Relaxation process of Fe(CuNb)SiB amorphous alloys investigated by dynamical calorimetry

Differential scanning calorimetry and dynamic differential scanning calorimetry were used to analyze the relaxation process of Fe(CuNb)SiB amorphous alloys. The Curie temperature(TC) evolution of the amorphous phase during relaxation as a function of heating rate, time and pre-annealing temperature were measured. Two distinct relaxation processes are observed, consequent with topological and chemical short range order changes

La calorimetría diferencial de barrido y su aplicación a la Ciencia de Materiales

Se pone de manifiesto la idoneidad de la técnica de calorimetría diferencial de barrido para la caracterización de materiales. Se presentan ejemplos específicos de aplicación de dicha técnica en el estudio de los fenómenos ligados a la transición vitrea y cinética de cristalización de vidrios calcogenuros y metálicos así como en el estudio de la reordenación de fases desordenadas metastables

La calorimetría diferencial de barrido y su aplicación a la Ciencia de Materiales

Se pone de manifiesto la idoneidad de la técnica de calorimetría diferencial de barrido para la caracterización de materiales. Se presentan ejemplos específicos de aplicación de dicha técnica en el estudio de los fenómenos ligados a la transición vitrea y cinética de cristalización de vidrios calcogenuros y metálicos así como en el estudio de la reordenación de fases desordenadas metastables

On the Mechanism of Milling Induced Disordering in AlFe

The evolution of the B2-AlFe phase during mechanical grinding in Ar has been examined as a function of milling time by X-Ray diffraction, transmission Moessbauer spectroscopy and differential scanning calorimetry. Short and long range disorder was observed to increase with the mechanical treatment up to the attainment of a steady state. The evolution of the long range order parameter and of the local atomic configurations at Fe sites were analyzed in terms of possible mechanisms for milling induced disordering. The kinetics of the thermal reordering was studied under continuous heating and isothermal calorimetric regimes. Modeling of the reordering processes by diffusion controlled growth of pre-existing ordered grains is presented as well as the estimated values of both the enthalpy and the activation energy of the reordering process. The results are consistent with a nonuniform distribution of disorder throughout the sample and will be compared with preceding information on related systems.Departamento de Físic

Mechanical milling of the intermetallic compound AlFe

The intermetallic compound AlFe in its ordered B2 phase has been ground under Ar in a ball-milling device. The system evolution under mechanical work has been examined as a function of time of milling by x-ray diffraction, transmission Mossbauer spectroscopy, and differential scanning calorimetry. Short and long range disorder was observed. The evolution of the long range order parameter with milling time is analyzed up to the completion of the solid state reaction when a steady state value is reached. The short range order evolution is consistent with a nonstatistical order distribution throughout the sample but mainly distributed in two regions with different degrees of order each. Kinetic analysis of the reordering and recrystallization has been per- formed under continuous heating and isothermal calorimetric regimes. Modeling of these processes is pre- sented as well as the estimated values of both the enthalpy and the activation energy of the reordering process. Results are compared with preceding information on related systems.Facultad de Ciencias Exacta

180 diffusion through amorphous SiOs and cristobalite

Secondary ion mass spectrometry was used to profile the diffusion of oxygen in polycrystalline β-cristobalite and vitreous SiO2. The tracer concentration profiles of cristobalite are consistent with a model based on two mechanisms: bulk and short-circuit diffusion. The profiles of partially crystallized samples containing vitreous SiO2 and β-cristobalite were fitted using the sum of two complementary error functions and taking account of some interstitial-network exchange. The bulk oxygen diffusivity, in the temperature range 1240-1500 °C, is about five times greater for vitreous silica than for β-cristobalite

Effect of minor Co additions on the crystallization and magnetic properties of Fe(Co)NbBCu alloys

The effect of partial replacement of Fe by Co (up to 8 %) on thermal stability, structure and magnetic properties of FeNbBCu alloys has been explored in this paper. The results indicate that Co reduces the stability against crystallization of the amorphous alloy and stabilizes the nanocrystalline phase prior to the further precipitation of metastable boride phases. Transmission Mössbauer spectroscopy reveals differences in the hyperfine interactions between the alloys: Co raises the mean hyperfine field of the amorphous state and differences in the nanocrystalline bcc-Fe(Co) environments between the alloys occur depending on the amount of Co near-neighbours in the bcc-Fe structure. The addition of Co has also a notable effect on the magnetic properties of both amorphous and nanocrystalline alloys increasing the Curie temperature, which shows a linear dependence with the Co composition, and the saturation polarization.Peer ReviewedPostprint (author’s final draft

Influencia de la atmósfera de sinterización en la estabilidad térmica de cerámicas de hidroxiapatita reforzadas con zircona

En este trabajo se estudia la influencia de la atmósfera de sinterización sobre la estabilidad térmica de cerámicas de hidroxiapatita (HA) reforzadas con partículas de circona parcialmente estabilizada con magnesia (Mg-PSZ). Los cuerpos verdes fueron obtenidos por prensado uniaxial y las sinterizaciones se realizaron en aire y en oxígeno húmedo. El estudio por difracción de rayos-X y espectroscopía infrarroja permitió comprobar que la atmósfera húmeda evita la descomposición de la hidroxiapatita, todo lo contrario a lo que sucede en aire donde es evidente la presencia del zirconato cálcico (CZ) en la interfaz entre la partícula de circona y la matriz de HA. La caracterización microestructural de los materiales por Microscopía Electrónica de Barrido permitió apreciar el desarrollo de tamaño de grano de los materiales sinterizados. El estudio del comportamiento mecánico mediante ensayos de indentación reveló un aumento de la tenacidad a la fractura en el caso de los materiales que presentaban Mg-PSZ con respecto a la HA pura