Indiana University-Purdue University Indianapolis (IUPUI) / Background and Rationale: As compared with glass-based ceramics, zirconia has gained considerable popularity in restorative dentistry due to its superior mechanical properties. Clinically, however, zirconia ceramics pose a significant challenge regarding the achievement of a reliable and durable bond to resin-based cements. Thus far, it has been established that zirconia bond to resin-based cements can be enhanced after different surface conditioning methods, such as airborne particle abrasion with aluminum oxide particles. Meanwhile, another major issue pertaining to bonding of ceramic restorations is related to its potential contamination before cementation. Briefly, after sandblasting and clinical try-in procedures, zirconia can be contaminated with saliva and/or blood. As with many metals, zirconium shows a strong affinity towards the phosphate group found in saliva and other fluids, which reacts with the zirconia surface and makes bonding very difficult. Recently, a new cleaning agent called Ivoclean® (Ivoclar-Vivadent), which is an alkaline suspension of zirconium oxide particles, has been introduced in the market to remove contamination from zirconia in an effort to improve bonding to resin cements. Objective: The purpose of this study was to evaluate the influence of saliva contamination and the effect of several cleaning methods, including Ivoclean on resin bond strength to zirconia. Materials and Methods: Eighty square-shaped specimens (ϕ = 12 mm x 12 mm x 3 mm) of yttria-stabilized full-contour zirconia (Diazir®, Ivoclar-Vivadent, Amherst, NY) were sectioned from zirconia blocks using a water-cooled diamond blade. Then, these specimens were embedded in acrylic resin, and their surfaces gradually finished with silicon carbide papers (600 grit to 1200 grit). The prepared zirconia surfaces were sandblasted with 50-μm aluminum oxide particles for 15 s, under 2.5 bars and from distance of 10 mm. After sandblasting the specimens were cleaned in an ultrasonic bath containing distilled water for 5 min and air-dried for 10s. All samples were equally divided into 4 groups (n = 20) according to the cleaning method. Airborne particle abraded specimens without contamination was served as the control group. Remaining groups were contaminated with saliva, and subjected to different cleaning protocols, namely: Ivoclean®, 70% isopropanol, and no treatment. Two resin cement buttons (Multilink – Ivoclar-Vivadent, Amherst, NY) were built over each zirconia surface and light-cured following the manufacturer recommendations. The influence of contamination and surface cleaning methods on ceramic bond durability were examined after 24 h on half of the samples in each group (n = 10, n = 20), and the other half (n = 10, n = 20) specimens will undergo 6000 thermocycles (TC) before shear bond testing in the universal testing machine. Conclusion of Expected Outcomes: The shear bond strength of resin cement to zirconia led to a significant improvement after cleaning with Ivoclean both immediately and after thermal aging.

