Redox properties of nanostructured lanthanide-doped ceria spheres prepared by microwave assisted hydrothermal homogeneous co-precipitation.

In this work, nanostructured LnxCe(1-x)O2-δ (Ln: Gd and Pr; x = 0.1 and 0.2) spheres were synthesized by microwave assisted hydrothermal homogeneous co-precipitation and their properties were characterized by synchrotron radiation XRD, X-ray absorption near-edge spectroscopy (XANES) and scanning and high-resolution electron microscopy (SEM and HRTEM). In situ XRD and XANES experiments were carried out under reducing and oxidizing conditions in order to investigate the redox behaviour of these materials. The nanostructured mixed oxide spheres were found to have a cubic crystal structure (Fm3m space group). The spheres were composed of nanoparticles with an average crystallite size of about 10 nm. The Ln(0.1)Ce(0.9)O2-δ compositions exhibited the highest specific surface area (∼ 60 m(2) g(-1)). In situ XRD experiments showed an increase in lattice parameters upon reduction, which was attributed to the reduction of Ce(4+) and Pr(4+) cations to Ce(3+) and Pr(3+), which have larger radii, and to the associated increase in VO concentration. This increase in lattice parameters was considerably more pronounced for PrDC than GDC, and was explained by the considerably larger change in ionic radius for Pr upon reduction. XANES absorption experiments at the Ce and Pr L3-edge showed that the changes observed upon reduction of the Pr-containing samples resulted mostly from the formation of Pr(3+) rather than Ce(3+), and supported the previously reported proposal that Pr(3+) has a stabilizing effect on Ce(4+).

Mechanism of electric-pulse-induced resistance switching in manganites.

We investigate the electric-pulse-induced resistance switching in manganite systems. We find a "complementarity" effect where the contact resistance of electrodes at opposite ends show variations of opposite sign and is reversible. The temperature dependence of the magnitude of the effect reveals a dramatic enhancement at a temperature T*, below the metal-insulator transition. We qualitatively capture these features with a theoretical model, providing evidence for the physical mechanism of the resistance switching. We argue that doping control of the electronic state of the oxide at the interfaces is the mechanism driving the effect.

Phase diagram of La(5/8-y)Nd(y)Ca(3/8)MnO(3) manganites.

We report a detailed study of the electric transport and magnetic properties of the La(5/8-y)Nd(y)Ca(3/8)MnO(3) manganite system. Substitution of La(3+) by smaller Nd(3+) ions reduces the mean ionic radius of the A-site ion. We have studied samples in the entire range between La-rich and Nd-rich compounds (0.1

Sorption of antimony onto hydroxyapatite.

We prepared synthetic hydroxyapatite [HAP; Ca5(PO4)(3-x)(CO3)x(OH)(1+x) (x = 0.3)] and then investigated this material's ability to remove trivalent antimony [Sb(III)] from water. The HAP was characterized by X-ray diffraction analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. The sorption of Sb(III) to HAP was measured over an Sb(III) concentration range of 0.05-50 mg L(-1), at constant ionic strength (I = 0.01 mol dm(-3)) in equilibrated aqueous suspensions (34 g dm(-3)) for 5 < pH < 8 in vessels that were closed to the atmosphere. Under these conditions, we found that HAP particles were enriched in Ca after incongruent dissolution of the solid. More than 95% of the Sb(III) in solution adsorbed to the solid-phase HAP in <30 min. The equilibrium distribution of Sb(III) (solid vs liquid phase) was characterized by a Langmuir model with gamma(max) = 6.7 +/- 0.1 x 10(-8) mol m(-2) (1.4 +/- 0.2 x 10(-4) mol dm(-3) g(-1)) and K(ads) = 1.5 +/- 0.2 x 10(3) dm3 mol(-1). As Sb adsorption occurred, the pH of the isoelectric point (pH(iep)) of the HAP suspensions declined from 7.7 to 6.9. This finding supports the idea that the negative surface potential of the HAP increased due to the adsorption of Sb as a charged species. The decline in pH(iep) during Sb adsorption plus the thermodynamic description of the Sb(III)-HAP-H2O system suggest likely surface reactions for the interaction of Sb with HAP. We discuss the efficiency of Sb removal from water by HAP in the context of phosphate enrichment.

Pathological mineralizations: calcifications and Si-bearing particles in soft tissues and their eventual relationship to different prostheses.

Polarizing microscopy (PM), scanning electron microscopy (SEM), x-ray dispersive analysis (EDAX), x-ray diffraction (XRD), and infrared spectrometry (IR) were used to study the following pathological mineralizations: calcifications and silicon(Si)-bearing mineralizations in cerebral tissue from an epileptic child; traces of Si-bearing particles in periprosthesic mammarian tissue, and calcifications in capsular mammarian tissue from a patient with a silicone gel mammarian implant, and 2 calcium-bearing compounds, a typical apatitic calcification, and a nonphosphorous-bearing calcification in arterial tissues. In this tissue we also found Si-bearing particles due to an artifact from glassware.

Aluminum-containing particles in synovial fluid of a patient with normal renal function and chondrocalcinosis.

A 48-year-old Caucasian woman presented a tender effusion of small volume, with a mild increase in skin temperature in her right knee and wide spread chondrocalcinosis found radiologically. She had normal renal function, had undergone a gastrectomy, and was receiving therapeutic doses of aluminum hydroxide antacids. Synovial fluid analysis showed small, irregular, nonbirefringent particles that stained intensely positive with the alizarin red stain. Scanning electron microscopy, energy dispersive X-ray analysis, and microprobe analysis showed aluminum and variable concentrations of chlorine and/or oxygen in isolated small spherical particles (average diameter about 15 micro). Neither phosphorus nor calcium was ever detected in the aluminum containing particles. These findings strongly suggest the presence of a mixture of aluminum hydroxide and some form of aluminum hydroxide chloride; neither was previously reported in synovial fluid of patients with normal renal function. Aluminum-containing particles should be considered an explanation for unexplained particles in joint fluid and may be a factor in some arthritis.