Papers by Keyword: Positron Annihilation Technique

Abstract: Effect of electric field treatment with different intensities on vacancy of Inconel 718 aged at 1073 K was investigated. The positron annihilation lifetime (PAL) and corresponding concentration of vacancies were measured by positron annihilation technique. It was found that atomic vibration at lattice site can be promoted by an external electric field performed on Inconel 718 superalloy during aged at elevated temperature. Some atoms owing the higher vacancy formation energy or larger radius will jump out from the normal lattice sites and form defects, which is leading to the increase of PAL of monovacancy. Under continuous effect on electric field, monovacancies will transform to three-dimensional vacancies of lower energy and vacancy clusters. Moreover, the vacancy concentration of Inconel 718 superalloy can be improved evidently by electric field treatment, and the average PAL of vacancies can be up to 6.3% when the electric field intensity is up to 8 kV/cm, which is very useful for controlling the microstructures evolution and properties of the superalloy, such as solute redistribution and precipitations.

Abstract: Positron annihilation techniques (PAT) have recently been successfully employed for the characterization of phase transitions in metals and compounds. In the present study, positron annihilation lifetime (PAL) measurements have been carried out on a nanocrystalline titania (TiO2) in the form of powders that had been heat-treated at temperatures ranging from 300 to 1273K. The PAL spectra were analyzed into two lifetime components. The shorter lifetime τ1 (185-300 ps) is attributed to positron annihilation in vacancies and the longer lifetime τ1 (400-580 ps) to positrons in microviods at interfaces. The rutile phase of TiO2 powders was utilized as a reference in order to compare their behavior with the commercially supplied and widely available anatase phase (Degussa P25). The influence of the heat-treatment upon the nanostructure during the transition of the anatase to rutile phase were also investigated by X-ray diffraction (XRD), TEM and BET surface area methods. Understanding of this effect is expected to enhance our knowledge of the morphology and nanocrystallite size of TiO2 powders and their T-dependence, and hence their physical properties.

Abstract: Positron annihilation technique is a well known technique to characterize the defects in a material. These defects can be identified by positron annihilation lifetime and coincidence Doppler broadening of positron annihilation radiation measurement. In this chapter we report the room temperature positron annihilation lifetime for single crystalline ZnO. From our study it is confirmed that the present crystal contains V_Zn–hydrogen complexes with low open volumes. Another important nuclear solid technique is the Mossbauer Spectroscopic technique which has been used to probe the local magnetic properties of a solid. Here we have summarized Mossbauer spectroscopic studies on ferrites.