Ciência & Tecnologia dos Materiais最新文献

A method for simultaneous removal of CO₂, SO_X and NO_X from industrial flue gases through the injection of ozone diluted in nitrogen, oxygen or nitrogen/oxygen mixtures, as an oxidizing agent and with the addition of specific sequestrants, that induce the precipitation of nitrates and sulphates, is presented. This new process is related with the conventional CO₂ removal method using chemical absorption, but presents as main innovation the possibility to remove also simultaneously SO_X and NO_X.

Over the last two decades, the authors have been using concentrated solar beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or natural gas. In recent works, nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH₃ gas with suppressed extent of dissociation (uncracked NH₃) was attempted under heating with concentrated solar beam. It was demonstrated that mono-nitride δ-MoN of Mo and sub-nitride ɛ-Fe₂N of Fe that are known to be impossible to synthesize in N₂ gas environment even at elevated N₂ gas partial pressure p(N₂) up to 300 bar were successfully synthesized by the reactions of these metals in stream of NH₃ gas under heating with concentrated solar beam up to 800 °C.

In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH₃ gas under irradiation of concentrated solar beam. After 90 min heating in uncracked NH₃ under concentrated solar beam up to 800 °C, X-ray diffraction (XRD) characterization of the reaction products showed certain extent of nitriding progressed for all the specimens in spite of relatively low reaction temperature for short reaction duration.

A novel system for electromagnetic navigation in bronchoscopy (NaviCAD) to improve peripheral lesion targeting and diagnostic is currently under development. The virtual bronchoscopy module of this system, including the collision and resolution algorithm, together with some preliminary tests on a complex phantom are presented in this paper. The NaviCAD system consists of a planning and orientation software, a navigation forceps, and an electromagnetic tracking system connected to a computer running the NaviCAD software. NaviCAD can be used with any bronchoscopy system, it has a short set-up procedure time and learning curve. The system proves to be easy to use, accurate and useful for experienced users and novices, with precision in reaching targets in sub-segmental bronchi where a video-bronchoscope cannot reach.

The aim of the present work is to study the combined effect of TiO₂ nanotubes, developed by means of electrochemical anodization on pure titanium adherends, and of the adhesive epoxy resin reinforced with carbon nanotubes (CNTs), on the quasi-static three-point bending behaviour of titanium-titanium single lap adhesive joints. A specific combination of parameters, namely time, type of electrolyte and voltage, has been selected in order to develop nanotubes with optimum geometry in an effort to achieve single lap adhesive joints with enhanced mechanical strength. The mechanical performance of the single lap joints as well as the bonding efficiency of the nano-composite adhesive were studied by means of three point bending and tensile shear tests, while the nano-structural topography was investigated through Scanning Electron Microscopy (SEM) observations. Following the above procedure an increase on the order of 82% in flexural strength for the thus manufactured single-lap adhesive joints was achieved, while the flexural modulus of the joints remained unaffected.

Epoxy resin composites reinforced with different weight fractions of TiO₂ micro-particles 0.2 μm in size (1%, 5%, 10%, 15%wt) and of TiO₂ nano-particles 21 nm in size (0.5%, 1%, 3%wt) were manufactured. The quasi-static mechanical properties of both nano-composites and micro-composites were investigated and compared through tensile testing. The experimental results were predicted and the degree of matrix-particle adhesion and particle dispersion were evaluated, by the Property Prediction Model (PPM) developed by the first author. The composites were also subjected to creep-recovery tests as well as to relaxation tests in order to investigate their viscoelastic behaviour. The experiments were carried out at different filler-weight fractions and loading conditions. Non-linear viscoelastic behaviour was observed in all cases and appropriate models were applied in order to describe, and/or predict the viscoelastic behaviour of all materials tested. A fair agreement between experimental results and theoretical predictions was observed for both viscoelastic and static results.

