INDEX temperature expansion

The most important properties of commercial glasses are the density, refractive index, thermal expansion coefficient, glass transformation temperature, strength and elastic modulus, and chemical durability. These properties will be reviewed for each of the major categories of commercial glasses. 

Most of the other properties of vitreous silica are only slightly affected by the hydroxyl concentration. While it is possible to measure the effect of hydroxyl content on the density, refractive index, thermal expansion coefficient, dielectric constant, and other properties of vitreous silica, the effects are very small as compared to those for the flow and optical transmission behavior. The density of commercial vitreous silica ranges from 2.197 to 2.203 gcm while the refractive index is 1.457 0.003 for most products. Since the effects of hydroxyl on the properties of vitreous silica are of the same magnitude as the effects of changes in fictive temperature, it is very difficult to separate the effect of hydroxyl from those of thermal history. 

The reference temperature NDT, RTf, is also an index temperature used as a normalization tool to compare the behaviour of different materials and different heats of materials. The RTndt is determined according to procedures outUned in the ASME Boiler and Pressure Vessel Code (ASME, 2013 a) and is a combination of the NDT temperature and Charpy impact test results. Briefly, the RTndt is the higher of either the NDT temperature or Tso - 60°F (33 C), where T q is the temperature at which three Charpy impact specimens achieve energy and lateral expansion values of at least 50 ft-lb (68 J) and 0.035 in. (0.89 mm), respectively. A more detailed discussion of this reference temperature can be found in Chapter 1. Similarly, for WWER RPVs, the CVN-based temperature called the critical temperature of brittleness, 21, is used as a reference temperature. These references are discussed in subsequent sections as used for various test methods. 

By an assortment of thermodynamic manipulations, the quantities dn/dp and [N (d G/dp )o] can be eliminated from Eq. (10.48) and replaced by the measurable quantities a, /3, and dn/dT the coefficients of thermal expansion, isothermal compressibility, and the temperature coefficient of refractive index, respectively. With these substitutions, Eq. (10.48) becomes... 

T and are the glass-transition temperatures in K of the homopolymers and are the weight fractions of the comonomers (49). Because the glass-transition temperature is directly related to many other material properties, changes in T by copolymerization cause changes in other properties too. Polymer properties that depend on the glass-transition temperature include physical state, rate of thermal expansion, thermal properties, torsional modulus, refractive index, dissipation factor, brittle impact resistance, flow and heat distortion properties, and minimum film-forming temperature of polymer latex... 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Investigating coextrusion of com meal and WPI, Onwulata et al. (2003b) found that the melt temperature of the extmdate was more of an indicator of physical properties than specific mechanical energy. Quality attributes such as breaking strength, color, and expansion index were related to melt temperature measured at the die. 

The transition between crystalline and amorphous polymers is characterized by the so-called glass transition temperature, Tg. This important quantity is defined as the temperature above which the polymer chains have acquired sufficient thermal energy for rotational or torsional oscillations to occur about the majority of bonds in the chain. Below 7"g, the polymer chain has a more or less fixed conformation. On heating through the temperature Tg, there is an abrupt change of the coefficient of thermal expansion (or), compressibility, specific heat, diffusion coefficient, solubility of gases, refractive index, and many other properties including the chemical reactivity. 

Both kinetic and thermodynamic approaches have been used to measure and explain the abrupt change in properties as a polymer changes from a glassy to a leathery state. These involve the coefficient of expansion, the compressibility, the index of refraction, and the specific heat values. In the thermodynamic approach used by Gibbs and DiMarzio, the process is considered to be related to conformational entropy changes with temperature and is related to a second-order transition. There is also an abrupt change from the solid crystalline to the liquid state at the first-order transition or melting point Tm. 

C poly 1,4-isoprene has a specific gravity of 0.91, a coefficient of linear expansion of 67 X 10 9 cm/cm C, and a refractive Index of 1.5191. This and other elastomers retain their characteristic mobility at temperatures above the Tt. They are brittle at temperatures below Tg. 

Commercial barrier resins which are used as packaging films and blown bottles are produced by blending copolymers of acrylonitrile, ethyl acrylate, and butadiene with selected copolymers of acrylonitrile. These barrier resins have a Tg of about 125 C, a coefficient of linear expansion of 6.7 X 10 5 cm/cm C, a heat deflection temperature of 77 C, and an index of refraction of 1.511. These resins are resistant to nonoxidizing alkalis and acids and are decomposed by mineral acids. 

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