Chromium Oxide Particles Research Articles

Wear particles from metal-on-metal total hip replacements: Effects of implant design and implantation time

Detailed characterization of wear particles is necessary to understand better the implant wear mechanisms and the periprosthetic tissue response. The purposes of the present study were to compare particle characteristics of current with older designs of metal-on-metal (MM) total hip replacements (THRs), and to determine the effect of implantation time on wear particle characteristics. Metal wear particles isolated from periprosthetic tissues from 19 patients with MM THRs of current and older designs and at different implantation times (very short, longer, and very long) were studied using transmission electron microscopy and energy dispersive X-ray analysis. The particles from the current design implants with implantation times of not more than 15 months (very short-term) were almost exclusively round to oval chromium oxide particles. In all other cases, although the predominance was still round to oval chromium oxide particles, greater proportions of cobalt-chromium-molybdenum (Co-Cr-Mo) particles, mainly needle-shaped, were detected. Very long-term THRs implanted for more than 20 years had the highest percentage of needle-shaped Co-Cr-Mo particles. Particle lengths were not markedly different between the different designs and implantation times except for the current design implants of not more than 15 months, which had a significantly smaller mean length of 39 nm. In conclusion, the implant design did not seem to have a significant influence on particle characteristics whereas the implantation time appeared to have the most effect on the particles. It should be noted that, because of the limited number of tissue retrievals available, some uncertainty remains regarding the generality of these findings.

Comparison of in vitro with in vivo characteristics of wear particles from metal-metal hip implants.

The purpose of the present study was to compare wear particles isolated from metal-metal (MM) hip implants worn in an orbital bearing simulator with particles from similar MM total hip replacement (THR) implants worn in vivo. Comparison of these particles is important because it will help to assess the overall suitability of this type of hip simulator for reproducing in vivo wear and for producing physiological wear particles suitable for biological studies of in vitro cellular response. Commercial grade components made of ASTM F75 (cast) alloy were evaluated. Simulator tests were performed in 95% bovine calf serum with a 28-mm-diameter implant. Wear particles were collected from 0 to 0.25 million cycles (run-in wear period) and 1.75 to 2 million cycles (steady-state wear period). Tissues from seven patients with MM implants (surface replacement or stem type) were harvested at revision surgeries (after 1-43 months). Metal wear particles were isolated from serum lubricant or tissues using an enzymatic protocol that was previously optimized to minimize particle changes due to reagents. After isolation, particles were centrifuged, embedded in epoxy resin, and characterized by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDXA). Results of EDXA on particles from the hip simulator primarily indicated a predominance of particles containing Cr and O but no Co (most likely chromium oxide particles), and fewer CoCrMo particles presenting varying ratios of Co and Cr. Image analysis of TEM micrographs demonstrated that the majority of the particles from the simulator were round to oval, but a substantial number of needle-shaped particles were also found, especially from 0 to 0.25 Mc. The particles generated from 0 to 0.25 Mc had an average length of 53 nm, whereas those generated from 1.75 to 2 Mc had an average length of 43 nm. In vivo, EDXA and TEM analysis of particles that were retrieved from two patients at 23 and 43 months respectively, revealed that they were the most comparable in composition, average length (57 nm), and shape to particles generated in the hip simulator during the run-in wear period. Because a large clinical retrieval study in the literature suggested that a run-in wear regime might occur in vivo for some 6-36 months, the fidelity of the simulator of the present study was strongly supported. However, some uncertainties existed, including the finding that the particles isolated from the other five patients generated from 1 month up to 15 months (shorter implantation times than the other two patients) were smaller and mostly contained only Cr and O (no Co). In the opinion of the authors, this particular very short term patient group was somewhat atypical. Therefore, despite these uncertainties, the present study was deemed to support the ability of the orbital bearing hip simulator to produce physiological wear particles.

Evidence of weak ferromagnetism in chromium(III) oxide particles

Evidence of weak ferromagnetism in chromium(III) oxide particles

Evidence of weak ferromagnetism in chromium(III) oxide particles

The low temperature (4<T(K)<350) magnetic properties of chromium(III) oxide particles have been studied. A clear evidence of the presence of weak ferromagnetism is observed below 250 K. The magnetisation curves as a function of the applied field show coercive fields due to the canted antiferromagnetism of the particles. Around 55 K a maximum is observed in the zero-field-cooled curves; this maximum can be assumed as a blocking temperature, similarly to ultrafine ferromagnetic particles.

