Dilatometry, parameters

Recent work (7) has confirmed a previous observation of a fee phase (13) as the high temperature form of Pa the bcc form predicted (14) by extrapolating the variation of the expansion coefficients in the different lattice directions was never detected. Dilatometry and differential thermal analysis were used in an attempt to clear up controversy in the literature on the polymorphism of Am (15). There seem to be at least 3 different phases, the dhcp (" ot" ) phase stable up to about 650°C, a " 3 -phase" existing until 1050°C, followed by the high temperature form between 1050°C and the melting point. It is unknown which of the latter phases corresponds to the fee form observed. At variance with previous work, but according to recent results (16), the room temperature form of Cf is dhcp (not hep), and there are two different fee forms above 600 and 725°C, respectively, with different lattice parameters. 

To ensure optimum conditions for a direct comparison of DSA data with results obtained by other methods, devices were constructed to provide simultaneous measurement of additional parameters [11]. The equipment for simultaneous measurements by DSA, differential thermal analysis (DTA), thermogravimetry/differential thermogravimetry (TG/DTG) or dilatometry, available from Netzsch Ltd, Germany, ensures the optimal conditions for direct comparison of the results [12]. 

Table 7.5 Summaty of TECs for various MAX phases determined from both high-temperature diffraction and dilatometry. Numbers in parentheses are estimated standard deviations in the last significant figure of the refned parameter.

Polymerisation of vinyl toluene in quaternary microemulsions containing cetyltrimethylammonium bromide as the cationic surfactant was studied using laser Raman spectroscopy and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil-soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerisation, energy of activation, particle diameter, number of polymer particles, molecular weight of polyvinyl toluene and number of polymer chains per latex particle were investigated. The dependencies of the kinetic and latex size parameters on the initiators and co-surfactants are discussed in terms of the efficiency of the initiators in initiating the polymerisation and on the interfacial partitioning behaviour of various co-surfactants. 19 refs. 

The technique of loading dilatometry, in which a small, controlled uniaxial stress Pj is applied to a powda- compact during sintering has been used to investigate the simultaneous occurrence of densification and creep, as well as their interaction (57,58). Parameters such as the stress intensity factor < > and the sintering stress 2 can be determined from the data. In the experiments, simultaneous measurement of the time-dependent axial and radial strains allows the determination of the... 

The truly impressive feature of NELF is that it is a completely predictive model of small molecule sorption in glassy polymers, if information about the polymer partial density, P2, is known. Unfortunately, P2 is obtained firom dilatometry data, and these data exist for only a very small number of penetrant-polymer systems, which limits the general practical applicability of the model. In light of this shortcoming, two approaches have been used to make NELF more widely applicable. The first approach assumes that the pol5mier partial density is equal to the density of the pure polymer, p2° (96). This approach limits NELF to low pressures, where no polymer swelling occurs however, in this pressure range, NELF is still completely predictive. The second approach to increase the applicability of NELF introduces one or two adjustable parameters (95). In this approach, the poljnner partial density is assumed to vary linearly with pressure such that... 

SAXS is a widely used method for the investigation of lamellar structure in the two phase systems. To obtain structural parameters, such as the average crystal separation and crystal thickness, the one dimensional elecbon density correlation function is often used. In syndiotactic poly(propylene) the one dimensional model calculation [24] can be applied since the amorphous phase and crystalline phase form one-dimensional stacks of crystalline lamellae. But in the case of monoclinic iPP, electron microscopy reveals the existence of unique cross-hatched lamellar stracture [25-30], and the applicability of the one dimensional model has been questioned by Albrecht and Strobl [31]. These researchers used SAXS and dilatometry to study structure development in PP, and presented a scheme to check for the feilure of the... 

Thermomechanical analysis thus permits a quick comparison of different materials. As long as instrumental and measuring parameters are kept constant, quantitative comparisons are possible. In Sect. 6.5, some more detailed applications of dilatometry and thermomechanical analysis to melting and crystallization are collected, as well as a discussion of the analysis of materials under tension. 

For the experimental determination of viv, it is necessary to independently measure the absolute concentration of monovacancies in the specimen. Such experiments were performed at elevated temperatures, where the equilibrium concentration of monovacancies is high enough to make the contribution from trapped positrons to the PL spectrum significant [110]. Kluin et al. [107] have correlated positron lifetime, dilatometry and lattice parameter experiments. Another way is to perform electron irradiation at low temperature [109]. The irradiation-induced Frenkel pairs are frozen in the lattice, and their concentration may be obtained by measuring the residual resistivity and dividing it by the resistivity of a Frenkel pair. 

Where is the initial density. Cyclic dilatometry technique is used to measure viscosity. After curve fitting the parameters C, Qv are determined to be 13.888, 19.2 and 14335, respectively. The viscous Poisson s ratio is assumed to be given by... 

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