Melting of Nanoparticles

The melting temperature of nanoparticles can be 10K-100K lower than the bulk materials due to higher value of surface by volume ratio. According to Gibb's-Thomson relation:-  4 1 sl m m b f s d d T T H             But there has also supper heating phenomenon in case of embedded nanoparticle. Now we are going to discus melting of Zn-nanoparticles. Zinc is widely used in galvanizing steel products to prevent surface corrosion and in a variety of alloys. ZnO nanoparticles are used for ultraviolet radiation absorption, as electro-optic and piezoelectric materials. As a part of our discussion we discus the melting behavior in two conditions (i) when the zinc particles are in isolated states and (ii)when they are confined by a ZnO shell of increasing thickness formed by the surface oxidation. WE will discus this topic using DSC and TEM. EXPERIMENTAL METHODS:-Nanocrystaline zinc sample was 99.9+% purred and the average particle size is 35-80nm. The container was opened inside a glovebox in inert atmosphere. The zinc is kept in several sealed glass vials. Purity of bulk zinc materials was greater than 99.9%. Two calorimeters were used: One was a Perkin-Elmer Pyris Diamond differential scanning calorimeter and the second a Thermal Analysis Q-100 assembly. The purge gas used for the first instrument was ultra high purity Ar and for the second equipment was ultra high purity N2. The instruments were calibrated against the melting point and enthalpy of melting of indium. For measuring the specific heat, Cp, of zinc nanoparticles over the 623 to 703 K range, the calorimeter was calibrated with sapphire of known Cp. In the calorimeter two aluminium DSC pans are differed by weight ~0.5mg. Base line obtained by averaging several heating scans at 20K/min of two aluminium empty pans was substracted from the measured flow curve. Thus, errors from the weight difference between two DSC pans were eliminated. The experiment was done varying scan rate and each time separate sample vials are used and it was ensured that the oxidation of the nanoparticles to ZnO was minimum or negligible. The Cp values measured by the two methods agreed within ~1%. Figure 1. Specific heat of nanoparticles and bulk zinc is plotted against the temperature. The specific heat data for bulk zinc from Grønvold and Stølen are plotted for comparison. For microstructural observations and chemical …