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Chapter VIII Micro-hardness studies…
al [59] have reported room temperature Vickers micro-hardness studies on
(100) and (001) planes of KDP crystals grown from urea doped solutions.
They found increased in hardness values for doped crystals compared to pure
KDP crystals. Similarly, Podder [60] earlier concluded in his study that Vicker
micro-hardness exhibited higher mechanical stability of urea doped crystals
than KCl doped.
The values of Vickers hardness Hv calculated using equation (8.1) is
compiled in table (8.1). The plots of Hv Vs load for pure and 0.3 wt. %, 0.4 wt.
% and 0.5 wt. % amino acids (L-histidine, L-threonine, DL-methionine) doped
KDP crystals are shown in figure (8.5a -8.5c). From these figures it is
observed that the micro-hardness decreases rapidly with increasing load and
then attains nearly a constant value. During indentation, the indenter first
penetrates the distorted zone of the surface layer. Therefore, one observes a
decrease in the hardness of the material for increasing load. As the depth of
indentation increases with load, the effect of the inner layers become more
and more prominent than the surface layer and the indenter reaches a depth
at which undistorted material exists and hence, no change is observed in the
value of hardness with load [61]. From figure (8.5 a,b,c) one can also observe
that as the doping of amino acids increase the Vickers micro-hardness value
decrease slightly with comparison to pure KDP. It can be conjectured that the
doping of amino acid softens the KDP crystal up to a marginal extent. The
effect of doping of amino acids on Vickers micro-hardness of KDP crystals
can be studied from table (8.1).
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