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The objective of this work is to recycle the printed circuit boards of electronic equipment discarded and mix them with polypropylene (PP) to produce a new composite. Six types of mix of discarded printed circuit boards were analyzed: new boards with and without copper, used boards without components and with and without copper, used boards without components and without copper, used boards with copper track, used boards with copper track and burned and used boards with components. Boards were disintegrated and employed as reinforcement with polypropylene matrix (5% m/m). Specimens were produced for flexural and impact tests. Results showed that specimen’s properties depend on the mix composition. In all of the cases, pure PP properties were enhanced when it was replaced by 5% of waste materials discard.

ZrO2(Y2O3)-based ceramics with coloring gradient can facilitate the development of dental prosthesis by the improvement of esthetic properties. In this work, ZrO2 powders with different particle sizes were investigated. White and yellow zirconia powders (TOSOH Corporation-Japan) were characterized by particles size distribution using nanoSight-LM20 analyzer. Furthermore, samples were characterized by X-Ray diffraction, Scanning Electron Microscopy and relative density. Compacts with two layers, one white and one yellow were uniaxially pressed at 80MPa and sintered at 1530°C-120min. The yellow-powder presented average particles size of 180±66nm, while the white-powder presented particles size of 198±73nm. After sintering, full dense ceramics with tetragonal phase were obtained. The linear shrinkage of the yellow and white-layer was 22.75% and 22.05% respectively. This difference in shrinkage is important in the machining of prostheses in ceramic CAD/CAM systems, because they lead to difficulties in adapting this customized prosthesis in patients.

Ceramic composites developed for glass infiltration in ceramic substract has as main advantage the reduction of fabrication temperatures of ceramic parts compared to the solid state sintering. In this work, spinell based-ceramics infiltrated with glass rich in lanthanum, aiming applications in dental ceramics, were developed and studied. Pre-sintered spinell substrates with porosity of 10, 15 and 20% were infiltrated with glass at temperature 1120°C-120min, using heating and cooling rate of 10°C/min. The composites present relative density superior 98.6% in every investigated condition, and X-ray diffraction indicated the phase MgAl2O4, as unique crystalline phase detected. Hardness Vickers varying between 850-1000HV and fracture toughness varying between 3.0 to 4.5MPa.m1/2 were obtained for composites with variation of intergranular phase quantity. The evaluation of residual thermal stress indicates that compressive thermal stress are generated in every composition varying from 70-90MPa, for compositions containing between 10 to 20% of infiltrated glass, respectively. Theoretical calculations indicate that the excellent quantity of inter-granular phase infiltrated must be 17%, for obtaining better resistance to crack propagation in this material.

In this work, the preparation of Al2O3-TiO2 ceramics by high-energy ball milling varying the molar fraction in 1:1 and 3:1 was investigated. The powder mixtures were processed in a planetary mill at 250rpm and a ball-to-powder weight ratio of 5:1, for 120min. Compacts were obtained by cold pressing at 100MPa. These specimens were heated at 1000◦C for 30min to promote the water evaporation, and subsequently sintered at 1500◦C for 240min. Samples were characterized by relative density and X-ray diffraction. Hardness and fracture toughness were determined by Vickers Indentation Method. The crystallite sizes were lower than 420 and 560Å in Al2O3-TiO2 and 3Al2O3-TiO2 powders, respectively. After sintering, XRD analysis indicates Al2TiO5 and Al2O3/Al2TiO5 as major crystalline phases for Al2O3-TiO2 and 3Al2O3-TiO2 compositions, respectively. The relative density of the Al2O3-TiO2 ceramics was higher than 90% in both compositions. However, hardness and fracture toughness results of 10.7GPa or 10.5GPa and 3.2MPa.m1/2 or 2.6MPa.m1/2 for Al2O3-TiO2 and 3Al2O3-TiO2 mixtures respectively, indicates that microstructure duplex composed by Al2O3 and Al2TiO5 grains lead to improvement of toughness of these ceramics.

