The structure and chemical durability in the vitreous part of the system 60P2O5-2Cr2O3-xFe2O3-(38 - x)Na2O phosphate glasses (with 3 ≤ x ≤ 33 mol%) were investigated using various techniques such as IR spectroscopy,...The structure and chemical durability in the vitreous part of the system 60P2O5-2Cr2O3-xFe2O3-(38 - x)Na2O phosphate glasses (with 3 ≤ x ≤ 33 mol%) were investigated using various techniques such as IR spectroscopy, X-ray diffraction and M?ssbauer spectroscopy. The presence of Cr2O3 and the increase of Fe2O3 at the expense of Na2O in the glass network lead to a large number of covalent and rigid Fe-O-P and Cr-O-P bonds. The infrared and XRD spectra indicate a radical change of structure and show that the increase of the Fe2O3 content favors the depolymerization of the vitreous network towards pyrophosphate chains. The presence of Cr2O3 in the glass seems to favor the covalent Cr-O-P bonds linked to the most probable cyclic metaphosphate chains. However, when the Fe2O3 content increases (≥23 mol%), its impact on the glass network is stronger than that of Cr2O3. The infrared and XRD spectra indicate a radical change of structure and show that the increase in Fe2O3 content favors the depolymerization of the vitreous network to short pyrophosphate chains. The results of M?ssbauer spectroscopy indicate the presence of both Fe (III) and Fe (II) ions which occupied more or less deformed octahedral sites. The growth of the glass transition temperature (Tg) with the increase of the iron oxide in the vitreous network, leads to an improvement of the glass rigidity. This explains the decrease of the ionic radius of the iron and the reinforcement of the interconnection of the chains of vitreous networks. The structure of sodium-chromium-iron phosphate glasses can be considered largely as pyrophosphate units linked to ferric and ferrous ions in octahedral or deformed octahedral coordination. The dissolution rate is 200 times lower than that of the silicate glasses.展开更多
We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are ...We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have+4 state.EuRhO_(3) powders are found to be antiferromagnetic with a second order magnetic transition at Neel temperature(T_(N)=2.9 K).Analysis of the magnetic susceptibility versus temperature data in terms of the Curie=Weiss law:(χ=C/(T-θ_(W))) for T>T_(N),yields θ_(W)=-3.1 K and effective magne tic moment μ_(ff)^(exp),which is close to the theoretical value μ_(eff)^(theo).The magnetic entropy change(-Δ_(SM)),was determined by em ploying the thermodynam ic Maxwell's relation.At μ_0H=5 T and near T_(N),ΔS_(M)^(Max) and relative cooling power(RCP) exhibit large values of 33.7 J/(kg·K) and 238 J/kg,respectively.The large magnitude of-Δ_(SM) and RCP show that the EuRhO_(3) compound could be a potential candidate to be used in cryogenic magnetic refrigeration.展开更多
This works aims at preparing at room stable Na2FeO4 and tracking its degradation over time. The synthetic, during this step, was carried out by electrochemical method. The latter was given maximum focus because of its...This works aims at preparing at room stable Na2FeO4 and tracking its degradation over time. The synthetic, during this step, was carried out by electrochemical method. The latter was given maximum focus because of its simplicity and the high degree of purity of the resulting product with respect to wet and dry method. This paper reviews the development of the electrochemical method applied to the synthesis of stable at room Na2FeO4, optimizing the parameters impacting the performance of the oxidation of iron(II) in to iron(VI) in alkaline NaOH, saturated at a temperature of 61°C and a current density of 1.4 A/dm2, in order to simplify the synthesis process, to minimize the cost and to improve the production of iron(VI) to meet the growing demand of ferrate(VI) useful for water treatment. The supervision of the degradation of synthesized Na2FeO4 shows its stability over a period of 10 months, which makes storage and transport easier. The phases obtained were characterized by IR spectrometry, X-ray, M?ssbauer, spectroscopy and thermogravimeric analysis.展开更多
文摘The structure and chemical durability in the vitreous part of the system 60P2O5-2Cr2O3-xFe2O3-(38 - x)Na2O phosphate glasses (with 3 ≤ x ≤ 33 mol%) were investigated using various techniques such as IR spectroscopy, X-ray diffraction and M?ssbauer spectroscopy. The presence of Cr2O3 and the increase of Fe2O3 at the expense of Na2O in the glass network lead to a large number of covalent and rigid Fe-O-P and Cr-O-P bonds. The infrared and XRD spectra indicate a radical change of structure and show that the increase of the Fe2O3 content favors the depolymerization of the vitreous network towards pyrophosphate chains. The presence of Cr2O3 in the glass seems to favor the covalent Cr-O-P bonds linked to the most probable cyclic metaphosphate chains. However, when the Fe2O3 content increases (≥23 mol%), its impact on the glass network is stronger than that of Cr2O3. The infrared and XRD spectra indicate a radical change of structure and show that the increase in Fe2O3 content favors the depolymerization of the vitreous network to short pyrophosphate chains. The results of M?ssbauer spectroscopy indicate the presence of both Fe (III) and Fe (II) ions which occupied more or less deformed octahedral sites. The growth of the glass transition temperature (Tg) with the increase of the iron oxide in the vitreous network, leads to an improvement of the glass rigidity. This explains the decrease of the ionic radius of the iron and the reinforcement of the interconnection of the chains of vitreous networks. The structure of sodium-chromium-iron phosphate glasses can be considered largely as pyrophosphate units linked to ferric and ferrous ions in octahedral or deformed octahedral coordination. The dissolution rate is 200 times lower than that of the silicate glasses.
文摘We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have+4 state.EuRhO_(3) powders are found to be antiferromagnetic with a second order magnetic transition at Neel temperature(T_(N)=2.9 K).Analysis of the magnetic susceptibility versus temperature data in terms of the Curie=Weiss law:(χ=C/(T-θ_(W))) for T>T_(N),yields θ_(W)=-3.1 K and effective magne tic moment μ_(ff)^(exp),which is close to the theoretical value μ_(eff)^(theo).The magnetic entropy change(-Δ_(SM)),was determined by em ploying the thermodynam ic Maxwell's relation.At μ_0H=5 T and near T_(N),ΔS_(M)^(Max) and relative cooling power(RCP) exhibit large values of 33.7 J/(kg·K) and 238 J/kg,respectively.The large magnitude of-Δ_(SM) and RCP show that the EuRhO_(3) compound could be a potential candidate to be used in cryogenic magnetic refrigeration.
文摘This works aims at preparing at room stable Na2FeO4 and tracking its degradation over time. The synthetic, during this step, was carried out by electrochemical method. The latter was given maximum focus because of its simplicity and the high degree of purity of the resulting product with respect to wet and dry method. This paper reviews the development of the electrochemical method applied to the synthesis of stable at room Na2FeO4, optimizing the parameters impacting the performance of the oxidation of iron(II) in to iron(VI) in alkaline NaOH, saturated at a temperature of 61°C and a current density of 1.4 A/dm2, in order to simplify the synthesis process, to minimize the cost and to improve the production of iron(VI) to meet the growing demand of ferrate(VI) useful for water treatment. The supervision of the degradation of synthesized Na2FeO4 shows its stability over a period of 10 months, which makes storage and transport easier. The phases obtained were characterized by IR spectrometry, X-ray, M?ssbauer, spectroscopy and thermogravimeric analysis.
