Hydroxyapatite structure

Wilson, Prosser Powis (1983) studied the adsorption of polyacrylate on hydroxyapatite using infrared and chemical methods. They observed an exchange of ions and concluded that polyacrylate displaced surface phosphate and calcium, and entered the hydroxyapatite structure itself (Figure 5.2). They postulated that an intermediate layer of calcium and aluminium phosphates and polyacrylates must be formed at the cement-... 

Figure 1. Stoichiometric calcium hydroxyapatite structure projected on a, b, plane. (Suzuki)...

FIGURE 39.6 Hydroxyapatite structure projected down the c-axis onto the basal plane (From Posner A.S., Peiloff A., and Diorio A.D. 1958. Acta. Cryst. 11 308-309.)... 

Mostafa NY, Brown PW (2007) Computer simulation of stoichiometric hydroxyapatite structure and substitutions. J Phys Chem Solid 68(3) 431—437... 

Posner, A.S., Perloff, A., and Diorio, A.R (1958) Refinement of the hydroxyapatite structure, Acfa Cryst. 11, 308. Determined atom positions, bond lengths, and lattice parameters for the HA crystal structure. 

As shown in Figure 10.11, the absorption bands at 1455 cm indicate the presence of stretching vibrations of CO3 groups in hydroxyapatite structure. AB of 1045 cm belongs to vibrations of PO4 and HPO4 groups in hydroxyapatite... 

These techniques are bas not only on the principle that lead-containing phosphates with the apatite structure are highly insoluble, but also that rapid reactions occur with apatite and lead ions at the sohd/aqueous solution interface [12, 13, 15, 20, 29, 48, 53, 56]. Removal of lead from aqueous solutions using synthetic hydroxyapatite gives aqueous lead concentrations below the maximum contamination level after Ih [12, 53]. Other workers [9] observed the formation of calcium-lead apatite solid-solutions after 3 mins contact between synthetic hydroxyapatite and aqueous solutions containing lead, and no lead was detected in the aqueous solution after 24 h contact. However, the efficiency of lead removal depends on the characteristics of the phosphate rock employed [15]. It has been shown that the composition and crystallinity of the phosphate influence the speed of the surface reactions [4, 44]. More highly crystalline solids have lower solubilities and dissolution rates, making the apatite less reactive [4]. The presence of fluoride in the hydroxyapatite structure decreases its solubility and dissolution rate, while the presence of carbonate decreases structural stability, and increases solubility and the dissolution rate [4, 35]. 

Thermal decomposition of hydroxyapatite structure induced by titanium and its dioxide. J. Mater. Sci. 

An extensive and systematic study on cationic and anionic substitution in hydroxyapatite structures was carried out. Lead and vanadium were chosen for the exchange, due to their known effects on the redox and catalytic properties of hydroxypatites. Hydroxyapatites with variable Pb and V contents, were synthesized and characterized by multinuclear, including the unusual " Ca, NMR spectroscopy. Solid-state NMR allowed an analysis of the chemical environment of every ion after substitution into the hydroxyapatite network. ... 

TGA-DSC analysis presented in Figure 16.1 shows a fourth thermal event between 480-715 °C, with a maximum at 653 °C, accompanied by a mass loss of about 3% between 600-800 °C. At about the same temperature range (600-900 °C), a 2-3% weight loss was also identified by other studies. This can be associated to either the formation of additional crystals of hydroxyapatite or another phosphate [32] or to a release of carbonate groups from the hydroxyapatite structure [7,9,12,19,29,30]. 

The dilatometry analysis (Figure 16.2) discloses a massive bone tissue contraction, which starts at about 600 C and continues until 1260 C, corresponding to the elimination of carbonate groups and water molecules from the hydroxyapatite structure, and a slight crystallization [28,45]. 

Figure 4,30 A clinographic view of the hydroxyapatite structure. The density for hydroxyapatite is about 3.3 g/cc. 

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