Results 1 - 10 of 281
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[en] This study analyses, first, the influence of sodium carbonate content on the behaviour of the ceramic tile body composition during the different manufacturing process stages (preparation of the suspension, pressing, and firing), as well as on unfired tile mechanical strength. It has been verified that sodium carbonate can be used as a binder in ceramic tile compositions, since small percentages considerably enhance dry tile mechanical strength. It has furthermore been determined that for each composition there is an optimum addition content, with high increased mechanical strength (up to 70%), without this noticeably affecting the rheological behaviour of the suspension to be spray dried. These results are currently being patented (patent application P200930148). Once the binding effect of sodium carbonate had been verified, it was sought to establish its action mechanism. For this purpose, drops of mixtures of a standard ceramic composition and increasing quantities of sodium carbonate were prepared. The drops were rapidly dried and the granules were characterised by scanning electron microscopy. It was thus verified that the most likely sodium carbonate action mechanism was formation of solid bridges by crystallisation. (Author)
[en] Structural features that enhance Li mobility in fast ion conductors with perovskite (Li3xLa2/3-xTiO3 series) and Nasicon structure (Li1+xTi2-xAlx (PO4)3 series) have been investigated. From the analysis of quadrupolar interactions, the local symmetry and exchange processes between structural sites occupied by lithium have been deduced to investigate local motions of lithium in conduction paths of analyzed compounds. The study of spin-lattice (T1) and spin-spin (T2) relaxation times made possible the analysis of the temperature dependence of Li residence times at structural sites. The comparison of these values with those deduced from conductivity (ac and dc-measurements) allowed the study of Li-motion mechanisms. The onset of long range motions requires the analysis of low frequency measurements (T2 relaxation and dc-conductivity). The non- Arrhenius behaviour, often observed in fast ion conductors, has been ascribed to order/disorder transitions. At increasing temperatures, Li motions become less correlated, producing the decrement of activation energy. In analyzed compounds, a direct measurement of diffusion coefficients has been obtained from NMR experiments performed with the pulse field gradient (PFG) technique. Finally, it is emphasized the importance of the vacancy percolation in conductivity processes. (Author)
[en] We have synthesized NiFe2O4 (φ ∼6 nm) and Fe3O4 (φ∼30 nm) magnetic nanoparticles by solvothermal synthesis; furthermore the Fe3O4 nanoparticles have been coated with a SiO2 shell of approximately 5 nm of thickness by the Stober method. In the study of the dielectric properties as a function of the frequency, temperature and applied magnetic field, we observe a magnetocapacitive behavior (MC) at room temperature and under a moderate magnetic field (H=0.5T), that is specially important in the case of the Fe3O4, nanoparticles (MC 6%). On the other hand, the NiFe2O4 and Fe3O4atSiO2 samples present smaller magnetocapacitive effects: MC∼ 2% y MC∼ 1%, respectively. These MC values, that are higher than those reported in the literature for other related magnetic nanoparticles, corroborate the theoretical model proposed by Catalan in which the combination of Maxwell-Wagner effects and magnetoresistance promote the appearance of stronger magnetocapacitive effects. (Author)
[en] The obtaining of mechanical properties as elastic modulus and hardness of enamel and dentin has been an important topic of study in material science. Due to the small size of the samples, nano indentation test becomes an ideal technique for determining the mechanical properties of these structures. Despite numerous studies, there is no agreement on the values of elastic modulus and hardness. The present study analyzes the mechanical properties variability of enamel and dentin for two different bovine teeth by a conventional nano indentation test. Also, this work compares the elastic modulus and hardness by two different nano indentation techniques: conventional method (CM) and continuous stiffness measurement method (CSM). Two bovine incisor teeth were extracted, cleaned and stored at 4 degree centigrade immersed in distilled water during one month. They were transversally sectioned and the crowns were cross-sectioned into 2 mm thick slices, obtaining 6 sections from each tooth. All sections were polished and kept fully hydrated in artificial saliva at room temperature for 24 hours. On each section, CT and CSM nano indentation tests were carried out to obtain the elastic modulus and hardness of enamel and dentin. Both elastic modulus and hardness decrease as indentation load increases. However differences on mechanical properties values have been obtained depending of the nano indentation technique applied. (Author)
[en] The influence of varying proportions of different types of fly ash (used in place of feldspar) and different sintering temperatures on the sintered properties of ceramic tile bodies was evaluated. The results indicated that sintering ceramic tiles with a high fly ash content at a high temperature caused a decrease in the properties because of bloating. The ceramic samples containing a higher amount of fly ash that were sintered at low temperature exhibited lower water absorption, larger shrinkage and strength because of the densification observed also in microstructural investigation. (Author) 25 refs.
