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Made available in DSpace on 2021-06-25T11:09:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-04-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Fracture resistance and translucency are among the most important properties for the use of lithium silicate glass ceramics as dental prostheses, both being greatly influenced by the temperature of the crystallization heat treatment. In this work, the effect of short time heat treatments at different temperatures on the lithium metasilicate (Li2SiO3) → lithium disilicate (Li2Si2O5) phase transformation and resulting properties was investigated. Commercial Li2SiO3 samples were heat treated under vacuum for 7 min, at 820 °C, 830 °C and 840 °C, to induce the phase transformation into Li2Si2O5. The heat treated samples were characterized by their phase composition (XRD), microstructure, mechanical properties (Vickers Hardness, fracture toughness, bending strength and elastic parameters) and translucency. The results indicate that 814 °C is the onset temperature for the crystallization of lithium disilicate (Li2Si2O5). A progressive conversion of Li2SiO3 into Li2Si2O5, besides the reduction of the amorphous phase content is observed with increasing temperature. Furthermore, the increasing amount of the Li2Si2O5 phase and the concomitant reduction of the amount of amorphous phase resulted in a slight reduction of the hardness from 6.13 ± 0.22 to 5.76 ± 0.17 GPa, a slight increase in fracture toughness from 1.30 ± 0.02 to 1.60 ± 0.03 MPa m1/2 and in a significant improvement of the bending strength from 166 ± 22 to 303 ± 59 MPa. The improvement in mechanical properties is associated with the reduction of amorphous phase and increasing amount of the Li2Si2O5 phase, which is composed of elongated grains with high aspect ratio. However, translucency diminished 40% comparing samples treated at 820 °C or 840 °C, which is attributed to the reduction of the amount of intergranular amorphous phase. UNESP/FEG Universidade Estadual Paulista - Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas UERJ/FAT Universidade do Estado do Rio de Janeiro Faculdade de Tecnologia, Rod. Presidente Dutra, km 298 UFF/ISNF Universidade Federal Fluminense, Av. Dr. Silvio Henrique Braune, 22, Centro UFSJ Universidade Federal de São João DeĺRei, Pça Frei Orlando 170, S. J.del Rei-MG UNESP/FEG Universidade Estadual Paulista - Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas CNPq: 308684/2013-3 CNPq: 311119/2017-4 FAPERJ: E-26-201.476/2014 FAPERJ: E26-202.997/2017

In this work an alumina-yttrium aluminum garnet (Al2O3-YAG) cutting tool was developed and characterized aiming application in dry machining of nodular (spheroidal) cast iron. Ceramic powders containing 85 wt.% Al2O3 and 15 wt.% Y3Al5O12(YAG) were homogenized, compacted, and sintered at 1600 ºC for 2h at a heating rate of 5 °C/min. The sintered ceramic presented relative density of 98.3 ±0.2%. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) revealed α-Al2O3 and YAG as crystal phases, both with equiaxed grains with average sizes of 1-4 𝜇m (Al2O3 phase) and 0.7-1 𝜇m (YAG phase). In addition, this ceramic composite presented Vickers hardness and fracture toughness of 15.2 ±0.2 GPa and 4.6 ±0.3 MPa.m1/2, respectively. The dry machining performance of the Al2O3-YAG cutting tool was compared with that of a commercial cemented carbide cutting tool using cutting speed (VC) of 200 and 500 m/min, feed rate (f) of 0.25 and 0.10 mm/rev, and axial depth of cut (ap) of 0.60 mm. The results showed that the best setting for the cemented carbide cutting tool was obtained at VC=200 m/min and f=0.25 mm/rev, which produced the best machinability with average surface roughness (Ra) of 3.516 μm, cutting length (LC) of 6000 m, and maximum flank wear (VBmax) of 0.58 mm. For the Al2O3-YAG cutting tool, the best setting was achieved at VC=500 m/min and f=0.10 mm/rev, which produced Ra=0.848 μm, LC=12,293 m, and VBmax=0.54 mm.