Purpose: The purpose of this study was to evaluate the fracture strength of monolithic FDPs of multi-layered zirconia (YML) with different connector dimensions and placement in the disc. Material and method: Forty 3-unit monolithic anterior FDPs were produced, 212223, and divided in four groups (n=10) based on the different connector dimensions and strategies for placement in KATANATM Zirconia Yttria Multi-Layered (YML)-disc. The groups were as follows: EB12, produced with 12 mm  connector dimension and EB7, with 7 mm  connector dimension which were both placed in Enamel layer and Body layer 1 (flexural strength: 750 and 1000 MPa, respectively) in the disc, BB12, with 12 mm  connector dimension and BB7, produced with 7 mm  connector dimension both placed in Body layer 2 and 3 (both with 1100 MPa) in the disc. The specimens were artificially aged by 10 000 cycles in thermocycling. Then, one random specimen was selected from each group (4 in total) and cemented onto the model, subsequently loaded to fracture using a universal testing machine. The result was compiled and reported descriptively. Result: The FDP in group BB12 remained intact and fracturing only occurred in this model at 893 N. The FDP in group BB7 demonstrated the highest fracture strength (972 N), followed by EB12 (842 N) and EB7 which showed the lowest fracture strength (465 N). All these three FDPs broke mesially on the pontics. Conclusion: Within the limitations of this pilot study, the following conclusions can be drawn: the fracture strength of monolithic FDPs of multi-layered zirconia is affected by the connector dimension. Placement of FDPs with a small connector area should be avoided in the layers with lower strength. The choice of model material affects the result. / Syfte: Syftet med föreliggande pilotstudie var att undersöka brotthållfastheten påmonolitiska broar av flerskiktad zirkonia (YML) med olika konnektordimensioneroch placering i disken. Material och metod: Totalt framställdes 40 stycken 3-leds monolitiska anteriorabroar, 212223. Broarna delades in i 4 grupper (n=10) efter olikakonnektordimensionering och placering i KATANATM Zirconia YttriaMulti-Layered (YML)-disken. Grupperna var enligt följande: EB12 med 12 mm²konnektordimension och EB7 med 7 mm² konnektordimension där broarnaplacerades i både Enamel Layer och Body Layer 1 (med 750 respektive 1000 MPai böjhållfasthet) i disken. Broarna i grupperna BB12 med 12 mm²konnektordimension och BB7 med 7 mm² konnektordimension placerades i BodyLayer 2 och Body Layer 3 (med 1100 MPa böjhållfasthet för respektive lager) idisken. Broarna genomgick termocykling, 10 000 cykler. Därefter valdes fyrabroar slumpmässigt ut, en bro från varje grupp, och cementerades på modell.Slutligen genomfördes ett brotthållfasthetstest med en universaltestmaskin tillsfraktur uppstod. Resultatet sammanställdes och redovisades deskriptivt. Resultat: Bron i grupp BB12 förblev intakt och fraktur skedde enbart i modellen(893N). Bron i grupp BB7 visade högst brotthållfasthet: 972N, följt av bron igrupp EB12 som visade brotthållfasthet på 842N och bron i grupp EB7 påvisadeden lägsta brotthållfastheten: 465N. Dessa tre broar frakturerade mesialt på dethängande ledet. Slutsats: Inom ramen för föreliggande pilotstudies begränsningar kan följandeslutsatser dras: brotthållfastheten på monolitiska broar i flerskiktad zirkoniapåverkas av konnektordimensioneringen. Placering av broar med mindrekonnektorarea än rekommendationen ska undvikas i skikten med lägre hållfasthet.Valet av modellmaterial har betydelse och påverkar resultatet.

OBJECTIVE: Flexural strength values of multilayer zirconia may vary depending upon the specimen dimension, layers distribution, especially the layer in maximum tension side, i.e., loading configuration. Although the previous studies have examined flexural strength of the separate layers in one zirconia disc, capturing flexural strength across all layers of multilayer zirconia is still challenging yet important for their clinical indications. The objective of this study aimed to evaluate the flexural strength of multilayer graded translucent zirconia by three loading configurations with the full thickness of layers. MATERIALS AND METHODS: Four types of zirconia materials were selected namely KATANA Yttria Multi Layered (KATANA YML, Kuraray Noritake), IPS e.max ZirCAD Prime (ZirCAD Prime, Ivoclar Vivadent), and Origin Beyond + Hybrid (Origin Beyond, B&D Dental Technologies) multilayer zirconia, as well as monolithic InCoris translucent zirconia (inCoris TZI, Dentsply Sirona). The bar specimens were prepared by sectioning the zirconia discs with diamond blade to get the dimensions of 31.0 mm x 4.6 mm x 11.0 mm for KATANA YML and Origin Beyond, 42.0 mm x 6.4 mm x 13.1 mm for ZirCAD Prime, and 31.0 mm x 4.2 mm x 10.0 mm for inCoris TZI. The specimens were sintered with a Zircar high temperature furnace by following the protocols of manufacturers accordingly. The four longitudinal surfaces of all bar specimens for all materials were polished with diamond discs in a sequence of 125, 70, 45, 15, and 6 mm, and down to 0.5 mm finish. All polished specimens were subjected to the annealing treatment at 1000 oC for 15 min before mechanical testing. The three-point bend testing with three loading configuration was performed for flexural strength on the Universal Testing Machine (Instron 5566A) with a loading rate of 0.5 mm/min. The fracture surfaces of these bar specimens were examined by a field emission scanning electron microscope. The yttria (Y2O3) and hafnia (HfO2) concentrations were analyzed by energy disperse spectroscopy on polished surfaces. RESULTS: The highest mean 3 point bending flexural strength for all layers direction was for inCoris TZI with 786.55 MPa, whereas the lowest for Origin Beyond with 505.36 MPa. The inCoris TZI had overall highest flexural strength with vertical (enamel or dentin layer in tension) of 845.18 MPa. ZirCAD Prime had overall highest flexural strength with the loading configuration of dentin layer in tension of 906.22 MPa while Origin Beyond had the lowest flexural strength of 686.79 MPa. Under the loading configuration of enamel layer in tension, the flexural strength of all three multilayer materials ZirCAD Prime, Origin Beyond and KATANA YML had no significant difference, having a strength value range of 498-504 MPa. The dentin layer had the lowest yttria concentration while the enamel had the largest one, and the transition layer was between them. The distribution of hafnia concentration of different layers for all multilayer materials was consistent. CONCLUSION: Within the limitations of this in vitro study, we can conclude that material, and loading configurations as well as the interaction between material and loading configurations had a significant effect on flexural strength of multilayer zirconia. ZirCAD Prime showed a significantly higher flexural strength than KATANA YML whereas Origin Beyond had the lowest flexural strength. The flexural strength of dentin layer in tension was significantly higher than all layers in tension, while the flexural strength of all layers was significantly higher than enamel layer in tension. The yttria concentration of multilayer zirconia gradually increased from dentin layer to enamel layer whereas the hafnia concentration was consistent across different layers. These findings in this study could enrich the knowledge of clinicians when selecting the multilayer zirconia materials in the clinical settings.

