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Cr Ions (cr + ion)

Distribution by Scientific Domains

Polymers and Materials Science	40%

Selected Abstracts

The entrapment of corrosion products from CoCr implant alloys in the deposits of calcium phosphate: A comparison of serum, synovial fluid, albumin, EDTA, and water

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 8 2006
A. C. Lewis
Abstract Physical wear of orthopedic implants is inevitable. CoCr alloy samples, typically used in joint reconstruction, corrode rapidly after removal of the protective oxide layer. The behavior of CoCr pellets immersed in human serum, foetal bovine serum (FBS), synovial fluid, albumin in phosphate-buffered saline (PBS), EDTA in PBS, and water were studied using X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The difference in the corrosive nature of human serum, water, albumin in PBS and synovial fluid after 5 days of immersion was highlighted by the oxide layer, which was respectively 15, 3.5, 1.5, and 1.5 nm thick. The thickness of an additional calcium phosphate deposit from human serum and synovial fluid was 40 and 2 nm, respectively. Co and Cr ions migrated from the bulk metal surface and were trapped in this deposit by the phosphate anion. This may account for the composition of wear debris from CoCr orthopedic implants, which is known to consist predominantly of hydroxy-phosphate compounds. Known components of synovial fluid including proteoglycans, pyrophosphates, phospholipids, lubricin, and superficial zone protein (SZP), have been identified as possible causes for the lack of significant calcium phosphate deposition in this environment. Circulation of these compounds around the whole implant may inhibit calcium phosphate deposition. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1587,1596, 2006 [source]

Ethylene polymerization behavior of Cr(III)-containing montmorillonite: Influence of chromium compounds

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009
Kazuhiro Yamamoto
Abstract Montmorillonite was treated with Cr(NO3)3, Cr(acetate)3, and Cr(acac)3 to give three catalyst precursors, Cr-MMT-1, Cr-MMT-2, and Cr-MMT-3, respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr-MMT-1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr-MMT-1 and mostly the outer surface region for the other two catalysts. Aluminosilicate-supported Cr catalysts exhibited reactivity similar to that of Cr-MMT-2 and Cr-MMT-3. However, more of the low-molecular-weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n -Bu2Mg and Et2Zn in the place of Et3Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high-molecular-weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272,2280, 2009 [source]

Effect of Yttrium and Erbium Ions on Epitaxial Phase Transformations in Alumina

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003
Deirdre D. Ragan
The effect of low concentrations of Y, Er, and Cr solutes on the amorphous-to-, transformation and on the ,-to-, transformation in aluminum oxide has been studied in situ by time-resolved reflectivity. The activation energies of the two transformations with these dopants are the same as in undoped alumina, being 4.1 ± 0.1 and 5.2 ± eV, respectively. Although not affecting the activation energies, Y, Er, and Cr do affect the transformation kinetics. Y and Cr ions decrease the ,-to-, transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as ,6 ppm retard the ,-to-, transformation and concentrations of 32 ppm essentially stop the transformation occurring within the times and temperatures accessible within the present experiment, thereby preventing quantification of the effect of Er on the ,-phase transformation. Erbium also retards the amorphous-to-, transformation relative to undoped alumina whereas yttrium and chromium accelerate it. [source]

Relation between Mössbauer spectroscopy and geometrical frustration factors in MCr1.9857Fe0.02O4 (M = Co, Zn)

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007
Kang Ryong Choi
Abstract In order to elucidate the role of Cr ions in MCr2O4(M = Co, Zn) exhibiting geometrically frustration and multiferroic property, we have substituted a small amount of Fe ions for Cr sites and investigated the magnetic behavior of Fe ions with Mössbauer spectroscopy. The crystal structure was found to be single-phase cubic spinel with space group of Fd3m. The lattice constants a0 and the internal structural parameter (x) of the oxygen were determined to be 8.340, 8.331 Å and 0.261 and 0.260, respectively. The Mössbauer absorption spectra at 4.2 K show that the well-developed two sextets are superposed with small difference of hyperfine fields(Hhf). The hyperfine fields of CoCr1.9857Fe0.02O4 and ZnCr1.9857Fe0.02O4 were determined to be 490 , 480 kOe and 460 , 450 kOe, respectively. Isomer shift values (,) of the two sextets are found to be 0.33 , 0.35 mm/s relative to those of Fe metal, which are consistent with the high spin Fe3+ charge state. From the results of Mössbauer measurement, it is suggested that Cr3+ ions have two different magnetic sites, and there is a correlation between hyperfine fields and degree of magnetic geometrical frustration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cr1.45Tl1.87Mo15Se19, a monoclinic variant of the hexagonal In3Mo15Se19 type

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009
P. Gougeon
The monoclinic compound Cr1.45Tl1.87Mo15Se19 (chromium thallium pentadecamolybdenum nonadecaselenide) represents a variant of the hexagonal In3Mo15Se19 structure type. Its crystal structure consists of an equal mixture of Mo6Se8Se6 and Mo9Se11Se6 cluster units. The Mo and Se atoms of the median plane of the Mo9Se11Se6 unit, as well as three Cr ions, lie on sites with m symmetry (Wyckoff site 2e). The fourth Cr ion is in a 2b Wyckoff position with site symmetry. [source]