Effects of Moisture and Stresses on the Structure and Properties of Polyester Resin

The results of a complex study of structural changes in a cured Norpol 440 polyester resin under the action of damp environment and mechanical loading are presented. A considerable effect of absorbed moisture on the structure and some characteristics of the material is revealed by using thermophysical methods and X-ray diffractometry. The joint effect of moisture and mechanical stress is estimated by investigating the creep in stationary and nonstationary moisture conditions. The anisotropy of the material structure formed during creep is evaluated from the results of dilatometric measurements. It is found that the degree of anisotropy of the material after creep accompanied by moisture sorption is higher than that after creep in the conditions of moisture equilibrium with atmosphere. It is established that the aftercure and relaxation of the residual creep deformation come to an end at heating to 80-85°C. At a further rise in temperature and repeated heating, changes in the material structure are not observed.     

Phase Transitions,Thermal Desorption of Gases,and Electroconduction in BaCeO<Subscript>3</Subscript>, a Base for High-Temperature Protonic Conductors

Investigations of phase transitions in barium cerate are carried out by methods of dilatometry and differential scanning calorimetry. Thermal desorption of gases and temperature dependences of electroconduction in dry and humid air are studied. Barium cerate exhibits complex polymorphism, undergoing a number of structural conversions at 300– 1300 K. The peaks in the spectra of thermal desorption of CO₂ and H₂O correlate with variations in the crystal lattice. Structural changes in BaCeO₃ affect activation energies for the carrier transport and the shares of partial conductivities.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 620–626.Original Russian Text Copyright © 2005 by Kuz’min, Gorelov, Vaganov, Korzun, Kazantsev, Aksenova, Khromushin.     

Phase equilibria in the ternary system PbO−P2O5−PbCl2

Journal of Thermal Analysis and Calorimetry - In the ternary system PbO?P2O5?PbCl2, the partial ternary system Pb5Cl2O4?Pb3Cl2O2?Pb10(PO4)6Cl2 was examined by thermal,...     

Thermal behaviour of amorphous Li2ZrO3 prepared by sol-gel technique

The results of the investigations of thermal behaviour of Li₂ZrO₃, prepared in the amorphous state by means of sol-gel technique are demonstrated. The thermal treatment was carried out in air under constant heating rate of 5 deg·min^–1 and cooling rate of 2.5 deg·min^–1. The methods of DTA, TG, Emanation Thermal Analysis (ETA) and dilatometry were used, for characterization of the thermal behaviour in dynamic conditions. The X-ray diffraction patterns were used for characterization of the phase changes observed by TA Methods.

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Zusammenfassung Ergebnisse aus Untersuchungen des thermischen Verhaltens von Li₂ZrO₃, hergestellt mittels einer Sol-Gel-Technik im amorphen Zustand werden dargelegt. Die thermische Behandlung wurde in Luft bei einer konstanten Aufheizgeschwindigkeit von 5 Grad·min^–1 und einer Abkühlgeschwindigkeit von 2,5Grad·min^–1 durchgeführt. Zur Beschreibung des thermischen Verhaltens unter dynamischen Verhältnissen wurden DTA, TG, Emanationsthermoanalyse und Dilatometrie angewendet. Zur näheren Charakterisierung der bei TG beobachteten Phasenumwandlungen wurde Röntgendiffraktion verwendet.

     

The decomposition of edta-gel precursors in the production of BSCCO superconductors

The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. The thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. The effects of substitution of Pb for Bi on the temperatures of formation of the superconducting phases is also discussed. STA has also been carried out under varying oxygen partial pressures to determine the effects of oxygen pressure on the formation and decomposition of the phases involved in the production of the 2223 compound.     

Thermoanalytical studies of the processing of bulk and thin film BSCCO highT c superconductors by the Edita-Gel route

The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. Ther thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. Thin film preparation of Bi-based highT _c superconductors have been carried out on MgO (100). Grain orientation of oxide thin films has been investigated. Well orientated 2212 grains have been achieved, with the (001) planes parallel to the substrate. The EDTA-gel method has been modified by the addition of glycerol to achieve the appropriate viscosity for spin coating. STA has been used to study the decomposition of these modified gels for the formation of thin films.     

