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Internal Residual Stresses in Sintered and Commercial Low Expansion Li(2)O-Al(2)O(3)-SiO(2) Glass-Ceramics

SERBENA, Francisco C.; SOARES, Viviane Oliveira; PEITL, Oscar; PINTO, Haroldo; MUCCILLO, Reginaldo; ZANOTTO, Edgar D.
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
614.9379%
We performed Synchrotron X-ray diffraction (XRD) analyses of internal residual stresses in monolithic samples of a newly developed Li(2)O-Al(2)O(3)-SiO(2) (LAS) glass-ceramic produced by sintering and in a commercial LAS glass-ceramic, CERAN (R), produced by the traditional crystal nucleation and growth treatments. The elastic constants were measured by instrumented indentation and a pulse-echo technique. The thermal expansion coefficient of virgilite was determined by high temperature XRD and dilatometry. The c-axis contracts with the increasing temperature whereas the a-axis does not vary significantly. Microcracking of the microstructure affects the thermal expansion coefficients measured by dilatometry and thermal expansion hysteresis is observed for the sintered glass-ceramic as well as for CERAN (R). The measured internal stress is quite low for both glass-ceramics and can be explained by theoretical modeling if the high volume fraction of the crystalline phase (virgilite) is considered. Using a modified Green model, the calculated critical (glass) island diameter for spontaneous cracking agreed with experimental observations. The experimental data collected also allowed the calculation of the critical crystal grain diameters for grain-boundary microcracking due to the anisotropy of thermal expansion of virgilite and for microcracking in the residual glass phase surrounding the virgilite particles. All these parameters are important for the successful microstructural design of sintered glass-ceramics.; CNPq/Brazil[151917/2006-0]; FAPESP/Brazil[07/08179-9]; FAPESP/Brazil[05/53241-9]; CNPq; Brazilian Synchrotron Light Laboratory (LNLS)/MCT[XRD1-5824]; Brazilian Synchrotron Light Laboratory (LNLS)/MCT[XRD1-6712]

Slow crack growth and reliability of dental ceramics

GONZAGA, Carla Castiglia; CESAR, Paulo Francisco; MIRANDA JR., Walter Gomes; YOSHIMURA, Humberto Naoyuki
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
614.25543%
Objective. To determine the slow crack growth (SCG) and Weibull parameters of five dental ceramics: a vitreous porcelain (V), a leucite-based porcelain (D), a leucite-based glass-ceramic (E1), a lithium disilicate glass-ceramic (E2) and a glass-infiltrated alumina composite (IC). Methods. Eighty disks (empty set 12mm x 1.1mm thick) of each material were constructed according to manufacturers` recommendations and polished. The stress corrosion susceptibility coefficient (n) was obtained by dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates immersed in artificial saliva at 37 degrees C. Weibull parameters were calculated for the 30 specimens tested at 1MPa/s in artificial saliva at 37 degrees C. The 80 specimens were distributed as follows: 10 for each stress rate (10(-2), 10(-1), 10(1), 10(2) MPa/s), 10 for inert strength (10(2) MPa/s, silicon oil) and 30 for 10(0) MPa/s. Fractographic analysis was also performed to investigate the fracture origin. Results. E2 showed the lowest slow crack growth susceptibility coefficient (17.2), followed by D (20.4) and V (26.3). E1 and IC presented the highest n values (30.1 and 31.1, respectively). Porcelain V presented the lowest Weibull modulus (5.2). All other materials showed similar Weibull modulus values...

Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

Silva, Maurício A.P.; Messaddeq, Younes; Briois, Valerie; Poulain, Marcel; Ribeiro, Sidney J. L.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: 200-206
ENG
Relevância na Pesquisa
701.0886%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); A partir de resultados de experimentos de fusão e choque térmico, o domínio vítreo foi identificado no sistema PbF2-CdF2-B2O 3. Vidros puros e dopados com Er3+ foram preparados e vitrocerâmicas foram obtidas a partir de tratamentos térmicos adequados. A fase cristalina foi identificada como beta-PbF2. Estudos estruturais foram efetuados por difração e absorção de raios X e o papel desempenhado pelos átomos de Pb2+ e Cd2+ na estrutura vítrea foi estabelecido a partir destas técnicas. Os resultados sugerem que, com a cristalização, os íons Er3+ são segregados na fase cristalina.; The vitreous domain was established in the PbF2-CdF2-B2O 3 system from melting and quenching experiments. Er3+ containing glasses were prepared and glass ceramics were obtained by selected heat-treatments. Lead fluoride was identified (beta-PbF2) as the crystalline phase. Structural studies were performed in some glassy and partially crystallized samples by means of X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure (EXAFS) measurements. The role of Cd2+ and Pb2+ atoms on the glass network formation and also on the crystallization behavior was put forward by these techniques. After crystallization Er3+ atoms segregated in the crystal phase.

Lead-cadmium oxyfluoride glasses and glass-ceramics

Silva, MAP; Briois, V; Poulain, M.; Messaddeq, Y.; Ribeiro, SJL
Fonte: Natl Inst Optoelectronics Publicador: Natl Inst Optoelectronics
Tipo: Artigo de Revista Científica Formato: 799-808
ENG
Relevância na Pesquisa
709.1511%
Glasses and glass-ceramics have been obtained in oxyfluoride systems involving lead and cadmium fluorides and one of the well-known glass former oxides SiO2, B2O3 and TeO2. Vitreous domains were established and a wide range of compositions including high heavy metal contents lead to stable glasses. Amorphous structures have been studied by short-range order spectroscopy techniques (Raman scattering and x-ray absorption) and molecular basic structures have been identified. Besides the usual oxides, the role of glass former could also be proposed for cadmium ions. Special attention has been paid for crystallization process. Cubic lead fluoride, cubic lead tellurite, tetragonal tellurium oxide and a solid solution of the type Pb1-xCdxF2 are obtained as crystallization products depending on the composition and temperature of heat treatments. Pb1-xCdxF2 solid solutions are well known superionic materials and obtaining this solid solution as a crystal phase could be very interesting for applications concerning ionic electrical conduction properties. The addition of rare earth ions led to the control of the crystallization process. In the presence of the nucleating ion only the cubic form beta-PbF2 was identified. Rare earth ions are present in the crystal phase and crystal-like spectroscopic properties were observed suggesting interesting applications for these perfectly transparent glass ceramics in photonics.

Innovating transparent glass ceramics based on Ga2S3-GeS2-CsCl

Ledemi, Y.; Bureau, B.; Calvez, L.; Roze, M.; Guillevic, E.; Audebrand, N.; Poulain, M.; Messaddeq, Y.; Zhang, X. H.
Fonte: Natl Inst Optoelectronics Publicador: Natl Inst Optoelectronics
Tipo: Artigo de Revista Científica Formato: 899-903
ENG
Relevância na Pesquisa
712.0899%
In this paper, we describe the preparation of glass ceramics in the Ga2S3 - GeS2 - CsCl system Visible and infrared transmitting glass ceramics were reproducibly obtained by appropriated heat treatment of the base glass Crystals with controllable size of about 40 nm were homogeneously generated in the glassy matrix X-ray diffraction characterizations have shown that gallium acts as nucleating agent in this material, giving rise to alpha-Ga2S3 crystals Improved thermo-mechanical properties such as dilatation coefficient and resistance to fracture propagation have been observed in the prepared glass ceramics

Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Ziemath, Ervino C.; Aegerter, Michel A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 216-225
ENG
Relevância na Pesquisa
705.99375%
Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.

Transparent Er3+-activated lead fluorogermanate glass ceramics

Rolli, Raffaella; Bueno, Luciano A.; Ribeiro, Sidney J.L.; Messaddeq, Younes; Bettinelli, Marco; Speghini, Adolfo; Ferrari, Maurizio; Armellini, Cristina; Montagna, Maurizio; Righini, Giancarlo C.; Pelli, Stefano
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 133-134
ENG
Relevância na Pesquisa
711.9991%
Transparent glass ceramics containing β-PbF2:Er 3+ nanocrystals were obtained through appropriate thermal treatments of a glass of molar composition 60PbGeO3-10PbF2-30CdF 2 doped with 0.5 mol% Er3+. Their optical properties, as well as upconversion processes among erbium ions in the glass and glass ceramic matrix were studied. From absorption spectra, Judd-Ofelt parameters and radiative transition rates for several excited levels were calculated. Emission spectra in the visible and NIR regions were collected, and stimulated emission cross sections were obtained by McCumber theory for the 4F 13/2→4I15/2 transition at 1.5 μm. Red and green upconversion emissions were measured in glass and glass ceramics upon excitation at 980 nm; lifetimes were measured in order to assess the upconversion mechanisms.

