Search

Phosphate glasses are an important group of materials for wide applications. They have received attention as biomaterials, eco-fertilizers, in optoelectronic devices, waste immobilization, etc. The subject of the studies is binary Al 2 O 3 –P 2 O 5 glass, seen by ab initio molecular dynamics simulations. In the paper, Mayer's Bond Order analysis was employed as a suitable tool to observe the changes in the network due to Al 2 O 3 substitutions. As well as, the bonding properties across the atoms in the network, which were characterized by electron localization function. The basic structural properties of the glasses are presented. The simulations showed that oxygen atoms in [PO 4 ] tetrahedrons create a weak covalent bond between the atoms. The interaction spreads across the whole phosphate network via bridging oxygens. Whereas, there is no such interaction between the atoms in [AlO x ] polyhedrons. In the case of the Al 2 O 3 rich glasses, there are evidence non-network oxygen atoms which influence the distribution of phosphate structural units predicted based on the O/P ratio. The possibility of estimation of the oxygens in an experiment is discussed. The atoms building the network are going to take specific values of the total bond orders and the glass network is an interplay between atoms' affinity to saturate bond orders and the glass network neutrality. [ABSTRACT FROM AUTHOR]

Phosphate glasses are materials that can be used in many technological fields. Their possible application may be limited due to the existence of easily hydrated P–O–P bonds. Addition of Al 2 O 3 , Fe 2 O 3 strongly improves the durability of the glasses. The subject of the studies are iron-polyphosphate glasses in which iron is gradually substituted by aluminum. The glasses have been tested using FT-IR, Raman, and Mössbauer spectroscopies. The obtained experimental results were compared to the theoretical prediction of the glass network structure by ab initio molecular dynamics. It was shown that the substitution leads to an increase in the glass network polymerization. The glass network is inhomogenous with Al/Fe-rich and poor regions. In the poor regions, Al/Fe cations are glass network modifiers whereas in the rich they can be the glass network formers. Mayer's Bond Order analysis was used to describe bonding mechanisms in the glasses. The existence of the mix-valence iron atoms has been postulated. [ABSTRACT FROM AUTHOR]

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 NaSO as a one of components such the waste on thermal properties and crystallization ability of 60PO-20FeO-20AlO glass was studied. It was observed that NaSO decreases transformation temperature and increases Δ C. The glass characteristic temperatures, glass crystallization ability and crystallizing phases were determined. NaSO increases the glass crystallization ability which could be related with Δ C 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 60PO-40FeO glass and showed the structural similarity between these glasses. [ABSTRACT FROM AUTHOR]

A composite with the 0.8CaZrO 3 –0.2CaFe 2 O 4 general formula was prepared by means of a double sintering process. Temperature of 1400 °C was found suitable to obtain the composite based on scanning electron microscopy and X-ray diffraction analysis. Phase composition, crystal structure, Mössbauer effect, microstructure and dielectric properties were studied. The influence of Fe ions on the CaZrO 3 structure has been reported. It was found that Fe substituted Zr in CaZrO 3 and vice versa in CaFe 2 O 4 in the amount about 1.5 at% in both cases. The approximated formula of the obtained composite was 0.8Ca(Zr 0.9 Fe 0.1 )O 3 –0.2Ca(Fe 0.8 Zr 0.2 ) 2 O 4 . The SEM observations revealed that liquid CaFe 2 O 4 occurred as a filling phase between CaZrO 3 grains which significantly enhanced densification of the material and influence on its properties. The dielectric constant reached the value of 170 at 1 MHz and the accompanying dissipation factor was very low – 0.005. [ABSTRACT FROM AUTHOR]

The chemical reaction of the formation of compounds within the structure of solid as a reaction medium-internal reactions-is the subject of the article. The mechanism of these reactions on the example silicate mineral structure and nanocrystallization of oxide glasses is considered. Local atoms interaction analysis based on the electronegativity of and ionicity of the chemical bonds values helps to understand this mechanism and predict course of intrastructural thermal processes. [ABSTRACT FROM AUTHOR]

Vitrification has been recognized as the best method of the neutralization and immobilization of the radioactive and toxic waste. Toxic elements are introduced into the structure of chemically durable glasses (waste glass). SiO2-B2O3-Al2O3-Na2O glass is one of the most commonly used waste glass. Radioactive 137Cs is often a dangerous contaminant of hospital and laboratory waste. Incineration of these waste and vitrification of ash by its co-melting with borosilicate glass is the perspective method of immobilization of this nuclide for safety waste storing. The influence of the partial substitution of Na by Cs and of the introduction of CaO as the main waste incineration ash component in the SiO2-B2O3-Al2O3-Na2O waste glass on the change of its structure, crystallization ability, and physical properties were studied. [ABSTRACT FROM AUTHOR]

