thermal spray apparatus capable of directing plasticized powders against a substrate for deposition of a protective coating thereon is disclosed . various structural details of the apparatus of the present invention enable the attainment of high particle velocities without melting the particles . the apparatus is built around the concept of reducing the temperature of a hot plasma stream after the hot plasma stream is generated . particles are injectedinto the hot plasma stream only after the medium is cooled . in detailed embodiments , a generated plasma is cooled by the addition of a diluent gas or by passing the generated plasma through an elongated heat exchanger upstream of the point at which the powders are to be injected .