Completeness of β-phase decomposition reaction in Cu–Al–Ag alloys

The completeness of ??-phase decomposition reaction in the Cu?C11wt%Al?Cxwt%Ag alloys (x?=?0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that ??-phase transformations are highly dependent on cooling rate and on the presence of Ag. On slow cooling, the silver presence prevents the ??- and ??₁-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.     

Calorimetric study and thermal analysis of Al–Sn system

The results of calorimetric study and thermal analysis of binary Al–Sn system are presented in this paper. The Oelsen calorimetry was used in thermodynamic analysis. Following thermodynamic properties were determined at 727 °C: activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies. The energetics of mixing in liquid Al–Sn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit. Thermal analysis of selected alloys in Al–Sn system was done using differential thermal analysis. Defined characteristic phase transition temperatures were used for comparison with calculated phase diagram of investigated system. Good agreement with available literature data was obtained. Structural analysis of selected alloys was done using optic microscopy.     

Al–Ga–Zn Phase Diagram. Calorimetric study of the isobaric invariants

The Al–Ga–Zn ternary phase diagram presents two isobaric invariant reactions: a eutectic at 23±1°C and a metatectic at 123±1°C [1–3]. Calorimetric measurements on the two isobaric invariant reactions have been carried out. First the Tammann method has enabled us to determine the composition of their limits on five isopletic cross sections. Then, the compositions of the invariant phases have been determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric study of Sb-modified Ge–Se–Te glassy alloys

The glassy compositions of Ge ₁₆ Se ₅₂ Te _32?x Sb _x system, obtained using rapid melt quenching technique, have been characterized by calorimetric study at different heating rates in this study. A systematic investigation of the crystallization kinetics is carried out for these compositions. Composition corresponding to atomic % 8 of Sb has good thermal stability. The material exhibits the unique thermal properties, which makes it suitable to use for electrical or memory switching devices. Various thermal parameters, activation energies of glass transition and crystallization are calculated using relevant approaches.     

Calorimetric investigation of Al–Zn alloys using Oelsen method

The results of calorimetric study of binary Al–Zn system done according to the Oelsen thermodynamic method are presented in this paper. Main thermodynamic properties, including activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies were determined at 1,000 K. Positive deviation from Raoult law was noticed, with minimal values of ΔG ^M about ?3 kJ mol^?1 and maximal values of ΔG ^E about +2 kJ mol^?1. The energetics of mixing in liquid Al–Zn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit, and weak affinity between Al and Zn atoms in the system was observed. Differential thermal analysis and light optic microscopy were applied in the frame of characterization of investigated binary alloys and phase diagram examination, and the results obtained were in accordance with available literature data.     

Calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system

The results of calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system are presented in this article. The research was carried out experimentally, using Oelsen calorimetry in temperature interval 800–1,000 K, and by thermodynamic calculation, applying general solution model in temperature interval 800–1,600 K. The enthalpy space diagram, the enthalpy isotherm diagram, as well as the values for zinc activities, partial and integral molar Gibbs excess energies have been determined. Comparison of experimentally obtained results and the results calculated by general solution model was done at the temperatures 800, 900, and 1000 K, which indicated a good mutual agreement.     

Calorimetric study of the oxidation of Al–Mg alloys for the prediction of healing of the double oxide film defect

The oxidation of Al alloys containing 0.3–4.5 wt% Mg in an atmosphere with a very low oxygen partial pressure (<0.5 ppm, to depict the atmosphere within a double oxide film defect) was studied using differential scanning calorimetry and scanning electron microscopy. The results showed that a newly formed Al₂O₃ layer held in an Al–Mg melt first transformed to MgAl₂O₄ spinel and then to MgO. This mechanism was the same for all the Al alloys containing 0.3–4.5 wt% Mg, but the kinetics of the transformations were different and depended on the Mg content of the melt. The results also suggest that the two layers of a double oxide film defect that is held in an Al melt containing 0.3–4.5 wt% Mg can heal (i.e. bond to each other) if held in the liquid metal for a long enough period of time.     

Does coarsening begin during the initial stages of spinodal decomposition?

The initial stages of spinodal decomposition were studied by subjecting a critical blend of model polyolefins to a pressure quench and monitoring the evolution by time-resolved small angle neutron scattering. Contrary to the predictions of the widely accepted Cahn-Hilliard-Cook theory, we demonstrate that coarsening of the phase-separated structure begins immediately after the quench and occurs throughout the initial stages of spinodal decomposition.     

