Preparation and Mechanical Properties of Carbon Fiber Reinforced Multiphase Epoxy Syntactic Foam (CF-R-Epoxy/HGMS/CFR-HEMS Foam)

Short carbon fiber (CF), epoxy-hardener (EP-hardener), and expanded polystyrene (EPS) beads were used to prepare CF-reinforced hollow epoxy macrospheres (CFR-HEMS) by the "rolling ball method". The multiphase epoxy syntactic foam (ESF) was prepared with CFR-HEMS, the EP-hardener system, and hollow glass microspheres (HGMS) by the "compression modeling method". In this experiment, the influences of the stacking volume fraction, wall thickness, and inner diameter of the CFR-HEMS and HGMS types and contents in the EP-hardener system on the properties of the ESF were studied. In addition, CFs with different meshes were used to reinforce hollow epoxy macrospheres (HEMS) to study the effect of different kinds of CFs on the compressive strength of the ESF. During the mixing of the EP-hardener and HGMS (EP-hardener-HGMS), 300 AW CFs with different contents were added to the system to enhance the compressive strength of the ESF. The CFR-HEMS spherical wall was combined tightly with the EP-hardener-HGMS system by a scanning electron microscope (SEM). The ESF, which has better properties relatively in the experiment, can be used in 2673 m deep water and provide 490 kg/m³ buoyancy, which can be of help in the preparation of buoyancy materials in detection systems and oil extraction systems in the deep sea.

Development and Mechanical Characterization of HGMS-EHS-Reinforced Hollow Glass Bead Composites

Hollow glass microsphere-reinforced epoxy hollow spheres (HGMS-EHSs) were prepared by a "rolling ball method" using expanded polystyrene beads, HGMSs, and epoxy resin (EP). The three-phase epoxy syntactic foam (epoxy/HGMS-EHS-HGMS composite) was fabricated by combining HGMS-EHS as a lightweight filler with EP and HGMS by a "molding method". The HGMS-EHS and epoxy curing agent systems were well mixed by scanning electron microscopy. Experiments show that higher HGMS-EHS stack volume fraction, lower HGMS-EHS layer number, higher HGMS-EHS diameter, lower HGMS-EHS density, higher HGMS volume fraction, and lower HGMS density result in a decrease in the density of the three-phase epoxy syntactic foam. However, the above factors have the opposite effect on the compressive strength of the three-phase epoxy syntactic foam. Therefore, in order to obtain the "high-strength and low-density" three-phase epoxy syntactic foam, the influence of various factors should be considered comprehensively to achieve the best balance of compressive strength and density of the three-phase epoxy syntactic foam. This can provide some advice for the preparation of buoyancy materials for deep sea operations.

Preparation and Properties of C/C Hollow Spheres and the Energy Absorption Capacity of the Corresponding Aluminum Syntactic Foams

The present study focuses on the preparation and characterization of lab-scale aluminum syntactic foams (ASFs) filled with hollow carbon spheres (HCSs). A new and original process for the fabrication of HCSs was explored. Firstly, expanded polystyrene beads with an average diameter of 6 mm and coated with carbon fibers/thermoset phenolic resin were produced by the “rolling ball” method. In the next step, the spheres were cured and post-cured, and then carbonized at 1050 °C under vacuum to form the HCSs. The porosity in the shell of the HCSs was decreased by increasing the number of impregnation–carbonization cycles. The aluminum syntactic foams were fabricated by casting the molten aluminum into a crucible filled with HCSs. The morphology of the hollow spheres before and after carbonization was investigated by scanning electron microscope (SEM). The compressive properties of the ASF were tested and the energy absorption capacities were calculated according to stress–strain curves. The results showed that the ASF filled with HCSs which had been treated by more cycles of impregnation–carbonization had higher energy absorption capacity. The aluminum syntactic foam absorbed 34.9 MJ/m³ (28.8 KJ/Kg) at 60% strain, which was much higher than traditional closed cell aluminum foams without particles. The HCSs have a promising future in producing a novel family of metal matrix syntactic foams.

Rigid thermosetting epoxy/multi-walled carbon nanotube foams with enhanced conductivity originated from a flow-induced concentration effect

Rigid epoxy/MWCNT foams were innovatively prepared using expandable microspheres, a flow-induced concentration effect increases the inter-connectivity caused by the thermally triggered expansion of microspheres, improving the electric conductivity.