Crystal Research and Technology
Cryst. Res. Technol. 43, 193 (2008) - Abstract -

Microhardness studies of nanocrystalline calcium tungstate

V. M. Anandakumar and M. Abdul Khadar*

Department of Physics, Mahatma Gandhi College, Thiruvananthapuram 695 004, India
*Centre for Nanoscience and Nanotechnology and Department of Physics, University of Kerala, Kariavattom P O, Thiruvananthapuram 695 581, India

Keywords nanocrystals, microhardness, indentation, calcium tungstate, Hall-Petch relation
PACS 61.46.Hk, 62.25.+g, 81.07.Bc, 81.16.Be
DOI 10.1002/crat.200710987

Nanocrystals of calcium tungstate (CaWO4) of three different grain sizes were synthesized through chemical precipitation technique and the grain sizes and crystal structure were determined using the broadening of X-ray diffraction patterns and transmission electron microscopy. The microhardness of compacted pellets of nanocrystalline calcium tungstate (CaWO4) with different grain sizes were measured using a Vickers microhardness tester for various applied loads ranging from 0.049 N to 1.96 N. The values of microhardness showed significant reverse indentation size effect at low indentation loads. The microhardness data obtained for samples of different grain sizes showed grain size dependent strengthening obeying normal Hall-Petch relation. The dependence of compacting pressure and annealing temperature on microhardness of the nanostructured sample with grain size of 13 nm were also studied. The samples showed significant increase in microhardness as the compacting pressure and annealing time were increased.




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