Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo₅SiB₂ and Mo₃Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.     

Attenuating Effects of Dieckol on Hypertensive Nephropathy in Spontaneously Hypertensive Rats

Hypertension induces renal fibrosis or tubular interstitial fibrosis, which eventually results in end-stage renal disease. Epithelial-to-mesenchymal transition (EMT) is one of the underlying mechanisms of renal fibrosis. Though previous studies showed that Ecklonia cava extracts (ECE) and dieckol (DK) had inhibitory action on angiotensin (Ang) I-converting enzyme, which converts Ang I to Ang II. It is known that Ang II is involved in renal fibrosis; however, it was not evaluated whether ECE or DK attenuated hypertensive nephropathy by decreasing EMT. In this study, the effect of ECE and DK on decreasing Ang II and its down signal pathway of angiotensin type 1 receptor (AT1R)/TGFβ/SMAD, which is related with the EMT and restoring renal function in spontaneously hypertensive rats (SHRs), was investigated. Either ECE or DK significantly decreased the serum level of Ang II in the SHRs. Moreover, the renal expression of AT1R/TGFβ/SMAD was decreased by the administration of either ECE or DK. The mesenchymal cell markers in the kidney of SHRs was significantly decreased by ECE or DK. The fibrotic tissue of the kidney of SHRs was also significantly decreased by ECE or DK. The ratio of urine albumin/creatinine of SHRs was significantly decreased by ECE or DK. Overall, the results of this study indicate that ECE and DK decreased the serum levels of Ang II and expression of AT1R/TGFβ/SMAD, and then decreased the EMT and renal fibrosis in SHRs. Furthermore, the decrease in EMT and renal fibrosis could lead to the restoration of renal function. It seems that ECE or DK could be beneficial for decreasing hypertensive nephropathy by decreasing EMT and renal fibrosis.     

Enhanced Bone Regeneration in Variable-Type Biphasic Ceramic Phosphate Scaffolds Using rhBMP-2

Our aim was to investigate the bone regeneration capacity of powder-type biphasic ceramic scaffold (BCP powder), block-type BCP (BCP block), and collagen-added block-type BCP (BCP collagen) with different concentrations of recombinant human bone morphogenetic protein 2 (rhBMP-2) in an animal model. Four rabbits were assigned to each of the following groups: no graft + rhBMP-2 (0.1/0.2 mg/mL), BCP powder + rhBMP-2 (0.1/0.2 mg/mL), BCP block + rhBMP-2 (0.1/0.2 mg/mL), and BCP collagen + rhBMP-2 (0.1/0.2 mg/mL), i.e., a total of 32 rabbits. Polycarbonate tubes (Φ 7 mm × 5 mm) for supporting scaffolds were fixed into a 7 mm round border. Subsequently, 0.1 mL of rhBMP-2 solutions with different concentrations was injected into the tubes. Both radiological and histomorphometric analyses showed that osteogenesis was not enhanced by increasing the concentration of rhBMP-2 in all groups at both 3 and 6 weeks. Radiological analysis showed that bone formation was higher in the BCP collagen group than in the BCP powder and BCP block groups at both rhBMP-2 concentrations at 3 weeks. rhBMP-2 enhanced bone formation; however, as the concentration increased, bone formation could not be enhanced infinitely. Collagen-added alloplastic graft material may be useful for mediating rapid bone formation in initial stages.     

Fabrication of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method

In this study, we investigate the effect of oxide dispersion strengthening on mechanical properties by dispersion of nano-sized Ta₂O₅ particles in Mo-Si-B alloy. A Mo-Si-B core-shell powder consisting of two intermetallic compounds of Mo₅SiB₂ and Mo₃Si as the core and nano-sized Mo solid solution surrounding intermetallic compounds was fabricated by chemical vapor transport. And Mo-Si-B core-shell powder with uniformly dispersed nano-sized Ta₂O₅ particles on the surface of a Mo solid solution shell was produced by a wet blending process with TaCl₅ solution and heat treatment. Then, pressureless sintering was performed at 1400°C for 3 h under a H₂ atmosphere. The hardness and fracture toughness of the Ta₂O₅-dispersed Mo-Si-B alloy were measured using Vickers hardness and 3-point bending tests, respectively. The Vickers hardness and fracture toughness of the fabricated Mo-Si-B-Ta₂O₅ alloy were more improved than that of the Mo-Si-B alloy fabricated using core-shell powder with no addition of Ta₂O₅ particles (Mo-Si-B alloy: 353 Hv, 13.5 MPa·√m, Mo-Si-B-Ta₂O₅ alloy: 509 Hv, 15.1 MPa·√m).     

