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[en] Refractory materials are widely used in various industrial fields due to their outstanding properties and performance in aggressive environments. However, although creep resistance is one of the most important properties for the selection of these materials, few researches were carried out focused on the fundamentals and technological understanding of their performance at high temperatures. In this context, this work addresses: 1) the creep mechanisms, 2) the mathematical models proposed for the analysis and to forecast the creep deformation at high temperature, 3) technical procedures and experimental testing, and 4) a critical analysis of some basic and practical aspects considering the literature available on this issue. Based on the collected information, mathematical models (such as the Projection concept) were considered as a powerful tool for the prediction of the refractories creep behavior, helping to identify the main creep mechanisms in these materials and to induce the development of optimized compositions able to attend the end-users requirements. (Author)
[en] This paper reports the effects of refractory Nb metal on the structural heterogeneity of a CuZr metallic glass. Cu50Zr50 metallic glass was taken as model material, and different quantities of Nb element (5 at% and 10 at%) was considered to comparatively study heterogeneity. The as-spun metallic glassy ribbons were examined with x-ray diffraction, differential scanning calorimetry and dynamic mechanical analysis. The results indicate that Nb element can decrease the glass-forming ability but enhance the glass transition temperature and thermal stability. For heterogeneity, the addition of 5 at% of Nb element will weaken the heterogeneity and the addition of 10 at% of Nb element will improve the heterogeneity. This work also disclosed that the time window from the onset temperature to the peak temperature of β relaxation for (Cu0.5Zr0.5)90Nb10 is larger than that for (Cu0.5Zr0.5)95Nb5, suggesting that Nb element may suppress the local motion from a smaller region to a larger region in the metallic glass. (paper)
[en] Highlights: • Four types of new refractory HEAs are designed. • These HEAs mainly consist of a simple BCC solid solution. • The formation mechanism of β-Ti is proposed. • Oxidation resistance is improved by adding Ti and Si, but reduced by adding V. -- Abstract: High-entropy alloys (HEAs) are defined as the alloys composed of at least five principal elements in equimolar or near equimolar ratios, which can facilitate the formation of simple solid solutions during solidification. Recent studies suggested that the refractory HEAs exhibited great promise for high temperature structural materials. However, their oxidation behavior had received little attention. In the present study, Cr, Al and Si elements were added to improve the oxidation resistance, four types of new refractory HEAs were designed and synthesized, including NbCrMoTiAl0.5 (H-Ti), NbCrMoVAl0.5 (H-V), NbCrMoTiVAl0.5 (H-TiV) and NbCrMoTiVAl0.5Si0.3 (H-TiVSi0.3). Their microstructures and oxidation behavior were studied. As expected, these refractory HEAs mainly consist of a simple body-centred cubic (BCC) refractory metal solid solution (RMss) due to the high mixing entropy effect. Solidification process and thermodynamic analysis were investigated to explain the formation mechanism of their microstructures. For all the refractory HEAs, the oxidation kinetics at 1300 °C follows a linear behavior. The oxidation resistance of the HEAs is significantly improved with Ti and Si addition, but reduced with V addition
[en] Magnesium-chrome refractory have been used with success at high temperatures in different metallurgist processes, such as iron and steel, cement industry and non ferrous pyro metallurgist processes. In particular in the smelting, in the processes of reforming of raffinate of copper. Those materials have good characteristics in relation with the use and the requirements of heat shock resistance. However, they represent an important problem for the environment. The aim of this research was to investigate the interactions between the slag generated in the converter Peirce-Smith in copper and Magnesium-chrome refractory bricks. The infiltration events and chemical attacks in the refractory material caused by the slag formed during the copper conversion process have been studied by means of the development of the different laboratory tests at temperatures of until 1300 Celsius degrade
[en] Activated sintering of high-refractory non-oxide compounds, under the influence of various physical and chemical factors on the shrinkage kinetics, was described. The sintering process was presented as a chemical reaction, but the degree of activation was determined quantitatively taking into account the change in temperature adequate to the maximum shrinkage rate during heating at a constant rate or the change in the order of reaction during isothermal sintering. It was found out that activation characterized the initial stage and that it was caused either by changes in dispersion of powders, or by the heating rate up to the isothermal temperature, or by additives, or by the influence of the atmosphere or the vacuum. The influence of ultrasonic vibrations on the shrinkage kinetics was examined. In the initial sintering stage ultrasonic vibrations activate the process, but during a long-lasting influence, they disactivate it, causing decay of the structure
[en] Magnesium-chrome refractory have been used with success at high temperatures in different metallurgist processes, such as iron and steel, cement industry and non ferrous pyro metallurgist processes. In particular in the smelting, in the processes of reforming of raffinate of copper. Those materials have good characteristics in relation with the use and the requirements of heat shock resistance. However, they represent an important problem for the environment. The aim of this research was to investigate the interactions between the slag generated in the converter Peirce-Smith in copper and Magnesium-chrome refractory bricks. The infiltration events and chemical attacks in the refractory material caused by the slag formed during the copper conversion process have been studied by means of the development of the different laboratory tests at temperatures of until 1300 celsius degrade.
[en] We derive analytical formulas for the firing rate of integrate-and-fire neurons endowed with realistic synaptic dynamics. In particular, we include the possibility of multiple synaptic inputs as well as the effect of an absolute refractory period into the description. The latter affects the firing rate through its interaction with the synaptic dynamics.
[en] The Al2O3-MgO-C refractories, of great technological interest for its excellent properties, are used in a wide range of furnace lining applications such as iron and steel. These materials are composed of various grades of alumina, magnesia, graphite and metallic additives, which are added to a resin that acts as binder. The variety of components oxides, metals and polymers makes the study of these refractories a complex task. Considering this diversity to characterize these materials has been used several techniques: X-ray fluorescence, plasma emission spectroscopy and gravimetry, complemented by X-ray diffraction, differential thermal analysis and thermogravimetry and reflected light optical microscopy. This paper provides a methodology for chemical and mineralogical characterization of these refractory materials. The results of chemical analysis together with the qualitative information on the crystalline phases and the raw materials with which they are formulated have been used to quantify the composition of the refractories using rational analysis. The data obtained by the different techniques validate the methodology developed. (Author) 23 refs.