[en] The present work investigates the possibility of adopting a new kinematics at the industrial polishing lines of porcelain stoneware tile. An alternative motion of the transverse oscillation of the polishing heads is proposed, in which no radical changes in the industries facilities are required. The basic idea is to replace the purely sinus motion of the polishing heads by a rather trapezoid wavelike motion. In theory this could be achieved simply by adopting regular delays at the transverse oscillation motion. Consequences of this alternative kinematics were quantitatively analyzed considering the spatial homogeneity of polishing expected for tiles. Such homogeneity was represented by the coefficient of variation of the distribution of polishing time over the surface, which was in turn determined by means of computational simulations, taking into account the effect of multiple polishing heads. (Author) 10 refs.
[en] The present work studies the principal variables of control in the manufacturing process of construction pieces of the Metropolitan Area of San Jose de Cucuta by extrusion and pressing techniques for its forming. The investigation was taken out using clayey samples of the two principal geological formations of the region where the raw material is taken for processing at an industrial level. The clayey samples milling was made by dry means as well as by moisture means and its particle size was measured. Subsequently the forming process was taken over by using an hydraulic press and extruder with vacuum system , both equipment s at laboratory scale, the pieces shaped were dry and firing between 980 degree centigrade and 1180 degree centigrade at the end of the process the tests were made to determine water absorption, contraction and mass loss at the pieces firing. The study results left to see that the extrusion technique allowed a faster vitrification for the region's clay in comparing with the pressing technique, the contractions of drying and firing are less marked on the pressing techniques with standard deviations much lower than in extrusion. (Author) 13 refs.
[en] The results of a study carried out in the shaping of a clay located at Zulia (North of Santander, Colombia) and the influence of wet milling on the structural and mechanical performance are presented. The study was carried out by shaping the material by extrusion as this is the technique most used in the ceramic industry of the region and subsequent sintering treatment between 900°C to 1200°C. For the development of the analyzes, the specimens were formed with two pastes prepared by dry and wet milling. The structural behavior, its mechanical resistance and technological aspects such as contraction and densification, among others, were evaluated. The results indicate improvements in structural and mechanical properties decreases to 18.8% in porosity and increases up to 72.1% in resistance to external loads increasing the commercial value for coating products and masonry. The results showed that the wet milling can be used to improve the extrusion process, the technological characteristics of the materials and the commercial value of the same, an important aspect in regional companies.
[es]Se presentan los resultados de un estudio realizado en el conformado de una arcilla del Zulia (Norte de Santander, Colombia) y la influencia de la molienda húmeda en el comportamiento estructural y mecánico. El estudio se llevó a cabo conformando el material por extrusión por ser esta la técnica más utilizada en la industria cerámica de la región y posterior tratamiento de sinterización entre 900°C hasta 1200°C. Para el desarrollo de los análisis se conformaron probetas con dos pastas preparadas por molienda en seco y en húmedo. Se evaluó el comportamiento estructural, resistencia mecánica y aspectos tecnológicos como contracción y densificación, entre otros. Los resultados obtenidos indican mejoras en propiedades estructurales y mecánicas con descensos hasta del 18,8% en la porosidad e incrementos hasta de un 72,1% en resistencia a cargas externas, incrementando el valor comercial para productos de revestimiento y mampostería. Se evidenció que la molienda en húmedo puede ser usada para mejorar el proceso de extrusión, las características tecnológicas de los materiales y el valor comercial de lo mismos, aspecto importante en las empresas regionales.
[en] This work is concerned to study the sintering rate and mass transport mechanism in ceramic engobes. Specimens of engobes were prepared from a determined formulation by slip casting. Sintering was carried in two steps: (i) at constant heating rate of 7.5 degree centigrade/min and (ii) with an isothermal treatment, during 120 min. According to the dilatometric curves obtained with the engobe sintering during isothermal treatment, the dominant sintering mechanism and the rate of reactions, between the 775 and 975 degree centigrade, were determined. The results showed that between 775 and 800 degree centigrade, the sintering rate can be described by ln[d(ΔL/L0)/dt] = -5.64 + 1.77.E10-3T. At higher temperatures, from 850 to 975 degree centigrade, this rate can be expressed by ln[d(ΔL/L0)/ dt] = -30.73 + 3.E10-2T. The dominant transport mass mechanisms were the grain rearrangement, solution-precipitation and grain boundaries reaction. (Author)
[en] Fuel cells generate electricity and heat during electrochemical reaction which happens between the oxygen and hydrogen to form the water. Fuel cell technology is a promising way to provide energy for rural areas where there is no access to the public grid or where there is a huge cost of wiring and transferring electricity. In addition, applications with essential secure electrical energy requirement such as uninterruptible power supplies (UPS), power generation stations and distributed systems can employ fuel cells as their source of energy. The current paper includes a comparative study of basic design, working principle, applications, advantages and disadvantages of various technologies available for fuel cells. In addition, techno-economic features of hydrogen fuel cell vehicles (FCV) and internal combustion engine vehicles (ICEV) are compared. The results indicate that fuel cell systems have simple design, high reliability, noiseless operation, high efficiency and less environmental impact. The aim of this paper is to serve as a convenient reference for fuel cell power generation reviews. (Author)