Made available in DSpace on 2021-07-14T10:26:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-13. Added 1 bitstream(s) on 2021-07-14T11:30:01Z : No. of bitstreams: 1 S0366-69132020000100030.pdf: 2969385 bytes, checksum: 6f7cb1d7980557e113a2dfcaefef07cc (MD5) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) O objetivo deste estudo foi caracterizar e avaliar as propriedades físicas e mecânicas de uma zircônia experimental para aplicação odontológica e comparar os resultados da resistência à flexão biaxial com a simulação de elementos finitos (MEF). Amostras de zircônia tetragonal estabilizada com ítria (Y-TZP) foram sinterizadas a 1475 °C/2 h e caracterizadas por difração de raios X, microscopia eletrônica de varredura, densidade relativa, resistência à flexão usando teste de pistão em três bolas (P-3B) e módulo de Young. A partir dos resultados de resistência à flexão, foram realizadas simulações numéricas utilizando o software Abaqus. O modelo completo utilizou 70216 elementos. Os resultados apontaram para densificação total em amostras sinterizadas, ZrO2 tetragonal e cúbica como fases cristalinas, tamanho de grão de 0,6±0,2 μm, módulo de Young de 195±4 GPa, resistência à flexão de 1191±9 MPa e módulo de Weibull m=16,3. A simulação numérica indicou uma resistência à flexão próxima de 1100 MPa, com diferença menor que 7% em relação aos resultados experimentais. Os resultados foram comparados associando as propriedades físicas e mecânicas de Y-TZP com seus fenômenos intrínsecos, como a transformação tgm e o domínio ferroelástico. The objectives of this study were to characterize and evaluate the physical and mechanical properties of an experimental zirconia for dental application and compare the biaxial flexural strength results with the finite element simulation (FEM). Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic samples were sintered at 1475 °C/2 h and characterized by X-ray diffraction, scanning electron microscopy, relative density, flexural strength using piston-on-three balls (P-3B) test and Young’s modulus. From the flexural strength results, numerical simulations were performed using Abaqus software. The complete model used 70216 elements, considering the components of the test. The results indicated full densification of sintered samples, ZrO2-tetragonal and ZrO2-cubic as crystalline phases, and average grain size of 0.6±0.2 μm. Mechanical characterization of sintered samples indicated Young’s modulus of 195±4 GPa, flexural strength of 1191±9 MPa and Weibull modulus m=16.3. FEM simulation indicated a flexural strength close to 1100 MPa, with a difference lower than 7% in relation to the experimental results. The results were compared associating the physical and mechanical properties of Y-TZP with its intrinsic phenomena such as tgm transformation and ferroelastic domain. Universidade Federal Fluminense, Escola de Engenharia Industrial Metalúrgica de Volta Redonda Universidade do Estado do Rio de Janeiro, Faculdade de Tecnologia de Resende Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá FAPERJ: E26-201.476/2014; E26-202.997/2017; E26-211.760/2015 CNPq: 311119/2017-4; 305194/2015-1

