Search

We attempted to study the immune response in M. rosenbergii by melanization reaction produced by plasma phenoloxidase (PO) activity. The substrate affinity of the PO enzyme was determined using different phenolic substrates, and it was found that the diphenols were only oxidized. The enzyme was characterized as catechol oxidase type of PO and L-3,4 dihydroxyphenylalanine (L-DOPA) showed the highest substrate affinity to the enzyme. The biochemical parameters that determined optimum enzyme activity were found to be 2.5 mM L-DOPA at an absorbance of 470 nm, 10 mM Tris–HCl buffer at pH 7.5, temperature at 25°C, and 15 min incubation. Kinetic characteristics of plasma were studied from the M. rosenbergii. The hemocyanin was isolated by gel filtration chromatographic technique using Sephadex G-100. The M. rosenbergii hemocyanin (MrHC) showed only one band with a molecular weight of 325 kDa on native polyacrylamide gel electrophoresis (PAGE) when stained with Coomassie Brilliant Blue (CBB) and bathocuproine sulfonic acid. The reduction of MrHC protein in SDS-PAGE displayed three subunits with a molecular weight of 74, 76, and 78 kDa, respectively. Determination of optimal condition for PO activity of plasma has also been attempted. The plasma optimal condition taken for the MrHC was tested for its ability to oxidize diphenols such as L-DOPA was shown only PO activity. These results showed that in the presence of PO and peroxidase inhibitors, phenylthiourea (PTU) and tropolone respectively have decreased plasma and MrHC PO activity. This indicates that hemocyanin triggers innate immunity probably through one of its subunits that function as the active moiety.

To the first time, thermal conductivities of spark plasma sintered β-sialons (Si3Al3O3N5) procured from combustion synthesis (CS) with no sintering additive were measured by the laser flash method at room temperature. A full densification occurred when these materials were sintered at 1600 °C with a simultaneous pressure of 50 MPa. XRD analyses indicated that single phase β-sialons were formed after SPS though the combustion synthesized β-sialon powders had considerable amounts of silicon impurities. Thermal conductivity values increased with sintering temperature and attained a maximum of 5.49 W m−1 K−1 for fully densified β-sialons sintered at 1700 °C for 10 min.

The influence of different raw material mixtures on β-sialon (Si6−zAlzOzN8−z, 1 ⩽ z ⩽ 4) formation through mechanical activation coupled combustion synthesis (MA-CS) was investigated in low nitriding atmosphere of 1 MPa without diluent inclusions. The MA-CS performed for the first time on sialon raw materials with milling time of 18 min obtained sialons more than three times as pure as those obtained by CS of mixtures ball milled to 1 h (z = 3). The starting materials containing silicon, aluminum, and alumina (z = 4) after MA-CS had an increment of sialon amounts up to 88 mass%.

Fully dense multiwall carbon nanotubes (MWCNT)/SiO2 nanocomposites with MWCNTs contents of 5 and 10 vol% have been processed by spark plasma sintering, and the electrical conductivities of the nanocomposites were evaluated at temperatures ranging from 5 to 300 K. It has been found that the incorporation of MWCNTs converted an insulating silica nanoceramic into metallically conductive composites. The room-temperature conductivities of the nanocomposites, with over 14 orders of magnitude compared with pure silica, are in the range of 8 and 65 S/m. Also, it was interestingly found that the conductivity increased linearly with temperature from 5 to 300 K.

Thermal conductivities of fully dense multi-wall carbon nanotube/silica nanocomposites processed by spark plasma sintering were evaluated using a laser flash technique. It was found that incorporation of 5 and 10 vol.% carbon nanotube improved the conductivities of the nanocomposites, and this improvement was enhanced with increasing sintering temperature and duration. A maximum conductivity of 4.08 W m −1 K −1 was measured for 10 vol.% carbon nanotube-containing nanocomposites sintered at 1050 °C for 10 min.

The mechanical response of four different types of hot pressed yttrium stabilized α/β composite SiAlON ceramics was investigated by scratch testing in order to interpret their severe wear behavior. A progressive loading scratch tester with both rough and smooth spherical diamond styluses was used to analyze the variation in mechanical response with roughness of stylus. The extent of subsurface damage produced by the different styluses on a 50% β-content composite was also investigated using a visualization technique with plasma etching, which has been previously developed by one of the authors. When scratched by the rough stylus, quasi-plastic deformation recognized in the form of grain release after plasma etching was present predominantly in the surface, and the use of this stylus was regarded to be more appropriate for comparing the results of scratch tests with those of severe wear due to similarity of crack formation between grain dislodgement in severe wear and subsurface damage in the scratch tests. The work required to produce damage and groove formation ( W dg ) when scratched by the rough stylus was evaluated for all test materials and it was found that the worn volume under severe wear follows the reverse order of W dg .

The influence of diluent addition on purities of β-Si5AlON7 powders synthesized by mechanically activated combustion synthesis (MA-CS) under a very low nitrogen atmosphere of 1 MPa was investigated. The purity of β-Si5AlON7 powders increased with diluent concentrations in raw materials and had a maximum value of 91% when 40 mass% of diluents were added, a 25% more pure when compared to powders procured without diluents. In contrast, when diluents were included 50% or more, the combustion synthesis (CS) reaction did not occur due to reduced exothermic heat. The results also showed that the particle sizes of β-Si5AlON7 powders synthesized with 40 mass% of diluents were only one-tenth when compared to powders synthesized without diluents.

Fine β-sialon (Si6−zAlzOzN8−z, 1

–sialons (Si6-zAlzOzN8-z, z=3) synthesized by mechanically activated combustion synthesis (MA-CS) at a low N2 pressure of 1 MPa, were sintered by Spark Plasma Sintering (SPS) and thermal conductivity was measured at room temperatures. Specimens were fully densified at 1600oC for 10 mins. and showed only –sialon phases confirmed by x-ray diffraction patterns though un-reacted Si was present as impurities after MA-CS. Thermal conductivities increased with sintering temperature and had a maximum value 5.49 W m-1 K-1 for specimens sintered at 1700oC.