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1
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Positron Lifetime Measurements of Subsurface Region in Aluminium Alloy and Aluminium Alloy Composite after Dry Sliding

100%
Dryzek E.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
753-760
EN
This paper presents positron lifetime studies of the subsurface region of AK12 aluminium alloy and Al_2O_3-particle-reinforced AK12 aluminium alloy composite after sliding against steel in the pin-on-disc machine. The defect depth profile detected in the AK12 alloy extended up to 300μm but for the composite AK12 the range of this profile was significantly shortened to less than 90μm. The positron lifetime dependence on depth evidences a steep gradient of defect concentration near the surface. The subsurface zones have been also examined using scanning electron microscopy.
2
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Positron Annihilation Studies of the Subsurface Zone in Aluminium Alloys

64%
Dryzek E., Dryzek J.
Acta Physica Polonica A
|
2006
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vol. 110
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issue 5
569-575
EN
The paper presents positron lifetime studies of the subsurface region of the aluminium cast AK64 alloy containing silicon as a main alloying element after sliding against stainless steel in the pin-on-disc tester. The subsurface zone of the depth exceeding 150μm has been detected. The scanning electron microscopy revealed only the plastically deformed region occurring at the depth up to ca. 50μm and cracks at the depth less than 30μm. The comparison with the results obtained for the AK12 alloy containing almost a twice higher amount of silicon demonstrates the influence of the hard silicon rich particles on the total depth of the subsurface zone. A higher amount of hard particle prevents to some extend the propagation of defects inside the material.
3
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Positron Implantation Profile in Kapton

64%
Dryzek J., Dryzek E.
Acta Physica Polonica A
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2006
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vol. 110
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issue 5
577-582
EN
The discussion presented in the paper focuses on processes accompanying positron implantation in condensed matter. They finally constitute the positron implantation profile which generally does not exhibit the exponential behavior as it is concluded from the Monte Carlo simulation made using the EGSnrc 4.0 code. The simulation was performed for the kapton and two commonly used positron sources ^{22}Na and ^{68}Ge/g^{68}Ga. New formula for the implantation profile was proposed.
4
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Positron Annihilation Lifetime Spectroscopy of ABS Objects Manufactured by Fused Deposition Modelling

64%
Dryzek M., Dryzek E.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1506-1508
EN
Positron annihilation lifetime spectroscopy was used to study acrylonitrile butadiene styrene (ABS) specimens manufactured using fused deposition modelling to explore possibilities of identifying differences in molecular structure. The set of specimens was prepared including square tiles and long rectangular tiles (100 mm and 200 mm long) with all filament roads parallel to the longer edge. All types of tiles were produced with various infill line distance parameter resulting in different overlapping of the roads in horizontal and vertical directions. The slight increase of the ortho-positronium lifetime indicating increase of the mean free volume radius was observed for the longest tiles for which influence of weld interface is expected to be most pronounced. No differences were observed for different infill line distance parameters.
5
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Positron Lifetime Studies of the Subsurface Zones Created under Dry and Lubrication Conditions

64%
Dryzek J., Dryzek E.
Acta Physica Polonica A
|
2001
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vol. 99
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issue 3-4
351-354
EN
We present the measurement of the positron lifetime spectra in the subsurface zones in copper samples with surfaces damaged in dry and lubrication conditions. We observe that close to the damaged surface the single vacancies were present, but deeper in the sample treated in the dry condition the vacancy clusters were detected. A zone with dislocations was located deeper than the zone with the vacancies and their clusters.
6
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Structural Changes in Surface-Modified Polymers for Medical Applications

64%
Pamula E., Dryzek E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1485-1493
EN
Biological properties of synthetic polymers can be improved by surface modification with the use of liquid oxidizers. A resorbable biomedical polymer - poly(glycolide-co-ε-caprolactone) (PGCL) was incubated in 0.1 M NaOH for 2, 6, 16, and 24 h, followed by excessive washing and drying in vacuum. Surface properties of the materials before and after modification were evaluated: wettability by contact angle measurements, topography by atomic force microscopy, and chemical functions by infrared spectroscopy. Applied modification improved wettability of PGCL due to creation of chemical oxygenated functionalities, and resulted in a slight alternation of the surface topography and roughness. In order to determine whether NaOH incubation caused structural changes in bulk of PGCL, positron annihilation lifetime spectroscopy, differential scanning calorimetry and viscosity measurements were performed. It was found that the ortho-positronium lifetime in PGCL declines as a function of modification time. It suggests that NaOH incubation causes structural changes in PGCL not only on the surface but also in bulk.
7
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Reverse Transformation of Deformation Induced Martensite in Austenitic Stainless Steel