Made available in DSpace on 2019-10-06T15:35:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) In this work, the influence of milling strategy and cutter wear on the flexural strength of sintered Y-TZP ceramics machined in a CAD-CAM system, was investigated. Pre-sintered Y-TZP blocks were machined with tungsten carbide (WC) milling cutters and divided into three groups: a) samples machined with New Cutting Tools (NCT); b) samples machined with End-of-life cutting tools (ELCT); and c) samples machined and subsequently polished. The samples were machined parallel and perpendicularly to the diameter of pre-sintered Y-TZP blocks aiming to evaluate the effect of the machining orientation on roughness. After cutting, the specimens were sintered at 1530 °C for 2 h and characterized. After sintering, dense Y-TZP samples presenting grain size average of 0.81 ± 0.23 μm, hardness of 1205 ± 12 HV, K C of 7.7 ± 0.4 MPam 1/2 and flexural strength of 1207 ± 199 MPa were obtained. Furthermore, the control roughness (polished surfaces) presented R a = 0.058 ± 0.011 μm. The surface roughness of the samples was influenced by the machining methodology using NCT mills, with R a = 0.386 ± 0.149 μm and R a = 0.292 ± 0.105 μm for samples machined parallel and perpendicularly to the pre-sintered Y-TZP blocks, respectively. The use of ELCT led to a roughness increasing (R a = 0.582 ± 0.183 μm for samples milled perpendicularly, and R a = 0.919 ± 0.164 μm for samples cut parallel to the pre-sintered blocks. The flexural strength of the sintered Y-TZP decreases with use of ELCT as consequence of surface roughness increasing, resulting from wear of WC mills, which presented chippings with sizes ranging from 30 to 340 μm in the cutting edge. Universidade do Estado do Rio de Janeiro - Faculdade de Tecnologia de Resende UERJ-FAT, Rodovia Presidente Dutra, km 298 Universidade Estadual Paulista - Faculdade de Engenharia de Guaratinguetá UNESP/FEG, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas Centro Universitário de Volta Redonda - UniFOA, Av. Paulo Erlei Alves Abrantes, 1325 - Três Poços Instituto Militar de Engenharia Materials Science Department, Pça Gen. Tibúrcio, 80, Praia Vermelha Universidade Estadual Paulista - Faculdade de Engenharia de Guaratinguetá UNESP/FEG, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas CNPq: n° 311119/2017-4 FAPERJ: n° E26-201.476/2014

Made available in DSpace on 2020-12-12T01:36:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01. Added 1 bitstream(s) on 2021-07-15T15:07:18Z : No. of bitstreams: 1 S1516-14392020000200213.pdf: 1560168 bytes, checksum: 64925fad320f6d376a40a8fbd4619748 (MD5) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) In this work, CoCrMo-base alloys specimens were produced by additive manufacturing using selective laser melting (SLM) as well as CAD/CAM milling. For SLM specimens, spherical particles were laser processed at 1320°C under argon atmosphere and submitted to thermal stress relieving at 750°C-45min. Specimens from CoCrMo blocks were milled by CAD/CAM machining and sintered at 1300°C-60min. The materials from both techniques were characterized by relative density, dilatometry, SEM/BSE, OM and XRD analysis. The mechanical properties were determined by Vickers hardness and tensile tests. The specimens from both techniques exhibited single phase γCo (FCC) and CTE of 14 x10-6 °C-1. Relative density of 95.4%/ 85.6%, hardness values near 400HV/ 350HV and UTS of 905MPa/ 780MPa were measured for SLM and CAD/CAM specimens, respectively. Higher relative density is the main factor for increased mechanical properties of SLM specimens. On the other hand, both SLM and CAD/CAM specimens present properties in accordance with ISO-22674 recommendations, compatible with dental applications such as bridges containing four or more elements as well as fully dense pontics. Universidade do Estado do Rio de Janeiro - UERJ Faculdade de Tecnologia - FAT, Rod. Presidente Dutra, km 298 Universidade Federal Fluminense - UFF Escola de Engenharia Industrial Metalúrgica de Volta Redonda - EEIMVR, Av. Trabalhadores, 420 Centro Universitário de Volta Redonda- UNIFOA, Av. Paulo Erlei Alves Abrantes, 1325 Universidade Estadual Paulista - UNESP Faculdade de Engenharia de Guaratinguetá -FEG, Av. Ariberto Pereira da Cunha, 333 eUniversidade de São Paulo - USP Escola de Engenharia de Lorena - EEL, área II, Polo Urbo Industrial Gleba AI6, s/n Universidade Estadual Paulista - UNESP Faculdade de Engenharia de Guaratinguetá -FEG, Av. Ariberto Pereira da Cunha, 333 FAPERJ: E-26/103.216/2011 FAPERJ: E26-202.997/2017

