Marek Nocuń

Specific features of the IR spectra of silicate glasses

Abstract The glassy state of matter, in contrast to crystalline solids, is characterized by a lack of long-range order. In the structure of glasses, the bond lengths and bond angles are not fixed. As a consequence the vibrational spectra of glassy sustances exhibit various band shapes. The bands in these spectra are characterized by complex shapes and significant widths resulting in difficulties in the determination of the main spectral parameters, such as the number of bands, their positions and intensities. These difficulties limit the application of vibrational spectroscopy in the study of the structure of glasses. The main goal of the present work is to show that an appropriate procedure of decomposition of the complex bands in the spectra makes it possible to obtain important information on the structure of solid glassy substances. The procedure proposed is based on (a) minimization of the number of bands, and (b) comparison with the spectra of crystalline analogues. The number of components in a complex band and its parameters are found by analysis of the second derivative of the spectrum, using Fourier self-deconvolution as proposed by Griffiths and Pariente (Trends Anal. Chem., 5 (1986) 209). According to the procedure proposed, the spectra of the crystalline and glassy analogues of the following substances were decomposed: SiO2 (silica), K[AlSi2O6] (leucite) and Li(AlSi2O6) (spodumene). This decomposition of the complex bands in the spectra of glassy substances meant that their structures could be more readily deduced. It was shown that as well as the bands corresponding to the crystalline analogues in the spectra of glasses, there are bands responsible for characteristic features of the structure of glasses.

An XPS/SEM/EDX study of the early oxidation stages of the Fe19Cr5Al(+Y) alumina-forming alloys

Abstract The scale development on the unmodified and yttrium-implanted Fe19Cr5Al and Fe19Cr5Al0.27Y alloys at 1173 K during oxidation exposures up to 15 min was studied by means of XPS, SEM and EDX. The commercial material Kanthal APM was used as reference. A particular advantage of the XPS method relied on the possibility to distinguish between metallic and oxidized states of the elements. The scale evolution occurred in all cases via the same stages. At the beginning three-layered scales appeared, consisting of the outermost iron oxide, intermediate chromia and innermost alumina. The alumina, being thermodynamically the most stable oxide in this system, successively grew towards the scale/gas interface. Although alumina constituted the majority of scales formed during 15 min exposures, the other oxides were still present in the outermost parts of the scales. The fraction of the iron oxide and chromia in the scale was higher on the yttrium-implanted material than on the other alloys. No remarkable differences were observed regarding this fraction between the yttrium-free unimplanted and yttrium-bearing alloys. Metallic iron and chromium were found for shorter oxidation periods below their oxides. Subsequently, after 15 min exposure, the uniform distribution of the metallic iron and chromium in the scales were observed in all alloys except for the yttrium-implanted one.

Thermal properties of 60P2O5–20Fe2O3–20Al2O3 glass for salt waste immobilization

Vitrification is the most effective method of hazardous waste immobilization. Toxic elements are incorporated into a glass structure. Iron alumino-phosphate glasses are presently being considered as a matrix for storage of a radioactive waste which cannot be vitrified using conventional borosilicate waste glasses. Influence of Na2SO4 as a one of components such the waste on thermal properties and crystallization ability of 60P2O5–20Fe2O3–20Al2O3 glass was studied. It was observed that Na2SO4 decreases transformation temperature and increases ΔCp. The glass characteristic temperatures, glass crystallization ability and crystallizing phases were determined. Na2SO4 increases the glass crystallization ability which could be related with ΔCp heat capacity accompanying glass transition changes. The glass internal structure rebuilding accompanying the sodium content increase is considered. The obtained results were compared with structural model previously developed for 60P2O5–40Fe2O3 glass and showed the structural similarity between these glasses.

Titanium coated with functionalized carbon nanotubes--a promising novel material for biomedical application as an implantable orthopaedic electronic device.

The aim of the study was to fabricate titanium (Ti) material coated with functionalized carbon nanotubes (f-CNTs) that would have potential medical application in orthopaedics as an implantable electronic device. The novel biomedical material (Ti-CNTs-H2O) would possess specific set of properties, such as: electrical conductivity, non-toxicity, and ability to inhibit connective tissue cell growth and proliferation protecting the Ti-CNTs-H2O surface against covering by cells. The novel material was obtained via an electrophoretic deposition of CNTs-H2O on the Ti surface. Then, physicochemical, electrical, and biological properties were evaluated. Electrical property evaluation revealed that a Ti-CNTs-H2O material is highly conductive and X-ray photoelectron spectroscopy analysis demonstrated that there are mainly COOH groups on the Ti-CNTs-H2O surface that are found to inhibit cell growth. Biological properties were assessed using normal human foetal osteoblast cell line (hFOB 1.19). Conducted cytotoxicity tests and live/dead fluorescent staining demonstrated that Ti-CNTs-H2O does not exert toxic effect on hFOB cells. Moreover, fluorescence laser scanning microscope observation demonstrated that Ti-CNTs-H2O surface retards to a great extent cell proliferation. The study resulted in successful fabrication of highly conductive, non-toxic Ti-CNTs-H2O material that possesses ability to inhibit osteoblast proliferation and thus has a great potential as an orthopaedic implantable electronic device.

