Structural transformations in carbon nanotubes during thermal spray processing

This study compares the interaction of carbon nanotubes (CNTs) with the flame/energy sources during different thermal spray processes viz. plasma spraying (PS), high-velocity oxy fuel spraying (HVOF), cold spraying (CS), and plasma spraying of liquid precursor (PSLP). CNTs were successfully retained as reinforcement in metal and ceramic composite coatings in all thermal spray processes except PSLP. The retention of CNT structure is attributed to micron size metal/ceramic powder which acts as a carrier and thermal shield against high heat in plasma spraying (PS) and high-velocity oxy fuel spraying (HVOF). However, vaporization of CNTs occurred in PSLP under the intense heat of the plasma which is attributed to phase transformation in unshielded CNTs.