1. Combined effect of build orientation and energy density on density and mechanical properties of selectively laser melted Co-Cr-W-SiSnehashis Pal, Igor Drstvenšek, 2022, izvirni znanstveni članek Opis: The selective laser melting (SLM) process for manufacturing metals continues to be
challenging in terms of achieving the maximum metallurgical properties that the process can
provide. There are a variety of manufacturing parameters in the process that have individual
characteristics, and when combined with other variables, the characteristics can be varied.
However, in this study, the two most important manufacturing parameters, namely build direction
and laser power, were considered to investigate their effects on density and tensile properties.
Previously, the best scanning speed, hatch spacing, and layer thickness were determined, which
directly affect the volumetric energy density in the SLM process. In this study, three different
orientations and three different laser powers were selected, namely the X, Y, and Z directions and
55 W, 75 W, and 95 W laser power, respectively. Significant differences in product density were
observed for the samples fabricated in the different orientations and with the different laser
powers. The specimens fabricated in the Z direction always exhibit higher strength and ductility,
which are significantly different from the specimens fabricated in the X and Y directions, while
the laser power was 75 W and 95 W, respectively
Ključne besede: cobalt-chromium alloy, orientation, density, tensile strength, ductility, selective laser melting
Objavljeno v DKUM: 25.09.2024; Ogledov: 0; Prenosov: 8
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2. Investigation of the best manufacturing orientation of Co-Cr-W-Si dental prosthetic elements in the selective laser melting processSnehashis Pal, Janez Gotlih, Igor Drstvenšek, 2022, izvirni znanstveni članek Opis: It is well known that Selective Laser Melting (SLM) does not provide the same mechanical
properties in all directions of the part. This is due to the microstructural grain orientation and
pore shape in SLM products. Therefore, depending on the direction of the pressure applied to the
SLM product, a different manufacturing orientation is required to achieve the best mechanical
properties. Changing the microstructural grain orientation is difficult through SLM, but a process
to reduce the size and number of the pores can be discovered through different combinations
of manufacturing parameters. In prosthodontics, pressure is usually applied in the vertical
direction, which leads to compression and bending of crowns with bridges. The compressive
load can be easily absorbed in the crowns, but the bending force has a significant effect here.
Therefore, a product with high tensile strength and high ductility is needed to survive longer.
Considering these requirements, this study determined the best parameters for laser processing
by SLM method to reduce porosity and improve mechanical strength and ductility of Co-CrW-Si alloy products. The result is a relative product density of 100% for cubic specimens and a
yield strength, ultimate tensile strength, and elongation at break of the tensile specimens of 900
MPa, 1200 MPa, and 15%, respectively, obtained in specimen build-up in the Z direction with a
laser power of 60 W and a scanning speed of 450 mm/s. Eventually, the best orientation for the
production of dental prosthetic elements using the SLM process was determined.
Ključne besede: cobalt-chromium alloy, dental implant, density, tensile strength, ductility, selective laser melting
Objavljeno v DKUM: 03.07.2024; Ogledov: 78; Prenosov: 8
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3. Loss of oxygen atoms on well-oxidized cobalt by heterogeneous surface recombinationDomen Paul, Miran Mozetič, Rok Zaplotnik, Jernej Ekar, Alenka Vesel, Gregor Primc, Denis Đonlagić, 2023, izvirni znanstveni članek Opis: Calorimetry is a commonly used method in plasma characterization, but the accuracy of the method is tied to the accuracy of the recombination coefficient, which in turn depends on a number of surface effects. Surface effects also govern the kinetics in advanced methods such as atomic layer oxidation of inorganic materials and functionalization of organic materials. The flux of the reactive oxygen atoms for the controlled oxidation of such materials depends on the recombination coefficient of materials placed into the reaction chamber, which in turn depends on the surface morphology, temperature, and pressure in the processing chamber. The recombination coefficient of a well-oxidized cobalt surface was studied systematically in a range of temperatures from 300 to 800 K and pressures from 40 to 200 Pa. The coefficient increased monotonously with decreasing pressure and increasing temperature. The lowest value was about 0.05, and the highest was about 0.30. These values were measured for cobalt foils previously oxidized with oxygen plasma at the temperature of 1300 K. The oxidation caused a rich morphology with an average roughness as deduced from atomic force images of 0.9 µm. The results were compared with literature data, and the discrepancy between results reported by different authors was explained by taking into account the peculiarities of their experimental conditions.
