Abstract
Spraying distance (SD) is one of the main parameters that can affect the spraying process - its efficiency as well as deposit's character. The reason lies in a different thermal history of particles corresponding to different spraying distances. Variation in the structure, preferred orientation, variation of the phase contents and/or in the chemical composition of deposits can be then found for different SDs. Consequently, properties of coatings can greatly vary, not only in the resistance state but also on deposit's annealing. Some materials are, however, more and some less sensitive to that effect. The goal of this work is to compare CaTiO3 samples produced by plasma spraying with WSP at SD = 350 and 450mm with sintered samples. The following properties were compared: microhardness, thermal expansion coefficient, permittivity and reflectivity. Porosity and the differential thermal analysis of resistance and annealed deposits were also compared. Perovskite CaTiO3 belongs among materials very stable during spraying - neither chemical nor phase differences were found between the feedstock powder, free-flight particles, as-sprayed deposit and annealed deposit. Despite that there are significant differences in behavior of deposits and freestanding parts sprayed from different SDs. All the recorded differences for CaTiO3 plasma sprayed deposits with varying SDs must be therefore accounted to the deposit's structural differences, such as pore and splat sizes and shapes and preferred orientation. Additional differences on annealing can be probably attributed to the different amount of "stored" thermal energy in deposits due to the varying SD. However, there is a lower limit for SD assuring a quality deposit on spraying.
