Ciência & Tecnologia dos Materiais最新文献

Proper waste handling and sustainable recycling approaches are emerging topics for environmental safety and ecomanufacturing technologies. Steel chips resulting from new machining procedures are good candidates as new raw material for innovative recycling approaches due to their unique characteristics. The objective of this study was to characterize as-quenched H13 (AISI- SAE) tool steel chips produced by a machining procedure. Microhardness tests, SEM/EBSD and TEM techniques were used for hardness evaluation and microstructural characterization. Chips display a highly strained submicron-nanocrystalline grain structure with hardness up to 6.2 GPa. Such characteristics suggest the chips are suitable for powder manufacturing processes such as ball milling instead of atomization process.

The aim of the present research was to fabricate and study crystal structure and phase composition of Bi₅FeTi₃O₁₅ (BTFO) ceramics exhibiting Aurivillius - type structure. By means of simultaneous thermal analysis and X-ray diffraction analysis the process of synthesis of BTFO ceramics has been studied. Mixed oxide method followed by pressureless sintering was used for ceramics preparation. Three endothermic thermal effects have been revealed on heating the stoichiometric mixture of initial powder oxides within the temperature range ΔT = 700-1200°C, while only one strong endothermic peak was found on heating the powder after calcination. The weak endothermic peaks were ascribed to the melting points of intermediate surface phases based on Bi₂O₃-rich phase formed at low temperature. X-ray diffraction studies have shown that BFTO ceramics consisted of Bi₅FeTi₃O₁₅ and Bi₄Ti₃O₁₂ phases in amount of 88.3% and 11.7% (weight fraction), respectively.

The presence of pollutants in water is a recurring issue that is continuously addressed by governmental, intergovernmental, hybrid and non-governmental organizations and their action programs. Activated carbons (ACs) are currently used as adsorbents for waste water treatment. Combining the need to create and improve new carbon materials with the use and recovery of industrial by-products as precursors, we can achieve a balance between the high performance of these type of carbon adsorbents, cheap and sustainable sources of precursors.

AC samples were produced from medium-density fibreboard (MDF) and particleboard (PB) in monolithic form trough physical activation with carbon dioxide (CO₂) and chemical activation with K₂CO₃. Physical activated carbons were found to be essentially microporous with narrow pores and apparent surface areas (Abet) between 804 and 926 m²/g and chemical activated samples present wider pores, with Abet ranging from 951 to 1032 m²/g.

Liquid phase adsorption studies were made for several dyes both in a static and dynamic adsorption modes. In static mode high values of removal were achieved after 5 h, being this the time period used in the dynamic experiments, where some samples reached almost 100% removal.

Micromanufacturing has increased rapidly at scientific, technological and industrial levels. However, this evolution has not been followed by a parallel development of Non Destructive Testing (NDT) techniques. The available techniques are, generally, unable to detect microdefects. In this work, two types of microgeometries were produced by Micro Powder Injection Molding (μPIM) of stainless steel AISI316L: specimens for tensile tests (simple geometry) and microscrews (complex geometry). During the process optimization, different injection conditions of temperature and pressure were tested, as well as various temperatures for thermal debinding and sintering. Throughout the process, detectable and undetectable defects by NDT techniques were produced, which were used in the assays to assess the role of bacteria in the detection of defects. After adding bacterial suspensions of Staphylococcus aureus or Rhodococcus erythropolis cells, the microcomponents were subjected to magnetic or electric fields to facilitate mobility of bacteria towards the defects. This new methodology to detect defects produced during microfabrication can be a good solution for inspection of microdefects.

In order to evaluate the performance of high strength concrete reinforced with Dramix 5D 65/60 BG fibres, with non-deformable hook and ultra-high tensile strength, 24 beams were subjected to shear, with different fibre content (0, 15, 30 and 50 kg/m³), with and without stirrups in the shear span. In a second test campaign, 18 of those beams were tested again in the opposite end, with a variable shear span/effective depth (a/d) ratio in order to evaluate the influence of this parameter in the shear crack pattern and shear resistance. A probabilistic approach was followed to derive the corresponding design value of the shear strength (a procedure herein named by Design Assisted by Testing, DAT), which was then compared with the design shear strength determined according to recommendations of RILEM, EHE and FIB. Test results of both campaigns showed a significant increase in shear strength in relation to beams without fibres. Besides that, the design values of the shear strength derived from test results (DAT) were considerably higher than the design shear resistance provided by design codes.

