Thermal stability of glasses from the Fe4(P2O7)3–Fe(PO3)3 system (original) (raw)
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The glass formation and crystallization studies on iron phosphate–silicate glasses
Journal of Thermal Analysis and Calorimetry
The assessment of impact of incorporation of various amount of Fe 2 O 3 at the expense of MgO and CaO on the glassy phase formation and thermal stability exhibited in P 2 O 5-SiO 2-K 2 O-MgO-CaO-Fe 2 O 3 system was carried out. The characteristic temperatures for iron phosphate-silicate glasses and glass-crystalline materials were designated from associated DSC curves. Selected samples were subjected to the process of induced crystallization, and products combined with particular exothermic effects were identified. Combination of DSC, XRD and SEM-EDS methods enabled to collect invaluable data concerning the course of crystallization of not only iron phosphate-silicate glasses subjected to the process of induced crystallization, but also glass-crystalline materials obtained directly through melt-quenched technique. The amount of particular crystalline products associated with selected devitrificates was determined via Rietveld technique. Results of the conducted study indicated that Fe 2 O 3 addition conduces to the decrease in crystallization temperatures and thermal stability which was reflected in calculated values of DT and K W parameters. Concomitantly, glass with 20 mol% iron (III) oxide addition exhibited significantly improved, distinctive thermal stability among the materials in the analyzed series. The connection of crystalline phases with gradual alterations in polymerization degree of glass matrix was also established. The performed study is a contribution to the knowledge of iron phosphate glasses family and associated glass-crystalline materials. Keywords Glass-forming ability Á Crystallization process Á Fe 2 O 3 Á Iron phosphate-silicate glasses & Justyna Kuczek
Effect of melting temperature and time on iron valence and crystallization of iron phosphate glasses
Journal of Non-Crystalline Solids, 1999
The effect of melting temperature and time on iron valence, dissolution rate (DR) in deionized water, and crystallization of iron phosphate glasses was investigated using a 40Fe2O3–60P2O5, mol%, batch composition. The concentration of Fe2+ ions in these glasses increased from 17% to 57% as melting temperature increased from 1150°C to 1450°C, but remained nearly constant at about 20% for melting
Elaboration and Structural Investigation of Iron (III) Phosphate Glasses
The regular melting-quenching method allowed isolating very large vitreous domains within the ternary system Li 2 O-P 2 O 5-Fe 2 O 3 at 1100˚C. The vitrification and crystallization effects are discussed in terms of phosphorus pentaoxide concentration (mol%). In the course of the present study, we analyzed chemical durability along the glass domain and many sample glasses were isolated. We noticed that our compounds demonstrated very high chemical resistance to attack, even with very highly concentrated mineral acid solutions. This behavior can be assigned to the presence of poorly crystalline phases in these glasses, which tended to increase as the Fe 2 O 3 content increased. This property is a prerequisite for many interesting industrial applications. XRD, IR spectroscopy and SEM micrographs allowed an efficient investigation of the structural changes versus composition within ternary diagrams. The results were found to be consistent with the regular structural changes of phosphate glasses.
Journal of Non-Crystalline Solids, 2008
The thermal properties (expansion, Tg and TSOFT.) of glasses, having 56-66% P 2 O 5 , 14.8-34.2% Fe 2 O 3 and 2-25 wt% additions of SiO 2 , Al 2 O 3 , Na 2 O and UO 2 , were comparatively estimated from dilatometric measurements in similar conditions. The Tg reversibility was clearly verified by varying the heating rates between 1 and 5 °C min−1. From linear equations fits of the various glass properties as functions of the six components it is suggested the iron, sodium and uranium oxides decrease the thermal expansion (for 50 < T < 300 °C), Tg and TSOFT. From DTA/XRD analysis of three glasses it was confirmed the crystallization tendency decreased with increasing the UO 2 level in the glasses. Leaching test data for two compositions containing Na 2 O suggest addition of UO 2 increases the chemical durability of the related glass.
Glass formation from iron-rich phosphate melts
Journal of Non-Crystalline Solids, 2010
Iron-rich phosphate glasses with nominal Fe/P ratios between 1.0 and 1.6 were prepared by a rollerquenching technique. The critical cooling rates (CCR) for glass formation were estimated by differential thermal analysis and found to be in the range of 10 3 -10 4°C /s for the iron-rich melts, compared to 1-10°C/s for conventional iron phosphate melts with nominal Fe/P ratios near 0.50. The Fe(II)/Fe total fraction in the quenched glasses increases with melt time and temperature, and ranges between 0.30 and 0.55 for the glasses studied. Raman spectroscopy indicates that the structures of the iron-rich phosphate glasses are based on isolated orthophosphate tetrahedra, similar to what are found in α-FePO 4 .