Infrared-to-visible frequency upconversion in transparent glass ceramics containing trivalent-rare-earth-doped nanocrystals

Gouveia-Neto, Artur S.; Da Costa, Ernande B.; Bueno, Luciano A.; Ribeiro, Sidney J.L.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 132-139
ENG
Relevância na Pesquisa
713.2708%
In this work we report on visible upconversion emission in Er 3+-, and Ho3+-doped PbGeO3-PbF 2-CdF2-based transparent glass ceramics under 980 nm infrared excitation. In erbium-doped vitroceramic samples, blue(410 ran), green(530, and 550 nm) and red(660 nm) emission signals were generated, which were identified as due to the 2H9/2, 2H 11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, respectively. Intense red(650 nm) upconversion emission corresponding to the 5F5 - 5I8 transition and very small blue(490 nm) and green(540 nm) signals assigned to the 5F 2,3 - 5I8 and 4S2, 5F4 - 5I8 transitions, respectively, were observed in the holmium-doped samples. The 540 nm is the dominant upconversion signal in Ho3+-doped vitroceramics under 850 nm excitation. The dependence of the upconversion processes upon pump power and doping concentration are also investigated, and the main routes for the upconversion excitation processes are also identified. The comparison of the upconversion process in transparent glass ceramics and the precursor glass was also examined and the results revealed that the former present higher upconversion efficiencies.

Osteoconductivity of modified fluorcanasite glass-ceramics for bone tissue augmentation and repair

Bandyopadhyay-Ghosh, S.; Faria, P. E. P.; Johnson, A.; Felipucci, D. N. B.; Reaney, I. M.; Salata, L. A.; Brook, I. M.; Hatton, P. V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 760-768
ENG
Relevância na Pesquisa
716.4913%
Modified fluorcanasite glasses were fabricated by either altering the molar ratios of Na 2O and CaO or by adding P 2O 5 to the parent stoichiometric glass compositions. Glasses were converted to glass-ceramics by a controlled two-stage heat treatment process. Rods (2 mm x 4 mm) were produced using the conventional lost-wax casting technique. Osteoconductive 45S5 bioglass was used as a reference material. Biocompatibility and osteoconductivity were investigated by implantation into healing defects (2 mm) in the midshaft of rabbit femora. Tissue response was investigated using conventional histology and scanning electron microscopy. Histological and histomorphometric evaluation of specimens after 12 weeks implantation showed significantly more bone contact with the surface of 45S5 bioglass implants when compared with other test materials. When the bone contact for each material was compared between experimental time points, the Glass-Ceramic 2 (CaO rich) group showed significant difference (p = 0.027) at 4 weeks, but no direct contact at 12 weeks. Histology and backscattered electron photomicrographs showed that modified fluorcanasite glass-ceramic implants had greater osteoconductivity than the parent stoichiometric composition. Of the new materials...

Infrared to visible up-conversion emission in Er3+/Yb 3+ codoped fluoro-phosphate glass-ceramics

Ledemi, Yannick; Amraoui, Mohammed El; Ferrari, Jefferson L.; Fortin, Pier-Luc; Ribeiro, Sidney J.L.; Messaddeq, Younès
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 825-832
ENG
Relevância na Pesquisa
714.1949%
Erbium Er3+ and ytterbium Yb3+ codoped fluoro-phosphate glasses belonging to the system NaPO3-YF 3-BaF2-CaF2 have been prepared by the classical melt-quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV-visible and near-infrared spectroscopy. Transparent and homogeneous glass-ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X-ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite-type cubic crystals based during the devitrification process. Finally, infrared to visible up-conversion emission upon excitation at 975 nm has been studied on the Er3+ and Yb 3+ codoped glass-ceramics as a function of thermal treatment time. A large enhancement of intensity of the up-conversion emissions-about 150 times- has been observed in the glass-ceramics if compared to the parent glass one, suggesting an incorporation of the rare-earth ions (REI) into the crystalline phase. © 2012 The American Ceramic Society.