The yttria stabilized zirconia, ZrO2 (Y2O3) has been widely used in dental prosthesis manufactured by CAD/CAM technique. This material is developed in the form of pre-sintered blocks, which are machined by extracting various customized prosthesis and generating a loss of about 30% of material. ZrO2(Y2O3) is notably a toughening for other ceramics, and has a high cost, so reusing discards these applications less noble, is strategically interesting. In this work the proposal is to recover discharges of ZrO2 (Y2O3) arising from prosthetic laboratories, reprocess them in order to reduce the particles size and subsequently sintering, demonstrating the potential use in applications less noble in dentistry. Discharges Residual of ZrO2-(Y2O3) were fragmented and then sieved to particle size separation. Powders of smaller than 63 μm were uniaxially pressed at different pressures. The compacts were characterized by the relative density showing green density of the order of 40%. After characterization, compacts were sintered at 1550°C-2h. The sintered material was characterized as its relative density and crystalline phases.

In this work, compacting powders of different ZrO2(Y2O3) are investigated relating the particle size, compaction pressure, and use of binders. Powders of ZrO2 stabilized with 3mol % Y2O3 with an average particle size of 0.15 to 0.7μm presence of both bonding and 0.15μm without addition of binder, were uniaxially compacted with pressures of 30 to 115MPa. Green density between 40% and 50% were obtained. The results indicate that powders sized less densification above 1400°C, while the larger sizes only after reaching full densification above 1500°C. Crystallographic characterization indicates that the powders have a percentage of monoclinic phases in the range of 15% to 26%, but only after sintering tetragonal phase is identified.

ZrO2 ceramics are one of the most important materials used in dental prostheses production, due to their excellent mechanical resistance and chemical inertness in the mouth environment. Nevertheless, the combination of low pHs and fluoride presence is able to reduce the chemical stability of these ceramics. In this work, the resistance of commercial blocks of micrometric and nanometric sized Y2O3-stabilized ZrO2 ceramics (ProtMat Materiais Avançados® and Ivoclar®) was evaluated in Fusayama artificial saliva of different pHs with (and without) the presence of fluoride ions. The study was based on the analysis of the amount of Zr4+ and Y3+ ions dissolved in the artificial saliva after different exposure times using ICP OES technique. The XRD technique was also employed to investigate the phase transformations occurring during the degradation process in artificial saliva. The micrometric sized ZrO2 ceramics presented higher resistance in the artificial saliva than nanometric sized structures.

The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.

A considerable increase in the ceramic products demand occurred due to the evolution of dental restoration techniques and these materials must resist to the complex mouth environment. The pH of saliva can decrease significantly due to the ingestion of acidic foods and beverages and mainly due to reactions occurring during bacteria metabolism that lead to the formation of organic acids. Fluorides are also present in the mouth since fluorides are usually added in drinking water, mouth washes, tooth pastes and gels for the prevention of plaque and caries formation. The combination of low pH and presence of fluorides can lead to the formation of HF and HF2- which are detrimental to metallic and probably to ceramic devices. In this work, commercial blocks of ZrO2 ceramics (ProtMat Materiais Avançados® and Ivoclar®) were immersed in Fusayama artificial saliva of different pHs and fluoride concentrations. The properties of the as-produced ceramics (crystalline phases (XRD), microstructure (SEM), roughness (3D surface topography AFM) and mechanical resistance – Vickers hardness (Hv) and fracture toughness (KIC) were evaluated. Some of these properties were also determined after the immersion tests as well as the mass variation of the samples in order to evaluate the resistance of these ZrO2 ceramics to degradation under these conditions.

Commercial α−Si3N4, Al2O3 and a mixed yttrium and rare earth oxides, RE2O3, were used as starting-powders. Powder batches were milled using different Al2O3/RE2O3 contents, as additive. Hot-pressing was done at 1750oC-30 min-20MPa in N2 atmosphere. Specimens neat to 6x3x3mm3 were polished and characterized by XRD and SEM. Specimens were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 1300oC in air. Higher additive amounts resulted in larger grains of higher aspect ratios and in a decreased anisotropy in the hot-pressed ceramics. The compressive creep behavior depends on the intergranular phase content. While higher amounts of additives resulted in higher creep rates, • ε , and higher stress exponents, n, the activation energy Qss, has been inferior for samples with lower additive contents. Grain sliding has been identified to be the predominant mechanism responsible for creep deformation of these ceramics.

