K. Kowalski

Surface segregation in yttria-stabilized zirconia by means of angle resolved X-ray photoelectron spectroscopy

Surface segregation of cations in undoped and titanium-doped yttria-stabilized zirconia was studied in air in the temperature range from 800 to 1400°C. Surface composition and distribution of the elements across the surface layer was examined using angle resolved X-ray photoelectron spectroscopy. The annealing procedure induced a silicon-rich surface layer of low zirconium concentration. The yttrium concentration only slightly increased at the surface. Enrichment factor of titanium in the titanium-doped yttria-stabilized zirconia was found to be higher than that of yttrium. No significant correlation between segregation of other cations was found.

XPS studies of nitrogen-containing conjugated polymers–palladium systems

Polyaniline (PANI) and polypyrrole doped with chloride ions (PPyCl) have been treated with PdCl 2 solutions in HCl of various concentrations. Basing on the results of XPS studies it is shown that the differences in the redox and basic properties of both polymers lead to different mechanisms of their interactions with palladium ions present in the PdCl 2 solutions studied. Thus, in the PdCl 2 solutions of low acidity in which [PdCl 2 (H 2 O) 2 ] predominates, both polymers are oxidized with simultaneous reduction of a part of Pd 2+ to Pd 0 . In the PdCl 2 solutions of high acidity in which [PdCl 4 ] 2 is the major complex, reduction of Pd 2 does not occur. Owing to stronger basic properties of PANI than those of PPyCl, palladium is incorporated into the former polymer as anionic chlorocomplexes via protonation reaction. In the case of PPyCl the situation is more complex. Detailed analysis of the possible surface reactions taking place in the PPyCl Pd systems studied is given in the paper.

Three-dimensional information on the phase domain structure of thin films of polymer blends revealed by secondary ion mass spectrometry

We describe the technique of dynamic secondary ion mass spectrometry developed to determine three-dimensional phase domain structures of films of polymer blends. The polymers are composed of light elements or are labeled with deuterium or heavy elements. The applicability of this method to various polymer blends forming thin and ultrathin films with flat and undulated air/film interface is discussed.

Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

Abstract In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl2 aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl2 solutions of lower acidity PPyOH was oxidatively doped and Pd0 and Pd2+ were incorporated into the polymer matrix. Pd2+ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd–N bond). Additionally, deprotonation of PPyOH occurred in the PdCl2 solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl3(H2O)]− on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)–palladium systems prepared in similar PdCl2 solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process. PPyOH was less reactive towards palladium species in the PdCl2 solutions of higher acidity where [PdCl4]2− was the dominant complex. PPy–palladium systems containing exclusively Pd2+ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid–base reaction or coordination of palladium ions by the polymer chain (Pd–N bond formation). Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts.

Diffusion of calcium in yttria stabilized zirconia ceramics

Abstract Bulk and grain boundary diffusion of calcium in yttria fully stabilized zirconia was studied in air in the temperature range from 1100 to 1400°C. Secondary ion mass spectrometry (SIMS) was used to determine the diffusion profiles as average concentration vs. depth in the B-type kinetic region. The obtained results allowed the calculation of the temperature dependence of the bulk diffusion coefficient D and the grain boundary diffusion parameter D′δs . Activation energies of these processes amount to 333 and 367 kJ mol −1 , respectively. Diffusion data of calcium were compared to those of titanium obtained previously using the same zirconia material.

Grain boundary diffusion in CoO

Abstract The diffusion of 60 Co, 63 Ni, and 45 Ca at 953 °C and 51 Cr at 953 and 1109 °C was measured in polycrystalline CoO scales by means of the radioactive tracer sectioning technique. High density scales were obtained by the oxidation of high purity Co plates at 1000 and 1200 °C in air. The diffusion penetration profiles exhibit two well distinguishable slopes which correspond to different diffusion regimes. The bulk diffusion coefficient, D , determined from the diffusion profile of the higher slope, is in a good agreement with the bulk diffusion data reported elsewhere. The product corresponding to the grain boundary diffusion, D ′ δα , where D ′ is the grain boundary diffusion coefficient, δ is the grain boundary thickness, and α is the segregation enrichment factor, was determined from the diffusion profile of the lower slope. It was found that the grain boundary diffusion enhancement factor, f = D ′ δα / D , for 60 Co and 63 Ni assumes similar values, which are one order of magnitude larger than those for 45 Ca and 51 Cr. The presence of Ca within the grain boundaries of CoO was confirmed using both autoradiography and SIMS methods. It has been revealed that the diffusion coefficient for both Ni and Ca in CoO, determined at 953 °C, exhibits the same value for specimens prepared at 1000 and 1200 °C, in spite of their different porosity and different grain size.

