Anupam Mitra

Synthesis and Corrosion Resistance of High-Silica Zeolite MTW, BEA, and MFI Coatings on Steel and Aluminum

High-silica zeolite ZSM-12Na n (Al n Si 28-n O 56 )∼4H 2 O with n = 2 (MTW), Beta Na n (Al n Si 64-n O 128 ) with n = 7 (BEA), and ZSM-5 Na n (SiO 96-n O 192 )∼16H 2 O with n < 27 (MFI) coatings were synthesized by hydrothermal crystallization without seeding using a new two-silica method on Al-alloy (Al-2024-T3 and Al-6061-T4) and stainless steel (SS-304). The pure-silica MTW and BEA coatings synthesized in this study have not been previously reported. All coatings are continuous and have excellent adhesion The as-synthesized zeolite coatings were tested by a dc polarization technique and found to he highly corrosion resistant in severely corrosive acidic (0.5 M H 2 SO 4 aqueous solution) and alkaline (0.1 M NaOH aqueous solution) media. In particular, a pure-silica MFI coating of only a few hundreds of nanometers thickness was formed within a relatively short crystallization time (e.g., 15 min), and was shown to provide sufficient protection against corrosion.

Synthesis of pure-silica MTW powder and supported films

Abstract High-silica MTW (ZSM-12) was synthesized by a new two-silica method in 8 h in hydroxide medium with tetraethylammonium hydroxide as structure-directing agent. Sodium metasilicate was used as the 1st silica source and shown to induce nucleation/crystallization of MTW in presence of a 2nd silica source such as fumed silica, silica gel and colloidal silica. The synthesis products were characterized by techniques including scanning electron microscopy, X-ray diffraction, magic angle spinning nuclear magnetic resonance, Fourier transform infrared, TGA/DTA, and nitrogen adsorption. The two-silica method was also used successfully to obtain MTW films/membrane on various substrates such as nonporous Al-alloy, porous and nonporous stainless steel and porous α-alumina tubes.

Hierarchical zeolite structures with designed shape by gel-casting of colloidal nanocrystal suspensions

Hierarchical zeolite structures with designed shapes were fabricated by a ceramic processing method—gel-casting of colloidal nanocrytal suspensions.

22-O-04-Characterization of corrosion-resistant zeolite coatings on Al alloys

Publisher Summary Zeolite films have been developed for corrosion-resistant coatings on aluminum (Al) alloys and other metals. This chapter discusses thermal and thermal shock stability and mechanical properties, such as cutting, impact, bending, and abrasion of ZSM-5 coatings on Al alloys. The results show that the coatings have good thermal/thermal-shock stability, adhesion and wear-resistance, and are flexible to certain extent. Thus, zeolite coating is a potential candidate for the corrosion protection of Al alloys and other metals.

Surface Patterns by Solvent Evaporation of Colloidal Zeolite Suspension

Surface patterns of porous zeolite structures such as knotted-rope web and wrinkled honeycomb were obtained by dynamic self-assembly of zeolite nanoparticles during solvent evaporation of colloidal zeolite suspension. The study shows that extra ethanol in zeolite synthesis solution is crucial for pattern formation. The addition of ethanol helps produce zeolite nanoparticles with a specific range of particle size during the hydrothermal synthesis. It also provides uniform dynamic driving force for pattern formation during its preferential evaporation. In addition, surface patterns vary with suspension compositions. The patterned zeolite structures have a well-defined bimodal pore size distribution (i.e., 0.55 nm and 2.6 nm) with high BET surface area of 680∼750m 2 &/g.