The influence of Fe2O3 additions on the microstructure, mechanical properties and translucence of zirconia with 3 mol-% or 5 mol-% Y2O3 was evaluated. Samples were pressed with different thickness and sintered at 1475, 1500, 1550 and 1600°C for 2 h. Density, phases, microstructure, roughness, strength and translucency were analyzed. All samples showed densification greater than 99%. After sintering at 1600°C, the phase analysis revealed only tetragonal ZrO2 in samples with 3% Y2O3, while in samples with 5% Y2O3 the cubic ZrO2 phase was identified. Significant increase in the grain size was noted, when increasing the Y2O3 content from 3% to 5% from 0.8 µm to 2.3 µm for sintered samples at 1600°C. The strength was affected with Y2O3 content and no relevant influence of the Fe2O3 on density, microstructure or mechanical properties. Visible reflectance spectroscopy analyses, related to the CIELab scale, indicate variation in the contrast ratio as function of thickness of samples and coloring agent Fe2O3 content.

The planning and execution of the adequate welding procedure for the superduplex stainless steel (SAF 2507 SDSS) in multiple passes is a complex technological task since thermal cycling may cause the precipitation of harmful phases, such as the sigma (σ) and chi (χ) phases. For this reason, technical standards limit the maximum interpass temperature (T.I.) in an extremely conservative manner at 100 °C. In order to investigate a possibly wider temperature range for this procedure, SAF 2507-SDSS tubes were subjected to autogenous Tungsten Inert Gas (TIG) welding with interpass temperatures ranging from 150°C to 400°C. The different welding zones were characterized by microscopy, Vickers microhardness, and polarization corrosion tests. The results indicated that in the Fusion Zone (FZ), columnar grains of ferrite were formed surrounded by allotriomorphic austenite (AA), besides intragranular austenite (AI) and Widmanstätten austenite (AW). The heat-affected zone (HAZ) had a lower ferrite content and was composed of equiaxed grains of ferrite, also surrounded by AA, besides AI and AW. Hardnesses varied between HV272 and HV293, regardless of the region or the interpass temperature used. Furthermore, the corrosion resistance has not been significantly affected by the interpass temperatures between 150 °C and 400°C.

resumo: Neste trabalho, diferentes amostras de cinza volante (CV-A e CV-B) classificadas como tipo F foram usadas para a produção dos AAM. A amostra CV-A apresentou uma maior concentração de Fe2O3 (6,1%) em comparação a amostra CV-B (3,8%). A razão SiO2/Al2O3 foi de 3,52 e 3,34 para as amostras CV- A e CV-B, respectivamente. O tamanho médio das partículas (D50) foi de 19,7 µm (CV-A) e 30,8 µm (CV-B), enquanto a massa específica foram 2,38 e 2,21 g/cm3, respectivamente. A resistência mecânica das amostras produzidas com a CV-A foi de 80 MPa enquanto valores próximos de 44 MPa foram obtidos com a CV-B. Essa variação foi relacionada com os diferentes tamanhos médios das partículas da cinza. A diminuição da resistência foi relacionada com o álcali em excesso no sistema. Pequenas variações nos valores de porosidade e densidade foram observadas nas amostras produzidas.

abstract: In this work, different samples of fly ash (FA-A and FA-B) classified as type F as used to produce the AAM samples. The FA-A presented a higher Fe2O3 content than FA-B, 6.1 to 3.8 wt.%, and a slightly higher SiO2/Al2O3 ratio of 3.52 in comparison to 3.34 of FA-B. The average particle size (D50) of fly ash A was 19.7 µm and of fly ash B 30.8 µm, while the specific mass of the ashes A and B were 2.38 and 2.21 g/cm3, respectively. The results revealed that the mechanical strength of the AAM produced with fly ash A was higher than fly ash B, close to 80 and 44 MPa, respectively. The variation of the strength has been attributed to the different SiO2/Al2O3 ratios and different particle sizes. The mechanical strength decreased with increasing curing time, which is attributed to excess alkali in the system. Only very small differences in porosity and density have been found.

