MOD) processes has been studied. Powders obtained from different precursor solutions were analyzed with respect to their decomposition and crystallization. Using a spin-coating technique, Pb(ZrxTi1−x)O3 films with zirconium concentrations ranging from x=0.2 to 0.75 have been deposited on Pt-electroded Si wafers. The lattice constants of the perovskite films and their dielectric and ferroelectric properties (permittivity, remanent polarization, coercive field strength) have been measured as a function of the zirconium concentration. The results are compared to the data obtained on bulk ceramics. For Pb(ZrxTi1−x)O3 films with a composition located at the morphotropic phase boundary (x≊0.53) the influence of the processing and the lead excess of the starting solutions on the film properties was examined. First measurements on the resistance degradation of thin Pb(Zr0.53Ti47)O3 films deposited by the MOD process are reported.

Flow analysis of silicate rocks for zirconium

A flow analysis system involving the on-line configuration of an anion-exchange column has been examined to enrich and determine trace concentrations of zirconium of several ppm to hundred ppm levels in silicate rocks and minerals. About 100 mg of sample is decomposed by fusion with a mixture of boric acid and lithium carbonate and taken up with 1 M hydrochloric acid to a total of 100 ml. Depending upon the concentration of zirconium, either a 1- or 4-ml aliquot is introduced into an aqueous carrier stream, merged with sulphuric acid and passed through a small volume anion-exchange column. The enriched zirconium is then back eluted with hydrochloric acid, colour-developed with Arsenazo III, and detected spectrophotometrically at 665 nm.

Geochemistry of the Cretaceous Shales and Its Implication on Regional Tectonics and Correlation: Wyoming and Montana

The Cretaceous strata of north-central Wyoming and south-central Montana consist of shale, mudstone, and sandstone with minor conglomerate, coal, and bentonite. The primary objective in this paper is to utilize the mineralogical and geochemical data of the critical and dominant lithofacies group comprised of shale and mudstone to reevaluate regional tectonics, provenance aspects, and correlation of the Cretaceous foreland basin sediments. Relative abundances of nickel, zinc, lanthanum, and cerium in the marine samples can be attributed largely to the organic-rich nature and presence of mineral phase apatite in the marine group. The abundance of these trace elements is presumably related to the proximity of local bedrock source region and distinctive clay mineral suite in the marine sediments. Low concentrations of zirconium, titanium, and chromium in nonmarine Cloverly mudrock indicate an alkaline to peralkaline original sediment (ash) composition as opposed to trachytic to dacitic component for the marine group. Furthermore, the marine sequences in the Cretaceous foreland basin are related to thrust load-induced flexure. Overall geochemical behavior of the analyzed samples seems to be related more to confidently to tectonism rather than different provenance. This geochemical classification can be utilized for stratigraphic correlation of the several lenticular sandstone members encased withinmore » the various Cretaceous units and offers an excellent opportunity for future oil and gas exploration in this region.« less

Sputtering of thin films of Pb(ZrTi)O3

Abstract Pb(ZrTi)O3 thin films of some selected Zr/Ti-ratios were produced by reactive dc diode sputtering and rftriode sputtering respectively. Films, which were sputtered at substrate temperatures of about 1000 K show the typical ferroelectric behaviour. An additional effect with thin ferroelectric Pb(ZrTi)O3 films is that the morphotropic phase boundary is shifted to higher concentrations of zirconium in the solid solution.

Effect of zirconium concentration on nodule formation during cyclic oxidation of Fe-15Cr-4Al alloy at 1300�C

The effect of small concentrations of zirconium on the cyclic oxidation behavior of Fe-15Cr-4Al was investigated at 1300°C. The zirconium concentrations studied were 0.2, 0.55, and 1 wt.%. Each cycle consisted of a 1-hr isothermal period followed by 30-min cooling of the sample in air. Nodule formation was observed in higher zirconium-containing alloys, 0.55% and 1% zirconium, and the base alloy. The nodules formed at the corners and edges of the specimen and grew with increasing number of cycles. EDAX and line scans of cross section of oxidized samples demonstrated that the nodules were composed of iron oxides. Suggestions are given regarding the mode of nodule formation. Results show that additions of 0.2% zirconium and 1% yttrium to the base alloy suppress the nodule formation and provide the best resistance to cyclic oxidation.

