László Dévényi

Tracking the physical aging of poly(ethylene oxide): A technical note

Summary and ConclusionsPhysical aging of 2 types of PEO could be tracked by the combination of PALS, DSC, and SEM methods. After storing the samples at 40°C±2°C and 75%±5% RH, a decrease in the o-Ps lifetime values and an increase in the melting enthalpies as a function of storage time indicated a reorientation of the polymer chains. The limitations of monitoring enthalpy relaxation confirm the importance of methods that track volume relaxation, such as PALS. Structural changes could be observed even after a short storage time (4 weeks), which highlights the effect of further investigations of the influence of physical aging on the properties of PEO-containing dosage forms.

Stent Fracture Analysis

Almost half of the deaths in the European Union are a consequence of cardiovascular diseases, which can be reduced significantly by dietary changes, physical activity and suitable medications. Since changing lifestyle and healthcare is a slow process, a more efficient and quicker solution is to improve medical devices. Stents are mesh-structured implants, which support arterial wall and allow dilatation of the narrowed section. The material analyses of stents removed from cadavers allow further development and improvement of these special devices. Despite of the widespread application of stents, not many publications deal with their technical analysis and most of them have a medical approach. This paper presents a technical analysis of three stents removed from cadavers. The results may promote the evaluation of the stent development. Until now these kind of feedback was missing from the improvement cycle.

Hydrogen in the Plastic Deformed Steel

The solubility of hydrogen in iron and steels are affected by temperature and crystal structure. At lower temperatures (below about 400°C), the excess hydrogen, beyond that which is soluble (and therefore dissolved) interstitially, is retained in the steel in other sites commonly referred to as ”traps”. At room temperature, the dissolved hydrogen may be only a small fraction of the total hydrogen content. The movement of hydrogen in steel occurs by the migration of atoms through the lattice. The hydrogen diffusion takes place with interstitial mechanism. Trapping enhances the solubility of hydrogen but decreases the diffusivity. In practice hydrogen transmissibility is characterized by TH value. We have studied the effect of the cold rolling on the TH value for Al-killed low carbon enamelling-grade steel sheets. The microstructures of the samples were formed from ferrite, carbides and some non-metallic inclusions. Reducing the thickness of the steel sheets by cold rolling in carbides appears ruptures, microcavities, and the dislocation density increases in ferrite grains. Cold work increases the hydrogen permeation time. The average of TH values after hot rolling was 0.6; after about 72 % thickness reductions by cold rolling the average TH values was 101.4.

Hydrogen permeability with dislocation in low carbon, aluminium-killed, enamel-grade steels

Abstract The role of dislocations on hydrogen permeation time of Al-killed, unalloyed low-carbon steels was investigated using a special high-resolution double crystal diffractometer operated at a rotating copper anode with fine focus. Information about dislocation character and Burgers vector populations are given by strain anisotropy. Generally, the hydrogen permeability increases or decreases with dislocation densities but hydrogen accumulation proved to be less favourable near a screw dislocation than an edge dislocation.

The Effect of Microstructure on the Wear Phenomena

When investigating the wear phenomena often there is a need for studying the wear process on the basis of variable parameters (microstructure, surface roughness, and load). A new experimental method was developed thorough several set of tests, by which the effects of the mentioned parameters in the wear process can be examined. The method is based on the ball/plane contact which is suitable for examination of the local wear phenomena. There is a point like contact at the beginning of the experiments. The equipment gives the opportunity to analyse the “behaviour” of the specimens depending on the given load (normal load), on the rotations per minute, and on the surface roughness (Ra). The roughness of the counter ball does not change during the tests because of the random walk motion of the ball. A good understanding of the microstructure and its influence on wear resistance is of great importance to designers and engineers in selecting wear-resistant materials [1]. Under conditions of severe wear, the original structure with higher hardness does not exhibit a better wear resistance [2]. The experimental results demonstrate the influence of the local microstructure on the mechanism of the wear process and the dependancy of wear resistance as a function of the microstructure.

