Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm₂Fe₁₇N_x, prepared by the nitrogenation of Sm₂Fe₁₇ powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm₂Fe₁₇N_x. It was found that there were large differences in thermal behavior between the starting Sm₂Fe₁₇, crystalline Sm₂Fe₁₇N_x (x≈1.7) and amorphous Sm₂Fe₁₇N_x(x～7). The thermal decomposition behavior of Sm₂Fe₁₇N_3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

Effect of Ag-doping of nanosized FeMgO system on its structural, surface, spectral, and catalytic properties

The effects of Ag-doping on the physico-chemical, spectral, surface, and catalytic properties of the FeMgO system with various Fe₂O₃ loadings were investigated. The dopant (Ag) molar ratio varied between 0.01 % and 0.05 %. The techniques employed for characterisation of catalysts were TG/DTG, XRD, ESR, N₂ adsorption at ?196°C, and catalytic decomposition of H₂O₂ at 25?C35°C. The results obtained revealed that the investigated catalysts consisted of nanosized MgO as the major phase, apart from the MgFe₂O₄ and/or Fe₃O₄ phases. ESR result of the FeMgO system revealed the presence of paramagnetic species as a result of Ag-doping. The textural properties including SBET, porosity and St were modified by Ag-doping. The doping process with Ag-species improved the catalytic activity of the FeMgO system. Increasing the calcination temperature from 400°C to 800°C increased the catalytic activity (k*_{30 °C}) of 0.05 AgFeMgO in H₂O₂ decomposition by 21.2 times.     

Thallium alloys of the rare earth: Sm?TI Phase diagram and molar volumes of the rare earth thallides

The Sm? Tl system has been studied by differential thermal, metallographic and X-ray analyses. The following intermediate phases were observed: Sm₂Tl (decomposes at 1030 ± 10°C); Sm₅Tl₃ (decomposes at 1060 ± 10°C); SmTl (melting point, 1220 ± 20°C); Sm₃Tl₅ (decomposes at 940 ± 10°C); SmTl₃ (melting point, 870 ± 5°C). Three eutectics occur: β-Sm—Sm₂Tl (840 ± 10°C, 18.0 ± 0.5 at % Tl); Sm₃Tl₅—SmTl₃ (860 ± 5°C, 72.0 ± 0.5 at % Tl); SmTl₃—β-Tl (～303°C, greater than 99.5 at % Tl); there is an eutectoidal reaction at 760 ± 10°C and 10 ± 1 at % Tl (decomposition of β-Sm phase). Following crystal structures have been determined or confirmed: Sm₂Tl hexagonal hP6—Ni₂In-type, Sm₅Tl₃ tetragonal tI32—W₅Si₃-type, SmTl cubic cI2—W or cP2—CsCl-type, SmTl tetragonal tP4—AuCu I-type, Sm₃Tl₅ orthorhombic oC32—Pu₃Pd₅ like-type, SmTl₃ cubic cP4—AuCu₃-type. The characteristics of the phase diagram and the molar volumes of the Sm? Tl compounds are compared with those of other RE? Tl alloys and briefly discussed.     

The crystallization of anatase and the conversion to bronze-type TiO2 under hydrothermal conditions

When the anatase form of TiO₂ was heated at a constant rate of 6°C/min to 450°C it crystallized from hydrated amorphous TiO₂ gel at 170°C in pure water or at <150°C in NaOH solutions. The uptake of Na⁺ ions into crystallized anatase affected the reactions subsequent to this initial crystallization while only anatase crystals continued to grow with increasing temperature in pure water. Immediately after the nearly amorphous second stage at 325°C, conversion from colloidal anatase particles to square sheet-shaped bronze-type TiO₂ crystals began at 350°C and was complete at 425°C in 0.5 M NaOH. This conversion was considered to proceed via crystallographic shear rather than via dissolution and precipitation since this also happened with thermal treatment to 700°C in air.     

Investigation of the CeFe binary system

The CeFe binary system was investigated and an FeCe binary phase diagram was proposed. This system consists of

• 1.(i) two peritectic reactions, γ-Fe + L → Ce₂Fe₁₇ and Ce₂Fe₁₇ + L → CeFe₂, occurring isothermally at 1063°C and 925°C respectively;
• 2.(ii) a eutectic reaction, L → CeFe₂ + Ce, occurring isothermally at 592°C with eutectic containing 83.3 at.% Ce (92.6 wt.% Ce);
• 3.(iii) a peritectoid reaction, γ-Fe + Ce₂Fe₁₇ → α-Fe(Ce), occurring isothermally at 922 °C.

The solid solubility of cerium in iron in the temperature range 850–900 °C was found to be less than 0.04 at.% (0.1 wt.%). The Curie temperature of α-Fe(Ce) was slightly lowered with increasing cerium content in solid solution.     

