Papers by Keyword: PALS

Abstract: This study investigates Halloysite Nanotube (HNT) dispersibility in ethanol-water mixtures – 0% and 10% ethanol at 100, 300, and 500 ppm HNT concentrations. Overall, the study finds that changes in HNT concentration linearly affect the response variables and showed that the 10% ethanol solvent has a higher zeta potential, smaller particle size, higher viscosity, and settling velocity. The enlargement of HNT particles at 10% ethanol while keeping better stability than water solvent is unexpected and can open novel studies about the dispersion of HNT in this solvent system.

Abstract: In this study, the use of a 3D printer for sample holder fabrication and polymer sample preparation for positron analysis was explored. Custom printed 3D holders may be rapidly made and modified for a variety of thin-film, crystalline, or other diversely-shaped samples. For positron studies a 3D printer allows for the preparation of standard and unique polymer samples. In an initial study, a mesoporous-patterned ABS sample was attempted, without success. Various polymers (ABS, PLA, and PETG) and the same polymers with varied additives (carbon fiber or carbon nanotubes) were studied before and after printing. The different polymers and those with additives are distinguishable via PALS. Samples show a consistently lower I₃ value after printing, suggesting a decrease in defect quantity for the printed polymer versus the as-received polymer filament.

Abstract: The purpose of this study is to evaluate the irradiation defects of 12Cr-ODS steels induced by He/H ions, to provide basic understanding concerning development of fusion reactor components. Firstly, single He、H ion implantation and He/H ion co-implantation of 12Cr-ODS steels were performed at room temperature; and then SIMS were used to determine the He/H ion depth; finally, the irradiation induced defects were investigated by PALS and TEM. Characterization of the implanted samples with SIMS shows that He/H ions are mainly distributed at 4-6μm depth, consistent with the SRIM simulation. The PALS results show that the positron lifetime of H ions implanted samples increases slightly with increasing incident ions fluence, while for He and He/H ion implantation it is reversed. In addition, TEM results demonstrate that after irradiation, cavities are created in all samples, and He ion irradiation produce seriously larger damage compared to H ion. The positron lifetime results can be mainly ascribed to the difference of He and H ion interaction with defects.

Abstract: In the present work first results on structural properties of three commercial isomers of polybutadiene rubber are presented. To this aim, rheometry, PALS, DSC and swelling techniques were used. Different samples were prepared containing diverse amounts of dycumil peroxide as crosslinking agent and vulcanized at 433 K.A correlation among the experimental results obtained using different techniques is also discussed.

Abstract: Chemical modification of chitosan, specially grafting with different polymers is an important strategy in the production of bio-based materials with enhanced properties. In the present study, chitosan was grafted with n-butyl acrylate, in a surfactant-free emulsion polymerization. Stable dispersions with high grafting efficiency were obtained and the microstructure of the casted films was analyzed by positron annihilation lifetime spectroscopy and small angle X-ray scattering. Results are discussed in terms of the number and distribution of the grafting sites.

Abstract: We follow changes in the micro structure at several distances from the weld nugget of friction stir welded AlCuLi-alloy (AA2198) plates occurring due to the tool movement and the created heat by employing different methods: Small Angle X-ray Scattering (SAXS), giving information on type, size and density of precipitates, Differential Scanning Calorimetry (DSC), giving information on formed precipitates by their dissolution signal, and positron annihilation lifetime spectroscopy (PALS), being sensitive to vacancies and dislocations as well as to the formation and growth of precipitates. We start by characterizing the base material as a reference and proceed via the heat-affected zone to the weld nugget. By the use of complementary methods, we obtain information on structure, kind and distribution of precipitates and correlate this with hardness measurements.

Abstract: Still nowadays in integrated circuits manufacturing, few materials patterns are defined by a wet etch on patterned deep UV photoresist. From dies to dies generation, an optical performance improvement is required, hence an evolution with thinner and thinner positive resist. This makes these latter more sensitive to wet chemical etchant through the polymer, reducing their protection of the underneath material. Following characterizations enable a clear understanding of BHF (Buffered HF) benefits versus diluted HF during a gate oxide definition.

Abstract: The structure, point defect and ordering parameter of Fe25Al samples is examined with the Mössbauer spectroscopy Positron Annihilation Lifetime Spectroscopy XRD and SEM. The studies are carried out for samples in as-cast state and after heat treatments: annealing for 24 hours at 900°C (or 1050°C) and either slow cooling with furnace or quenching to oil. Among the research method used, Mössbauer spectroscopy for determination of hyperfine structure parameters was adopted. These parameters, sensitive to changes in spin and charge electron densities in the nearest neighbourhood of a Mössbauer isotope nucleus, caused by specific configurations of atoms, are directly connected with the degree of ordering of a compound. Spectral analysis has been carried out using an authors’ software developed based on a theoretical model relating the shape of a Mössbauer spectrum to the sample microstructure. It has been shown that Mössbauer spectroscopy enables quantitative evaluation of the degree of ordering of phases occurring in samples characterised by large graining, in the case of which it is not possible to determine the long-range order parameter by X-ray diffraction. The PALS method only one type of defects is detected. The positron lifetime in these defects (V) suggests that they are quenched-in Fe-monovacancies (VFe). The vacancy concentration strongly depends on the rate of cooling.

Abstract: The modification of the extended Tao-Eldrup model accounting ortho-positronium quenching in air is presented. Taking into account quenching by oxygen molecules adsorbed on the surface of porous material gives reasonable agreement between results of the model and the experimental positron annihilation lifetime spectroscopy data. Pore size distributions calculated using this model from the spectra for MCM 41 mesoporous sieve obtained in air, oxygen or vacuum are compared and discussed taking into account effect of ortho-positronium migration from small open pores to the larger ones. The rates of ortho-positronium quenching by air (47.2 µs-1 MPa 1), oxygen (220 µs-1 MPa-1) or nitrogen (1.7 µs-1 MPa-1) obtained from pressure dependences of the lifetimes observed in MCM 41 agree reasonably with the experimental results of other authors, if the correction for oxygen adsorbed on the surface is applied.

Abstract: Self-assembled amphiphile systems are utilized in a wide variety of applications including drug delivery and energy storage. Nano-scale physical and chemical interactions govern the packing of self-assembled amphiphilic molecules, resulting in thermodynamically stable phases of defined geometries. Possible phases include micellar, hexagonal, cubic, lamellar and sponge phases. The internal nano-structure of the amphiphile self-assembly materials plays an important role in the properties of these systems and their application. To date small angle x-ray scattering (SAXS) has been the most common technique used to characterise their structure. We explore positron annihilation lifetime spectroscopy (PALS) as an alternative and/or complementary technique for this purpose, using the phytantriol/water system. While PALS is a well established technique for characterising many materials, the coexistence of aqueous and hydrophobic regions in a soft self-assembled amphiphile material poses a challenge to the analysis and interpretation of the results. In order to alleviate these difficulties we developed a computer program for general-purpose PALS data analysis called PAScual. Amongst the most salient features of this new code are the possibility to perform bounded fits and the option of using advanced algorithms to provide a more robust and unbiased fit: on the one hand, it incorporates a global nonlinear optimisation routine based on the Simulated Annealing algorithm and, on the other hand it gives information on the reliability of the results by means of a Markov Chain Monte-Carlo Bayesian Inference method. In this work we present the newly developed PALS data analysis techniques as well as the results for the phytantriol/water system, comparing them with additional data obtained from complementary techniques.