Application of thin-film DTA to amorphous selenium layers

A system of evaporated thin-film Ag-Bi thermocouples was used as a differential temperature sensor for DTA measurements. The crystallization of thin amorphous selenium layers was observed by means of this method. The presented method may be useful in studying the thermal transformations of thin films that have different compositions and various applications.

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Zusammenfassung Das System von aufgedampften Ag-Bi Dünnschicht-Thermoelementen wurde als Differentialtemperatursensor zu DTA-Messungen eingesetzt. Die Kristallisation dünner amorpher Selenschichten wurde durch diese Methode verfolgt. Die beschriebene Methode kann bei der Untersuchung thermischer Umwandlungen der dünnen Schichten verschiedener Zusammensetzungen Anwendung finden.

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Résumé Des thermocouples en films minces évaporés Ag-Bi ont été utilisés pour la détection de la différence de température en ATD. On a observé, par cette méthode, la cristallisation des couches minces de sélénium amorphe. La méthode présentée peut être utile dans l'étude des transformations thermiques des pellicules minces de compositions différentes et d'applications diverses.

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Ag-Bi , . . .

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The work was financially supported by the Ministry of Science, Higher Education and Technology, according to Contract No. MR-I-21.     

Thermal analysis and longtime stability of amorphous Co100−xBx alloys

Crystallization behaviour of amorphous Co_100?xB_x alloys (17 <x ≤ 40) has been investigated by differential thermal analysis (DTA) and dynamic temperature X-ray diffraction (DTXD) methods in the freshly prepared state and at a period of about eight years after preparation. The crystallization temperatures lie in the range 670 K–760 K. An average decrease of about 1.25 K/year over a period of eight years has been observed to take place in the crystallization temperatures of these materials. The value of heat of crystallization (ΔH _cr) and activation energy lie in the range 2.3 kJ/g-at – 5.9 kJ/g-at and 2.1 eV – 2.4 eV, respectively. The phases obtained at crystallization temperatures during DTXD analysis have been discussed.     

Application of DTA for controlling the heat treatment of E AlMgSi alloys

The phase changes in the solid state in E AlMgSi alloy are discussed. The dissolution and precipitation processes are investigated by DTA, and the results can be applied to control the technological parameters of dissolution heat treatments.

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Zusammenfassung Die Autoren erörtern die Phasenänderungen in festem Zustand in E AlMgSi-Legierungen. Die Lösungen- und Fällungsvorgänge werden mittels der DTA-Methode untersucht, wodurch die Versuchsegebnisse bei der Kontrolle der technologischen Parameter der Hitzebehandlung von Lösungen eingesetzt werden⁵ können.

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Résumé Etude par ATD des changements de phases dans l'état solide de l'alliage E AlMgSi et des processus de dissolution et de précipitation. Les résultats peuvent être appliqués au contrôle des paramètres technologiques des traitments thermiques.

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E AlMgSi, . . .

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Paper presented at the Scientific Session on Thermal Analysis held at Balatonfüred, Hungary, on 14–16 October 1976.     

The effects of concentration and heating or cooling rate on the DTA curves of Al-Ce alloys

The crystallization of Al-Ce alloys was studied by DTA. The melting and freezing DTA curves of the investigated alloys exhibit two peaks, corresponding to the transformations of a high-purity phase and the eutectic phase, respectively. The peaks could be separated during both freezing and melting by changing the heating or cooling rate. The final temperature of the phase transformation is marked by the starting temperature of the second peak. A slight shoulder on the DTA peak, even on the opposite side to the maximum point, may correspond to the final temperature.The connection between the reaction time and the peak temperature for the sample was studied at different cooling and heating rates.It was concluded that a knowledge of the structure and composition of the studied system is necessary in the interpretation of the DTA curves.