Biosynthesis and Photocatalytic Properties of SnO<Subscript>2</Subscript> Nanoparticles Prepared Using Aqueous Extract of Cauliflower

This work reports the biosynthesis of Sn(OH)₂ using aqueous extract of fresh cauliflower (Brassica oleracea L. var. botrytis), and the subsequent preparation of SnO₂ nanoparticles at two different annealing temperatures of 300 and 450 °C for 2 h. The obtained SnO₂ nanoparticles were denoted as S1 and S2 for the samples prepared at 300 and 450 °C, respectively. XRD analysis identified rutile tetragonal phase of SnO₂ nanoparticles and TEM results gave a quasispherical and spherical morphologies for S1 and S2 respectively of the size range 3.62–6.34 nm. The optical properties were studied with UV–vis and photoluminescence (PL) spectroscopies, and the nanoparticles showed blue shift in their absorption edges. The observed emission peak in the PL spectra found around 419 nm is attributable to oxygen vacancies and defects. Photocatalytic activities of the nanoparticles (S1 and S2) were studied using methylene blue (MB) under ultraviolet light irradiation and the results reveal 91.89 and 88.23% degradation efficiency of MB by S1 and S2 respectively over a period of 180 min.     

Synthesis and characterization of CaTiO3-(Sm,Nd)AlO3 microwave ceramics via sol–gel method

0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ (CTSA) ceramic nanopowders were synthesized via sol–gel method using the ethylene diamine tetraacetic acid as a chelating agent. Thermal analysis, Fourier transform infrared spectroscopy and X-ray diffraction were used to character the decomposition of precursor and phase transformation process of derived oxide powders. Single phase and well-crystallized 0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ powders with particle size of 30–40 nm were obtained by calcination at 800 °C. Dense ceramic was successfully obtained from the ultrafine powders sintered at 1,325 °C, almost 100 °C lower than 1,415 °C required for conventional powders. Compared with those prepared by conventional solid-state method, the CTSA ceramics derived from sol to gel process sintered at a lower temperature showed better microwave dielectric properties of ε_r ~ 39, Q × f over 50,000 GHz and small τ_f ~ ?7.1 ppm/K.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal decomposition of Prussian blue under inert atmosphere

The thermal decomposition of Prussian blue (iron(III) hexacyanoferrate) under inert atmosphere of argon was monitored by thermal analysis from room temperature up to 1000?°C. X-ray powder diffraction and ⁵⁷Fe M?ssbauer spectroscopy were the techniques used for phase identification before and after sample heating. The decomposition reaction is based on a successive release of cyanide groups from the Prussian blue structure. Three principal stages were observed including dehydration, change of crystal structure of Prussian blue, and its decomposition. At 400?°C, a monoclinic Prussian blue analogue was identified, while at higher temperatures the formation of various polymorphs of iron carbides was observed, including an orthorhombic Fe₂C. Increase in the temperature above 700?°C induced decomposition of primarily formed Fe₇C₃ and Fe₂C iron carbides into cementite, metallic iron, and graphite. The overall decomposition reaction can be expressed as follows: Fe₄[Fe(CN)₆]₃·4H₂O????4Fe?+?Fe₃C?+?7C?+?5(CN)₂?+?4N₂?+?4H₂O.     

IR structural evidence of hydrotalcites derived oxidic forms

Ni–Al hydrotalcite-like compounds with the general formula [Ni_1−xAl_x(OH)₂](CO₃)_x/2⋅mH₂O, where 0.25≤x≤0.66, were synthesised using coprecipitation at a constant pH, and were treated hydrothermally. The structures of the oxidic forms obtained by calcination of the hydrotalcites at 450°C and 900°C, respectively, were investigated using X-ray diffraction and, mainly, IR and UV–VIS spectroscopy. A NiO phase was identified by XRD in all calcined samples; an additional oxidic phase — the nickel spinel, NiAl₂O₄ — developed at 900°C. IR spectroscopy results gave supplementary information about the incipient, local organisation of cations in the interstices of the oxygen atoms lattice. IR spectra were different, depending on the samples' composition. In case of the HT precursors calcined at 450°C a structure like a transition alumina (γ-Al₂O₃) was found as a main oxidic phase in samples with a high Al-content; IR spectra of the samples with a high Ni content evidenced NiO as the main oxidic phase; in case of these latter samples, the formation of an oxidic structure with a spinel-type local order was identified at this temperature. This structure developed to an inverse nickel spinel oxidic phase at 900°C, as shown by the IR absorption bands. The NiO structure in the samples with a high Ni content at 450°C was found also in the oxides obtained by calcination at 900°C. The spinel-type local order was also observed by UV–VIS spectroscopy in case of the HT precursors calcined at 450°C, by the presence of both absorption bands of the tetrahedral and octahedral Ni(II) ions in the Al₂O₃ lattice and of octahedral Ni(II) ions in the NiO lattice. The same absorption bands were found also in the samples calcined at 900°C, proving that the NiAl₂O₄ spinel identified has a partial inverse structure, with the Ni(II) ions both in tetrahedral and octahedral crystalline fields. Our found structural data were in accord with the models proposed in the literature.     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7�C�� pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7?C?? are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide $ {p_{{{{\rm{O}}_{{2}}}}}} $ range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500?C300?°C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045?S/m under wet oxygen at 500?°C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500?°C and protons becoming increasingly important below this temperature.     