Gelcasting is a novel method of forming ceramics and has been increasingly employed in preparing complex-shaped, near-net-shape advanced materials. In this work, alumina, zirconia and alumina-zirconia bioceramics were shaped by gelcasting, using MAM-MBAM monomer system, with subsequent sintering and characterization. High purity tetragonal ZrO2 (3mol%Y2O3) and .Al2O3 powders were used as starting powders. Powder mixture containing 80 wt.% of alumina and 20 wt.% of tetragonal zirconia were obtained by milling/homogenization. In all cases, the suspension obtained had at least 55 vol.% solid loading. Ceramic bodies were demolded, dried and characterized by green relative density. The compacts were sintered in air at 1550 and 15750C, for 120 minutes, with controlled heating-rate to facilitate organic compounds removal. Sintered samples were characterized by relative density, and analyzed by X-Ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined using Vicker’s indentation method.

In this study, the influence of La-rich glass addition and sintering conditions on the densification and mechanical properties of 3 mol.%Y2O3-stabilized tetragonal zirconia polycrystals (3Y-TZP) ceramics were evaluated. High-purity tetragonal ZrO2 powder stabilized with 3 mol.% Y2O3 and La2O3-Rich glass were used as starting powders. Two compositions, ZrO2 containing 5 and 10 wt.% of a La2O3-rich glass were studied in this work. The starting powders were mixed/milled by planetary milling, dried at 90ºC for 24 hours, sieved through a 60 mesh screen and uniaxially cold pressed under 80 MPa. The samples were sintered in air at 1200, 1300 and 1400ºC for 60min, and at 1450ºC for 120min, with heating and cooling rates of 10ºC/min. Sintered samples were characterized by relative density, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The mechanical properties, hardness and fracture toughness, were obtained by Vickers indentation method. Dense sintered samples were obtained for all conditions. Samples sintered at 1300ºC for 60 min presented the optimal mechanical properties with hardness of 1170 kgf.mm-2 and fracture toughness of 8.3 MPam1/2.

In this work the influence of isothermal sintering time on the microstructural development of ZrO2-Al2O3 composite was studied. Powder mixture of ZrO2 containing 20 wt% Al2O3 was prepared by milling, compaction and sintering at 16000C, in air. The isothermal sintering time at 16000C was varied between 0 and 1440 min. The sintered samples were characterized in terms of phase composition and relative density. Their microstructures were characterized by grain size distributions and average grain size. These results were evaluated using the classic grain growth equation as a function of time, determining the grain growth exponent of these materials. Furthermore, the microstructural aspects were related to the mechanical properties (Vicker’s hardness and fracture toughness) of these composites.

In this work, the effects of alumina additions on the properties of the ZrO2-Al2O3 ceramic composites were investigated. Samples of ZrO2 with Al2O3 additions varying between 0 and 30wt-% were prepared. The powder mixtures were milled, compacted by uniaxial cold pressing and sintered at 16000C, in air, for 2 hours. The sintered samples were characterized by their relative density, phase composition and microstructure. As mechanical properties at room temperature, their Vickers hardness and fracture toughness were determined: In all sintering conditions and Al2O3 amounts, the samples presented relative density higher that 99%. The Al2O3 addition produces a linear increase of the hardness, reaching values between 1350 and 1610 HV for the addition of 0 and 30% of alumina, respectively. The fracture toughness was near to 8 MPam1/2 in all conditions. The phase composition, microstructure and relative density were correlated in order to interpret the mechanical properties obtained.

