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Search Results: 1 - 10 of 536465 matches for " A. O.;Hotza "
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Efeito das propriedades dos esmaltes e engobes sobre a curvatura de revestimentos ceramicos
Dal Bó, M.;Melchiades, F. G.;Boschi, A. O.;Hotza, D.;
Ceramica , 2012, DOI: 10.1590/S0366-69132012000100019
Abstract: the interaction between support-glaze and support-engobe were studied separately regarding the central curvature of ceramic tiles. were formulated two glazes samples and four engobes samples, these were applied on a particular type of ceramic support with classification in the group b-iib, by norma abnt nbr 13.818/1997 - iso 13006. some characteristics were measured as "thermal expansion coefficient" and "shrinkage difference between support-engobe". a method was suggested d for evaluation of interaction between support-engobes and support-glazes. the results showed that, for interaction support-glazes the superposition of dilatometric curves method is well implemented; for interaction support-engobe, a statistical test was conducted with factorial design 22, indicating that the variable "shrinkage difference between support-engobe" is the variable significant to describe the central curvature of ceramic tiles.
Alumina-Based Ceramics for Armor Application: Mechanical Characterization and Ballistic Testing
M. V. Silva,D. Stainer,H. A. Al-Qureshi,O. R. K. Montedo,D. Hotza
Journal of Ceramics , 2014, DOI: 10.1155/2014/618154
Abstract: The aim of this work is to present results of mechanical characterization and ballistic test of alumina-based armor plates. Three compositions (92, 96, and 99?wt% Al2O3) were tested for 10?mm thick plates processed in an industrial plant. Samples were pressed at 110?MPa and sintered at 1600°C for 6?h. Relative density, Vickers hardness, and four-point flexural strength measurements of samples after sintering were performed. Results showed that the strength values ranged from 210 to 300?MPa depending on the porosity, with lower standard deviation for the 92?wt% Al2O3 sample. Plates (120?mm × 120?mm × 12?mm) of this composition were selected for ballistic testing according to AISI 1045, using a metallic plate as backing and witness plates in the case of penetration or deformation. Standard NIJ-0108.01 was followed in regard to the type of projectile to be used (7.62 × 51?AP, Level IV, 4068?J). Five alumina plates were used in the ballistic tests (one shot per plate). None of the five shots penetrated or even deformed the metal sheet, showing that the composition containing 92?wt% Al2O3 could be considered to be a potential ballistic ceramic, being able to withstand impacts with more than 4000?J of kinetic energy. 1. Introduction Ceramics have been considered one of the most important materials for lightweight armor applications due to their low density, high compressive strength, and high hardness [1]. Ceramic materials for using as ballistic armor must be sufficiently rigid to fragment the bullet and reduce its speed, transforming it into small fragments that should be stopped by the layer of flexible material that supports the ceramic. Thus, it is necessary that the ceramic material presents high elastic modulus and high hardness [2]. Fracture toughness is also a very important requirement for this application. The main ceramic materials used commercially in the development of ballistic armors are Al2O3, B4C, SiC, and ceramic matrix composites (CMCs) such as Al2O3/ZrO2 system. High cost, processing hindrances, and restrictions to predict ballistic performance from the properties of the material are some drawbacks of ceramic armors [3]. Alumina provides the best cost-benefit ratio among advanced ceramics, featuring high modulus of elasticity, high refractoriness, high hardness, and relatively lower cost. However, because of its low fracture toughness and low flexural strength, ballistic performance of alumina is lower when compared to SiC and B4C [4]. The properties of the alumina may be improved, either by introducing zirconia or by the manufacturing
Fabricación y caracterización de espumas de alúmina para aplicación en quemadores porosos radiantes
Herrera, A.M.;álvarez, O.;Escobar, J.;Moreno, V.;Oliveira Jr., A.A.M.;Hotza, D.;
Matéria (Rio de Janeiro) , 2012, DOI: 10.1590/S1517-70762012000200004
Abstract: in radiant porous burners, the heat source requires a solid porous matrix where the combustion reaction takes place, in which the heat transfer is performed more efficiently. this work is based on a study of the alumina suspension rheology, where parameters as viscosity and tixotropy were the guide to select the appropriate formulation for the ceramic foam fabrication by the replica method. the precursor polymeric foams presented higher porosity and permeability, due to their thin walls and 99% open cells. the highest mechanical strength under compression was obtained for the formulation with the highest solid fraction, under the same test conditions.
