A numerical method based on domain decomposition to solve coupled conduction-radiation physics using parallel computing within large porous media

A domain decomposition approach is developed to solve coupled conductive– radiative heat transfer within highly porous materials. In this work, a Kelvin–cell foam with five cells in each direction which has ˇ15.6 × 106 of voxels is considered. The coupled heat transfer is solved using the finite volume method where deterministic ray tracing is used to calculate radiative exchange. The temperature distribution is computed and cross–validated with the distribution obtained using a commercial software STAR–CCM+.

Modified Starch Highly Porous Materials

A technique for starch modification by graft polymerization of acrylamide has been developed. The obtained copolymer is soluble in a wide range of pH 2 - 12. The modification of starch made it possible to freely combine it with aqueous acid solutions of chitosan, in order to achieve a synergistic effect of their properties. A porous material based on modified starch and its mixtures with chitosan, which has high sorption characteristics, has been developed. The resulting material is promising as a sorbent of heavy metal ions and packing materials for transportation and storage.

Advances in Enzyme and Ionic Liquid Immobilization for Enhanced in MOFs for Biodiesel Production

Biodiesel is a promising candidate for sustainable and renewable energy and extensive research is being conducted worldwide to optimize its production process. The employed catalyst is an important parameter in biodiesel production. Metal–organic frameworks (MOFs), which are a set of highly porous materials comprising coordinated bonds between metals and organic ligands, have recently been proposed as catalysts. MOFs exhibit high tunability, possess high crystallinity and surface area, and their order can vary from the atomic to the microscale level. However, their catalytic sites are confined inside their porous structure, limiting their accessibility for biodiesel production. Modification of MOF structure by immobilizing enzymes or ionic liquids (ILs) could be a solution to this challenge and can lead to better performance and provide catalytic systems with higher activities. This review compiles the recent advances in catalytic transesterification for biodiesel production using enzymes or ILs. The available literature clearly indicates that MOFs are the most suitable immobilization supports, leading to higher biodiesel production without affecting the catalytic activity while increasing the catalyst stability and reusability in several cycles.

Highly porous nature of C-type asteroid 162173 Ryugu revealed by thermal imaging from Hayabusa2

<p>Thermal imaging, or thermography, has revealed the surface physical state of the C-type near-Earth asteroid 162173 Ryugu (Okada et al., 2020). The asteroid is the target body of JAXA Hayabsua2 asteroid sample return mission, and it has been characterized through remote sensing and surface experiments, and will be deeply and accurately investigated by analysis of returned sample. Thermal observations are among such multi-scale observations, providing a new insight into understanding planetary evolution process.</p> <p>Thermal infrared imager TIR (Okada et al., 2017; 2020) was used to take one-rotation global thermal images of Ryugu at every 6° step, from the home position (20 km altitude) or from the Mid-Altitude (5 km altitude). There were two big surprises contrary to the predictions before arrival at Ryugu: i) flat diurnal temperature profiles compared to the case of non-rough surface, and ii) non-cold spots identified for most of boulders. The flat diurnal temperature profiles and its maximum temperature in a day indicate that Ryugu must have very rough surfaces made of highly porous materials, derived from the thermal inertia of 300 ± 100 J K<sup>-1</sup>s<sup>-0.5</sup>m<sup>-2</sup> (hereafter, tiu). Non-cold boulders indicate that boulders are less consolidated or compacted than typical carbonaceous chondrite meteorites, and shows the same thermophysical properties as the surroundings. TIR was also used to take close-up thermal images during the descent operations, and to have proven that the surface of asteroid is covered with fragments of porous rocks, larger than several centimeters in diameter. The typical size of fragments larger than thermal skin depth (~35 mm) results in similar thermal properties between the boulders and their surroundings. We also consider the surface roughness effect (Shimaki et al., 2020) to obtain the maps of thermal inertia ( 225 ± 45 tiu) and the roughness (0.41 ± 0.05) at the same time, corresponding to very rough surfaces made of highly-porous materials. This thermal inertia is basically consistent with the value (282 +93/-35 tiu) by in situ measurement using a thermal radiometer MARA on MASCOT lander (Grott et al., 2019). Furthermore, in the close-up thermal images, there were found boulders colder by 20 °C or more, indicating the thermal inertia of typical carbonaceous chondrite meteorites.</p> <p>Considering these results, we proposed a formation scenario of Ryugu: fluffy cosmic dusts gathered to form porous planetesimals, and then much larger sized but still porous bodies. A low degree of consolidation and alteration has occurred at most of the body, while a higher degree of consolidation or alteration proceeded at the deep interior. Huge meteoritic impacts destroyed and fragmented the bodies, and part of those fragments were re-accreted to form the next generation, rubble-pile bodies (asteroids). Boulders found on Ryugu might have originated from the deep interior of parent bodies, so that most of them are very porous and less consolidated but some of them are relatively dense materials similar to carbonaceous chondrites, which might have originated from the interior. Due to YORP effect, the rotation rate decreased to current one, and the current shape of a spinning top-shape were formed. Analysis of returned sample will make progress in our knowledge of the planetary formation process.</p>

Advances in Manufacturing Composite Carbon Nanofiber-Based Aerogels

This article provides an overview on manufacturing composite carbon nanofiber-based aerogels through freeze casting technology. As known, freeze casting is a relatively new manufacturing technique for generating highly porous structures. During the process, deep cooling is used first to rapidly solidify a well-dispersed slurry. Then, vacuum drying is conducted to sublimate the solvent. This allows the creation of highly porous materials. Although the freeze casting technique was initially developed for porous ceramics processing, it has found various applications, especially for making aerogels. Aerogels are highly porous materials with extremely high volume of free spaces, which contributes to the characteristics of high porosity, ultralight, large specific surface area, huge interface area, and in addition, super low thermal conductivity. Recently, carbon nanofiber aerogels have been studied to achieve exceptional properties of high stiffness, flame-retardant and thermal-insulating. The freeze casting technology has been reported for preparing carbon nanofiber composite aerogels for energy storage, energy conversion, water purification, catalysis, fire prevention etc. This review deals with freeze casting carbon nanofiber composite materials consisting of functional nanoparticles with exceptional properties. The content of this review article is organized as follows. The first part will introduce the general freeze casting manufacturing technology of aerogels with the emphasis on how to use the technology to make nanoparticle-containing composite carbon nanofiber aerogels. Then, modeling and characterization of the freeze cast particle-containing carbon nanofibers will be presented with an emphasis on modeling the thermal conductivity and electrical conductivity of the carbon nanofiber network aerogels. After that, the applications of the carbon nanofiber aerogels will be described. Examples of energy converters, supercapacitors, secondary battery electrodes, dye absorbents, sensors, and catalysts made from composite carbon nanofiber aerogels will be shown. Finally, the perspectives to future work will be presented.

Mechanochemical synthesis of highly porous materials

Mechanochemistry became a powerful and popular method for the preparation of various porous materials.