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Zusammenfassung Die Kristallisation von Al-Ce-Legierungen wurde mittels DTA untersucht. Die Schmelz- und Erstarrungs-DTA-Kurven der geprüften Legierungen weisen zwei Peaks auf, welche der Umwandlung einer Phase hohen Reinheitsgrades, bzw. der eutektischen Phase entsprechen. Die Peaks konnten sowohl während des Erstarrens als auch während des Schmelzens durch Änderung der Aufheiz- oder Abkühlgeschwindigkeit getrennt werden. Die Endtemperatur der Phasenumwandlung wird durch die Anfangstemperatur des zweiten Peaks angedeutet. Eine kleine Schulter des DTA-Peaks, selbst an der entgegengesetzten Seite des Maximums, kann der Endtemperatur entsprechen.Der Zusammenhang zwischen der Reaktionszeit und der Peak-Temperatur der Probe wurde bei verschiedenen Aufheiz- und Abkühlgeschwindigkeiten untersucht.Es wurde gefolgert, daß bei der Deutung von DTA-Kurven die Kenntnis der Struktur und Zusammensetzung des untersuchten Systems nötig ist.

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Résumé La cristallisation d'alliages Al-Ce a été étudiée par ATD. Deux pics apparaissent sur les courbes ATD lors de la fusion et de la cristallisation des alliages étudiés. L'un est dû à la transformation de la phase de haute pureté et l'autre à la phase eutectiques. Les pics peuvent être séparés en changeant les vitesses de chauffage et de refroidissement, tant à la fusion qu'à la cristallisation. La température finale de la transformation de phase est marquée par la température initiale du second pic. Un faible épaulement du pic ATD, même du côté opposé au maximum, peut correspondre à la température finale.Le rapport entre la durée de la réaction et la température du pic a été étudié pour diverses vitesses de refroidissement et de chauffage.On en conclut que l'interprétation des courbes ATD exige de connaître la structure et la composition du système étudié.

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1-. , , , . , , . . , , . . , , .

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Paper presented at the Scientific Session on Thermal Analysis held at Balatonfüred, Hungary, on 14–16 October, 1976.

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The authors are grateful to Mrs. M. Laár for the excellent preparation of the alloys. Thanks are due to Miss K. Papp and Mr. J. Szeleczki for their help in the thermal analysis. We are also indebted to Mrs. M. Horváth for the metallographic work.     

Vibrations in amorphous silicon and its alloys

Amorphous silicon (a-Si) is a material of considerable technological importance, especially for photovoltaic cells. It is usually “doped” with hydrogen and a number of other elements (B, P, F, C, N). Spectroscopy of the extended vibrations of the Si-network and the local modes induced by the dopants is widely used for the characterization of the material. In this paper data obtained with Raman, ir, and neutron spectroscopy are discussed with emphasis on the local modes of hydrogen and other impurities.     

电沉积非晶态镍磷合金的研究

本文用电化学方法, X射线衍射及电子能谱方法研究了阴极恒电位沉积非晶态镍磷合金镀层,实验结果表明,影响镍磷合金非晶结构的主要因素是镀层中的磷含量,当磷含量大于9%时,镀层具有良好的非晶结构,镀层中镍和磷主要以元素态形式存在,磷的析出具有诱导共析特点。     

DTA analysis of the system CuCl2-KCl

Mixtures of CuCl₂ and KCl in molar ratios of Cu to K of from 0.5 to 1.0 were heated at 473 K in an air atmosphere, and then subjected to DTA analysis in the temperature range 293–773 K. A number of endothermic processes were observed, the extents of these depending on the molar ratio of Cu to K in the mixture.

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Zusammenfassung DTA-Untersuchungen haben ergeben, daß in Mischungen von CuCl₂ und KCl mit molaren Cu/K-Verhältnissen von 0,5–1,0 nach Erhitzen in Luft bei 473 K im Temperaturbereich von 293 bis 773 K eine Reihe von endothermen Prozessen verlaufen. Das Ausmaß dieser Prozesse hängt vom Cu/K-Verhältnis der Gemische ab.

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( 0,5 1,0) 293–773 , , .

     

The instrument constant in DTA. Theory of sensing units in DTA instruments

Volume-isothermal and surface-isothermal sensing units with a gas-phase thermal barrier are described. Use of the two-point method of DTA with the surface isothermal sensing unit permits experimental determination of the internal heat resistance of the sample holder (of the reaction zone), thereby allowing elucidation of the mechanism (topochemistry) of the reaction and the finding of more exact kinetic data via a novel method of split heat capacities.