Made available in DSpace on 2019-10-06T16:48:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-02 Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) This study evaluated the effect of the surface roughness parameters on the flexural strength of Yttria-partially stabilized zirconia, Y-TZP ceramics: ZrO2 (3 mol%) or ZrO2 (5 mol%), as function of different surface finishing protocols: polishing or alumina (Al2O3) blasting. Zirconia discs were manufactured by CAD/CAM prototyping and sintered at different temperatures. The specimens were characterized by X-ray diffraction, scanning electron microscopy, biaxial flexural strength test and 3D profilometry. In all specimens tetragonal Y2O3-ZrO2 was observed to be the main crystalline phase. The 3D profilometry indicated that alumina blasting of ZrO2 (3 mol%) increased the roughness Ra around 16–26 times as opposed to the polished surfaces, and approximately 38 times for ZrO2 (5 mol%) specimens when compared to the polished samples. The results of flexural strength indicate that groups of ZrO2 (3 mol% Y2O3) ceramics present a reduction of 21–23% from polished to alumina blasted specimens. In the group of ZrO2 (5 mol% Y2O3) ceramics, a flexural strength reduction of 37.5% was observed. A correlation between flexural strength, failure size and different roughness parameters: Ra (arithmetic average of the absolute values of the profile heights over the evaluation length), Rz (measure of the ordinates of the five highest peaks and the five deepest valleys along the specimen's length) and PV (mean values of peak and valley measured in the specimen space) is proposed and indicates that Rz and PV should not be neglected in a systematic evaluation of the surface roughness effect on the bulk mechanical properties of dental ceramics. Catholic University of Rio de Janeiro Department of Chemical and Materials Engineering PUC-Rio, Marques de São Vicente St 225, Gávea Fluminense Federal University / Faculty of Dentistry - Institute of Health of Nova Friburgo, Dr. Silvio Henrique Braune St, 22 - Downtown University of Toronto / Faculty of Dentistry, 124 Edward St #539 State University of Rio de Janeiro – Faculty of Technology, Presidente Dutra Highway, km 298 São Paulo State University - Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal das Colinas São Paulo State University - Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal das Colinas FAPERJ: E26-201.476/2014

In dentistry, metal-free ceramic systems are used to improve optical properties in dental restorations. Ceramics based on tetragonal zirconia ZrO2-Y2O3 are used in the manufacturing of dental prostheses for being biocompatible and for presenting proper mechanical and optical properties. Most of tetragonal zirconia blocks are commercialized in one only hue, which difficult the achievement of high aesthetic performance due to the tooth’s polychromatic characteristics. This work proposes to obtain tetragonal zirconia blocks fabricated by uniaxial cold pressing in different hues which could provide ceramic prostheses with better aesthetic results in less time. Zirconia blocks in two different colors were produced and characterized for their physical properties and mechanical resistance. The colors difference between the layers was obtained by using different amounts of Fe2O3. Ceramics with relative density superior to 99% were obtained by sintering the materials at 1530oC for 120 minutes. The mechanical properties evaluated indicated hardness close to 1270HV and fracture toughness of 7MPa.m1/2. Blocks with different hues may be an alternative in order to favor the aesthetics in the cervical region and decrease the amount of ceramic veneering.

Made available in DSpace on 2020-12-12T00:55:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-02-01 Financiadora de Estudos e Projetos Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2. Universidade do Estado do Rio de Janeiro - UERJ Faculdade de Tecnologia de Resende, Rod.Presidente Dutra, Km 298 Universidade de São Paulo-USP Escola de Engenharia de Lorena Departamento de Engenharia de Materiais Polo Urbo Industrial, Gleba AI-6 Universidade Federal de Alfenas-UNIFAL Instituto de Ciência e Tecnologia, Rod. José Aurélio Vilela, 11999 Universidade Estadual Paulista - Unesp Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Cunha, 333 Universidade Federal de São João Del-Rei - UFSJ Campus Santo Antônio, Pça Frei Orlando 170 Universidade Estadual Paulista - Unesp Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Cunha, 333 Financiadora de Estudos e Projetos: 01.10.0805-00 CNPq: 311119/2017-4 CNPq: 551048/2011-5 FAPERJ: E26-202.997/2017

