The mineral of cortical bones has been studied in newborn, growing, and adult rats and in the calf and cow, using X-ray diffraction and infrared spectroscopy during the thermal decomposition of bones and by microassay of carbonate. The mineral of all the bone samples, regardless of species or age, was found to be a calcium-deficient apatite containing both CO3(2-) and HPCO4(2-) ions in the crystal lattice. The crystal size, Ca/P molar ratio, and CO3(2-) ion content of cortical bone all increased with increasing age in both the rat and the bovine. The Ca/P ratio varied from 1.51 in newborn rats to 1.69 in adults but remained that of Ca-deficient apatite even though its value was close to that of stoichiometric hydroxyapatite (1.67). Both the carbonate ion and the hydrogenophosphate ion contents varied from one animal species to another and with age within a given species. Maturation was correlated with an increase in carbonate ion content, which replaced the HPO4(2-) ions. In contrast, the calcium ion number per unit formula did not vary during maturation. Cortical bone mineral, in both species, regardless of age, can therefore be represented by the following formula: Ca8.3 (PO4)4.3 (CO3)x(HPO4)y(OH)0.3; y decreased and x increased with increasing age, (x + y) being constant, equal to 1.7.
Types of "H2O" in human enamel and in precipitated apatites are characterized using X-ray diffraction, infrared (IR) absorption spectroscopic and thermogravimetric analyses. Changes in lattice parameters (principally in the a-axis dimensions) and in the character of the IR absorption bands are correlated with weight losses at pyrolysis temperatures of 100 degrees to 400 degrees C and with effect of rehydration and reignition of previously ignited samples. This study demonstrated that the loss of "H2O" below 200 degrees C is reversible and causes no significant change in the lattice parameter of these apatites, whereas loss of "H2O" between 200 degrees and 400 degrees C is irreversible and causes a contraction in the a-axis dimension. It is proposed that two general types of "H2O" are present in these apatites: (a) adsorbed H2O--characterized by reversibility, thermal instability below 200 degrees C, and lack of effect on lattice parameters; and (b) lattice H2O--characterized by irreversibility, thermal instability between 200 and 400 degrees C, and induction of expansion in the a-axis dimensions of human enamel and precipitated apatites. Lattice H2O is assumed to be due to H2O-for-OH and/or HPO4-for-PO4 substitutions in these apatites. Loss of adsorbed H2O caused sharpening of the OH absorption bands in the spectra of these apatites. Loss of lattice H2O caused the appearance of P-O-P absorption bands (due to the presence of P2O74- group) in precipitated apatites containing small amounts of CO32-.
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