Modelling Possibilities of the Medieval Bloomery Process under Laboratory Conditions

Two different models have been developed under laboratory conditions based on the experiences of smelting experiments carried out in bloomery furnaces patterned on some excavated 10-12th century ones. Using Rudabánya iron ore, experiments were conducted in a closed pot and in a small open shaft furnace. During the experiments the air supply, the temperature and the weight of the iron ore and the charcoal were measured. SEM-EDX analyses were performed on bloom pieces obtained from the experiments. The results of the modelling may be correlated with the results of the previous smelting experiments. The model is sufficient for investigating some adequate parameters of the medieval bloomery technology, e.g. the iron yield.

Phosphor/sulphur ratio : An indicator of malignant uterus change

The purpose of the present study was to establish a correlation between gynaecological diseases (myoma, adenocarcinoma) and phosphor/sulphur (P/S) ratios of different regions of the uterus. Routine histological specimens were reexamined with the intention to select representative regions of the uteruses for element analysis. Conventional hematoxylin-eosin-stained sections were used to identify histological alterations by light microscopy. Scanning electron microscopic (SEM) and energy-dispersive spectroscopic (EDS) investigations were carried out to analyze the morphology and the related element composition of the samples. The results of the nonparametric statistical test (Wilcoxon rank-sum test) indicate that the P/S ratios were significantly higher in adenocarcinoma (0.8891 +/- 0.0757) than in myoma (0.4713 +/- 0.0306). P/S ratios of different pathologic regions of uteruses seem worth examining in a larger study population. Combination of routine histological examinations with element analysis of specimens may have useful applications in patients who have undergone radiation therapy and may identify a pattern for local recurrence at certain sites.

Comparing Two Examination Methods for Measuring Metal to Artery Ratio of Coronary Stents

This article shows two examination methods to measure the metal to artery ratio of stents. Our goal was to further develop the previously used measuring method in order to make it suitable for the integration into the quality control process of endovascular stent manufacture to provide more realistic data. The previous method was performed manually using rotating equipment under a stereomicroscope. The new method is an automatic method using an integrated scanner and a rotating engine. Both methods aimed at converting the cylindrical stent into a flattened two-dimensional image in order to enable the measurement of stent surface area by imaging software. From the image we can determine the cell sizes, the maximum achievable stent diameter, and the structure of the stent pattern. Each measurement process was tested on different types of stents. Our findings showed that the methods gave similar results, the largest differences are speed and accuracy.

Recrystallization of Boron Containing and Boron-Free Low Carbon Steels Investigated by Thermoelectric Power and Hardness Measurements

The measurement of thermoelectric power is a powerful method to investigate the metallurgical processes occurring in steels. In this study, four low carbon cold rolled steel sheets having different composition were investigated. The cold rolled sheets were heated up at heating rate 20 °C/hour up to different temperatures, whilst the change of thermoelectric power and hardness have been measured at room temperature after slow cooling. The thermoelectric power of steels increases with temperature until the recrystallization finishes. The raise of thermoelectric power during recrystallization is ranging between 50 and 160 nV/K, depends on the composition of the sheet. Specimens consist of boron exhibit lower thermoelectric power after recrystallization than the steel without any boron, probably due to metastable borocarbide dissolution. This fact could be a good starting point to investigate the effect of boron on thermoelectric power of steels.

Grain Boundary Investigation of AISI 304 Type Steel Using EBSD

This paper deals with the investigation of grain boundary engineering processes in case of AISI 304 type austenitic stainless steel. The effects of the thermo-mechanical treatments for the modification of the grain boundary structure are demonstrated on the special grain boundaries. The proper thermo-mechanical treatments can increase the fraction of the CSL-boundaries. Since the CSL-boundaries are resistant against intergranular degradation processes, materials owning enhanced properties can be developed due to these treatments. The investigation of the grain boundary character distribution is carried out by automated electron back scattered diffraction (EBSD) measurements after different thermo-mechanical treatment processes. The effect of the heat treatment duration on the grain boundary structure is examined; the optimal treatment is represented. It is shown by experimental results, that the parameter settings of the evaluation method strongly influence the obtained results.