Calorimetric study of the ZrMo1.5V0.5–H2 system

Journal of Thermal Analysis and Calorimetry - The study of the ZrMo1.5V0.5–H2 system had been carried out by calorimetric method, plotting P–C isotherms and X-ray diffraction analysis....     

Calorimetric study of the molecular complex formation of glycyl–glycyl–glycine with 18-crown-6 in aqueous organic solvents

Russian Journal of General Chemistry - The influence of water–ethanol (H2O–EtOH), water–acetone (H2O–MeAc) and waterdimethylsulfoxide (H2O–DMSO) solvents on the...     

Theoretical study on decomposition of γ-halo allylalkoxide and β-halo acrylate ions

β, γ-Substituted γ-halo allylalkoxide ions decompose to form a halogen ion, formaldehyde, and an alkyne under mild conditions, for example at room temperature. The E isomer does not differ from the Z isomer in terms of activation energy. We attempted to shed light on the mechanism of the reaction by using ab initio molecular orbital calculations. The observed propensity was confirmed by the present calculation on model molecules, γ-chloro allylalkoxide ions. We conducted further calculations and compared the alkoxide results with a similar reaction of β-haloacrylate ions that release carbon dioxide instead of formaldehyde. This similar reaction needs heating as high as 150°C. The activation energy of the acrylate ions (36–39 kcal mol⁻¹) was calculated to be about 10 kcal mol⁻¹ higher than that of the alkoxide ions. The activation energy of the E acrylate ion is smaller by 0.8 kcal mol⁻¹ than that of the Z isomer at the MP2/6-31+G**//RHF/6-31+G* level of theory. This is consistent with experimental results. While the ready deprotonation from the carboxylic group does not activate the acrylate ion very much, the alkoxide ion is destabilized to a great degree in the process of anion formation. The difficulty in deprotonation that proceeds from the neutral molecule is seen in the difference in the activation energies for the decomposition of the corresponding anions. Therefore, the pK _a of a hydroxy or a carboxylic group plays the leading role in determining the magnitude of activation energies of allyl halides with a negatively charged fragment. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

X-ray diffraction study of self-propagating high-temperature synthesis in the Zr–Al–C system

The phase formation process in the Zr–Al–C system during self-propagating high-temperature synthesis (SHS) has been studied by time resolved X-ray diffraction (TRXRD). The “nonuniqueness” of SHS routes in ternary solid-phase systems depending on synthesis initiation conditions has been established. No formation of ternary compounds belonging to the class of MAX phases has been observed in the considered system. It has been shown that the reaction responsible for the propagation of the combustion wave is the synthesis of ZrC, if SHS is initiated by a high-temperature pulse, and the end product also incorporates intermetallide zirconium phases. At the same time, the sequential formation of the Zr[Al] solid solution, the ZrAlC _х phase, and the intermetallide ZrAl₃, ZrAl₂, and Zr₂Al₃ phases occurs in the bulk ignition of the 2Zr–Al–C mixture under the conditions of great heat withdrawal during the reaction between an Al melt and Zr particles. No initiation of the Zr–C reaction takes place due to a low enthalpy of the reactions between aluminum and zirconium.     

TG–DSC–FTIR–MS study of gaseous compounds evolved during thermal decomposition of styrene-butadiene rubber

The thermal decomposition behavior of styrene-butadiene rubber was studied using a system equipped with thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and mass spectroscopy. Two different experiments were conducted. From these experiments, thermogravimetric analysis results indicated a mass loss of 58 % in the temperature range of ~290–480 °C and a mass loss of 39 % in the temperature range beyond 600 °C. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed the presence of oxides, even at 1,000 °C, accounting for the Zn, Mg, Al, Si, and Ca in the original sample.     

Pattern recognition methods in the study of thermal decomposition of α-amino acids

There are many examples in the literature of a strict relation between the pathways of decomposition of a drug substance and chemical structure of its molecule. For this reason, a study has now been performed on the relation between thermal decomposition of ??-amino acids and their chemical structure. To achieve this goal, a group of a dozen or so compounds was chosen at random, and the results obtained using the DTA, TG and DTG analyses of their thermal decomposition were interpreted by highly advanced multivariate methods, principal component analysis and cluster analysis. By this statistical analysis, the influence of specific functional groups on thermal decomposition of ??-amino acids was determined. It has been found that first two principal components explain together more than 75?% of variance, and in an exceptional case, about 90?%. The third stage of decomposition was that at which the thermoanalytical data were best correlated with chemical constitution of a compound. It has also been recognized that a better discrimination among the analysed compounds was obtained for the DTA data set. The results can be useful for identification of a relation between the pathway of degradation of a drug substance and chemical structure of its molecule, and for predicting chemical stability of the compounds studied.