Oxidation mechanism of Ni−P alloys

The powders of Ni?P alloys containing 13% of phosphorus were obtained by precipitation from the solution. The oxidation of Ni?P alloys in polythermal conditions was studied. It was found that oxidation of Ni?P alloys goes through stages and that intermediate products of the oxidation are: Ni₂P and Ni₂P₂O₇. The final products of oxidation process are NiO and Ni₃(PO₄)₂. The sequence of chemical reactions describing the oxidation of Ni?P alloys was proposed.     

Phase transformations in Al-Zn alloys solidifying at various rates

The influence of the alloying elements magnesium, copper and silicon on phase transformations in Al-60 wt% Zn alloy solidified at rates from 0.4 up to 65 deg/s has been investigated by means of DTA method.The dendritic segregation of zinc in the solid solution manifested itself by changes of the shape of the respective parts of the cooling or heating curves between the solidus and liquidus temperatures. The appearance of non-equilibrium transformations has been recorded as peaks in the last stage of crystallization.The shift of liquidus and eutectic temperatures in the direction of lower temperatures was observed in dependence on the cooling rate.Thermal analysis carried out at various cooling rates revealed nonequilibrium transformations at higher velocities. The occurrence of such effects was confirmed using X-ray microanalysis.

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Zusammenfassung Mittels DTA wurde der Einfluß der Legierungselemente Magnesium, Kupfer und Silizium auf Phasenumwandlungen in Al-60m% Zn-Legierungen mit Erstarrungsgeschwindigkeiten zwischen 0,4 und 65 K/s untersucht.Die dentritische Segregation von Zink in Mischkristallen macht sich durch Unterschiede des Verlaufes der jeweiligen Abschnitte der Abkühloder Aufheizkurven zwischen Solidus- und Liquidustemperaturen deutlich. Das Auftreten von Nicht-Gleichgewichts-Umwandlungen wurde als Peak im letzten Abschnitt der Kristallisierung aufgezeichnet.Die Verschiebung von Liquidustemperaturen und Eutektika in Richtung niedriger Temperaturen wurde als Funktion der Kühlgeschwindigkeit beobachtet.Die bei verschiedenen Kühlgeschwindigkeiten durchgeführte Thermoanalyse deckte das Auftreten von Nicht-Gleichgewichts-Umwandlungen bei höheren Geschwindigkeiten auf. Das Auftreten solcher Effekte wurde durch Anwendung von Röntgen-Mikroanalyse bekräftigt.

     

铀合金动态力学性能的研究

本文利用分离式霍布金生压杆研究了四种国产铀合金的动态力学性能,给出了这些材料随应变率和环境温度变化的本构关系。实验结果表明,国产铀合金具有与钨合金相当的动态强度,是钨穿甲弹中弹芯材料的极好替代物。     

Structural evolution of Co clusters on Cu90Co10 upon annealing

A granular alloy, composed of cobalt embedded in a copper matrix, was studied by using EXAFS and magnetotransport measurements as function of annealing parameters (temperature and annealing time). The results suggest that different annealing routes can reach the same final state. For annealing temperatures up to 450°C, the results indicate the coalescence of cobalt atoms, resulting in magnetic particles with increasing size. On the other hand, the annealing at 500°C shows a rapid formation of cobalt particles and then the re-dissolution of cobalt atoms in the copper matrix.     

197Au Mössbauer Study of Bimetallic Nanoparticles Prepared by Sonochemical Technique

Mössbauer measurements with circularly polarized radiation were performed on a nanocrystalline, disordered Fe₄₈Al₅₂ alloy. The analysis of the data for various polarization states resulted in the characterization of the hyperfine magnetic field distribution and the dependence of the average z-component of hyperfine field on the chemical environment. An increasing number of Al in the first coordination shell causes not only a decrease of magnetic moments but also introduces noncollinearity.     

