Papers by Author: Andrzej Roman Olszyna

Abstract: The purpose of the study was to identify the influence of the amount of fluoride release from glass ionomer cements on survival of bacterial strains responsible for the development of secondary caries. All developed cements had an antibacterial impact on the strains used in the study. The study demonstrated that the cements exhibit greater antibacterial activity against Streptococcus mutans than Streptococcus sanguinis. The numbers of bacteria count in cultures on the developed cements were approximately 10 times lower compared to the control culture after 24 h, 48 h, 72 h and 7 days. The developed cements had initially (1-2 days) greater antibacterial impact against the strains used in the study, which corresponds to the greatest daily amount of fluoride released from the cements. Following the initial period, the antibacterial activity of all the cements remained roughly at the same level.

Abstract: The research of obtained bioglasses in the form of silver-containing powders were presented in this paper. The research conducted in order to determine antimicrobial activity under in vitro conditions of bioglasses. The results confirmed that these bioglasses Z-5, Z-8 and B-I inhibit the growth of most micro-organisms during the tested period and could be used in surgical treatment of the most advanced parodontium illnesses.

Abstract: The paper is concerned with the thermal properties of cathodic ceramic targets built on the basis of zirconium oxide modified with rare earth metal oxides such as La2O3, Nd2O3, and Gd2O3. The experiments also included the production of the TZ-3Y, TZ-3Y+20mol% coatings (La2O3, Gd2O3) using the EB-PVD method, and characterization of these coatings. Within the temperature range examined (20 to 120oC), the targets that contained rare earth metal oxides appeared to have lower thermal conductivity λ (2.07-1.22 Wm-1K-1) than the TZ-3Y target (3.6-3.05 Wm-1K-1). The present study was a continuation of our earlier experiments devoted to the examinations of zirconium oxide ceramic targets intended for producing refractory, heat-resistant nanocrystalline coatings.

Abstract: The present study is concerned with the morphology, physical properties and biocidal activity of Al2O3-Ag nanopowders produced by two methods: thermal decomposition-reduction and the silver nitrate reduction. The innovative method of thermal decomposition-reduction has been described in our earlier publication and is protected by our patent application, whereas the silver nitrate reduction method is commonly used in industry at the present. The nano-powders produced by these two methods differ considerably from one another in terms of their morphology and physical properties. The proposed method of thermal decomposition-reduction gives Al2O3-Ag nano-powders which are not only much less agglomerated with the average agglomerate sizes below 1 µm, but also the average size of their particles is considerably smaller (below 60 nm). Moreover, their specific surface is larger (above 200 m2g-1) and they have good bactericidal and fungicidal properties.

Abstract: A good selection of growth parameters (in-situ etching, C/Si ratio, growth rate) enables obtaining of ~1nm high steps of epitaxial layers, which are comparable to the size of an elementary cell (8°off-axis) and achieve the density of BPD=8•103/cm2. Due to crystallization on substrates with low misorientation (<2°off-axis) it is possible to obtain epitaxial layers substantially lacking in BPD dislocations. However, a slightly more developed surface with Ra=1-2.5nm (1.25°, 2°off-axis) characterizes these layers. By lowering the C/Si ratio, morphology of layers crystallized on substrates with low misorientation was improved. Extending growth rate improved both the crystallographic quality of the grown layers and their polytype stability. Nevertheless, growth without BPDs, also referred to as the homogeneous (4H) polytypic growth on 4H-SiC on-axis substrates, is the most efficient way of defect elimination.

Abstract: Technology of thermal ceramic barriers (TBC) has been chiefly designed for materials with a single thermal barrier of the 7YSZ type. A high content of Y2O3 ensures a good phase stability of the YSZ material. In search for other alternative materials suitable for TBC, the material most often examined is modified zirconium oxide. The modification consists of stabilizing the ZrO2 powder with Y2O3 and doping it with La, Gd and Nd. This paper presents the results of studies on producing cathodic zirconium oxide-based ceramic targets intended for depositing refractory heat-resistant nano-crystalline TBC coatings. The targets are characterized by a high density (close to its theoretical value) and have a homogeneous phase and chemical structure.

Abstract: The electron backscatter diffraction (EBSD) detector placed inside a commercial scanning electron microscope (SEM) has been used to study of different SiC polytypes. Different growth conditions in chemical vapor deposition (CVD) method were applied to obtain the 3C- and 4H-SiC polytypes epitaxial layers. Growth processes were conducted on the Si-face on-axis 4H-SiC substrates. The growth temperature was in the range of 1300-1620°C and the reactor pressure was 75mbar. The initial C/Si ratio was varied from 0.075 reaching final value of 1.8. It was observed that intentional ramping of the C/Si ratio at the first stage of the growth clearly influences the 4H/3C factor. The growth temperature and ramping of the C/Si ratio were the main parameters to achieve a homogeneous 3C and 4H-SiC epitaxial layers.

Abstract: Paper presents a novel application of magnetostrictive delay lines, which give a possibility of real time monitoring of strain in ceramic components. Magnetostrictive delay line was based on highly magnetostrictive Fe-Si-B amorphous alloy ribbon, mounted outside of ceramic component, what is a new solution for increasing sensor’s sensitivity. Developed specially for this sensor, hybrid digital-analog signal processing unit covers the sample-and-hold integrated circuit. The achived sensitivity and repeatability of the sensor confirms, that such solution is suitable for ceramic machine tool monitoring.

Abstract: Crystallographic quality of the epitaxial layers depends on the process temperature, partial pressures of active components and the surface polarity and also on the crystallographic quality of the subsurface layer resulting from the preparation of the substrate. The polishing etching in hydrogen-propane atmosphere of 4H-SiC substrate of different orientations and polarity was studied. The optimization of the polishing etching has been achieved with respect to the flow of C3H8, the duration and the temperature of the process. The investigation of the surface of SiC substrate before and after in situ polishing-etching in H2+C3H8 atmosphere was carried out by Nomarski interference contrast microscopy (DIC) and atomic force microscope (AFM).

Abstract: The influence of in situ etching of Si-face n-4H-SiC wafers in H2 and propane on the surface morphology of the grown epi-layers were examined using differential interference contrast (DIC) optical microscopy and atomic force microscope (AFM). Two defect-selective etching techniques were applied in order to reveal the type and spatial distribution of defects in the substrates and epi-layers. It was found that for the flow applied in this experiment propane plays a significant role for the etching process. Depending on temperature and etching time we obtained completely different picture of substrate surface morphology. The propane etching was verified as a tool for substrate surface improvement.