Materials Science Forum Vols. 498-499

Abstract: 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.

Abstract: The Bi-Sr-Ca-Cu-O system has been one of the most studied superconducting ceramic materials for industry applications. The most of the studies with this aim are on silver/ceramic composites, due to the benefits and great compatibility of this metal with the oxide. In this paper we describe a systematic and comparative study on Ag/BSCCO composite, made by the citrate route, in which the ceramic pellets are sintered in the presence of silver powder using several proportions and having several granulations. It was observed that the introduction of fine (0.5 and 2 μm) silver powder in the proportions of 5 wt. % always implies in a better critical current density compared to the no silver pellet. According to the results, the silver powder in excess of 5 wt.% may not promote best electrical properties, depending on the size of the silver particles.

Abstract: The alkaline activation of Portland cement based materials, ground granulated blast furnace slag and pozzolans has been accomplished with success since the decade of 40, in several countries. The practicability of the use of the alkalis opens new opportunities for the production of special binders with properties different from those presented by the ordinary Portland cement. Besides the chemical composition, the mechanical strength of these alkali-activated materials depends a lot on the reactivity of the raw material, property that is influenced mainly by the specific surface area and crystalline degree of the raw material. Thus, an experimental program was carried out aiming at evaluating the influence of these variables in the compressive strength, at 3, 7 and 28 days of age, for mortars manufactured using alkaline activation of kaolinitic soils. The results have shown that the most suitable combination, in terms of mechanical strength and economy of energy, was the mortar manufactured with soil receiving a ½ hour grinding time and calcined at 650oC during four hours.

Abstract: Portland cement is by far the most important binding material used in both civil construction and oil well cementing. However, especially in the latter application, its brittle nature impairs its ability to withstand dimensional changes due to thermal gradients (RT to approximately 200°C), typical of heavy-oil recovery operations. This often results in extensive cracking of the cement sheath and debonding of the cement-casing interface, which leads to loss of zonal isolation, gas migration and production of water and oil through the well annular. Portland-Polyurethane composites have been formulated and tested in an attempt to improve the deformation ability of the cement during thermal cycles without affecting the pumping behavior or high-temperature resistance of the material. Preliminary results confirmed that the addition of small contents of polyurethane considerably improved the plasticity of the cement in approximately 50% as well as decreased porosity and permeability. No significant changes were observed in the rheological behavior of the composite slurries with respect to plain Portland cement.

Abstract: The tensile strength of Portland cement may be increased by additional reinforcement. This is usually accomplished by means of steel rods, fibers or particles, which are mixed to the slurry. In an attempt of increasing toughness and tensile strength of hardened cement pastes, the present work describes the behavior of composites consisting of Portland reinforced by natural polymer particles for oil well cementing. The main purpose of the study was to select plastic and environmentally friendly powdered materials capable of filling the typical porosity developed on hardened Portland cement. Preliminary results suggested that the tensile strength of plain Portland hardened slurries could be increased by as much as 40% by adding 10% of reinforcement.

Abstract: The densification of carbon fiber substrates by chemical vapor deposition (CVD) is a process quite used since the fifties, for manufacturing carbon reinforced with carbon fiber composites (CRCF). The process is based in thermal decomposition of a gas which contains carbon in its molecules and the resulting pyrolytic carbon is continually deposited onto de carbon fiber substrate. For this experiment the substrate material was made of carbon fiber felt. The deposition was performed by isothermal process at atmospheric pressure and at temperature of 1050 oC. Methane (CH4) gas was used as carbon bearer and nitrogen (N2) as the carrier gas. Different volumetric ratio of N2 and CH4 (N2:CH4) were used in order to get an optimum densification of the substrate. Optical and electron scanning microscopy and density measurements were used to characterize the impregnated material. An increase in ratio of N2 and CH4 increase the overall deposition for the same time interval.

Abstract: The recycling of industrial residues has being intensified all over the world, mainly due to the increase of the impact to the environment, and the growing volume of solid residues that put in risk the public health and degrade the natural resources. So, the aim of this work is to study the potentiality of the residue from kaolin industry, as ceramic raw material to produce porcelanate gres. A composition was formulated, mixed and forming by pressing (from 30 MPa to 50 MPa). After, it was sinterized at temperatures of 1180°C, 1200°C, 1220°C and 1240°C. The samples were submitted to physical and mechanical tests and characterized by X-ray diffraction and scanning electron microscopy. The preliminary results from physical and mechanical properties showed that the residue can be used to produce porcelanate gres according to Brasilian Norms (NBR 13818), at temperatures of 1220°C and 1240°C.

Abstract: The main goal of this work is to demonstrate that the use of recycled material originated from SiC ceramics is viable. These ceramics were produced by commercial starch consolidation process. Before calcination stage, surplus of these materials always appears. This surplus is rich in SiC and starch. Samples were made by material previously milled in automatic mortar and sieved (100 Tyler). Later, 10% of distilled water was added to the material and the mixture was pressed at 40 MPa. In order to characterize the ceramic, three point flexural test were made, according to the ASTM C1161/94 norm. The results were analyzed by Weibull statistical method. Apparent density and porosity measures also were made, according to ASTM C20/87 norm. A verification of the surface was made in the fracture area by the depth from focus method and SEM image analysis. The results showed that the recycling process is fully viable, being a good economic option and reduce possible pollutant effect to the environment.

Abstract: In the development and manufacture stages of floor and wall ceramic tiles, firing shrinkage is basically determined by the combination of raw materials and frequently used as quality control parameters. This configures the ideal scenario to apply the techniques of experiments design, often used in various other areas, to model those properties of such ceramics bodies. In this work, ten formulations of three different raw materials, namely a clay mixture, potash feldspar and quartz (triaxial compositions) were selected and processed under conditions similar to those used in the ceramics industry. With the experimental results, a regression model was calculated, relating linear shrinkage with composition. After statistical analysis and verification experiments, the significance and validity of the model was confirmed. The regression model can then be used to select the best combination of those three raw materials to produce a ceramic body with specified properties.

Abstract: This article presents a method to optimize the formulation of ceramic masses for coatings using the statistical design of experiments. The project of simplex mixtures in pseudocomponents considered six control factors (wt. %): talc, quartz, limestone, phyllite, dolomite and clay and three response variables: linear retraction, bending resistance and water absorption. The proposed method was implemented in the stages: (1) identification of the problem, (2) planning and execution of the experiments and (3) optimization and discussion of the results. The optimization method is defined through the simulation, imposing the restrictions that each response demands.