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Stoichiometric hydroxyapatite

Fig. 11.17 XRD patterns of bone hydroxyapatite and sintered stoichiometric hydroxyapatite. (Bone hydroxyapatite was obtained by heating bone of pig at 600°C). Fig. 11.17 XRD patterns of bone hydroxyapatite and sintered stoichiometric hydroxyapatite. (Bone hydroxyapatite was obtained by heating bone of pig at 600°C).
The dehydration of alcohols on stoichiometric and nonstoichiometric (calcium-deficient) hydroxyapatite (series 8 and 9 in Table II) gave results consistent with the above findings. Although there is a difference in the reaction temperature, it is evident that with the nonstoichiometric catalyst, which must be more acidic, the slope found is more negative than that with the stoichiometric calcium phosphate. [Pg.168]

Synthetic hydroxyapatite prepared by mixing stoichiometric amounts of aqueous solutions of calcium nitrate and ammonium phosphate was used in this study. The pH of the boiling suspension was maintained at about 10 by flowing a mixture of NH and throughout the precipitation process. The precipitate was repeatedly washed until the conductivity of the supernatant liquid was observed to be constant. The washed sample was freeze-dried and analyzed. An elemental analysis of the batch preparation showed the Ca/P molar to be ratio 1.64, with the predominant impurity being 2... [Pg.314]

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. [Pg.134]

The nonstoichiometry of CaHAP has received extensive attention in medical and solid-state science, because the CaHAP formed in the calcified tissues or synthesized is mostly non- stoichiometric. Bett et al.[8] have reported that the catalytic activity of Ca-deficient CaHAP for the dehydration of butanol can be related to the surface acidic hydrogens of HPO4" produced to maintain the electrical neutrality. Joris and Amberg [9, 10] have pointed out that the catalytic activity of cation-deficient CaHAP and strontium hydroxyapatite (abbreviated SrHAP) for the similar dehydration reaction is due to the acidic hydrogens of the H2O molecules located in OH -defects caused by the deficiency of Ca + or Sr " " ions rather than those of the surface HPO ions. [Pg.301]

Grown on Hydroxyapatite Seeds Stoichiometric amounts of CafNOjij and ammonium phosphate solutions were added to a boiling dispersion containing hydroxyapatite as seeds. The pH was maintained at 10 with gaseous NH,. The precipitate was water-washed and freeze-dried. [Pg.728]

Figure 1. Stoichiometric calcium hydroxyapatite structure projected on a, b, plane. (Suzuki)... Figure 1. Stoichiometric calcium hydroxyapatite structure projected on a, b, plane. (Suzuki)...
Figure 3. Rate of formation (600°C) of carbon dioxide from carbon monoxide on stoichiometric (Ap-S) and nonstoichiometric (Ap-N) hydroxyapatite for various P(02). Figure 3. Rate of formation (600°C) of carbon dioxide from carbon monoxide on stoichiometric (Ap-S) and nonstoichiometric (Ap-N) hydroxyapatite for various P(02).
The 02 species formed on the stoichiometric hydroxyapatite can react with carbon monoxide, CO + O2 - CO2 + O (6)... [Pg.677]

The substitution by other ions reduces the theoretical stoichiometric Ca/P ratio of 1.67 of hydroxyapatite to values for bone-like apatite of less than 1.6 (LeGeros, 1991), even as low as 1.4 (Weng etal., 1994). This non-stoichiometry of biological apatite can be described by the approximate formula (Young and Holcomb, 1982 Hattori and Iwadate, 1990 Liu et al., 2001). [Pg.92]

Reactions (1) and (2) have been postulated by Kokubo (1997) and subsequently electrochemically confirmed. The conversion of amorphous calcium titanate to calcium phosphate (Figure 5.2d,e) may be initiated by the formation of a thin layer of calcium phosphate with the configuration of the Posner s cluster, Ca3(P04)2 3 (reaction (5)) that has been shown to have the energetically most stable configuration (Onuma et al., 2000). This amorphous layer takes up more calcium and phosphate ions from the SBF to form OCP (reaction (6)) with Ca/P = 1.33 and finally stoichiometric hydroxyapatite (reaction (7)) with... [Pg.120]

The existence of OHAp as products of partial dehydroxylation of hydroxyapatite was postulated earlier (Bredig, Franck and Fiildner, 1933 Trombe and Montel, 1978) but the existence of OAp was subject to controversy for many years until it has now been well established thanks to modern analytical techniques (e.g., Gross and Pluduma, 2012 see Chapter 6.2.1.4). Liao etal. (1999) reported that (i) a small amount of OH- ions is always present in the structure of OAp and (ii) even a loss of 75% of the chemically bound water maintains the apatite channel structure. The limiting composition is then Ca10(PO4)6(OH)0 5O0 75 that corresponds to a water loss of 1.34% (Trombe and Montel, 1971). Hence, partially dehydroxylated hydroxyapatite (designated OHAp) could be described either as a non-stoichiometric... [Pg.265]

De Leeuw, N., Bowe, J.R., and Rabone, J.A.L. (2007) A computational investigation of stoichiometric and calcium-deficient oxy-and hydroxyapatite. Earaday Discuss., 134, 195-214. [Pg.299]


See other pages where Stoichiometric hydroxyapatite is mentioned: [Pg.354]    [Pg.351]    [Pg.282]    [Pg.327]    [Pg.163]    [Pg.324]    [Pg.541]    [Pg.238]    [Pg.157]    [Pg.673]    [Pg.91]    [Pg.118]    [Pg.119]    [Pg.133]    [Pg.137]    [Pg.139]    [Pg.165]    [Pg.169]    [Pg.182]    [Pg.184]    [Pg.263]    [Pg.266]    [Pg.267]    [Pg.272]    [Pg.274]    [Pg.289]    [Pg.312]    [Pg.327]    [Pg.327]    [Pg.329]    [Pg.329]    [Pg.331]    [Pg.332]    [Pg.395]    [Pg.400]    [Pg.404]    [Pg.405]   
See also in sourсe #XX -- [ Pg.200 , Pg.354 ]

See also in sourсe #XX -- [ Pg.377 ]




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