On the other hand, increasing the temperature of the heat treatment causes an increase in the size of the ZnO nanoparticles. The crystal size of ZnO nanoparticles increases 1448 Food Bioprocess Technol (2012) 5:1447–1464 slowly from about 18 nm at 400 °C to 21 nm at 600 °C, but incre ases rapidly above 600 °C, reachi ng 36 nm at 800 °C (Ao et al., 2006).MCP is suitable for large-scale ZnO nanoparticle production due to its simplicity and low cost. Moreover, this process is attractive from an environmental point of view since the reactions involved do not include organic solvents (Lu et al., 2008). Moreover, drawbacks of the process such as particle agglomeration during milling are minimized by the presence of the salt matrix, which is then removed prior to calcination by a simple washing procedure.Physical Vapor Synthesis (PVS) In the PVS process, plasma arc energy is applied to a solidprecursor in order to generate vapor at high temperature (Fig. 2). The plasma arc provides the energy needed to induce reactions that lead to supersaturation and particle nucleationwhen the precursor is injected into the plasma. This generally decomposes them fully into atoms, which can then react or condense to form particles when cooled by mixing with cool gas or by expansion through a nozzle (Swihart, 2003).In this method, a reactant gas is added to the vapor, which is then cooled at a controlled rate and condensed to form nanoparticles. The nanoparticles produced by the PVS process consist of discrete, fully dense particles of defined
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