New techniques for manufacturing of biomaterials using additive/substrate manufacturing such as melting laser sintering (SLM) or CAD/CAM milling use micrometric metal powders to build custom parts. CoCrMo alloys are commonly used as biomaterials due to biocompatibility, high corrosion resistance and good mechanical properties. In this work, Cr-Co-based powder was obtained by mechanical alloying of Cr-Co-Mo-W alloy, using different Ball/Powder-Ratios (BPR) and thermal treatments. The powders were deagglomerated and characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). Based on SEM micrographs, the particle size analysis was used to compare the particles spheroidizing degree, using Feret’s diameter. The XRD patterns shown Co(solid-solution) as crystalline phase. The results of particles size indicates a decrease of Feret’s diameter in BPR (Ball/Powder-Ratio) from 4:1 to 6:1 understanding that from this ratio there is no significant decrease of this relation but there is an average size increase with losses in morphological aspect. The comparison between atomized powders and powder developed in this work indicates that atomized products present relation close to one which indicates there is uniformity in the particles spherical shape. Comparing ground powders from 6:1 ratio (before and after thermal treatment) there is a considerable decrease of Feret’s diameter being it decreased from 1.75 to 1.4, an increase of about 46% in particles spheroidizing. Keywords: Co-Cr-Mo-W alloy, High-Energy Ball Milling, powder morphology; characterization .

Made available in DSpace on 2018-12-11T17:10:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-11-01 Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) The aim of this work is to obtain and evaluate the mechanical and thermal properties of low Density Polyethylene (LDPE) composites reinforced with fibers from Australian King Palm fibers. Raw fibers were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. The chemical composition of the fibers was also evaluated. After characterizing the fibers were mixed into the LDPE, in proportions of 5, 10, 15 and 20% (wt/wt) using a thermokinetic mixer model MH-50H. Furthermore tensile, flexural and impact specimens were prepared for evaluation of mechanical properties. The composites were analyzed through SEM micrographs of fractured surfaces and thermal analysis. The results indicate that the reinforcement decreases the thermal stability of the composites, but caused an increase the mechanical properties of the composites. The composites reinforced with of raw fibers 20% (wt/wt) showed significant increase in the tensile strength, flexural and impact. Departamento de Mecânica e Energia Universidade do Estado do Rio de Janeiro/UERJ Centro Universitário de Volta Redonda/UniFOA Departamento de Materiais e Tecnologia Faculdade de Engenharia de Guaratinguetá Universidade Estadual Paulista-UNESP Departamento de Materiais e Tecnologia Faculdade de Engenharia de Guaratinguetá Universidade Estadual Paulista-UNESP FAPERJ: E-26/010.002016/2014 FAPERJ: E-26/201.481/2014

Made available in DSpace on 2020-12-12T02:24:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Objectives: The aim of this study was to evaluate the effect of hydrothermal aging on the mechanical properties and translucency of dental zirconia with different levels of translucency. Methods: Three different types of dental yttria-stabilized zirconia were used: 3Y-TZP (ZrO2 - 3 mol.% Y2O3) of medium opacity (designated Z3OP), 3Y-TZP of medium translucency (Z3MT), and 5Y-PSZ (ZrO2 - 5 mol.% Y2O3) of high translucency (Z5HT). A total of 120 specimens were sintered (n = 40 specimens/group). The control group (sintered→polished→heat-treated) and the aged group (sintered→polished→heat-treated→hydrothermally degraded at 134 °C, 2 bar, 5h) were characterized by relative density, quantitative phase analysis by X-ray diffraction using the Rietveld method, microstructural analysis by scanning electron microscopy, surface roughness and translucency. All groups were submitted to a biaxial flexural strength test. Data analysis using Kruskal-Wallis, Nemenyi (p-value = 0.05), and Weibull statistics were used. Results: All sintered specimens presented full densification. After aging, an increase of the m-ZrO2 phase content was observed for the Z3OP group. On the other hand, Z3MT and Z5HT did not show any m-ZrO2 phase, indicating resistance to the hydrothermal degradation. Smaller grains were observed in the Z3MT group in relation to Z3OP group and the Z5HT group presented a bimodal grain distribution, where the largest grains were associated to cubic ZrO2. Z3OP exhibited a slight increase in roughness as a function of degradation, while the roughness remained statistically stable in the other groups. Translucency was little influenced by degradation, but considerably affected by increasing thickness. The Z5HT samples were the group with the highest translucency among the control groups. Z3OP exhibited the highest flexural strength, while being the most susceptible to hydrothermal degradation. The lowest values were presented by Z5HT in all groups, due to the high concentration of c-ZrO2 grains. Conclusion: Hydrothermal aging is less critical to the flexural strength of zirconia-based materials than the materials’ composition and microstructure. Z5HT zirconia showed the highest translucency, however the measured difference is not visually perceptible. Z5HT was considered the most resistant to hydrothermal degradation. Fluminense Federal University Faculty of Dentistry Institute of Health of Nova Friburgo, Dr. Silvio Henrique Braune St, 22 - Downtown Pontical Catholic University of Rio de Janeiro Department of Chemical and Materials Engineering PUC-Rio, Marques de São Vicente St 225, Gávea University of Toronto Faculty of Dentistry, 124 Edward St #539 State University of Rio de Janeiro Faculty of Technology, Presidente Dutra Highway, Km 298 São Paulo State University Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal Das Colinas São Paulo State University Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal Das Colinas CNPq: 308684/2013-3/311119/2017-4 FAPERJ: E-26-201.476/2014

