Effects of nonframework metal cations and phonon scattering mechanisms on the thermal transport properties of polycrystalline zeolite LTA films

Abstract

Articles you may be interested inAnomalous thermal conductivity by surface phonon-polaritons of polar nano thin films due to their asymmetric surrounding media J. Appl. Phys. 113, 084311 (2013); 10.1063/1.4793498Extracting phonon thermal conductance across atomic junctions: Nonequilibrium Green's function approach compared to semiclassical methods An inelastic incoherent neutron scattering study of water in small-pored zeolites and other water-bearing mineralsWe present a systematic study to investigate the effects of nonframework cations and the role of phonon scattering mechanisms on the thermal transport properties of zeolite LTA, via experiment and semiempirical lattice dynamics calculations. Our study is motivated by the increasing interest in accurate measurements and mechanistic understanding of the thermal transport properties of zeolite materials. The presence of a nanostructured pore network, extra-framework cations, and tunable framework structure and composition confer interesting thermophysical properties to these materials, making them a good model system to investigate thermal transport in complex materials. Continuous films of zeolite LTA with different nonframework cations ͑Na + , K + , and Ca +2 ͒ were synthesized and characterized. The thermal conductivity was measured using the three-omega method over a wide range of temperature ͑150-450 K͒. These are the first thermal conductivity measurements performed on bulk LTA, so they are more accurate than previous measurements, which involved the use of compacted zeolite powders. Our data showed significant dependence of the thermal conductivity on the extra-framework cations as well the temperature. The thermal conductivities of the zeolite LTA samples were modeled with the relaxation time approximation to the Boltzmann transport equation. The full phonon spectra for each type of LTA zeolite were calculated and used in conjunction with semiempirical relaxation time expressions to calculate the thermal conductivity. The results both validated, and suggested the limitations of, this modeling approach. Optical phonons dominated the thermal conductivity and boundarylike scattering was found to be the strongest phonon scattering mechanism, as also observed in MFI zeolite.

Temperature Dependent Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

“…In fact, the predicted thermal conductivity was insensitive to the Umklapp scattering relaxation time τ U since τ U ≫ τ B and τ U ≫ τ D for all temperatures considered and all phonon frequencies up to the Debye cut-off frequency of ω D /2π = 8 THz. Similar conclusions were reached by Hudiono et al [17] and Greenstein et al [32] for MFI and LTA zeolite between 150 and 450 K.…”

“…By analogy with other studies [14,16,17,30,32], the parameters A = 1.38 × 10 −42 s 3 , B = 4.24 × 10 −21 s/K, and l B = 0.95 nm in Equation (3) were obtained by fitting the predictions of Equations (1) to (3) to the experimental data over the entire temperature range explored. Figure 2 shows that the calculated thermal conductivity from Equations (1) to (3) agreed within 6% of the experimental data for the PSZ MFI film for all temperatures between 30 and 315 K. It establishes that using the Debye dispersion relation instead of the complete phonon dispersion was sufficient to predict the thermal conductivity of MFI zeolite films.…”

Enhanced Thermal Conductivity in a Diamine-Appended Metal–Organic Framework as a Result of Cooperative CO2 Adsorption

“…Here, the newly formed hydrogen-bonded ammonium carbamate chains (see Figure c) provide an additional heat transfer pathway along the framework channels. The thermal conductivity of e-2–Zn 2 (dobpdc)–CO 2 is notably 2–3 times higher than that of conventional activated carbon and comparable to that of zeolites MFI and MEL, , which are extensively deployed in gas storage and separation applications. Importantly, as a result of this enhanced thermal conductivity upon CO 2 adsorption, less active cooling of e-2–Zn 2 (dobpdc) would be required in a practical separations process.…”