Coefficient of thermal expansion glass transition temperatures

What are heat capacity, specific heat, thermal conductivity, coefficient of thermal expansion, glass transition temperature, melting temperature, and degradation and decomposition ... 

Glass transition temperature (Tg), coefficients of thermal expansion (CTE) at temperatures below and Ugher Tg, and the modulus of elasticity in the rubbery state (Eoo) were investigated. In the case of aligned polymers the thermal and mechanical properties were measured in the direction perpendicular and parallel to the magnetic field applied to the samples. 

Oxyhalide Glasses. Many glasses contain both oxide and haUde anions. The introduction of haUdes into an oxide glass typically serves to reduce the glass-transition temperature, T, and to increase the coefficient of thermal expansion. Oxyfluorophosphates have been investigated as laser host... 

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. 

Items 1 and 2 are experimentally measurable, but it should be borne in mind that highly heat-resistant seals may come at, or near, their glass transition temperature (Tg) during a cooling event, and the coefficient of thermal expansion changes in this region. 

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. 

Alterations by moisture exposure are very weak but shrinkage and coefficients of thermal expansion are high, as for other crystalline polymers. Moreover, the glass transition temperature is at room temperature. Creep resistance is low. 

Explosives and Binders Coefficients of Thermal Expansion CTE, Glass Transition Temperatures Tgr and Pressed Densities... 

Aluminum borate whiskers are produced commercially by an external flux method. Chlorides, sulfates, or carbonates of alkali metals are added to alumina and boric oxide (or boric acid) and the mixture is heated to 800°C-1000°C to produce aluminum borate whisker (length 10-30 pm and diameter 0.5-1.0 pm). It has a melting point of 1440°C, a very low coefficient of thermal expansion, and an excellent chemical resistance toward acids. The aluminum borate whisker was reported to be effective in improving not only the thermal degradation but also the glass transition temperature of epoxy76... 

Flexibilizers generally cannot be used to counteract internal stress in high temperature adhesive because of their relatively low glass transition temperature and thermal endurance properties. However, most high-temperature adhesive systems incorporate metallic fillers (generally aluminum powder) to reduce the coefficient of thermal expansion and degree of shrinkage. 

In order to select materials that will maintain acceptable mechanical characteristics and dimensional stability one must be aware of both the normal and extreme thermal operating environments to which a product will be subjected. TS plastics have specific thermal conditions when compared to TPs that have various factors to consider which influence the product s performance and processing capabilities. TPs properties and processes are influenced by their thermal characteristics such as melt temperature (Tm), glass-transition temperature (Tg), dimensional stability, thermal conductivity, specific heat, thermal diffusivity, heat capacity, coefficient of thermal expansion, and decomposition (Td) Table 1.2 also provides some of these data on different plastics. There is a maximum temperature or, to be more precise, a maximum time-to-temperature relationship for all materials preceding loss of performance or decomposition. Data presented for different plastics in Figure 1.5 show 50% retention of mechanical and physical properties obtainable at room temperature, with plastics exposure and testing at elevated temperatures. 

Table 10.6. Thermal properties of Si02 and some commercial glasses (Holloway 1973). TG temperature of glass transition below which the glass behaves as a rigid crystalline solid, Ts softening temperature above which the glass is soft enough to be worked or moulded, CTE coefficient of thermal expansion.

Fractional Free Volume and Coefficient of Thermal Expansion. The shift constants c and C2 from the WLF equation are not only fitting parameters that describe the frequency-temperature relation of a given polymer, but they are also related to chemical structure. Ferry has shown (6) that these constants can be related to the fractional free volume and coefficient of thermal expansion of the free volume, which have physical meaning in terms of the polymer structure. One can define the free volume at the glass transition divided by the total volume as fg and the coefficient of thermal expansion of... 

Further cooling of the polymer below results in a further decrease in V, which again follows the coefficient of thermal expansion of the solid polymer, until there is a change in slope of the plot at the glass-transition temperature, Tg. This is a second-order transition (in contrast to melting, which is a first-order transition) since there is a discontinuity in the second derivative of the free energy with respect to temperature and pressure, i.e. 

Experimental results and modeling strategy for the determination of stresses in thermosets used in microelectronics are presented. The bending beam technique for in situ stress measurement is particularly emphasized. This technique is here extended to determine the glass transition temperature, Tg, and the product of the elastic modulus and coefficient of thermal expansion,... 

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