Reaction pathway to the synthesis of anatase via the chemical modification of titanium isopropoxide with acetic acid

Anatase nanoparticles were obtained through a modified sol-gel route from titanium isopropoxide modified with acetic acid in order to control hydrolysis and condensation reactions. The modification of Ti(O(i)Pr)(4) with acetic acid reduces the availability of groups that hydrolyze and condense easily through the formation of a stable complex whose structure was determined to be Ti(OCOCH(3))(O(i)Pr)(2) by means of FTIR and (13)C NMR. The presence of this complex was confirmed with FTIR in the early stages of the process. A doublet in 1542 and 1440 cm(-1) stands for the asymmetric and symmetric stretching vibrations of the carboxylic group coordinated to Ti as a bidentate ligand. The gap of 102 cm(-1) between these signals suggests that acetate acts preferentially as a bidentate rather than as a bridging ligand between two titanium atoms. The use of acetic acid as modifier allows the control of both the degree of condensation and oligomerization of the precursor and leads to the preferential crystallization of TiO(2) in the anatase phase. A possible reaction pathway toward the formation of anatase is proposed on the basis of the intermediate species present in a 1:1 Ti(O(i)Pr)(4):CH(3)COOH molar system in which esterification reactions that introduce H(2)O into the reaction mixture were seen to be negligible. The Rietveld refinement and TEM analysis revealed that the powder is composed of isotropic anatase nanocrystallites.

Repeatability of corrosion parameters for titanium-molybdenum alloys in 0.9% NaCl solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electronic ceramics based on polycrystalline SnO2, TiO2 and (Sn xTi1-x)O2 solid solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of an experimental 4% titanium tetrafluoride varnish on dental erosion by a soft drink

Objectives: This in vitro study assessed the effect of an experimental 4%TiF4 varnish on enamel erosion.Methods: Sixty bovine enamel blocks were randomly allocated to each type of varnish:Duraphat((R)) -D (NaF, 2.26%F), Duofluorid((R))-F(NaF, 2.71% F), TiF4-T(2.45%F) and no-fluoride-P. After application of the varnishes, the blocks were subjected to six sequential pH cycles (cola drink for 10 min and artificial saliva for 50 min, each) per day, during 4 days. After the pH cycles, the blocks were maintained in artificial saliva for 18 h. Enamel alterations were determined in the 2nd and 4th days, using profilometry (wear) and microhardness (%SMHC) tests. Data were tested using ANOVA and Tukey's tests (p < 0.05).Results: the mean %SMHC (+/- S.D.) at the 2nd and 4th day was, respectively, D (-77.26 +/- 5.04(a) and -88.59 +/- 5.11(A)), F (-76.79 +/- 7.82(a) and -88.78 +/- 6.10(A)), T(-88.28 +/- 3.19(b) and -92.04 +/- 2.54(A,B)) and P (-87.96 +/- 2.23(b) and -94.15 +/- 1.14(B)). The mean wear (mu m +/- S.D.) at the 2nd and 4th day was, respectively, D (3.16 +/- 0.32(a) and 7.56 +/- 0.90(A)), F(3.35 +/- 0.78(a,b) and 7.92 +/- 0.98(A)), T (3.81 +/- 0.43(b) and 7.69 +/- 0.76(A)) and P (3.43 +/- 1.13(a,b) and 7.31 +/- 0.53(A)).Conclusions: the NaF varnishes reduced the softening, but had no effect on the reduction of the wear. The TiF4 varnish was not able to reduce the softening and wear. (C) 2007 Elsevier Ltd. All rights reserved.

The use of ultrasound for cleaning the surface of stainless steel and nickel-titanium endodontic instruments

Aim the aim of this study was to evaluate the efficacy of ultrasound in cleaning the surface of stainless steel and Ni-Ti endodontic instruments.Methodology Twenty nickel-titanium instruments (10 Quantec files and 10 Nitiflex) and 20 stainless steel K-files (10 Maillefer-Dentsply and 10 Moyco Union Broach) were removed from their original packages and evaluated using a scanning electron microscope. Scores were given for the presence of residues on the surface or the instruments. The instruments were then cleaned in an ultrasonic bath containing only distilled water or detergent solution for 15 min, and re-evaluated, using scanning electron microscopy.Results Before cleaning, a greater amount of metallic debris was observed on the nickel-titanium Quantec instruments (P < 0.05), when compared to those made of stainless steel. Statistical analysis showed that the use of ultrasound was effective for cleaning the instruments, regardless of the irrigating solution or the instruments type (P < 0.05).Conclusions the use of ultrasound proved to be an efficient method for the removal of metallic particles from the surface of stainless steel and Ni-Ti endodontic instruments.

