Pavleta Knutsson

The influence of platinum on the oxidation and sodium sulfate induced hot corrosion of NiAl diffusion coatings

Abstract Oxidation and corrosion properties at 900°C of two coatings, one containing platinum and the other platinum-free, on IN792 were investigated. During the corrosion exposures, sodium sulfate salt was situated in the furnace together with the coated specimens. The temperature of the salt was kept above its melting point but lower than the temperature of the coating i.e. 900°C. The exposure times ranged from 100 to 1000 h. The formed oxide scales were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and scanning transmission electron microscopy techniques. It is shown that the presence of Pt improves the protective properties of the coating against corrosion. The propagation stage of corrosion on the platinum-free coating is reached already after 100 h of exposure. On the other hand the scale formed on the platinum-rich samples still appeared to be protective even after 500 h. The details concerning structure and chemistry of the scales formed are presented and discussed.

Evaluation of a passive sampler for the speciation of metals in urban runoff water

Metals in urban runoff water need to be monitored in order to estimate fluxes and assess their impact on the aquatic environment. Passive sampling is a useful and reliable emerging tool for measuring time averaged concentrations of metals in water bodies. This paper describes the deployment of a passive sampler to measure Cu, Ni and Zn in an urban runoff water treatment facility. The concentrations derived from the passive samplers are compared to concentrations obtained from an automated water sampler which provides pooled spot water samples and to model predictions from the visualMINTEQ computer speciation code. Results show that visualMINTEQ predictions partly describe the metal speciation in non-equilibrium systems. In addition we conclude that passive samplers are useful for monitoring and characterization of metal speciation under chemodynamic conditions.

Use of natural ores and waste materials as oxygen carriers for chemical-looping combustion

The increasing CO2 levels in the atmosphere require an immediate action in order to avoid irreversible climate changes. Chemical-looping combustion (CLC) is an innovative technology that provides an energy and cost-effective separation of CO2 for further capture and storage and thereby helps to mitigate the anthropogenic CO2 emissions from thermochemical fuel conversion. The solid oxygen carrier is a core component of every CLC system and the choice of the oxygen carrier depends on the fuel and operation conditions. Low-cost oxygen carriers tend to be more suitable for the process as the lifetime of the oxygen carrier material is often limited by side reactions with fuel ash, or by carryover losses in the ash separation. A series of natural ores and waste products have been investigated as potential oxygen cares, such as Mn-ore, Fe-ore, ilmenite. The materials are chosen based on their content of oxides that have proven to have promising oxygen transporting capabilities. The results lead to summary of criterion for further screening of the existing materials for more reactive and better suited candidates for the process.