No description available.

In recent years, both hafnia and zirconia have been looked at closely in the quest for a high permittivity gate dielectric to replace silicon dioxide in advanced metal oxide semiconductor field effect transistors (MOSFET). Hafnium dioxide or HfO2 is chosen for its high dielectric constant (five times that of SiO2) and compatibility with stringent requirements of the Si process. As deposited, thin hafnia films are typically amorphous but turn polycrystalline after a post-deposition anneal. To control the phase composition in hafnia films understanding of structural phase transitions is a first step. In this dissertation using first principles methods we consider three phase transitions of hafnia and zirconia: monoclinic to tetragonal, tetragonal to cubic and amorphous to crystalline. Because the high surface to volume ratio in hafnia films and powders plays an important role in phase transitions, we also study the surface properties of hafnia. We discuss the mechanisms of various phase transitions and theoretically estimate the transition temperatures. We find two types of amorphous hafnia and show that they have different structural and electronic properties. The small energy barrier between the amorphous and crystalline structures is found to cause the low crystallization temperature. Moreover, we calculate work functions and surface energies for hafnia surfaces and show the surface suppression of the phase transitions. / text

Purpose: to assess the retentive strengths of passive fit esthetic anterior restorations using three commercially available cements. Methods: Three resin dies were fabricated from the intaglio surface of each restoration type. Each die was prepared following the current accepted guidelines on primary anterior tooth crown preparation. The three prepared teeth were replicated to produce 30 dies for each of the three restoration types. The prepared teeth were further separated into nine groups of 10 teeth each. Thirty EZ Pedo Crowns, 30 NuSmile Primary Crowns and 30 Unitek crowns were cemented using hand pressure employing the luting cement assigned to the corresponding group. The units were allowed to cure for 7 days. The force required to dislodge the restoration was tested using the Instron Universal Testing Machine. The data was statistically analyzed using a two-way ANOVA to analyze the force required to dislodge the restorations. A two-way logistic regression was used to analyze the failure types. Results: There were no significant differences in restoration retention rates between restoration types (P = 0.4412) but there were significant differences between types of cements used. (P < .0001). The differences with regard to cement types were consistent across the restoration groups (P = 0.7682). Tukey’s HSD multiple comparison procedure indicated FujiCem was significantly more retentive than either Fuji I or Ketac Cem cements and there were no significant differences in restoration retention rates between the Fuji I and Ketac Cem cements. Conclusion: The type of restoration did not matter between cements but cement type did matter with FujiCem cement being more retentive than the other types of cements tested.

