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Transition properties first-order transitions

Transition properties first-order theory of oscillator strengths (FOTOS)... [Pg.35]

A feature of a critical point, line, or surface is that it is located where divergences of various properties, in particular correlation lengths, occur. Moreover it is reasonable to assume that at such a point there is always an order parameter that is zero on one side of the transition and tliat becomes nonzero on the other side. Nothing of this sort occurs at a first-order transition, even the gradual liquid-gas transition shown in figure A2.5.3 and figure A2.5.4. [Pg.649]

Figures 4.14a and b are the analogs of Figs. 4.3a and b they schematicaUy describe second- and first-order transitions, respectively. It is the discontinuity in these second-order properties that characterizes a second-order transition. Figures 4.14a and b are the analogs of Figs. 4.3a and b they schematicaUy describe second- and first-order transitions, respectively. It is the discontinuity in these second-order properties that characterizes a second-order transition.
Mech nic lProperties. Extensive Hsts of the physical properties of FEP copolymers are given in References 58—63. Mechanical properties are shown in Table 3. Most of the important properties of FEP are similar to those of PTFE the main difference is the lower continuous service temperature of 204°C of FEP compared to that of 260°C of PTFE. The flexibiUty at low temperatures and the low coefficients of friction and stabiUty at high temperatures are relatively independent of fabrication conditions. Unlike PTFE, FEP resins do not exhibit a marked change in volume at room temperature, because they do not have a first-order transition at 19°C. They ate usehil above —267°C and are highly flexible above —79°C (64). [Pg.360]

The phase transiton from a paraelectric to a ferroelectric state, most characteristic for the SbSI type compounds, has been extensively studied for SbSI, because of its importance with respect to the physical properties of this compound (e.g., J53, 173-177, 184, 257). The first-order transition is accompanied by a small shift of the atomic parameters and loss of the center of symmetry, and is most probably of a displacement nature. The true structure of Sb4S5Cl2 106), Bi4S5Cl2 194), and SbTel 108,403) is still unknown. In contrast to the sulfides and selenides of bismuth, BiTeBr 108) and BiTel (JOS, 390) exhibit a layer structure similar to that of the Cdl2 structure, if the difference between Te, Br, and I (see Fig. 36) is ignored. [Pg.408]

We have already stated that the a-[3 transition of quartz may be described as a A transition overlapping a first-order transition. The heat capacity function for the two polymorphs is thus different in the two stability fields, and discontinuities are observed in the H and S values of the phase at transition temperature T rans cf section 2.8). For instance, to calculate the thermodynamic properties of ]8-quartz at T = 1000 K and P = bar, we... [Pg.373]

The crystal property perhaps most sensitive to structure is density and, conversely, the increase in density of a crystal with pressure is accompanied by significant structural changes. The latter can be of two types - either a smooth variation of the free parameters of the structure with pressure, or a first-order transition to a new structure type. [Pg.138]

The T of crystalline polymers may be determined by observing the first-order transition (change in heat capacity value) by DTA or by DSC (ASTM-D3418). Some comparative information on thermal properties of polyolefins may be obtained from the melt index. To determine the melt index, the weight of extrudate or strand under a specified load and at a specified temperature is measured. Melt index values are inversely related to the melt viscosity. [Pg.35]

The most common applications of DSC are to the melting process which, in principle, contains information on both the quality (temperature) and the quantity (peak area) of crystallinity in a polymer [3]. The property changes at Tm are often far more dramatic than those at Tg, particularly if the polymer is highly crystalline. These changes are characteristic of a thermodynamic first-order transition and include a heat of fusion and discontinuous changes in heat capacity, volume or density, refractive index, birefringence, and transparency [3,8], All of these may be used to determine Tm [8],... [Pg.123]

Normally the second-order crossover is completed in a pressure span 50 kB. In the case of SmS the first-order transition coming at 6 — 1/2 kB (at 300 K) precipitates the compound almost from the onset of crossover to a stage (as gauged from the observed lattice contraction) approximately 3/4 of the way through the ICF state. Possibly 30 kB more brings a completion of crossover (5), and a termination of the (ICF) anomalous electromagnetic properties (see App 4). [Pg.70]

Tg can be determined by studying the temperature dependence of a number of physical properties such as specific volume, refractive index, specific heat, etc. First-order transitions, such as the melting of crystals, give rise to an abrupt change or discontinuity in these properties. However, when a polymeric material undergoes a second-order transition, it is not the primary property (the volume), but its first derivative with respect to temperature, (the coefficient of expansion), which becomes discontinuous. This difference between a first and second-order transition is illustrated in Figure 10. [Pg.22]

Mechanical properties of FEP are in general similar to those of PTFE with the exception of the continuous service temperature, 204°C (400°F) as compared with that of PTFE (260°C or 500°F). Unlike PTFE, FEP does not exhibit a marked volume change at room temperature because it is lacking the first-order transition at 19°C. FEP resins are useful above -267°C ( 1490F) and are highly flexible above -79°C (-110°F).42... [Pg.40]

Electrical and Magnetic Properties of MEM(TCNQ)2 Contrary to TEA(TCNQ)2, the chain structure in MEM(TCNQ)2 [24,25] is found to go discontinously from a very weak dimerization above 335 K to a strong dimerization below 335 K. This is a first-order transition which is reminiscent here of a 4kF transition, although there is still no symmetry breaking [28]. An additional tetramerization also starts to develop continuously below 19 K. This last transition, which now involves symmetry breaking, can be identified with a true second-order 2kF transition [17,18,28] (see Section 7). [Pg.327]

In conclusion, we have constructed a model for the in-termolecular interactions in solid C o. The basic structural properties calculated are in good agreement with experiments. It is shown that around T, 270 K the structure undergoes a first-order transition from the high-... [Pg.107]


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See also in sourсe #XX -- [ Pg.2 , Pg.1206 , Pg.1207 ]




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First transitions

First-order properties

Order properties

Properties transitive

Transition first-order

Transition properties

Transitivity properties

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