Artículos y presentaciones en Congresos
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- Contribucion a revistaAcceso AbiertoDense mullite–zirconia–zirconium titanateceramiccomposites by reactionsintering(2015) Rendtorff Birrer, Nicolás Maximiliano; Gómez, Sofía; Gauna, Matías; Conconi, María Susana; Suárez, Gustavo; Aglietti, EstebanMaterials from the Al2O3–SiO2–ZrO2and the Al2O3–SiO2–ZrO2–TiO2systems have several high temperature applications because they present the good refractoriness, chemical inertness, adequate mechanical and thermo-mechanical behaviors with a relatively good cost: performance ratio. In this work stoichiometric (3:2:1) molar incompatible mixtures of alumina (Al2O3), zircon (ZrSiO4) and titania (TiO2) were slip casted and sintered in a 1300–1500°C temperature range in order to obtain mullite (3Al2O3·2SiO2), zirconia (ZrO2) and zirconium titanate (ZrTiO4) dense triple ceramic composite. Both sintering and reaction occurred after the thermal treatments. Reaction progress and densification evolutions were established. Dense Triplex composite materials were achieved after 1500°C treatments. The reaction-sintering was followed by XRD, TG–DTA, and dilatometry. Densification started at 1100°C and the chemical reactions only started above 1300°C. Aluminum titanate (Al2TiO5) was found to be an intermediate of the reaction after 1400°C treatments. Materials treated below 1300°C presented a partial densification of the unreacted starting powders. Resulting ceramic materials were characterized. The crystalline phases were evaluated, as well as the texture properties. The achieved microstructure consisted in interlocked multiphase ceramic with zirconia (monoclinic) grains. The achieved Hv andKICreached 9GPa and 4.3MPam1/2respectively. The dense and interlocked ceramic microstructure and relative high mechanical properties of the developed material encourages several high temperature applications. Finally it can be pointed out that after 1500°C treatments some detrimental grain growth was observed.
- ArtículoAcceso AbiertoIntensity of sulfonitric treatment on multiwall carbon nanotubes(2017) Gómez, Sofía; Rendtorff Birrer, Nicolás Maximiliano; Aglietti, Esteban; Sakka, Yoshio; Suárez, GustavoWe present a study of sulfonitric treatment and its effect on MWCNTs at different temperatures (90, 110, 130 and 150°C) using DRX, XPS, FTIR, Raman spectroscopy, TEM and zeta potential. It was found that oxidation starts with the C-C and C-H bonds generating different oxidized groups from alcohol to carboxylic acid, following a sequential oxidation. Given that heterocoagulation needs a maximum zeta potential gap between the ceramic and the MWCNT surface and it significantly exist a risk of manipulate acids at high temperature it is recommended to use acid treatment of CNT at 110 °C for generating ceramic composites by heterocoagulation.
- ArtículoAcceso AbiertoMonoclinic - tetragonal zirconia quantification of commercial nanopowder mixtures by XRD and DTA(University of Chemistry and Technology (Prague), 2015) Gauna, Matías; Conconi, María Susana; Gómez, Sofía; Suárez, Gustavo; Aglietti, Esteban; Rendtorff Birrer, Nicolás MaximilianoThe phase quantification in ceramic nanopowders presents technological interest for studying and design purposes. Especially in zirconia ceramics where the mechanical and transport properties are strongly affected by the crystalline composition. In this work we present the comparison XRD based methods and differential thermal analysis methods for phase characterization and specially quantification. A complete series of commercial nanopowders mixtures (D50 ≈ 0.1 μm) of monoclinic zirconia (m) and partially stabilized zirconia (t: 3 % yttrium oxide) was studied. X ray diffraction (XRD) was performed and the relation m:t was quantified by the so called Garvie-Nicholson (G-N), Toraya and Rietveld method. A complete reversible DTA analysis was carried out to the same mixtures. Both m-t and t-m martensitic thermal transformations were observed and pondered for the m-ZrO2 containing samples. The graphical integration was performed and employed for the construction of a calibration curve in the studied composition range. The results were compared, the Toraya method presented equivalent results in comparison with the Rietveld method. The G-N method presented appreciable differences (≈ 10 %). To assume a direct proportion of the m-ZrO2 content with the peak area resulted in important errors but if a simple calibration curve is constructed, the DTA method presents accurate quantification with results comparable to the best XRD based quantification.
- ArtículoAcceso AbiertoRelation between mechanical and textural properties of dense materials of tetragonal and cubic zirconia(2016) Gómez, Sofía; Suárez, Gustavo; Rendtorff Birrer, Nicolás Maximiliano; Aglietti, EstebanIn the current paper we present a study of the sinterability of two zirconia (ZrO2) nanopowders with different content of yttrium oxide (Y2O3) 3 and 8 % tetragonal and cubic zirconia, respectively. After sintering between 900-1500ºC, the samples were characterized in terms of their density and porosity using Archimedes technique. Their grain size was evaluated using scanning electron microscope (SEM). Vickers hardness and fracture toughness (KIC) were measured by the indentation method. The results showed that pores are almost eliminated at sintering temperatures higher than 1400ºC and grain size is larger due to the agglomerates formed as a result of grain growth. Vickers hardness evaluated at 1400ºC sintering temperature is greater than that obtained at 1500ºC due to the grain growth produced at this temperature. In addition, we show a correlation between Vickers hardness and the porosity, obtained by evaluating empirical and theoretical models.
- ArtículoAcceso AbiertoSurface modification of multiwall carbon nanotubes by sulfonitric treatment(2016) Gómez, Sofía; Rendtorff Birrer, Nicolás Maximiliano; Aglietti, Esteban; Sakka, Yoshio; Suárez, GustavoCarbon nanotubes are widely used for electronic, mechanical, and optical devices due to their unique structural and quantum characteristics. The species generated by oxidation on the surface of these materials permit binding new reaction chains, which improves the dispersibility, processing and compatibility with other materials. Even though different acid treatments and applications of these CNT have been reported, relatively few research studies have focused on the relationship between the acid treatment and the formation of nanodefects, specific oxidized species or CNT surface defects. In this work, multiwall carbon nanotube (MWCNT) oxidation at 90°C was characterized in order to determine the acid treatment effect on the surface. It was found that oxidized species are already present in MWCNT without an acid treatment, but there are not enough to cause water-based dispersion. The species were identified and quantified by infrared spectroscopy and X-ray photoelectron spectroscopy. Also, transmission electron microscopy observations showed not only modifications of the oxidized species, but also morphological damage on the surfaces of MWCNT after being subjected to the acid treatment. This effect was also confirmed by Raman spectroscopy. The acid treatment generates higher oxidized species, decreasing the zeta potential in the whole pH range.