Maria Preda

Al2TiO5 preparation starting with reactive powders obtained by sol-gel method

Abstract Individual Al 2 O 3 , TiO 2 and SiO 2 , as well as binary Al 2 O 3 -TiO 2 powders have been obtained by sol-gel method, polymeric route. The obtained powders have been characterized by X-ray diffraction (XRD), IR-spectrometry and transmission electron microscopy (TEM) methods. In the used experimental conditions amorphous, submicronic, monodisperse powders have been obtained. The preparation of Al 2 TiO 5 and of some compositions situated in the Al 2 TiO 5 -Al 6 Si 2 O 13 pseudobinary system has been realized by solid-state reaction starting with the mentioned above powders. The thermal treatment schedule of the pressed powder mixtures has been established according to the results of differential thermal and thermogravimetric analysis (DTA/TGA). The formation of the compound has been followed by XRD, dimensional variation of the samples and apparent density measurements. The results obtained starting with reactive powders have been compared with those obtained starting with commercial powders. The samples have shown a high reactivity and the formation of tialite was enhanced. However the sintering tendency was not essentially increased.

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al2O3–TiO2–MgO and Al2O3–TiO2–SiO2 systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al2TiO5. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.

Sintered Hydroxyapatite with Additives

In present paper the sintering behaviour of HAP in the presence of 5 and 10wt% NC2P was studied. Relative density of 67-72% were obtained for samples sintered at temperatures ranged between 1000-1150°C. The shrinkage data revealed the formation of a liquid phase at 1100°C. This process was accompanied by the density increase and the porosity diminution respectively. The phase composition was investigated by X-ray diffraction. Even the major phase identified was 3CaO . P2O5, however small amounts of HAP were also detected until 1150°C. The IR spectra confirmed the presence of a HO ions in the HAP lattice at temperatures lower than 1150 0 C. Introduction Hydroxyapatite (HAP) is an inorganic compound of human bone, beside other phosphates, calcium carbonate, etc. It has two very important properties for the medical applications namely high bioactivity and good biocompatibility. The biocompatibility consists in the development of a strong chemical bond between the human bone and the HAP-based ceramics. Due to this characteristic HAP is especially used in reparatory orthopaedic and dental surgery. HAP can be obtained on synthetic way by various methods: chemical precipitation, sol-gel and hydrothermal route, etc. HAP contains one water molecule in its formulae, which can be released at temperatures between 600 and 850°C. However, due the reversibility of the reaction in the humid environment, HAP remains hydrated even at higher temperature [1]. Different additives are often used in order to improve the HAP properties. Santos and all [2] have studied the influence of glasses with compositions which belong to the P2O5-CaO-Na2O-SiO2 and P2O5-CaO-Na2O-Al2O3 systems, on the sintering behaviour of HAP fired at 1350 0 C with a soaking time of one hour. They have noticed an important increase of fracture toughness. The content of used glass was of 2 to 4% and the samples were fired in the range of 1200 to 1300°C for one hour at maximum temperature and cooled in the furnace. It was confirmed that there is only one crystalline phase, 3CaO . P2O5 at 1350°C there, the dissociation of HAP being total. Several substitutions of the host ions in the HAP lattice, such as CO3 2which can replace HO and PO4 3, F on the PO4 3sites, as well as Mg 2+ and Na + incorporated on the Ca 2+ sites were earlier reported [3]. The influence of other additives such as CaF2, Li2O, Na2O, NaPO3 and NaPO4 was also studied [4]. The calcium fluoride was found to be improper because it can react with HAP leading to the formation of free calcium oxide, which determines flaws appearance of products. Lithium oxide has a good influence on sintering of samples at high temperature when an eutectic melt is formed between 3CaO . P2O5 and Li3PO4. The NaPO3 and Na3PO4 compounds do not exhibit a significant effect concerning the density increase, because the lack of the liquid phase at the grains boundary. The aim of the work is to study the sintering behaviour of some HAP-based ceramics with sodium oxide used as additive. The compositions considered are located on the tie line HAPNa2O . 2CaO . P2O5 of the quathernary Na2O-CaO-P2O5-H2O system. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2091-2094 doi:10.4028/www.scientific.net/KEM.264-268.2091

Influence of Hydrothermal Method on the Aluminum Titanate Synthesis

Eutectoid decomposition and mechanical properties limit the well-known properties of aluminum titanate desired in several applications. In order to minimize these limitations new synthesis routes and additives were studied. In the present work, aluminum titanate precursor powders were prepared by hydrothermal method, starting with metal alkoxide reagents. The influence of Al and Ti sources and the experimental conditions were investigated by XRD, IR spectroscopy, DTA/TG and TEM methods. The aluminum titanate precursor powders obtained by hydrothermal method presented good homogeneity and very small grain size. XRD and evaluation of ceramic properties established the evolution of phase composition during sintering in the 12501400oC ranges.