The solubility and oxidation state of nickel in silicate melt at low oxygen fugacities: Results using a mechanically assisted equilibration technique

The solubility of Ni in a silicate melt has been measured using a new, mechanically assisted equilibration technique over a wide range of controlled ƒO2 values. The melt composition corresponds to the 1 atm eutectic in the system CaAl2Si2O8-CaMgSi2O6 + 10 wt% CaO. The experiments were performed at 1300°C and over an ƒO2 range of 10−8.5 to 10−13.75, and over a temperature range of 1270 to 1390°C at a constant gas mixing ratio ( ). The experiment consists of a sample of melt contained within a crucible of Ni metal and held in a 1 atm gas mixing furnace. A Ni spindle is entered into the sample from above and continuously rotated at a constant angular velocity using a viscometer head. The stirring of the sample serves to accelerate the approach to equilibrium between the liquid sample and the metal crucible (and spindle). This arrangement allows relatively rapid equilibration of Ni content following changes to higher or lower ƒO2 values. Samples of the melt may be taken at any time for analysis and thus the equilibrium solubility of Ni in the silicate melt may be determined from unambiguous experimental reversals. The Ni contents of samples, analysed both by INAA and by ICP-AES, range from 25 to 5300 ppm. The data presented in this paper indicate that the oxidation state of Ni in the investigated melt is Ni2+ over the entire range of ƒO2 investigated. This conclusion contrasts with recent reports in the literature of an inflection in the ƒO2 dependence of Ni solubility, which has been interpreted as solution of neutral Ni at low ƒO2 (Morse et al., 1991; Colson, 1992; Ehlers et al., 1992). We also present data for the temperature dependence of Ni solubility in the investigated melt. The solubility decreases with increasing temperature at constant ƒO2. The present results are in good agreement with the metal-loop-equilibration experiments reported by Holzheid et al. (1994)

OWNERSHIP STRUCTURES AND R&D INVESTMENTS OF U.S. AND JAPANESE FIRMS: AGENCY AND STEWARDSHIP PERSPECTIVES.

This study analyzes the impact of ownership structure on R&D investments in the United States and Japan. It begins with the premise that U.S. and Japanese firms have distinct patterns of ownership that may result in disparities in R&D investments. Agency theory and stewardship theory are used to hypothesize about the relationship between ownership and R&D investments. Empirical evidence shows that the level of ownership concentration, and its impact, differ across countries. We argue that these differences result from a mixture of motives and incentives

Inhibition of Toll-Like Receptor 2-Mediated Interleukin-8 Production in Cystic Fibrosis Airway Epithelial Cells via the α7-Nicotinic Acetylcholine Receptor

Cystic Fibrosis (CF) is an inherited disorder characterised by chronic inflammation of the airways. The lung manifestations of CF include colonization with Pseudomonas aeruginosa and Staphylococcus aureus leading to neutrophil-dominated airway inflammation and tissue damage. Inflammation in the CF lung is initiated by microbial components which activate the innate immune response via Toll-like receptors (TLRs), increasing airway epithelial cell production of proinflammatory mediators such as the neutrophil chemokine interleukin-8 (IL-8). Thus modulation of TLR function represents a therapeutic approach for CF. Nicotine is a naturally occurring plant alkaloid. Although it is negatively associated with cigarette smoking and cardiovascular damage, nicotine also has anti-inflammatory properties. Here we investigate the inhibitory capacity of nicotine against TLR2- and TLR4-induced IL-8 production by CFTE29o- airway epithelial cells, determine the role of α7-nAChR (nicotinic acetylcholine receptor) in these events, and provide data to support the potential use of safe nicotine analogues as anti-inflammatories for CF

The oxidation state and coordination environment of antimony in silicate glasses

Antimony K-edge X-ray absorption near edge structure (XANES) spectra were recorded for Sb in glasses of five synthetic CaO-MgO-Al2O3-SiO2 (CMAS) compositions and a simplified mid-ocean ridge basalt (MORB). The glasses were quenched from melts equilibrated at 1300 °C, atmospheric pressure, and oxygen fugacities (fO2) from logfO2 = –9 to 0 (ΔQFM from −1.7 to 7.3, where ΔQFM is the fO2 in log units relative to the quartz-fayalite-magnetite buffer), and 1400 °C, 1.0 GPa and logfO2 = +4.7 (ΔQFM+11.0). Comparison with model compounds (Sb, Sb2O3, β-Sb2O4, MnSb2O4 and Zn7Sb2O12) indicates that the oxidation state of Sb changes from Sb3+ to Sb5+ over the range of fO2 investigated. Using the spectra of the most reduced and oxidised glasses as end-members the oxidation state of Sb, Sb5+/ΣSb (where ΣSb = Sb3+ + Sb5+), was determined from the spectra of other samples by linear combination fitting. At terrestrial fO2s nearly all Sb occurs as Sb3+ in these silicate melts. The stability of Sb5+ was found to be positively correlated with the CaO content and optical basicity of the melts. Extended X-ray absorption fine structure (EXAFS) spectra were recorded for glasses prepared at pressures from 1.0 to 3.0 GPa, for which Sb5+/ΣSb = 0 and 1, and for a synthetic Sb-bearing sample of anorthite. The Sb3+O and Sb5+O bond lengths in the glasses are similar (1.938(4) and 1.964(5) Å, respectively) and suggest trigonal pyramidal coordination of Sb3+and octahedral Sb5+. The Sb3+O bond length did not change with pressure. Anorthite (CaAl2Si2O8) was found to readily incorporate Sb as Sb5+ on a tetrahedral site.L.A.M. thanks the Australian National University for the award of an International Student PhD scholarship