Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

<p>Soft porous crystals (SPCs) have attracted a lot of attention recently due to their great potential for a wide range of gas storage and separation applications. They can undergo large-amplitude phase transitions under external stimulus such as mechanical pressure, gas adsorption, and temperature while retaining their structural integrity. However, the thermal conductivity of SPCs is usually very low, owing to the porous structure and weak coordination bond, which would heavily influence their work performance. Hence, understanding the thermal transport in SPCs especially considering their dynamic features becomes extremely crucial. </p> <p>In this paper, taking the isorecticular DUT series as an example, the effect of phase transition from the large pore (lp) phase to narrow pore phase (np) on thermal transport in SPCs is comprehensively investigated by molecular dynamics (MDs) simulation together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity (). Specifically, we demonstrate here that the np phase of DUT-48 crystal after phase transition has a larger density but owns a smaller thermal conductivity. This abnormal effect of phase transition is in contrast to the previous finding that the SPCs with larger density possess a larger thermal conductivity. For other DUT crystals including DUT-47, DUT-49, DUT-50, and DUT-151, the np phase is found to have a higher thermal conductivity than their lp phase counterpart, which are as expected. This complicated effect of phase transition on thermal transport in SPCs can be explained by a porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process. This finding is expected to fill the gap in understanding the complicated effect of phase transition on the thermal transport in SPCs.</p>

Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

<p>Soft porous crystals (SPCs) have attracted a lot of attention recently due to their great potential for a wide range of gas storage and separation applications. They can undergo large-amplitude phase transitions under external stimulus such as mechanical pressure, gas adsorption, and temperature while retaining their structural integrity. However, the thermal conductivity of SPCs is usually very low, owing to the porous structure and weak coordination bond, which would heavily influence their work performance. Hence, understanding the thermal transport in SPCs especially considering their dynamic features becomes extremely crucial. </p> <p>In this paper, taking the isorecticular DUT series as an example, the effect of phase transition from the large pore (lp) phase to narrow pore phase (np) on thermal transport in SPCs is comprehensively investigated by molecular dynamics (MDs) simulation together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity (). Specifically, we demonstrate here that the np phase of DUT-48 crystal after phase transition has a larger density but owns a smaller thermal conductivity. This abnormal effect of phase transition is in contrast to the previous finding that the SPCs with larger density possess a larger thermal conductivity. For other DUT crystals including DUT-47, DUT-49, DUT-50, and DUT-151, the np phase is found to have a higher thermal conductivity than their lp phase counterpart, which are as expected. This complicated effect of phase transition on thermal transport in SPCs can be explained by a porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process. This finding is expected to fill the gap in understanding the complicated effect of phase transition on the thermal transport in SPCs.</p>

A Study on the Reduction Behavior of FeO by Analyzing Pore Characteristics Using the Labyrinth Coefficient at High Temperature

The effect of extrinsic porosity on the reduction behavior of FeO was evaluated by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and the Brunauer–Emmett–Teller (BET) technique and analyzed using the labyrinth coefficient of FeO. The extrinsic pore exhibited an abnormal effect on reduction behavior in the range of less than 50% reduction degree, despite the increase in apparent porosity. SEM and BET analysis indicated that the abnormal reduction behavior by extrinsic pores at the initial reduction stage was speculated to be due to the characteristic of extrinsic pore that is open only at one end. However, the overall porosity and reduction rate after a 40% reduction revert to the normal relationship. In addition, the experimental results indicated that the abnormal effect of the extrinsic pores in the initial stage was mitigated by an increase in the temperature. The abnormal effect of extrinsic porosity on FeO reduction was mathematically analyzed using the labyrinth coefficient. It can be summarized that not only the number of pores, but also their quality and distribution are important in determining the reduction rate.

Unveiling Abnormal Effect of Temperature on Enantioselectivity in Palladium-mediated Decabonylative Alkylation of MBH Acatate

An unusual temperature-enantioselectivity relationship was observed in the newly developed palladium-catalysed enantioselective nucleophilic substitution of cyclic Morita-Baylis-Hillman acetate and 4,4,4-trifluoro-1-phenyl-1,3-butanedione. In this transformation, higher enantioselectivity was achieved at an abnormallyhigh...

Swarm of fragments from the Tunguska event

ABSTRACT The Tunguska event took place on 1908 June 30. It was accompanied by an abnormal effect on the Earth's atmosphere, manifesting itself through ‘white nights’. These nights were associated with a dispersion of cosmic matter and the formation of a field of noctilucent clouds with a uniquely large size of over 10 million km2. However, overall, the cosmic matter was scattered over a territory of around 18 million km2. The most likely cause of the Tunguska event was the flux of fragments from the broken-up cometary object. The destruction of the cosmic body over Siberia, according to local inhabitants, was marked by numerous sound phenomena. After analysing eyewitness accounts, we can conclude that there were at least two major objects at the Tunguska event. The largest object exploded over the Taiga and caused damage to the forest. In addition, there were several dozen fragments of around 10 m in size, as well as many fragments of a smaller size.