Ethyl Cellulose-Assisted Host-Guest Framework for Depositing Solution-Processed Yttria Films on the Inner Surface of...

Straightforward deposition protocols to coat flat surfaces are widely available. However, there are multiple constraints in coating a concave or convex surface, especially on the inner surface of narrow tubes. Coated surface helps in corrosion protection, internal cleanliness, strength, and alloy casting, and it also enhances product aesthetics. In the present work, a solution-based deposition protocol was developed to coat oxide films (Y₂O₃, Al₂O₃ among others) of tunable thickness (400 nm to 4 μm) on the inner surface of quartz tubes (inner diameter (ID) ∼ 2, 3, 5, 6, and 10 mm; length (L) ∼ 20, 110, and 500 mm) with the help of a venturimeter-based apparatus. In the course of this study, it was revealed that coating on the curved surface needed substantial optimization of the deposition parameters to minimize mainly the tearing and thinning of the film. Choice of organic solvents, acetic acid, precursor concentrations, and solution containing a binder element, such as ethyl cellulose (EC), was optimized to achieve homogeneous coating. An optimal upward air flow (speed 44 m/min) was maintained during drying the coating to prevent solvent condensation prior to annealing the film at 500-1000 °C in air for 30 min. The coating was studied with X-ray diffractometry (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and Raman spectroscopy. These coated tubes were used as a mold during injection casting of Ni rod at 1450 °C. Surface of the cast Ni was studied for Si as well as yttrium contaminations with EDAX. Raman spectra from a demolded quartz tube (retrieved from casting chamber) revealed characteristic A_g and F_g vibrational modes of cubic Y₂O₃ phase, indicating good thermal stability and adhesive features of the present coating.