Effects of expanded graphite content on the performance of MgO-C refractories

Expanded graphite was introduced into a MgO-C refractory to suppress its thermal expansion and thus enhance thermal shock resistance. The refractory was prepared by mixing MgO powders (particle size = 75 μm and 1 mm), antioxidant and curing agents, flake and expanded graphite, and a novolak-type phenolic resin at 50°C. This was followed by aging at 20°C for 24 h, compacting by uniaxial pressing, curing at 210°C for 5 h, and heat treatment at 1500°C. With an increase in expanded graphite content from 0 to 4 wt.%, the bulk density decreased, apparent density remained unchanged, and apparent porosity increased. The gaps created in the vicinity of MgO particles because of this increase in apparent porosity buffered the thermal expansion of MgO. This increased resistance to thermal shock up to 1500°C. However, the increase in expanded graphite content also had a detrimental effect reflected in the decrease in fracture strength and increase in the residual strain after repeated thermal shock. This contradiction indicates that composition optimization is important for the practical performance enhancement of MgO-C bricks. The optimum content of the expanded graphite was determined as 2 wt.%.     

A Reliable Method to Measure the Adhesive Force with a Tiny Amount of Adhesive Material

A new method is proposed and developed to measure adhesive forces by use of the force-distance curve of a micro cantilever with an extremely small amount of testing material such as adhesive proteins. The contact area should be well-controlled at a reasonable value. Even though the area is desired to be as small as possible, a contact region of several micrometers by several micrometers is adopted in order to avoid obtaining meaningless measured values and uncertainty in the contact areas. An AFM cantilever is used after having been modified with a micro glass bead to enlarge the contact area for adhesion. A glass plate with micro-scale circular patterns is fabricated from a glass wafer by micro-machining processes in order to control precisely the contact area in adhesion tests. In the proposed method the adhesive materials are directly applied to the bead attached at the AFM cantilever before it is applied on the top area of the truncated cone on the fabricated glass plate. The developed method is applied to measure the adhesive forces of Cell-Tak® (which is a commercial extracted mussel adhesive) and recombinant Mgfp-5 (which is a recombinant mussel adhesive protein) and the statistical credibility of the measured adhesive force data is enormously improved as a result.     

Microscopically-viewed relationship between the chain conformation and ultimate Young's modulus of a series of arylate polyesters with long methylene segments

Relationship between the chain conformation in the crystal lattice and the ultimate Young's modulus has been discussed on the basis of the crystal structural information revealed by the X-ray diffraction analysis for a series of arylate polyesters with long methylene segments (–[–COC₆H₄CO–O(CH₂)_mO–]_n–). The X-ray structural analysis revealed that the molecular chains take the all-trans-zigzag conformations for all of the even-numbered polyesters and their model compounds as well as the odd-numbered polyesters with the methylene segmental length longer than (CH₂)₁₄. These chain conformations have been correlated well to the ultimate Young's modulus along the chain axis or the crystallite modulus E_c, which has been estimated experimentally by the X-ray diffraction method under a constant stress and also predicted theoretically using the X-ray-analyzed crystal structures on the basis of the molecular mechanics method. The E_c was found to show the minimum at around m = 4–6 and increased gradually with an increment of m and approached the crystallite modulus of polyethylene, 235 GPa (X-ray value) ∼ 316 GPa (calculate) at an infinite m value. This behavior of E_c as a function of the number of methylene segmental units m was reasonably interpreted by developing the theoretical equation of E_c for a simplified zigzag chain model composed of a repetition of two linear rods representing the benzene–ester and methylene segmental parts respectively. These findings may promise that the mechanical property of arylate polyester can be controlled by adjusting the methylene segmental length m.     

Lattice distortion and residual stress of a carbon‐doped TiZrN coating

The mechanism of hardness improvement of a TiZrN coating by carbon doping was investigated in terms of the residual stress and the lattice deformation. Carbon was doped using laser carburization to improve the hardness of TiZrN, which was increased from 3025 HV to 3388 HV. The lattice parameter was calculated through Rietveld refinement in order to analyze the behavior inside the lattice due to carbon doping, which showed that the parameter increased from 4.21 Å to 4.44 Å after the carbon doping process. The diffraction pattern was analyzed using an electron beam to identify the lattice state of the coating layer, and lattice distortion was revealed through a diffused ring pattern. The compressive residual stress was increased by 48%, which was identified through the sin²Ψ method using the lattice constant change due to carburization. After the carbon doping, the hardness of the TiZrN was increased by 10%, which was attributed to the expansion distortion generated in the TiZrN lattice and the increase of the compressive residual stress.     

Removal of As(V) from aqueous solutions by waste crab shells

Waste crab shell, which has some functional groups like -NHCO or NO₂ groups, was used as an adsorbent to remove arsenate ions (As (V)). The functional groups in crab shells were confirmed by FT-IR analysis. Waste crab shell had a high uptake capacity of 35.92 mg/g-dry mass for arsenate ion at pH 4, and the regression curve using the Langmuir isotherm equation fit well with the experimental data. The effects of pH, loading of crab shells, and time on uptake capacity of arsenate ions were also investigated. The adsorption capacity of arsenate ions was increased as the pH value was increased because the amount of negative arsenic species increased as the pH value was increased. Waste crab shells could remove arsenate ions of about 45% with 0.5 g of loading amount, and adsorption of arsenate ions was almost completed in 30 min when initial concentration of arsenate ions was 100 and 9.3 mg/L, respectively. Considering recycling of crab shell, it could be an economical and promising adsorbent.     