Abstract: Mössbauer spectroscopy has been applied to determine the content and position of Fe2+ and Fe3+ in the structure of vitrified municipal waste incineration ashes as well as their change with temperature increase. Vitrified ashes are the iron-rich calcium aluminosilicate glasses. Fe clustering charaterized by a change of coordination number accompaning its incorporation into the structure of pyroxene as it crystallizes in the glass, was studied. [Copyright &y& Elsevier]

Phosphate glasses can be used in many applications fields like medicine, optoelectronics, environmental protection, etc. Their properties are strongly dependent on the glass network structure. The paper presents classical molecular dynamics simulations studies of the influence of the gradual addition of CaO on structural features of 55P 2 O 5 -30Fe 2 O 3 -15FeO glass. The base glass is built of different lengths chains and rings which are being shortened due to CaO addition. Thus, the glass network depolymerization takes place. The phosphate network is joined by iron-oxygen polyhedrons which increase polymerization of the network. The increase of non-network oxygen ions is observed what can be related to the rising of Ca and Fe ions aggregation. The aggregation of calcium is the most dominant at the low concentration of this oxide. The effect leads to the observation of the glass network non-homogeneity. The increase of the CaO concentration causes expansion of the Ca-rich regions which finally extend over the entire glass network for the CaO content above 45%. Above this point, the phosphate network is mostly composed of isolated Q0 structural units. The P-O-P bridges are broken more easily than P-O-Fe due to an increase in the modifier content. [ABSTRACT FROM AUTHOR]

The subject of the studies is polyphosphate glass of 19Al 2 O 3 -19Fe 2 O 3 -62P 2 O 5 composition. The glass was investigated with the application of experimental methods like FT-IR, Raman, and Mössbauer spectroscopy. The obtained results were compared to theoretical studies which were conducted on different theory levels like MD, CPMD and DFT simulations. According to the conducted studies the phosphate network is built of different length chains which are joined by iron-oxygen and aluminum-oxygen polyhedrons which increase polymerization and rigidity of the glass network. The iron ions are nonuniformly distributed and form rich and poor regions. Mössbauer hyperfine interaction parameters were calculated and compared with the obtained experimental results. It was observed linear dependence of Mayer's bond order parameters on bond lengths and values of full valency were calculated. The values are comparable to the formal charges what gives an easy possibility to distinguish between Fe(III) and Fe(II) ions. [ABSTRACT FROM AUTHOR]

The present paper analyzes the impact of incorporation of various amounts of Fe 2 O 3 into phosphate-silicate glasses. Amorphous solids in the P 2 O 5 SiO 2 K 2 O MgO CaO system with constant molar ratio of P 2 O 5 and SiO 2 as 41: 6 and 0÷30 mol.% iron oxide addition were successfully obtained. Fe 2 O 3 was incorporated at the expense of CaO and MgO. Materials were subjected to Raman and Mössbauer studies in order to analyze their structure. Transformation between glasses with low Fe 2 O 3 addition and samples containing more than 4 mol.% iron ions was reflected on Raman and Mössbauer spectra. Diverse valent states and coordination of iron ions manifested themselves in results of Mössbauer study. The role of iron ions as network modifiers and formers was also implied. The performed study constitutes an invaluable basis for further analysis of the obtained materials, whereas the provided methods can be applied for many challenging projects, hence making them a scientific novelty. [ABSTRACT FROM AUTHOR]

Multiferroic 0.5BiFeO3-0.5Pb(Fe0.5Ta0.5)O3 solid solution is a material that exhibits ferroelectric and antiferromagnetic orderings in ambient temperature. The solid solution was obtained as a result of a conventional reaction in a solid state. The obtained material is a dense, fine-grained sinter whose surface was observed by scanning electron microscopy (SEM) and stoichiometry was confirmed by energy dispersive X-ray spectroscopic (EDS) analysis. According to the X-ray powder diffraction (XRD) measurements, the main phase is R3c space group with admixture of Pm-3m regular phase. Small contribution of pyrochlore-like phase was also observed. Mössbauer spectroscopy suggested random distribution of Fe3+/Ta5+ cations in the B sites of ABO3 compound. Reduction of the magnetic hyperfine field with an increase in the substitution of Ta5+ in Fe3+ neighbourhood was also observed. [ABSTRACT FROM AUTHOR]

