CHARACTERISTICS OF Al-Fe SINTERS MADE BY THE POWDER METALLURGY ROUTE

The Al/Fe material was prepared by the powder metallurgy route with an additional intermediate stage which was a centrifuge of powder mixture. The application of the centrifuge stage was applied to obtain circular phase distribution of Al-rich phases in a sintered material. Iron powder with a particle size under 100 μm and aluminum powder with a particle size of about 25 μm, were used as starting materials. To determine the effect of centrifuging time on the distribution of Fe-Al particles, scanning electron microscopy (SEM, EDS) and XRD techniques were used. Microstructure observations show the influence of the centrifuging time on the distribution of Fe particles. It was observed that a longer centrifuging time caused changes in the ratio concentration of elements and allowed the growth of the intermetallic phase at the interface between solid Al and Fe particles

Influence of Internal Scrap on Mechanical Properties of Selected Cobalt Alloys

This paper presents the results of mechanical tests carried out on two different commercially available cobalt alloys applied indental prosthetics for the production of frame dentures. The test samples were obtained by the method of investment casting using as a charge pure primary materials and pure primary materials mixed with various additions of process scrap (25, 50, and 75%). The tests showed that the alloys could not reach the mechanical properties reported by the manufacturer in either case. In the case of the alloy without the addition of tantalum, the general conclusion was that both the plastic and strength properties decreased with increasing amounts of the introduced process scrap. The mechanical properties (mainly elongation) of the alloy containing Ta reached the highest values in the samples containing 75% of the process scrap. Examinations of fractures carried out by SEM have revealed their varied character – ductile or transcrystalline. All of the samples tested showed the presence of dendrites and solidification areas, with shrinkage porosity occurring in the internal sample zones

A Novel Approach for Durability Evaluation of Metal Protective Coatings in Dynamic Interplay with the Liquid Alloy

The article describes a new test method to quickly evaluate the durability of a protective coating to dynamic contact with liquid metal. The essence of the method is the movement of a drop of liquid metal inside a rotating ring, covered from the inside with the protective coating under test. The parameters determined in the test are analogous to the classic pin-on-disk tribological test. The method was tested for the system: liquid alloy 2017A vs. AlTiN coating on a copper substrate. The test temperature was 750°C, and exposure times ranged from 30 to 90 minutes. Sliding path equivalent for the metal droplet/coating system ranged from 31.6 to 95 m. The study, which included visual evaluation of the surface of the samples, followed by phase and microstructural analysis, showed the high efficiency of the method for assessing the lifetime of protective coatings on contact with liquid metal. The investigated issue was also analyzed from the model side taking into account changes in the diffusion coefficient at the contact of liquid metal with the substrate, occurring with the progressive degradation of the protective coating

3D PET image reconstruction based on Maximum Likelihood Estimation Method (MLEM) algorithm

Positron emission tomographs (PET) do not measure an image directly. Instead, they measure at the boundary of the field-of-view (FOV) of PET tomograph a sinogram that consists of measurements of the sums of all the counts along the lines connecting two detectors. As there is a multitude of detectors build-in typical PET tomograph structure, there are many possible detector pairs that pertain to the measurement. The problem is how to turn this measurement into an image (this is called imaging). Decisive improvement in PET image quality was reached with the introduction of iterative reconstruction techniques. This stage was reached already twenty years ago (with the advent of new powerful computing processors). However, three dimensional (3D) imaging remains still a challenge. The purpose of the image reconstruction algorithm is to process this imperfect count data for a large number (many millions) of lines-of-responce (LOR) and millions of detected photons to produce an image showing the distribution of the labeled molecules in space.Comment: 10 pages, 7 figure

Studies of discrete symmetries in decays of positronium atoms

A positronium - a bound state of electron and positron - is an eigenstate of parity and charge conjugation operators which decays into photons. It is a unique laboratory to study discrete symmetries whose precision is limited, in principle, by the effects due to the weak interactions expected at the level of 10−14 and photon-photon interactions expected at the level of 10−9. The Jagiellonian Positron Emission Tomograph (J-PET) is a detector for medical imaging as well as for physics studies involving detection of electronpositron annihilation into photons. The physics case covers the areas of discrete symmetries studies and genuine multipartite entanglement. The J-PET detector has high angular and time resolution and allows for determination of spin of the positronium and the momenta and polarization vectors of annihilation quanta. In this article, we present the potential of the J-PET system for studies of discrete symmetries in decays of positronium atoms

Plastic scintillators for positron emission tomography obtained by the bulk polymerization method

This paper describes three methods regarding the production of plastic scintillators. One method appears to be suitable for the manufacturing of plastic scintillator, revealing properties which fulfill the requirements of novel positron emission tomography scanners based on plastic scintillators. The key parameters of the manufacturing process are determined and discussed.Comment: 7 pages, 4 figure

Application of the compress sensing theory for improvement of the TOF resolution in a novel J-PET instrument

Nowadays, in positron emission tomography (PET) systems, a time of fl ight (TOF) information is used to improve the image reconstruction process. In TOF-PET, fast detectors are able to measure the difference in the arrival time of the two gamma rays, with the precision enabling to shorten signifi cantly a range along the line-of-response (LOR) where the annihilation occurred. In the new concept, called J-PET scanner, gamma rays are detected in plastic scintillators. In a single strip of J-PET system, time values are obtained by probing signals in the amplitude domain. Owing to compressive sensing (CS) theory, information about the shape and amplitude of the signals is recovered. In this paper, we demonstrate that based on the acquired signals parameters, a better signal normalization may be provided in order to improve the TOF resolution. The procedure was tested using large sample of data registered by a dedicated detection setup enabling sampling of signals with 50-ps intervals. Experimental setup provided irradiation of a chosen position in the plastic scintillator strip with annihilation gamma quanta

Analysis procedure of the positronium lifetime spectra for the J-PET detector

Positron Annihilation Lifetime Spectroscopy (PALS) has shown to be a powerful tool to study the nanostructures of porous materials. Positron Emissions Tomography (PET) are devices allowing imaging of metabolic processes e.g. in human bodies. A newly developed device, the J-PET (Jagiellonian PET), will allow PALS in addition to imaging, thus combining both analyses providing new methods for physics and medicine. In this contribution we present a computer program that is compatible with the J-PET software. We compare its performance with the standard program LT 9.0 by using PALS data from hexane measurements at different temperatures. Our program is based on an iterative procedure, and our fits prove that it performs as good as LT 9.0.Comment: 4 figures, 8 page