Isothermal dilatometry

The kinetics were studied by adiabatic calorimetry [18] and high vacuum isothermal dilatometry [21, 22]. The calorimeter and the dilatometers were fitted with electrodes [21] for measuring the conductivity of the reaction mixtures. 

Bee] Light microscopy, TEM, high speed dilatometry, isothermal dilatometry 800-400°C, Fe-5 mass% Cr-0.2 mass% C, Fe-10 mass% Cr-0.2 mass% C, y, a + y -H M23C6, M7C3, martensite, bainite... 

Figure 21. Dual dilatometry effect of ram pressure on isothermal propellant cure...

E. Other Methods, IR or Raman spectroscopy. X-ray diffraction, solid-state NMR, dilatometry, and moisture sorption isotherm may be used as tools for the qualitative or quantitative study of polymorphism. Brief descriptions of these techniques may be found elsewhere in this chapter. 

The kinetics of copolymerization or curing of epoxy resins with cyclic anhydrides initiated by tertiary amines was investigated by chemical analysis 52,65,73,74,90) differential scanning calorimetry isothermal methods electric methods , dynamic differential thermal analysis , IR spectroscopy dilatometry or viscometry Results of kinetic measurements and their interpretation differ most authors agree, however, that the copolymerization is of first order with respect to the tertiary amine. 

Sve] DTA, XRD, microstmeture analysis, dilatometry, magnetometry Liquidus surface, 1000°C isothermal section and one TIC vertical section in the Cr-ZrCr2-ZrFe2-Fe composition range... 

Dielectric relaxation spectroscopy (DER), e.g. [103-105], DER monitors the mobility of dipolar groups in the polymer and also of small dipolar molecules (e.g. water) that may be dissolved in the polymer system. Corresponding to mechanical measurements, the maxima of dissipated energy indicate phase transition processes. Dilatometry, pVT measurements, e.g. [50,106]. These measurements unequivocally show a first order transition by a step in V T) and a bend if there is a glass transition. The important partial derivatives isobaric expansivity and isothermal compressibility can be derived from the corresponding measurements. The method is, however, quite time consuming and not widely used. 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

A quantitative, isothermal measurement of the crystallization kinetics, usable for analysis by the Avrami method, is illustrated in Fig. 3.98 by the upper left curve. Similar curves can be generated by dilatometry or adiabatic calorimetry as described in Sects. 4.1 and 4.2. At time zero, one assumes that the isothermal condition has been reached. The dotted segments of the heat-flow response are then proportional to the heat of crystallization evolved in the given time intervals and can be converted directly into the changes of the mass fraction of crystallinity after calibration or normalization to the total heat evolved. An independent crystallinity determination... 

Figure 4.67[A] shows a typical isothermal experiment carried out with a DSC. Similar experiments could be carried out with isothermal calorimeters, dilatometry and other teehniques sensitive to crystallinity changes. After attainment of steady state at point 0, the experiment begins. At point 1, the first heat flow rate is observed, and when the heat flow rate reaches 0 again, the transition is complete. The shaded area is the time integral of the heat flow rate, and if there is only a negligible instrument lag, it represents the overall kinetics. In case of an excessive heat flow-rate amplitude, lag calibrations with sharply melting substances of similar thermal conductivity may have to be made (see Figure 4.22). Processes faster than about 1 min...

Thermomechanical analysis (TMA) is a technique that measures the deformation of a substance under non-oscillatory load or strain as a function of temperature or time. Thermo-dilatometry (see Section 2.2.4) is a technique that measures dimensional changes of a sample as a function of temperature or time. Both of these techniques can be applied using the same apparatus. The sample is heated or cooled at a certain rate, or is maintained isothermally at a fixed temperature. 

The simplest volume recovery experiment performed is the down-jump. In this experiment, a material initially above Tg and at equilibrium is subjected to a temperature down-jump to an aging temperature Ta below Tg. The isothermal evolution of volume at T, as indicated by the downward arrow in Figure 1, is monitored with time via length or volume dilatometry. Figure 2 shows tjq)i-cal data replotted from Kovacs data (9) for a series of aging temperatures for poly(vinyl acetate). These curves, called intrinsic isotherms, are plotted as the relative departure from equilibrium 5 versus the logarithm of time, with S defined as... 

Reduction in surface area and open porosity for a powdered sample is not readily measured by dilatometry. Density, BET adsorption isotherms, or emanation thermal analysis (ETA) are the applicable techniques. The latter is accomplished in a scanning temperature mode and, therefore, is capable of more rapidly identifying the significant temperature regimes. ETA involves substantial effort in sample preparation, however. A radioactive gas or its parent must be incorporated into the... 

The kinetics of crystallization, which is of interest for both academic and industrial reasons, is preferably studied under isothermal conditions by DSC, dilatometry or TOA. These methods reveal the overall crystallinity, volume (vf) or mass wf) crystallinity as a function of time (f), and the general Avrami equation can be applied ... 

Fig. 5.24. sPP Crystallization isotherms as given by the time dependence of P (from SAXS, filled symbols) and of the density change dp (from dilatometry, open symbols). The initial slope indicates a kinetic power law P [Pg.186]

Most kinetic studies of isothermal crystallization rely on dilatometry and on the Avrami equation, relating the variation of the total density of the system (p) to the duration of the phenomenon. Measurements are more precise when the difference between the density of the crystalline phase (pc) and that of the liquid phase (pz.) is large. 

The decrease in volume that accompanies physical aging is known as volume recovery or volume relaxation. Dilatometry (Dil) can be used to follow the volume relaxation in glasses by monitoring the time-dependence of the volume change on aging. The material is either cooled from above Tg to the aging temperature 7], (down-jump) and the isothermal volume contraction is measured or the sample is heated in the glassy state (up-jump), in which case an expansion follows. 

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