A bench rotary kiln was used to produce pure YBa2Cu3O6+x by continuous
calcination of spray-roasted precursor powder using a countercurrent
air flow to avoid a reaction between evolved CO2 and the product. Prod
uct agglomeration caused a spread in the velocity distribution, requir
ing the use of extra calcination for a pure product. High-purity YBa2C
u3O6.6 was obtained at 940-degrees-C for 0.9 vol % solid loading, an a
verage residence time of 75 min, and Ntheta (N = rotation rate, theta
= inclination) between 3 and 4.5 rpm deg. However, at a residence time
of 77 min, increased product agglomeration at 2.5 rpm deg caused inco
mplete conversion to YBa2Cu3O6.6. Increasing the average residence tim
e above 75 min increased the oxygen content of the product, with pure
orthorhombic YBa2Cu3O6.9 forming at 160 min. Due to reaction and tempe
rature induced changes in particle size and shape, existing correlatio
ns cannot predict the dependence of the average solid residence time o
n the operating conditions.