Key Engineering Materials Vol. 674

Abstract: The aim of this work was to evaluate the effect of precursor materials used in the synthesis on the Sr incorporation levels into the hydroxyapatite (HAp) lattice and to characterize the synthesis products. HAp powders containing various amounts of Sr were synthesized through three different precipitation routes. In all cases, the as-synthesized products were found to be pure HAp. However, atomic absorption spectrometry analysis showed that by reacting orthophosphoric acid with calcium hydroxide and strontium hydroxide, as well as by reacting diammonium hydrogen phosphate with calcium nitrate tetrahydrate and strontium nitrate a significant proportion of the Sr added, did not substitute into the HAp lattice. X-ray diffraction analysis revealed that the effect of substituting relatively high amounts (up to 3.69 ± 0.37 wt.%) of Sr into the HAp lattice was to decrease the cristallinity. Brunauer-Emmett-Teller (nitrogen absorption) analysis showed that the incorporation of Sr reduced particle sizes of the precipitated HAp products. Contrary, scanning electron microscopy revealed that the incorporation of Sr increased length of the precipitated needle-like particles.

Abstract: This study explores possible ways to make Additive Manufacturing (AM) a cradle-to-cradle process, that is, use the leftover from one process as the raw material for another process. The main goal of this study is to develop a set of new polymeric blends with innovative properties, suitable for using in 3-D printing of prosthetic limbs using Fused Deposition Modeling (FDM) technology. Sustainable acting is achieved by reusing polymeric material left over from Selective Laser Sintering (SLS) processes for making raw material for FDM processes. Test specimens of polyamide 12 (PA-12) in its virgin form and used- , un-sintered form alongside specimens of used PA blended with TPU, aramid, or graphite, were produced in a micro-injection moulding machine and then tested for their mechanical properties. This paper provides information about the differences in mechanical characteristics of these different material blends. An unexpected but positive finding was that the differences between virgin and recycled PA-12 are insignificant. The aforementioned additives influenced PA-12 by producing specimens that responded with predictable characteristics which is a significant accomplishment as it lays the groundwork for the next stages of the project.

Abstract: Ceramic materials have become of high industrial importance in some applications as their properties outperform ones of metallic components. However, use of ceramics is limited due to the difficulties in shaping. Electrically conductive ceramics can be machined by Electro-Discharge Machining (EDM) irrespective of its hardness or strength. In this study, yttria stabilized zirconia (YTZP) conductive composite was produced by incorporation of the cost-effective graphene coated alumina nanofibers (ANFC) into the matrix. Almost fully dense YTZP/5 vol.% ANFC nanocomposite was obtained by spark plasma sintering (SPS) at 1250 °C with uniaxial pressure of 40 MPa. Scanning electron microscopy observation of the microstructures showed that ANFCs were homogeneously dispersed in the matrix. Addition of ANFC resulted in slightly decreased mechanical properties, but the electrical resistivity of the composite dropped 9 orders of magnitude compared to monolithic zirconia, exhibiting 1.4 Ω∙m, satisfying the required condition for the EDM.

Abstract: Cellulose nanocrystals (CNCs) have generated increasing attention in the past few years as potential sources of innovative bionanomaterials. This study focuses on an alternative method of nanocellulose particle preparation, using ammonium persulfate, and compares this to existing techniques. Nanoparticles were prepared using 4 different methods: thermocatalytic method, TEMPO oxidation, the acid hydrolysis and oxidation with ammonium persulfate. With the ammonium persulfate method, the grinding time of the oxidised cellulose is reduced drastically to only 0.5h, and results in an average nanoparticles size of 404.5 nm, zeta potential of -26.4 and crystallinity degree of 80%. Based on comparison of these parameters to results from existing techniques, oxidising cellulose using ammonium persulfate appears to be a promising alternative.

Abstract: Wood-based nanoparticles fabricated by different optimized methods – acid hydrolysis, thermocatalytic destruction and TEMPO catalysed oxidation – show the potential to improve the physical-mechanical and biological properties of polymer-matrix biocomposites. In this work, the influence of obtained nanoparticles on physical-mechanical and biological properties of chitosan-matrix biocomposite was investigated. The results showed that wood-based nanoparticles are promising constituents of polymer-matrix biocomposites.

