Short range ordering and phase separation in rapidly quenched Ni80 57Fe1P19 amorphous alloys solution treated at different temperatures

Electrochemical measurements and Mössbauer spectroscopy were used to study a rapidly quenched Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloy solution treated between 920 and 1500 °C. Different short range orderings were shown in amorphous alloys solution treated at different temperatures. This finding can be associated with phase separation occurring in the liquid state. This phase separation can be inherited in slightly relaxed amorphous state.     

Study of the crystallization kinetics in amorphous Fe83P17 alloy

The crystallization kinetics of Fe₈₃P₁₇ amorphous alloy has been studied by Mössbauer spectroscopy and X-ray diffractometry. The samples were annealed isothermally at two different temperatures (315 °C and 325 °C). During isothermal annealing of the samples three phases were observed: crystalline Fe₃P phase, crystalline -Fe phase and the amorphous phase. The value of the Avrami exponent was found to be about 2.0 at each annealing temperature. This suggests that the growth rate of the crystals is controlled by volume diffusion and the nucleation rate decreases during crystallization. The activation energy obtained for the overall crystallization process was 193±43 kJ mol^–1.     

Mullite Fibre Mats by a Sol-Gel Spinning Technique

Fine grained, microcrystalline mullite (Al_4+2x Si_2–2x O_10–x) fibre mats with a web-like structure were fabricated by a sol-gel spinning technique using a multi-orifice spinneret. Points of contact in gel fibre mats helped in the formation of a web-like fibrous body having reasonable strength and very little dust formation after calcination. Strong and resilient fibres with diameters in the range 3–12 m were obtained by a single-step sol-gel method from spinnable sols devoid of organics as the binder aid. Crystallization of -alumina and mullite at about 900°C and 1250°C, respectively was confirmed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Thermogravimetry (TG) indicated the removal of most of the volatiles at about 500°C accompanied by a weight loss of about 48%. Scanning electron microscopy (SEM) shows the presence of small grains (80–150 nm in size) in the fibres calcined at 1250°C. Fourier transformed infrared spectroscopy (FTIR) indicated the sequence of transformations taking place during heat-treatment of gel fibres at different temperatures. The individual fibres in the mats calcined at 1250°C exhibited a tensile strength of 1300–1600 MPa.     

Mössbauer studies in thermally treated iron-samarium mixed oxide system

Mössbauer spectroscopy and X-ray diffractometry have been used to study Sm–Fe mixed oxides (with different SmFe atomic ratios) annealed at 550, 850, 1000 and 1250 °C. The room temperature Mössbauer spectra can be interpreted in terms of one, two or three sextets and in some cases by an additional doublet depending on the composition and the heat treatment. The sextets have been associated with SmFeO₃ perovskite, Sm₃Fe₅O₁₂ garnet and -Fe₂O₃ hematite. These results are in agreement with those of X-ray diffractometric measurements, which give a clear, evidence of the presence of these phases.     

Phase separation and structure transition of undercooled Fe75Cu25 melts

The rapid quenching processes of Fe₇₅Cu₂₅ melt at different cooling rate are investigated by molecular dynamics simulation based on embedded atom method. Fe₇₅Cu₂₅ alloy ribbons are prepared by single roller rapid quenching. Liquid–liquid phase separation (LLPS) happens and the Cu-rich droplets embedded in the Fe-rich matrix can be observed both in simulation and experiments. Stronger interaction of homogeneous atom pairs than that of heterogeneous atom pairs leads to LLPS, controlled by nucleation growth mechanism in Fe₇₅Cu₂₅ melt, and quite different from that in Fe₅₀Cu₅₀ melt, which is controlled by spinodal decomposition mechanism. During the crystallisation process after LLPS, the new nuclei form only in Fe-rich regions; various multiply twinning boundaries are formed due to the minimisation of interfacial energy and only the homogeneous atomic stacking shows mirror symmetry along twinning boundary. The results provide atomic-scale understanding of phase separation mechanism and structure transition of Fe₇₅Cu₂₅ melt during rapid cooling processes.     

Die Bildung von kristallinem Böhmit in gemeinsam gefällten AlFe(III)-Hydroxiden unter hydrothermalen Bedingungen

Under mild hydrothermal conditions originally amorphous aluminium hydroxide coprecipitated with iron(III)ions as Al_0,5Fe_0,5(OH)₃ transforms into aluminium hydroxide crystalline phases which are not observed in products of ageing of pure aluminium hydroxide.By X-ray diffraction analysis, IR spectroscopic studies and microscopic observations it has been found that due to the presence of iron(III) hydroxide it is possible to stabilize the trihydoxide of aluminium i.e. bayerite until 130–140°C. Moreover, with increasing temperature well crystallized boehmite is obtained instead of the usually formed pseudoboehmite.Experiments revealed that the formation of crystalline boehmite does not take place as a process of pseudoboehmit crystallites growth but only as a result of bayeriteboehmite transformation.

