A stone chest found in 1971 near one of the largest early Christian basilicas in Northern Dalmatia (Croatia) contained brass tiles decorated with various biblical scenes. An archaeological study ...confirmed the thesis that the fragments of brass tiles are most likely the remains of a wooden chest made in the 4th century AD, and that this is one of the best preserved archaeological finds of its kind in the world as one of the biblical scenes shows Mary, together with a record of her name (Maria). Based on the preserved brass tiles, a reconstruction of the wooden chest was made in 1973 with tiles glued onto a plastic frame. Subsequent studies have shown that such a reconstruction was not adequate, as some of the brass tiles were destroyed (disintegrated), and they were not connected properly into a whole that could represent the original. For the new reconstruction of this archaeological object it was necessary to carry out a material analysis, including the chemical composition of the brass tiles, as well as to find a solvent for the glue which could be used to remove the brass tiles from the plastic framework without any additional destruction. Based on extensive investigations and material analyses including the following techniques (SEM, EDX, FTIR, DSC), the starting points for the restoration process of the wooden chest with brass tiles were set, as well as the proposal for the appearance of the new chest.
In this research work, we synthesised poly(methyl methacrylate) (PMMA) enriched with 2 wt.% zinc oxide nanoparticles (ZnO) through conventional heat polymerisation and characterised its ...microstructure. It was found that the distribution of ZnO nanoparticles was homogeneous through the volume of the PMMA. The mechanical testing of the PMMA-ZnO composite primarily included the determination of the compressive properties on real dentures, while density measurements were performed using a pycnometer. The testing of functional properties involved the identification of the colour of the new PMMA-ZnO composite, where pure PMMA acted as a control. In the second step, the PMMA-ZnO cytotoxicity assays were measured in vitro, which were shown to be similar to the control PMMA. Based on this, it could be concluded that the newly formed PMMA-ZnO composite did not induce direct or indirect cytotoxic effects in L929 cell cultures; therefore, according to ISO/DIN 10993-5:2009, this composite was categorised as non-cytotoxic.
The development of new multicomponent nanoparticles is gaining increasing importance due to their specific functional properties, i.e., synthesised new complex concentrated nanoparticles (CCNPs) in ...the form of powder using ultrasonic spray pyrolysis (USP) and lyophilisation from the initial cast Ag20Pd20Pt20Cu20Ni20 alloy, which was in the function of the material after its catalytic abilities had been exhausted. Hydrometallurgical treatment was used to dissolve the cast alloy, from which the USP precursor was prepared. As a consequence of the incomplete dissolution of the cast alloy and the formation of Pt and Ni complexes, it was found that the complete recycling of the alloy is not possible. A microstructural examination of the synthesised CCNPs showed that round and mostly spherical (not 100%) nanoparticles were formed, with an average diameter of 200 nm. Research has shown that CCNPs belong to the group with medium entropy characteristics. A mechanism for the formation of CCNPs is proposed, based on the thermochemical analysis of element reduction with the help of H2 and based on the mixing enthalpy of binary systems.
Introduction/Objective. The objective of this paper is to describe the microstructure and mechanical properties of sintered Co-Cr alloy and to emphasize its advantages and disadvantages with respect ...to the microstructure and mechanical properties of cast Co-Cr alloy. Methods. Base Co-Cr alloy, EOSint M EOS Co-Cr SP2 (EOS GmbH, Munch, Germany), was used for the purpose of this research as the base material for sintering metal structures of metal-ceramic restorations. Metal sintering was conducted by using EOSint M 280 device of German origin in a stream of neutral gas ? argon. After that, the alloy was heated over a period of 20 minutes at the temperature of 800?C. The chemical composition of the alloy was determined by energy dispersive spectroscopy. Microstructure of the tested alloy samples was examined under an optical metallographic and scanning electron microscope. Physical and mechanical properties were measured in a universal testing machine. The samples were prepared according to the standard ISO 527-1:1993. Results. Chemical composition of the sintered Co-Cr alloy, determined by applying energy dispersive spectroscopy, indicated the same qualitative but different quantitative composition compared to cast Co-Cr alloys. The microstructure of the sintered Co-Cr alloy is lamellar in nature, with two dominant phases: ?-Co and/or ?-Cr (fcc ? face-centered cubic) and ?-Co (hcp ? hexagonal close-packed). Mechanical properties of the Co-Cr alloy obtained by applying selective laser melting technology compared to the cast Co-Cr alloy are superior or approximately the same. Conclusion. Selective laser melting of the Co-Cr alloy is a good example of new technologies based on digitization. Together with other digitized procedures, this technology is an introduction to a new era in dentistry popularly called Dentistry 4.0. The advantages of the selective laser melting technology with respect to the conventional technology of casting Co-Cr alloy metal structures are precise metal structure fitting and eco-friendly technology.
