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The goal of the present paper was to study the behavior of commercially available pristine multi-walled carbon nanotubes (MWNTs) under microwave irradiation (exposures up to 200 s) in vacuum, by means of several experimental techniques. An intense glow and heating of the nanotube samples were observed. Raman spectra, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) images of the processed nanotubes did not show considerable changes as compared to those for pristine MWNTs. Closer structural investigation by means of conventional and high-resolution transmission electron microscopy (TEM and HRTEM, respectively) revealed an increase in the occurrence of open nanotube ends, whereas the sidewalls remained generally unchanged. The possibility of increase in the number of entry ports for gases was verified by employing temperature programmed desorption experiments with mass spectrometric detection (TPD-MS) with pristine and microwave-irradiated MWNTs exposed to atmosphere. The overall adsorption capacity did not change, whereas the rate of adsorption increased roughly by twice for the nanotubes irradiated for 200 s as compared to pristine MWNTs, which is consistent with selective opening of the nanotube ends.

A modified sol-gel process for synthesizing nanocrystalline hydroxyapatite powders (nHA) for biomedical applications, using tetrahydrated calcium nitrate [Ca(NO3)2∙4H2O] and phosphorous pentoxide [P2O5] as precursor, is presented and discussed. The powders were washed and heat-treated at different temperatures and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The total process time reached with this modified process was less than 16 h. The results showed that there was an increment in size of the HA nanocrystals (nHA) when treated at different temperatures, ranging from 30 nm for the sample treated at 600°C to 500 nm for the sample heat-treated at 1200°C.