Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

Abstract

This paper reports the room temperature cross-plane thermal conductivity of pure silica zeolite PSZ MEL (Socony Mobil -eleven) and MFI (Socony Mobile -five) thin films. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The mass fraction of nanoparticles within the suspension varied from 16 to 55%. This was achieved by varying the crystallization time of the suspension. The thin films consisted of crystalline MEL nanoparticles embedded in a nonuniform and highly porous silica matrix. They featured porosity, relative crystallinity and MEL nanoparticles size ranging from 40 to 59%, 23 to 47% and 55 to 80 nm, respectively. PSZ MFI thin films were made by in-situ crystallization, were b-oriented, fully crystalline and had a 33% porosity. Thermal conductivity of these PSZ thin films was measured at room temperature using the 3ω method. Despite increases in (i) relative crystallinity, (ii) MEL nanoparticle size, and (iii) yield, as the nanoparticle crystallization time was increased, the cross-plane thermal conductivity of the MEL thin films remained nearly unchanged around 1.02±0.10 W/m·K. Indeed, the effects of these parameters on the thermal conductivity were compensated by the simultaneous increase in porosity. PSZ MFI thin films were found to have similar thermal conductivity as MEL thin films even though they had smaller porosity. Finally, the average thermal conductivity * Address all correspondence to this author.† Address all correspondence to this author.of the PSZ films was three to five times larger than that reported for amorphous sol-gel mesoporous silica thin films with similar porosity and dielectric constant.