64%
Dryzek E., Sarnek M.
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vol. 125
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issue 3
710-713
EN
Cumulative isochronal annealing of stainless steel 1.4307 samples deformed by compression was investigated using the Doppler broadening of the annihilation line measurements. Higher level of plastic deformation is accompanied not only by higher concentration of defects but also by higher amount of α' martensite. The annealing studies revealed creation of defects in the temperature range between 450C and 650C pointing out the reverse transition of α' martensite to austenite. This is confirmed by magnetic susceptibility and microhardness measurements.
8
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Estimate of the Crystallite Size for Nanocrystalline AISI 316L Stainless Steel and Armco Iron Processed by Hydrostatic Extrusion Using Variable Energy Positron Beam

51%
Sarnek M., Dryzek E., Horodek P., Pachla W.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1598-1601
EN
The paper presents the results of research of nanocrystalline AISI 316L type stainless steel and nanocrystalline Armco pure iron processed by severe plastic deformation using hydrostatic extrusion method. Surface and subsurface of the steel samples extruded at different pressure were investigated using variable energy positron beam. It enabled us to determine the positron diffusion length and compare its values with those for annealed AISI 304 stainless steel. Furthermore positron lifetime and microhardness were measured for all the samples and X-ray diffraction was used to estimate the crystallite size.
9
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Defect Profile Induced by Friction and Wear Processes Detected by Positron Annihilation Method

51%
Dryzek J., Dryzek E., Cleff B.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
129-133
EN
The positron annihilation studies of defect profile in Cu samples whose surfaces were exposed to the friction and wear processes are presented. The values of the S-parameter and its dependences on the depth from the Cu surface are the functions of the value of the load applied in the sliding contact between two metals. It indicates possibilities of applying the presented measurement method in the industry.
10
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Preferential Positron Annihilation in Binary Alloys

51%
Kuriplach J., Dryzek E., Dryzek J., Šob M.
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vol. 95
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issue 4
605-611
EN
The effect of preferential positron annihilation at individual constituent atoms in binary alloys is examined theoretically and experimentally. In particular, the results of recently studied alloys Fe-Al and Mg-Cd together with new preliminary results for the Sn-In system are discussed and summarised. In the case of the Sn-In system, the concentration dependencies of positron annihilation rates and Doppler broadening spectra are analysed.
11
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Hydrolytic Degradation of Poly(L-Lactide-co-Glycolide) Studied by Positron Annihilation Lifetime Spectroscopy and Other Techniques

51%
Pamuła E., Dryzek E., Dobrzyński P.
Acta Physica Polonica A
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2006
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vol. 110
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issue 5
631-640
EN
Changes of the poly(L-lactide-co-glycolide) structure as a function of degradation time in phosphate-buffered saline for 7 weeks were investigated by gel permeation chromatography, differential scanning calorimetry, nuclear magnetic resonance (^1H NMR), and positron annihilation lifetime spectroscopy. Surface properties as wettability by sessile drop and topography by atomic force microscopy were also characterized. Chain-scission of polyester bonds in hydrolysis reaction causes a quite uniform decrease in molecular weight, and finally results in an increase in semicrystallinity. Molecular composition of the copolymer and water contact angle do not change considerably during degradation time. Atomic force microscopy studies suggest that the copolymer degrades by "in bulk" mechanism. The average size of the molecular-level free volume holes declines considerably after one week of degradation and remains constant till the sixth week of degradation. The free volume fraction decreases as a function of degradation time.
12
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Free-Volume and Tensile Properties of Glass Fibre Reinforced Polyamide 6 Composites

51%
Dryzek E., Wróbel M., Juszyńska-Gałązka E.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1501-1505
EN
The tensile properties and free volume of commercially available modified polyamid 6 and polyamid 6 composites with 15 and 30 wt% of glass fibre were the subject of the studies. The tensile test allowed us to obtain the stress-strain curves and determine the tensile properties of the polyamid 6 samples. The positron lifetime measurements were performed for the samples before the test and for the samples in the vicinity of the break after they failed. The composites exhibited slightly lower values of the ortho-positronium lifetime and therefore smaller size of the local free volumes in comparison to polyamid 6 without reinforcement. The analysis of the positron lifetime spectra indicated size distribution of the free volume. The initially narrower distributions for the composite samples became broader as a result of the deformation. The deformation caused also increase of the ortho-positronium intensity in the obtained positron lifetime spectra.
13
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Positron Annihilation in Cotton Cellulose

51%
Golonka P., Mayer J., Dryzek E.
Acta Physica Polonica A
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2001
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vol. 99
|
issue 3-4
363-367
EN
The changes of the cotton fibre microstructure as a result of annealing at temperatures from 20ºC to 300ºC were investigated by positron lifetime spectroscopy and differential scanning calorimetry. The aim of the paper was to examine the cotton cellulose thermal degradation process.
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