1,721,006 research outputs found
Three Dispersed Magnetorheological Fluids in Dampers for Manufacturing Applications
Full text linkMagnetorheological fluids (MRFs) are included in the class of “smart materials” since their viscosity can be quickly and reversibly changed upon the application of an external magnetic field.
Even if MRF technology is exploited nowadays in many different fields (civil engineering, automotive, biomedical), very few manufacturing applications are on the market at the moment because of MRFs main drawback: sedimentation.
This thesis aims to put the basis for the development of an innovative MRF damping device for manufacturing applications and to design an innovative MRF with improved response to the sedimentation to be employed in the damping device for manufacturing applications.
The study starts from an accurate bibliographic investigation on MRF based devices, chemical features of MRFs and MRF formulations. This corpus of knowledge was organized into a model which can be used to explain the relationship between the functional requirements an MRF based device has to meet and the corresponding combination of chemical and physical properties of the fluids and the device itself (and so the MR operational mode selected); so, a rationale is provided to select the best fluid for the specific application, with particular focus on damping devices. Once the knowledge on the MRF damping functioning is gained, it can be extended to manufacturing applications. So, the designing process of a novel MRF-based damper for manufacturing applications is thus a consequence of the corpus of knowledge collected in this thesis.
The experimental section of this work focuses, then, on the formulation of a novel three-dispersed MRF for damping devices with enhanced resistance to sedimentation. The experimental fluids were tested from the point of view of sedimentation and magnetization behavior. With regards to sedimentation, interesting results were reached
Stiff and tough hydrophobic cellulose-silica aerogels from bacterial cellulose and fumed silica
No full textThis work reports hydrophobic and compressible cellulose- silica composite aerogels prepared by freeze drying fumed silica (FS) infiltrated bacterial cellulose (BC) hydrogels. Compression modulus of cellulose silica (BC-FS) aerogels increase from 0.22 MPa up to 3.83 MPa with respect to pure freeze dried BC. BC with 8% silica (BC-FS-8) aerogel demonstrated excellent robustness and is compressible with full elastic recovery for 50 cycles without any substantial drop in mechanical strength. All aerogels exhibit more than 96 % porosity, specific surface up to 420 m2/g, density ranging from 0.01 to 0.04 g/cm3 and thermal conductivity less than 0.04 W/mK. Hydrophobic aerogels demonstrated excellent oil absorption properties from oil/water mixture, with an oil uptake up to 28 times of its original weight. The cyclic test conducted for oil absorption shows that the aerogel can be used at least 10 times for oil recovery without any substantial reduction in the uptake capacity
Diatomite/silver phosphate composite for efficient degradation of organic dyes under solar radiation
No full textIn this study, an effort has been made to synthesize diatomite/silver phosphate (DT/AgP) composites and dye degradation test was carried out to evaluate the photocatalytic activity under solar light irradiation. Diatomite–silver phosphate composites with different DT/AgP ratios were prepared by precipitation of Ag3PO4 on diatomite that led to the formation of small Ag3PO4 particles on the diatomite surfaces. UV–visible diffuse reflectance analysis shows that DT/AgP composites can absorb visible wavelength, whereas TiO2 catalyst only work under UV irradiance. Compared to pure AgP, the composite samples show higher specific surface area measured by Brunauer–Emmett–Teller analysis. Dye degradation test under solar light irradiation reveals that the photocatalytic reaction follows a pseudo-first-order rate law and the composite catalyst with DT/AgP ratio 1:0.8 shows better catalytic activity towards both rhodamine B and methyl orange degradation. As reference, a well-known commercial TiO2 (Evonik-P25) was used in dye degradation test. It could be presumed that deposition of silver phosphate clusters (Ag3PO4, AgP) on diatom frustules (diatomite) provided an efficient photocatalyst activated by solar light irradiation
Silver-Functionalized Bacterial Cellulose as Antibacterial Membrane for Wound-Healing Applications
No full textBacterial cellulose (BC) functionalized with silver nanoparticles (AgNPs) is evaluated as an antimicrobial membrane for wound-healing treatment. A facile green synthesis of silver nanoparticles inside the porous three-dimensional weblike BC network has been obtained by UV light irradiation. AgNPs were photochemically deposited onto the BC gel network as well as they were chemically bonded to the cellulose fiber surfaces. AgNPs with a narrow size distribution along with some aggregates in the BC network were evidenced from the morphological analyses. A highly crystalline nature of the BC membranes was observed in X-ray diffraction measurements, and the presence of metallic silver confirmed the photochemical reduction of Ag+ Ag0 in Ag/BC composites. Antibacterial activity of the hybrid composites, such as pellicles, performed against the Gram-negative bacteria (Escherichia coli) by disk diffusion and growth dynamics methods showed high bacteria-killing performance. No significant amount of silver release was observed from the Ag/BC pellicles even after a long soaking time. As composite pellicles are preserved in a moist environment that also favors wound recovery, by combining all of these properties the material could be useful in wound-healing treatments
Is nano-TiO2 alone an effective strategy for the maintenance of stones in Cultural Heritage?
