Paweł Stoch

Thermal properties of phosphate glasses for salt waste immobilization

Vitrification is the most effective method of the hazardous waste immobilization. Toxic elements are incorporated into glass structure. Iron phosphate glasses are presently being considered as a matrix for storage of the radioactive waste which cannot be vitrified using a conventional borosilicate glass. Influence of Na2SO4 as one of the components such the waste on thermal properties and crystallization ability of iron phosphate waste 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. It is shown that ΔCp is a suitable, structure-sensitive glass crystallization ability, parameter.

Crystal structure and Mössbauer study of FeAl2O4

Abstract In this work the synthesis of hercynite from Fe2O3 and Al2O3 powders was carried out by arc-melting method under the protective argon atmosphere. The obtained material was characterized with the use of powder X-ray diffractometry (XRD) and Mössbauer spectroscopy (MS). A Mössbauer effect in hercynite obtained by the arc-melting method indicated the cations distribution in the spinel structure among the tetrahedral and octahedral interstices. The presence of Fe2+ ions was detected in both tetrahedral and octahedral sites while Fe3+ ions occupied only the octahedral interstices. The approximate formula of the obtained iron-aluminate spinel was as follows (Fe2+0.77Al3+0.23) (Fe3+0.07Fe2+0.05Al0.88)2O4.

Structural role of Fe in the soil active glasses.

Glasses of the SiO(2)-P(2)O(5)-K(2)O-MgO-CaO-Fe(2)O(3) system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of iron addition on the structure of glasses was evaluated by FTIR spectroscopy (with spectra decomposition) and (57)Fe Mössbauer spectroscopy. The chemical activity of glasses in the 2 mass% citric acid solutions was measured by the ICP-AES method. It has been found that the formation of domains with structure similar to phosphates with chemically stable P-O-Fe(3+) and P-O-Fe(2+) bonds decreases the glass solubility under conditions simulating the soil environment.

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.

Mössbauer spectroscopy study of 60P2O5-40Fe2O3 glass crystallization

Abstract 60P2O5-40Fe2O3 glass was synthesized and 57Fe Mössbauer spectroscopy study was presented. The main goal of the research was to investigate structural changes of local environment of iron ions during gradual crystallization of the glass. It was observed that some changes were evidenced at temperature of heat treatment higher than 400°C, above which content of tetrahedrally coordinated Fe3+ was increased in cost of octahedral sites. This led to formation of areas of nucleation of α-FePO4. Crystallization of α-Fe3(P2O7)2 and Fe2P2O7 was also observed.

Electrical resistivity, Curie temperature and band structure of Ho(Fe1−xCox)2 compounds

Electrical resistivities for Ho(Fe1−xCox)2 C15 Laves phases were measured in a wide temperature region (13–1000 K) and the residual, phonon and magnetic resistivities contributing to them were separated. Moreover, the parameters characterizing resistivity dependence on temperature and composition, including the Debye temperature, were determined. The differential of the magnetic part of electrical resistivity against temperature was used to estimate Curie temperatures. The Curie temperature changes approximately parabolically, increases with x, reaches a maximum at x = 0.3 and then strongly decreases for higher x values. Some results of 3d and 4s electronic band structure, calculated using the full-potential linearized augmented plane wave (FLAPW) method, are presented. A distribution function for the densities of states is introduced, and a way of defining 3d and 4s band half-widths as well as band splitting energy is proposed. The calculated 3d and 4s band splitting energies for Fe, Co and stoichiometrically weighted transition metal M are presented. A simple statistical-type formula describing the Curie temperature of Ho(Fe1−xCox)2 intermetallics related to FLAPW results is proposed.

Bronchopulmonary Dysplasia Prediction using Logistic Regression

The prognostic value of some continuos measurement parameters calculating Bronchopulmonary Dysplasia predictor is the main goal of the paper. The most important question is, if the continuous measurement of parameters can help us to build a better algorithm solving Bronchopulmonary Dysplasia prediction problem?

Position of Fe ions in MgO crystalline structure

Abstract Magnesium oxide (MgO) is one of the most important raw materials in many branches of industry. Magnesium oxide is a popular refractory raw material because of its high refractoriness and high resistance to basic slags and environment. In many cases, use of MgO is limited by its properties, especially the presence of secondary phases like iron oxides. The amount and distribution of iron oxides can strongly influence the technological properties of MgO and depend on the manufacturing method, particularly the heat-treatment process. The aim of the study was to evaluate the influence of the heat-treatment process on amount and distribution of iron ions in a magnesium oxide lattice. The 57Fe Mössbauer effect measurements of fused and sintered magnesium oxide samples doped by the iron oxide were conducted. Investigation reveals in both cases the presence of Fe2+ as well as Fe3+ ions. Fe2+ ions occupy Mg2+ octahedral sites in the MgO lattice, whereas the Fe3+ ions are located in highly distorted octahedral coordination. The amount of Fe2+ varies from around 66% for fused samples to 30% for sintered samples.

The effect of mechanical activation on the thermal reactions of P2O5–Al2O3–Fe2O3–Na2O phosphate glasses

The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the Tg temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.

Hyperfine interactions in Ho(Fe1−xCox)2 compounds at 77 K

Synthesized, x-ray studied Ho(Fe1−xCox)2 compounds (x= 0–1) have a pure cubic Fd3m, C15, MgCu2-type crystal phase. The unit cell parameter decreases nonlinearly with the composition parameter x. Mossbauer effect spectra collected at 77 K for the Ho(Fe1−xCox)2 series were composed of a number of locally originated subspectra due to random Fe/Co nearest neighbourhoods. Hyperfine interaction parameters, i.e. the isomer shift, the magnetic hyperfine field and the quadrupole interaction parameter, were determined from the fitting procedure of the spectra for the individual nearest neighbourhoods and also as average values for the sample as bulk. As a result of Fe/Co substitution, Slater–Pauling-type dependences for magnetic hyperfine fields corresponding to both the local area and the sample as bulk were observed. A correlation between the local magnetic hyperfine fields and the average magnetic hyperfine fields was noticed, and this was related to weak and strong ferromagnetism of the transition metal sublattice. The obtained magnetic hyperfine fields were compared to analogous data known for compounds with other rare earths. A numerical formula for describing the magnetic hyperfine field as a function of the composition parameter x and rare earth spin S was proposed.