Preparation And Properties Of Bi-continuous Hollow Glass Microsphere/Epoxy Resin Matrix Solid Buoyancy Materials

Hollow glass microsphere(HGM)/resin-based syntactic foams are characterized by low density,high strength and elastic modulus,high specific strength and specific modulus.These foams are important buoyancy materials used in deep sea exploration,oil exploitation,ships,and other marine equipment.However,the performance of domestically-manufactured HGM is relatively poor,and high-performance HGM relies on being imported.The prepared syntactic foams have a poor uniformity,low mechanical properties,internal pore defects,and poor interfacial properties between HGM and the matrix.Also,it is difficult to obtain uniform dispersion of the reinforcing phase,and this has a serious effect on the integrated performance of syntactic foams.Therefore,the preparation of a uniform,high-performance syntactic foam material that does not have pore defects is of great significance.In this paper,domestically-manufactured HGM was used as raw material,and a method for preparing bi-continuous HGM/resin-based syntactic foam material via vacuum-assisted resin transfer molding is proposed.This solves the following problems:the pores inside the matrix cannot be eliminated,the uniformity of material is poor,and the reinforcing effect of the reinforcing phase is poor.The microstructure and integrated properties of the syntactic foam material were systematically studied,and the fracture damage mechanism of syntactic foam material and the hybrid reinforcing mechanism of reinforcing phase were found.HGM porous ceramics were prepared via that stacking-sintering method.The density of the HGM porous ceramics increased with the sintering temperature and real density of HGMs.When the sintering temperature was 700?and the holding time was 1h,the microspheres were intact and had the lowest open porosity(about 35vol%).According to Stokes'law,using polyacrylamide as a thickener increased the viscosity of the HGM aqueous slurry and reduced the floating rate of HGM.Thus,a uniformly dispersed,stable HGM aqueous slurry with a good fluidity was prepared.Through gel-casting,HGM porous ceramics can be prepared with a volume fraction ranging from 30vol%to 55vol%.The compressive strength of ceramics increased with sintering temperature and density,and the relative strength increased with the relative density.This is consistent with the power function proposed by Gibson and Ashby for the relationship between relative strength and relative density.The HGM ceramics with 30vol%-65vol%HGM were used as a preform,and the HGM/resin-based syntactic foam material with a bi-continuous structure was prepared via VARTM.The effects HGM type and content on the density,mechanical properties,and water absorption of the composite materials were systematically studied.The density of syntactic foams ranged from 0.567g/cm~3 to 1.002g/cm~3,and the experimental density was basically the same as the theoretical density.From microscopic morphology observation,it is concluded that there were no pores in the matrix.The density,compressive strength,and flexural strength of the composite foam material decrease with HGM content.The breakage of HGM and the epoxy resin matrix as well as the destruction at the interface between HGM and the resin matrix were the main reasons for the failure of the composite foams under a compressive load.It was concluded that erosion of HGM and interface between HGM and the resin matrix by water molecules were the main reasons for the increase in water absorption and the decrease in mechanical properties.To study the reinforcing effect and reinforcing mechanism of reinforcing phases that have different morphologies,graphene(GO),carbon nanotubes(CNTs),and in situ nano-SiO2 particles were used as reinforcing phases to improve the properties of syntactic foams.GO and CNTs with a lamellar structure/HGM preform with?58vol%HGM were prepared via freeze drying,and GO and CNT-reinforced composite foam materials were prepared via VARTM.Under the action of ice crystals,GO and CNTs in the HGM preform are distributed in a directional lamellar state without agglomeration.The density of the syntactic material increases with increases in the GO and CNT contents,and the compressive strength increases 13.35%by GO and24.52%by CNTs,respectively.The reinforcing mechanism is that GO and CNTs enhance the strength of the resin matrix and that CNTs increase the interfacial bonding strength between HGM and the resin.The water absorption rate of the syntactic foams is reduced because of the barrier effect of GO with respect to water molecules and because of the hydrophobic effect of CNTs.Finally,silica sol infiltrated the preform with?65vol%HGM via vacuum impregnation.The in-situ nano-SiO2/HGM preform was successfully prepared via the drying method at ambient pressure.The nano-SiO2 content in the HGM preform can be controlled by adjusting the content of anhydrous ethanol in silica sol.The in-situ nano-SiO2-reinforced syntactic foam materials were prepared using VARTM.The highest density of the composite material was 0.721g/cm~3,increase of 5.41%in density;the compressive strength was 107.5MPa,increase of 29.1%in strength.The uniformly dispersed nano-SiO2 particles provide a larger interface;this increases the fracture work and simultaneously hinders the motion of epoxy macromolecular chains and the propagation of cracks.Also,nano-SiO2 increases the surface roughness of HGM and enhances the interfacial bonding strength between HGM and the resin matrix,and this further enhances the mechanical properties of the syntactic foams.