Relationship between Rheological Behaviour and Final Structure of and YSZ Foams Produced by Replica
S. Y. Gómez,O. A. Alvarez,J. A. Escobar,J. B. Rodrigues Neto,C. R. Rambo,D. Hotza
Advances in Materials Science and Engineering , 2012, DOI: 10.1155/2012/549508
Abstract: Using rheological parameters of ceramic suspensions, it is possible to taylor the structure of the ceramic foams produced by replica. This method consists in the impregnation of a polymeric flexible template (polyurethane foam) with a ceramic suspension (slurry) containing the appropriate additives, followed by burning out organic compounds and additives and sintering the ceramic structure. In this work, ceramic foams were produced by the replica method from Al2O3 and 3% Y2O3-ZrO2. Rheological parameters of the ceramic suspensions were investigated to improve the mechanical performance of final structures. Different types and quantities of raw materials were combined in order to select the formulations for ceramic foams. The parameters that have a significant influence on the process are the binder type and the amount of solids. Significant changes on the hysteresis area of the suspensions resulted in a lower density of macrodefects in the material. Likewise, when the shear rate viscosity is enhanced, the thickness of the struts increased proportionally. Lastly, when the hysteresis area magnitude and the ceramic thickness increased, the material with higher uniformity was internally densified, and the stress concentration of the internal defects was smoothed 1. Introduction Ceramic foams (CFs) are a particular subset of ceramic materials with cellular structure (interconnected net of solid struts), which have properties depending both on material and topology [1]. The importance of the CF resides in the properties acquired from the synergy of the porous structure and the ceramic material. Properties such as high surface area, high permeability, and low density, due to the high porosity (usually higher than 70%), in addition to the characteristics that are inherent to ceramic materials, allow applications such as catalytic supports [2], filters for metal smelting [3], filters for hot gases [4], porous burners [5], and bone implants [6]. Ceramic foams may be manufactured by the replication method or by different types of foaming techniques [7]. These methods have in common the use of ceramic suspensions, differing in how the structure is shaped. Replica, which is the most common manufacturing method, consists in impregnating a polymeric foam with a ceramic suspension followed by a thermal treatment in which the organic substances are decomposed and the remaining ceramic structure is sintered. Ceramic suspensions are generally required to present shear-thinning behaviour to be suitable for the process [8]. In agreement with data related to ceramic foams
Modelo matemático aplicado ao processo de extrus?o de argilas
Andrade, F. A.;Al-Qureshi, H. A.;Hotza, D.;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000200008
Abstract: the clays when mixed with water acquire the property known as plasticity, which plays a key role during processing. the techniques used to characterize the plasticity often do not show quantitative results that allow its application in mathematical models of the forming process of clays. this study aimed to develop a mathematical model for calculating the average pressure of extrusion, evaluating the plasticity through compression tests. then, the theoretical results of the extrusion pressure were compared to experimental results and a good agreement was found between them. it was possible to observe a correlation between effective stress of compression and extrusion pressure. for the extrusion process modeling equation, the effective stress obtained by compression test was a significant parameter that reveals the behavior of the clay during processing.
Otimiza??o da resistência mecanica de corpos ceramicos em fun??o de matérias-primas e restri??es de propriedades tecnológicas
Correia, S. L.;Hotza, D.;Segad?es, A. M.;
Ceramica , 2005, DOI: 10.1590/S0366-69132005000300010
Abstract: in the development and manufacture stages of floor and wall ceramic tiles, technological properties are basically determined by the combination of raw materials and processing conditions. when process parameters are kept constant, the technique of experiments with mixtures can be used to model those properties of such ceramics bodies. in the present study, ten formulations of three selected raw materials, namely a clay mixture, potash feldspar and quartz sand, were processed under conditions similar to those used in the ceramic tile industry, and characterized. from the experimental results, regression models were calculated, relating each technological property (bending strength, bulk density, water absorption, linear firing shrinkage, thermal expansion coefficient) with the proportions of raw materials. the regression models were then used to delimit the composition range suitable to produce porcelainized stoneware ceramic bodies (restrictions in the final properties), subjected to restrictions imposed by the manufacture process.
