FRSN - Ciencia y Tecnología - Centro DEYTEMA

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Author: search.filters.author.Brandaleze, ElenaSubject: search.filters.subject.dilatometry

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    Structural evolution of an Al2O3-MgO•Al2O3 castable in the range 1000-1600°C
    (Mind Authors Inc., 2020-11-10) Benavidez, Edgardo; Brandaleze, Elena
    Thermal and structural characteristics of an alumina-spinel castable (containing 2.5 wt.% CaO) was studied. The specimens were cast (8.0 wt.% water), cured in air at ambient temperature (48 h), then dried at 100°C (24 h) and prefiring at 500°C (3 h). Thermal behavior was analyzed by dilatometries at constant heating rate (5°C/min) up to 1600°C, and at constant temperature (range: 1000-1500°C). Crystallographic phases were determined by XRD and microstructures were analyzed by SEM/EDS. Specimens heat treated at 1000°C and 1200°C showed Al2O3 (A) and MgAl2O4 (MA) as main phases. Between 1200-1300°C, the 2Al2O3∙CaO (CA2) formation is promoted. Calcium hexaluminate 6Al2O3∙CaO (CA6) is detected from 1400°C. The presence of CA6 increases at 1500°C and 1600°C. From dilatometric curves, alternating expansion contraction zones were observed in the range 1000-1600°C. This behavior is associated to (i) the CA2 and CA6 formation, and (ii) the sintering/densification of ceramic grains with probable liquid phase assistance. Thus, considering the temperature profile, generated in service, through this material, both the formation of CA2 and CA6 and the sintering evolution during the first hours, lead to volumetric contractions and expansions in different zones. These volumetric changes generate mechanical stresses that can cause faults in the material.
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    Thermal analysis techniques applied to study wear mechanisms of black refractories used in the steel continuous casting process
    (Springer, 2019-06-01) Brandaleze, Elena; Benavidez, Edgardo
    In this paper, the results are correlated with information obtained through conventional techniques such as optical microscopy (OM) and scanning electron microscopy (SEM) including EDS analysis and EBSD, that are used to characterize different structural aspects on the refractory material and of the interface with the moud flux adhered on the nozzle. The thermodynamic simulation of the corrosion also contribute with relevant information associated to the main goal of this paper. By the thermochemical simulations, the chemical reactions in the system between nozzle and mold flux are justified. All this information is useful to stablish the coorrosion mechanisms and to predict the dynamic process conditions that cause the damage in the refractory material, in order to improve the nozzle performance.
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    Analysis of DTA and dilatometric data used to study the behaviour of a mould flux
    (2019-06-01) Benavidez, Edgardo; Santini, Leandro; Brandaleze, Elena
    In the present work a casting powder containing ≈ 36 wt% SiO2, ≈ 31 wt% CaO, 13 wt% Na2O, and 10 wt% CaF2, was used as starting material. A mass of 10 g of the mould powder was placed in a graphite crucible and melted at 1300°C. After 15 minutes at this temperature, the melt was poured onto a stainless steel inclined plate. By this method, solid glass layers were produced, which were sectioned into bars 10-15 mm in length to be used in dilatometric tests. Some of these bars were ground to powder to perform DTA runs. Both tests (DTA and dilatometry) were carried out at different heating rates: 5, 10 and 15 ºC/min, in air atmosphere, up to 900°C. Data of glass transition temperature (Tg), and crystallization peak temperature (Tc) were obtained from DTA and dilatometric runs. From these data, several non-isothermal methods based on Kissinger, Augis-Bennet, Ozawa, and Cheng models, were used to study the crystallization kinetics. Based on these models, the activation energy of crystallization (E), the frequency factor () and the crystallization rate constant (k) were calculated. A subsequent study was followed to determine the Avrami exponent and the crystallized fraction. The crystallographic phases were determined by XRD and the microstructure of samples, treated between 400-900 ºC, was observed by optical and electronic microscopy.