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Zusammenfassung Volumen- und oberflÄchenisotherme Me\fühler mit thermischer Gasphasenbarriere werden beschrieben. Bei Verwendung von oberflÄchenisothermen Me\fühlern kann nach der DTA-Zweipunktsmethode der innere WÄrmewiderstand bestimmt werden, wodurch die AufklÄrung des Mechanismus (Topochemie) der Reaktion und die Ermittlung genauerer kinetischer Daten über eine neue SpaltwÄrmekapazitÄts-Methode ermöglicht wird.

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- . , 2- - ( ), ( ) .

     

Simulation of the infrared spectra of amorphous silicon alloys

The infrared absorption spectra of hydrogenated amorphous silicon alloys have been simulated using MOPAC. The calculated spectra compare well with those obtained experimentally. Simulation studies have also been carried out on the effect of contamination of hydrogenated amorphous silicon by common atmospheric contaminants: oxygen and nitrogen. These studies provide a basis for the study of diffusion and reconstruction of amorphous silicon alloys during annealing and photodegradation. This article indicates that infrared spectroscopy, combined with molecular modeling, could be used to study the molecular mechanisms associated with the photodegradation of amorphous silicon alloys. © 1996 by John Wiley & Sons, Inc.     

Glass-forming ability and crystallization kinetics of amorphous palladium-boron alloys

Palladium-boron alloys have been prepared to check their ability to produce metallic glasses when spun from the melt.An amorphous alloy with 31.5 at.% boron obtained in the form of ribbon has been submitted to both isothermal and non-isothermal DSC tests. The isothermal crystallization kinetics have been analyzed according to the Avrami law for phase transformations in solids.The n exponent of the law has been determined to obtain information on the geometrical features of the growing crystals. A confirmation of the calculated n value has been sought through an analysis of non-isothermal DSC peaks     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

A new method for studying crystallization of amorphous alloys

Experiments on the crystallization of amorphous Fe?Si?B alloys were carried out by thermogravimetric analysis (TG). This new method gives us some important information about the magnetic phase transformation of amorphous alloys, especially the magnetic volume change in crystallization beside the energy change obtained by the traditional DSC and DTA methods. Crystallization activation energies of Fe?Si?B amorphous alloy are calculated from both TG and DTA curves. The experiment also showed that the addition of Nb, Cu and Mo would influence the crystallization transition temperature of amorphous Fe?Si?B alloys greatly.     

Electrochemical behaviour of Ni-Co amorphous alloys in alkaline solutions

The dissolution processes of amorphous G15 (Ni₅₈Co₂₀B₁₂Si₁₀) and G16 (Ni₂₅Co₅₀B₁₀Si₁₅) alloys in carbonate-bicarbonate buffers (8.9≤pH≤10.5) have been studied using voltammetry and stationary polarization techniques combined with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Results indicate that the electrochemical processes are dependent on the applied potential, the alloy composition, and the pH and ionic strength of the electrolyte. An enhancement of the corrosion processes is observed when the pH and the ionic strength are increased and when the Co content of the alloy diminishes. Furthermore, XPS provided information about the composition of the surface layer. Electronic Publication     

Mössbauer study of hydrogenated Fe-Zr amorphous alloys

The effect of electrochemical hydrogenation was investigated in Fe₉₀Zr₁₀ and Fe₈₉Zr₁₁ amorphous alloys by means of⁵⁷Fe Mössbauer spectroscopy. Significant changes in the Mössbauer spectra as well as in the hyperfine field distribution of hydrogenated samples were found with increasing hydrogen concentration. It was established that the dependence of Curie temperature on hydrogen content had a maximum, and the hydrogen had two mean localization sites. By comparing the Mössbauer spectra of hydrogenated samples as-quenched and annealed before hydrogenation it was shown that low-temperature relaxation processes were going on at aging temperature as low as 150°C in this amorphous alloy and the low-temperature relaxation processes modify the localization of hydrogen. The combination of the hydrogenation and Mössbauer techniques gives a very sensitive method for detecting structural changes.     

The instrument constant in DTA. Theory of sensing units in DTA instruments

The theory of block-type sensing units is reviewed. The two-point method of DTA is described and appropriate computation formulae are derived. The failure of the existing blocktype sensing units to conform to the assumptions of the theory is demonstrated.     

