Abstract
Brittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si3N4 and Al2O3 nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. The PSZs were thermally cross-linked and pyrolyzed under isostatic pressure in nitrogen. A combination of mechanical, chemical, density, and microscopy characterizations was used to determine the effects of these fillers. Si3N4 and Al2O3 nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (JIC) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Nanotubes were also effective in maintaining the integrity of the samples during pyrolysis. The modulus and hardness of PDCs correlated positively with their apparent density; this can provide a fast way to assess future PDCs. The improvement in fracture toughness was attributed to crack deflection and bridging observed in the micro-indentation cracks in the modified PDCs. The specific toughness of the modified PDCs was 4 × higher than that of high-purity alumina, and its specific modulus reached that of commercially available technical ceramics. These PDCs can also easily take different shapes and therefore are of interest in protective armor, propulsion, thermal protection, device packaging and biomaterial systems.
Highlights
Brittleness is a major limitation of polymer-derived ceramics (PDCs)
The mechanical properties of PDCs based on PSZ were improved by adding three different nanoscale fillers ( Al2O3, Si3N4, and CNTs) and using an isostatic pressure of 30 MPa during pyrolysis
The specific modulus of the modified PDCs was similar to technical ceramics, while these PDCs were tougher and much easier to form into complex shapes
Summary
Brittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si3N4 and Al2O3 nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. Si3N4 and Al2O3 nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (JIC) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Passive fillers dilute the preceramic polymer and decrease the amount of gas generated and the associated volume shrinkage This can reduce the possibility of forming cracks/voids during pyrolysis[12,20]. (Al2O3 and Si3N4 nanoparticles as well as carbon nanotubes) added to a commercial PSZ resin on the properties of the resulting PDCs, which are characterized in terms of composition, density, harness, modulus, and fracture toughness to guide the selection of these fillers for future studies (e.g. on 3D–4D printing of PDCs)
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