Preparation And Properties Of Negative Thermal Expansion Materials And Their Epoxy Composites

Epoxy matrix composites have been widely applied in the cryogenic field because of their high specific strength, specific stiffness, good electrical insulation and heat insulation performance at cryogenic temperature. However, high thermal expansion coefficient of epoxy matrix composites easily results in the thermal expansion mismatch problems between epoxy matrix composites and other materials. The excellent negative thermal expansion ZrW2O8was doped into epoxy resin to reduce thermal expansion coefficient of epoxy composites, expanding the application of epoxy composites in the cryogenic field. Preparation and properties of negative thermal expansion material ZrW2O8and its epoxy composites were mainly studied in this paper. Furthermore, ZrW2-δMoδO8solid solutions and ZrW1.6Mo0.4O8/epoxy composites were preliminary studied.The precursor ZrW2O7(OH)2(H2O)2was synthesized by hydrothermal method with (NH4)6W7O24·6H2O and ZrOCl·8H2O as raw materials. ZrW2O8was obtained after the precursor was sintered at a certain temperature. The synthesized ZrW2O8and its precursor are strongly similar in morphology, show rodlike shape and grow along a specific direction. ZrW2O8obtained from6～8mol/L HC1is fine and uniform.The cryogenic mechanical properties of ZrW2O8doped epoxy composites are improved. The tensile and bending strengths of the composites at77K increase initially up to the maximum at9.9wt%ZrW2O8. The maximum values are127.09MPa and102.07MPa, respectively. With the increase of ZrW2O8amount, thermal expansion coefficient of the composites gradually decreases between77K and300K. Thermal expansion coefficient of the composites with24.8wt%ZrW2O8reduces to37.33×10-6K-1, which is19.86%lower than that of epoxy matrix without ZrW2O8.A series of ZrW2-δMoδO8solid solutions with different mole ratios of W6+and Mo6+were synthesized by replacing W with Mo during the hydrothermal synthesis process of ZrW2Os. With the increase of Mo substitution amount, the crystal structures of ZrW2-δMoδO8gradually vary from α-ZrW2O8to β-ZrW2O8. Thermal expansion coefficient of ZrW1.6Mo0.4O8/epoxy composites will gradually reduces with the increase of ZrW1.6Mo0.4O8amount, which is similar to the effect of ZrW2O8on thermal expansion coefficient of ZrW2O8/epoxy composites. Thermal expansion coefficient of the composites reduces from46.58×10-6K-1to37.58×10-6K-1when ZrW1.6Mo0.4O8increases from0to24.8wt%.