Transitions alpha

The metallurgical experiments showed that the beta-alpha transition of the tin coating did not occur at irradiation doses of 3-5 Mrad and 6-7.5 Mrad at 5, —30, and —90°C and that the tensile properties, impact ductility, peel strength of soldered lap joints, and microstructure of commercial tinplate and solder were not affected by the irradiation conditions that are used in the sterilization of meat products. 

The core of the crystalline region of irradiated PE contains residual free radicals. These diffuse slowly to the interface with the amorphous region, where, in the presence of dissolved oxygen, whose equilibrium concentration is maintained by diffusion, they initiate an autooxidative chain of degradation.89 Postirradiation annealing in an inert atmosphere at a temperature above the alpha-transition temperature (85°C) leads to a rapid mutual reactions of the free radicals and eliminates the problem.90... 

We have performed coincidence measurements to establish that the 38 ns half-life previously measured [Led78] belongs to the 27.4 keV level. The relevant portion of the Pa decay scheme is shown in Fig.3. The major alpha transitions populate the 29.9 and 46.4 keV levels very little intensity occurs at the 27.4 keV level. The 29.9 keV level decays to the ground state by a fast highly converted Ml transition and the 46.4 keV level decays via the 27.4 keV level. Both the 29.9 and 18.9 (46.4-27.4) keV transitions generates Ac L X-rays. 

The carbon chain is in a planar zigzag orientation and forms an orthorhombic lattice with interpenetration of adjacent chains.61 As a result of this structure, ETFE has an exceptionally low creep, high tensile strength, and high modulus compared to other thermoplastic fluoropolymers. Interchain forces hold this matrix until the alpha transition occurs at about 110°C (230°F), where the physical properties of ETFE begin to decline and more closely resemble perfluoropolymers properties at the same temperature. Other transitions occur at -120°C (-184°F) (gamma) and about -25°C (-13°F) (beta).62... 

Calculate the wavelength of the Lyman alpha transition (Is hydrogen and in He" ". Express the results in both nm and cm ... 

Figure 10. Normalized dielectric loss for PVAc s alpha transition...

The notion of order of an heterogeneous reaction, relative to the initial product is meaningless if this is considered as pure in its phase. TUCKER and HREN (ref.17) reviewed different attempts to build models of gamma to alpha transition. Most of them are summarized in table 2... 

In the present research, variables associated with physical aging near the alpha transition were used to examine the beta transition of a poly(amide-imide). After sample drying, the relationship between the beta transition s activation enthalpy and thermal history was explored. 

Zhou, G. et al. (1986). Studies on the beta-form of isotactic polypropylene. 1. characterization of the beta-form and study of the beta-alpha-transition during heating by wide angle X-ray-diffraction. Makromol. Chem., Vol. 187, Issue 3, pp. 633-642. 

Zoned belite with yellow or muddy colors in outer zone Differences in absorption of impurities produced by alpha prime to alpha transition (Ono, Kawamura, and Soda, 1968)... 

A related issue is that the modulus is a viscoelastic property, as evidenced by the temperature/strain-rate dependence, and that for most poljnners (at least those without a large beta transition near the alpha transition) time-temperature superposition of, for example, the shear relaxation modulus is valid (80). Further, G Sell and McKenna (81) have shown that the 5neld stress vs strain rate also seems to obey time-temperature superposition. Hence there is a correlation between the viscoelastic properties and the yield response of pol5uners, though one that is not generally stated explicitly. We note that some of the models mentioned previously, such as those of Caruthers group (41,42), Tervoort and co-workers (40), and Knauss and Emri (35), are (nonlinear) viscoelastic models that have yield arising due to the nonlinear response induced by the material clock (see Viscoelasticity). 

The alpha transition involves long segments of the polymer chain where the movement causes other chain segments to move out of the way. These cooperative main-chain motions become increasingly prevalent at the Tg and can be used to define the Tg of a material. 

The beta transition involves chain segments that are shorter than those in alpha transitions. For that reason, they occur below the Tg of the material. 

The alpha-transition is associated with crystalline relaxations occurring below the melting point of PE. 

The alpha transition, which involves motion in long segments of the main polymer chain, is related to the T. The beta transition involves rotation of short-chain ester side groups and therefore occurs below the Tg. The frequency dependency of the beta T can be used to calculate the activation energy for the molecular motion, which provides important information for characterising the structure and predicting the performance of polymeric materials. In a dielectric analysis experiment, the calculated activation energy for the beta transitions in PMMA was 17.7 kcal/mol. This correlates well with the values calculated from DMA and creep experiments. 

Figures 13.6(a) and (b) show the alpha and beta transitions obtained in dielectric thermal analysis of PET. The alpha transition (Tg) is affected by the large-scale micro-Brownian motion in the amorphous (non-crystalline) phase. The Brownian motion is observed as a peak in the 1 Hz loss factor cnrve at about 90 °C. The beta transition is considered to be a resnlt of main-chain motion involving the ester groups.

There are no abrupt transitions. The dynamic loss modulus or storage modulus (E") which relates to the polymer s ability to absorb mechanical shock and the mechanical loss factor tan delta (E /E ) show that glass transition of the polymer is at -30 C and that there is an alpha transition around 60 C. In general, the KYHAR homopolymer possesses useful mechanical properties from -80 c to 150 C. 

The use of differential scanning calorimetry to identify secondary transitions in thermoplastics is studied. The temperature and breadth of the secondary transition are related to the those of the alpha transition in a variety of methacrylate, acrylate and styrene polymers, as well as polycarbonate. The effect of thermal history and the position and sharpness of these endothermic transitions is discussed. Some comparisons are made between this technique and results obtained via dielectric analysis and dynamic mechanical analysis obtained in the laboratory. 7 refs. 

The glass transition of PPS was studied by means of DSC, FTIR spectroscopy and energy dispersive X-ray diffraction. All of the techniques showed the alpha-transition of the polymer. The results of the different techniques were consistent if the onset temperature for the DSC experiments was taken as representative of the glass transition. The glass transition temperature was found to vary as a function of the heating rate. The activation energy of the glass transition process was calculated by means of a theoretical model. The results were discussed. 47 refs. 

Thermodynamic equation of state Boltzmann constant Affine deformation Gaussian distribution Phantom chain approximation Phantom model Constrained fluctuation model Slip-link model Nonaffine slip tube model Mooney-Rivlin equation Visoelasticity of elastomers Alpha transition Beta transition Gamma transition Storage modulus... 

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