Raman and XRD study on brookite-anatase coexistence in cathodic electrosynthesized titania

Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy-hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solidliquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium-tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X-ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile-free mixture of brookite and anatase at temperatures as low as 200 degrees C that persists up to 800 degrees C, when pure anatase dominates. The amount of brookite in the brookiteanatase mixture reaches a maximum at 400 degrees C. This very simple method for obtaining a brookiteanatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright (C) 2011 John Wiley & Sons, Ltd.

On the electrical conductivity of Ti-implanted alumina

Ion implantation of metal species into insulators provides a tool for the formation of thin, electrically conducting, surface layers with experimenter-controlled resistivity. High energy implantation of Pt and Ti into alumina accelerator components has been successfully employed to control high voltage surface breakdown in a number of cases. In the work described here we have carried out some basic investigations related to the origin of this phenomenon. By comparison of the results of alumina implanted with Ti at 75 keV with the results of prior investigations of polymers implanted with Pt at 49 eV and Au at 67 eV, we describe a physical model of the effect based on percolation theory and estimate the percolation parameters for the Ti-alumina composite. We estimate that the percolation dose threshold is about 4 x 10(16) cm(-2) and the maximum dose for which the system remains an insulator-conductor composite is about 10 x 10(16) cm(-2). The saturation electrical conductivity is estimated to be about 50 S/m. We conclude that the observed electrical conductivity properties of Ti-implanted alumina can be satisfactorily described by percolation theory. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697900]

Porcelain monolayers and porcelain/alumina bilayers reinforced by Al2O3/GdAlO3 fibers

Aim. This work tested the effect of the addition of Al2O3/GdAlO3 longitudinal fibers in different contents to veneering porcelain of two dental all ceramic systems. Methods: Fibers (0.5 mm diameter) obtained by the Laser Heated Pedestal Growth (LHPG) method were added to bar-shaped specimens made by veneer porcelain (monolayers) or both the veneer and the core ceramic (bilayers) of two all-ceramic systems: In-Ceram Alumina - glass infiltrated alumina composite (GIA) and In-Ceram 2000 AL Cubes - alumina polycrystal (AP) (VITA Zahnfabrik). The longitudinal fibers were added to veneering porcelain (VM7) in two different proportions: 10 or 17 vol%. The bars were divided into nine experimental conditions (n = 10) according to material used: VM7 porcelain monolayers, VM7/GIA, VM7/AP; and according to the amount of fibers within the porcelain layer: no fibers, 10 vol% or 17 vol%. After grinding and polishing the specimens were submitted to a three point bending test (crosshead speed = 0.5 mm/min) with porcelain positioned at tensile side. Data were analyzed by means of one-way ANOVA and a Tukey's test (alpha = 5%). Scanning electronic microscopy (SEM) was conducted for fractographic analysis. Results. Regarding the groups without fiber addition, VM7/AP showed the highest flexural strength (MPa), followed by VM7/GIA and VM7 monolayers. The addition of fibers led to a numerical increase in flexural strength for all groups. For VM7/GIA bilayers the addition of 17 vol% of fibers resulted in a significant 48% increase in the flexural strength compared to the control group. Fractographic analysis revealed that the crack initiation site was in porcelain at the tensile surface. Cracks also propagated between fibers before heading for the alumina core. Conclusions. The addition of 17 vol% of Al2O3/GdAlO3 longitudinal fibers to porcelain/glass infiltrated alumina bilayers significantly improved its flexural strength. 10 vol% or 17 vol% of fibers inclusion increased the flexural strength for all groups. (C) 2011 Elsevier Ltd. All rights reserved.

NIR luminescent Er3+/Yb3+ co-doped SiO2-ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol gel Er3+ and Yb3+ co-doped SiO2-ZrO2 are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO2/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 degrees C after annealing from 23 up to 500 min, depending on the ZrO2 content Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO2 nanocrystals dispersed in a silica-based glassy host Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er3+ ions was observed for the Yb3+- codoped planar waveguides, denoting an efficient energy transfer from the Yb3+ to the Er3+ ion. (C) 2012 Elsevier B.V. All rights reserved.

