Electronic Stopping of Slow Protons in Oxides: Scaling Properties.

Electronic stopping of slow protons in ZnO, VO_{2} (metal and semiconductor phases), HfO_{2}, and Ta_{2}O_{5} was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al_{2}O_{3} and SiO_{2} reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density.

Quantitative determination of element concentrations in industrial oxide materials by laser-induced breakdown spectroscopy.

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) method is employed for quantitative determination of oxide concentrations in multi-component materials. Industrial oxide materials from steel industry are laser ablated in air, and the optical plasma emission is collected by spectrometers and gated detectors. The temperature and electron number density of laser-induced plasma are determined from measured LIBS spectra. Emission lines of aluminium (Al), calcium (Ca), iron (Fe), manganese (Mn), magnesium (Mg), silicon (Si), titanium (Ti), and chromium (Cr) of low self-absorption are selected, and the concentration of oxides CaO, Al(2)O(3), MgO, SiO(2), FeO, MnO, TiO(2), and Cr(2)O(3) is calculated by CF-LIBS analysis. For all sample materials investigated, we find good match of calculated concentration values (C(CF)) with nominal concentration values (C(N)). The relative error in oxide concentration, e(r) = |C(CF) - C(N)|/C(N), decreases with increasing concentration and it is e(r) ≤ 100% for concentration C(N) ≥ 1 wt.%. The CF-LIBS results are stable against fluctuations of experimental parameters. The variation of laser pulse energy over a large range changes the error by less than 10% for major oxides (C(N) ≥ 10 wt.%). The results indicate that CF-LIBS method can be employed for fast and stable quantitative compositional analysis of multi-component materials.

LA-ICP-MS analysis of waste polymer materials.

Waste polymer materials were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The concentrations of 35 elements were determined by using different types of external standards, namely glass and polyethylene (PE) based. Prior to the LA-ICP-MS analysis of determined elements, Na and/or Zn were used as internal standards. The investigations concentrated mainly on the detection of Cr, As, Cd, Sn, Sb, Hg, and Pb. Using PE-based calibration standards, the measured concentrations in the waste polymers were within 49% of the wet chemical data. The determined deviation was up to 102% when using the glass standards. Trace concentration of As and Hg (and also of S) could be determined with a concentration below 1 mg/kg. However, Hg provided very low intensity with a high relative standard deviation (RSD) and was therefore not further evaluated. Cryomilling of polymers was applied to reduce the particle size of the material and improved the precision and accuracy of LA-ICP-MS analysis. On average, the LA-ICP-MS results showed a deviation from the wet chemical reference analysis of 38% and an RSD of 56% for pressed polymer powder samples prepared by cryomilling. In general, waste pellets without sample preparation (i.e., use of pellets as delivered) are too heterogeneous, not suitable for micro-beam techniques, and showed a strong matrix dependence. With homogeneous pellets that appear similar to each other agreement in the determined concentrations was found for some elements.