Dariusz Burnat

Homogeneous functional Ni–P/ceramic nanocomposite coatings via stable dispersions in electroless nickel electrolytes

Stable nanoparticle dispersions in concentrated electrolytes are prerequisite for a variety of advanced nanocomposites prepared by deposition techniques. In this work we investigate the synthesis of electroless Ni-P/functional ceramic coatings from concentrated electrolytes containing functional nanoparticles such as TiO(2), α-Fe(2)O(3), ITO, and CeO(2). Stable nanoparticle dispersions in both low and high phosphorus electrolytes are achieved at plating temperatures (80-90 °C) by a generalized scheme employing comb-polyelectrolyte and antifreeze additives. Dispersion stability at room temperature is achieved in both low and high phosphorus EN media using anionic comb-polyelectrolyte surfactants with polyether side chain of 1100 g/mol. The optimal surfactant concentration is determined by zeta-potential and thermo-gravimetric analysis. Without additives the dispersions flocculate and sediment between 65 and 80 °C. Such phenomenon is believed to be associated with a critical flocculation temperature (CFT). The CFT is also weekly dependent on the particle type and the high ionic strength media. Addition of antifreeze additives such as propylene glycol and urea to the dispersions restores stability and increase the CFT for all particles. We estimate an average increase of the CFT by 1.5-2 °C per 1% additive for all particles and electrolytes. While the particle stabilization scheme is generalized in this work, the composite EN plating proved highly dependent on particle type. Baths containing ITO nanoparticles showed no plating reactions and those containing α-Fe(2)O(3) no nanoparticle co-deposition. In contrast, homogeneous Ni-P/TiO(2) and Ni-P/CeO(2) nanocomposites with up to 22 vol.% nanoparticles are produced. The possible application of the stabilization principles developed here for other functional nanocomposite systems is discussed.

Smart material concept: reversible microstructural self-regeneration for catalytic applications

This paper presents a proof-of-concept study and demonstrates the next generation of a “smart” catalyst material, applicable to high temperature catalysis and electro-catalysis such as gas processing and as a catalyst for solid oxide cells. A modified citrate-gel technique was developed for the synthesis of LaxSr1−1.5xTi1−yNiyO3−δ. This method allowed the synthesis of single phase materials with a high specific surface area, after the first calcination step at temperatures as low as 650 °C. Up to 5 at% of nickel could be incorporated into the perovskite structure at this low calcination temperature. X-ray powder diffraction and microscopy techniques have proven the exsolution of nickel nanoclusters under low oxygen partial pressure. The amount of exsoluted nickel nanoparticles was sensitive to surface finishing, whereby much more exsoluted nanoparticles were observed on pre-treated and polished surfaces as compared to original ones. Increasing A-site deficiency leads to a larger number of nickel particles on the surface, indicating a destabilizing influence of the A-site vacancies on the B-site metal cations. Repetitive redox cycles prove that the nickel exsolution and re-integration is a fully reversible process. These materials working in a cyclic and repetitive way may overcome the drawbacks of currently used conventional catalysts used for high temperature systems and overcome major degradation issues related to catalyst poisoning and coarsening-induced aging.

Investigations on the Redox Performance of Pure and Doped CeO2 by Comparing Solid State Reaction and Pechini Synthesis

Undoped and doped ceria were synthesized by a solid state reaction and a polymerized—complex method. Microstructural and phase development of MxCe1-xO2-δ (M = Zr, Hf; 0 ≤ x ≤ 0.2) were examined using X-ray diffraction and scanning electron microscopy. Redox properties were investigated by thermogravimetric analysis and a remarkable increase of the oxygen storage capacity of ceria with increasing dopant concentration was demonstrated. ZrxCe1-xO2 and HfxCe1-xO2 solid solutions at x = 0.2 were shown to release double the amount of oxygen during reduction compared to undoped ceria. The solid state reaction synthesis produces materials with excellent redox performance up to 15 mol% dopant concentration and is otherwise equivalent with materials produced by Pechini synthesis.