Recently, a new high-temperature ternary Cr(III) phase (Wuboraite, CaAl 2 Cr 2 IIIO 7) was synthesized in the Al 2 O 3 –CaO–Cr 2 O 3 system. However, its formation & chemical transformation mechanism is yet to be explored in detail. And here, we investigated the system between 500 and 1600 °C under the air and argon (Ar) atmosphere via solid-state reaction using XRD, TG-DSC, XPS, and leaching tests. Wuboraite formation starts at different temperatures (∼1500 & ∼1100 °C) under different atmospheres (air and Ar). The intermediate compounds, CaCrVIO 4 and CaCr 2 IIIO 4 , formed under air and Ar atmospheres, play a crucial role in wuboraite conversion given proper temperature and stoichiometry. [ABSTRACT FROM AUTHOR]

Iron phosphate glasses are materials that can have many applications like durable matrixes in waste immobilization techniques, biomaterials, optoelectronic devices, etc. Their possible usage is related to their glass network and thermal properties. The influence of Na2O content on thermal properties and crystallization ability of iron phosphate glass of base composition 30 Fe2O3–70 P2O5 mol% were studied. Increasing the content of Na2O causes a decrease in transformation temperature and increase in ΔCp. Characteristic temperatures, thermal stability and crystallizing phases were determined. Increasing content of sodium causes depolarization of iron phosphate glass network which causes a continuous change in ΔCp and glass transformation temperature. Discontinuous change in some glass properties suggests structure rebuilding about 30 mol% of Na2O. [ABSTRACT FROM AUTHOR]

Phosphate glasses are important materials in many fields. However, their usage can be limited due to water corrosion. Addition of Al2O3 significantly improves the water resistance, and as such, the glass of superior water durability can be obtained. Thus, it may be considered as a matrix for waste immobilization. In the paper, thermal properties of 60P2O5–(40−x)Al2O3–xNa2O glasses are presented. The materials were investigated with the application of DSC/TG method and observations of shape change during heating in a heating microscope. Water durability studies are also presented. It was evidenced that glass of low Na2O content crystallizes during heating, which limits their application in waste vitrification. Nevertheless, the obtained glass–ceramic material is characterized by a superior water resistance. The water durability decreases with sodium content. The obtained results are discussed from a waste immobilization point of view, and the optimal glass composition containing 15 mol% of Na2O is indicated due to it low viscosity, melting temperature and very good water resistance. [ABSTRACT FROM AUTHOR]

Phosphate glasses are materials which are important from the fundamental and practical point of view. Among them of special interest in the nuclear industry can be considered iron-phosphate glasses. The materials by its relatively low viscosity, melting temperature, good chemical durability, and glass network flexibility can be used as a matrix for nuclear waste immobilization. The subject of the studies is polyphosphate glass of composition 70P 2 O 5 –30Fe 2 O 3 which structural changes after β-irradiation are presented. The glass was irradiated from a90Sr/90Y source which is one of the biggest origins of damages in nuclear waste glasses. The pristine glass and the glass after irradiation were investigated using FTIR and Raman spectroscopy. The pristine glass is built of rather short chains which are joined by iron-oxygen polyhedrons. The homogenous glass structure becomes inhomogeneous with the formation of phosphorous enriched and depleted regions after irradiation. Additionally, the formation of oxygen which can dissolve in the glass or can create oxygen bubbles was detected. The glass network changes have a tendency to saturation for high doses. • Phosphorous depleted and enriched regions. • Oxygen bubbles formation. • Glass network depolymerization. [ABSTRACT FROM AUTHOR]

In this work spinel series with the general formula Fe1-xMnxAl2O4 (where x = 0, 0.3, 0.5 and 0.7) were synthesized and characterized with respect to their structure and microstructure. X-ray diffractometry (XRD) was used to identify the phase composition that revealed a single phase spinel material. Rietveld refinements of the XRD patterns were carried out in order to determine the lattice and oxygen positional parameters of the spinel compounds. Mössbauer effect measurements were performed at room temperature to determine the local chemical environment of the Fe ions, their valences, and degrees of spinels inversion. It was shown that an increase in the Mn content led to a decrease in the ratio of Fe2+ to Fe3+. The results obtained from Mössbauer spectroscopy (MS) were used to establish the chemical formulas of the synthesized spinels. Finally, the microstructure that was observed using scanning electron microscopy (SEM) showed a compact microstructure with an octahedral crystal habit. [ABSTRACT FROM AUTHOR]

We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb3+ and Tm3+ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of 5D4 → 7F3 (550 nm for Tb3+) and 1D2 → 3F4 (450 nm for Tm3+) were observed. It was also found that Tb3+ and Tm3+ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm3+ emission was dominant. At higher temperatures, the electrons occupying Tm3+ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm3+ centers simultaneously decreased. At the highest temperatures, emission took place from Tb3+ recombination centers, but only from deeper 5D4 level-related traps which had not been emptied at a lower temperature range. [ABSTRACT FROM AUTHOR]