     

Phase equilibrium and intermediate phases in the Eu–Sb system

Rapid heating rate thermal analysis, X-ray diffraction, fluorescence spectrometry, and differential dissolution method were used to study the high-temperature phase equilibrium in the Eu–Sb system within the composition range between 37 and 96 at% Sb. The techniques were effective in determination of the vapor–solid–liquid equilibrium since intermediate phases except Eu₄Sb₃ evaporated incongruently after melting. A thermal procedure was developed to determine the liquidus and solidus lines of the T−x diagram. Six stable phases were identified: two phases, EuSb₂ and Eu₄Sb₃, melt congruently at 1045±10 °C and 1600±15 °C, the Eu₂Sb₃, Eu₁₁Sb₁₀, Eu₅Sb₄, and Eu₅Sb₃ phases melt incongruently at 850±8 °C, 950±10 °C, 1350±15 °C, and 1445±15 °C, respectively. The exact composition shifting of Sb-rich decomposable phases towards Eu₄Sb₃, the most refractory compound, was determined. The topology of the Eu–Sb phase diagram was considered together with that of the Yb–Sb system.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Mössbauer study of ferric oxide particles as products of thermal decomposition of iron/III/benzoate

The products of the thermal decomposition in air of iron/III/benzoate [Fe₃/C₆H₅COO/₆/OH/₂]OH.H₂O have been studied using conventional thermal analysis, X-ray diffraction measurements and mainly Mössbauer spectroscopy. The decomposition occurs in the temperature range 200–350°C. It was possible to identify benzoic acid and ferric oxide as final products. Above 300°C, the observed ferric oxide showed a particle size distribution, which depends on the heating temperature and the heating time interval, as evidenced by the following detected phases: superparamagnetic -Fe₂O₃ and magnetically ordered state with crystal structure of the phases -Fe₂O₃ and -Fe₂O₃. Also, two iron/III/ benzoate complexes having four and three ligands within the coordination sphere are suggested as intermediate products.     

Thermogravimetric studies of the synthesis of cas from gypsum, CaSo4·2H2O and phosphogypsum

Using a heating rate of 2°C min^–1, CaS reacts with oxygen in air from 700°C to form CaSO₄, with a complete conversion at 1100°C. Synthesis of CaS from the reaction between CaSO₄ containing compounds and carbon compounds in air would not be possible, as the carbon reacts from 600°C with oxygen in the air to give CO₂. Heating stoichiometric amounts of carbon and pure CaSO₄, synthetic gypsum or phosphogypsum in a nitrogen atmosphere, results in the formation of CaS from 850°C. Using a heating rate of 10°C min^–1, the formation of CaS is completed at 1080°C. Addition of 5% Fe₂O₃ as a catalyst lowers the starting temperature of the reaction to 750°C. Activation energy values at different fraction reaction values () differ between 340 and 400 kJ mol^–1. The relationship between the activation energy values and conversion () indicates that the reaction proceeds via multiple steps.     

Structural-Chemical Transformations of Two-Dimensional Iron-Oxygen Nanostructures in the Course of Transport Reduction

Transport reduction was shown to allow finely controlling the Fe^{+ 3}/Fe^{+ 2} ratio in iron-oxygen two-dimensional nanostructures (nanolayers, thickness 3-15 Å) on silica. It was found by Müossbauer spectroscopy that isolated surface iron-oxygen groups >-Si-O-Fe(OH)₂ and (>-Si-O-)₂FeOH are not reduced at 400-600°C, which is explained by their covalent bonding with silica. The transport reduction of samples with applied nanolayers (one and four) at T 600°C was shown to form bulk phases [iron(II) silicate and metallic iron] on the silica surface. The features of structural-chemical transformations on transport reduction of iron-oxygen nanolayers on supports are primarily associated with the specifics of phase formation in nanostructures.     