PREPARATION OF GLASSES AND GLASS CERAMICS OF HEAVY METAL OXIDES CONTAINING SILVER: OPTICAL, STRUCTURAL AND ELECTROCHEMICAL PROPERTIES

Bregadiolli, Bruna A.; Souza, Ernesto R.; Sigoli, Fernando A.; Caiut, Jose M. A.; Alencar, Monica A. S.; Benedetti, Assis V.; Nalin, Marcelo
Fonte: Soc Brasileira Quimica; Sao Paulo Publicador: Soc Brasileira Quimica; Sao Paulo
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
610.33195%
PREPARATION OF GLASSES AND GLASS CERAMICS OF HEAVY METAL OXIDES CONTAINING SILVER: OPTICAL, STRUCTURAL AND ELECTROCHEMICAL PROPERTIES. Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonimce band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Morphological, structural, optical and dielectric properties of 91SiO 2:4Li2O:4Nb2O5:1Dy2O 3 (% mole) glass prepared by sol-gel

Valente, M.A.; Peres, M.; Nico, C.; Monteiro, T.; Graça, M.P.F.; Sombra, A.S.B.; Silva, C.C.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
606.9179%
We report on the structural, morphological and optical characterization of glass and glass-ceramic samples, with nominal composition of 91SiO 2:4Li2O:4Nb2O5:1Dy2O 3 (% mole). The samples were heated treated in air in the temperature range between 500 °C and 800 °C. The glass-ceramics samples start to crystallize at temperatures above 600 °C and besides the SiO2 and LiNbO3 crystalline phases, sub micron DyNbO4 precipitates were identified by X-ray diffraction and scanning electron microscopy for temperatures above 750 °C. Using Raman spectroscopy was possible to identify the vibration modes assigned to the crystalline phases detected by the XRD analysis. Also, the performed Photoluminescence Spectroscopy analysis suggest that the optical activation of Dy3+ ions in the glass and glass-ceramics hosts was found to be dependent of the heat treatment temperature. Intraconfigurational transitions between the 4F 9/2 and 6HJ(=15/2, 13/2) multiplets of Dy 3+ ions were only observed for samples without the presence of the DyNbO4 crystalline phase. Moreover, for samples heat treated between 500 °C and 700 °C the intensity ratio of the 4F9/26H13/2 and 4F9/26H 15/2 transitions of the lanthanide ion changes, suggesting different ion environments which are dependent on the thermal annealing temperature. The dielectric measurements revealed that ′ value depends mainly in the number of network modifier ions and the relaxation phenomenon observed at frequencies above 10 kHz...

Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

Silva,Maurício A.P.; Messaddeq,Younes; Briois,Valerie; Poulain,Marcel; Ribeiro,Sidney J. L.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2002 EN
Relevância na Pesquisa
701.0886%
The vitreous domain was established in the PbF2-CdF2-B2O 3 system from melting and quenching experiments. Er3+ containing glasses were prepared and glass ceramics were obtained by selected heat-treatments. Lead fluoride was identified (beta-PbF2) as the crystalline phase. Structural studies were performed in some glassy and partially crystallized samples by means of X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure (EXAFS) measurements. The role of Cd2+ and Pb2+ atoms on the glass network formation and also on the crystallization behavior was put forward by these techniques. After crystallization Er3+ atoms segregated in the crystal phase.

