Thermal expansion coefficients determination

The linear thermal expansion coefficient determination of filled polyketone systems... 

The cubic thermal expansion coefficient, determined from the specific volume vs. temperature plot, both before and after the densification process, (run II), is ap = 2.0 10 " (7), typical of that for glassy polymers. 

Values of thermal-expansion coefficients to be used in determining total displacement strains for computing the stress range are determined from Table 10-52 as the algebraic difference between the value at design maximum temperature and that at the design minimum temperature for the thermal cycle under analysis. 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

On the experimental side, one may expect most progress from thermodynamic measurements designed to elucidate the non-configurational aspects of solution. The determination of the change in heat capacity and the change in thermal expansion coefficient, both as a function of temperature, will aid in the distinction between changes in the harmonic and the anharmonic characteristics of the vibrations. Measurement of the variation of heat capacity and of compressibility with pressure of both pure metals and their solutions should give some information on the... 

The glass transition temperature of a dilute system, according to the free volume changes, is determined by the diluent volume fraction Vd, and changes of the thermal expansion coefficient, a, at Tg by using ... 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

Since the glass transition corresponds to a constant value of the relaxation time [15], dTjdP is just the pressure coefficient of Tg. Comparing Equations 24.10 and 24.13, we see that the scaling exponent is related to quantities—thermal pressure coefficient, thermal expansion coefficient, Tg, and its pressure coefficient—that can all be determined from PVT measurements... 

The thermal expansion coefficients of PVCL and a copolymer in water, tfpol> were determined by PPC as a function of temperature (Fig. 23) [180]. The plots can be divided into four temperature ranges. Below the transition temperature, 10 < T < 30 °C, g i for PVCL remains constant, while in the case of PVCL-g-34, apoi has a negative slope. In both cases, apoi undergoes a sharp... 

Table 9-3 lists thermal expansion coefficients for a number of substances. Water behaves in an unusual fashion. The thermal expansion coefficient decreases with increasing temperature up to about 4°C, after which the thermal expansion coefficient increases with temperature. Coefficients for water are readily determined from the steam tables. 

Consider Problem 9-9, part a. This time use alcohol as a liquid medium with a thermal expansion coefficient of 1.12 X 10 3/°C. The heat capacity of the alcohol is 0.58 kcal/kg °C, and its density is 791 kg/m3. Determine the relief size required. 

Glass transition temperature is one of the most important parameters used to determine the application scope of a polymeric material. Properties of PVDF such as modulus, thermal expansion coefficient, dielectric constant and loss, heat capacity, refractive index, and hardness change drastically helow and above the glass transition temperature. A compatible polymer blend has properties intermediate between those of its constituents. The change of glass transition temperature has been a widely used method to study the compatibility of polymer blends. Normally, the glass transition temperatme of a compatible polymer blend can be predicted by the Gordon-Taylor relation ... 

Additional comment deserve magnetostriction measurements near the ordering temperature 7c reflecting critical phenomena. Few data for critical expansion is available, such as have been reported by Dolejsi and Swenson (1981) for the case of Gd metal. The thermal expansion coefficient in the critical region should assume the form 1(7 — Tc)/Tc °-The critical exponent or should be the same as for the specific heat and depend only on the universality class (dimensionality, No. of degrees of freedom) of the system. For Gd metal this universality class has been determined by Frey et al. (1997). 

Since the interferometer used for (dn / dT)c>p measurement is heated completely, and not just the cuvette, it has been made out of Zerodur (Schott, Mainz), which has a negligible thermal expansion coefficient. Precise values of the refractive index increments are crucial for the determination of the thermal diffusion coefficient and the Soret coefficient. The accuracy achieved for (dn / dc)ftP is usually better than 1 %, and the accuracy of (dn / dT)rp better than 0.1 %. 

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