No full textTiO2-based nanocoatings have been becoming more and more widespread during last years in Cultural Heritage: they seem to be able to keep stone surfaces self-cleaned and to prevent the formation of biofouling. However, the efficiency of these coatings is strongly dependent on the substrate (i.e.: porosity and roughness) and on the amount of TiO2. Thus, this study experimentally investigates on the self-cleaning and anti-biofouling efficiency of a nano-TiO2 dispersion (without any organic or inorganic additive) applied on six different types of natural stones (three limestones, two sandstones and one tuff) usually used in Cultural Heritage, where high porosity and roughness can be found and the TiO2 amount cannot be increased in order to avoid any chromatic variation of the substrate. Water was used as solvent so as to reduce the risk of exposition of hazardous materials and to eliminate any chemical action on stones. The self-cleaning power of the coating was evaluated by measuring its ability at discolouring organic dye Methylene Blue, while its anti-biofouling efficiency was assessed by an accelerated growth test under controlled climatic conditions of two algal microorganisms, namely Chlorella mirabilis and Chroococcidiopsis fissurarum. Results show that, even if the photocatalytic and biocide power of nano-TiO2 itself is well known in literature, its application for the maintenance of stones in Cultural Heritage does not seem to be an effective strategy, especially when stones are highly porous and rough. Roughness and porosity of stones, in fact, can limit the efficiency of TiO2, which is thus not able to powerfully keep the stone substrate cleaned or slow down algal proliferation
Optical and electrochemical properties of cerium-zirconium mixed oxide films deposited by sol-gel and r.f. sputtering
No full textSTUDIO DI UN’APPLICAZIONE IN CAMPO AERONAUTICO DI COMPOSITI STRUTTALI IBRIDI RESISTENTI AL FUOCO
No full textIn the aeronautical/aerospace structural design the increasing demands of materials having high
mechanical performance, has led to the a wide use of Polymeric Matrix Composites (PMCs) mainly
reinforced by carbon fibers (Carbon Fiber Reinforced Plastics, CFRP). The main drawbacks in the use
of such composites are due to high sensitivity to environmental features and low working
temperatures; moreover, these materials do not tolerate the fire exposure because of the inflammability
of both the matrix and the fibers.
In order to develop a composite that combines the structural performance of CFRP with a good
strength to high temperatures and fire, in the present work the use of a hybrid composite consisting of
a CFRP laminate joined to proper layers of ceramic matrix composite (CMC), has been investigated.
Preliminary experimental tests carried out to assess the numerical model, and subsequent mechanical
and thermal numerical simulations, have corroborated the reliability of the hybrid composite proposed
Preparation and characterisation of titania/hydroxyapatite composite coatings obtained by sol-gel process
Full text linkIn the present work a titania network encapsulating a hydroxyapatite particulate phase is proposed as a bioceramic composite coating. The coating on a titanium substrate was produced starting from a sol containing a mixture of titania colloidal particles and hydroxyapatite submicron particles using the dip-coating technique. The microstructure, the morphology and the surface chemical composition of the coating were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Adhesion tests were also performed. These analyses showed that the obtained coating was chemically clean, homogeneous, rough, porous, with a low thickness and well-defined phase composition as well as a good adhesion to the substrate. Copyright © 2001 Elsevier Science Ltd
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