Development of alpha-SiAlON-SiC ceramic composites by liquid phase sintering

In this work, in situ alpha-SiAlON-SiC ceramic composites were obtained,by, liquid phase sintering, using SiC as reinforcement. Different beta-SiC powder contents (0-20 wt.%), were added to Si3N4-AlN-RE2O3. powder mixtures, and compacted by cold isostatic pressing. The samples were sintered at 1950 degrees C for 1 h, in N-2 atmosphere. Sintered: samples were characterized by relative density, weight loss, X-ray diffraction and scanning electron microscopy. Furthermore, mechanical properties such as hardness and fracture toughness were determined by Vickers indentation method. Lattice parameters of the alpha' phase did not considerably change with increase of SiC content. However, morphology, average grain size and aspect ratio of the alpha' phase were considerably changed with increase of the SiC content. These behavior influences significantly the mechanical properties of this hard ceramic composite. (C) 2006 Elsevier Ltd. All rights reserved.

Sol-gel Eu3+/Tm3+ doped transparent glass-ceramic waveguides

Eu3+ and Tm3+ doped lanthanum fluoride and lanthanum oxyfluoride are obtained from Eu3+, Tm3+ containing lanthanum fluoracetate solutions. The nature of the crystal phase obtained could be controlled by the temperature of heat treatment. Spectral characteristics of Eu3+ doped crystal phases were sufficiently different to allow utilization of Eu3+ as structural probes. Tm3+ emission at the technologically important spectral region of 1450nm could be observed for the fluoride and oxyfluoride crystal phases. The large bandwidth obtained (around 120nm) suggests potential applications in optical amplification. SiO2-LaF3-LaOF composite materials were also prepared. It is observed that for heat treatments above 800degreesC, fluorine loss, probably in the form of SiF4 hinder the observation of Tm3+ emission. Eu3+ spectroscopic characteristics clearly show the evolution of a fluoride like environment to an amorphous oxide one as the temperature of heat treatment increased. Thin films obtained by dip-coating on V-SiO2 substrates and treated at 300degreesC, 500degreesC and 800degreesC display guided modes in the visible and infrared regions. Optical characteristics (refractive index and films thickness) were obtained at 543.5, 632.8 and 1550nm. Attenuation as low as 1.8dB/cm was measured at 632.8nm. (C) 2004 Published by Elsevier B.V.

Ceramic Primer Heat-Treatment Effect on Resin Cement/Y-TZP Bond Strength

The purpose of this study was to evaluate the effect of different heat-treatment strategies for a ceramic primer on the shear bond strength of a 10-methacryloyloxydecyl-dihydrogen-phosphate (MDP)-based resin cement to a yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic. Specimens measuring 4.5 x 3.5 x 4.5 mm(3) were produced from Y-TZP presintered cubes and embedded in polymethyl methacrylate (PMMA). Following finishing, the specimens were cleaned using an ultrasound device and distilled water and randomly divided into 10 experimental groups (n=14) according to the heat treatment of the ceramic primer and aging condition. The strategies used for the experimental groups were: GC (control), without primer; G20, primer application at ambient temperature (20 degrees C); G45, primer application + heat treatment at 45 degrees C; G79, primer application + heat treatment at 79 degrees C; and G100, primer application + heat treatment at 100 degrees C. The specimens from the aging groups were submitted to thermal cycling (6000 cycles, 5 degrees C/55 degrees C, 30 seconds per bath) after 24 hours. A cylinder of MDP-based resin cement (2.4 mm in diameter) was constructed on the ceramic surface of the specimens of each experimental group and stored for 24 hours at 37 degrees C. The specimens were submitted to a shear bond strength test (n=14). Thermal gravimetric analysis was performed on the ceramic primer. The data obtained were statistically analyzed by two-way analysis of variance and the Tukey test (alpha=0.05). The experimental group G79 without aging (7.23 +/- 2.87 MPa) presented a significantly higher mean than the other experimental groups without aging (GC: 2.81 +/- 1.5 MPa; G20: 3.38 +/- 2.21 MPa; G100: 3.96 +/- 1.57 MPa), showing no difference from G45 only (G45: 6 +/- 3.63 MPa). All specimens of the aging groups debonded during thermocycling and were considered to present zero bond strength for the statistical analyses. In conclusion, heat treatment of the metal/zirconia primer improved bond strength under the initial condition but did not promote stable bonding under the aging condition.

