Dilatometric techniques

Dilanacin, molecular formula and structure, 5 98t Dilantin, folic acid and, 25 803 Dilatancy, 21 717 Dilatant flow, 7 280t 8 728 Dilatant fluids, 11 768, 769 Dilatometers, vitreous silica in, 22 441 Dilatometric techniques, 13 436... 

Surface tension and density of liquid alloys have been studied by Moser et al. (2006). Measurements by maximum bubble pressure and dilatometric techniques were carried out in an extensive range of temperatures on liquid alloys close to the ternary eutectic Sn3 3Ag0 76Cu with different Sb additions, which decrease surface tension and density. The experimental data were discussed in comparison also with values calculated on the basis of different models. 

Dilatometric technique can also be used for determination of polymerization rate in the case of multimonomer polymerization. However, in this case calibration of the dilatometric method is more complex. The substrates and products are both polymers with similar molecular weights. Difference in density during the course of polymerization is connected only with the conversion of double bonds to the single bonds. It is difficult to obtain a macromolecular product in which double bonds are fully converted to single bonds. Calibration must be based on simultaneous measurements of Ah and independent method (e.g., IR spectroscopy) and calculation of (1/dp l/d]vi). 

Lane38 measured the rate of hydrolysis of ethyl acetate at 25°C in 11 -79% sulphuric acid by both spectrophotometric and dilatometric techniques. He also measured spectrophotometrically the concentration of the conjugate acid of the ester in solution by measuring the absorptivity at 190 nm, and extrapolating to zero time, and by the change in the chemical shift of the acetyl protons. He found a linear relation between the ionization ratio and Hammett s acidity function... 

Studies of such systems are reported in the literature. Worsfold and Bywater (28) determined kp for the anionic homopolymerization of a-methylstyrene in tetrahydrofuran solution and Allen, Gee, and Stretch (I, 2) studied the polymerization of styrene in dioxane. Both groups utilized the dilatometric technique to follow the reaction and show the absence of termination. 

Michaud has observed a B to a crystal transition, on heating anhydrous barium dihydroxide, at 250°C (7) and at 246 C (8) by both thermal and dilatometric techniques. In the absence of water vapor, the high temperature a form is maintained on cooling to room temperature (7 ). This "metastable" state has been confirmed by others (9, ) This present JANAF Table considers only the a-form. A transition temperature of 521 + 2 K (248 2 C) is adopted. 

The thermal expansion of solids depends on their structure symmetry, and may be either isotropic or anisotropic. For example, graphite has a layered structure, and its expansion in the direction perpendicular to the layers is quite different from that in the layers. For isotropic materials, ay w 3 a . However, in anisotropic solid materials the total volume expansion is distributed unequally among the three crystallographic axes and, as a rule, cannot be correctly measured by most dilatometric techniques. The true thermal expansion in such case should be studied using in situ X-ray diffraction (XRD) to determine any temperature dependence of the lattice parameters. 

Ciapetta and Kilpatrick (14) used a dilatometric technique to investigate the kinetics of the hydration of isobutene in perchloric acid solution at 25 C. ... 

Crystallization is characterized by several physical phenomena. With regard to rubbers, a crystal unit cell is of higher density (1.0 g/cm for NR) than is amorphous unfilled rubber (0.91 g/cm for NR). Crystallization is thus accompanied by an increase in density (i.e., decrease in volume) of up to 10%. Small volume changes (less than 3% for NR) have been measured by both hydrostatic balance and dilatometric techniques. Crystallite formation also involves the evolution of heat of fusion, and calorimetry has been used to derive values for the rate and degree of crystallization in NR in broad agreement with volume change data. 

The RUCI3-catalysed polymerization of methyl methacrylate CH2=C(Me)C02Me, initiated by Bu"NH2 in the presence of CCI4 in DMSO, has been investigated with the aid of a dilatometric technique at 60 °C. The kinetic data thus obtained suggest the formation of a charge-transfer complex between Bu"NH2, Ru(III), and CCI4. 

Employing a dilatometric technique, Booth and coworkers determined the melt behavior of fractionated PPO as a function of crystallization temperature and by this technique found the thermodynamic melting point for PPO to be near 82° (Fig. 31), surprisingly 100° C lower than that of POM. These authors also detected three dilatometric transitions for partially isotactic material. The first below 60° was ascribed to the melting of lamellar crystals of limited thickness arising from the isotactic sequence. The other two transitions which depended on Tf- were attributed to the melting of lamellae with thicknesses determined by primary nudeation. 

It is interposed between the system and the source of light to cause periodic interruption of the light. The cut out portion determines the value r. (For example, a rotating sector with 1 3 opening corresponds to r = 3.) The blinking frequency as well as t and f are determined by the speed of sector rotation. The polymerization rate is conveniently determined by dilatometric technique (p. 321). The rate measured with the rotating sector present is the average polymerization rate (Rp) while that measured without the sector present is the steady-state rate of polymerization Rp)s-... 

If the pressure coefficient and the enthalpy of the transition are known, the volume change of the transition can be calculated. From the value obtained above for the latent heat, Equation (1) predicts a volume increase, SV/V, of order 0.1 % at the LCOT for the Mw=85K P(rf-S-Ii-nBMA) at atmospheric pressure. To confirm the volume change experimentally, dilatometric techniques are usually employed, where mercury displacement in a fine bore capillary provides the high precision necessary to detect such small changes. Although dilatometry studies are in progress, x-ray reflectivity was employed as an altmiative route to access bV/V experimentally where a high precision in the measurement of thickness can be achieved. 

The Tg of methyl methacrylate-MA copolymers have also been studied over the broad range 8.4-49.8 mol % anhydride.Analogous to the acry-lated system, Tg increased with MA content in the copolymer. Using a dilatometric technique, the Tg of the copolymers over this range varied from 118.5 to 147.0°C. The results were discussed in terms of the chain stiffness of each copolymer. The product of TgAa, where Aa is 0.107, was nearly constant regardless of the copolymer composition. 

Kinetic studies of the copolymerization in acetic anhydride, using a dilatometric technique, showed that the order of the reaction with respect to the product of the monomer concentrations is close to 0.5. Also, the rates were slightly enhanced as MA concentrations were increased. This tends to indicate that the alternating copolymerization occurs by successive addition of the monomers. 

Chitosan for polymerization of sodium 4-styrenesulfonate was transformed to hydrochloride in order to cause strong ionic interaction between the monomer and the template. By the dilatometric technique, it was found that the reaction rate increases with increasing [T]/[M] ratio within the range 0-0.25 up to about 2.5 and then is stable. On the basis of this observation, the authors assumed a pick-up mechanism for this process. 

Cermets are a potential class of composites, in which, however, the question of bonding at the ceramic-metal interface plays a key role non bonding reduces the composite with respect to properties as Young s modulus, electrical conductivity or thermal expansion to those of the porous matrix phase material. This is why a new dilatometric technique is used to study the bonding between ceramic and metal phases selected to produce cermets. 

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