391 research outputs found
Characterization of a defective PbWO4 crystal cut along the a-c crystallographic plane: structural assessment and a novel photoelastic stress analysis
Among scintillators, the PWO is one of the most widely used, for instance in
CMS calorimeter at CERN and PANDA project. Crystallographic structure and
chemical composition as well as residual stress condition, are indicators of
homogeneity and good quality of the crystal. In this paper, structural
characterization of a defective PbWO4 (PWO) crystal has been performed by X-ray
Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Photoelasticity in
the unusual a-c crystallographic plane. XRD and EDS analysis have been used to
investigate crystallographic orientation and chemical composition, while stress
distribution, which indicates macroscopic inhomogeneities and defects, has been
obtained by photoelastic approaches, in Conoscopic and Sphenoscopic
configuration. Since the sample is cut along the a-c crystallographic plane, a
new method is proposed for the interpretation of the fringe pattern. The
structural analysis has detected odds from the nominal lattice dimension, which
can be attributed to the strong presence of Pb and W. A strong inhomogeneity
over the crystal sample has been revealed by the photoelastic inspection. The
results give reliability to the proposed procedure which is exploitable in
crystals with other structures.Comment: 18 pages, 10 figures, revised versio
Bone-anchored hearing implant surgery: our experience with linear incision and punch techniques.
Beads for Cell Immobilization: Comparison of Alternative Additive Manufacturing Techniques
The attachment or entrapment of microbial cells and enzymes are promising solutions for various industrial applications. When the traps are beads, they are dispersed in a fluidized bed in a vessel where a pump guarantees fresh liquid inflow and waste outflow without washing out the cells. Scientific papers report numerous types of cell entrapment, but most of their applications remain at the laboratory level. In the present research, rigid polymer beads were manufactured by two different additive manufacturing (AM) techniques in order to verify the economy, reusability, and stability of the traps, with a view toward a straightforward industrial application. The proposed solutions allowed for overcoming some of the drawbacks of traditional manufacturing solutions, such as the limited mechanical stability of gel traps, and they guaranteed the possibility of producing parts of constant quality with purposely designed exchange surfaces, which are unfeasible when using conventional processes. AM proved to be a viable manufacturing solution for beads with complex shapes of two different size ranges. A deep insight into the production and characteristics of beads manufactured by AM is provided. The paper provides biotechnologists with a manufacturing perspective, and the results can be directly applied to transit from the laboratory to the industrial scale
Biomedical Co-Cr-Mo Components Produced by Direct Metal Laser Sintering
Direct Metal Laser Sintering (DMLS) is an additive manufacturing technique based on a laser power source that sinters powdered materials using a 3D CAD model. The mechanical components produced by this procedure typically show higher residual porosity and poorer mechanical properties than those obtained by traditional manufacturing techniques. In this study, samples were produced by DMLS starting from a Co-Cr-Mo powder (in the \u3b3 phase) with a composition suitable for biomedical applications. Samples were submitted to hardness measurements and structural characterization. The samples showed a hardness value remarkably higher that those commonly obtained for the same cast or wrought alloys. In fact, the HRC value measured for the samples is 47 HRC, while the usual range for CAST Co-Cr-Mo is from 25 to 35 HRC. The samples microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX) in order to clarify the origin of this unexpected result. The laser treatment induced a melting of the metallic Co-Cr-Mo powder, generating a phase transformation from the \u3b3 (fcc) to the e (hcp) phase. The rapid cooling of the melted powder produced the formation of e (hcp) nano-lamellae inside the \u3b3 (fcc) phase. The nano-lamellae formed an intricate network responsible for the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields, where a high degree of personalization is required
Solid-state phase transformations in thermally treated Ti-6Al-4V alloy fabricated via laser powder bed fusion
Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained \u3b2 in \u3b1' martensite of the as-produced (#AP) sample. The retained \u3b2 was not detectable byXRDanalysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the \u3b1 \u2194 \u3b2 transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained \u3b2 phase plays a key role in the \u3b1' \u2192 \u3b2 transformation kinetics
Effects of build orientation and element partitioning on microstructure and mechanical properties of biomedical Ti-6Al-4V alloy produced by laser sintering
