Role of suspension preparation in the spray drying process to obtain nano/submicrostructured YSZ powders for atmospheric plasma spraying

Abstract

Thermal barrier coatings were manufactured by atmospheric plasma spray process from YSZ powders. These powders were made by a reconstitution process which consists in a spray-drying of suspensions followed by thermal treatment of the granules.Nano-and submicron-sized YSZ particles were used as starting material. Feeding well dispersed suspension to spray-drying chamber is the first key step in the reconstitution process. With this aim, concentrated, stable YSZ suspensions were obtained by means of the optimisation of the preparation conditions. Then reconstituted granules were produced by spray-drying of the YSZ suspensions and the following thermal treatment which was optimised.The reconstituted powders were then successfully deposited on austenitic stainless steel coupons by APS. The findings in this work proved that the reconstituted powders characteristics which in turn are related to the starting suspension properties affect the final coating microstructure in terms of the amount of unmelted zones.

Aqueous suspension processing of multicomponent submicronic Y-TZP/Al 2 O 3 /SiC particles for suspension plasma spraying

“…3b. The isoelectric point occurs at pH6, in good agreement with previously reported values [30][31][32]. The addition of 0.2 wt% PAA shifts down the iep to pH 3 and provides large values of zeta potential at neutral pH (-60 mV at pH 6).…”

“…As starting raw materials, the following commercially available powders were used: 1) α-alumina (CT3000SG, Almatis, Germany), with an average particle size of 0.5 µm and a specific surface area of 8 m 2 /g; tetragonal zirconia polycrystals doped with 3 mol% Y2O3 (TZ-3YS, Tosoh, Japan), with an average particle size of 0. was selected as a deflocculant for both oxides [24,30,31] and a synthetic polyelectrolyte (PKV, Produkt KV5088, Zschimmer-Schwarz, Germany) with unknown composition (but that it is thought to be of polycarboxylic nature), which has demonstrated its suitability for the dispersion of non-oxide ceramics, such as SiC powder [29]. In order to perform the measurements, diluted suspensions of every powder were prepared to a concentration of 0.01 g/L using KCl 0.01 M as inert electrolyte and adjusting the pH values with HCl and KOH 1M solutions.…”

Alumina-zirconia coatings obtained by suspension plasma spraying from highly concentrated aqueous suspensions

“…In addition, a commercial salt (DURAMAX TM D-3005, Rohm & Haas/Dow Chemicals, USA) of polyacrylic acidbased polyelectrolyte (PAA), with 35 wt% active matter, was used as dispersant in order to achieve the colloidal stability of the powders in water. This dispersant has been used in other previous works with alumina and zirconia powders [18,19].…”

“…The pH values were determined with a pH-meter (Titrino DMS 716, Metrohm, Switzerland) and they were adjusted with HCl and KOH solutions. Zeta potential measurements are suitable to establish the optimal amount of dispersant in the suspensions [12,18].…”

“…In previous works, the colloidal stabilisation of Al2O3 and Y-TZP powders was addressed and colloidal stabilisation curves at different PAA contents were determined [18,19]. Such curves permit to establish the maximum amount of PAA which is available to adsorb onto the particles.…”