No abstract

X-ray diffraction, infrared absorption spectroscopy, and chemical investigation have been carried out on deproteinated samples of turkey leg tendon at different degrees of calcification. The inorganic phase consists of poorly crystalline B carbonated apatite. On increasing calcification, the apatite crystal size, as well as its thermal stability, increase while the relative magnesium content is reduced. On the other hand, synchrotron X-ray diffraction data clearly indicate that apatite lattice parameters do not change as the crystals get larger. At the last stage of calcification the crystal size, chemical composition, and thermal conversion of the apatite crystallites approximate those of bone samples, which have been examined for comparison. The results provide a quantitative relationship between relative magnesium content and extent of apatite conversion into B-tricalcium phosphate by heat treatment. Furthermore, they suggest that the smaller crystallites laid down inside the gap region of the collagen fibrils are richer in magnesium than the longer ones that fill the space between collagen fibrils.

SUMMARY High‐pressure scanning electron microscopy (HPSEM) is a promising new family of techniques. The present knowledge of these techniques is reviewed and a new set of criteria developed for optimizing signal detection in HPSEM with a view to preserving specimen integrity. For this purpose, amplification of contrast signals generated in HPSEM was examined by computing the effect of ionization over a range of pressures and biasing fields, routinely used for this technique. The influence of secondary ionization due to ion impact was included in the calculations. To check the calculated results, the experiments were performed in the HPSEM apparatus in a nitrogen atmosphere. A divergence between the experimental values and the calculated values was found. This was removed by taking into account the effect of recombination of charge carriers. Inductive currents generated in the HPSEM environment are transient and do not affect the conclusions of this study. The gas pressure, biasing fields and beam current for preserving specimen integrity and obtaining good micrographs were selected from the data. Experimental measurements of noise are reported, and criteria for optimizing the signal‐to‐noise ratio for performing HPSEM are discussed. The application of these criteria has shown that specimen current detection can be more advantageous than other methods and configurations of detection and was capable of obtaining high/medium‐resolution micrographs.