Thesis IDENTIFICACIÓN DE LA ESTRUCTURA CRISTALINA DE LA FASE Ti4Pt3 EN EL SISTEMA BINARIO Ti-Pt
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Date
2018
Authors
ARANCIBIA POBLETE, FERNANDA PAZ
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Abstract
En el año 2004, Biggs et al. [1], realizaron una revisión del diagrama de fases Ti-Pt en el rango de composición 30-60 at.% Pt en el cual determinaron una nueva fase. De acuerdo a los investigadores, esta fase evidenció una composición estequiométrica de Ti4Pt3 en el rango de composición 41-44 at.% Pt. Desafortunadamente, no lograron caracterizar cristalográficamente dicha fase. Más tarde, Tello [2] re-estudiaron el diagrama de fases Ti-Pt en el rango de composición 30-50 at.% Pt y propusieron que la fase Ti4Pt3 posee una estructura cristalina pseudo-hexagonal. Por lo tanto, en este estudio se identificó una estructura cristalina para la fase Ti4Pt3 que mejor se ajusta a los datos experimentales de difracción de rayos x obtenidos.Se fabricaron tres muestras cuya composición fueron 41,7 at.% Pt, 42,8 at.% Pt y 43,4 at.% Pt en el laboratorio Desarrollo de Materiales del Instituto Max-Planck para Química Física de Sólidos (Dresden- Alemania), las cuales fueron analizadas por microscopía electrónica de barrido y difracción de rayos x.La microestructura en estado as-cast reveló principalmente dendritas de la fase Ti4Pt3 y eutéctico Ti3Pt + ¿-TiPt en las zonas interdendríticas. Por otra parte, en las muestras tratadas térmicamente se observó que a medida que aumenta el porcentaje de platino la matriz consiste casi en su totalidad en Ti4Pt3. Al estudiar los difractogramas obtenidos por difracción de rayos x, se observó que algunos reflejos corresponden a las fases conocidas Ti3Pt y ¿-TiPt mientras que otros no pudieron ser indexados. Se propuso que estos reflejos no indexados corresponden a la fase Ti4Pt3.Para identificar dicha fase, se recopiló en la literatura existente información sobre otras fases con estequiometria A4B3 las cuales fueron agrupadas en familias con igual estructura cristalina y, dentro de estos grupos, en subgrupos con igual grupo espacial. Esta información recopilada fue contrastada con el difractograma experimental obtenido para la muestra de composición 41,7 at.% Pt.Finalmente, se sugiere que la estructura cristalina ortorrómbica con grupo espacial Cmcm (Nr. 63) del tipo Er3Ge4 corresponde al mejor modelo considerando los patrones de difracción. Los parámetros de red obtenidos después de realizar los ajustes en el programa MAUD corresponden a: a= 3,2179 Å, b= 10,3419 Å y c= 13,8765 Å con volumen de celda igual a 461,7988 Å3.
In 2004, Biggs et al. [1] revisited the Ti-Pt phase diagram in the composition range 30-60 at.% Pt and found a new phase with Ti4Pt3stoichiometricin the composition range 41-44 at.% Pt. Unfortunately, the researchers did not determine the crystal structure of that phase. Later, Tello [2] re-visited the Ti-Pt phase in the composition range 30-50 at. %Pt and suggested that the Ti4Pt3 phase has a pseudo-hexagonal cristal structure. Therefore, the goal of this work is to identify the crystal structure of theTi4Pt3 phase that fits the experimental x-ray diffraction data.Three alloys of composition 41.7 at.% Pt, 42.8 at.% Pt and 43.4 at.% Pt were fabricated in the Materials Laboratory of the Max-Planck-Institut für Chemische Physik fester Stoffe (Dresden- Germany). The alloys were analyzed in the as-cast condition and in the heat treated condition (1000 °C for 168 hours) using scanning electron microscopy and x-ray diffraction.The microstructure in the as-cast condition revealed dendrites of the Ti4Pt3 phase and the eutectic Ti3Pt + a -TiPt in the interdendritic regions . On the other hand, the heat treated samples revealed a microstructure consisting mostly of Ti4Pt3 phase as the platinum content increases. The x-ray diffraction patterns revealed the presence of the Ti3Pt and a-TiPt phases. The remaining peaks that were not indexed correspond to the reflections of the Ti4Pt3phase. A literature review was carried out to collect crystallographic information of of other compounds with A4B3 stoichiometry and, later, these compounds were grouped into familes of equal crystal structure and, inside this group, into families of equal space group. This theoretical information was compared with the experimental diffraction pattern obtained for the 41.7 at.% Pt alloy. Finally, the crystal structure suggested for the Ti4Pt3 phase corresponds to an orthorhombic crystal structure with space group Cmcm (Nr. 63) of the type Er3Ge4 which corresponds to the best model that fits the experimental diffraction pattern. Additionally, the adjusted structural parameters obtained with the software MAUD are: a = 3.2179 A, b = 10.3419 A and c = 13.8765 A with cell volume corresponds to 461,7988 A3.
In 2004, Biggs et al. [1] revisited the Ti-Pt phase diagram in the composition range 30-60 at.% Pt and found a new phase with Ti4Pt3stoichiometricin the composition range 41-44 at.% Pt. Unfortunately, the researchers did not determine the crystal structure of that phase. Later, Tello [2] re-visited the Ti-Pt phase in the composition range 30-50 at. %Pt and suggested that the Ti4Pt3 phase has a pseudo-hexagonal cristal structure. Therefore, the goal of this work is to identify the crystal structure of theTi4Pt3 phase that fits the experimental x-ray diffraction data.Three alloys of composition 41.7 at.% Pt, 42.8 at.% Pt and 43.4 at.% Pt were fabricated in the Materials Laboratory of the Max-Planck-Institut für Chemische Physik fester Stoffe (Dresden- Germany). The alloys were analyzed in the as-cast condition and in the heat treated condition (1000 °C for 168 hours) using scanning electron microscopy and x-ray diffraction.The microstructure in the as-cast condition revealed dendrites of the Ti4Pt3 phase and the eutectic Ti3Pt + a -TiPt in the interdendritic regions . On the other hand, the heat treated samples revealed a microstructure consisting mostly of Ti4Pt3 phase as the platinum content increases. The x-ray diffraction patterns revealed the presence of the Ti3Pt and a-TiPt phases. The remaining peaks that were not indexed correspond to the reflections of the Ti4Pt3phase. A literature review was carried out to collect crystallographic information of of other compounds with A4B3 stoichiometry and, later, these compounds were grouped into familes of equal crystal structure and, inside this group, into families of equal space group. This theoretical information was compared with the experimental diffraction pattern obtained for the 41.7 at.% Pt alloy. Finally, the crystal structure suggested for the Ti4Pt3 phase corresponds to an orthorhombic crystal structure with space group Cmcm (Nr. 63) of the type Er3Ge4 which corresponds to the best model that fits the experimental diffraction pattern. Additionally, the adjusted structural parameters obtained with the software MAUD are: a = 3.2179 A, b = 10.3419 A and c = 13.8765 A with cell volume corresponds to 461,7988 A3.
Description
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Keywords
ESTRUCTURA CRISTALINA , SISTEMA BINARIO TI-PT , TI4PT3