The sintering and grain growth behaviour of ceramic–carbon nanotube nanocomposites

The production of advanced fine-grained alumina by carbon nanotube addition

“…Figure 2d also shows individual and homogenously dispersed CNTs in the alumina matrix. This is consistent with our previous work where CNTs were located at the grain boundaries and retard grain coarsening by reducing their mobility during sintering [12]. Therefore, homogenous dispersion of CNT is crucial for achieving narrow grain size distribution in the final heat treated alumina.…”

“…CNTs lower the hardness of the composite despite it having a >10 times finer grained microstructure as compared to alumina (figure 2), due to their graphitic (lubricating) nature and poor cohesion with alumina grains [10,22]. In comparison, ceramic dopants [38] and CNTs [12] suppress grain growth and improve the sinterability of alumina, their effect on the mechanical properties is quite different. For instance, there is no difference in hardness between an undoped alumina and the MgO/ Y 2 O 3 doped (500 ppm) alumina [38].…”

“…The grain size of the alumina (4.86 ± 0.81 µm) is much coarser than that of the alumina + 1 vol.% CNT composite (0.39 ± 0.19 µm, figure 2). In previous work, the effect of carbon black (CB) on densification and grain growth was also studied [12]. As compared to CB, CNTs significant refine final grain size of alumina and a much lower sintering temperature is required for full-densification of alumina composite [12].…”

“…In previous work, the effect of carbon black (CB) on densification and grain growth was also studied [12]. As compared to CB, CNTs significant refine final grain size of alumina and a much lower sintering temperature is required for full-densification of alumina composite [12]. Higher magnification analysis of alumina (figure 2b) shows very fine porosity on the grains.…”

“…In the case of ceramic matrix composites (CMCs) [7], CNTs have been reported to improve the electrical conductivity [4,5], thermal conductivity [8], fracture strength [5] machinability [9], indentation fracture toughness [10], and contact damage resistance [11]. We recently reported that CNT addition significantly retards grain growth and lowers the full densification sintering temperature of polycrystalline CMCs [12]. The fine microstructure that this produces is advantageous improving mechanical properties.…”