Properties Of Iron Phosphate Glasses Research Articles

Short-Range Structure and Thermal Properties of Iron Phosphate Glasses

Short-Range Structure and Thermal Properties of Iron Phosphate Glasses

Effect of molybdenum on structural features and thermal properties of iron phosphate glasses and boron-doped iron phosphate glasses

The variations of structure and thermal properties in iron phosphate glasses and boron-doped iron phosphate glasses due to MoO3 addition up to 50 mol% were investigated and compared in detail. The results show that MoO3 depolymerizes the phosphate networks resulting in a higher connectivity of the networks through [MoO4] units and the formation of Mo–O–P bonds diversifies the cross-linking of the glass networks, leading to the conversion of long phosphate chains to pyrophosphate units and/or orthophosphate units. These structure variations cause the decrease of glass transition temperature, thermal stability and glass formation ability of iron phosphate glasses. Moreover, the MoO3 loading, thermal stability and glass formation ability of iron phosphate glasses were improved by boron. The reasons on the improved properties are also explained and analyzed. The obtained conclusions provide researchers with the role of Mo in structure and properties of phosphate glasses for Mo containing nuclear waste immobilization.

Effects of alkaline-earth metal oxides on structure and properties of iron phosphate glasses

In order to figure out the effects of alkaline-earth metal oxides on structure and properties of iron phosphate glass, the glass system (100-x) (60P2O5–40Fe2O3)-x RO (RO=MgO, CaO, SrO, x=5,10,15,20mol%) was investigated. Structure and properties were studied by XRD, FTIR, DSC, while chemical durability tests were carried in acid and alkali solution under harsh conditions for 120h. Results from XRD show that not all glasses are amorphous. There are several crystals emerging in the three series of glasses. Meanwhile, FTIR tests demonstrate that as more RO was doped, the glass network depolymerized,with phosphate chains turning shorter; vibrations of all bands indicate the formation of P–O–R bands. Densities of all samples would move up with more RO, glasses with SrO being higher than those doped with MgO and CaO. The glass transition temperature (Tg) of all glasses increases, while the glass crystalline temperature (Tc) of glasses containing MgO and CaO grows up as well. However, glasses with SrO slump dramatically, which deteriorates thermal stability in this system. As for the chemical stability, weight loss for all glasses falls eventually with time both for acid and alkali solutions. The residential materials after alkali corrosion have several crystals when removed to XRD tests. Meanwhile, almost all samples left more intact after acid corrosion when compared with those suffering from alkali corrosion, indicating the superior acid resistance to alkali for glasses.

Effects of Calcium Oxide Addition on the Structure and Thermal Properties of Iron Phosphate Glasses

The calcium iron phosphate glasses were prepared and measured by X-ray diffraction, Fourier transform infrared spectra, Raman spectra, and differential scanning calorimetry. X-ray diffraction analysis has confirmed that all compositions are amorphous. Infrared and Raman spectra indicated that the glass formed the P‒O‒Fe and P‒O‒Ca bonds in Q1 units and (P‒O− Ca2+−O‒P) ionic cross-links in Q2 units. Increasing calcium oxide content in glass compositions was brought about by the Q1 to Q2 conversion, which resulted in the more formation of the non-bridging oxygen (P‒O− Ca2+−O‒P) ionic cross-links. The change of glass transition temperature and thermal stability is consistent with structural modification of the glasses. The analyses of the spectra revealed that calcium oxide played the dual role as a network former and modifier. Oxygen to phosphorus molar ratio about 3.0 would contain the relatively higher concentration of Q1 and Q2 units.

Effects of lanthanum addition on the structure and properties of iron phosphate glasses

The structural properties of xLa2O3–(100−x)(0.4Fe2O3−0.6P2O5) (x=0, 1, 2, 3, 4, 6, 8mol%) glasses have been investigated by XRD, DTA, IR and Raman spectroscopy. XRD analysis has confirmed that the majority of samples are X-ray amorphous, and crystallization occurs when the glass containing 6mol% La2O3, the crystalline phase is LaPO4. The IR spectra show that the glass structure does not produce any fundamental change with addition of La2O3 in the glass formation range, which consists predominantly of pyrophosphate, Q1 units. However, Raman spectra indicate that depolymerization of the phosphate network with the addition of La2O3 content. The glass transition temperature (Tg) increased with increasing La2O3 content for the glasses, which indicates that the addition of La2O3 increases the thermal stability of glasses in this series.