In this work, mechanical property of magneto rheological elastomeric (MREs) composite is investigated using iron as filler distribution. The MREs composite were fabricated using irregular shaped iron particles with size range varies from 50 -150 μm in matrix of elastomeric polymer. The matrix such as ZA22 was considered with 1:1 catalyst ratio as the binder with 30 Vol % of filler content. The fillers were incorporated within the matrix of elastomer using silicon oil as additive binder in the composite. The open circuit solenoid coil was designed as the magnetic circuit for magnetic flux intensity. Various magnetic field intensities were induced to observe the mechanical properties of the MREs composites. Hysteresis loss was observed in MRE samples due to dissipation of energy during compression of the composite material. Improved engineering strength of the MRE is observed on varying magnetic field of intensity and constant at 0.3 Tesla.

This manuscript reports on the fabrication of closed-cell aluminium alloy foams reinforced with carbon nanotubes (CNTs) through a novel approach that combines the powder metallurgy method with colloidal processing step that grants uniform dispersion of CNTs into the aqueous suspension of all powder components. Spraying the as prepared suspension into liquid nitrogen followed by lyophilisation enables obtaining homogeneous spherical granules to be used in the powder metallurgy method. Besides ensuring good dispersion of all powder components in the system, the non-agglomerated form of CNTs and the expansion upon foaming foster their structural integrity under stretched conditions in the final foams for an efficient load transfer.

Naturally occurring and sustainable materials can be used as a template to create biomimetic/biomorphic ceramics, known as Ecoceramics (environmentally conscious ceramics). In this work, cork was chosen as template to produce novel ceria (CeO₂) ecoceramics, for applications in water splitting for H₂ production via direct concentrated solar thermochemical fuel production (TCFP). The cork powder was pyrolised at 900 °C and the resulting carbon skeleton was infiltrated with an aqueous CeO₂ precursor, and then heated at 1000 °C for 2 h to produce the ecoceramic. The cellular structure of the cork was maintained, with hexagonal cell dimensions of 20-30 μm in diameter, but the grains were nanoscale at ≤100 nm. XRD data confirmed that CeO₂ was the only crystalline phase obtained. An important feature was that, while the rectangular side walls were maintained to hold the three-dimensionally ordered macroporous (3DOM) cellular cork structure, the rear hexagonal walls were pierced repeatedly through the structure, unlike in the original cork structure, which will allow gasses such as H₂ to permeate well into the structure, greatly increasing the reactive area available for catalysis. The next step will be to test the capabilities of both the regular, porous 3DOM structure and the nanoscale grains for thermochemical water splitting to produce hydrogen under direct concentrated solar energy.

Current stenting solutions commonly employ metal alloys and are permanent. This fact has the consequence of diverse long term risks for the patients, e.g. Restenosis, late-term stent Thrombosis, etc. One possible solution to attenuate these problems is the use of polymer or metallic based bioabsorbable stents that tend to be degraded by corrosion and completely eliminated after their scaffolding duties are fulfilled. Additionally, there is a need to find new ways of deploying these devices. A route to fulfill this goal, can be the design of stents that eliminate the necessity of balloon expansion and are able to self-expand by their own deformation mechanism, for example by possessing auxetic behavior. The objective of this study is the modeling of a stent that reveals auxetic behavior and is composed by a biodegradable material (AZ91D Magnesium alloy), to embrace both recent tendencies on stenting designs. It is shown that the defined stent modeling is able to expand when stretched (auxetic behavior) and reveals a deformation mechanism that may be interesting for further development. In conclusion, the combination of both biodegradable and auxetic characteristics shown in this study may be a future step in the evolution of these medical devices.

The paper gives a short overview of geometrical characterization, experimental testing, computational modelling and finite element analysis of various cellular metals: Advanced Pore Morphology (APM) foam, open-cell aluminum foam, Metallic Hollow Sphere Structure (MHSS) and cellular metals with uni-directional pores (UniPore). The geometrical analysis and characterization is based on the analysis of micro computed tomography scans and proper recognition of their internal cellular structure, taking into account statistical distribution of morphological and topological properties. The results of conducted geometrical analysis provided means to develop methodology for proper 2D and 3D geometrical modelling of irregular cellular structures and consequent formation of computational models. These were used to study the compressive and bending behavior of analyzed cellular structures by means of quasi-static and dynamic nonlinear computational simulations (using engineering codes ABAQUS and LS-DYNA), validated by experimental tests.