A facile route for hydroxyapatite densification with an increased heating rate

The densification behavior of hydroxyapatite nanorods prepared by chemical precipitation method in open reactor conditions was investigated by application of different heating rates. The non-isothermal processing was performed with 2, 10, and 50 degrees C/min up to 1200 degrees C and yielded fully dense ceramics. The implementation of the higher heating rate provided grain size refinement from micrometer level for the slowest ramp, down to 250 nm in the case of processing with 50 degrees C/min, without any drawbacks regarding final density. The relative amount of retained structural hydroxyl groups in sintered ceramics was gradually increased with the heating rate. Furthermore, the qualitative level of optical translucency was increased with a higher heating rate which can be explained by the beneficial alignment of HAp nanorods during the fast heating rate processing, achieved microstructural refinement, and higher amount of structural hydroxyl groups

Are the program packages for molecular structure calculations really black boxes?

In this communication it is shown that the widely held opinion that compact program packages for quantum–mechanical calculations of molecular structure can safely be used as black boxes is completely wrong. In order to illustrate this, the results of computations of equilibrium bond lengths, vibrational frequencies and dissociation energies for all homonuclear diatomic molecules involving the atoms from the first two rows of the Periodic Table, performed using the Gaussian program package are presented. It is demonstrated that the sensible use of the program requires a solid knowledge of quantum chemistry