Biomechanical and histologic evaluation of non-washed resorbable blasting media and alumina-blasted/acid-etched surfaces

Objectives: To compare the biomechanical fixation and histomorphometric parameters between two implant surfaces: non-washed resorbable blasting media (NWRBM) and alumina-blasted/acid-etched (AB/AE), in a dog model. Material and methods: The surface topography was assessed by scanning electron microscopy, optical interferometry and chemistry by X-ray photoelectron spectroscopy (XPS). Six beagle dogs of similar to 1.5 years of age were utilized and each animal received one implant of each surface per limb (distal radii sites). After a healing period of 3 weeks, the animals were euthanized and half of the implants were biomechanically tested (removal torque) and the other half was referred to nondecalcified histology processing. Histomorphometric analysis considered bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Following data normality check with the Kolmogorov-Smirnov test, statistical analysis was performed by paired t-tests at 95% level of significance. Results: Surface roughness parameters Sa (average surface roughness) and Sq (mean root square of the surface) were significantly lower for the NWRBM compared with AB/ AE. The XPS spectra revealed the presence of Ca and P in the NWRBM. While no significant differences were observed for both BIC and BAFO parameters (P>0.35 and P>0.11, respectively), a significantly higher level of torque was observed for the NWRBM group (P = 0.01). Bone morphology was similar between groups, which presented newly formed woven bone in proximity with the implant surfaces. Conclusion: A significant increase in early biomechanical fixation was observed for implants presenting the NWRBM surface.

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier Inc. All rights reserved.

Microtensile bond strength of composite resin to glass-infiltrated alumina composite conditioned with Er,Cr:YSGG laser

Tribochemical silica-coating is the recommended conditioning method for improving glass-infiltrated alumina composite adhesion to resin cement. High-intensity lasers have been considered as an alternative for this purpose. This study evaluated the morphological effects of Er,Cr:YSGG laser irradiation on aluminous ceramic, and verified the microtensile bond strength of composite resin to ceramic following silica coating or laser irradiation. In-Ceram Alumina ceramic blocks were polished, submitted to airborne particle abrasion (110 mu m Al(2)O(3)), and conditioned with: (CG) tribochemical silica coating (110 mu m SiO(2)) + silanization (control group); (L1-L10) Er,Cr:YSGG laser (2.78 mu m, 20 Hz, 0.5 to 5.0 W) + silanization. Composite resin blocks were cemented to the ceramic blocks with resin cement. These sets were stored in 37A degrees C distilled water (24 h), embedded in acrylic resin, and sectioned to produce bar specimens that were submitted to microtensile testing. Bond strength values (MPa) were statistically analyzed (alpha a parts per thousand currency sign0.05), and failure modes were determined. Additional ceramic blocks were conditioned for qualitative analysis of the topography under SEM. There were no significant differences among silicatization and laser treatments (p > 0.05). Microtensile bond strength ranged from 19.2 to 27.9 MPa, and coefficients of variation ranged from 30 to 55%. Mixed failure of adhesive interface was predominant in all groups (75-96%). No chromatic alteration, cracks or melting were observed after laser irradiation with all parameters tested. Surface conditioning of glass-infiltrated alumina composite with Er,Cr:YSGG laser should be considered an innovative alternative for promoting adhesion of ceramics to resin cement, since it resulted in similar bond strength values compared to the tribochemical treatment.

Ultra-low friction coefficient in alumina-silicon nitride pair lubricated with water

In a ball-on-disc wear test, an alumina ceramic body sliding against a silicon nitride ceramic body in water achieved an ultra-low friction coefficient (ULFC) of 0.004. The profilometer and EDX measurements indicated that the ULFC regime in this unmated Al2O3-Si3N4 pair was achieved because of the formation of a flat and smooth interface of nanometric roughness, which favored the hydrodynamic lubrication. The triboreactions formed silicon and aluminum hydroxides which contributed to decrease roughness and shear stress at the contact interface. This behavior enables the development of low energy loss water-based tribological systems using oxide ceramics. 13 2012 Elsevier B.V. All rights reserved.