In this work, SiC ceramics were prepared by liquid phase sintering using 10 wt.% of AlN and Y2O3 mixtures in the proportion of 4:1 and 2:3 as additives Sintering was done in a graphite resistance heated furnace at 2080oC under 0.2 MPa N2 atmosphere for 1h. Part of the samples was further heat-treated at 2000oC for 4h to allow grain growth. The microstructures of the sintered samples were analyzed using polished and plasma etched surfaces. Furthermore, relative densities, weight loss during sintering and SiC-polytype distributions are reported.

Ceramic composites developed for glass infiltration in ceramic substract has as main advantage the reduction of fabrication temperatures of ceramic parts compared to the solid state sintering. In this work, spinell based-ceramics infiltrated with glass rich in lanthanum, aiming applications in dental ceramics, were developed and studied. Pre-sintered spinell substrates with porosity of 10, 15 and 20% were infiltrated with glass at temperature 1120°C-120min, using heating and cooling rate of 10°C/min. The composites present relative density superior 98.6% in every investigated condition, and X-ray diffraction indicated the phase MgAl2O4, as unique crystalline phase detected. Hardness Vickers varying between 850-1000HV and fracture toughness varying between 3.0 to 4.5MPa.m1/2 were obtained for composites with variation of intergranular phase quantity. The evaluation of residual thermal stress indicates that compressive thermal stress are generated in every composition varying from 70-90MPa, for compositions containing between 10 to 20% of infiltrated glass, respectively. Theoretical calculations indicate that the excellent quantity of inter-granular phase infiltrated must be 17%, for obtaining better resistance to crack propagation in this material.

In this work, the preparation of Al2O3-TiO2 ceramics by high-energy ball milling varying the molar fraction in 1:1 and 3:1 was investigated. The powder mixtures were processed in a planetary mill at 250rpm and a ball-to-powder weight ratio of 5:1, for 120min. Compacts were obtained by cold pressing at 100MPa. These specimens were heated at 1000◦C for 30min to promote the water evaporation, and subsequently sintered at 1500◦C for 240min. Samples were characterized by relative density and X-ray diffraction. Hardness and fracture toughness were determined by Vickers Indentation Method. The crystallite sizes were lower than 420 and 560Å in Al2O3-TiO2 and 3Al2O3-TiO2 powders, respectively. After sintering, XRD analysis indicates Al2TiO5 and Al2O3/Al2TiO5 as major crystalline phases for Al2O3-TiO2 and 3Al2O3-TiO2 compositions, respectively. The relative density of the Al2O3-TiO2 ceramics was higher than 90% in both compositions. However, hardness and fracture toughness results of 10.7GPa or 10.5GPa and 3.2MPa.m1/2 or 2.6MPa.m1/2 for Al2O3-TiO2 and 3Al2O3-TiO2 mixtures respectively, indicates that microstructure duplex composed by Al2O3 and Al2TiO5 grains lead to improvement of toughness of these ceramics.

ZrO2(Y2O3)-based ceramics with coloring gradient can facilitate the development of dental prosthesis by the improvement of esthetic properties. In this work, ZrO2 powders with different particle sizes were investigated. White and yellow zirconia powders (TOSOH Corporation-Japan) were characterized by particles size distribution using nanoSight-LM20 analyzer. Furthermore, samples were characterized by X-Ray diffraction, Scanning Electron Microscopy and relative density. Compacts with two layers, one white and one yellow were uniaxially pressed at 80MPa and sintered at 1530°C-120min. The yellow-powder presented average particles size of 180±66nm, while the white-powder presented particles size of 198±73nm. After sintering, full dense ceramics with tetragonal phase were obtained. The linear shrinkage of the yellow and white-layer was 22.75% and 22.05% respectively. This difference in shrinkage is important in the machining of prostheses in ceramic CAD/CAM systems, because they lead to difficulties in adapting this customized prosthesis in patients.