Made available in DSpace on 2019-10-06T17:12:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-10-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Objectives: The properties of lithium-silicate dental glass-ceramics are very sensitive to heat treatments which are conducted after CAD/CAM (Computer Aided Design/Computer Aided Machining) processing. In particular, temperature variations inside the furnace chamber which may occur between different models of furnaces may result in altered mechanical properties of these materials. In this work, the effect of thermal treatment parameters on the transformation of lithium metasilicate (Li2SiO3) into lithium disilicate (Li2Si2O5) and on the resulting mechanical properties has been investigated. Methods: Lithium metasilicate samples. containing 59 vol% of amorphous phase, were thermal treated under vacuum at 820 °C for up to 9 min or at 840 °C for 7min (as control group). The samples were characterized by X-ray diffraction analysis using the Rietveld refinement and scanning electron microscopy. Hardness and fracture toughness (n = 30 indentations/group) were evaluated by the Vickers indentation technique. The elastic properties were measured by the Impulse Excitation Technique and the flexural strength (n = 15/group) was measured using the piston-on-three-ball (P–3B) testing assembly. Complementary Weibull statistic were conducted as statistical analysis. Results: The results indicate a progressive reduction of the Li2SiO3 phase with increasing isothermal holding time at 820 °C until the conversion into Li2Si2O5, is completed for treatments longer than 7 min. A complete transformation of Li2SiO3 into Li2Si2O5 has also been observed for the control group of samples treated at 840 °C for 7min. Samples of the control group exhibited hardness, fracture toughness, Young's modulus and Poisson ratio 5.76 ± 0.17 GPa, 1.60 ± 0.03 MPa m1/2, 100.3 GPa e 0.21, respectively. The reduction of the thermal treatment temperature to 820 °C reduced the fracture toughness and the Young's modulus between 5-10%. Furthermore, the fracture strength was significantly reduced by approximately 71%, because of the lower amount of elongated Li2Si2O5 grains and higher amount of residual amorphous phase. Conclusion: In general, the glass-ceramic material containing residual amorphous phase associated with various crystalline phases, presented a reduction of its mechanical properties in relation to the lithium disilicate glass-ceramic. The reasons for these differences in the mechanical behavior are discussed by analyzing the influences of different phenomena such as thermal expansion anisotropy, residual stresses, amorphous phase content and microstructure on the properties. UNESP/FEG Universidade Estadual Paulista Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas USP/EEL Universidade de São Paulo Escola de Engenharia de Lorena Campus II, Polo Urbo Industrial Gleba AI6, s/n UERJ/FAT Universidade do Estado do Rio de Janeiro Faculdade de Tecnologia, Rod. Presidente Dutra, km 298 UFSJ Universidade Federal de São João Del´Rei, Pça Frei Orlando 170 UNESP/FEG Universidade Estadual Paulista Faculdade de Engenharia de Guaratinguetá, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas CNPq: 308684/2013-3 CNPq: 3311119/2017-4 FAPERJ: E-26-201.476/2014

