Key Engineering Materials Vol. 674

Abstract: We describe the mass-spectrometric approach to the analysis of the water release in the course of wear experiments in vacuum conditions. The approach is tested in wear experiments with polyurethanes and their composites.

Abstract: Biomaterials used in bone repair must satisfy certain criteria in order to perform without undesirable immunological response. They must be biocompatible and should inhibit bacteria adhesion on the surface, that could led to strong inflammatory process and implant failure. Our study reveals a synergistic effect on bioactivity and bacteriostasis effect of the TiO₂ ceramics with different surface properties and provides insight into the design of better biomedical implant surfaces. The results show that UV light irradiation has great impact on hidrophilicity of TiO₂ ceramics, but little effect on the sample bacteriostatic effect and bioactivity. TiO₂ ceramic samples showed no or very low bacterial adhesion. Nevertheless, in vitro bioactivity showed TiO₂ ceramic that was thermally treated at lower temperature. Thus for bone repair it’s suggested to use TiO₂ ceramic sintered at lower temperature in order to provide bioactivity with bacterostatic effect and use UV-light irradiation to improve hidrophilicity.

Abstract: Journal bearings are widely used in heavy industry and in internal combustion engine applications. There is a need to increase the power density of various machine parts which leads to increased bearing loads and reduced lubrication film thicknesses. This type of development may increase deformations on the bearing surfaces which need to be considered in the bearing design process.The main purpose of this work was to develop a parameterized calculation model for hydrodynamic radial journal bearings which takes into account elastic and thermal deformations of the bearing surfaces. Hydrodynamic calculations were based on the numerical solving of the Reynolds equation by assuming rigid surfaces. Elastic and thermal deformations of the bearing and shaft surfaces were calculated by using the finite element method. It is concluded that elastic and thermal deformations are partly canceling each other out at the loaded side of the bearing and depending on the sliding speed and the external normal force either one of them could be more significant.

Abstract: This work presents a method that enables the cheap production of surfactant-free stable metal nanoparticles in air. The silver nanoparticles are good candidates for new applications in green housing. Recently, we demonstrated usage of air-stable silver MNPs as biocidal coatings instead of chemical agents for protection of straw bales used in a green housing construction. Application of the silver nanoparticles as antifungal agents needs a method that does not neutralize their biocidal properties as a result of the testing method. In this study, we discuss the usual methods that are used for the antibacterial property testing and the development of a method that allows demonstrating the antifungal properties of metal nanoparticles.

Abstract: In current research three different prepared calcium deficient hydroxyapatite samples were evaluated for dental application. Lyophilized (lyoCDHAp), spray dried (spCDHAp) powders and wet precipitates (pCDHAp) were characterized by XRD, FTIR, SEM and BET analysis. Results showed, that various drying processes did not affect initial crystallinity, phase and chemical composition of samples. Small agglomerates (up to 2 μm) beside separated particles for lyoCDHAp and spCDHAp were observed in SEM analysis. LyoCDHAp and spCDHAp powders could be used as desensitizing component in the dentifrice, while pCDHAp could be more resorbable due to smaller particle size and induce remineralization of caries sites in the enamel.

Abstract: The study investigates alterations in surface morphology of microcrystalline diamond (MCD) film under reciprocating sliding test conditions. The MCD film was grown by microwave plasma enhanced chemical vapor deposition (MW-PECVD) on (100)-oriented Si wafer. The surface morphology was characterized by optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and mechanical profilometry. The formation of ripples on the wear scar surfaces was observed. The normalized wear rate (mm³/mN) of diamond film was evaluated using different approaches in order to understand the influence of diamond film deflection to wear.

Abstract: Nitrocarburized steel surfaces are often used in tribological forming applications due to their beneficial sliding properties. One typical application field can be found in bending machines where the nitrocarburized layer can withstand massive volume loss and prevent from adhesion of the work sheet material. However, under non-lubricated sliding conditions abrupt failure of the nitrocarburized layer can occur, which results in pronounced increase of friction and wear. In order to characterise the wear mechanisms of nitrocarburized surfaces under non-lubricated sliding conditions, a lab-scale study was carried out. Different nitrocarburizing processes including plasma, gas and salt bath nitrocarburizing were investigated. Oscillating sliding tests with DIN 100Cr6 bearing steel cylinder sliding against nitrocarburized plate were performed at contact pressures typical for bending machines. Evaluation of wear was performed by white-light interferometer with measurements of the wear-scar topography and a subsequent calculation of the average wear depth. A strong influence of the nitrocarburizing process on friction and wear behaviour was observed. This behaviour could be correlated with the microstructure of the compound layer.

Abstract: The paper deals with the effectiveness of blended phosphonate-based superplasticizers (PHN) for ready mixed concrete. Two phosphonates (PNH1 and PNH2) were added in different percentage to naphthalene sulphonate (NSF) or polycarboxylates (PCEs) based admixtures to improve both compatibility with different cements and workability retention of concrete. The performance of the obtained concrete mixtures was compared to concretes manufactured with the pure NSF or PCE based admixtures. Concretes with the same initial workability (flow table > 580mm) were produced at a temperature of 20 °C and 30 °C. Workability was measured at 0, 30 and 60 minutes to evaluate the flow retention performances of blended superplasticizers. Compressive tests were carried out to study the influence of the superplasticizer on concrete strength gain at the age of 1, 7 and 28 days. PNH1 in combination with NSF improved workability retention with respect to pure NSF, but caused a reduction in the early compressive strength when the dosage exceeded 0.10% (dry polymer vs. cement mass). Dosage of hybrid PCE-PNH superplasticizers to attain the targeted workability was lower with respect to hybrid PNH1/NSF admixtures. PNH1 was more effective than PNH2 in hybrid PCE admixtures in terms of workability retention. A threshold value for PNH dosage (about 0.18 - 0.20 %) exists also in hybrid PCE superplasticizers, but it is about two times higher than that of hybrid PNH1/NSF.

Abstract: In situ observation of AZ61 Mg alloy with 5 wt. % of Al₂O₃ in the SEM was performed to study influence of the weight fraction of Al₂O₃ particles on the deformation and fracture description during the tensile test. Structure of the experimental materials was also analysed; microstructures were heterogeneous, with randomly distributed globular Al₂O₃ particles (average diameter of 25 nm) and Mg₁₇Al₁₂ intermetallic phase (average diameter of 0.4 mm). It was shown that during the tensile deformation the failure of Mg₁₇Al₁₂ particles and decohesion of the matrix-Al₂O₃ particles interphase boundary started simultaneously. Decohesion resulted from the different physical properties of matrix and Al₂O₃ particles. The influence of the Al₂O₃ weight fraction on the final fracture was evident; for the material with 5 wt. % of Al₂O_3, the fracture surface was approximately perpendicular to the loading direction. The fracture surface had transcrystalline ductile character.

Abstract: Acrylonitrile butadiene styrene (ABS) terpolymer is one of the major plastics in IT equipment waste stream. In the current research secondary ABS (s-ABS) is blended with polycarbonate (PC) by forming one of the most popular thermoplastics engineering system. The effect of organically modified montmorillonite clay (OMMT) on the tensile properties and thermal stability of PC+10wt.%s-ABS blend is investigated. Increase in stiffness, strength and thermal stability is observed along with rising OMMT content. Highest increments of the aforementioned properties are observed within the OMMT range of 1-1,5 wt.%.