Ključne besede: heterogeneous surface recombination, recombination coefficient, cobalt, cobalt oxide, temperature dependence, pressure dependence, plasma, oxygen
Objavljeno v DKUM: 26.03.2024; Ogledov: 228; Prenosov: 18
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4. The magnetic and colloidal properties of $CoFe_2O_4$ nanoparticles synthesized by co-precipitationSašo Gyergyek, Mihael Drofenik, Darko Makovec, 2014, izvirni znanstveni članek Opis: Magnetic $CoFe_2O_4$ nanoparticles were synthesized by co-precipitation at 80 °C. This co-precipitation was achieved by the rapid addition of a strong base to an aqueous solution of cations. The investigation of the samples that were quenched at different times after the addition of the base, using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) and X-ray powder diffractometry, revealed the formation of a Co-deficient amorphous phase and $Co(OH)_2$, which rapidly reacted to form small $CoFe_2O_4$ nanoparticles. The nanoparticles grew with the time of aging at elevated temperature. The colloidal suspensions of the nanoparticles were prepared in both an aqueous medium and in a non-polar organic medium, with the adsorption of citric acid and ricinoleic acid on the nanoparticles, respectively. The measurements of the room-temperature magnetization revealed the ferrimagnetic state of the $CoFe_2O_4$ nanoparticles, while their suspensions displayed superparamagnetic behaviour.
Ključne besede: cobalt ferrite, nanoparticles, co-precipitation, colloidal suspensions, magnetic properties
Objavljeno v DKUM: 30.08.2017; Ogledov: 2809; Prenosov: 107
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5. PB(II) AND HG(II) IONS ADSORPTION USING SURFACE MODIFIED SUPERPARAMAGNETIC IRON OXIDE NANOPARTICLES2014, doktorska disertacija Opis: Cobalt ferrite (CoFe2O4) nanoparticles prepared via co-precipitation method were modified with tetraethoxysilane (TEOS) and additional funkcionalized with 3-mercaptopropyl trimethoxysilane (MPTMS) with purpose of cleaning waste water contaminated with heavy metal ions (Pb2+ and Hg2+).
The influence of different experimental parameters (reaction time, reaction temperature and different TEOS:MPTMS ratios) on silica coating of CoFe2O4 nanoparticles and additional on thiol group was systematically studied. Silanes adsorb to the particle surface with alkoxy (Si(OR)4) groups at one end, while functional substituents (-SH) at the opposite end stay extended into surrounding aqueous medium and chemically interact with heavy metal contaminates.
Thiol functionalized CoFe2O4 nanoparticles were characterized using IR spectroscopy, X-ray diffraction (XRD), transmission electron microscopy/high-resolution transmission electron microscopy (TEM/HRTEM), energy-dispersive X-ray spectroscopy (EDXS) and vibrating-sample magnetometer (VSM).
The thiol functionalized CoFe2O4 nanoparticles were used for Pb2+ and Hg2+ions adsorption from aqueous media. Effect of treatment has been demonstrated using atomic absorption spectroscopy (AAS).
Ključne besede: cobalt ferrite, magnetic nanoparticles, tetraethoxysilane, 3-mercaptopropyl trimetoxysilane, thiol group, lead, mercury, adsorption
Objavljeno v DKUM: 02.12.2014; Ogledov: 3217; Prenosov: 212
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