Kinetic-fluorimetric study of the activator effect of zirconium(IV) on the air oxidation of morin catalysed by manganese(II)

A kinetic study of the activator effect of zirconium(IV) on the manganese(II)-catalysed air oxidation of morin has been made. The effect of ammonia, ethanol, morin, manganese(II) and zirconium(IV) concentrations and of temperature was examined in order to obtain the optimum conditions for the determination of zirconium(IV) and to establish the kinetic dependence of each of these variables for the catalysed and activated reactions. The reaction was followed by measuring the decrease in fluorescence at 548 nm, with an excitation wavelength of 417 nm. A kinetic-fluorimetric method for the determination of zirconium(IV) is proposed. The calibration graphs were obtained by applying the fixed time, fixed concentration, initial rate and rate constant methods. The method is linear up to 250 ng ml–1 of zirconium(IV). The precision was calculated for the different methods applied and was always smaller than 3%. The main interferences were due to BeII, CuII and MgII. Moreover, the zirconium(IV)'s activator effect has been used to improve the kinetic-fluorimetric determination of manganese(II). The method is linear up to 60 ng ml–1, with a detection limit of 0.26 ng ml–1 for manganese(II), and a sensitivity enhancement of about 50% is obtained in the presence of the activator.

Effect of Zirconium Concentration on High Temperature Cyclic Oxidation Behavior of Fe‐15Cr‐4Al at 1150°C

The effect of zirconium (0.2, 0.55, and 1 weight percent) additions to the base alloy, Fe‐15Cr‐4Al, on cyclic oxidation at 1150°C in air was investigated. Each cycle consisted of 1h holding at temperature followed by half an hour air cooling and every alloy was subjected to 32 cycles. The cyclic oxidation was observed to depend on the zirconium concentration. The lowest zirconium concentration (0.2%) imparted the maximum oxidation resistance. For comparison purposes a similar study was carried out for an alloy containing 1% yttrium. This alloy showed the best resistance to cyclic oxidation. SEM, EDAX, and EPMA of the cross sections of oxidized samples were carried out. The formation of nodules was observed in the scale formed on alloys containing zirconium and yttrium. EDAX of the nodules revealed them to be iron rich with small concentrations of zirconium, chromium, and aluminum.

The influence of zirconium on decomposition in high strength aluminium alloys

In high strength Al-Zn-Mg and Al-Zn-Mg-Cu alloys dynamical recrystallization during hot working is successfully suppressed by metastable Al 3Zr precipitates that are formed during the homogenization treatment. The density, size and distribution of Al 3Zr particles were varied by using different Zirconium concentrations (0–0,2 wt % Zn) and homogenization procedures. Two calorimetric methods were used to study the influence of Al 3Zr-particles on the precipitation of GP-Zones during cold ageing and of metastable phases (η', R) during warm ageing respectively. Cold ageing was found to be retarded whereas warm ageing turned out to be enhanced by Al 3Zr-partic1es. An explanation is given on the basis of the conservation of dislocations and subgrain boundaries by Al 3Zr-partic1es.

The crystallisation of CoZr amorphous alloys in the range Co92Zr8 to Co21Zr79

The authors present a crystallisation study of sputter-deposited Co100-xZrx amorphous alloys prepared at zirconium concentrations between 7 and 80 at.%. The transformation of these alloys from the amorphous to the equilibrium crystalline state has been investigated by thermal analysis, X-ray diffraction and electrical resistance measurements. Their crystallisation temperatures were determined by differential scanning calorimetry (DSC) and by resistance measurements as a function of temperature. X-ray diffraction was used to identify the final phases after heating. The behaviour of the activation energy with composition suggests that there may be a eutectic at the composition Co40.8Zr59.2. The activation energies of the samples are calculated by means of Kissinger plots and the heats of crystallisation are also calculated. Correlations between the thermal analysis and resistance results are discussed.