Mechanistic aspects of Pt-modified β-NiAl alloy oxidation

Abstract The effects of Pt addition (5, 10 and 15 at.%) on the high temperature oxidation behaviour of the intermetallic compound β-NiAl were studied at 1150°C under both isothermal and thermal cycling conditions. The scale growth mechanism was assessed using two-stage oxidation exposures with 18O2 as a tracer in conjunction with high-resolution secondary ion mass spectrometer analysis of isotopic distributions. The scale morphologies were further characterized using secondary electron microscopy, Pt was found to reduce slightly the scale growth rate and improve considerably its resistance to spallation but it did not affect the sequence of scale development. Instead, it slowed the rate at which the scale developed. The α-Al2O3 scales that were eventually established were duplex in structure, consisting of a compact inner layer and a thinner outer layer. This outer layer consisted of ridges and grew by the coarsening of these and/or by a dislocation climb mechanism.

On the application of SIMS to study the oxidation mechanisms of alumina formers

Abstract Secondary ion mass spectrometry (SIMS) is widely used to investigate the oxidation mechanism of alumina formers, being various MeCrAl (Me=Fe, Ni, Co) alloys and β-NiAl intermetallic compound. Frequently, it is combined with dedicated oxidation exposures, mostly in atmospheres containing different amounts of oxygen tracer (18O2) in order to investigate the scale growth mechanism. However, there are several practical aspects which have to be taken into account during planning the oxidation experiments as well as during interpretation of their results in order to avoid misleading conclusions. In particular, the effects related to the formation of non-uniform scales as well as to the relationship between the exposure conditions and the scale microstructure and morphology at various stages of its growth should be dealt with. This paper discusses the implications of sputtering process with respect to elemental in-depth distribution profiling and the results of the oxidation mechanism investigation of various alumina formers by means of SIMS. It is shown that the obtained shapes of the SIMS profiles and images strongly depend on the choice of the exposure conditions and on the analysis parameters, including the spatial resolution. The exposure conditions are related to the scale microstructure and morphology, the evolution of which occurs during the oxidation process. Formation of duplex alumina scale is reported which comprises an inner more compact sub-layer and an outer ridged and less-compact sub-layer.

Thermopower and electrical conductivity of single crystal and polycrystalline CoO

Abstract Comparative studies of both electrical conductivity and thermopower (Seebeck effect) were carried out for undoped Co1z.sbnd;yO involving both single crystal and polycrystalline specimens within the temperature range 1223–1473 K and under oxygen partial pressure range 10–105 Pa. It was observed that the reciprocal of oxygen pressure exponent determined by thermopower (nα) and electrical conductivity (nσ) for both single crystal and polycrystalline CoO increases with temperature. The parameter nα assumes much higher values than nσ for both specimens. The mobility of electron holes increases with non-stoichiometry (y) for both the single crystal and the polycrystalline specimen. Based on the electrical conductivity data on temperatures it was concluded that conduction in CoO occurs according to the hopping model rather than the band model. The effect of p(O2) on the exponent of the oxygen pressure dependence have been considered in terms of interactions between the defects in this region.

Sulphidation and oxidation of the Ni22Cr10Al1Y alloy in H2/H2S and SO2 atmospheres at high temperatures

The Ni22Cr10Al1Y alloy was exposed in H2/H2S gas mixture under the sulphur pressure 10−3 and 1 Pa as well as in SO2 at 1173 and 1273 K. At ps = 1 Pa the sulphidation rate was relatively high and the reaction obeyed the linear rate law. Under these conditions a nickel/nickel sulphide eutectic was formed. At ps = 10−3 Pa nickel sulphides became unstable and the sulphidation rate was significantly lower. The reaction obeyed the parabolic rate law. The oxidation rate of the alloy in SO2 was lower than that in any of the H2/H2S atmospheres. The sulphide scales formed during sulphidation in H2/H2S had complex microstructures and compositions, with sulphospinel and sulphide phases being present, e.g. NiCr2S4, Ni3S2, CrxSy. As the temperature increased and the sulphur pressure decreased, these phases were replaced by the chromium-rich sulphide phase. Various oxides formed during oxidation of the alloy in SO2.