Silica-filled composites, thermal shock resistance

A comparison of critical temperature differences of resins filled with several ceramic particulates is shown in Figure 4. The volume fraction of all these composites is 34.2%. The critical temperature difference of epoxy filled with hard particulates was classified into three groups on the basis of thermal shock resistance. Composites filled with a strong particulate, such as silicon nitride or silicon carbide, showed high thermal shock resistance. Some improvement in thermal shock resistance was recognized for silica-filled composites. Composites filled with alumina or aluminum nitride showed almost comparable or lower resistance compared with the neat resin. 

Figure 5 shows the effects of filler content on thermal shock resistance at c/R - 0.2 for composites of silicon nitride, silicon carbide, silica, and alumina. The thermal shock resistance of resin filled with silicon nitride increases linearly with the volume fraction. The value of the thermal shock resistance is high, especially at higher volume fraction (Vf > 40%), that is, thermal shock resistance reaches 140 K (Figure 5a). The thermal shock resistance of composite filled with silicon carbide increases rapidly with the increase of filler content, and it reaches 135 K at Vf of 40%, which is similar to the case of silicon nitride (Figure 5b). In the case of silica-filled composites there is also an increase, but above a 30% volume fraction a plateau is reached (Figure 5c). Alumina-filled composites show a decrease in thermal shock resistance with filler content, then an almost constant value starting at Vf = 20% (Figure 5d).

The relationship between the ratio (ATc)exp/(ATc)cal and the volume fraction Vf is shown in Figure 9, where (ATc)exp is thermal shock resistance obtained by experiment. Where (ATc)exp/(ATc)cal = 1, it means that the thermal shock resistance can be evaluated well with equation 1. The thermal shock resistance of composites filled with silicon nitride, silica, and alumina can be especially evaluated at lower volume fractions. However, for silicon carbide, the ratio is not unity but greater than 1, and so the prediction of thermal shock resistance made with equation 1 is a conservative evaluation. In the case of alumina, on the other hand, the ratio (ATc)exp/(ATc)cal decreases remarkably with increasing Vf. These values of (ATc)exp/(ATc)cal are almost constant at lower volume fractions in every case. 

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

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See also in sourсe #XX -- [ ]

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