Effect of small concentrations of zirconium on high temperature oxidation behaviour of Fe-15 Cr-4 Al

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Ethylene propylene diene terpolymers produced with a homogeneous and highly active zirconium catalyst

AbstractEPDM terpolymers with ethylidene norbornene as diene monomer could be prepared by means of a soluble Ziegler catalyst formed from biscyclopentadienyl zirconium dimethyl and methylaluminoxane. The overall activities lie between 100 and 1000 kg EPDM/(molZr h bar), obtainable at zirconium concentrations as low as 5 × 10−7 mol/L. After an induction period (0.5–5 h) the polymerization rates increased and then leveled to a value which was constant for several days. From copolymerization kinetics reactivity ratios r12 = 31.5, r21 = 5 × 10−3, and r13 = 3.1 could be derived, and by 13C‐NMR spectroscopy r12 · r21 = 0.3 was found (1: ethylene, 2: propylene and 3: ethylidene norbornene). The regiospecifity of the catalyst toward propylene leads exclusively to the formation of head‐to‐tail enchainments. The diene polymerizes via vinyl polymerization of the cyclic double bond, and the tendency to branching is low. Molecular weights were estimated between 40,000 and 160,000. The average molecular weight distribution of 1.7 is remarkably narrow. Glass transition temperatures of −60 to −50°C could be observed. The cure behavior and the physical properties of cured samples were also tested.

Magnetism and electron-mass enhancement in zirconium-rich Fe-Zr and Co-Zr metallic glasses.

The magnetic properties of Fe-Zr and Co-Zr melt-spun metallic glasses have been examined in the range of zirconium concentrations greater than about 50 at. %. In the paramagnetic region both systems are highly enhanced magnetically. There is no evidence for local moments and Fe-Zr becomes a weak itinerant ferromagnet for Zr concentrations less than 62.5 at. %. Values are given for electron-mass enhancement due to spin fluctuations.

Mandelazo I As A Reagent For Zr(IV) Determination

A spectrometric study of the reaction of the Zr(IV) ions with Mandelazo I was carried out. Absorption spectra revealed that the maximum absorption of the zirconium compound appears at a wavelength (316 nm) different from the maxima of the reagent (253 and 390 nm). Beer-Lambert law is followed for zirconium concentrations of the order of 8.8 x 10/sup -5/ M (i.e. 8 ..mu..g Zr(IV)/mL). Possible interferences of ions such as Be(II), Cu(II), Zn(II), Al(III), Th(IV), U(VI), Mn(II), Fe(III), Co(II) and Ni(II) were investigated in connection with some masking agents such as SO/sub 4//sup 2 -/ and C/sub 2/O/sub 4//sup 2 -/. Also, the solid state Zr(IV)- Mandelazo I compound was prepared and characterized by nitrogen and thermogravimetric analyses.

Solvent Extraction Chemistry and Kinetics of Zirconium

Abstract The solvent extraction behavior of zirconium in the HN03-tributyl phosphate (TBP) system can be explained based on the existence of four principal aqueous species, Zr4+, ZrOH3+, Zr3(OH)8+ 4, and oxo-polymers. The Zr4+ and ZrOH3+ species are extractable and are in equilibrium with inextractable Zr3(OH)8+ 4. The oxo-polymers are formed by heat, are-inextractable, and are not: in equilibrium with the other species. The aqueous equilibria and their equilibrium quotients have been previously determined. In the present study, these equilibria were used along with both tracer and macro zirconium concentrations (oxo-polymers excluded by extraction and back scrubbing) to determine the distribution equilibrium constants for both the Zr4+ and ZrOH3+ ions. The four equilibrium constants give excellent fits to both tracer and macro-zirconium distribution data. The concentrations of the extractable zirconium species which are calculated from the equilibria have been used to begin examining the extraction kinet...

The foam separation of zirconium(IV) from aqueous solutions

The foam separation of zirconium(IV) from chloride solutions has been investigated over the 1.8–12 pH range using sodium lauryl sulphate or cetyl(trimethyl)ammonium bromide as collectors. The effects of gas flow rate, bubbling time, collector and zirconium(IV) concentrations, ageing of the metal ion, and ionic strength have been studied and the results are discussed in relation to the hydrolytic behaviour of zirconium(IV). Under optimum conditions,ca. 99.5% removal can be achieved.

YTTRIUM AND ZIRCONIUM AS GEOCHEMICAL GUIDE ELEMENTS IN SOIL AND STREAM SEDIMENT SEQUENCES

SummaryYttrium and zirconium concentrations, taken as representative for the abundances of the heavy minerals xenotime and zircon in soils and stream sediments of the Schwarzach valley in eastern Bavaria, were found to be closely correlated, the Zr/Y ratio averaging 9.7 (r = 0.90 for 73 samples). The uniformity of this ratio ‐ despite considerable local variations of the individual concentrations—indicates its suitability for tracing back soils and sediments to the parent rocks.