Coefficient of thermal expansion values

Coefficient of thermal expansion. Values of about 140 x 10 have been reported [13.3]. 

Coefficient of Thermal Expansion. Values of the average linear coefficient of thermal expansion for some Al-based materials at temperatures of practical significance are given in Table 3.1-15. Alloying leads to... 

Stresses also arise in polyesters due to their high coefficients of thermal expansion. Values for polyesters are in the range of 36 to 72 x 10- mm/mm/°C, whereas those for steel are typically only 11 x 1(T mm/mm/°C [17], Fillers and reinforcements are important for minimizing the stresses caused by temperature changes. 

The coefficient of thermal expansion is defined as the fractional change in length or volume of a material for a unit change in temperature. The coefficient of thermal expansion values for different plastics are of considerable interest to design engineers. Plastics tend to expand and contract anywhere from six to nine times more than materials such as metals. This difference in the coefficient of expansion... 

Coefficient of thermal expansion values, as well as compositions and other properties of the aluminum and copper alloys used for electrical wiring, are presented in Table 18.2. 

Room-T emperature Linear Coefficient of Thermal Expansion Values for Various Engineering Materials... 

This table lists values of /3, the cubical coefficient of thermal expansion, taken from Essentials of Quantitative Analysis, by Benedetti-Pichler, and from various other sources. The value of /3 represents the relative increases in volume for a change in temperature of 1°C at temperatures in the vicinity of 25°C, and is equal to 3 a, where a is the linear coefficient of thermal expansion. Data are given for the types of glass from which volumetic apparatus is most commonly made, and also for some other materials which have been or may be used in the fabrication of apparatus employed in analytical work. 

Table 7 gives the composition of gold alloys available for commercial use. The average coefficient of thermal expansion for the first six alloys Hsted is (14-15) X 10 j° C from room temperature to ca 1000°C two opaque porcelains used with them have thermal coefficient expansion of 6.45 and 7.88 X 10 from room temperature to 820°C (91). The HV values of these alloys are 109—193, and the tensile strengths are 464—509 MPa (67-74 X 10 psi). For the last four alloys in Table 7, the HV values are 102—216, and the tensile strengths are 358—662 MPa (52-96 x 10 psi), depending upon thermal history. 

Automated soldering operations can subject the mol ding to considerable heating, and adequate heat deflection characteristics ate an important property of the plastics that ate used. Flame retardants (qv) also ate often incorporated as additives. When service is to be in a humid environment, it is important that plastics having low moisture absorbance be used. Mol ding precision and dimensional stabiUty, which requites low linear coefficients of thermal expansion and high modulus values, ate key parameters in high density fine-pitch interconnect devices. 

A key factor in the suitabihty of cokes for graphite production is their isotropy as determined by the coefficient of thermal expansion. After the calcined coke was manufactured into graphite, the axial CTE values of the graphite test bars were determined using a capacitance bridge method over a temperature range of 25 to 100°C. The results are summarized in Table 24. Also included in the table are bulk density measurement of calcined cokes and the resistivity values of their graphites. 

The other principal thermal properties of plastics which are relevant to design are thermal conductivity and coefficient of thermal expansion. Compared with most materials, plastics offer very low values of thermal conductivity, particularly if they are foamed. Fig. 1.10 shows comparisons between the thermal conductivity of a selection of metals, plastics and building materials. In contrast to their low conductivity, plastics have high coefficients of expansion when compared with metals. This is illustrated in Fig. 1.11 and Table 1.8 gives fuller information on the thermal properties of pl tics and metals. 

The change in shape of a material when it is subjected to a change in temperature is determined by the coefficient of thermal expansion, aj- Normally for isotropic materials the value of aj will be the same in all directions. For convenience this is often taken to be the case in plastics but one always needs... 

There are standard procedures for determining aj (e.g. ASTM 696) and typical values for plastics are given in Table 1.2. It may be observed that the coefficients of thermal expansion for plastics are higher than those for metals. Thus if 50 mm lengths of polypropylene and stainless steel are each heated up by 60°C the changes in length would be... 

Thermal expansion — as elasticity — depends directly upon the strength of the intermolecular forces in the material. Strongly bonded materials usually expand little when heated, whereas the expansion of weak materials may be a hundred times as large. This general trend is confirmed by Table 5.1. The coefficient of thermal expansion a was found to be lower in the crosslinked polymers and higher in the less crosslinked or thermoplastic materials as observed by Nielsen [1], In addition, Table 5.1 presents the Young s moduli E of the polymers at ambient temperatures as well as the products a2E. The values of oc2E are all close to 13.1 Pa K 2 with a coefficient of variation of 1.6%. 

Both of these are equations are approximate and are useful only for giving estimates of the value of the of the polyblend or copolymer. To calculate values of more accurately requires additional information such as the coefficients of thermal expansion of both components in both their liquid and glassy states. Given the uncertainty in the numerical value of T, which as we have seen depends on the method by which has been determined, there is little point in developing such arithmetical refinements. 

Case 2. For data sets that do not meet the criteria of Case 1, but contain acceptable values over a temperature range of at least two degrees, the results are smoothed using a linear function of temperature with an estimated coefficient of thermal expansion. A table of smoothed recommended values is presented. 

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