Photo-induced electron transfer in supramolecular materials of titania nanostructures and cytochrome c

In the present paper, we report on the molecular interaction and photochemistry of TiO2 nanoparticles (NPs) and cytochrome c systems for understanding the effects of supramolecular organization and electron transfer by using two TiO2 structures: P25 TiO2 NPs and titanate nanotubes. The adsorption and reduction of cytochrome c heme iron promoted by photo-excited TiO2, arranged as P25 TiO2 NPs and as nanotubes, were characterized using electronic absorption spectroscopy, thermogravimetric analysis, and atomic force microscopy. In an aqueous buffered suspension (pH 8.0), the mass of cytochrome c adsorbed on the P25 TiO2 NP surface was 2.3 fold lower (0.75 mu g m(-2)) than that adsorbed on the titanate nanotubes (1.75 mu g m(-2)). Probably due to the high coverage of titanate nanotubes by adsorbed cytochrome c, the low amount of soluble remaining protein was not as efficiently photo-reduced by this nanostructure as it was by the P25 TiO2 NPs. Cytochrome c, which desorbed from both titanium materials, did not exhibit changes in its redox properties. In the presence of the TiO2 NPs, the photo-induced electron transfer from water to soluble cytochrome c heme iron was corroborated by the following findings: (i) identification by EPR of the hydroxyl radical production during the irradiation of an aqueous suspension of TiO2 NPs, (ii) impairment of a cytochrome c reduction by photo-excited TiO2 in the presence of dioxane, which affects the dielectric constant of the water, and (iii) change in the rate of TiO2-promoted cytochrome c reduction when water was replaced with D2O. The TiO2-promoted photo-reduction of cytochrome c was reverted by peroxides. Cytochrome c incorporated in the titanate nanotubes was also reversibly reduced under irradiation, as confirmed by EPR and UV-visible spectroscopy.

Gold ion implantation into alumina using an “inverted ion source” configuration.

We describe an approach to ion implantation in which the plasma and its electronics are held at ground potential and the ion beam is injected into a space held at high negative potential, allowing considerable savings both economically and technologically. We used an “inverted ion implanter” of this kind to carry out implantation of gold into alumina, with Au ion energy 40 keV and dose (3–9) × 1016 cm−2. Resistivity was measured in situ as a function of dose and compared with predictions of a model based on percolation theory, in which electron transport in the composite is explained by conduction through a random resistor network formed by Au nanoparticles. Excellent agreement is found between the experimental results and the theory.

Photoluminescence of core-shell nanoparticles made from yttrium stabilized zirconia powder grain coated with alumina

A YSZ@Al2O3 nanocomposite was obtained by Al2O3 coating on the surface of yttrium stabilized zirconia via a polymeric precursor method. The resulting core–shell structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and PL spectra. The TEM micrographs clearly show a homogeneous Al2O3 shell around the ZrO2 core. The observed PL is related to surface–interface defects. Such novel technologies can, in principle, explore materials which are not available in the bulk single crystal form but their figure-of-merit is dramatically dependent on the surface–interface defect states.

Relationship between elastic and mechanical properties of dental ceramics and their index of brittleness

The purpose of the study was to verify the effects of a number of materials' parameters (crystalline content; Young's modulus, E; biaxial flexure strength, sigma(i); Vickers hardness, VH; fracture toughness, K-Ic; fracture surface energy, gamma(f); and index of brittleness, B) on the brittleness of dental ceramics. Five commercial dental ceramics with different contents of glass phase and crystalline particles were studied: a vitreous porcelain (VM7/V), a porcelain with 16 vol% leucite particles (d.Sign/D), a glass-ceramic with 29 vol% leucite particles (Empress/E1), a glass-ceramic with 58 vol% lithium-disilicate needle-like particles (Empress 2/E2), and a glass-infiltrated alumina composite with 65 vol% crystals (In-Ceram Alumina/IC). Discs were constructed according to manufacturers' instructions, ground and polished to final dimensions (12 mm x 1.1 mm). Elastic constants were determined by ultrasonic pulse-echo method. sigma(i) was determined by piston-on-3-balls method in inert condition. VH was determined using 19.6 N load and K-Ic was determined by indentation strength method. gamma(f) was calculated from the Griffith-Irwin relation and B by the ratio of HV to K-Ic. IC and E2 showed higher values of sigma(i), E, K-Ic and gamma(f), and lower values of B compared to leucite-based glass-ceramic and porcelains. Positive correlations were observed for sigma(i) versus K-Ic, and K-Ic versus E-1/2, however, E did not show relationship with HV and B. The increase of crystalline phase content is beneficial to decrease the brittleness of dental ceramics by means of both an increase in fracture surface energy and a lowering in index of brittleness. (C) 2012 Elsevier Ltd and Techna Group Sri. All rights reserved.