The geopolymer binder is a relatively new class of inorganic binding material of elevated mechanical strength and good chemical properties. This can be produced using clay minerals or byproducts of the industrial processes, such as metakaolin, fly-ash and blast furnace slag. In this work, geopolymers were produced by alkaline activation of a Brazilian fly-ash with simple and compound solutions (NaOH and NaOH + Na2SiO3). The hardened specimens presented values of the mechanical strength close to 48 MPa when the activator used presented SiO2/Na2O ration close to 1.0 after 24 h of curing at 65 ºC. The increase of the temperature to 90 ºC favored the reactions of the N-A-S-H gel (geopolymer) formation and compression strength increased to values close to 90 MPa after 24 h. It has been found that physical properties, such as density and porosity, varied when different SiO2/Na2O rations was present in alkaline solutions. Time, temperature of curing and particle size of fly-ash modified the mechanical and physical proprieties of hardened inorganic binder. Was observed the diffraction phases related to zeolitic phases and carbonate new bands of absorption were related to reactions of Na2O in excess with atmospheric CO2. The variation of SiO2/Na2O modified the microstructural of the hardened specimens.

ZrO2(Y2O3)-based ceramics are widely used as biomaterials due to high fracture toughness, resulting from the tetragonal-monoclinic phase transformation in which the ceramic is submitted during crack propagation. In this context, studies involving the possibility of optimization of the tetragonal phase are important for the properties improvement of this ceramic. This study investigated the recovery of tetragonal phase from a previously transformed ZrO2(3 mol% Y2O3) ceramic. Zirconia samples were sintered at 1450 °C, at 1530 °C - 2 h and at 1600 °C - 4 h, in order to obtain materials with distinct microstructural features. The sintered samples were characterized by relative density, X-ray diffraction and scanning electron microscopy. Samples sintered at 1450 °C, 1530 °C - 2 h and 1600 °C - 4 h, presented relative densities of 94.2, 99.6 and 99.7% with grains size averages of 0.28, 0.49 and 1.31 µm, respectively. All samples were submitted to milling to induce the tetragonal→monoclinic phase transformation presenting 5, 50 and 65 vol% of monoclinic phase. Subsequently, heat treatments between 400 °C and 1200 °C were conducted to retransform monoclinic in tetragonal phase. It has been found that the smaller the grain size after sintering, the lower the necessary annealing temperatures for fully recovering of tetragonal phase. Annealing temperatures of 950, 1100 and 1200 °C were sufficient to recover almost fully the tetragonal phase.

The amount of waste rubber has gradually increased over recent years because of over-growing use of rubber products. The disposal of waste rubber has caused serious environmental problems. The incorporation of recycled materials into cementitious composites is a feasible alternative that has gained ground in civil construction. The performance of such materials is much affected not only by the rubber addition, but also the particle size which has been controversially reported in the literature. In order to investigate the single effect of rubber particles into cement based materials, rubber cementitious composites were prepared with no silica particle additions. A full factorial design has been conducted to assess the influence of the rubber particle size (0.84/0.58 mm and 0.28/0.18 mm); mass fraction used (5, 15 and 30%); and water/cement ratio (0.35 and 0.50) on the physic-mechanical properties of the composites. The materials were characterized through apparent density, porosity, compressive strength, flexural strength, modulus of elasticity and microstructural analysis. The interactions of rubber particle size, rubber fraction and water/cement ratio affected significantly the density and compressive strength of the composites. The apparent porosity was influenced mainly by the rubber particle size. The flexural strength was affected by the main factors and the modulus of elasticity was affected by the interaction factors rubber particle size and fraction, and rubber fraction and w/c ratio.

