Fiberglass, thermal expansion

All VGCF was graphitized prior to composite consolidation. Composites were molded in steel molds lined with fiberglass reinforced, non-porous Teflon release sheets. The finished composite panels were trimmed of resin flash and weighed to determine the fiber fraction. Thermal conductivity and thermal expansion measurements of the various polymer matrix composites are given in Table 6. Table 7 gives results from mechanical property measurements. 

The major use of boric acid is as the starting material for its anhydride, boron oxide, B203. Because it melts (at 450°C) to a liquid that dissolves many metal oxides, boron oxide (often as the add) is used as a flux, a substance that cleans metals as they are soldered or welded. Boron oxide is also used to make fiberglass and borosilicate glass, a glass with a very low thermal expansion, such as Pyrex (see Section 14.21). 

Controlling Thermal Expansion. The rate of thermal expansion is a function of the components used in the base material and their relative concentrations. The resin system will have a relatively high coefficient of thermal expansion compared to fiberglass cloth or other types of inorganic reinforcements. 

In controlling z-axis expansion, the key factors to consider are the choice of resin system, the resin system Tg, and the resin content of the base materials. Fillers in the resin system, in addition to the fiberglass cloth, can also be used to lower the CTE of the material. Table 8.1 compares the thermal expansion of several commercially available base materials. These values can vary significantly based on the exact resin content of the material or PCB tested. In multilayer PCBs, the amount of copper in the sample will also have a significant impact as the z-axis expansion of copper is very low compared to the resin system. 

The thermal expansion and contraction due to cooldown is often the primary concern in the operation of these large tanks. After several cooling and warming cycles, the perlite tends to compact to such an extent as to cause structural damage to the inner vessel. Fortunately, this problem has been solved by attaching a resilient blanket of compressed fiberglass to the inner shell to handle the necessary expansion and compression occurring in the insulation space. 

These copolymers are thermally stable, but they have slightly lower tensile strengths than the homopolymer The copolymer has a lower heat deflection temperature (110 C) and a low coefficient of friction and specific gravity. When reinforced by 25% fiberglass, the copolymer has a heat deflection temperature of 160 C, a coefficient of linear expansion of S.O X 10 cm/ cm C, a specific gravity of 1.61, and much higher tensile and flexural strengths than the unfilled copolymer. 

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