Calcium phosphates with different Ca/P molar ratio can be obtained depending the
precipitation conditions such as pH and temperature. In this work the effect of the pH’s variation
during the H3PO4 addition in the synthesis of hydroxyapatite-HA, (Ca/P molar ratio 1.67)
by neutralization method, was studied. The H3PO4 addition’s rate was 1.0, 1.5, 8.0 mL.min-1
and in other experiment the H3PO4 was added at a time. After the addition was completed the
pH ranged from 7-12. The suspensions were kept during 24 hours for ripening. The precipitate
was separated from the suspension by vacuum filtration, washed with distilled water and
dried at 70°C/24h. Afterwards the materials were analyzed by thermogravimetric analysis
(TGA) with heating rate of 10°C/min in air. The calcination of the powders was accomplished
at 800°C/3h with heating rate of 10°C.min-1. The powders were characterized by X-ray diffraction
(XRD), infrared spectrometry (FTIR), specific surface area (BET), and scanning electron
microscopy (SEM). The results indicated that the ratio of addition of the acid can influence
both the morphology and the formation of the phases (HA and TCP) in the obtained
powders.
The polymeric precursor method was successfully used to synthesize Co x Zn 7Àx Sb 2 O 12 (x = 0-7) powders. Pigments were evaluated using colorimetry, X-ray diffraction, UV-vis and infrared spectroscopy. The optical band gap values vary with the Co 2+ substitution. These results suggest that the concomitant presence of Co and Zn in the spinel lattice leads to the rupture of the Végard law, as well as other properties of the studied system, such as unit cell volume. The Co-richer samples display a higher absorbance than the Co-lean samples. The high absorption of the Co 7 Sb 2 O 12 sample at most of the visible region makes this compound a candidate for a black pigment. It was shown that color depends on the site where the chromophore ion is located, in agreement with the ligand field theory. #
With the aim of obtaining materials with applications in pigments, Co x Zn 7-x Sb 2 O 12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for the synthesis of a zinc antimoniate spinel, Co x Zn 7-x Sb 2 O 12 (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two alcohols -both presented the spinel phase (Co, Zn) 2.33 Sb 0.67 O 4 . Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb 2 O 6 .
Nanocrystalline hydroxyapatite was prepared by a precipitation method with add of ultrasonic
irradiation. In this work the effect of H3PO4 addition rate during synthesis and the influence of
the magnesium incorporation into apatite were studded. The results revealed that the morphology
and cristalinity of synthesized nanopowders are significantly affected by ultrasonic irradiation. Monophase
hydroxyapatite was obtained when magnesium was added into HA lattice during the synthesis
with ultrasonic irradiation.
Oxides with spinel structures have been studied for many decades as they have been used in a variety of applications like pigments and refractories. They have also been used as a model structure to evaluate the relative stability of ions in octahedral and tetrahedral sites. Zinc-antimony spinels (Zn 7 Sb 2 O 12 ) were synthesized by the Pechini method and the cation Zn 2+ was substituted by Co
2+, taking into consideration the stoichiometry of Co x Zn 7-x Sb 2 O 12 (x = 0 -7). Characterization of the thermal properties of pyrolyzed powders was carried out with a TG/DTA analyzer, and mass losses were determined as a function of the cobalt content in the resin. The powders were calcined at temperatures in the range 600 to 1000 °C and characterized by XRD, BET and IR spectroscopy. Maximum cristalinity was obtained in powders calcined at 1000 °C. Materials with x = 5 -7 revealed the presence of a secondary phase (Co, Zn)Sb 2 O 6 . Infrared analysis facilitated in the determination of the possible sites of Zn 2+ , Co 2+ and Sb 2+ ions in the lattice.
Hydroxyapatite (HA) doped with europium (HAEu) offers the advantage of making the hydroxyapatite a fluorescent biomarker, allowing their imaging through emissionin vivoandin vitrotests. Several authors had been based their studies about europium site occupation (CaI and CaII) in hydroxyapatite by the lanthanide ion luminescence, verifying the influence of the method of synthesis and concentration of the dopant ion. In this study HA nanoparticles doped with 1.4 mol% of trivalent europium were synthesized by co-precipitation method and thermal treated at different temperatures (600°C and 1200°C). A careful evaluation of the influence of the excitation wavelength of europium luminescence in the HAEu was performed and it has been verified that both the characteristics transitions of europium, at CaI and CaII sites, and the luminescent intensity are dependent on the excitation wavelength. The non-observance of this fact can lead to erroneous conclusions about the site occupation of europium in hydroxyapatites.
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