Materials Science Forum Vols. 727-728

Abstract: In this paper, the rheological behaviors of dispersions of two types of clays a kaolin and a smectitic clay from Paraíba State, Northeastern Brazil, were investigated. Both clays are mainly employed by ceramics industries in the Southern States of São Paulo and Santa Catarina. Viscosity measurements of dispersions in water and three types of alcohols (methanol, ethanol, and propanol) were carried out in a concentric cylinder geometry viscometer. The concentration of the dispersions was 20 wt.% of clay in water-alcohol suspensions containing up to 75 wt.% of each one of the three alcohols. The results are compared and discussed.

Abstract: Al₂O₃-Nb₂O₅ has been widely explored as one of the most used material for sintering mixing in the literature, due to its excellent hardness properties, used in armor. In this study, Al₂O₃-Nb₂O₅ and Y₂O₃-Nb₂O₅ powders were prepared, with 50% in mole fraction of each oxide. The mixtures were subjected to high energy milling in an eccentric ball mill for 3 h, dried and sieved in a sieve vibrator. The green bodies were compacted at 70 MPa and sintered from 1250 to 1650 °C for 3 h, at 100 °C steps. The materials were characterized by quantitative X-Ray diffraction (XRD) using Rietveld method and by mass loss. The Al₂O₃-Nb₂O₅ mixtures experienced a weight loss of 84% at sintering temperatures of 1550 and 1650 °C.

Abstract: Several CAD/CAM systems are available to dental prosthesis laboratories that can be used to make all-ceramic copings and frameworks. In Brazil, the use of these systems presents low demand, due principally the high blocks ceramics cost used for theses systems. The ceramic blocks are imported. To increase the dental ceramic CAD/CAM applications is necessary develop and produce the ceramics blocks in Brazil. The purpose of the present work is to compare the mechanical properties of blocks of zirconium developed in the Brazil (ProtMat® Co) and imported (VITA). It was determined the mechanical and physics properties of the two types of blocks of zirconium stabilized with ytria. The blocks have been sinterized at 1530 °C and their mechanical and physics properties were measured. The x-ray diffraction analysis showed only tetragonal phase, which improve the blocks toughness. The Vickers hardness and fracture toughness were 1300HV and 9 MPam^1/2, respectively. High bending fracture resistance was obtained for both materials with average values of 910MPa. The Weibull modulus was m=10 for Brazilian and imported blocks. It was not observed an important difference among the microstructures and mechanical properties of the analyzed zirconium blocks.

Abstract: Extrusion of a clay body is the most applied process in the ceramic industries for manufacturing structural blocks. Nowadays, the assembly of such blocks through a fitting system is gaining attention owing to the saving in material and reducing in the cost of the building construction. However, this fitting system requires a press-molding, rather than extrusion, to allow blocks to be fabricated with different shapes. In this work, the ideal composition of clay bodies incorporated with granite powder waste was investigated for the production of press-molded ceramic blocks. An experimental design was applied to determine the optimum properties and microstructures. Press load of 15 ton and temperatures from 850 to 1050°C were considered. The results indicated that mechanical strength of 30 MPa and water absorption of 15% could be attained with the incorporation of up to 17% of granite powder waste.

Abstract: Ceramic bricks are one of the most widely used materials in both commercial and residential buildings. Ceramic bricks play a relevant role in the Brazilian economy. The basic input material for this industry is red clay. As environmental problems increase, the need for environment-friendly building design increases. To achieve this, architects and engineers need reliable data on the environmental impacts of various building materials, including ceramic bricks. In this paper a comparative Life Cycle Assessment between two ceramic brick production units in Santa Catarina State, Brazil, has been carried in a comparative approach. Key impact categories, including fossil fuel use, global warming, ozone depletion, ecotoxicity, and human toxicity were assessed. The analysis has shown a particular relevance of the respiratory effects in both systems and the critical point has been found in the fuel used in the furnace for firing the bricks which are responsible, during the ring process, for the relevant CO₂ emissions.

Abstract: Silicon carbide is used to produce abrasive and high-temperature structural ceramic materials due to its mechanical and chemical properties. The possible applications of porous silicon carbide ceramics are diesel engines catalysers and molten metal filters. In the last years the starch gained importance as a pore-forming and consolidation agent, due to it is environmental friendly and easily processing. The current work uses starch (corn, rice and potato) as pore forming and consolidation agent. The samples sintered at different sintering times were characterized by density and microstructure (XRD, SEM). The results show that the samples presented porosity between 20 and 40% and the microstructures obtained is homogeneous with a pore size similar to the starch particle added.

Abstract: Ceramics are widespread used in restorative dentistry, mainly due to their aesthetics features. However, adequante bond strenght of this type on restoration to tooth structure spawned several investigations which aim to develop a clinical protocol for ceramic surface treatment. The objective of this study was to evaluate the influence of air temperature on the drying process of silane agent and the adhesion of feldspar and yttrium stabilized zirconia. They were divided into three groups (n=10): control; room temperature dried silane; and silane drying at 70º C. Then, composite resin cylinders were bonded to the samples and taken to a shear test. The results showed that air temperature rise, in silane drying, improved bonding resistance in Y-TZP ceramics, nevertheless in feldspatic ceramics, the bonding resistance was not altered.

Abstract: When it comes to providing reliable adhesion of low silica content alumina ceramic, hydrofluoric acid etching along with silanization has not shown sufficient efficacy because the microstructure of high-alumina content ceramics is unable to degrade them. The objective of this study was to analyze the effect of surface sandblasting of zirconia-based ceramic stabilized by yttria as used in dental prostheses, using a SEM and roughness average. The samples were divided in control, no surface treatment; Al₂O₃ sandblasting; Al₂O₃ sandblasting and Al₂O₃ + SIC particles 110 µm average sized; Al₂O₃ sandblasting and Al₂O₃ + SIC particles 110 µm average sized milled for 2 hours; Al₂O₃ sandblasting and Al₂O₃ + SIC particles 110 µm average sized milled for 6 hours. The Al₂O₃ sandblasting and the 2-hour milled Al₂O₃ + SIC particles showed better results and better characterization of roughness in SEM with the silica deposition on the samples surface.

Abstract: Ceramic products made from red clay to move the economy of Rio Grande do Norte. Among the most common ones are outstanding bricks, tiles and slabs in different sizes and shapes. In perspective to seek products with good quality in the ceramic industry, the characterization of the raw material is essential for obtaining an excite end product. The municipality of Apodi located in the Upper West Rio Grande do Norte has the ceramic industry as a sector of great economic importance in the site. However the absence of technology for characterization of the clays found in the region is the major problem for local entrepreneurs. The objective this study is to characterize the red clay one of the ceramics used by the municipality of Apodi-RN. The procedure will be done through the testing of Plasticity, Liquidity, linear shrinkage, absorption water, porosity, XRD and EDX.

Abstract: The scheelite occurs mainly in northeastern Brazil, with highest abundance in the states of Rio Grande do Norte and Paraíba - Scheelite Seridó Province. Mining is considered an activity that provides a high environmental degradation due to the large amount of minerals and waste involved. Most mining companies have no technologies or processes that allow the recycling of mineral waste generated. The aim of this study is to evaluate the influence of different percentages of reject on the mechanical properties of scheelite and aesthetic (staining of the final product after firing) of the clay of the city of Boa Saúde - RN. The raw materials used were characterized by XRD, XRF and particle size analysis. Assay was performed by water absorption, linear retraction and bending tests on three points for the characterization of the final product. The raw materials used were from the city of Currais Novos-RN.