In this work, silicon carbide ceramics were developed by liquid phase sintering using AlN-Y2O3 as additive. Two compositions were obtained using SiC powders and different contents of AlN-Y2O3. The powders were mixed/homogeneizated and subsequently dried and deagglomerated. Powder mixtures were compacted by cold isostatic pressing. Samples were sintered at 2080oC, for 1h, under 0.2 MPa-N2 atmosphere. Sintered samples were characterized by X-Ray diffraction and density. The oxidation behavior was investigated and related to the densification and additive-content. Samples were submitted to the tests at 1200, 1300 or 1400oC, in air for 120 hours. Weight gain of the samples is plotted as function of the exposure time, obtaining the evolution of the oxidation on the surface of the samples. Based on the results, the parabolic oxidation content (kp) and activation energy were determined. The results indicate that the samples present parabolic behavior in all conditions. The activation energy results indicate that the phenomena of diffusion of oxygen ions into the oxide layer and interfacial reactions between oxide layer and intergranular phase are the responsible for oxidation mechanism.

Neste trabalho foram preparados materiais cerâmicos a base de carbeto de silício, sinterizados com a adição de AlN-Y2O3. Quatro composições foram obtidas, variando-se as quantidades e composições dos aditivos. Ensaios de oxidação foram realizados em temperaturas variadas (1200, 1300 e 1400ºC), fixando o tempo de exposição em 120 horas. Os resultados foram relacionados com a densificação e composição das amostras. A partir dos resultados do ganho de massa em função da área superficial, obtiveram-se os valores do coeficiente de crescimento parabólico da taxa de oxidação (k p). Dos resultados obtidos, observou-se que as composições apresentam um comportamento parabólico da taxa de oxidação, em todas as composições estudadas. Observou-se, ainda, um aumento efetivo da oxidação em função do grau de porosidade em algumas amostras. Por outro lado, a estequiometria utilizada na composição dos aditivos influenciou os resultados. Aditivos com maior teor de Y2O3 em relação ao teor de AlN apresentaram melhores resultados com menores taxas de oxidação.

Cerâmicas à base de zircônia tetragonal estabilizada com ítria (ZrO2(3%Y2O3)) possuem excelentes propriedades mecânicas, devido a uma peculiar transformação de fases que ocorre nos grãos desta cerâmica durante o crescimento de uma trinca. O crescimento da trinca gera tensões compressivas sobre os grãos tetragonais metaestáveis, os quais se transformam em monoclínicos, promovendo uma expansão volumétrica de 3 a 5%, a qual impede que a trinca continue crescendo nas condições de carregamento mecânicos inicialmente utilizados, o que produz aumento da resistência à fratura, e tenacidade deste material. Neste trabalho são apresentados os resultados do estudo da recuperação da fase tetragonal pela utilização de tratamentos térmicos, em zircônia envelhecida por desgaste, durante a preparação de próteses dentárias. Blocos cerâmicos pré-sinterizados à base de ZrO2(3%Y2O3) foram sinterizados em três condições distintas, quais sejam, 1450°C - 0h, 1530°C - 2h e 1600°C - 4h. Cada lote de amostras sinterizado foi submetido análise de densidade relativa, difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). Parte das cerâmicas sinterizada foi fraturada, e a superfície de fratura foi re-examinada por DRX e MEV. Outra parte foi fragmentada visando a transformação martensítica, que gera a fase monoclínica no material, e em seguida caracterizada por DRX. Os resultados da densificação e análise microestrutural indicaram densidade relativa de 94,2%, 99,6% e 99,75%, tamanho médio de grão de 0,28?m, 0,49m e 1,31m, para amostras sinterizadas a 1450°C - 0h, 1530°C - 2h e 1600°C - 4h respectivamente. Após fragmentação, os teores de fase monoclínica medidos foram da ordem de 58%, 43% e 4,5% que correspondem a aproximadamente 65% vol, 50% vol e 6% vol. Tratamentos térmicos realizados a 950°C, 1100°C e 1200°C foram necessárias para recuperação de 100% de fase tetragonal, em amostras sinterizadas a 1450°C - 0h, 1530°C - 2h e 1600°C - 4h, respectivamente. Tetragonal zirconia-based ceramic stabilized with (ZrO2(3%Y2O3)) have excellent mechanical properties due to a peculiar phase transformation that occurs in this ceramic grains during the growth of a crack. The crack growth generates compressive stresses on the metastable tetragonal grains, which are transformed into monoclinic, promoting a volumetric expansion of 3 to 5% which prevents the crack continues to grow under conditions of mechanical loading initially used, which produces the increased fracture strength and toughness of this material. This paper presents results of the recovery of the tetragonal phase by the use of thermal treatments in zirconia aged for wear during the preparation of dental prostheses. ZrO2(3%Y2O3) pre-sintered ceramic blocks were sintered in three different conditions: 1450°C-0h, 1530°C-2h and 1600°C-4h. Sintered samples were characterized by relative density, X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Part of the sintered samples was fractured and the fracture surface was re-examined by XRD and SEM. Another part was milled aiming generates a martensitic transformation (monoclinic phase), and characterized by XRD. The results of densification and SEM analysis indicates relative density of 94.2%, 99.6% and 99.75%, average grain size of 0.28?m, 0.48m and 1.31m, for samples sintered at 1450°C-0h, 1530°C-2h and 1600°C-4h respectively. After milling, the monoclinic phase content was 58%, 43% e 4,5% corresponding to 65% vol, 50% vol e 6% vol. For samples sintered at 1450°C-0h, 1530°C-2h e 1600°C-4h, heat treatments of 950°C, 1100°C and 1200°C were performed respectively, for recuperation of 100% of tetragonal phase.

