Temperature dependent thermal conductivity of pure silica MEL and MFI zeolite thin films

Abstract

Several studies have reported the thermal conductivity of powdered zeolites [12][13][14][15]. Effects of temperature, filling gas, moisture, and pressure were investigated [12][13][14][15]. In addition, Greenstein et al. [16] and Hudiono et al. [17] measured thermal conductivity of PSZ MFI zeolite films with thickness ranging from 10 to 20 µm and temperature varying from 150 to 450 K. The MFI films were synthesized by secondary growth through a seeded hydrothermal process on alumina substrates. The measured thermal conductivity of (h0l)-oriented PSZ MFI films varied from 1.0 to 1.4 W/m·K in the temperature range considered [17]. That of calcined and uncalcined c-oriented PSZ MFI films deposited on silicon substrates was found to range from 0.75 to 1.1 W/m·K and 1.0 to 1.6 W/m·K, respectively [16]. More recently, Coquil et al. [18] measured room temperature thermal conductivity of PSZ MFI and MEL zeolite thin films. The MFI thin films were b-oriented, fully crystalline, and had a porosity of 33%. The MEL thin films featured porosity, relative crystallinity, and particle size ranging from 40% to 59%, 23% to 47%, and 55 to 80 nm, respectively. The authors found the thermal conductivity to be around 1.02±0.10 W/m·K for all films despite their different porosity, relative crystallinity, and nanoparticle size. Methods and Experiments 2.1 Sample film preparationSynthesis of PSZ MFI and MEL thin films investigated in the present study were previously described in detail [1,6,18]. MFI thin films were synthesized by in situ crystallization and were b-oriented. The MEL films were prepared by spin coating a zeolite nanoparticle suspension onto silicon substrates. The MEL suspension was synthesized by a two-stage process [1]. The first stage consisted of a 2 days heating and stirring of a tetraethylorthosilicate (TEOS) based solution at 80 • C resulting in a MEL nanoparticle suspension. The second stage corresponded to the growth of the MEL nanoparticles from the same solution in a convection oven at 114 • C. Finally, MEL thin films were obtained by spin-coating the solution onto silicon substrates. Both relative crystallinity and nanoparticle size of the PSZ MEL increased as the second stage synthesis time increased. Here, the relative crystallinity is defined as the ratio of the micropore volume to the micropore volume of a fully crystalline PSZ MEL microcrystal [1]. Four different sets of MEL films corresponding to four different second stage synthesis times (15, 18, 21 and 24 hours) were studied. Note that all the MEL and MFI thin films were made hydrophobic by vapor-phase silylation with trimethylchlorosilane as described in Ref. [1].

Laser induced temperature-jump time resolved IR spectroscopy of zeolites

“…This gave a value of κ = 0.25 ± 0.1 W m −1 K −1 for simulations with T Init from 125–300 °C. The predicted value of κ increases with temperature which is consistent with the results obtained for measurements of thin films, 41–43 although the κ values determined from our experiments are approximately 4 times smaller, possibly indicating the much lower level of thermal contact between crystallites than in a pure film. It was not possible to derive a value for the thermal conductivity that produced cooling behaviour consistent with the experimental observations at 80 and 100 °C, indicating that at these temperatures there are additional effects from adsorbed water that the simulations do not account for.…”

Hot-Electron-Induced Dissociation of H2on Gold Nanoparticles Supported on SiO2

“…Isolated AuNPs were simulated as being half-embedded inside a SiO 2 matrix. The local change in temperature on the AuNP due to plasmonic heating can be expressed as normalΔ T = σ abs I 4 π R β κ normalm where σ abs is the integrated absorption cross section over the entire visible range (450–1000 nm), I is the laser intensity, R is the radius of the spherical AuNP, β is the thermal capacitance coefficient depending on the NP aspect ratio (β = 1 + 0.96587[ln 2 (AR)], β = 1 for a spherical NP), and κ m denotes the temperature-dependent thermal conductivity of the surrounding dielectric (SiO 2 ) . Finite-difference time-domain (FDTD) simulations were performed to calculate the absorption cross sections of the 1% Au/SiO 2 photocatalyst.…”

Phonon Conductivity of Nanoparticles Embedded in Dielectric Material

“…. In the literature, there is another expression for the phonon–phonon scattering rate due to the umklapp process i.e., Bw 2 T exp(− T D / T )] . In our case the phonon–phonon interaction does not play any important role as we discussed in the results and discussion section 4.…”

“…There is considerable interest in understanding heat transport in nanomaterials . Nanomaterials with high thermal conductivity can be used to fabricate temperature‐dependent nanodevices.…”

“…Currently, the thermal conductivity in nanomaterials has gained the most attention and it is believed to be the most significant parameter which is responsible for the enhanced heat conduction in these materials. Several researchers have reported experimental and theoretical studies on the thermal conductivity of nanofluids and nanomaterials . For example, thermal conductivity experiments were performed by Wong et al for three different micro composites.…”