Sol-gel synthesis of titania-alumina catalyst supports

Titanium oxide is a good candidate as new support for hydrotreating (HDT) catalysts, but has the inconvenience of presenting small surface area and poor thermal stability. To overcome these handicaps TiO2-Al2O3 mixed oxides were proposed as catalyst support. Here, the results concerning the preparation, characterization and testing of molybdenum catalyst supported on titania-alumina are presented. The support was prepared by sol-gel route using titanium and aluminum isopropoxides, chelated with acetylacetone (acac) to promote similar hydrolysis ratio for both the alcoxides. The effect of nominal complexing ratios [acac]/[Ti] and of sol aging temperature on the structural features of nanometric particles was analyzed by quasi-elastic light scattering (QELS) and N-2 adsorption isotherm measurements. These characterizations have shown that the addition of acac and the increase of aging temperature favor the full dispersion of primary nanoparticles in mother acid solution. The dried powder presents a monomodal distribution of slit-shaped micropores, formed by irregular packing of platelet primary particles, surface area superior to 200 m(2) g(-1) and mean pore size of about 1 nm. These characteristics of porous texture are preserved after firing at 673 K. The diffraction patterns of sample fired above 973 K show only the presence of anatase crystalline phase. The crystalline structure of the support remained unaltered after molybdenum adsorption, but the surface area and the micropore volume were drastically reduced. (C) 2002 Published by Elsevier B.V. B.V.

Immobilization of pectinmethylesterase from acerola (Malpighia glabra L.) in porous silica

The total and partially purified enzyme pectinmethylesterase from acerola fruit was covalently immobilized on porous silica particles. These efficiency values were 114% for the total PME and 351% for the partially purified PME. In both forms the immobilization resulted in compounds with high thermal stability.

Evaluation of shear bond strength at the interface of two porcelains and pure titanium injected into the casting mold at three different temperatures

Statement of problem. Titanium has physical and mechanical properties, which have led to its increased use in dental prostheses despite casting difficulties due to high melting point and formation of oxide layers which affect the metal-ceramic bond strength.Purpose. This in vitro study evaluated the shear bond strength of the interface of 2 dental porcelains and pure titanium injected into a mold at 3 different temperatures.Material and methods. Using commercially pure (cp) titanium bars (Titanium, Grade I) melted at 1668degreesC and cast at mold temperatures of 430degreesC, 700degreesC or 900degreesC, 60 specimens were machined to 4 x 4 mm, with a base of 5 x 1 mm. The 4-mm surfaces were airborne-particle abraded with 100 mum aluminum oxide before applying and firing the bonding agent and evaluating the 2 porcelains (Triceram/Triline ti and Vita Titankeramik). Ten specimens were prepared for each temperature and porcelain combination Shear bond testing was performed in a universal testing machine, with a 500-kg load cell and crosshead speed of 0.5 mm/min. The specimens were loaded until failure. The interfaces of representative fractured specimens of each temperature were examined with a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Data for shear bond strength (MPa) were statistically analyzed by 2-way ANOVA and the Tukey test (alpha = .05).Results. The results showed significant differences for the metal/porcelain interaction effect (P = .0464). There were no significant differences for the 2 porcelains (P = .4250). The Tukey test showed a significant difference between the pair cp Ti 430degreesC Triceram and cp Ti 900degreesC Triceram, with respective mean values and SDs of 59.74 +/- 11.62 and 34.03 +/- 10.35 MPa.Conclusion. Triceram porcelain showed a bond strength decrease with an increase in the mold temperature for casting titanium. The highest bond strength for Vita porcelain and the best metal-ceramic interface observed with the SEM were found with the mold temperature of 700degreesC.