Effect of Ni coating on SiC particles to synthesize Al based Metal Matrix Composites

Aluminum Metal Matrix Composites (MMC) have been essentially studied due to their superior physical, mechanical and Tribological wear properties. Al MMC’s are finding applications in aerospace, automobile and general engineering industries owing to their favorable microstructure and improved mechanical behavior. In the present investigation Al based MMC with SiC were synthesized by liquid metallurgy technique. This paper is aimed to study the influence of Ni coating on SiC particles to fabricate Al MMC in addition to tribological and wear properties. The result shows that SiC content can be added to Al matrix up to a volume fraction of 15%. The hardness measurements suggest that an increase in SiC content was responsible for improved hardness value. Al with 15% of SiC resulted a hardness value of 115 HV.The microstructure examinations clearly demonstrated that SiC particles were uniformly distributed in Al matrix. The interface between matrix and reinforcement has been substantially improved while coating SiC particles with Ni. The EDX results also confirmed the presence of Ni on SiC particles. Tribological wear properties of Al-SiC composite suggest that presence of SiC has strong influence on improving the sliding wear resistance under various test conditions. The improved bonding between SiC and Al matrix by Ni coating resulted in further improvement in sliding wear performance. The influence of applied load, sliding distance and pressure during sliding was discussed in detail

The delivery of copper for thylakoid import observed by NMR

The thylakoid compartments of plant chloroplasts are a vital destination for copper. Copper is needed to form holo-plastocyanin, which must shuttle electrons between photosystems to convert light into biologically useful chemical energy. Copper can bind tightly to proteins, so it has been hypothesized that copper partitions onto ligand-exchange pathways to reach intracellular locations without inflicting damage en route. The copper metallochaperone Atx1 of chloroplast-related cyanobacteria (ScAtx1) engages in bacterial two-hybrid interactions with N-terminal domains of copper-transporting ATPases CtaA (cell import) and PacS (thylakoid import). Here we visualize copper delivery. The N-terminal domain PacS(N) has a ferredoxin-like fold that forms copper-dependent heterodimers with ScAtx1. Removal of copper, by the addition of the cuprous-ion chelator bathocuproine disulfonate, disrupts this heterodimer, as shown from a reduction of the overall tumbling rate of the protein mixture. The NMR spectral changes of the heterodimer versus the separate proteins reveal that loops 1, 3, and 5 (the carboxyl tail) of the ScAtx1 Cu(I) site switch to an apo-like configuration in the heterodimer. NMR data ((2)J(NH) couplings in the imidazole ring of (15)N ScAtx1 His-61) also show that His-61, bound to copper(I) in [Cu(I)ScAtx1](2), is not coordinated to copper in the heterodimer. A model for the PacS(N)/Cu(I)/ScAtx1 complex is presented. Contact with PacS(N) induces change to the ScAtx1 copper-coordination sphere that drives copper release for thylakoid import. These data also elaborate on the mechanism to keep copper(I) out of the ZiaA(N) ATPase zinc sites