Direct Metal Laser Sintering (DMLS) technology was used to produce tensile and flexural samples based on the Ti-6Al-4V biomedical composition. Tensile samples were produced in three different orientations in order to investigate the effect of building direction on the mechanical behavior. On the other hand, flexural samples were submitted to thermal treatments to simulate the firing cycle commonly used to veneer metallic devices with ceramics in dental applications. Roughness and hardness measurements as well as tensile and flexural mechanical tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate sample microstructure. Results evidenced a difference in the mechanical response of tensile samples built in orthogonal directions. In terms of microstructure, samples not submitted to the firing cycle show a single phase acicular α’ (hcp) structure typical of metal parts subject to high cooling rates. After the firing cycle, samples show a reduction of hardness and strength due to the formation of laths of the β (bcc) phase at the boundaries of the primary formed α’ plates as well as to lattice parameters variation of the hcp phase. Element partitioning during the firing cycle gives rise to high concentration of V atoms (up to 20 wt%) at the plate boundaries where the β phase preferentially forms
Features of Vat-Photopolymerized Masters for Microfluidic Device Manufacturing
The growing interest in advancing microfluidic devices for manipulating fluids within micrometer-scale channels has prompted a shift in manufacturing practices, moving from single-component production to medium-size batches. This transition arises due to the impracticality of lab-scale manufacturing methods in accommodating the increased demand. This experimental study focuses on the design of master benchmarks 1–5, taking into consideration critical parameters such as rib width, height, and the relative width-to-height ratio. Notably, benchmarks 4 and 5 featured ribs that were strategically connected to the inlet, outlet, and reaction chamber of the master, enhancing their utility for subsequent replica production. Vat photopolymerization was employed for the fabrication of benchmarks 1–5, while replicas of benchmarks 4 and 5 were generated through polydimethylsiloxane casting. Dimensional investigations of the ribs and channels in both the master benchmarks and replicas were conducted using an optical technique validated through readability analysis based on the Michelson global contrast index. The primary goal was to evaluate the potential applicability of vat photopolymerization technology for efficiently producing microfluidic devices through a streamlined production process. Results indicate that the combination of vat photopolymerization followed by replication is well suited for achieving a minimum rib size of 25 μm in width and an aspect ratio of 1:12 for the master benchmark
On the Biomechanical Performances of Duplex Stainless Steel Graded Scaffolds Produced by Laser Powder Bed Fusion for Tissue Engineering Applications
This experimental study aims to extend the know-how on biomechanical performances of duplex stainless steel (DSS) for tissue engineering applications to a graded lattice geometry scaffold based on the F53 DSS (UNS S32750 according to ASTM A182) produced by laser powder bed fusion (LPBF). The same dense-out graded geometry based on rhombic dodecahedral elementary unit cells investigated in previous work on 316L stainless steel (SS) was adopted here for the manufacturing of the F53 DSS scaffold (SF53). Microstructural characterization and mechanical and biological tests were carried out on the SF53 scaffold, using the in vitro behavior of the 316L stainless steel scaffold (S316L) as a control. Results show that microstructure developed as a consequence of different volume energy density (VED) values is mainly responsible for the different mechanical behaviors of SF53 and S316L, both fabricated using the same LPBF manufacturing system. Specifically, the ultimate compressive strength (σUC) and elastic moduli (E) of SF53 are three times and seven times higher than S316L, respectively. Moreover, preliminary biological tests evidenced better cell viability in SF53 than in S316L already after seven days of culture, suggesting SF53 with dense-out graded geometry as a viable alternative to 316L SS for bone tissue engineering applications
Study of microstructure and magnetization reversal mechanism in granular CoCrPt:SiO2 films of variable thickness
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Investigation of the thermal stability of Mg/Co periodic multilayers for EUV applications
We present the results of the characterization of Mg/Co periodic multilayers
and their thermal stability for the EUV range. The annealing study is performed
up to a temperature of 400\degree C. Images obtained by scanning transmission
electron microscopy and electron energy loss spectroscopy clearly show the good
quality of the multilayer structure. The measurements of the EUV reflectivity
around 25 nm (~49 eV) indicate that the reflectivity decreases when the
annealing temperature increases above 300\degreeC. X-ray emission spectroscopy
is performed to determine the chemical state of the Mg atoms within the Mg/Co
multilayer. Nuclear magnetic resonance used to determine the chemical state of
the Co atoms and scanning electron microscopy images of cross sections of the
Mg/Co multilayers reveal changes in the morphology of the stack from an
annealing temperature of 305\degreee;C. This explains the observed reflectivity
loss.Comment: Published in Applied Physics A: Materials Science \& Processing
Published at
http://www.springerlink.com.chimie.gate.inist.fr/content/6v396j6m56771r61/ 21
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