Glass Ionomer Cements Based in TiO2 by Sol-gel Method

Glass ionomer cements are used in dentistry for applications such as luting cements and as restoratives materials, due to their ability to chemically bond to the tooth. The glasses used in the cements are based on calcium aluminum silicates and calcium fluoride. This study aimed at preparing a glass systems containing titanium oxide to be used in glass ionomer cements. Powders with the composition 47SiO2-13CaO-29Na2O-7P2O5-4TiO2 were synthesized by the sol-gel method, one prepared with TiO2 powder (A1) and the other with titanium tetraisopropoxide (A2). The obtained powders exhibited a specific surface area of 83.63 m2g-1 and 15.79 m2g-1 and pore diameter of 42.07 Å and 90 Å for A1 and A2, respectively. The XRD results indicated that the material is partially crystalline with weak diffraction peaks related to titanium oxide (anatase). The FTIR and Raman spectroscopy analyses showed that SiO4 tetrahedra are found in the same coordination both in the synthesized glasses network and in the commercial glass ionomer cements Vidrion C® Cementation and Maxion®R Restorative, used for comparative purposes. The introduction of Ti4+ ions in the powders developed in this work provided properties and the structural characteristics indicating their potential for applications as ionomer cements. DOI: http://dx.doi.org/10.17807/orbital.v11i1.1176 </p

Structural and magnetic characterization of maghemites prepared from Al-substituted magnetites

Synthetic aluminum-substituted maghemites were characterized by total chemical analysis, powder X-ray diffraction (XRD), Mössbauer spectroscopy (ME), and vibrating sample magnetometry (VSM). The aim was to determine the structural, magnetic, and hyperfine properties of &#947;-Fe2-xAl xO3 as the Al concentration is varied. The XRD results of the synthetic products were indexed exclusively as maghemite. Increasing Al for Fe substitution decreased the mean crystalline dimension and shifted all diffraction peaks to higher º2&#952; angles. The a0 dimension of the cubic unit cell decreased with increasing Al according to the equation a o = 0.8385 - 3.63 x 10-5 Al (R²= 0.94). Most Mössbauer spectra were composed of one sextet, but at the highest substitution rate of 142.5 mmol mol-1 Al, both a doublet and sextet were obtained at 300 K. All hyperfine parameters from the sub-spectra were consistent with high-spin Fe3+ (0.2 a 0.7 mms-1) and suggested a strong superparamagnetic component associated with the doublet. The magnetic hyperfine field of the sextets decreased with the amount of Al-substitution [Bhf (T) = 49.751 - 0.1202Al; R² = 0.94] while the linewidth increased linearly. The saturation magnetization also decreased with increasing isomorphous substitution