Characteristics of dissimilar laser-brazed joints of isotropic graphite to WC–Co alloy

The effect of Ti serving as an activator in a eutectic Ag–Cu alloy filler metal in dissimilar laser-brazed joints of isotropic graphite and a WC–Co alloy on the joint strength and the interface structure of the joint is investigated in this study. To evaluate the joint characteristics, the Ti content in the filler metal was increased from 0 to 2.8 mass%. The laser brazing was carried out by irradiating a laser beam selectively on the WC–Co alloy plate in Ar atmosphere. The threshold content of Ti required to join isotropic graphite to WC–Co alloy was 0.4 mass%. The shear strength at the brazed joint increased rapidly with increasing Ti content up to 1.7 mass%, and a higher Ti content was found to be likely to saturate the shear strength to a constant value of about 14 MPa. The isotropic graphite blocks also fractured at this content. The concentration of Ti observed at the interface between isotropic graphite and the filler metal indicates the formation of an intermetallic layer of TiC.     

13C and Alkali NMR Studies of Electronic and Structural Properties of Alkali Fullerides

Abstract

Extensive NMR experiments have been performed both on the ¹³C and the alkali NMR in A_nC₆₀. In the superconducting A₃C₆₀. evidences for uniaxial molecular rotations of the C₆₀ and for a low T structural anomaly will be given. The linear chain structure of A₁C₆₀ is revealed by Magic Angle Spinning NMR, while its magnetic properties are studied by ¹³C and ⁸⁷Rb wideband NMR.     

Amorphous carbon-matrix composites with interconnected carbon nano-ribbon networks for electromagnetic interference shielding

Carbon-matrix composites with self-assembly interconnected carbon nano-ribbon networks were fabricated using natural and inexpensive rice husks by impregnating the rice husks with transitional metal solutions and sintering. The nano-structure of the composite was characterized using transmission electron microscopy. The electromagnetic interference shielding effectiveness of the composite was evaluated in the frequency range of 30 kHz–1.5 GHz. The electrical conductivity was measured as a function of the sintering temperature. These characteristics were compared with those of carbon-matrix composites without nano-ribbon networks.     

Fracture- and Indentation-Induced Structural Changes of Sodium Borosilicate Glasses

It is known that indentation using a diamond indenter induces permanent densification to result in plastic or inelastic deformation of glass. However, it is still unclear whether a high tensile stress causes such a structural change or not. In this study, fracture- and indentation-induced structural changes of glasses with the compositions of 20 Na₂O − 40x B₂O₃ – (80−40x) SiO₂ (in mol%, x = 0, 0.5, 1, 1.5) are investigated. Two-point bending tests of the glass fibers are performed to apply a high tensile stress to the glasses, and Vickers indentation tests of the glasses are also carried out for comparison. The structural change of the glass is evaluated by using Raman spectroscopy. It is elucidated that a tensile side of the fractured fiber for every composition shows a permanent structural change, which is characterized by a lower wave number shift of Raman peak assigned to the Si-O-Si bending vibration mode. It is also found that the behaviors of Raman peaks of the fractured fiber are opposite to those of the indented glass under a high compressive stress.     

NOTE: SOLVENT EXTRACTION OF PLATINUM(IV) BY TRIOCTYLPHOSPHINE OXIDE

The equilibrium distribution of platinum(IV) between hydrochloric acid and trioctylphosphine oxide (T0P0) in toluene at 303 K was examined. From the concentration dependencies of the distribution ratio, it was determined that platinum(IV) is extracted as follows:

The extraction.equilibrium constant was found to be Ke = 3.6×10³.     

