To obtain porous carbon, the raw material is first charred, then subjected to activation. The essence of activation consists in opening the pores in the carbon material in the closed state. Activation is carried out in various ways with additives of substances, steam treatment .... You want to get it without activation. So you need to adjust the temperature, pressure. I think that it is possible to choose for each type of raw material such temperature, amount of air and pressure less than atmospheric to get pores.

Thank you for your answer Mr Mirgorod and following the discussion,

During my PhD thesis I noticed, that carbon powder (synthetized by electric arc discharge) has surface area around 200 m2/g. So then I heated the carbon under static air atmosphere (400 degC) during 4 hours. SSA increased up to 1000 m2/g... I also checked other temperatures like 450 and 500. In higher temperatures especially 500, surface stays at 200 m2/g... I do not know how I should explain this result. That is why I was thinking about self-ignition of the carbon at temperatures around 500 and higher what can influence the porosity... however I do not know how structure is changing exactly during this process...

Thank you for your answer and ideas.

You know that carbon can have several structures: graphite, diamond, carbin, and a different mixture of these structures. Otherwise, the electrons of the carbon atom can be on the surface in the state of sp3, sp2, sp hybridization. To do this, you need to use the method of x-ray photoelectron spectroscopy.

Thank you Mr Mirgorod. It is an important advice!

Self-heating ignition of natural reactive porous media

https://spiral.imperial.ac.uk › bitstream › Restuccia-F-2018-PhD-Thesisby F Restuccia

Probably, there are some impurities acting as additives that are responsible for changing surface area, may be due to conversion of carbon structures at this temperature. Structural features could be the main reason for this.