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+ -codoped PbGeO3-PbF2-CdF2 glass and glass-ceramic under infrared excitation is investigated. In Ho3+/Yb3+-codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the S-5(2) (F-5(4)) -> I-5(8), F-5(5) -> I-5(8), and S-5(2)(F-5(4)) -> I-5(7) transitions, respectively, was observed. Blue (490 nm) emission assigned to the F-5(2,3) -> I-5(8) transition was also detected. In the Tb3+/Yb3+-codoped system, bright UV-visible emission around 384, 415, 438, 473-490, 545, 587, and 623 nm, identified as due to the D-5(3)((5)G(6)) -> F-7(J)(J = 6, 5, 4) and D-5(4) -> F-7(J)(J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed. (c) 2007 Elsevier B.V. All rights reserved.

Cr3+ and Cr4+ luminescence in glass ceramic silica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Broadband NIR Emission in Sol-Gel Er(3+)-Activated SiO(2)-Ta(2)O(5) Glass Ceramic Planar and Channel Waveguides for Optical Application

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

Ceramic materials in dentistry: historical evolution and current practice

Dental ceramics are presented within a simplifying framework allowing for facile understanding of their development, composition and indications. Engineering assessments of clinical function are dealt with and literature is reviewed on the clinical behaviour of all-ceramic systems. Practical aspects are presented regarding the choice and use of dental ceramics to maximize aesthetics and durability, emphasizing what we know and how we know it.

Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr0.25Ti0.75]O-3 ceramic

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

Ceramic raw materials from the State of Maranhao, Brazil. Part 1: chemical and mineralogical characterization and technological properties of clays from Sao Luis, Rosario, Pinheiro and Mirinzal

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Adhesive Quality of Self-adhesive and Conventional Adhesive Resin Cement to Y-TZP Ceramic Before and After Aging Conditions

Purpose: This study evaluated the adhesive quality of simplified self-adhesive and conventional resin cements to Y-TZP in dry and aged conditions. Methods: Y-TZP ceramic blocks (N=192) (5 x 5 x 2 mm) were embedded in acrylic resin and randomly divided into two groups, based on surface conditioning: 96% isopropanol or chairside tribochemical silica coating and silanization. Conditioned ceramics were divided into four groups to receive the resin cements (Panavia F 2.0, Variolink II, RelyX U100 and Maxcem). After 24 hours, half of the specimens (n=12) from each group were submitted to shear bond strength testing (0.5 nun/minute). The remaining specimens were tested after 90 days of water storage at 37 degrees C and thermocycling (12,000x, 5 degrees C-55 degrees C). Failure types were then assessed. The data were analyzed using three-way ANOVA and the Tukey's test (alpha=0.05). Results: Significant effects of ceramic conditioning, cement type and storage conditions were observed (p<0.0001). The groups cleaned using alcohol only showed low bond strength values in dry conditions and the bond strength was reduced dramatically after aging. Groups conditioned using silica coating and silanization showed higher bond strengths both in dry and aged conditions. A high number of specimens failed prematurely prior to testing when they were cleaned using 96% isopropanol. Conclusion: Overall, silica coating and silanization showed higher, stable bond strengths with and without aging. The durability of resin-ceramic adhesion varied, depending on the adhesive cement type.

Effect of temperature on glass-ceramic films prepared by impregnation of commercial float glass surfaces with oxide powders under pressure

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nanomechanical properties of glass-ceramic films obtained by pressure impregnation of oxide powders on commercial float glass surfaces

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)