Characterization of phase transition of Ba2-xSrxIn2O5 by thermal analysis and high temperature X-ray diffraction

The phase transitions of Ba_2-xSr_xIn₂O₅ were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba_2-xSr_xIn₂O₅ with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba_2-xSr_xIn₂O₅ was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transformation-Governed Heating Techniques in Thermal Analysis I.

The author gives a detailed survey on thermogravimetric investigations under quasi-isothermal — quasi-isobaric conditions (Q-TG). According to the principle of the technique the heating of the sample is governed by the transformation itself according to the feed-back principle in a way that the transformations should take place at a strictly constant rate, slower by orders of magnitude than in the case of the conventional techniques. Due to this, the transformations take place under ideal conditions, near to physico-chemical requirements.Based on the obtained advantageous results further methods were elaborated, like thermo-dilatometry (Q-TD), evolved gas analysis (Q-EGA) and microdistillation under quasi-isothermal conditions.The second part of the present review deals with DTA and DSC techniques under quasi-isothermal conditions elaborated recentlyThis revised version was published online in November 2005 with corrections to the Cover Date.     

A computer controlled continuous dilution dilatometer for the determination of solute molar volumes and direct measurement of reaction volumes in solution

The design and operation of a computer controlled continuous dilution dilatometer utilizing a diode array detection system is presented. To test the accuracy and reproducibility of the technique, apparent molar volumes of dilute aqueous solutions of potassium ferricyanide and potassium ferrocyanide have been measured. To provide supporting data for high pressure studies of reaction volumes and molar volume change in solutions of high ionic strength, study of these electrolytes was extended by dilution into 0.1M and 1.0M potassium nitrate solutions rather than extrapolation to zero ionic strength as is normal. In addition, the system has been used to determine reaction volumes of some acid-base reactions by direct measurement, using the equipment as an automatic titration dilatometer.     

Thermophysical properties of azomethine ether main-chain liquid crystalline polymers at pressures to 200 MPa

This article reports on an experimental investigation of the equation of state and the transition behavior of main-chain thermotropic liquid crystalline polymers over a wide temperature range, and at pressures to 200 MPa. The materials studied were a series of azomethine ether polymers. A varying number n (= 4, 7, 8, 9, 10 and 11) of methylene spacer units in the backbone provided systematic variation of the structure. Experimental techniques used included high-pressure dilatometry (PVT measurements) to 200 MPa, high-pressure differential thermal analysis, also to 200 MPa, and conventional (atmospheric-pressure) differential scanning calorimetry (DSC). The equation of state of the materials can be well represented by the Tait equation in distinct regions, separated by a glass transition, T_g(P), a first-order transition to a nematic state, T_k-n(P), and a first-order transition to an isotropic melt state T_c(P). The atmospheric pressure values of T_k-n and T_c decreased with increasing number of spacer units and showed a clear odd-even effect. T_g and T_k-n both increased with pressure. The pressure dependence of T_c could not be observed due to the onset of degradation in the same temperature region. On isobaric cooling at 3°C/min, the crystallization from the nematic state occurred a few tens of degrees below T_k-n. This supercooling was independent of pressure for some materials, while for others it increased with increasing pressure. The values of the enthalpy and entropy associated with the first-order transition into the nematic state were lower than those of typical isotropic polymers at their melting transitions. The transition enthalpy did not have any systematic variation with increasing number of spacer units. Values of the transition enthalpy calculated from the Ciapeyron equation did not always agree with the values measured by DSC. This may be due to the two-phase nature of the low-temperature state. At the transition to the isotropic state, the transition enthalpy at P = 0 decreased with n and showed an odd-even effect. © 1994 John Wiley & Sons, Inc.