Heat capacity and thermodynamic functions of theRFe2 compounds (R =Gd,Tb, Dy,Ho, Er,Tm, Lu) over the temperature region 8 to 300 K

Experimental heat capacity data for the Laves phaseRFe₂ intermetallic compounds (R =Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been determined over the temperature range 8 to 300 K. The error in these data is thought to be less than 1%. Smoothed heat capacity values and the thermodynamic functions, (H°_T ? H°₀) and S°_T, are reported throughout the temperature range for theRFe₂ series. In addition, (G°₂₉₈ ? H°₀) at 298 K is reported for all theRFe₂ compounds. These data were analyzed and it was shown that the maxima in the thermodynamic functions near HoFe₂ are due to the magnetic contribution of the lanthanide element. The lattice contribution to the entropy at 300 K was estimated, and from this quantity the Debye temperature was calculated to be about 300 K, which is in good agreement with the low-temperature heat capacity. Furthermore, this analysis indicates that the apparent electronic specific heat constants, γ′, for TbFe₂, DyFe₂, and HoFe₂, reported earlier, are in error.     

The effect of calcination on morphology of phosphate coating and microstructure of sintered iron phosphated powder

Carbonyl iron powder was coated with phosphate layer using phosphating precipitation method. The phosphated powder was dried at 60 °C for 2 h in air and heat treated by calcination at 400 and 800 °C for 3 h in air. Cylindrical specimens density of ~6.5 g.cm^?3 based on iron phosphated powder calcined at 400 °C were sintered at 820, 900, 1110 °C in N₂ + 10%H₂ atmosphere and 1240 °C in vacuum for 30 min. The morphology and phase composition of the phosphate coating and sintered compacts were studied by scanning electron microscopy, atomic force microscopy (AFM) and X‐ray diffraction (XRD) analysis. Gelatinous morphology of dried phosphate coating (thickness of ~100 nm) containing nanoparticles of iron oxyhydroxides and hydrated iron phosphate was observed. From XRD, diffractogram indicated the presence of goethite α‐FeOOH, lepidocrocite γ‐FeOOH and ludlamite Fe₃(PO₄)₂.4H₂O. The calcined phosphate coating (thickness of ~ 400 nm) contained non‐homogeneous consistency of α‐Fe₂O₃ layer on iron particles, an inter‐layer of amorphous FePO₄ and Fe₃O₄ top layer. The transformation to crystalline FePO₄ structure occurred during calcination at 800 °C with the presence of α‐Fe₂O₃ forming a light top zone (rough morphology). The microstructure of compacts sintered in solid state at temperatures up to 900 °C has retained composite network character. A fundamental change in microstructure due to the liquid phase sintering occurred after sintering at temperatures of 1100 and 1240 °C. It was confirmed that the microstructure complex consists of spheroidized α‐Fe and α‐Fe₂O₃ phases surrounded by solidified liquid phase consisting various phosphate compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

Catalytic decomposition of CFC‐12 on solid acids SO42‐/MxOy (M?Zr,Ti, Sn,Fe, Al)

The catalytic decomposition of dichlorodifluoromethane (CFC‐12) in the presence of water vapor on a series of SO₄^2?‐promoted solid adds was investigated. CFC‐12 was decomposed completely on SO₄^2?/ZrO₂, SO₄^2?/TiO₂, SO₄^2?/SnO₂, SO₄^2?/ Fe₂O₃ and SO₄^2–/Al₂O₃ at 265°C, 270°C, 325°C, 350°C and 325°C, respectively, and the selectivity to by‐products was neglectable. Obvious deactivation was found on SO₄^2?/ZrO₂ and SO₄^2?/Al₂O₃, during several hours on stream, while the catalytic activity was maintained on SO₄^2?/TiO₂, SO₄^2?/SnO₂ and SO₄^2?/Fe₂O₃ for 240 h on stream.     