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.

Silver–Alumina Catalysts for Low-Temperature Methanol Incineration

The use of methanol as an alternative fuel for gasoline or diesel engines increases the unregulated CH3OH emission. γ-Al2O3 modified with Cu, Mn, Ce, K, Ag, Cu–Mn, Cu–Ce, Cu–Ag or Cu–K (0.5, 1.0, 0.5:0.5, 1.0:1.0 wt% of metal) catalysed the process of methanol incineration. The highest activity reached samples containing 1.0 wt% of silver. Dispersed Ag+ species on Al2O3 served as active species for selective oxidation of CH3OH to CO2 over both Ag/Al2O3 and Cu–Ag/Al2O3. Additionally, the XPS and EPR results revealed the AgO interface between the Ag2O and CuO in the Cu–Ag system.Graphical Abstract

On the influence of various physicochemical properties of the CNTs based implantable devices on the fibroblasts’ reaction in vitro

Abstract Coating the material with a layer of carbon nanotubes (CNTs) has been a subject of particular interest for the development of new biomaterials. Such coatings, made of properly selected CNTs, may constitute an implantable electronic device that facilitates tissue regeneration both by specific surface properties and an ability to electrically stimulate the cells. The goal of the presented study was to produce, evaluate physicochemical properties and test the applicability of highly conductible material designed as an implantable electronic device. Two types of CNTs with varying level of oxidation were chosen. The process of coating involved suspension of the material of choice in the diluent followed by the electrophoretic deposition to fabricate layers on the surface of a highly biocompatible metal—titanium. Presented study includes an assessment of the physicochemical properties of the material’s surface along with an electrochemical evaluation and in vitro biocompatibility, cytotoxicity and apoptosis studies in contact with the murine fibroblasts (L929) in attempt to answer the question how the chemical composition and CNTs distribution in the layer alters the electrical properties of the sample and whether any of these properties have influenced the overall biocompatibility and stimulated adhesion of fibroblasts. The results indicate that higher level of oxidation of CNTs yielded materials more conductive than the metal they are deposited on. In vitro study revealed that both materials were biocompatible and that the cells were not affected by the amount of the functional group and the morphology of the surface they adhered to.

The effect of alloyed and/or implanted yttrium on the mechanism of the scale development on β-NiAl at 1100°C

Abstract This paper reports on the comparison of scale development on unmodified β-NiAl which contains volume and surface additions of yttrium. This reactive element was incorporated using conventional alloying (0.05 or 0.1 wt%) and ion implantation. The materials containing alloyed yttrium were also implanted with yttrium to study the combined influence of volume and surface additions. A two-stage oxidation approach was applied with the use of 18O2 as a tracer. The reaction temperature was 1100°C and the samples were oxidised for up to 64 h. The scale growth mechanism was followed with the aid of in-depth distributions of the oxygen isotopes across the scale using secondary ion mass spectrometry, the surface morphology of the scales was observed using scanning electron microscopy, while their phase composition was determined using photoluminescence spectroscopy. Similar stages of the scale evolution were observed for the growing scales. Initially the oxide layer consisted of transient oxides, and at its surface more or less developed blade-like surface grains were observed. Subsequently, phase-transformation-related cracks and round patches appeared, and finally ridges which successively covered the outer surface of the scale and constituted the outer layer of a duplex scale developed. The mechanism of scale growth was a mixed outward and inward, and the relative contribution of both mechanisms varied depending on the analysed scale region and on the oxidation stage. The cracks and patches were regions where the transient aluminas were preferentially transformed into α-Al2O3. The ridges formed in cracks essentially consisted of α-Al2O3. For the initial stages of oxidation, the transient aluminas and α-Al2O3 co-existed in the scales, while subsequently the latter prevailed and finally, became the only phase found in the oxide layers. The evolution rate of the scale was affected by alloyed and implanted yttrium additions: the former exhibited minor and content-dependent effect while the latter significantly retarded it.

The mechanism of early oxidation stages of Fe20Cr5Al-type alloys at 1123 K

Abstract Fe20Cr5Al-type alumina forming alloys are known as α alumina-forming materials at relatively high temperatures (≥1273 K). This paper reports on the oxidation mechanism of commercial and synthetic Fe20Cr5Al alloys, at a considerably lower temperature, 1123 K. Some of the alloys were implanted with oxygen or yttrium ions prior to the oxidation exposure. Two-stage-oxidation, secondary ion mass spectrometry, secondary electron microscopy and lowangle X-ray diffraction were used as experimental tools. Results showed that even prolonged exposures are not sufficient to ensure that the scale consists essentially of α-Al2O3. Mechanisms involved from the observed scale morphology, microstructure and phase composition are discussed