Bioactivity of leucite containing glass - ceramics using natural raw materials

Stábile,Franco Matías; Volzone,Cristina
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
Relevância na Pesquisa
703.2511%
Glass compositions were carefully prepared, using natural quartz and potassium feldspar as a part of the starting raw materials. The solids were prepared so as to have theoretical stoichiometric leucite and 45S5 Bioglass in different L/Bg weight ratios between 0.43 - 1.00. Novel bioactive glass - ceramics, containing leucite, sodium calcium silicate and silicorhenanite, confirmed by XRD and FTIR, were obtained. Bioactivity tests were carried out on powdered and sintered disks forms. The immersion time was up to 25 days. Apatite formation on powders was studied by FTIR, and XRD and SEM were used to study bioactivity on disks. The materials developed an apatite layer on their surfaces within 6 days of immersion in simulated body fluid. The glass - ceramic with L/Bg ratio = 0.43 presented an apatite layer on all its surface, not so for the samples with 0.66 and 1.00 ratios, on which such layer was peeled off in most part of their surfaces.

Properties of glass-ceramics obtained from crystallization of the SiO2-Al2O3-MgO-Li2O system with addition of ZrO2

Souza Filho, Manoel Pereira de; Campos, Elson de; Moreira, Janaina Pardi; Lopes, Cristina Moniz Araujo; Melo, Francisco Cristóvão Lourenço de
Fonte: Trans Tech Publications Ltd Publicador: Trans Tech Publications Ltd
Tipo: Conferência ou Objeto de Conferência Formato: 369-374
ENG
Relevância na Pesquisa
716.0584%
This paper presents the study results with glass-ceramics obtained from base glass (MgO-Al2O3- SiO2-Li2O system) with addition of ZrO2 as nucleating agent. The glass was melted at 1650 degrees C for 3 h and at a heating rate of 10 degrees C/min. The molten glass was poured into a graphite mold to obtain monolithic samples and also in water in order to obtain particulate material. Such material was grinded and then pressed by both uniaxial and isostatic pressing methods before being sintered. Both the monolithic and pressed samples were performed under two different conditions of heat treatment so that their nucleation and crystallization occurred. In the first one, the samples were heated to 1100 degrees C with a heating rate of 10 degrees C/min. In the second one, there was an initial heating rate of 10 degrees C/min up to 780 degrees C, which was kept for 5 minutes. After that, the samples were heated to 1100 degrees C at a heating rate of 1 degrees C/min. Microhardness analyses showed that base glass presented values around 7.0 GPa. The glass-ceramics obtained from the powder sintering showed microhardness values lower than those obtained from monolithic samples. The highest hardness values were observed in the samples which were treated with two heating rates...

Mechanical properties and porosity of dental glass-ceramics hot-pressed at different temperatures

GONZAGA, Carla Castiglia; CESAR, Paulo Francisco; OKADA, Cristina Yuri; FREDERICCI, Catia; BENEDUCE NETO, Flávio; YOSHIMURA, Humberto Naoyuki
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
697.8963%
The objective of this work was to evaluate biaxial-flexural-strength (σf), Vickers hardness (HV), fracture toughness (K Ic), Young's modulus (E), Poisson's ratio (ν) and porosity (P) of two commercial glass-ceramics, Empress (E1) and Empress 2 (E2), as a function of the hot-pressing temperature. Ten disks were hot-pressed at 1065, 1070, 1075 and 1080 °C for E1; and at 910, 915, 920 and 925 °C for E2. The porosity was measured by an image analyzer software and s f was determined using the piston-on-three-balls method. K Ic and HV were determined by an indentation method. Elastic constants were determined by the pulse-echo method. For E1 samples treated at different temperatures, there were no statistical differences among the values of all evaluated properties. For E2 samples treated at different temperatures, there were no statistical differences among the values of σf, E, and ν, however HV and K Ic were significantly higher for 910 and 915 °C, respectively. Regarding P, the mean value obtained for E2 for 925 °C was significantly higher compared to other temperatures.; FAPESP; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); CNPq

Diopside-fluorapatite-wollastonite based bioactive glasses and glass-ceramics; Vidros e vitrocerâmicos bioativos à base de diópside-fluorapatite-wollastonite