Four dental porcelains for covering zirconia were sintered (fired) at 910-960 °C and characterized, focusing in analyzing reliability, physical and mechanical properties. Samples with relative density close to 99% presented leucite crystallization apart from residual amorphous phase. Hardness between 491±23 and 575±32 HV was different among all ceramics. Fracture toughness between 1.13±0.11 and 1.42±0.25 MPa.m1/2 was statistically different. Bending strength results were not different for three porcelain groups (73±9 to 75±12 MPa), with the exception of one specific group (62±4 MPa). Weibull analysis indicated bending strength between 73 and 75 MPa, Weibull modulus (m) between 5.7 and 7.1, while the ceramic with strength of 60 MPa presented m=13.6. The use of classical theory of fracture mechanics associated to the results of properties obtained in this work indicated the critical failure size in these ceramics lays between 65 and 90 μm and the theoretical fracture energy of porcelains is approximately from 10.5 to 16.3 J/m. It was concluded that the porcelains had different behavior, and it seems that there is no clear relationship among the studied properties. Resumo Quatro porcelanas dentárias para cobertura de zircônia foram sinterizadas (queimadas) a 910-960 °C e caracterizadas, focando na análise de confiabilidade, propriedades físicas e mecânicas. Amostras com densidade relativa próxima de 99% apresentaram cristalização de leucita, além de fase amorfa residual. Dureza entre 491±23 e 575±32 HV foi diferente entre todas as cerâmicas. Tenacidade à fratura entre 1,13±0,11 e 1,42±0,25 MPa.m1/2 foi estatisticamente diferente. Os resultados de resistência à flexão não foram diferentes para as porcelanas (73±9 a 75±12 MPa), com a exceção de um grupo específico (62±4 MPa). A análise de Weibull indicou resistência à flexão entre 73 e 75 MPa, módulo de Weibull (m) entre 5,7 e 7,1, enquanto a cerâmica com resistência de 60 MPa apresentou m=13,6. O uso de teoria clássica da mecânica da fratura, associado aos resultados das propriedades obtidas neste trabalho, indicou tamanho crítico do defeito nestas cerâmicas entre 65 e 90 μm e a energia de fratura teórica das porcelanas foi de 10,5 a 16,3 J/m. Concluiu-se que as porcelanas têm diferentes comportamentos e parece não haver clara relação entre as propriedades estudadas.