Reaction mechanism in the formation of perovskite Pb(Fe1/2Nb1/2)O3 by calcining of mixed oxides (CMO)

A calcining at 300°C and sintering process were proposed to obtain a pure perovskite phase Pb(Fe_1/2 Nb_1/2)O₃ from a 4PbO/Nb₂O₅/Fe₂O₃ mixture, which is calcined at 300°C for several days and sintered at various temperatures for 2h; the resultant powder was air quenched. The X-ray powder diffraction pattern of the sintered sample is carefully analyzed to identify intermediate phases. The effects of calcining at 300°C and sintering on obtaining PFN are based on the deformation of Pb₅Fe₄Nb₄O₂₁. A reaction mechanism for the calcining cycle of Pb(Fe_1/2 Nb_1/2)O₃ is proposed.     

Sm2O3Ga2O3 and Gd2O3Ga2O3 phase diagrams

Four definite compounds exist in the Sm₂O₃Ga₂O₃ binary phase diagram, namely: Sm₃GaO₆, Sm₄Ga₂O₉, SmGaO₃, and Sm₃Ga₅O₁₂. The $\text{3}\text{1}$ compound is orthorhombic (space group Pnna - Z.4) with the cell parameters: a = 11.40₀Å, b = 5.51₅Å, c = 9.07Å and belongs to the oxysel family. Sm₃GaO₆ and SmGaO₃ melt incongruently at 1715 and 1565°C; Sm₄Ga₂O₉ and Sm₃Ga₅O₁₂ have a congruent melting point at 1710 and 1655°C. With regard to the Gd₂O₃Ga₂O₃ system three definite compounds have been identified: Gd₃GaO₆, Gd₄Ga₂O₉, and Gd₃Ga₅O₁₂. Only the garnet melts congruently at 1740°C with the following composition: Gd_3.12Ga_4.88O₁₂. Gd₃GaO₆, and Gd₄Ga₂O₉ melt incongruently at 1760 and 1700°C. GdGaO₃ is only obtained by melt overheating which may yield an equilibrium or a metastable phase diagram.     

On the oxidation behaviour of monolithic TiB2 and Al2O3-TiB2 and Si3N4-TiB2 composites

In view of the susceptibility of TiB₂ to oxidation, the thermal stability of monolithic TiB₂ and of Al₂O₃-30 vol% TiB₂ and Si₃N₄-20 vol% TiB₂ composites was investigated. The temperature at which TiB₂ ceramic starts to oxidize is about 400°C, oxidation kinetics being controlled by diffusion up toT≈900°C and in the first stage of the oxidation at 1000°C and 1100°C (up to 800 min and 500 min respectively), and by a linear law at higher temperatures and for longer periods. Weight gains in the Al₂O₃-TiB₂ composite can be detected only at temperatures above ≈700°C and the rate governing step of the oxidation reaction is characterized by a one-dimensional diffusion mechanism atT=700°C andT=800°C and by two-dimensional diffusion at higher temperatures. Concerning the Si₃N₄-TiB₂ composite, three different oxidation behaviours related to the temperature were observed, i.e. up to ≈1000°C the reaction detected regards only the second phase; at ≈1000<T<≈1200°C, the diffusion of O₂ or N₂ through an oxide layer is proposed as the rate-governing step; atT〉=1200°C, a linear kinetic indicates the formation of a non protective scale.     

Low temperature relaxation in polypyromellitimide

The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N₂. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N₂. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N₂. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain.     

Magnetic properties and BSA adsorption of nano-Fe-embedded BaFe12O19 porous microfibers via organic gel-thermal selective reduction process

Magnetic nano-Fe-embedded BaFe₁₂O₁₉ (NFEB) porous microfibers with diameters about 1?C5???m were prepared by the organic gel-thermal selective reduction process. The NFEB porous microfibers were formed after reduction of the precursor Fe₂O₃?CBaFe₁₂O₁₉ microfibers at 350?°C for 1?h. The precursor Fe₂O₃?CBaFe₁₂O₁₉ microfibers were obtained by calcination of the gel fibers. In the NFEB porous microfibers, the cubic ??-Fe particles with size about 300?nm are homogeneously embedded in the hexagonal plate-like barium ferrite and the pore sizes are around 50?C150?nm. The magnetic properties of these NFEB porous microfibers are influenced by the mass ratio of ??-Fe/BaFe₁₂O₁₉ and reduction conditions. The NFEB porous microfibers with the designed soft (??-Fe)/hard (BaFe₁₂O₁₉) mass ratio of 1/2 obtained at 375?°C for 1?h have the enhanced saturation magnetization (M _sh ) of 73.9?Am²?kg^?1, coercivity (H _c ) of 81.6?kAm^?1 and remanence (M _r ) of 34.2?Am²?kg^?1, compared to the single phase of BaFe₁₂O₁₉ and ??-Fe microfibers. This enhanced magnetic properties can be attributed to the exchange-coupling interactions. The NFEB porous microfibers exhibit a higher BSA adsorption capability than each single phase of ??-Fe microfibers and BaFe₁₂O₁₉ microfibers. The BSA adsorption is analyzed.