Alumina/multiwalled carbon nanotube (MWNT) composites with different MWNT contents ranging from 0.5to10vol% were prepared by spark plasma sintering technique. The dc electrical conductivity and dielectric properties of the composites were investigated and percolation theory was applied to demonstrate the electrical property transition from insulator to conductor. The experimental results have shown that the electrical conductivity increased sharply as the content of MWNTs was close to percolation threshold of 0.79vol%. In the low frequency range, the dielectric constant reached as high as 5000 when the content of MWNTs was at 1.74vol% and nearly frequency independent.

Multi-wall carbon nanotubes (MWCNTs)-3 mol% yttria-stabilized zirconia (3Y-TZP) (MWCNTs-3Y-TZP) composite was prepared by spark plasma sintering. The complex permittivities of the composite have been measured in the Ku-band range (12.4-18 GHz) and it is found that both the real and imaginary permittivities of the composite increase with the increasing content of MWCNTs. The effect of the content of MWCNTs on the electromagnetic interference (EMI) shielding effectiveness (SE) of the composite has been evaluated, and it is found that the EMI SE of the composite increases with the increasing content of MWCNTs. An EMI SE value as high as 25-30 dB has been achieved in the Ku-band range for the composite with 9 wt% content of MWCNTs, indicating that the MWCNTs-3Y-TZP composite can be used as an effective EMI shielding material.

MWCNT/3Y‐TZP (3 mol% yttria‐stabilized tetragonal polycrystalline zirconia) composites with different multiwall carbon nanotube (MWCNT) contents were prepared by the spark plasma sintering technique. The effect of MWCNT addition on the electrical and dielectric properties of the composites at room temperature was studied. The experimental results showed that the DC conductivity of the composites demonstrated a typical percolation behavior with a very low percolation threshold between 1.0 and 2.0 wt% MWCNT content, and the dielectric constant was greatly increased when the MWCNT concentration was close to the percolation threshold, which was attributed to dielectric relaxation, the space charge polarization effect, and the percolation effect.

Ti 3 SiC 2 was prepared by hot-pressing sintering. The dielectric permittivity and electromagnetic interference (EMI) shielding effectiveness (SE) are measured for the Ti3SiC2 material and pure titanium (Ti) metal in the frequency range of 8.2–18 GHz (X-band and Ku-band). The results show that Ti3SiC2 material exhibits high complex permittivities at the measured frequencies. Compared to the EMI-SE achieved by pure Ti metal, an EMI-SE value as high as 35–54 dB has been achieved in the X-band and Ku-band frequencies for Ti3SiC2 material, which suggests that it should be an effective EMI shielding material for structural applications.

The electrical conductivity of a composite prepared by dispersing multiwall carbon nanotubes in yttria-stabilized tetragonal zirconia matrix, and subsequent spark plasma sintering, is studied. The dc conductivity of the composites follows a scaling law of the type σ∝(p-pc)t, yielding for the percolation concentration pc=0.017 and for exponent t=3.3. The experimental result of the temperature of the conductivity suggests that for temperatures larger than 35K, conduction can be attributed to thermal fluctuation induced tunneling of the charge carriers through the insulating zirconia separating by the multiwall carbon nanotube clusters. At lower temperatures, variable range hopping conduction may be a dominant conduction mechanism.

Ti 3 Si C 2 ∕ Al 2 O 3 composites were prepared by hot-pressing sintering process. The dielectric permittivity and electromagnetic interference (EMI) shielding effectiveness (SE) is measured for the composites at the frequency range of 12.4–18GHz (Ku band). The experimental results show that the composites exhibit high complex permittivities at Ku-band frequencies, depending on the Ti3SiC2 content; both the real and imaginary permittivities of the composites increase with the increasing Ti3SiC2 content. The EMI SE of the composite was greatly enhanced with the addition of the Ti3SiC2 filler and increase with the dc conductivity of the composites. The high value of EMI SE shows the potential of the Ti3SiC2∕Al2O3 composite as EMI shielding materials.

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