Permeation of n-hexane and 2,2-dimethylbutane (DMB) through two tubular ZSM-5 zeolite membranes was studied as a function of temperature and isomer partial pressures. The maximum permeation selectivity is 650, obtained at high n-hexane pressures. Though the single-gas isomers permeate at similar rates, the presence of n-hexane decreases the DMB permeance dramatically, whereas n-hexane permeation is unaffected by DMB. The nonzeolite pores appear to be different in size or number in the two membranes, whose pores saturate at different n-hexane pressures. Membranes with smaller nonzeolite pores exhibit pore saturation. The dependence of permeance on partial pressure and temperature indicates that most of the DMB permeance is through nonzeolite pores, which can be blocked by preferential n-hexane adsorption. These pores are larger than zeolite pores but are apparently in the nanopore size range.

The fluxes of aromatic molecules (p-xylene, o-xylene, and benzene) were measured as a function of temperature and feed partial pressure through several molecular sieve membranes (SAPO-5, SAPO-11, and mordenite) and three types of MFI membranes (silicalite-1, ZSM-5, and boron-substituted ZSM-5). Single-file diffusion appeared to control transport through the SAPO and mordenite membranes. Hence, those membranes showed ideal selectivities greater than 1 for benzene over the xylene isomers but no separation selectivities for the mixtures. Surface diffusion and activated gaseous transport were the controlling mechanisms for the MFI membranes. The highest p-xylene/o-xylene selectivities were obtained for a boron-substituted ZSM-5 membrane. At feed partial pressures of 2.1 kPa and at a temperature of 425 K, the best selectivities were 130 (ideal) and 60 (separation). Zeolite pores preferentially permeated p-xylene and took as long as 8 h to reach steady state. Nonzeolite pores preferentially permeated o-xylene after much shorter breakthrough times. Higher pressures of p-xylene distorted the membrane framework, resulting in increased o-xylene permeation and reduced selectivity. After reaching steady state, the flux of p-xylene through zeolite pores was stable for at least 10 h. The flux of o-xylene through nonzeolite pores was similarly stable at 373 K but continuously decreased for at least 12 h at 405 K.

Primary titania nanoparticles were coated with ultrathin alumina films using Atomic Layer Deposition (ALD). The deposited films were highly uniform and conformal with an average growth rate of 0.2 nm per coating cycle. The alumina films eliminated the surface photocatalytic activity of titania nanoparticles, while maintained their original extinction efficiency of ultraviolet light. Deposited films provided a physical barrier that effectively prevented the titania surface from oxidizing organic material whereas conserving its bulk optical properties. Parts fabricated from coated powders by pressureless sintering had a 13 % increase in surface hardness over parts similarly fabricated from uncoated particles. Owing to its homogeneous distribution, the secondary alumina phase suppressed excessive grain growth. Alumina films completely reacted during sintering to form aluminum titanate composites, as verified by XRD. Coated particles showed a pseudoplastic behavior at low shear rates due to modified colloidal forces. This behavior became similar to the Newtonian flow of uncoated nanoparticle slurries as the shear rate increased. Suspensions of coated particles also showed a decreased viscosity relative to the viscosity of uncoated particle suspensions.

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