Polymerization of allylbenzene with metallocene catalysts

Summary Homopolymerization of allylbenzene was carried out with various metallocene/methylaluminoxane (MAO) catalysts. Different polymerization behavior was observed depending upon the catalysts empolyed. rac-Et(Ind)₂ZrCl₂ and rac-Me₂Si(Ind)₂ZrCl₂ gave semicrystalline polyallylbenzenes while i-Pr(CpFlu)ZrCl₂ and CpTiCl₃ did not give any polymeric product. The Cp₂ZrCl₂ gave amorphous polyallylbenzene with low molecular weight. The effect of temperature on the polymerization was investigated with a constant Al/Zr ratio. The temperature showing maximum catalyst activity is higher for the ansa metallocene catalysts than Cp₂ZrCl₂ catalyst. The IR and NMR spectra indicated that the polyallylbenzene consisted of allylbenzene repeating unit and no isomerization occurred. Received: 7 December 1998/Revised version: 29 January 1999/Accepted: 9 February 1999     

Measurement of through-the-thickness variations of mechanical properties in SA508 Gr.3 pressure vessel steels using ball indentation test technique

The through-the-thickness variations of mechanical properties in SA508 Gr.3 pressure vessel steels were measured using the automated ball indentation (ABI) test technique. Key mechanical properties, such as the yield strength, ultimate strength, flow curve and hardness, were evaluated from indentation load-depth curves. The mechanical properties measured were location-dependent and the steepest gradients in the distributions of the mechanical properties appeared in the near-surface regions. The maximum through-the-thickness variations of the mechanical properties were in the range of 5–20% and they depended on the manufacturing process as well as the original wall thickness. It was concluded that the through-the-thickness variations in the mechanical properties were mainly caused by the location-dependent cooling rate during water quenching in the quality heat treatment which consisted of water quenching and tempering.     

Quality properties of pork sausage prepared with water-soluble chitosan oligomer

Emulsion type sausage was prepared with the addition of a chitosan oligomer (molecular weight 5000, 0.2%) and compared to a control. Sausages were aerobic- or vacuum-packaged and stored in a 4°C refrigerator for 3 weeks. Difference of microbial growth between the sample with added chitosan oligomer or control was not observed (P>0.05). Lipid oxidation was lower in the sausage with chitosan oligomer at 3 weeks in aerobic packaging (P<0.05) than in the control sausage. The surface color of the sausage with chitosan oligomer had higher Hunter color L*- and b*-value. Hunter color a*-values were lower in the chitosan oligomer-added sausage and the a*-value increased during storage regardless of packaging (P<0.05). Sensory panels did not detect any difference in color, flavor, texture, and overall acceptance, and mechanical texture analysis also showed no difference. Therefore, the quality of the sausage with added chitosan oligomer (0.2%) was acceptable.     

Random amplification of polymorphic DNA typing of Listeria monocytogenes isolated from meat

To investigate the epidemiological characteristics of Listeria monocytogenes isolated from imported or domestic meats, L. monocytogenes was isolated and identified through biochemical and serological tests, and epidemiological analysis of the isolates was carried out through the random amplification of polymorphic DNA (RAPD) method. Fifty-four isolates were identified as L. monocytogenes through biochemical tests, of which 36 (67%) were confirmed as serotype 1, and 18 (33%) were serotype 4, through the microagglutination test. In the molecular epidemiological analysis using RAPD method, the isolates could be classified into 10, 6 and 6 types using three random primers, PB1, PB4, and HLWL74, respectively. Forty composite profiles were identified by a combination of the three primers. RAPD analysis demonstrated the relationships between the isolates from beef from Korea and the USA, pork from Korea and Denmark. These results suggested that RAPD could be a useful typing tool for the epidemiological study of L. monocytogenes and other bacteria.     

Feasibility of compression ignition for hydrogen fueled engine with neat hydrogen-air pre-mixture by using high compression

Compression ignition of hydrogen engines with a homogeneous pre-mixture is a promising method to enhance the thermal efficiency as well as to reduce unique NO_x exhausted from the engine due to spatial reaction of the mixture. However, hydrogen gas has a relatively high self-ignition temperature. Therefore, compression ignition for a neat hydrogen-air pre-mixture is considered impossible to achieve without additives. Research on this has not yet been attempted for this reason.     

Radiation-laminar free convection in a square duct with specular reflection by absorbing-emitting medium

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10^-3 for the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.