Fabrication of chromium oxide nanoparticles by laser-induced deposition from solution

We have successfully deposited well-dispersed nanoscale chromium oxide particles by laser-induced solution deposition (LISD) from solution with CrCl 2 and organic solvents. The particles have narrow distributions about three sizes: 230, 350 and 400 nm and are uniform in composition and contain little contamination. We show that LISD is a new technique for producing nanoparticle chromium oxides with uniform composition, controllable size and high yield.

Effects of digestion protocols on the isolation and characterization of metal-metal wear particles. II. Analysis of ion release and particle composition.

The isolation of metal wear particles from hip simulator lubricants is important for understanding wear mechanisms and the tissue response to particulate material. Part I of this study demonstrated that isolation protocols involving digestion reagents can chemically attack metal-metal wear particles, reducing their size and changing their shape. In part II of this study, Co and Cr ion concentrations in solution after each digestion protocol were measured by flame atomic absorption spectrometry, and wear particle composition was determined by X-ray analysis spectra. The exposure of wear particles in water to alkaline solutions caused an increasing release of Cr ions in solution with alkaline concentration and time, and a corresponding decrease in particle Cr peak intensity on X-ray spectra. As a result, particles exposed to 12N KOH for 48 h displayed Co peaks and no Cr. In contrast, enzymatic protocols caused a release of Co ions in solution and a corresponding decrease in particle Co peak intensity on X-ray spectra, especially with sodium phosphate as a buffer. However, when isolating particles from 95% serum, there was an initial protective effect of serum proteins, presumably because of their binding to Co and Cr. As a result, the extent of Cr ion release from metal wear particles in 95% serum after alkaline treatments was diminished, although still present, whereas both enzymatic protocols resulted in a negligible release of Co and Cr ions into solution. Particle composition analysis after enzymatic treatments revealed the presence of chromium oxide particles and CoCrMo particles with variable Co/Cr ratios. After alkaline treatments, the chromium oxide particles increasingly disappeared with time and alkaline concentration, demonstrating a change in particle composition after these treatments. This study demonstrated that digestion reagents can induce chemical changes that affect particle composition. Of all the protocols tested, the enzymatic protocols were the least damaging to the particles and appeared to be the best compromise for isolation and characterization of metal particles, especially in 95% serum. Special care on the choice of buffers should be taken when isolating particles from a lower concentration of serum.

Ortho-alkylation of phenol derivatives with methanol over magnesium oxide catalysts. 1. Characterization of promoted magnesium oxide catalysts

Cr- and Pt-promoted magnesium oxide catalysts were used to catalyze ortho-alkylation of phenol derivatives in the presence of excess methanol. The characteristic properties of the MgO surface measured by XRD, SEM, BET, and TPD suggest that Cr exists as fine chromium oxide particles on the MgO surface, while a Pt and MgO interaction causes an increase of the BET surface area as well as of surface acid and base amounts. Cr/MgO shows a specialty for ortho-alkylation of phenol derivatives with methanol without forming O-alkylated products, i.e., anisole or methylated anisole. The catalytic activity and the stability of Cr/MgO are improved by the addition of a fairly small amount of Pt. The effect of Pt can be explained by the Pt and MgO interaction which increases both the acid and base amounts. A mechanism involving the reaction of phenol derivatives and methanol adsorbed simultaneously on acid–base pair sites is proposed.

Fabrication and Characterization of Chromium Oxide Nanoparticles/Thin Films

AbstractWell-dispersed nanoscale textured chromium oxide particles/thin films can be fabricated under certain conditions by laser-induced solution deposition (LISD) from organic solutions and by using selective organometallic chemical vapor deposition (OMCVD). The fabricated nanoparticles/thin films are characterized by scanning electron microscope (SEM), EDX, X-ray diffraction, and magnetic measurements. We have successfully demonstrated that the LISD and OMCVD are unique techniques for fabricating uniformly-distributed thin films but anistropic chromium oxide particles, which can be used in electro-magnetic devices. The magnetization measurements show that both types of chromium oxides are presented and that the Curie temperature Tc and the saturation magnetization field may be adjustable by controlling the stoichiometry.