SOLVENT EXTRACTION EQUILIBRIA OF GALLIUM (III) WITH ACIDIC ORGANOPHOSPHORUS COMPOUNDS FROM AQUEOUS NITRATE MEDIA

A comparative investigation on the solvent extraction equilibria of gallium(III) from aqueous nitrate media was conducted with three kinds of acidic organophosphorus compounds, di (2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl 2-ethyl-hexylphosphonic acid (EHEHPA) and di (2,4,4'-trimethylpentyl) phosphinic acid (DTMPPA), in toluene at 303 K. It was found that gallium(III) is extracted as 1:4 metal:reagent complexes with D2EHPA and EHEHPA and as a 1:3 complex with DTMPPA in the region of low loading ratio while it is extracted as 1:3 complexes with all reagents at high loading ratio. The extraction equilibrium constants with these extractants were evaluated for the former complexes as follows: K_e = 2.3xl0^-2, 8.5xl0^-3 and 1.3xl0^-4 for D2EHPA, EHEHPA and DTMPPA respectively.     

Adsorption of Metal Ions on A Novel Amine-Type Chelating Resin

Distribution equilibria were investigated for the adsorption of metal ions and acids on Sumichelate MC-10 resin, a polyethylene polyamine type of novel chelating resin. The total exchange capacities for HCl and HNO₃ were evaluated as 5.6 and 6.3 mol/kg dry resin, respectively. Adsorption of various divalent transition metals and precious metals was investigated from HCl on the chloride form of the resin. The adsorption of transition metals took place in the sequence Cd>Zn>Cu>Co>Mn. The adsorption of Pt(IV) was only slightly selective over Pd(II); however, the latter was selectively eluted with high concentrations of HCl. Adsorption of Ag(I), Zn(II) and Cu(II) was investigated from 1 mol/dm³ NH₄NO₃ on the free base form of the resin. It took place in the sequence Cu>Ag>Zn. The mechanism of the adsorption of metal ions mentioned above was qualitatively discussed.     

Synthesis of calcium carbonate vaterite crystals and their effect on stabilization of suspension polymerization of MMA

Spherical calcium carbonate vaterite crystals were synthesized and the effect of them on stabilization of suspension polymerization of methyl methacrylate was investigated. Suspension polymerization of methyl methacrylate could be stabilized with calcium carbonate vaterite crystals and sodium dodecylbenzene sulfonate of the concentrations from 25 to 100 ppm. Poly(methyl methacrylate) beads coated with spherical calcium carbonate vaterite crystals were prepared. With an increase in the concentration of sodium dodecylbenzene sulfonate from 25 to 100 ppm, the amount of calcium carbonate vaterite crystals adhered on the surface of poly methyl methacrylate bead increased and the mean diameters of the polymer beads decreased.     

Carbon-thermal reduction and nitridation of mixtures of SiO2 and Al2O3 · 2H2O

Sialon powders have been prepared by heating mixtures of SiO₂, Al₂O₃ 2H₂O and carbon in flowing nitrogen at 1470° C. The nitrogen content in the product powder increased with increasing added carbon, and was independent of both the flow rate of nitrogen gas and the surface area of pellet. The amount of SiO lost increased with an increase in the flow rate of nitrogen gas and surface area of the pellet and with a decrease in the amount of added carbon. A major part of the SiO evolved by the carbon reduction was trapped by carbon then consumed by carbon reduction and nitridation to form the sialon powder. The rest of the SiO was carried out of the system by the nitrogen gas. The amount of SiO lost and the nitrogen content can be estimated using the residual carbon content.     

Lyme disease in Mato Grosso do Sul State, Brazil: report of three clinical cases, including the first of Lyme meningitis in Brazil

The authors report the occurrence of the first three clinical cases of Lyme disease in Mato Grosso do Sul State, including the first case of Lyme meningitis in Brazil. These were identified by clinical and laboratorial criteria. Anti-Borrelia burgdorferi antibody search was carried out through ELISA and Western Blotting techniques, the former providing identification of IgG class antibodies alone, in one only of those cases. Through Immunoblotting, the following features were found in serum: 5 IgG and 2 IgM bands for the first case; 7 IgG and 2 IgM bands for the second; and 5 IgG and 6 IgM bands for the third. In the latter, presence fo specific antibodies was searched in liquor, due to lymphomonocitary meningitis occurrence, and one IgM band was detected. After antibiotic therapy, all patients exhibited significant clinical and laboratorial improvement in their conditions along with symptom regression to the present moment.