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Biocomposites of hemp fiber reinforced bio-based high density polyethylene (green PE-HD) were prepared using a maleic anhydride grafted styrene–ethylene/butylene–styrene (SEBS-g-MA) as a ...compatibilizer. Several compositions of biocomposites were prepared on a tween screw extruder using the full factorial design varying two factors with two levels. The mechanical and thermal properties of test specimens, prepared by injection molding, were investigated by tensile and bending tests, DMA, and ultra-fast differential dynamic calorimetry (Flash DSC). High stiffness and strength of biocomposites in comparison to neat green PE-HD indicate very good compatibility of the constituents. Stiffness of the samples without SEBS-g-MA is slightly higher than that of the samples with SEBS-g-MA. The thermal stability of biocomposites is for all samples drastically higher as compared to neat green PE-HD. The melting (Tm) and crystallization (Tc) temperatures of the biocomposites are shifted to higher temperatures. Incorporation of SEBS-g-MA together with hemp fiber into the matrix enhances strength, stiffness, impact strength and rises thermal stability. The novel biocomposites are suitable for applications such as technical parts, which require higher stiffness and thermal stability as compared to neat green PE-HD.
We investigated the effects of two different types of impact modifiers, i.e. core-shell rubber and aliphatic polyester, on the mechanical and thermal properties of polylactide (PLA) filaments for 3D ...printing. First, PLA/impact modifier blends with various concentrations of impact modifiers were prepared by melt blending in a co-rotating twin screw extruder and test specimens by injection molding. The mechanical and thermal properties of blends were investigated by tensile and bending tests, dynamic mechanical analysis (DMA) and Charpy impact test. It was found that core-shell rubber remarkably improved Charpy impact strength at loadings above 5 wt % (up to 746 %). As shown by DMA, the PLA/10 wt % core-shell rubber blend exhibited better damping performance as compared to neat PLA over the whole examined frequency range, especially at high frequencies, which explained the increase in impact strength. The filament for a fused deposition modeling (FDM), 3D printer was prepared from blend with the highest impact strength (PLA/10 wt % core-shell rubber), whereas PLA and acrylonitrile-butadiene-styrene copolymer (ABS) filaments were used for reference. Test specimens were prepared by using a consumer FDM 3D printer. The mechanical and thermal properties were investigated by tensile and bending tests, DMA, Charpy impact test, and ultra-fast differential scanning calorimetry (Flash DSC). Specimens from PLA blend exhibited 109 % increase in Charpy impact strength as compared to neat PLA. In contrast to injection molded specimens, 3D printed PLA blend exhibited higher tensile E modulus than neat PLA, which was ascribed to improved interlayer adhesion. Moreover, DMA and Flash DSC analysis of 3D printed specimens showed an increase in the glass transition temperature as compared to injection molded specimens. This phenomenon was ascribed to reduction of free volume because of slow cooling in 3D printing process, which is also the reason for increased tensile E modulus of the PLA blend. All tested PLA, PLA blend and ABS filaments were in amorphous state as shown by Flash DSC analysis. Bending test showed an increased toughness of PLA blend in comparison to neat PLA and also higher toughness as compared to ABS. The modified polylactide (PLA/10 wt % core-shell rubber) filament thus combines easy processability of PLA filament and impact toughness of ABS filament.
This work presents a review of Ultrasonic Spray Pyrolysis (USP) as a technique for the synthesis of gold nanoparticle (AuNPs). The synthesis mechanism involved the preparation of the precursor ...solution from Au (III) Acetate and the study of the process parameters. AuNPs were characterized with different techniques, such as DLS, UV-vis and SEM-EDX analyses. In the second step, the AuNPs` ink was prepared with the following procedure: (i) Concentration of the AuNPs through Rotavapor, (ii) Filtration of the concentrated AuNPs through Amicon Ultra 15 Centrifugal Filters. Then, it was used directly for printing on an Ag plate. In the final part, we present some information about AuNPs` future applications, which could be in printed electronics with conducted patterns.
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