Thermophysical features of carbon nanotubes frameworks formation by spark plasma sintering

Spark plasma sintering (SPS) is a promising technique to obtain consolidated samples of carbon nanotubes (CNTs). The standard enthalpies of formation (Delta H-f(298)0) of the sintered CNTs were determined by isothermal bomb calorimetry for the first time. It was found that Delta H-f(298)0 of CNTs decreased after its treatment at 800 degrees C at 10 and 30 MPa due to improvement of CNT structure and healing of the surface defects. After SPS at 1200 degrees C and at 30 MPa CNTs became less stable and their enthalpy of formation increased up to 35.88 +/- 5.40 kJ mol(-1) due to release of graphene layers, which exfoliated from the CNTs, that can help to combine several tubes in the consolidated structure. The oxygen-containing functional groups we found to eliminate from CNTs during sintering. Consolidated matter from them is appeared to be less stable than CNTs. All samples were characterized by thermal and elemental analysis, XPS, Raman spectroscopy and electron microscopy. (C) 2020 Elsevier Ltd. All rights reserved.