Materials Science Forum Vol. 805

Abstract: The fabrication of conventional red clay ceramics products for civil construction, such as bricks and roofing tiles, normally uses other raw materials like sand, in addition to clay, as a way to condition the final ceramic properties. Quartzite residues, from ornamental stone processing in the northeast region of Brazil, could be used as possible conditioner material for clay body in a ceramic industry owing to its similar characteristics to common sand. In the present work, complementing a recent publication on the same materials, a quartzite residue was characterized and its potential as a red clay ceramic addition was evaluated for different composition up to 40 wt%. The results indicated economical advantages in association with some technical benefits.

Abstract: The present study aims to examine the differences obtained in the technological properties of a ceramic formulation for tile after firing in two different environments, laboratory furnace and industrial furnace. For this, the ceramic formulation used in the production of semi-porous ceramic tile was characterized. Chemical, mineralogical and thermal analyses in the ceramic formulation were performed. The specimens were obtained by compacting and fired at maximum temperature of 1140 o C in laboratory and industrial furnaces. The technological tests performed were linear shrinkage, water absorption, bulk density and mechanical strength. Microstructure was assessed through X-ray diffraction analysis and scanning electron microscopy. The results showed that the different furnaces provided significant differences in the specimens analyzed such as higher mechanical strength and lower water absorption in samples fired in laboratory furnace, for example.

Abstract: The porcelain materials are composed of crystalline particles immersed in a vitreous matrix. This study has aimed to calculate the porcelain’s vitreous phase viscosity through the Vogel-Fucher-Tamman equation, VFT, to obtain eventually curved coating. We’ve formulated a standard mass, and over it we’ve added the proportions of 4, 8 and 15% of sodium feldspar, main former of the liquid phase, in order to verify its influence over the viscosity at the final vitreous phase. Concerning the standard mass, the addition of 4 and 8% has provoked a reduction of viscosity, while the addition of 15% resulted in a rise of viscosity. Because porcelain does not present a homogenous vitreous phase and crystalline particles, the VFT equation may have given us relative viscosity values. However, these values are coherent with glasses containing sodium, if one assumes that the crystalline phases have no influence over the system and that the vitreous phase has a homogenous composition.

Abstract: This study aims to characterize a new type of cement, produced from the mixture of common Portland cements, which could be used as an option in the cementing of oil wells. To enable this study a linear programming method was used for the composition of the new cement, then, characterization tests were performed through particle size analysis by laser diffraction, chemical analysis by EDX, thermogravimetric analysis, X-ray diffraction, setting time, compressive strength. The results allowed the conclusion that the new formulated cement presented low C₃A content, time setting superior to the Portland Cement for Oil Well, thermal stability up to 500 °C, low hydration kinetics and content of the main components coherent to the ABNT specifications.

Abstract: Selenium is a rare element in nature. It is used in the food, pharmaceutical, and glass industries. In commercial glasses, selenium is the element responsible for most of the pink or light red color, but its effect is primarily dependent on the oxidation state of the element in the glassy matrix. Besides, selenium is highly volatile, and as high as 80 wt% may be lost in the furnace during the industrial glass elaboration. The sol–gel method yields synthesized materials of high purity and homogeneity, and uses low processing temperatures. Samples of silica gels were obtained by sol-gel method, incorporating precursors of selenium, with the main objective of reducing selenium losses during its heating. The results of optical absorption, XRD and thermal analysis (TGA, DSC) of the gels are presented and discussed.

Abstract: The aim of this study was to obtain 4.5%mol Y₂O₃-doped ZrO₂ dense with submicrometer grain size and studying the effects of using oxygen flow during calcination in the electrical properties of bodies sintered. The powders were synthesized by the Pechini method. After synthesis, the resins were dried and the calcinations were performed in air and in oxygen flow at 600°C for 2 h. The powders were pressed with 1600 MPa and sintered by Two Step Sintering (TSS) at 1500°C / 5 min and 1200°C, 1300oC, 1400°C, remaining at these temperatures for 2 and 10 hours. The sinterized samples were characterized by X-ray diffraction, apparent density, scanning electron microscopy and impedance spectroscopy. The apparent densities were greater than 94% for all conditions of calcination and sintering. The value of the activation energy was 0.7eV for the grain and 0.9 eV for the grain boundaries.

Abstract: The objective of this study was to evaluate the microstructure of a ceramic based on yttria stabilized zirconia (Y-TZP) in blasting with aluminum oxide and its effect on the sintering. 25 pre-sintered Y-TZP blocks were obtained. Ten samples were blasted with alumina, and then all samples were sintered and divided into the groups: Control-no treatment; alumina G1-blasted with alumina and sintered; alumina and Rocatec G1-blasted, sintered, and Rocatec; alumina G2-sintered, alumina blasting; alumina and Rocatec G2-sintering, alumina blasting, and Rocatec. The samples were evaluated by a scanning electron microscopy. The qualitative analysis showed that the treated samples had an increase in the surface texture and that group 1– alumina and Rocatec– presented the silica incorporation to be regular and homogeneous. It was concluded that the treatment of pre-sintered surfaces is a good alternative in the bonding strength between the Y-TZP and the resin cements.

Abstract: Natural kaolinite clay collected in the State of Sergipe (northeast Brazil) was used as an adsorbent for the ions Pb²⁺, Cd²⁺, and Cu²⁺ present in aqueous solution. Adsorption equilibrium was reached rapidly, enabling use of a contact time of 30 minutes, and maximum adsorption was achieved at pH 7.0. For all three metal ions, the adsorption data could be fitted using the Langmuir isotherm and the adsorption process obeyed a pseudo-second order kinetic model.

Abstract: The elephant grass (Pennicetum purpureum) is traditionally used both as fresh feedstock for cattle and, dried, as fuel for ceramic production in Campos dos Goytacazes, Brazil. In the present work the bottom ash generated after dry grass incineration in a ceramic furnace was characterized for a possible addition into red clay ceramics. The characterization comprised the ash morphology by laser microscopy, scanning electron microscopy coupled with EDS and thermal behavior by thermogravimetry as well as differential thermal analysis. These results indicated that the elephant grass ash could be added into a clay body not only as a fluxing agent but also to improve the particles compaction before firing.

Abstract: Green sand molds are used in metal casting process. However, after heating, activated bentonite present in green sand loses the binding properties, and part of the foundry sand has to be discarded from the process. The ABNT NBR 15.984/2011 standard establishes the management of waste foundry sand (WFS) avoiding disposal in landfills. The objective of this work was to investigate the possibility of reusing the WFS from the study of its interaction with sodium silicate binder. Studies with silica sand and new green sand were performed in order to compare the results obtained with the WFS. The characterization of the samples was performed by measuring compressive strength, by X-ray diffraction, by optical microscopy and by scanning electron microscopy. The results showed that there is an interaction of the sodium silicate with the WFS as well as with the silica sand and green sand.