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Annihilation Lifetime Spectroscopy (annihilation + lifetime_spectroscopy)

Distribution by Scientific Domains
Polymers and Materials Science36%

Kinds of Annihilation Lifetime Spectroscopy

  • positron annihilation lifetime spectroscopy
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    Selected Abstracts

    Drying and Rewetting of Mature Cement Pastes Studied through Positron Annihilation Lifetime Spectroscopy

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001
    Giovanni Consolati
    Positron annihilation lifetime measurements have been conducted on mature cement pastes, subjected to drying and rewetting treatments that remove and restore the free water from the pastes, to study possible changes of the microstructure. Analysis of the results suggests that repeated drying followed by rewetting does not induce irreversible modifications in the configuration of the finest gel pores. [source]

    A study of dye molecule diffusion in human hair using positron lifetime spectroscopy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
    M. N. Chandrashekara
    Abstract The diffusion behavior of a commercial permanent liquid hair dye in human hair has been investigated using Positron Annihilation Lifetime Spectroscopy (PALS) and gravimetric sorption method. The o-Ps lifetime parameters ,3 and I3 decrease rapidly during the first 60 minutes of sorption time. This is understood in terms of dye molecules filling the free volume cavities in hair. The sorption results suggest that the dye molecule diffusion is essentially a Fickian process. In the latter part of the sorption, where positron parameters remain almost constant, mass increase might be due to surface adhesion. These two stages of sorption are well separated by the positron technique. The study shows that the free volume theory and positron technique, widely used in polymer research, may expediently be used to understand hair properties, more importantly diffusion of dye molecules. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Spoliation of a rigid gas permeable contact lens by sodium chloride: A free volume microprobe study

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
    M. V. Deepa Urs
    Abstract The interaction of one of the major inorganic ions present in tears, viz., sodium chloride (NaCl), with a rigid gas permeable contact lens, poly(Fluorosilicone acrylate) (FP92) has been investigated using Positron Annihilation Lifetime Spectroscopy (PLS) and refrac-tive index measurement. We monitored the changes in its free volume size and number density in the presence of NaCl solute trans-ported through diffusion. Based on PLS results, we propose that the adhesion of sodium chloride salt to the fluorine and methacrylate sites of FP92 results in zones of excess salt concentration. The changes in refractive index of the contact lens material due to the salt adhesion, correlates well with the changes in free volume of the material. Presence of sodium chloride perturbs the free volume of the lens material and hence its polarizability (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Temperature dependence of positronium lifetime in cylindrical pores

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
    R. Zaleski
    Abstract Positron Annihilation Lifetime Spectroscopy (PALS) results for ordered mesoporous silica sieves (MCM-41 and its fibre form MSF) are used to verify predictions of the Extended Tao-Eldrup (ETE) model. Cylindrical pores (R , 1,2 nm) in these materials have well defined geometry and size, thus the structure of MCM-41 and MSF reproduces the model assumptions. Positron lifetimes were measured in the range 100-500K. In MCM-41, due to low intensity of pore related ortho-positronium component, it is difficult to determine the component's lifetime precisely. Accuracy of the lifetime fitting is better for MSF, where temperature dependence is in a good agreement with the ETE model results. For comparison, the ETE model predictions fit the lifetime of the pore related component in the Vycor sample only for T > 200 K. Below this value the lifetime exceeds the model predictions by over 30%. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Effect of dendritic architecture on localized free volume of poly(ether ketone)s as probed by positron annihilation spectroscopy

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2004
    Seung-Yeop Kwak
    Model poly(ether ketone)s (PEKs) with architectural variations were studied by positron annihilation lifetime spectroscopy (PALS) to estimate the average void sizes on a sub-nanometer scale, in conjunction with the hyperbranched (H-), the linear (L-), and their 50:50 block combination (HLH-) structures. The PALS distribution confirmed the unique molecular architecture of the hyperbranched polymer, consisting of an interior cavity space formed by loosely linked core and chain ends of relatively tighter free volume space. [source]

    Positron Lifetime Study of the Crystal Evolution and Defect Formation Processes in a Scintillating Glass

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
    Jiaxiang Nie
    The crystal evolution and defect formation in scintillating glasses as a consequence of thermal annealing were studied by annihilation lifetime spectroscopy and UV-Vis absorption spectroscopy. The annihilation lifetime spectra and UV-Vis spectra were recorded on glass 50SiO2,45ZnO,5BaF2 before and after annealing at 580°C for 16, 32, and 48 h, respectively. The results show that the three lifetime components (,1, ,2, and ,3) and the corresponding intensities (I1, I2, and I3) change systematically with increasing annealing time. This reflects the crystal evolution and defect formation in the glass matrix. The continued crystal evolution was also revealed by the UV-Vis spectra, as the absorption edge of the material shifted to a lower energy with prolonged annealing. [source]