Hysteretic behavior of Fe0.9−qMn0.1Alq-disordered alloys: a Monte Carlo study

In this work we have simulated the Fe_0.9−qMn_0.1Al_q alloy series with Al contents ranging from 10 up to 50 at%, and for several system sizes. In the simulation, the atoms are randomly distributed on a body-centered cubic according to the atomic disorder achieved through quenching techniques for the experimental samples. In computing the thermodynamic quantities such as the magnetization per site as a function of an external applied magnetic field, we have employed a Monte Carlo algorithm based on a Metropolis dynamics implemented with a random site-diluted Ising model. In this model, we have taken into account nearest-neighbor interactions for which both the ferromagnetic (Fe–Fe) and antiferromagnetic (Fe–Mn, Mn–Mn) interactions are present. From the simulation of the hysteresis loops at room temperature, the remanence and the coercive force as a function of the Al concentration have been obtained. Finally, a comparison with the previous experimental data on coercivity obtained by means of vibrating sample magnetometry is also carried out and discussed.     

Finite-size calculations of FQHE states at filling ν=1/2

Summary We present the results of numerical calculations, performed in the spherical geometry, of FQHE states ofN≤12 electrons in the lowest Landau level at filling ν=1/2. The extrapolated value for the energy per particle is −0.469±0.005, in the usual unitse ²/a ₀. Densities and pair correlation functions of the ground states are computed. The pair correlations are ?Wigner-crystal-like?, with maxima corresponding to regular polyhedra. ForN=4, 8 and 10 we find that the system presents a broken rotational invariance which generalizes the broken particle-hole symmetry already known in different gauges. Quasi-particles, quasi-holes and the ?exciton? spectrum are computed, and some microscopic wave functions are examined. The quasi-particles and the quasi-holes are not localized; this suggests a possible ?deformability? of the system.

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Riassunto Si presentano risultati di alcuni calcoli numerici, eseguiti usando la geometria sferica, di stati FQHE diN≤12 elettroni nel livello di Landau piú basso a ?riempimento? ν=1/2. Il valore estrapolato dell'energia per particella risulta pari a −0.469±0.005, nelle usuali unitàe ²/a ₀. Si calcolano la funzione densità e la funzione di correlazione di coppia corrispondenti allo stato fondamentale. Le funzioni di correlazione di coppia sono ?tipo cristallo di Wigner? con massimi corrispondenti ai poliedri regolari. PerN=4, 8 e 10 noi troviamo che il sistema presenta una simmetria rotazionale rotta che generalizza la rottura della simmetria particella-buca che era già nota in altre scelte di gauge. Si calcolano le quasi-particelle, le quasi-buche e lo spettro degli ?eccitoni?, e si esaminano alcune funzioni d'onda microscopiche. Le quasi-particelle e le quasi-buche non sono localizzate; questo suggerisce una possibile ?deformabilità? del sistema.

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Резюме Мы предлагаем результаты численных вычислений, вьшолненных в сферической геометрии, FQHE состояний дляN≤12 электронов на низшем уровне Ландау при заполнении ν=1/2. Экстрополированная величина энергии на одну частицу составляет −0.469±0.005, в обыкновенных единицахe ²/a ₀. Вычисляются функции плотности и функции парных корреляций для основных состояний. Функции парных корреляций оказываюгся ?подобны кристаллу Вигнера? с максимумами, соответствующими обычным многогранникам. ДляN=4,8 и 10 мы получаем, что рассматриваемая система представляет нарушенную симметрию ?частица-дырка?, уже известную в других калибровках. Вычисляются квази-частицы, квази-дырки и спектр ?экситонов?. Исследуются некоторые микроскопические волновые функции. Квази-частицы и квази-дырки не локализованы, что предполагает возможность ?деформируемости? системы.

     

Elementary excitations for the Anderson model at finite temperatures

The elementary excitation spectrums for the Anderson model at finite temperatures are calculated by using the Bethe-ansatz solution. The formulation is based on the method of Yang and Yang, which was developed for the one-dimensional boson systems with the -function type interaction. We obtain the temperature dependence of the spin and the charge excitation spectrums. When the impurity level lies deeply from the Fermi level and the Coulomb interaction is suitably large, the resonant peak structure develops in the low energy region of the spin excitation spectrum and the hump structure grows around the impurity level of the charge excitation spectrum with decreasing temperature. Received: 21 January 1998 / Accepted: 17 March 1998     

ICP-AES法测定镍基高温合金中16个元素的方法研究

该方法采用ICP-AES法对镍基高温合金中16个元素进行了测定,系统研究了基体元素和共存元素对分析元素谱线的光谱干扰情况,进行了分析线的选择,测定了方法检出限,通过准确度试验和精密度试验,表明该方法准确、可靠、简便、快速。