O objetivo deste estudo foi avaliar o efeito de diferentes protocolos de desgaste nas características superficiais e comportamento mecânico da zircônia utilizada para confeccionar infraestruturas e pilares protéticos. Amostras em forma de barra foram obtidas e divididas em três grupos (n=21): Grupo C (controle, não recebeu nenhum tipo de modificação superficial), Grupo A (desgaste realizado com fresas diamantadas de granulação média e acabamento com fresas diamantadas de granulação fina, com caneta de alta rotação sob refrigeração abundante de água) e Grupo B (desgaste realizado com pedras diamantadas de granulação grossa e acabamento realizado com pedras diamantadas de granulação média, com peça de mão acoplada em motor de baixa rotação e sem refrigeração). A topografia e rugosidade superficial (Sa) foram obtidos por microscopia confocal a laser (n=21), o módulo de elasticidade dinâmico (n=21) foi obtido por uma técnica de excitação por impulso, a transformação de fase foi avaliada por meio de difração de raios-X (n=1) e fadiga mecânica acelerada foi realizada pelo método step stress (n=18). A análise estatística para rugosidade superficial e módulo de elasticidade foi ANOVA de um fator e teste complementar de Tukey e a resistência à fadiga foi comparada pela probabilidade de sobrevivência nos diferentes tipos de carregamento, quanto ao número de ciclos e a força. Houve diferença estatística entre os grupos para rugosidade superficial (Grupo A>Grupo B>Grupo C) (p&le;0,05)e módulo de elasticidade dinâmico (Grupo B>Grupo A=Grupo C) (p=0,003). A difração de raios-X revelou mudança de fase cristalina para os grupos desgastados, sendo que o Grupo C apresentou conteúdo cristalino somente na fase tetragonal, o Grupo A na fase tetragonal e monoclínica, e o Grupo B na fase tetragonal e cúbica. Não houve diferença estatística entre os grupos quando a taxa de sobrevivência foi comparada quanto ao número de ciclos e a força. Apesar do desgaste ter modificado as características superficiais, não houve prejuízo no comportamento mecânico da zircônia / The purpose of this study was to evaluate the effect of different grinding protocols on surface characteristics and mechanical behavior of Y-TZP used to manufacture copings and abutments. Bar-shaped specimens were obtained and divided into three groups (n=21): Group C (control, untreated), Group A (grinding was performed using medium diamond burs, finishing was performed using fine diamond burs and high-speed hand piece under constant water cooling) and Group B (grinding was performed using coarse diamond stone, finishing was performed using medium diamond stone and slow-speed hand piece without water cooling). After the specimen grinding, topography and surface roughness (n=21) were evaluated on laser confocal microscope, the Youngs modulus (n=21) was performed using the impulse excitation technique, crystallographic phase change was performed using an x-ray diffraction (n=1) and step-stress accelerated life testing (n=18) was performed. One-way ANOVA and Tukeys test were performed to analyze surface roughness and Youngs modulus, and step-stress accelerated life testing was compared by the probability of survival, considering the number of cycles and strength. There was statistically significant difference between groups considering surface roughness (Group A>Group B>Group C) (p&le;0,05) and Youngs modulus (Group B>Group A=Group C) (p=0,003). X-ray diffraction data showed that grinding leads to phase change, once Group C showed only tetragonal phase, Group A showed tetragonal and monoclinic phases and Group B showed tetragonal and cubic phases. There was no statistically significant difference among groups when the probability of survival was compared considering the number of cycles and strength. Although tested grinding protocols had modified the surface characteristics, did not damage the mechanical behavior of the zirconia