Preparation of CHF3 plasma polymeric composite membrane and characteristics of surface modification

Low temperature rf-plasma was used to create a plasma-treated polymeric composite membrane made from CHF₃, a material that is very thermally and chemically stable. The chemical and physical properties of the CHF₃ plasma polymers were variously changed by plasma treatment on membrane surface. CHF₃ plasma polymers were efficiently deposited on an aluminum oxide substrate with a pore size of 0.02 μm at the plasma polymerization time 60 min, the rf-power 160W, and the flow rate of the CHF₃ 16 sccm. It was found that O₂ plasma treatment had a much greater effect on the surface roughness of the CHF₃ plasma polymers than did Ar or N₂ plasma treatment. The attachment of functional groups to the CHF₃ plasma polymer surface as a result of plasma treatment increased the intensity of the oxygen functional group peak. It also increased the oxygen content and the O/C ratio. The plasma treatment also made to the surface that became to hydrophilic. The most effective hydrophilic surface modification occurred when the composite parameter ranged from 300-450 kJ·s/kg. It was confirmed that the gas permeability and selectivity changed as a result of crosslinking, chemical etching, and the importing of functional groups to the CHF₃ plasma polymeric membrane.     

Chromohalobacter is a Causing Agent for the Production of Organic Acids and Putrescine during Fermentation of Ganjang,a Korean Traditional Soy Sauce

Ganjang, a Korean traditional fermented soy sauce, is prepared by soaking doenjang‐meju (fermented soybeans) in approximately 20% (w/v) solar salt solution. The metabolites and bacterial communities during ganjang fermentation were simultaneously investigated to gain a better understanding of the roles of the microbial population. The bacterial community analysis based on denaturing gradient gel electrophoresis of 16S rRNA gene sequences showed that initially, the genus Cobetia was predominant (0 to 10 d), followed by Bacillus (5 to 74 d), and eventually, Chromohalobacter became predominant until the end of the fermentation process (74 to 374 d). Metabolite analysis using ¹H‐NMR showed that carbon compounds, such as fructose, galactose, glucose, and glycerol, probably released from doenjang‐meju, increased rapidly during the early fermentation period (0 to 42 d). After removal of doenjang‐meju from the ganjang solution (42 d), the initial carbon compounds remained nearly constant without the increase of fermentation products. At this point, Bacillus species, which probably originated from doenjang‐meju, were predominant, suggesting that Bacillus is not mainly responsible for ganjang fermentation. Fermentation products including acetate, lactate, α‐aminobutyrate, γ‐aminobutyrate, and putrescine increased quickly with the rapid decrease of the initial carbon compounds, while Chromohalobacter, probably derived from the solar salts, was predominant. Multivariate redundancy analysis indicated that the Chromohalobacter population was closely correlated with the production of the organic acids and putrescine during the ganjang fermentation. These results may suggest that Chromohalobacter is a causing agent responsible for the production of organic acids and putrescine during ganjang fermentation and that the solar salts, not doenjang‐meju, is an important microbial source for ganjang fermentation.     

Effect of acidity on the performance of a Ni-based catalyst for hydrogen production through propane steam reforming: K-AlSixOy support with different Si/Al ratios

Propane steam reforming (PSR) for the production of H₂ was catalyzed by a NiO/K-AlSi_xO_y catalyst synthesized with various Si/Al ratios (Si/Al = 0, 0.3, 0.5, 0.7, and 1.0). The effect of the Si/Al ratio on the acidity of the NiO/K-AlSi_xO_y catalyst for PSR was investigated. NiO/K-AlSi_xO_y gave a higher H₂ selectivity and stability during PSR than NiO/K-SiO₂ and NiO/K-Al₂O₃. The NH₃-TPD results showed that the acid quantity and strength of NiO/K-AlSi_xO_y changed significantly depending on the Si/Al ratio. With an increased Si/Al ratio, the densities of both weak and strong acid sites increased. The C₃H₈- and CO-TPD results indicated that desorption amounts increased significantly in all NiO/K-AlSi_xO_y catalysts relative to those of NiO/K-SiO₂ and NiO/K-Al₂O₃, and the adsorption amount increased with the Si/Al ratio. PSR results showed that the NiO/K-AlSi_xO_y catalyst exhibited much better stability than the NiO/K-SiO₂ and NiO/K-Al₂O₃ catalysts. This study confirms the following facts: when the acidity is appropriately adjusted for the catalyst, adsorption of the reaction gas increases, which eventually increases the reaction rate and also inhibits strong sintering between the nickel and the Al₂O₃ support. As a result, deterioration of the catalyst can be reduced.     

Characterization and identification of lipid-producing microalgae species isolated from a freshwater lake

Microalgal lipids are the oils of the future for sustainable biodiesel production. One of the most important decisions in obtaining oil from microalgae is the choice of species. A total of 45 algal cultures were isolated from a freshwater lake at Wonju, South Korea. Five microalgal isolates were selected based on their morphology and ease of cultivation under our test conditions. These cultures were identified as strains of Scenedesmus obliquus YSL02, Chlamydomonas pitschmannii YSL03, Chlorella vulgaris YSL04, S. obliquus YSL05, and Chlamydomonas mexicana YSL07 based on microscopic examination and LSU rDNA (D1-D2) sequence analysis. S. obliquus YSL02 reached a higher biomass concentration (1.84 ± 0.30 g L⁻¹) with a lower lipid content (29% w/w), than did Chla. pitschmannii YSL03 (maximum biomass concentration of 1.04 ± 0.09 with a 51% lipid content). Our results suggest that Chla. pitschmannii YSL03 is appropriate for producing biodiesel based on its high lipid content and oleic acid proportion.