Q2. What is the promising way to produce CNTs?
A ®rst way to produce CNTs is the arc-discharge between carbon electrodes in inert gas atmospheres, using Fe or Co as catalysts to increase both the quantity and length of the tubes and to favour the formation of SWNTs [8].
Q3. What is the effect of the residual porosity on the mechanical properties of CNTs?
The residual porositymay impair the mechanical resistance and a partial annihilation of the di erent reinforcement mechanisms may operate.
Q4. What is the role of CNTs in composites?
CNTs emerge as potentially attractive materials as reinforcing elements in composites, particularly in ceramic±matrix composites.
Q5. What is the Young's modulus of MWNTs?
Theoretical and experimental studies have shown that CNTs have excellent mechanical properties: the Young's modulus of MWNTs has been calculated to be up to 1.4 times that of a graphite whiskers [5] and values derived from thermal vibrations experiments performed on several MWNTs in a transmission electron microscope [6] are in the 0.4±3.7 TPa range.
Q6. What is the way to achieve a CNTsceramic composite?
to achieve a CNTs±ceramic composite from as-prepared CNTs, it would be necessary to disperse homogeneously CNTs in a ceramic powder.
Q7. How is the carbon obtained in the composite powders?
The authors have shown that to obtain carbon essentially in the form of nanotubes in the composite powders, it is necessary to operate from the stable a-solid solution rather than from amorphous or Z; solid solutions [11], and it is preferable to reduce the monophase oxide solid solutions (cat% Fe 4 10) rather than mixtures [12] of Al2O3-rich and Fe2O3-rich solid solutions.
Q8. What is the effect of the reduction vessel on the crystalline structure of the composite powder?
the reduced powder is so densely agglomerated that it retains the shape of the reduction vessel when transferred in a storage box.
Q9. What is the method to achieve a CNTs-ceramic composite?
The ®rst di culty to achieve a CNTs-ceramic composite from as-prepared CNTs, is to disperse homogeneously the CNTs in a ceramic powder.
Q10. How was the oxide solid solution reduced?
The oxide solid solutions were reduced in a H2±CH4 atmosphere at various temperatures (Tr) using di erent CH4 contents and during di erent times (tr), as required for the study.
Q11. What is the effect of increasing the reduction temperature in the gas atmosphere?
Increasing the reduction temperature Tr (Fig. 4a,b) enhances the carbon content in the nanocomposite powder (Cn) and favours the quantity of nanotubes( S) because of a higher CH4 supersaturation level in the gas atmosphere, but also provokes a decrease in carbon quality ( S/Cn).
Q12. What is the interlayer distance between graphene sheets?
The measured interlayer distance (0.34 nm) is very close to that measured between graphene sheets in graphite and no particular correlation appears between the chirality of concentric layers.
Q13. What is the method for synthesis of CNTs?
Milling the starting solid solution by the attrition method allows the synthesis of powders in which the relative dispersion of CNTs bundles and matrix grains is considerably enhanced (Fig. 2d).
Q14. What is the effect of the nanotubes?
Although some of the SEM observations seem to indicate that the nanotubes bundles could dissipate some fracture energy, the obtained mechanical propertiesshow that the reinforcement e ect that was expected from the addition of very long carbon nanotubes bundles is not observed.
Q15. What is the ratio of S /Cn?
The ratio S /Cn , can be considered as representing the quality of the nanotubes, a higher ®gure for S/Cn denoting a smaller average tube diameter and/or more carbon in tubular form [4,11,12], which the authors consider a better quality of carbon.