Analysis of surface and bulk composition of amorphous metallic alloys

Summary Surface and bulk composition of amorphous metallic alloys (AMA) has been analyzed by AES and SIMS. Original surface segregation and its variation has been studied in detail under the effect of different treatment techniques. Secondary ion energy distributions were measured for different structural states and primary ions. Data obtained can be used in practical SIMS analysis. Kinetical characteristics of secondary ion emission (SIE) are shown to be useful for surface characterization. Structure-sensitive SIE is changed greatly and irreversibly during transition from the amorphous to the crystalline state.

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Analyse der Oberflächen und Bulk-Zusammensetzung von amorphen Metall-Legierungen

     

Crystallization of Co75-xFexGe15B10 amorphous alloys

The crystallization behavior of Co_75-xFe_xGe₁₅B₁₀ (x=3.0, 4.6 and 6.0) amorphous alloys was monitored by differential thermal analysis and thermo-mechanical analysis. The crystallization process of the melt spun ribbons was interrupted at 450, 525, 650, 800 and 900°C and their microstructures were investigated by X-ray diffractometry. It was observed that the crystallization occurs in a sequential mode attributed to the formation of different types of precipitates. It was shown that the crystallization products change as a function of Fe content. After full crystallization, GeFe, Co₃B, FeGe₂ and Co₂Ge compounds were found as well as a Co rich solid solution. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure, energetics, and bonding of amorphous Au-Si alloys

First principles periodic calculations based on gradient-corrected density functional theory have been performed to examine the structure, energetics, and bonding of amorphous Au-Si alloys with varying Au:Si composition ratios. Our results predict that the Au-Si alloy forms the most stable structure when the Si content is around 40-50 at. %, with an energy gain of about 0.15 eV/atom. In addition, the volume change per atom in the alloy exhibits a distinctive nonlinear trend, with the minimum value around 60 at. % Si. The occurrence of the minimum in the Au-Si mixing energy and volume is attributed to strong hybridization of the Au 5d-Si 3p states. We also present variations in the radial distribution function and atomic coordination number as a function of Au:Si composition ratio, with discussion of the nature of local packing and chemical bonding in the Au-Si alloy system.     

Preparation and TG—DTA analysis of manganese silicon nitride

Manganese silicon nitride was prepared quantitatively as a precipitated phase by treating a Mn; Si-alloy (Mn: 1.84 w/o, Si: 1.12 w/o) in a mixture of 2% NH₃ and H₂ at 700°C. Nitriding was carried out in situ in a thermobalance and the nitrogen uptake was recorded as a function of time. The nitride phase was isolated and investigated by means of the combined TG-DTG-DTA technique both in an atmosphere of nitrogen at 25–1600°C and in a mixture of Ar+O₂ (p_O2 = 0.20 atm) at 25–1000°C. In the nitrogen atmosphere MnSiN₂ appears to be stable up to 1000°C. Oxidising the nitride in the Ar/O₂ mixture caused three distinct exothermic processes to occur at characteristic temperatures. The final oxidation products as identified by diffractometry and IR-spectroscopy are manganese oxide silicate (braunite) and silicon dioxide.     

SAXS study on the structure and crystallization of amorphous metallic alloys

The change in structure of several amorphous alloys as Fe-P-C, Fe-B and Pd-Au-Si alloys during isothermal ageing was examined using small angle X-ray scattering technique as well as transmission electron microscopy. The SAXS intensity was related to two different types of scattering sources depending on ageing period and temperature. As-splatted amorphous alloys and the specimens aged for short period at relatively low temperature, where specimens remained in amorphous state, showed a weak and spreaded SAXS intensity. This indicates an existence of electron density fluctuation in amorphous phase. The dimension of their scattering regions was estimated to be 1.8 to 2.4 nm for Fe-P-C alloys, and 1.2 to 0.8 rim. for Fe-B alloys, respectively, by analysing the electron density-density correlation function derived from observed SAXS intensity. The origin has been discussed based on one dimensional model. A compositional fluctuation was made clear to occur in fine scale of about 1 nm in amorphous Fe-B and Fe-P-C alloys. When the alloys were aged for longer period below their crystallization temperatures, fine crystalline particles precipitate; those are a two phase lamella structure of Fe₃P and-Fe for a Fe₈₃P₁₀C₇ alloy, an Ferich single phase for Fe₈₃B₁₇ alloy, and a Pd-rich single phase for Pd₇₆Au₆Si₁₈8 alloy, respectively. Their size and structure were determined from the analysis of SAXS data and TEM observation.