Internal fit of two all-ceramic systems and metal-ceramic crowns

Objectives: The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. Material and Methods: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey's multiple comparison test (p<0.05). Results: No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. Conclusions: The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

Carboxymethyl lignin as stabilizing agent in aqueous ceramic suspensions

Identifying new uses for residues of industries that process large quantities of biomass, as in bioethanol production, is essential for a sustainable development with reduced impact on the environment, which is the reason why many efforts have been devoted to find noble uses for lignins. in this study, a lignin obtained from sugarcane bagasse in a bioethanol producing plant was carboxymethylated to yield the water-soluble carboxymethyl lignin (CML), which was then used as stabilizing agent in aqueous alumina (Al2O3) suspensions. CML had a degree of substitution 0.46 +/- 0.01, in relation to the C9 unit of lignin, and behaved as a polyelectrolyte in a large pH range owing to the dissociation of carboxylic groups. The action of CML as stabilizing agent of alumina aqueous suspensions was investigated using viscometry, zeta potential, and photon correlation spectroscopy (PCS) measurements, mainly as a function of pH and time. Overall, the results showed that CML had a good performance as a deflocculating agent, because it led to dispersions with low viscosity and small change in particle size as a function of time. The positive effect from the addition of CML was confirmed in the morphological features of the material obtained from the alumina suspensions after elimination of water, as indicated by scanning electron microscopy. The stabilization of alumina suspensions afforded by CML opens the way for similar applications of modified lignins, whose electrical and structural properties may be tuned for specific uses in various industries, including the ceramic industry. (C) 2011 Elsevier B.V. All rights reserved.

Subcritical crack growth and in vitro lifetime prediction of resin composites with different filler distributions

Objectives. Verify the influence of different filler distributions on the subcritical crack growth (SCG) susceptibility, Weibull parameters (m and sigma(0)) and longevity estimated by the strength-probability-time (SPT) diagram of experimental resin composites. Methods. Four composites were prepared, each one containing 59 vol% of glass powder with different filler sizes (d(50) = 0.5; 0.9; 1.2 and 1.9 mu m) and distributions. Granulometric analyses of glass powders were done by a laser diffraction particle size analyzer (Sald-7001, Shimadzu, USA). SCG parameters (n and sigma(f0)) were determined by dynamic fatigue (10(-2) to 10(2) MPa/s) using a biaxial flexural device (12 x 1.2 mm; n = 10). Twenty extra specimens of each composite were tested at 10(0) MPa/s to determine m and sigma(0). Specimens were stored in water at 37 degrees C for 24 h. Fracture surfaces were analyzed under SEM. Results. In general, the composites with broader filler distribution (C0.5 and C1.9) presented better results in terms of SCG susceptibility and longevity. C0.5 and C1.9 presented higher n values (respectively, 31.2 +/- 6.2(a) and 34.7 +/- 7.4(a)). C1.2 (166.42 +/- 0.01(a)) showed the highest and C0.5 (158.40 +/- 0.02(d)) the lowest sigma(f0) value (in MPa). Weibull parameters did not vary significantly (m: 6.6 to 10.6 and sigma(0): 170.6 to 176.4 MPa). Predicted reductions in failure stress (P-f = 5%) for a lifetime of 10 years were approximately 45% for C0.5 and C1.9 and 65% for C0.9 and C1.2. Crack propagation occurred through the polymeric matrix around the fillers and all the fracture surfaces showed brittle fracture features. Significance. Composites with broader granulometric distribution showed higher resistance to SCG and, consequently, higher longevity in vitro. (C) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.