Preparation and characterization of sol–gel glasses containing chromium

The optical and structural characteristics of sol–gel SiO 2 powders and coatings containing Cr are reported. The samples were characterized using X-ray diffraction, micro-Raman, visible photoacoustic absorption spectroscopy (PAS), optical transmission spectroscopy and diffuse reflectance. Glasses with a wide range of colors were obtained either by varying the chromium concentration, in the range of 0.1–20% w/w, or by air heat treatments in the range of 100–500°C. These optical changes are explained in terms of the different chemical states adopted by the Cr into the SiO 2 matrix. Three absorption bands at 370, 460 and 600 nm were observed in the PAS, diffuse reflectance and optical transmission measurements. According to the ligand field theory, the last two bands are identified with electronic transitions in the d–d levels of Cr 3+; these two bands are better defined in the PAS measurements. The band at 370 nm, due to a ligand-to-metal charge transfer, in which chromium has the Cr 6+ valence state, is only observed using optical transmission measurements. X-Ray measurements show the formation of Cr 2O 3 particles only in the samples with 20% w/w of Cr after annealing at 500°C. The Raman spectra are not sensitive to the chromium oxide particles, but reveal the existence of isolated chromate- and dichromate-like structures.

Chromium Oxide Sub-Micron Particles Fabricated by a Unique Technique: Laser-Induced Solution Deposition

AbstractWe have demonstrated that well-dispersed sub-micron chromium oxide particles can be fabricated by laser-induced solution deposition (LISD) from the solution of CrCl2 solute dissolved in organic solvents containing THF and cyclohexane. The particles are uniform in composition and contain little contamination. The distribution of the particles is narrow in three sizes: 230 nm, 350 nm and 400 nm. We have discussed the kinetics of forming these three kinds of sub-micron particles and the difficulty in obtaining single-phase chromium oxide. We have successfully shown that LISD is a unique technique for fabricating submicron chromium oxide particles with uniform composition and controllable size with narrow particle size distribution. The kinetics (nucleation and growth mechanism) of forming three sizes of particles is discussed.

Morphology of chromium emissions from a laminar hydrogen diffusion flame

The morphology and size distribution of chromium oxide particles has been studied in laminar hydrogen diffusion flames. Nitrogen was added to vary the flame temperatures. Two sources of chromium compounds were introduced: chromium nitrate and chromium hexacarbonyl. In order to clarify the morphology of chromium oxide particles that were produced in the flame, a detailed investigation was carried out by scanning electron microscopy (SEM) after sampling with an isokinetic, dilution sampling probe. The morphology of the particles varied with the flame temperature and with the chromium source. The particles were characterized by porous structures, cenospheres, and agglomerated dense particles when chromium nitrate solution was added to the flames. At low to moderate temperatures, porous sintered cenospheric structures were formed, in some cases with a blow hole. At higher temperatures, an agglomerated cluster, which was composed of loosely sintered submicron particles was observed. SEM analysis revealed that the size distribution of chromium oxide particles was bimodal; submicron sizes were generated by the mechanism of cenosphere fragmentation. Chromium oxides formed from adding chromium hexacarbonyl to a hydrogen flame did not exhibit cenospheric structures. At high temperatures, a film of crystalline material was deposited onto a filter; at low temperatures very small agglomerated chains were found. The morphology of the metal particles is strongly dependent on the form in which the metal enters a flame.

X-Ray absorption spectroscopy: sensitive characterization of (model-) catalysts with the electron yield technique

Small chromium oxide particles (Cr2O3, CrO2) supported on titanium dioxide and oxidized Ag(111) single crystals were investigated by X-ray absorption spectroscopy at the oxygen K-edge. The spectra were collected in the electron yield mode in order to increase the surface sensitivity. The shape of the sharp split White line (WL) in the O K-edges spectra depended strongly on the oxidation state of the chromium ions in the probed samples suggesting that the WL can be used as an indicator of different environments in the supported chromium oxide films. On the other hand, the O K-edges of the oxidized Ag(111) crystal indicated that the formation of the distinct oxygen species at the surface and in the near-surface region was accompanied by a different silver-to-oxygen covalent interaction.

Surface Complexation Description of the Dissolution of Chromium(III) Hydrous Oxides by Oxalic Acid

Aqueous oxalic acid forms surface CrIII−oxalato complexes with suspended chromium(III) oxide particles; the FTIR spectra demonstrate that both carboxylate groups of the ligand are bound to surface CrIII. Surface complexation is followed by changes in the surface redox potential toward more negative values and by the dissolution of the oxide. The dissolving steady state potential is in the range −60 to −210 mV against SHE. During surface conditioning, traces of oxidants at the interface are reduced, and some reduced metal ions accumulate. Minor amounts of dissolved CrII are generated and can be collected at a vicinal ring electrode set at −60 mV. In agreement, dissolution kinetics suggest that generation of CrII by ligand-to-metal charge transfer within the surface complexes produces a large increase in the rate of phase transfer, as expected from the properties of CrIII and CrII. Added chromous salts also catalyze the dissolution through intervalence charge transfer within an oxalato-bridged CrIII−L−CrII ...

