Preparation and characterization of flax, hemp and sisal fiber-derived mesoporous activated carbon adsorbents

The first aim of this study was to investigate mesoporous activated carbon adsorbents from sisal, hemp, and flax fibers by cost-effective methods. Fibers were impregnated with low concentration (20 wt.%) phosphoric acid. Carbonization temperatures were defined by thermal analysis. Bast fibers (hemp, flax) decompose at lower temperatures (419.36℃, 434.96℃) than leaf fibers (sisal, 512.92℃). The second aim was to compare bast and leaf fibers-derived activated carbon adsorbents by determining physical adsorption properties, chemical compositions, scanning electron microscope, and Fourier transform infrared spectroscopy. Results showed that natural fibers have good candidates to prepare mesoporous activated carbon adsorbents with high surface area (1186–1359 m2/g), high mesopore percentage (60–72%), and high C content (80–86%). Even though leaf-derived activated carbon developed more mesoporous structure (72%), bast-derived activated carbons provided higher surface areas (Shemp = 1359 m2/g; Sflax = 1257 m2/g) and C content. Fourier transform infrared spectra for bast fibers-derived activated carbon adsorbents were quite similar while leaf fiber-derived activated carbon adsorbent had a different spectrum

A Novel CAE Method for Compression Molding Simulation of Carbon Fiber-Reinforced Thermoplastic Composite Sheet Materials

Its high-specific strength and stiffness with lower cost make discontinuous fiber-reinforced thermoplastic (FRT) materials an ideal choice for lightweight applications in the automotive industry. Compression molding is one of the preferred manufacturing processes for such materials as it offers the opportunity to maintain a longer fiber length and higher volume production. In the past, we have demonstrated that compression molding of FRT in bulk form can be simulated by treating melt flow as a continuum using the conservation of mass and momentum equations. However, the compression molding of such materials in sheet form using a similar approach does not work well. The assumption of melt flow as a continuum does not hold for such deformation processes. To address this challenge, we have developed a novel simulation approach. First, the draping of the sheet was simulated as a structural deformation using the explicit finite element approach. Next, the draped shape was compressed using fluid mechanics equations. The proposed method was verified by building a physical part and comparing the predicted fiber orientation and warpage measurements performed on the physical parts. The developed method and tools are expected to help in expediting the development of FRT parts, which will help achieve lightweight targets in the automotive industry

Preparation and characterization of flax, hemp and sisal fiber-derived mesoporous activated carbon adsorbents

The first aim of this study was to investigate mesoporous activated carbon adsorbents from sisal, hemp, and flax fibers by cost-effective methods. Fibers were impregnated with low concentration (20-‰wt.%) phosphoric acid. Carbonization temperatures were defined by thermal analysis. Bast fibers (hemp, flax) decompose at lower temperatures (419.36℃, 434.96℃) than leaf fibers (sisal, 512.92℃). The second aim was to compare bast and leaf fibers-derived activated carbon adsorbents by determining physical adsorption properties, chemical compositions, scanning electron microscope, and Fourier transform infrared spectroscopy. Results showed that natural fibers have good candidates to prepare mesoporous activated carbon adsorbents with high surface area (1186--1359-‰m2/g), high mesopore percentage (60--72%), and high C content (80--86%). Even though leaf-derived activated carbon developed more mesoporous structure (72%), bast-derived activated carbons provided higher surface areas (Shemp-‰=-‰1359-‰m2/g; Sflax-‰=-‰1257-‰m2/g) and C content. Fourier transform infrared spectra for bast fibers-derived activated carbon adsorbents were quite similar while leaf fiber-derived activated carbon adsorbent had a different spectrum

Thermal plasma processing of fine grained materials

Synthesis of advanced ceramic materials has been systematically investigated using non-transferred thermal plasma reactor. Low cost oxide feed materials has been used as the solid feed to the reactor while methane (CH_4 ) and argon (Ar) were used as reducing and carrier gases, respectively. A 2D computational fluid dynamics (CFD) based mathematical model was developed to understand the flow and temperature profiles inside the reactor. The concept was extended to a 3D model and a comparison was made with the results from 2D model. The velocity increases linearly with increase in the pressure in both the 2D and the 3D models while the maximum velocity from 3D model is lower by about 35-40 m/s at any given pressure. A decrease in the residence time was observed in the 3D model compared to the 2D model. An intermediate plasma gas pressure of 45 psi was used in experiments to ensure high temperatures and residence times in the reactor. Thermochemical calculations have been carried out to determine the molar ratio of the reducing gas to be used in TiO_2 -B_2 O_3 -CH_4 and SiO_2 -CH_4 system. The maximum theoretical yield of TiB_2 of about 82 mol% was obtained at a molar ratio of TiO_2 :B_2 O_3 :CH_4 = 1:1:5. Maximum theoretical yield of SiC of about 97 mol% was obtained at a molar ratio of SiO_2 :CH_4 =1:3 at a temperature of 1520ºC. Experiments were carried out using thermal plasma reactor to synthesize TiB_2 and SiC. The maximum yield of TiB_2 of about 40 mol% was obtained with a feed molar ratio of TiO_2 :B_2 O_3 :CH_4 = 1:1:5 and a power of 23.4 kW. Relatively higher solid feed rates increased the yield of TiB_2 . The TiB_2 spherical particles formed are in the range of 20-100 nm. A change in crystal structure was observed in TiO_2 from anatase to rutile. Experiments using a molar ratio of SiO_2 :CH_4 = 1:2 produced maximum yield of SiC of about 65 mol% at a solid feed rate of 5 g/min. Mostly spherical morphology with some nanorods have been observed. The presence of Si had been observed and was quantified using XRD, HR-TEM, Raman and XPS. (Published By University of Alabama Libraries

Perpendicular magnetic anisotropy materials for reduced current switching devices

Recently, spin-transfer switching of magnetic tunnel junctions (MTJ's) has become a very active area of research. It is theoretically postulated that using perpendicular magnetic anisotropy materials will substantially reduce the critical current density for switching, resulting in lower energy devices, while keeping the thermal stability high. A range of perpendicular anisotropy material systems, including (i) multilayers, (ii) crystalline alloys, and (iii) amorphous alloys have been intensively studied in this dissertation. The surface and bulk anisotropy, damping parameter, and structural properties of these material systems have been investigated. Magnetic tunnel junctions based on some of these perpendicular material schemes have been fabricated, and their transport properties have been measured and related to the anisotropy. We have found several promising approaches to magnetic tunnel junctions utilized in spin-torque transfer random access memory (STT-RAM). (Published By University of Alabama Libraries