Neste trabalho estudamos as propriedades eletrônicas e as estabilidades estruturais do cristal de ZrO2 e dos defeitos de vacância de oxigênio e impureza substitucional de cério. As investigações foram efetuadas através de simulações computacionais baseadas em métodos de primeiros princípios dentro do formalismo da teoria do funcional da densidade e utilizando o método APW + lo (Aumengted Plane Waves plus local orbitals), implementado no código computacional WIEN2k, dentro do esquema de supercélula, com relaxações atômicas tratadas de modo apropriado. A zircônia apresenta 3 fases estruturais, dependendo da temperatura. Sua fase mais estável é a monoclínica e, a altas temperaturas, ela apresenta as fases tetragonal e cúbica, sendo estas duas últimas as mais importantes para aplicações tecnológicas. Ela pode ser estabilizada em uma condição metaestável em uma estrutura quase cúbica quando crescida na forma de pós nanocristalinos, com tamanhos menores que um certo tamanho crítico. Outra maneira de se estabilizar as estruturas cúbica e tetragonal, a temperatura ambiente, é através da adição de dopantes, entre eles o cério. Nesses casos, estão sempre presentes vacâncias de oxigênio. Neste trabalho, para o cristal puro de ZrO2, foram calculadas as propriedades das estruturas cristalinas cúbica e tetragonal, constatando-se que a estrutura quase cúbica, proposta em várias investigações relatadas na literatura, pode ser interpretada como uma estrutura tetragonal de corpo centrado, com pequenos deslocamentos dos átomos de oxigênio na direção k . Destes resultados, propomos que nas análises dos dados experimentais obtidos por difração de raios-X e EXAFS (Extended X-ray Absorption Fine Structure) sejam utilizadas simulações onde a estrutura tetragonal de corpo centrado seja considerada como uma possível estrutura para o cristal. Dos estudos da vacância de oxigênio, obtivemos que sua presença quebra a simetria local do sistema e faz com que existam três diferentes distâncias entre um átomo de Zr e os átomos primeiros vizinhos de oxigênio, podendo, também, explicar resultados experimentais de difração de raios-X e EXAFS. Para o centro de impureza substitucional de Ce no sítio do átomo de Zr, nossos resultados apresentam uma possível explicação de porque as impurezas de Ce, em diferentes concentrações, estabilizam o ZrO2 nas estruturas tetragonal e cúbica. / In this investigation we studied the electronic properties and the structural stabilities of zirconia (ZrO2), as well as oxygen vacancy and Ce substitutional impurity. The investigations were carried by computational simulations using ab initio methods, based on the density functional theory and the APW + lo (Aumengted Plane Waves plus local orbitals) method, as implemented in the WIEN2k code, considering the supercell approach and atomic relaxations. Concerning the ZrO2 bulk, the tetragonal (quasi-cubic) phase is not thermodynamically stable at room temperature, but it can be retained in a metastable condition in nanocrystalline powders with crystallite sizes smaller than a certain critical size, or throught addition of dopants, for example cerium. In this cases, oxygen vacancies are always present. In this work we have obtained the properties of the cubic and tetragonal phases of ZrO2. From the results, we propose that the quasi-cubic structure presented in many articles can be understood as a body centered tetragonal structure, with small oxygen atoms displacement perpendicular to the k direction. Those results suggest that the analysis of the X-ray and EXAFS (Extended X-ray Absorption Fine Structure) data should include in the crystallographic model the body-center tetragonal structure. The results of the structural and electronic properties of the oxygen vacancy suggest that its presence could explain the different models of the Zr first neighbor oxygen shell. For the Ce substitutional impurity, our results present a possible explanation why these impurities, in several concentrations, are able to stabilize the ZrO2 in the tetragonal and cubic phases.

Tendo como vantagem a elevada resistência ao choque térmico da zircônia:magnésia e a alta condutividade iônica da zircônia:ítria, compósitos dessas cerâmicas foram preparados por meio da mistura, em diferentes concentrações, de eletrólitos sólidos de ZrO2: 8,6 mol% MgO e de ZrO2: 3 mol% Y2O3, compactação e sinterização. A caracterização microestrutural foi feita por meio de difração de raios X e microscopia eletrônica de varredura. A análise do comportamento térmico foi feita por dilatometria. As propriedades elétricas foram estudadas por meio de espectroscopia de impedância. Foi feita uma montagem experimental para monitorar a resposta elétrica gerada em função do teor de oxigênio a altas temperaturas. Os principais resultados mostram que os compósitos cerâmicos são parcialmente estabilizados nas fases monoclínica, cúbica e tetragonal, e apresentam comportamento térmico similar ao apresentado por eletrólitos sólidos de zircônia:magnésia de dispositivos sensores de oxigênio. Além disso, os resultados de análise de espectroscopia de impedância mostram que a adição da zircônia:ítria melhora o comportamento elétrico da zircônia:magnésia, e que resposta elétrica gerada é dependente do teor de oxigênio a 1000 °C, mostrando ser possível construir sensores de oxigênio utilizando compósitos cerâmicos. / Taking advantage of the high thermal shock resistance of zirconia-magnesia ceramics and the high oxide ion conductivity of zirconia-yttria ceramics, composites of these ceramics were prepared by mixing, pressing and sintering different relative concentrations of ZrO2: 8.6 mol% MgO and ZrO2: 3mol% Y2O3 solid electrolytes. Microstructural analysis of the composites was carried out by X-ray diffraction and scanning electron microscopy analyses. The thermal behavior was studied by dilatometric analysis. The electrical behavior was evaluated by the impedance spectroscopy technique. An experimental setup was designed for measurement the electrical signal generated as a function of the amount of oxygen at high temperatures. The main results show that these composites are partially stabilized (monoclinic, cubic and tetragonal) and the thermal behavior is similar to that of ZrO2: 8.6 mol% MgO materials used in disposable high temperature oxygen sensors. Moreover, the results of analysis of impedance spectroscopy show that the electrical conductivity of zirconia:magnesia is improved with zirconia-yttria addition and that the electrical signal depends on the amount of oxygen at 1000 °C, showing that the ceramic composites can be used in oxygen sensors.

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.