Detonation spraying of hollow microspherical alumina powder

摘要

At thermal, including detonating, spraying of metal oxides powders (Al_2O_3, ZrO_2, etc.) consisting of dense (fused and crushed) particles the main lack of process is essential inhomogeneity of aggregate state of particles in the section of spraying spot. It is explained by that, even knowing surface temperature of spraying particles, it is impossible to control the level of their bulk melting, due to low thermal conductivity of material and various residence times in the flow, which is characterized by considerable gradients of velocity and temperature ("trajectories" effect). All this does not allow obtaining the coatings with optimum characteristics. When spraying hollow microspherical powders "solid shell - inner gas cavity" it is possible to guarantee that the material of shell (thickness of 5-10 microns) is completely melted and temperature distribution in its cross-section is uniform. That is significant argument in favor of the powders consisting of hollow particles with low thermal conductivity. The purpose of the present work was carrying out model comparative investigations of coatings at detonating spraying of narrow-fractional hollow and dense α-Al_2O_3 powders.