Facile Synthesis of Pd Nanoparticle Modified Carbon Black for Electroanalysis: Application to the Detection of Hydrazine

Carbon black nanoparticles modified with palladium nanoparticles (Pd/CB) were prepared using a facile methodology. Stirring CB in an aqueous solution of palladium chloride was found to result in the spontaneous formation of Pd nanoparticles on the CB surface. The Pd/CB composite demonstrated high electrocatalytic activity towards hydrazine oxidation, with good stability and reproducibility. Three linear dynamic ranges of hydrazine determination were found between 5 µM and 50 mM. The limit of detection (LOD) for hydrazine was found to be 8.8 µM (based on 3σ). The sensitivity of unmodified CB to trace metal impurities present in certain common electrolytes is also noted.     

Quantification of grain boundary equilibrium segregation by NanoSIMS analysis of bulk samples

A technique for the quantification of equilibrium grain boundary segregation by high resolution secondary ion mass spectroscopy (NanoSIMS) on simple metallographically polished surfaces has been demonstrated for the model system of sulphur segregation to nickel grain boundaries. Samples of nickel containing 5.4 wt ppm of sulphur were annealed at different temperatures to achieve different equilibrium sulphur grain boundary concentrations, ranging from less than 1% to about 50% of a monolayer. Quantification was carried out from sulphur concentration profiles acquired across about 20 grain boundaries in each sample. An internal standard (nickel containing a known concentration of sulphur in solid solution) was used for calibration. It is found that, depending on the annealing temperature, the average grain boundary sulphur concentration ranges from 0.9 to 25.8 ng cm^–2 (or 1.7 10¹³ to 4.8 10¹⁴ atoms cm^–2), i.e. ~0.015 to ~0.43 monolayer. Thermodynamic analysis gives a segregation free energy of ?97.8 kJ mol^–1 and a grain boundary sulphur concentration at saturation of 26.7 ng cm^–2 (or 5.0×10¹⁴ atoms cm^–2), i.e. ~0.44 monolayer, in good agreement with previous measurements on this system. The limit of detection of the technique is shown to be as low as 0.24 ng cm^–2 (or 4.5×10¹² atoms cm^–2), i.e. ~0.004 monolayer, with a counting time of only 10 min. Copyright © 2012 John Wiley & Sons, Ltd.     

Line intensities of CO2 in the 2·7 micron region

Individual line intensities have been measured at 0·025 cm^?1 resolution and low pressures for the two strong Σ-Σ bands of C¹²O₂¹⁶ near 2.7 microns, as well as for their associated Π-Π hot-bands. Values of the rotationless dipole-moment matrix elements and vibration-rotation interaction coefficients are reported along with total band intensities. Results for the latter in cm^?2 atm^?1 at 296°K are: 25·7, 1·96, 39·3 and 3·23 for the 02⁰1-00⁰0, 03¹1-01¹0, 10⁰1-00⁰0, and 11¹1-01¹0 bands, respectively.     

The mixed alkali effect in lithium-sodium borate glasses

The electrical conductivity of a series of 0.35 (Li, Na)₂O·B₂O₃ glasses shows a minimum at the composition Na/(Na+Li)～0.6, which becomes stronger as the temperature is decreased; the activation enthalpy for electrical conductivity shows a maximum at this composition. In general, replacing 1% of the total oxygen concentration by chlorine or bromine (keeping the total alkali content fixed) in these glasses increases the conductivity; fluorine doping has an opposite effect. The mixed alkali effect, expressed in terms of the compositional dependence of the activation enthalpy for conductivity, is enhanced when borate glass is doped with fluorine, but is slightly diminished when doped with chlorine or bromine. The results are explained in terms of the structure of halogenated alkali-borate glasses, and discussed in relation to the origin of the mixed alkali effect.     

Tracer diffusion and electrical conductivity in sodium-cesium silicate glasses

The tracer diffusion coefficients of ²²Na and ¹³⁷Cs, and the electrical conductivity have been measured in the (Na, Cs)₂O:3SiO₂ glasses as a function of temperature and Cs/Na ratio. Complex impedance analysis was used for the conductivity measurements. The Haven ratio at 396.5°C increases from 0.3–0.4 in single-alkali glasses to 0.8 for the mixed-alkali compositions. The results are explained in terms of a single-jump mechanism; interactions between alkali ions and non-bridging oxygen ions, and between different alkali ions, produce the observed correlation effects.     

Mixed isotope electrical conductivity in lithium borate glasses

Electrical conductivity of (Li⁶/Li⁷)₂O·3B₂O₃ glasses with varying Li⁶/Li⁷ ratios has been measured as a function of temperature. The conductivity obtained after complex impedance analysis decreases continously and the activation enthalpy increases slightly as Li⁷ is substituted for Li⁶. This suggest that the difference in mass of the alkali ions is not the cause of the mixed alkali effect.     

The new cold neutron depth profiling instrument at NIST

The Cold Neutron Depth Profiling (CNDP) instrument at the NIST Cold Neutron Research Facility (CNRF) is now operational. The neutron beam originates from a 16 liter D₂O-ice cold source and passes through a filter of 13.5 cm of single crystal sapphire. The neutron energy spectrum may be described by a 65 K Maxwellian distribution. The sample chamber configuration allows for remote controlled scanning of 15 cm×15 cm samples and varying of both sample and detector angle. The improved sensitivity over the current thermal depth profiling instrument has permitted the first nondestructive measurements of¹⁷O profiles. Results of some of the first sample measurements are presented.