This study focuses on the development of a novel and simple catalyst-free one-stage gas phase synthesis process at atmospheric conditions for silicon carbide based nanomaterials. A mixture of high-purity quartz sand and graphite powder is heated as in air as under argon flow at atmospheric pressure using an industrial accelerator of nominal power 100 kW with a relativistic electron beam of continuous action. The carbothermal reduction reaction of silica occurs and micro granular hexagonal silicon carbide powder produced along with cubic phase SiC nanowires (SiCNWs) for different combinations of the process parameters. The mechanism of the formation of SiCNWs under gas flow is proposed, where Si nanoparticles act as an origin for the SiCNWs grow. The observed productivity shows that the process can be used for the large-scale production of high quality SiC nanowires as well as nano and micro powders of SiC.