Studies on Properties of Micro-Nano ZrO2 Particulate Metal Matrix Composites

A metal matrix composite (MMC) is a composite material with at least two constituent parts, one being a metal matrix and other is reinforcement. When at least three materials are present, it is called a hybrid composite. Aluminium is widely used in aerospace and automobile industries due to its low density and good mechanical properties, better corrosion resistance and wear, low thermal coefficient of expansion as compared to conventional metals and alloys. The aim involved in designing MMC materials is to combine the desirable attributes of metals and ceramics. This project is aimed at development of MMC having aluminium metal matrix with micro-nano particulate zirconium oxide reinforcement. Here aluminium (LM25) has been selected as base metal along with 12% ZrO2 (micro), 12% ZrO2 (nano) and 12% ZrO2 (6% micro + 6% nano) have been taken as reinforcements to produce MMC. The composite has been produced by liquid metallurgy technique (stir casting). The properties of chosen composite are compared with base metal for tension, wear, hardness, density and microstructure analysis. For the combination of Al-LM25 with 12% zirconium oxide (6% micro + 6% nano) the tensile strength (TS) and hardness had increased when compared to that of base metal and are between that of the micro and nano reinforced composite. The density of MMC cast is almost relevant to theoretical densities. For MMC, the wear rate increases for an increase in the speed for a given constant load and time. The microstructure study reveals that Al-LM25 and zirconium oxide have been distributed uniformly throughout the casting with less porosity.

Spatial and seasonal distribution of dissolved and particulate bioactive metals in Antarctic sea ice

Iron (Fe) has been shown to limit growth of marine phytoplankton in the Southern Ocean, regulating phytoplankton productivity and species composition, yet does not seem to limit primary productivity in Antarctic sea ice. Little is known, however, about the potential impact of other metals in controlling sea-ice algae growth. Here, we report on the distribution of dissolved and particulate cadmium (Cd), cobalt (Co), copper (Cu), manganese (Mn), nickel (Ni), and zinc (Zn) concentrations in sea-ice cores collected during 3 Antarctic expeditions off East Antarctica spanning the winter, spring, and summer seasons. Bulk sea ice was generally enriched in particulate metals but dissolved concentrations were similar to the underlying seawater. These results point toward an environment controlled by a subtle balance between thermodynamic and biological processes, where metal availability does not appear to limit sea-ice algal growth. Yet the high concentrations of dissolved Cu and Zn found in our sea-ice samples raise concern about their potential toxicity if unchelated by organic ligands. Finally, the particulate metal-to-phosphorus (P) ratios of Cu, Mn, Ni, and Zn calculated from our pack ice samples are higher than values previously reported for pelagic marine particles. However, these values were all consistently lower than the sea-ice Fe:P ratios calculated from the available literature, indicating a large accumulation of Fe relative to other metals in sea ice. We report for the first time a P-normalized sea-ice particulate metal abundance ranking of Fe >> Zn ≈ Ni ≈ Cu ≈ Mn > Co ≈ Cd. We encourage future sea-ice work to assess cellular metal quotas through existing and new approaches. Such work, together with a better understanding of the nature of ligand complexation to different metals in the sea-ice environment, would improve the evaluation of metal bioavailability, limitation, and potential toxicity to sea-ice algae.