Abstract: Nickel aluminate spinel (NiAl2O4) has received attention as a catalyst solid support due to its stability, strong resistance to acids and alkalis and high melting point. The properties and quality of the catalysts are heavily affected by crystal size, morphology, phase homogeneity and surface characteristics of the materials, which themselves are dependent on method and parameters of processing rout. In this work, we report on the fabrication of novel NiAl2O4 nanofibers covered by NiO nanolayer by combustion method.The XRD patterns show that the combustion technique was excellent to prepare NiO/NiAl2O4 nanofibers. The crystallite sizes of NiAl2O4 and NiO were found to be around 27 and 19 nm correspondingly. Scanning electron micrographs (SEM) and Energy dispersive X-ray (EDX) analysis showed that the NiO/NiAl2O4 nanofibers with more than 20 nm in diameter were consist of NiAl2O4 core and NiO outer layer.

Abstract: This paper addresses an innovative syntactic foam produced out of metal powder (Fe), fly ash cenospheres (CS) and clay ceramic syntactic foams composite material (CM). Due to the low density of CS (bulk density - 0.38 g/cm³), the average density of these foams is about 2.6-2.9 g/cm³. It was found that CS undergoes phase transformation during thermal treatment at a temperature of 1200°C. Microstructural observations reveal a uniform distribution of CS and Fe particles in the composite. Compressive strength, and friction coefficient of obtained Fe/CS CM are in the range between 149 - 344 MPa and 0.15 - 1.1, respectively. Dependence of compressive strength on firing temperature is demonstrated exhibiting the maximum at 344 MPa; however, dependence of coefficient of friction on a material properties, obtained at different firing temperature exhibits the minimum value of 0.15 at the firing temperature of 1150 °C. The obtained syntactic form was shown to be a candidate for wear resistant applications.

Abstract: In the present work the methods for producing flat and three-dimensional shielding screens from the perforated steel tape are proposed. The possible application variants of mentioned screens are offered and analyzed. Main attention is given for producing one-layer and multi-layer screens with cellular structure due to its relatively low weight and technological elasticity – complex three-dimensional structures could be done successfully.Examples of produced shielding screens from the perforated steel tape for protection from electromagnetic fields in different frequency range are offered and tested. The efficiency of a shielding material was determined by measuring the magnetic field before and after applying the shielding material. Distribution of the magnetic field behind the shielding screen was determined by software vector mapping. Shielding efficiency was measured for 1) a three-layer perforated steel screen; 2) an one-layer perforated steel screen - shielding screen was placed in between the magnetic field source and the measurement point forming a two dimensional screen; 3) copper composite sprayed screen. During experimental investigation it was established, that a three-layer perforated steel screen application allowed the 27% reduction in the magnetic field, while one-layer perforated steel screen gave only 12% reduction. Copper composite sprayed screen reduced magnetic field by 15%.Recommendations for producing the multi-layer perforated steel screen accordingly to shielding efficiency are elaborated and laid down. The discussed material carries also ecological significance, since the material is produced by waste products (after stumping etc.). Therefore the production of such materials comes with reduced cost both in light of capital expenditures and ecological footprint.

Abstract: The present article focuses on manufacturing of metal powder filled pultrusion profiles for electro-technical applications. Herein a set of test material has been reviewed, which was prepared with the aim to present an optimized composite structure with high metal powder content for magnetic slot wedge production, outperforming the products currently available by alternative technology – compression moulding.This article gives a short overview of incorporating fine metal powders as fillers into pultrusion process (including the technical challenges) and the experimental work done in the project. The selection and analysis of components have been briefly discussed along with the results of material tests conducted on prepared composite samples. Mechanical, dielectric and magnetic properties of the samples were studied at different filler loadings and compared to the properties of iron powder filled compressed laminates.Several application specific material properties were determined, including flexural strength according to ISO 178, volume and surface resistivity similarly to IEC 93, and relative permeability using vibrating sample magnetometer (VSM). Scanning Electron Microscope (SEM) and various image processing software were used to analyse the composition and microstructure of the material samples. Material test results are presented at different iron powder loadings from 20 to 55 wt% and recommendations given for optimal materials selection.