Analysis of the Glass-Forming Ability of Fe–Er Alloys,Based on Thermodynamic Modeling

The Fe–Er phase diagram and thermodynamic properties of all its phases are assessed by means of self-consistent analysis. To refine the data on phase equilibria in the Fe–Er system, an investigation is performed in the 10–40 at % range of Er concentrations. The temperature–concentration dependences of the thermodynamic properties of a melt are presented using the model of ideal associated solutions. Thermodynamic parameters of each phase are obtained, and the calculated results are in agreement with available experimental data. The correlation between the thermodynamic properties of liquid Fe–Er alloys and their tendency toward amorphization are studied. It is shown that compositions of amorphous alloys prepared by melt quenching coincide with the ranges of concentration with the predominance of Fe₃Er and FeEr₂ associative groups that have large negative entropies of formation.     

TMDSC and Atomic Force Microscopy Studies of Morphology and Recrystallization in Polyesters Including Oriented Films

The thermal and crystal morphological properties of poly[ethylene teraphthalate] (PET) and poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) biaxially oriented films were compared to amorphous and other isotropic semi-crystalline samples. Crystal melting as a function of temperature was characterized by temperature modulated DSC (TMDSC) and found to begin just above the glass transition for both oriented films. About 75°C above the glass transitions, substantial exothermic recrystallization begins and continues through the final melting region in oriented films. The maximum in the non-reversing TMDSC signal for the oriented films signifies the maximum recrystallization exothermic activity with peaks at 248°C and 258°C for PET and PEN, respectively. The final melting endotherm detected was 260°C and 270°C for PET and PEN, and is shown by the TMDSC data and by independent rapid heating rate melting point determinations to be due to the melting of species recrystallized during the heating scan. The results are compared with TMDSC data for initially amorphous and melt crystallized samples. The volume fraction of rigid species (F_rigid=total crystal fraction plus rigid amorphous or non-crystalline species) were measured by TMDSC glass transition data, and contrasted with the area fraction of rigid species at the oriented film surface characterized with very high resolution atomic force microscopy (AFM) phase data. The data suggest that the 11 nm wide hard domains in PET, and 21 nm wide domains in PEN film detected by AFM consist of both crystal and high stiffness interphase species.This revised version was published online in November 2005 with corrections to the Cover Date.     

Der Dreistoff: Re-Fe-B

Zusammenfassung Die Aufteilung der Phasenfelder im Dreistoff: Re-Fe-B wird bei etwa 1100°C ermittelt. Es treten zwei ternäre Phasen auf (Re_0.31–0.87Fe_0.69–0.13)₂₃B₆ mit Cr₂₃C₆-Typ (-Phase) und (Fe_0.75–0.86Re_0.25–0.14)₃B mit Ti₃P-Typ. Ähnlich wie die -Phase besitzt auch die Mischphase (Fe,Re)₂B einen ausgedehnten homogenen Bereich, dagegen ist der Austausch Re/Fe in Re₃B, Re₇B₃ und FeB nicht so ausgeprägt.

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The equilibria of the ternary system: Re-Fe-B have been established at a section of 1100°C, two ternary phases being detected. The -phase, isotypic with Cr₂₃C₆, is characterized by an extended homogenous region (Re_0.31–0.87Fe_0.69–0.13)₂₃B₆; (Fe_0.75–0.86Re_0.25–0.14)₃B crystallizes with the Ti₃P-type. A large portion of iron can be substituted by rhenium within the Fe₂B-phase. In contrast, the metal-metal substitution is much smaller for the other binary borides.

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Mit 3 Abbildungen     

On the interaction of copper with defects in gallium arsenide

The behavior in gallium arsenide of copper introduced through the melt has been investigated. Measurements have been made on the electrical and photoluminescent properties of single crystals that had either been quenched from T_cryst, slowly cooled after crystallization or thermally annealed at 1100°C after completion of the growth. On quenching from T_cryst, formation of very shallow acceptors is observed. On slow cooling or annealing at 1100°C, acceptor levels are formed of the order of 0.12 and 0.02 eV. The concentration of carriers for both levels diminishes with lower temperatures of annealing and with concentration of copper added. The 0.12 eV level is assigned to the center (Cu_GaV_Ga)⁻.     

Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe₂O₃ films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe₂O₃ films are anisotropic. The birefringence values (n) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe₂O₃ (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.     

