In this paper we discuss the mechanical and thermal properties of shape-memory polymer composites (SMPCs) filled with SiO2 nanoparticles. A series of SMPC samples was prepared using a commercially provided shape-memory polymer (SMP) filled with different mass fractions of 600-nm and 130-nm SiO2 particles. The mechanical properties of the SMPCs were determined by performing three-point bending (3PB) and Izod impact tests. The thermomechanical and thermal behaviors were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA).
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 915882In this paper we focus on the preparation of thin polymer coatings synthetized from 30-nm and 600-nm silica particles dispersed in polyvinyl chloride (PVC) and deposited on two different steel substrates: duplex DSS 2205 and austenitic AISI 316L steel. We show that a silica surface modification with silane IO7T7(OH)3 (trisilanol isooctyl polyhedral oligomeric silsesquioxane, POSS) significantly improves its dispersion properties when mixed with PVC. For comparison, the surface morphology and surface roughness of PVC coatings filled with both silanated and as-received (non-silanated) silica fillers were analyzed with scanning electron microscopy (SEM) and atomic force microscopy (AFM) when sprayed on the steel surface. The effect of the silica silanization is later on reflected in a decreased average surface roughness in the silanated, compared to non-silanated, silica/PVC-coatings. The wetting properties of the silanated and non-silanated silica/PVC-coatings on DSS 2205 and AISI 316L were investigated using contact-angle and surface-energy measurements, indicating an increased surface hydrophilicity in terms of a decreased static water contact angle and an increased total surface energy compared to the uncoated specimens. Finally, the beneficial corrosion resistance of the silica/PVC coatings was confirmed with potentiodynamic polarization spectroscopy in a 3.5% NaCl solution.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 5029914One of the constituent elements in Auger electron spectroscopy (AES) spectra that make their automatic analysis next to impossible is the background. To overcome this obstade and enable further processing, the background removal stage must provide the clear enough data for the techniques capable of automatically extracting the requested information from the AES spectra. It is also known that the background in AES spectra contains further information regarding the composition of the sample studied. Thus, although removed, this background should not be disregarded. In our work, the neural networks for data modeling or background function approximation were used. Neural networks were used for the determination of the general shape of the background in AES spectra. Neural networks are model-less approximators, meaning that they are capable of accomplishing the approximation tasks regardiess of any prior knowledge on the nature of the modeled system. According to our analysis, three distinctive parts of the background in the spectra were proposed. One of them is the so-called peak base. The use of the neural network for the substraction of the peak base is described further in this article.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 923818Because of their unique mechanical properties, shape memory and super plasticity, durability and biocompatibility, Ni-Ti alloys are the most important memory shape alloys for applications in a wide range of medical implants and devices. These alloys contain approximately equal Ni and Ti atomic concentrations, meaning medical applications are still hindered by the concern for the release of Ni into surrounding tissues. We have studied the surface composition of a melt-spun Ni-Ti shape memory alloy using different surface analytical techniques, namely, Auger electron spectroscopy and X-ray photoelectron spectroscopy, before and after testing its biocompatibility in vitro. We have found that the surface consists of an oxide layer of 10 to 20nm thickness, composed of Ti oxide and some Ni oxide with metallic Ni inhomogeneously distributed in the subsurface region.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 15760150Recent research has shown a dependence of the accelerated creep rate on the carbide particle distribution in martensite, with the creep rate depending on the number of carbide particles per unit of surface and their mutual distance. The aim of our work was to calculate the activation energy for different carbide particle sizes and particle spacings, using a modified equation for the creep rate calculation. For creep-resistant steel with a microstructure of ferrite matrix and a uniform distribution of M23C6 carbide particles the creep rate was calculated in the temperature range 540 °C to 630°C and a carbide particle size between 0.1 [mu]m and 0.4 [mu]m. An equal effect on the creep rate increase was found for all four carbide particle sizes. From the calculated creep rates a creep activation energy of 248.7 kJ/mol was calculated, independent of the particles size. The calculated creep activationenergy was found to be close to the self-diffusion activation energy in [alpha]-iron.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 951978