    Positron lifetime evolution during room temperature ageing in Al-Zn-Mg-(Cu)

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
    A. Dupasquier
    Abstract The effect on the formation of vacancy-solute clusters by the addition of small percentages of Cu to Al-Zn-Mg has been studied by positron annihilation lifetime spectroscopy. The results document the ability of Cu to increase the number of vacancies retained after quenching, by forming an additional population of vacancy-solute clusters in competition with pure Zn clusters. It has also been shown that Cu accelerates the decomposition of the alloy at 150°, thereby leaving a reduced supersaturation of the matrix after an early interruption. An unexpected result is that the curve positron lifetime vs, ageing time at RT displays the symptoms of a change in the nature of the coherent aggregates that occurs in about 10 hours of RT exposure. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Positron annihilation studies in plastically deformed Fe-Mn-Si-Cr-Ni-C

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
    J. De Baerdemaeker
    Abstract Fe-Mn-Si-Cr-Ni-C samples with deformations from 2 to 20% were investigated using positron annihilation spectroscopy, optical microscopy (OM) and X-ray diffraction (XRD). Both Doppler broadening of the annihilation radiation (DBAR) and positron annihilation lifetime spectroscopy (PALS) measurements were performed. The DBAR experiments, carried out using a slow positron beam, indicate a sudden increase in the defect concentration in between 4 and 6% deformation. This is confirmed by the lifetime measurements. In between 6% and 8% deformation the lineshape parameter significantly changes which coincides with the drastic increase of the concentration of the martensite phase as confirmed by XRD. Positron annihilation spectroscopy indirectly probe the ,/, martensitic phase transformation by probing correlated dislocations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Composition dependence of positron annihilation lifetime for Al-Pd-Re-Ru quasicrystal and 2/1-AlPdRu approximant crystal

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
    Y. Takagiwa
    Abstract Quaternary icosahedral Al-Pd-Re-Ru (i -Al71Pd20(Re1,xRux)9 (X = 0.4, 0.55, 0.7, 0.85)) quasicrystals and its 2/1-AlPdRu approximant crystal, 2/1-Al71Pd20Ru9, were investigated by positron annihilation lifetime spectroscopy. The positron annihilation lifetimes measured here are significantly longer than those of defect-free states estimated by compositionally weighting the constituent elements. This result suggests that high densities of structural vacancies exist in both i -Al-Pd-Re-Ru quasicrystals and 2/1-AlPdRu approximant crystal. For i -Al-Pd-Re-Ru quasicrystals, composition dependence of the positron annihilation lifetime is compared with that of the electrical conductivity. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Nanocrystalline alloys studied by positron annihilation lifetime spectroscopy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
    Martin Petriska
    Abstract Nanocrystalline alloys present a new class of materials that exhibit interesting magnetic properties. These stem primarily from the presence of crystalline grains with the size of several tens of nanometers embedded in a residual amorphous matrix. In this paper, we employ positron annihilation spectrometry to investigate the relation between positron lifetime and microstructure of the NANOPERM-type metallic Fe76Mo8Cu1B15 alloy. The behaviour of positron lifetime with respect to the annealing temperature is discussed for samples, which were prepared by one hour thermal treatment in a vacuum at temperatures ranging from 330 up to 700 °C. Samples in amorphous (as-quenched) state were analysed, too. The results of this work confirm that the optimum annealing temperature of 550 °C correlates with the minimum of free volume and coincide with the temperature at which superior magnetic properties are observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Effect of clay on the morphology of binary blends of polyamide 6 with high density polyethylene and HDPE- graft -acrylic acid

    POLYMER ENGINEERING & SCIENCE, Issue 5 2007
    Zhengping Fang
    Polyamide 6 (PA6)/HDPE/organo-bentonite (Oclay) and PA6/HDPE- grafted -acrylic acid (PEAA)/Oclay nanocomposites were prepared via melt compounding. The influence of Oclay on the morphology of composites was investigated. Scanning electron microscopy results revealed the size of the dispersed HDPE, and PEAA phase decreased with increasing Oclay content. Transmission electron microscopy and X-ray diffraction results revealed that the Oclay was predominately intercalated with some evidence of partial exfoliation. The majority of Oclay platelets were concentrated in the PA6 phase and in the interfacial region between PA6 and HDPE (PEAA). The Oclay platelets played the role of coupling species between the two polymers, increasing the interaction of the two phases in certain extent. These results were proved by FTIR and positron annihilation lifetime spectroscopy. Consequently, apparent emulsifying effect was induced. A schematic mechanism of the apparent compatibilization effect was presented. POLYM. ENG. SCI., 47:551,559, 2007. © 2007 Society of Plastics Engineers. [source]