A 3D simulation of the thermal plasma spraying process is reported. In particular, the effect of the radial injection of a carrier gas is taken into account for a dilute spray. The thermal history of powder particles of different sizes is predicted. It is shown that introduction of a carrier gas can lead to a significant modification of the plasma jet, and can have an effect on the thermal histories of the injected particles. The study is motivated by the processing of non-traditional materials, specifically nanostructured ceramics.