Kansal, Ishu
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
706.9179%
Bioactive glasses and glass–ceramics are a class of biomaterials which elicit special response on their surface when in contact with biological fluids, leading to strong bonding to living tissue. This particular trait along with good sintering ability and high mechanical strength make them ideal materials for scaffold fabrication. The work presented in this thesis is directed towards understanding the composition-structure-property relationships in potentially bioactive glasses designed in CaOMgOP2O5SiO2F system, in some cases with added Na2O. The main emphasis has been on unearthing the influence of glass composition on molecular structure, sintering ability and bioactivity of phosphosilicate glasses. The parent glass compositions have been designed in the primary crystallization field of the pseudo-ternary system of diopside (CaO•MgO•2SiO2) – fluorapatite (9CaO•3P2O5•CaF2) – wollastonite (CaO•SiO2), followed by studying the impact of compositional variations on the structure-property relationships and sintering ability of these glasses. All the glasses investigated in this work have been synthesized via melt-quenching route and have been characterized for their molecular structure, sintering ability, chemical degradation and bioactivity using wide array of experimental tools and techniques. It has been shown that in all investigated glass compositions the silicate network was mainly dominated by Q2 units while phosphate in all the glasses was found to be coordinated in orthophosphate environment. The glass compositions designed in alkali-free region of diopside – fluorapatite system demonstrated excellent sintering ability and good bioactivity in order to qualify them as potential materials for scaffold fabrication while alkali-rich bioactive glasses not only hinder the densification during sintering but also induce cytotoxicity in vitro...

Mechanical properties and porosity of dental glass-ceramics hot-pressed at different temperatures

Gonzaga,Carla Castiglia; Cesar,Paulo Francisco; Okada,Cristina Yuri; Fredericci,Catia; Beneduce Neto,Flávio; Yoshimura,Humberto Naoyuki
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2008 EN
Relevância na Pesquisa
697.8963%
The objective of this work was to evaluate biaxial-flexural-strength (σf), Vickers hardness (HV), fracture toughness (K Ic), Young's modulus (E), Poisson's ratio (ν) and porosity (P) of two commercial glass-ceramics, Empress (E1) and Empress 2 (E2), as a function of the hot-pressing temperature. Ten disks were hot-pressed at 1065, 1070, 1075 and 1080 °C for E1; and at 910, 915, 920 and 925 °C for E2. The porosity was measured by an image analyzer software and s f was determined using the piston-on-three-balls method. K Ic and HV were determined by an indentation method. Elastic constants were determined by the pulse-echo method. For E1 samples treated at different temperatures, there were no statistical differences among the values of all evaluated properties. For E2 samples treated at different temperatures, there were no statistical differences among the values of σf, E, and ν, however HV and K Ic were significantly higher for 910 and 915 °C, respectively. Regarding P, the mean value obtained for E2 for 925 °C was significantly higher compared to other temperatures.

Bioactive glasses and glass-ceramics; Vidrios y Vitrocerámicos Bioactivos

Aza Moya, Antonio H. de; Aza, Piedad N. de; Peña, P.; Aza Pendas, Salvador de
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 1550716 bytes; application/pdf
ENG
Relevância na Pesquisa
706.9179%
[EN] Since the late 1960´s, a great interest in the use of bioceramic materials for biomedical applications has been developed. In a previous paper, the authors reviewed crystalline bioceramic materials "sensus stricto", it is to say, those ceramic materials, constituted for non-metallic inorganic compounds, crystallines and consolidates by thermal treatment of powders at high temperature. In the present review, the authors deal with those called bioactive glasses and glassceramics. Although all of them are also obtained by thermal treatment at high temperature, the first are amorphous and the second are obtained by devitrification of a glass, although the vitreous phase normally prevails on the crystalline phases. After an introduction to the concept of bioactive materials, a short historical review of the bioactive glasses development is made. Its preparation, reactivity in physiological media, mechanism of bonding to living tissues and mechanical strength of the bone-implant interface is also reported. Next, the concept of glass-ceramic and the way of its preparation are exposed. The composition, physicochemical properties and biological behaviour of the principal types of bioactive glasses and glass-ceramic materials: Bioglass®...

Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Ziemath, Ervino C.; Aegerter, Michel A.
Fonte: Materials Research Society Publicador: Materials Research Society
Tipo: Artigo de Revista Científica Formato: 216-225
ENG
Relevância na Pesquisa
705.99375%
Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.