In this work lithium disilicate glass-ceramic and glasses based on the Li2O-SiO2 system have been investigated by replacing the high-purity SiO2 starting powder by silica obtained from rice husk. Glasses were developed at the stoichiometric composition of 66%.molSiO2:33%.molLiO2 using SiO2 obtained by thermochemical treatment of rice husk. The influence of rice husk-SiO2 on phase formation, microstructure, hardness and fracture toughness was determined and discussed. Investigations were carried out by means of differential thermal analysis, X-ray fluorescence, X-ray diffractometry and scanning electron microscopy. Amorphous and transparent glasses were obtained after melting. The glasses presented Tg near to 480 0C, crystallization peak at 660 0C in both glasses from different silica sources and Li2Si2O5 as the crystalline phase after heat treatment. The hardness (HV300gF) presented average values near to 430 HV for both high-purity and rice husk silica powders. Fracture toughness measurements present results near to 1.7 MP am1/2 for both compositions.

a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.

In this work, an yttrium and rare-earth oxides mixture, CRE2O3, produced at DEMAR-FAENQUIL, was used as sintering additive for silicon nitride (Si3N4) ceramics. Samples were produced by uniaxial hot-pressing, using mixtures of CRE2O3- Al2O3 or CRE2O3-AlN as additives. Four kind of hot-pressed Si3N4 were used as oxidation samples: Si3N4+ 5vol% or 20vol.% of CRE2O3-Al2O3 (forming only β-Si3N4 as crystalline phase), Si3N4+ 5vol.%CRE2O3-AlN (α-SiAlON+β) and Si3N4+ 20vol.%CRE2O3-AlN (only α-SiAlON). The oxidation behavior was evaluated at 13500C, in air up to 160 hours. The oxidation rate of Si3N4 ceramics increased with increasing CRE2O3/Al2O3 content, and oxidation kinetics obeyed the usual parabolic law. Pure α-SiAlONs (Si3N4 +20 vol.% CRE2O3-AlN) were high oxidation resistant with weight gain, after 160 hours, of 0.1 mg.cm-2, while β-Si3N4+20vol.%CRE2O3- Al2O3 showed a weight gain of 1.4 mg.cm-2 after only 10 hours. The oxidation behavior of these ceramics was comparable with ceramics sintered with Y2O3. This result confirms the possibility of the fabrication of high oxidation resistance Si3N4 ceramics using the low cost sintering additive CRE2O3.

The important factor to consider for successful ceramics composites development is the need of matching the whiskers and matrix characteristics, taking into account the chemical compatibility of the sintering aids utilized. The purpose of this work was to analyze and compare use of rare earth concentrate (CTR) and yttrium oxide, as sintering aids, and its influence in the densification and physical/mechanical properties of hot pressed and sintered Si3N4-SiC(w). The CTR powder materials present high yttrium oxide percentage and its production is cheaper than the additives usually used in ceramic materials, such as Y2O3. For physical and mechanical properties evaluation, specific mass, crystalline phases, micrographs analysis, microhardness and fracture toughness were measured, showing similar results between the two sintering aids. Therefore, this study shows the possibility of obtaining low processing cost products with the use of rare earth concentrate. Meanwhile, more characterization steps are necessary for analyzing its behavior at elevated temperatures.

The creep behavior of hot-pressed Si3N4 ceramics was investigated. The proposal of this work is to investigate the use of yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, as sintering additive, since the cost of production of this material is 80% inferior to Y2O3. These ceramics were obtained by uniaxial hotpressing using different additive contents and mixtures (CRE2O3-Al2O3 or CRE2O3- AlN). Compressive creep tests were carried out at 13000C and 300 MPa, in air. The Si3N4-CRE2O3-Al2O3 ceramics demonstrated that the creep resistance is inversely proportional to the additive content. Mixtures with high intergranular phase content presented low creep resistance due to high oxidation and more pronounced softening of the intergranular phase. Si3N4-CRE2O3-AlN ceramics demonstrated better creep resistance with a steady-state creep rate of 7 x 10-8 s-1. This behavior is related to the a-SiAlON content, a solid solution of Si3N4 that incorporates a great fraction of intergranular phase, decreasing the amount of intergranular phase.