Tires effective reutilization has become an important research topic in recent years due to the stockpiles increase that creates environmental problems. Recent European regulations forbid the tires burning and landfilling, setting several recycling objectives. Within this context, the reutilization of tire rubber recyclates into cement and polymer concrete materials, as reinforcement or aggregate replacement, has received lately a great attention. The present work aim is to analyse the modifications induced by tire rubber addition in the mechanical properties of polyester based polymer mortars (PM). The effect of different tire rubber fibre amounts (0.1, 0.4 and 0.5 wt.%) were analysed in this investigation. Plain polymer mortar was also prepared for comparison. Mechanical behaviour of both reinforced and plain polymer mortars formulations was assessed by flexural and compressive tests. Flexural and compressive strength improvements were particularly significant for PM trial formulation reinforced with the higher amount of tire rubber fibres. The observed trend on mechanical properties seems to indicate that higher increases could be achieved with higher amounts of tire rubber fibres. Thus, further experiments will be required in order to determine the critical amounts of rubber fibre reinforcement that define the turning points on material trend behaviour of PM.

Activated carbon adsorbents were produced from particleboard and medium-density fiberboard, industry originated wastes, without value added applications. These materials were characterized, showing a well-developed microporous structure reaching 0.58 cm³/g, and afterwards, their potential application for the removal of phenoxy acetic acids and substituted urea herbicide was evaluated. Studies in liquid phase were conducted in 2,4-dichlorophenoxy acetic acid (2,4-D), 4-chloro-2-methylphenoxy acetic acid (MCPA) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), being the obtained data linearized using the Langmuir and Freundlich equations. Results indicated high removal capabilities for the adsorptives in study, reaching 0.97, 1.37 and 1.87 mmol/g for diuron, 2,4-D, and MCPA respectively, allowing the conclusion that these materials should be studied further, having in mind real life applications.

The aim of this study is evaluating the interaction between several base pen grade asphalt binders (35/50, 50/70, 70/100, 160/220) and two different recycled plastics (EVA and HDPE), for a set of new polymer modified binders produced with different amounts of both recycled plastics. After analysing the results obtained for the several polymer modified binders evaluated in this study, including a commercial modified binder, it can be concluded that the new PMBs produced with the base bitumen 70/100 and 5% of each recycled plastic (HDPE or EVA) results in binders with very good performance, similar to that of the commercial modified binder.

There are several ways to change the final properties of composite materials, but the most common one is by adding different types of modifier fillers to the polymeric matrix. Over the last years, nano fillers have brought some interesting properties to composites. Until now, only few works were published concerning the effective impacts of resin binder modification with nano oxides, on mechanical properties of polymer mortars (PM). In this study, unsaturated polyester based PMs with enhanced mechanical performance are developed through polymer modification with nano-sized Al₂O₃ and ZrO₂ particles. Samples without and with nanoparticles (2.5 resin wt.%) were produced, and their mechanical/physical properties assessed by flexural, compressive and Shore D hardness tests. The PM modified with nano zirconia showed better mechanical performance compared to the unmodified PM; more thorough studies are nevertheless required in order to improve mix design formulations towards further enhancement of mechanical behaviour.

Biomedical devices introduced in the human body interact initially with blood cells, their success being dependent on the result of this interaction. This work aimed to obtain optimum biocompatibility and hemocompatibility of the titanium by plasma treatment. For this, discs of commercially pure titanium (CP) were subjected to plasma nitriding using different mixture of nitrogen and hydrogen; the effect of addition of hydrogen to the nitriding plasma was investigated. Before and after treatment, samples were evaluated in terms of topography and wettability using atomic force microscopy and sessile drop tests, respectively. The titanium biological response was evaluated in vitro through the application of platelet-rich plasma (PRP) on the surfaces modified and analysis of their behaviour from the point of view of surface tension and cell adhesion. Surface properties, such as roughness and wettability, were sensitive to the hydrogen/nitrogen ratio in the nitriding plasma, suggesting a strategy for producing different surfaces of biomedical devices. Results showed to be possible to obtain surfaces with different response to the adhesion of platelets, covering different applications.