Rama Mohan R Tallapragada
Articles written in Bulletin of Materials Science
Volume 32 Issue 5 October 2009 pp 471-479 Nanomatter
Next to atoms and molecules the powders are the smallest state of matter available in high purities and large quantities. The effect of any external energy on the shape, morphology and structure can thus be studied with relative ease. The present investigation deals with the effect of a non-contact external energy on the powders of antimony and bismuth. The characteristics of powders treated by external energy are compared with the as received powders (control). The average particle sizes, 𝑑50 and 𝑑99, the sizes below which 99% of the particles are present showed significant increase and decrease indicating that the energy had caused deformation and fracture as if the powders have been subjected to high energy milling.
To be able to understand the reasons for these changes the powders are characterized by techniques such as X-ray diffraction (XRD), surface area determination (BET), thermal analytical techniques such as DTA–DTG, DSC–TGA and SDTA and scanning electron microscopy (SEM).
The treated powder samples exhibited remarkable changes in the powder characteristics at all structural levels starting from polycrystalline particles, through single crystal to atoms. The external energy had changed the lattice parameters of the unit cell which in turn changed the crystallite size and density. The lattice parameters are then used to compute the weight and effective nuclear charge of the atom which showed significant variation. It is speculated that the external energy is acting on the nucleus through some reversible weak interaction of larger cross section causing changes in the proton to neutron ratios. Thus the effect is felt by all the atoms, and hence the unit cell, single crystal grain and grain boundaries. The stresses generated in turn may have caused deformation or fracture of the weak interfaces such as the crystallite and grain boundaries.
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