Steatite is a mineral which has been employed in the carving of elements in facades of Brazilian historical buildings and churches since the 17th century. Over the years, many of those historical buildings suffered the consequences of weathering with a current need for restoration. Recently a special cement-based mortar containing additions of fine powder waste from mineral extraction of steatite has been developed in Brazil, as a composite material for restoration of steatite elements. However, the incorporation of steatite waste reduces the flexural strength of the mortar and compromises the restoration of elements where gravity imposes tensile stresses. The addition of carbon fibres may overcome this issue and increase the flexural strength of the cement-steatite composite mortar. This work investigates the effect of carbon fibre addition on the bulk density and flexural strength of compacted precast cement-steatite composites. The results show that the addition of carbon fibres (i) effectively increases the mechanical strength, allowing for a higher amount of steatite powder waste in the mixes; (ii) reduces the weight of the structural elements. This new composite material would help to develop restoration techniques of historical buildings and serve as a disposal route of steatite powder waste in Brazil.

Mineral rock wastes are being widely investigated due to possible damage to the environment when discarded indiscriminately in the nature, but also because of their great potential as ceramic raw materials. This work aims to study the effect of steatite particle additions on the mechanical properties of clay composites. A comprehensive series of experiments have been conducted to assess the influence of: steatite particle size, steatite fraction and compacting pressure on the performance of clay composites. The composite of superior properties was manufactured with 20 wt. (%) of steatite, 100-200 US-Tyler of steatite particle size and 30 MPa of compacting pressure.

In this work, the static mechanical properties and cyclic fatigue life of 3 mol. (%) Y2O3-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics were investigated. Pre-sintered samples were sintered in air at 1600 °C for 120 minutes, and characterized by X ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined by Vicker's indentation method, and Modulus of Rupture was determined by four-point bending testing. Fully dense sintered samples, near to 100% of theoretical density, presented hardness, fracture toughness and bending strength of 13.5 GPa, 8.2 MPa.m½ and 880 MPa, respectively. The cyclic fatigue tests were also realized using four-point bending testing, within a frequency of 25 Hz and stress ratio R of 0.1. The increasing of load stress lead to decreasing of the number of cycles and the run-out specimens number. The tetragonal-monoclinic (t-m) ZrO2-transformation observed by X ray diffraction contributes to the increasing of the fatigue life. The 3Y-TZP samples clearly presents a range of loading conditions where cyclic fatigue can be detected.

The understanding of the creep behavior of silicon nitride (Si3N4) is extremely complex because of a large number of parameters influencing simultaneously the creep deformation of the materials. In general, the main creep mechanisms acting in these materials are grain boundary sliding or materials transport by solution-precipitation process. In this work, the creep behavior has been monitored by X ray diffraction analysis, determining the peak intensity ratio of the (101) and (210) planes of b-Si3N4. This characterization technical, allied the microstructural analysis can contribute to determination of creep mechanisms acting in material. The beta-Si3N4 grains are highly elongated with aspect ratios ranging between 3 and 11. Therefore, the intensity of the peaks related to the basal plane (101) tends to be higher when compared to the lateral planes (210). During creep deformation occurs alignment of the elongated beta-Si3N4 grains in the plane parallel to the direction of the applied load, reflecting in the peak intensity ratio. Crept samples presented variations in the (101)/(210) peak intensity ratio of beta-Si3N4 indicating that grain rotation can to be contributing with creep deformation. In this way, the use of X ray diffractometry as a mean to characterize microstructural changes during creep has been shown successfully.

Many methods are currently used to measure the fracture toughness of ceramic materials. Methods based on crack-length measurements of cracks introduced into the sample surface by the Vicker's indentor have the advantage that they are easy to use, but are very unreliable due to subcritical crack growth and the difficulty in determining the exact length of the cracks. Furthermore, depending on the crack shape there are many equations to calculate K Ic. Other methods like the Chevron Notch or Single Edge Pre-cracked Beam (SEPB) are often difficult to execute or expensive. The simple and inexpensive Single-Edge-V-Notched Beam (SEVNB) on the other hand gives reliable values of fracture toughness of ceramic materials. In this method a saw cut is tapered to a sharp V-notch using a razor blade sprinkled with diamond paste. Thus, it is possible to introduce a sharp crack with a notch width of less than 20 micrometers, necessary to conduct valid tests. In this investigation, fracture toughness measurements on LPS-SiC materials carried out by the indentation technique and the SEVNB method have been compared.