Thermal characterization of iron phosphate glasses for nuclear waste disposal

This paper reports on the thermal properties of iron phosphate glasses with the following wt.% composition: 40Fe 2O 3–60P 2O 5. Such glasses are currently being investigated for nuclear waste disposal. Open photoacoustic cell (OPC) and heat capacity techniques were performed to determine thermal diffusivity, thermal conductivity and heat capacity of the glasses. Results were compared with borosilicate glass where OPC and Thermal lens where performed. Moreover, the present paper demonstrates the semiconducting-like behavior of iron phosphate glasses.

Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB 2O 3–(40−x)Fe 2O 3–60P 2O 5 (x = 2–20, mol%) and xB 2O 3–(100−x)[Fe 2O 3–60P 2O 5] (x = 2–20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. T g increased with increasing B 2O 3 content for the glasses in the first series which indicates that the addition of B 2O 3 increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10 −9 gr/cm 2 min which are comparable to that of the base iron phosphate glass. When the B 2O 3 content was above 14%, new bands related to BO 4 tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe 2+ ions in glasses (Fe 2+/∑(Fe 2+ + Fe 3+)) was found to be 23% for the base glass while it was 10–22% for the boron doped glasses.

Mixed electronic–ionic conductivity in transition metal oxide glasses containing alkaline ions

In alkali free transition metal oxide glasses conductivity is described by small polaron hopping. The carrier concentration is related to the concentration of transition metal ions in different valence states. Generally ionic conduction depends on the alkali concentration and ion mobility. Assuming that the motion of alkali ions and polarons is independent one may expect that the electrical conductivity increases with the increase in the alkali content. However, real transition metal oxide glasses containing alkali show various behaviors – from strong conductivity anomalies to conductivity weakly dependent on alkali content. A comparison of the electrical properties of iron phosphate glasses containing different amounts of sodium ions and copper oxide glasses to other TMO glass systems has been performed. The influence of the role of transition metal oxide in the glass forming network on the electrical properties of glass has been outlined.

Iron redox equilibrium, structure and properties of iron phosphate glasses

Iron redox equilibrium, structure and properties were investigated for 40Fe 2O 3–60P 2O 5 (mol%) glasses melted at different temperatures. The Fe 2+/(Fe 2++Fe 3+) ratio increased from 17% to 50% as the melting temperature changed from 1150°C to 1400°C. The equilibrium constant, K, for the reaction of Fe 3+ being reduced to Fe 2+ varied with temperature as ln K=9.40–1.58×10 4/ T. The Raman and infrared spectra indicated that the basic iron pyrophosphate structure of the 40Fe 2O 3–60P 2O 5 (mol%) glasses did not change as the Fe 2+/(Fe 2++Fe 3+) ratio changed. All of the properties did not change to any major degree with increasing the melting temperature. The molar volume decreased while the density increased with increasing Fe 2+/(Fe 2++Fe 3+) ratio. It was found by DTA and XRD that two phases, Fe 3(P 2O 7) 2 and Fe 4(P 2O 7) 3, crystallized from the glass when the glass was heated in nitrogen. The crystallization behavior suggested that the amount of the crystal, Fe 3(P 2O 7) 2, may increase with increasing Fe 2+/(Fe 2++Fe 3+) ratio, which supported the opinion that there are some structural similarities between the iron phosphate glass and the crystalline Fe 3(P 2O 7) 2 in terms of the iron coordination number and bonding of the phosphate groups. The decrease in dc resistivity and increase in dielectric constant and dielectric loss tangent, which occurred with increasing the Fe 2+/(Fe 2++Fe 3+) ratio, were attributed to the increase of the electronic hopping from Fe 2+ ions to Fe 3+ ions.