Electronic and magnetic structure of the polymeric system di-imidazolato iron(II)

The polymeric system di-imidazolato iron(II) is synthesized from the reaction of either ferrocene or cyclopentadienyl-irondicarbonyl with imidazole. From Mössbauer measurements in the temperature range 4.2 KT448 K we find two different iron sites in the compound, denoted byA andB, respectively with ratio [A]/[B] = 1.79±0.03. From the isomer shift values we conclude that both Fe ^A and Fe ^B are in the ferrous high-spin state. Below 13.95±0.10 K both subspectra are considerably broadened due to magnetic ordering. From the analysis of the magnetic spectra we derive for the main componentV _zz of the electric field gradient tensorV _zz ^A >0 andV _zz ^B <0. Additionally, we investigate the thermal decomposition of the compound by thermogravimetry in the temperature range 20 °CT 750 °C and by Mössbauer spectroscopy in the temperature range 20 °CT505 °C. The decomposition takes place in four steps. The first step between 20 °C and 190 °C is due to the loss of imidazole nonbonded to iron(II). Comparing the amount of iron with that of pure imidazolato iron(II) we find the formula FeIz₂+0.70 (±0.02) IzH, with Iz standing for doubly deprotonated and IzH for deprotonated imidazole. Step 2 (193 °C<T<235 °C) and step 3 (400 °C<T<500 °C) are found from both methods. Step 4 is above 500 °C. Heat treatment and vacuum conditions affect the thermal decomposition products.Isomer shifts ^A and ^B , and temperature dependent quadrupole splittings E _Q ^A and E _Q ^B are explained using a simple ligand field picture for orbital splittings and occupancies of quasi-tetrahedrally (A) and quasi-octahedrally (B) coordinated ferrous high-spin compounds. Using finally the experimental ratio [A]/[B] = 1.79 we derive for the over-all chemical formula (1.79 Fe ^A Iz_4/2+Fe ^B Iz_4/2+2 IzH) _n = (FeIz₂+0.71 Iz) _–n in agreement with the result which we derived from investigating the thermal decomposition of our compound.Supported by Deutsche Forschungsgemeinschaft     

Synthesis and thermal decomposition of antimony(III) oxide hydroxide nitrate

The thermal decomposition of the only known antimony nitrate antimony(III) oxide hydroxide nitrate Sb₄O₄(OH)₂(NO₃)₂, whose synthesis routes were reviewed and optimized was followed by TG-DTA under an argon flow, from room temperature up to 750°C. Chemical analysis (for hydrogen and nitrogen) performed on samples treated at different temperatures showed that an amorphous oxide hydroxide nitrate appeared first at 175°C, and decomposed into an amorphous oxide nitrate above 500°C. Above 700°C, Sb₆O₁₃ and traces of -Sb₂O₄ crystallized.Author to whom all correspondence should be addressed     

Mössbauer,FT-IR,and XRD study on the crystallization of highly functional tungstate and vanadate glasses

⁵⁷Fe-Mössbauer spectra of 38Na₂O·61WO₃·⁵⁷Fe₂O₃ glasses, heat treated at 355°C for 5–150 min, show a change of the coordination number of Fe³⁺ from 6 (FeO₆ octahedra) to 4 (FeO₄ tetrahedra), as a result of the formation of Na₂W₂O₇ (Na₂O/WO₃=1/2), Na₂WO₄ (Na₂O/WO₃=1.0), FeWO₄, and Fe₂WO₆ phases.⁵⁷Fe-Mössbauer spectra of 25K₂O·65V₂O₃·10Fe₂O₃ glasses show a drastic decrease of and after the heat treatment at 340°C for 10–2100 min, since a homogeneous crystallization took place without a phase separation. A KV₃O₈ phase with the K₂O/V₂O₅ ratio of 1/3 was precipitated, and the ratio was equal to the K₂O/(V₂O₅+Fe₂O₃) ratio of the original 25K₂O·65V₂O₃·10Fe₂O₃ glass.     

Non-Isothermal Crystallization Behavior of β-Nucleated Isotactic Polypropylene/Multi-Walled Carbon Nanotube Composites with Different Melt Structures

In this study, the melt structure status of isotactic polypropylene/multi-walled carbon nanotubes composites (iPP/MWCNTs) nucleated with β-NA was tuned by changing the fusion temperature T _f . The non-isothermal crystallization behavior and subsequent melting behavior of the sample were studied in detail. The results showed that under different cooling rates (2, 5, 10, 20 and 40 deg/min), the crystallization temperature increased gradually with the decrease of T _f , meanwhile, when T _f was in the temperature range of 166–174°C where ordered structures survived in the melt (named Region II), the crystallization activation energy was significantly lower compared with the case T _f > 174°C or T _f < 166°C. On the subsequent melting curves, the occurrence of the melt structure can be observed at all the cooling rates studied; the location of the Region II was constant, which did not show dependency on the cooling rates; low cooling rate and relative low T _f within 166–174°C encouraged the formation of more β-phase triggered by melt structure.