Dissolution of Chromium Hydroxides Monitored by Turbidimetry

A turbidimetric method was used to study the dissolution kinetics of different chromium (hydr)oxides in aqueous HClO 4 . There was a very good agreement between the results obtained with this method and those obtained with a standard one (quantifying the amount of chromium released to solution at different reaction times, after the separation of the solid and liquid phases by centrifugation or filtration), revealing that turbidimetry can be used to monitor the dissolution behavior of the studied materials. Theoretical support for the use of turbidimetry in dissolution studies can be obtained from light scattering theory. Chromium (hydr)oxide particles were composed of a mixture of monomeric and low oligomeric Cr(III) species that dissolves almost instantaneously in HClO 4 (rapidly dissolving material) and a more polymerized material that undergoes dissolution at a lower and measurable rate (slowly dissolving material). The dissolution product was also a mixture of monomers and more polymerized Cr(III) species. Apparent activation energies (40-70 kJ/mol) for the dissolution of the slowly dissolving material were high enough to discard diffusion in aqueous solution as the rate-determining step and considerably lower than those corresponding to ligand exchange in Cr(III) species. This suggests that diffusion into the solid could be controlling the dissolution rate, although more direct evidence is needed.

Thermal degradation of chromium black solar selective absorbers

Chromium black solar selective surfaces which had been electroplated onto nickel substrates were annealed in air at 350°C. The composition and structure of the films were determined before and after annealing; the film is shown to consist initially of needle-like chromium oxide particles containing inclusions of chromium metal. As the film is annealed these particles become more spherical and the solar absorptance of the surface decreases dramatically. Calculations based on an idealized model of the film were able to reproduce the reflectance spectra of the surface after each annealing step and showed that the change in the shape of the particles is the most important factor in the thermal degradation of the chromium black surface.

Multimodal media for magnetic recording

Using mixtures of Co-Fe-Ni alloy particles with different coercivity populations, or mixtures of the alloy particles with other particulate ferro- or ferri-magnetic materials (also of differing coercivities), we have made magnetic recording media with little magnetic interaction between the two or more particle populations. Average coercivities of these separate particle populations need only be 200 Oe apart in order that "multimodal" action is achieved. Such multimodal media are characterized by successive pseudomajor hysteresis loops, which expand stepwise with the maximum applied field. Such recording media can contain as many sets of signals as the number of modes, the sets being eraseable in sequence independently of higher mode signals. Uses of such media include masking of a wanted signal recorded in a higher mode with another (meaningless) signal recorded in a lower mode, or the dubbing of editing information (which can later be erased). Since the mixing of iron or chromium oxide particles of widely differing coercivities does not generally yield a multimodal medium, the magnetic interaction in our systems is undoubtedly not the same as in the oxide systems.

Complex chemistry of hydrous chromium(III) oxide sol formation

Complex solution chemistry associated with formation and growth of hydrous chromium(III) oxide particles of narrow size distribution was investigated. The sols were prepared by heating dilute solutions of chromium(III) salts in the presence of sulfate ions. Upon removal of sol particles by filtration, complex solute species present in the electrolyte medium were separated and characterized using radio-paper electrophoresis. The results indicate that two solute species are involved in solid formation, and that multi-component equilibria are established. The effects of anion concentration and temperature are also discussed.

Observations on the Shape of Chromium Oxide Particles in Hydrogen + Oxygen + Nitrogen Pre-mixed and Diffusion Flames

CERTAIN metals, when introduced into pre-mixed, hydrogen + oxygen + nitrogen flames (T ∼ 2,000° K) burning above a Meker type burner, give a whitish, streaky appearance to the flame1. Such streaks appear, for example, when chromium, vanadium, titanium, cobalt, nickel or iron (to mention but a few) are introduced in the form of fine sprays of dilute salt solutions. These streaks almost certainly originate from chemiluminescent reactions involving H and/or OH radicals on the surfaces of particles of involatile oxides1, and their visible appearance alone clearly indicates that the particles consist of many molecular units. Light scattering and electron microscopy studies2,3 have shown similar particles to have sizes in the range 0.005–25µ.