Optimising mechanical strength and bulk density of dry ceramic bodies through mixture design
Correia, S. L.,Hotza, D.,Segad?es, A. M.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2005,
Abstract: In industrial practice, it is desirable to be able to predict, in an expeditious way, what the effects of a change in raw materials or the proportions thereof might be in the various processing steps towards the final product. When the property of interest is basically determined by the combination (or mixture) of raw materials, an optimisation methodology specific to the design of mixture experiments can be successfully used. In the present study, dry bending strength and bulk density were selected as the properties to model, given the simplicity of their experimental determination and because they are frequently used as quality control parameter in the development and manufacture stages of floor and wall ceramic tiles. Ten formulations of three raw materials (a clay mixture, potash feldspar and quartz sand) were processed in the laboratory under fixed conditions, similar to those used in the ceramics industry, and characterised. The use of this methodology enabled the calculation of valid regression models (equations) relating dry bending strength and bulk density with the contents, in the starting mixture, of the particular raw materials used. En el trabajo industrial es deseable poder predecir de manera efectiva, los efectos que los cambios en las materias primas o en sus proporciones pueden ejercer sobre las variables del proceso y como estos afectan al producto final. Cuando la propiedad de interés depende preferentemente de la mezcla de las materias primas, una metodología específica de optimización para el dise o de los experimentos de mezclas puede ser empleada con éxito. En este trabajo, la resistencia mecánica en seco y la densidad se emplearon como los parámetros de control en el desarrollo y producción de azulejos cerámicos para pavimento y revestimiento. Diez formulaciones a partir de tres materias primas ( una mezcla de arcilla, feldespato potásico y arena de cuarzo) fueron procesadas en el laboratorio bajo condiciones fijas que son similares a las empleadas en la industria cerámica y finalmente se procedió a su caracterización. El empleo de esta metodología permite el cálculo de modelos de regresión (ecuaciones) relacionando la resistencia mecánica y la densidad con el contenido en la mezcla de partida de las materias primas.
Prototipagem rápida de pilhas a combustível de óxido sólido
Hotza, D.;
Matéria (Rio de Janeiro) , 2009, DOI: 10.1590/S1517-70762009000400003
Abstract: rapid prototyping (rp) technologies can automatically manufacture near-net shape parts with complicated geometry from computer-aided design (cad) data. the three dimensional part is built up by powder consolidation in layers ("additive" or "generative" process). for this reason, these techniques are often referred to as solid freeform fabrication or layered manufacturing. in general, a five-step approach of the product development is commonly applied: creating a cad model, converting the cad model into stl format, slicing the stl file into cross-sectional layers, fabrication of the product, and finally surface finishing of the product. rp techniques have many benefits over traditional methods for model generation, tools and even construction of production-quality parts. for instance, in contrast to "subtractive" processes (e.g., drilling, milling, grinding) the "additive"-rp methods allow fabrication of products with complex geometries like undercuts, internal cavities or overhangs that cannot be manufactured by other approaches. additive rp methods also offer the possibility to generate parts with an orientated internal pore structure. rp techniques can significantly shorten fabrication times of solid oxide fuel cells (sofc) with small operational expenditure and reduced product costs when applied properly. technologies such as selective laser sintering (sls), laminated object manufacturing (lom) and 3d printing (3dp) may be used for the fabrication of fuel cell prototypes particularly for planar configuration.
Artigo revis?o: colagem de folhas ceramicas
Hotza, Dachamir;
Ceramica , 1997, DOI: 10.1590/S0366-69131997000400002
Abstract: tape casting is a fabrication technique of thin ceramic sheets with large surface areas which are used mainly in the electronic industry as substrates and multilayered capacitors. the process consists essentially in forming a slurry and in casting it through a doctor blade on a generally moving surface. after drying, a flexible, resistant tape is produced which can be then sintered. in this review some theoretical concepts involved in the slurry formulation, as well as technical points of the tape casting process are discussed.
Uso de pronomes no texto "Sendbrief von Dolmetschen" de Martinho Lutero
Hotza, Dachamir;
Revista Brasileira de Linguística Aplicada , 2010, DOI: 10.1590/S1984-63982010000300007
Abstract: this article presents an analysis about the use of pronouns in the text "sendbrief von dolmetschen" ("open letter on translating") originally written by martin luther in germany in 1530. the objective is to try to identify the addressee(s) referred by luther from frequency and location of pronouns use in this text. regarding the question about justification by belief, there is clearly a debate of ideas between luther and his opponents ("i" against "them"). when the question about the intercession of saints is concerned, the text is directed to his followers (noticeable use of "we"). it is concluded that there is not a single addressee, but many of them, which are highlighted along the text.
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