Thermal stability of Na2O–FeO–Fe2O3–P2O5 glasses
Journal of Non-Crystalline Solids, 2015
The crystallization tendencies of five series of Na 2 O-FeO-Fe 2 O 3-P 2 O 5 (NFP) glasses with different O/P (3.0-3.5) and Fe/P (0.13-0.67) ratios were studied. Characteristic temperatures, including the glass transition temperature (T g) and crystallization temperature (T x h), were obtained using differential thermal analysis (DTA), and liquidus temperatures (T L) were determined by microscopic evaluation of heat-treated samples. The compositional dependence of glass structure and the characteristic temperatures are discussed. The glass stability (GS) against crystallization is described using parameters based on the characteristic temperatures. For the glass series with O/P ratios near the pyrophosphate composition (O/P ~3.5), the glass stability goes through a minimum value around Fe/P ~ 0.3 to 0.4, which corresponds to the crystalline phase NaFeP 2 O 7 and Na 7 Fe 3 (P 2 O 7) 4 .
Thermal properties of Na2O–P2O5–Fe2O3 polyphosphate glasses
Journal of Thermal Analysis and Calorimetry
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.
Journal of Non-Crystalline Solids, 2002
The local environment around iron ions in iron phosphate glasses of starting batch composition 40Fe 2 O 3 -60P 2 O 5 (mol%) melted at varying temperatures or under different melting atmospheres has been investigated using Fe-57 M€ o ossbauer and X-ray absorption fine structure (XAFS) spectroscopies. M€ o ossbauer spectra indicate that all of the glasses contain both Fe(II) and Fe(III) ions. The quadrupole splitting distribution fits of M€ o ossbauer spectra show that Fe(II) ions occupy a single site whereas Fe(III) ions occupy two distinct sites in these glasses. When melted at higher temperatures or in reducing atmospheres, the Fe(II) fraction in the glass increases at the expense of Fe(III) ions at only one of the two sites they occupy. The pre-edge feature in the XAFS data suggests that the overall disorder in the nearneighbor environment of iron ions decreases with increasing Fe(II) fraction. The XAFS results also show that the average iron-oxygen coordination is in the 4-5 range indicating that iron ions have mixed tetrahedral-octahedral coordination. Ó
Journal of Thermal Analysis and Calorimetry
Iron phosphate-silicate glasses from P 2 O 5-SiO 2-K 2 O-MgO-CaO-Fe 2 O 3 system were subjected to the thermal and spectroscopic studies in order to gain information about their structure and thermal behavior in the range of glass transition effect. Research includes results obtained via DSC, MIR and DRIFT spectroscopy. Designated values of glass transition temperature and specific heat change slightly increases with Fe 2 O 3 incorporation. Spectra collected during thermal treatment of glasses containing 2 and 30 mol% Fe 2 O 3 exhibited various changes. Fe 2 O 3 addition affected the glass structure by its reinforcement and led to its preservation during thermal treatment. The connection between density, molar volume, oxygen packing density and the chemical composition's alteration were also established because of the direct dependence of physical properties and the structure. Obtained results supported thermal and spectroscopic studies. Conducted research is considered as a contribution to the knowledge about the family of iron phosphate glasses, which are known from their interesting properties and widely used applications.
Thermal behaviour of Fe-doped silicate–phosphate glasses
Journal of Thermal Analysis and Calorimetry, 2010
Thermal behaviour and structure of glasses from the SiO 2 -P 2 O 5 -K 2 O-MgO-CaO system modified by Fe 2 O 3 addition were studied by DSC, XRD and FTIR methods. It has been found that the replacement of MgO and CaO modifiers by Fe 2 O 3 in the structural network of silicate-phosphate glass results in decrease of the glass transition temperature (T g ) and heat capacity change (DC p ) accompanying the glass transformation. Simultaneously, the ability for crystallization, its course and the type of the forming phases depend on the relative proportions between iron and phosphorus as components forming the silicatephosphate structure. The type of the crystal phases forming in the course of heating the considered glass has been found to be in agreement with the character of the domains occurring in this glass, confirmed by FTIR examinations.