Revisiting pyroplastic deformation. Application for porcelain stoneware tile bodies E. Sánchez (a) , V. Sanz (a) , E. Cañas (a,*) , J. Sales (b) , K. Kayacı (c) , M.U. Taşkıran (c) , Ü.E. Anıl (c) , Ş. Türk (c)
The work addresses the effect of the particle size of a bioactive glass feedstock on the processing and microstructure of the resulting coatings obtained by atmospheric plasma spraying (APS). It was observed that the reduction of particle size negatively affects the flowability of the powder. In addition the thermal behaviour (weight losses, glass transitions, crystallisations, etc) also depended on the particle size of the glass powder.No coating was obtained with the coarser fractions (higher than 200 µm) due to their low melting degree in the plasma. For the intermediate fractions (200 to 63 µm) coatings were obtained but insufficient particle melting was produced. On the contrary, the finest fraction (<63 µm) needed a fluidiser which enabled the samples to be sprayed.
A bioactive glass was dry-milled and sieved in order to obtain powders with particle size finer than 63 µm. Two suspensions, with different particle size distribution (D50 = 8.3 µm and D50 = 2.2 µm), were subsequently obtained from milling those powders in an organic solvent (dipropylene glycol methyl ether) by using two different grinding steps. The obtained suspensions were characterised and stabilised to produce adequate feedstocks to be used in suspension plasma spraying technique. For that purpose, sedimentation tests as well as rheological characterisation were carried out on both suspensions. Only the suspension feedstock containing the finest particle size, managed to produce a coating with suitable thickness and adherence on the substrate when a TiO2 bond coat was used. Besides X-ray diffraction findings confirmed the amorphous nature of the obtained coatings. However coating microstructure displayed many round, closed pores and surface observation revealed the presence of abundant non-deformed splats.
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