A comparative study was made of Si3N4 sintered with two types of additives, namely, Y2O3/SiO2 and R2O3(ss)/SiO2, R2O3(ss) being a rare earth metal oxide in solid solution. The processing conditions for both types of Si3N4 were 14 vol% of additives and a sintering temperature of 1800 ºC for 30, 60 and 240 min. To compare the efficiency of the additives in the material's sintering process, the density, flexural strength, fracture toughness and hardness were measured and the phase composition and microstructure determined. The results indicated that R2O3(ss)/SiO2 as a sintering aid improved the material's high temperature strength and slowed down grain growth when compared with the Y2O3/SiO2 additive.

The objective of this work has been to compare the reliability of two Si3N4 ceramics, with Y2O3/Al2O3 or CTR2O3/Al2O3 mixtures as additives, in regard to their 4-point bending strength and to confirm the potential of the rare earth oxide mixture, CTR2O3, produced at FAENQUIL, as an alternative, low cost sinter additive for pure Y2O3 in the sintering of Si3N4 ceramics. The oxide mixture CTR2O3 is a solid solution formed mainly by Y2O3, Er2O3, Yb2O3 and Dy2O3 with other minor constituents and is obtained at a cost of only 20% of pure Y2O3. Samples were sintered by a gas pressure sintering process at 1900 °C under a nitrogen pressure of 1.5 MPa and an isothermal holding time of 2 h. The obtained materials were characterized by their relative density, phase composition and bending strength. The Weibull analysis was used to describe the reliability of these materials. Both materials produced presented relative densities higher than 99.5%t.d., b-Si3N4 and Y3Al5O12 (YAG) as cristalline phases and bending strengths higher than 650 MPa, thus demonstrating similar behaviors regarding their physical, chemical and mechanical characteristics. The statistical analysis of their strength also showed similar results for both materials, with Weibull moduli m of about 15 and characteristic stress values s o of about 700 MPa. These results confirmed the possibility of using the rare earth oxide mixture, CTR2O3, as sinter additive for high performance Si3N4 ceramics, without prejudice of the mechanical properties when compared to Si3N4 ceramics sintered with pure Y2O3.

In this work, the influence of the additive system on the liquid phase sintering of silicon carbide has been investigated. The additives employed were mixtures of AlN/Y2O3, Al2O3/Y2O3 and SiO2/Y2O3. The total additive content was fixed at 20 vol.-%, maintaining the Y2O3 content in each additive system at 35 vol.-%. Cold isostatically pressed samples were sintered at 1900, 2000 and 2100 °C under Ar atmosphere during 30 min. The most promising results have been obtained by samples with AlN/Y2O3 additions sintered at 2000 °C, exhibiting the smallest weight loss of about 6% and the highest flexural strengths of about 433 MPa. Samples with Al2O3/Y2O3 and SiO2/Y2O3 additions exhibited high weight loss, because of reactions of Al2O3 and SiO2 with the SiC matrix, forming gaseous species such as Al2O, SiO and CO, resulting in depletion of the liquid phase, and, consequently, in inferior final densities and mechanical properties. Concerning the SiO2/Y2O3 additive system, the reactions seem to be completed already at temperatures below 1900 °C, turning this additive mixture unsuitable. The microstructural analysis indicated only the presence of the <FONT FACE="Symbol">b</FONT>-SiC phase for all samples; no phase transformation of the <FONT FACE="Symbol">b</FONT>-SiC into <FONT FACE="Symbol">a</FONT>-SiC has been observed.