Materials Science Forum Vols. 730-732

Abstract: Molecular dynamics simulations were employed to analyze the mechanical properties of polymer-based nanocomposites with varying nanofiber network parameters. The study was focused on nanofiber aspect ratio, concentration and initial orientation. The reinforcing phase affects the behavior of the polymeric nanocomposite. Simulations have shown that the fiber concentration has a significant effect on the properties, with higher loadings resulting in higher stress levels and higher stiffness, matching the general behavior from experimental knowledge in this field. The results also indicate that, within the studied range, the observed effect of the aspect ratio and initial orientation is smaller than that of the concentration, and that these two parameters are interrelated.

Abstract: The mechanical behaviour of heterogeneous specimens under uniaxial tensile test is studied using finite element analysis. The difference between mechanical properties of adjacent regions in the heterogeneous specimen creates constraints which alter the strain path relatively to pure tension. A methodology for determining the local stress-strain curves is proposed and successfully tested numerically on the heterogeneous specimen composed by two materials with dissimilar plastic properties. This methodology has recourse to the same type of variables which are usually obtained experimentally with the digital image correlation technique.

Abstract: The present work intends to evaluate, using simple, exemplary cases, the importance of a full elasto-plastic analysis in fatigue design. A strain cycling situation (-ε to ε) was modelled with ABAQUS considering two situations: firstly a linear σ vs. ε relationship was assumed, and secondly, the real cyclic σ vs. ε curve was used to model each cycle, which includes a small plastic deformation. The case of change of cross section in a steel shaft subjected to constant torsion and cyclic bending was analysed through finite element modelling using ABAQUS.

Abstract: Cellulose/silica derived hybrids materials (CSH), functionalized with aluminium, calcium, and propylammonium ions, were tested for their possible use in the removal of arsenic from aqueous solutions with controlled compositions to levels lower than 10 μg As/L. CSH were synthesized by sol-gel method using bleached pulp, as source of cellulose fiber, and tetraethoxysilane (TEOS) as main silica precursor. The silica network, made in situ, contained various anchored cations such as propylammonium (CSH-PA), aluminium (CSH-Al) and, calcium (CSH-Ca). Thin films or mesoparticles of silica were deposited on cellulose fibers as shown by SEM and XRD. These hybrid materials were immersed in controlled ionic strength aqueous solutions with arsenic concentrations lower than 0.2 mg As/L. The best performance was shown by CSH-PA that was able to remove a maximum of 20 % of the total arsenic concentration.

Abstract: Spent Ni-MH batteries are not considered too dangerous for the environment, but they have a considerable economical value due to the chemical composition of electrodes which are highly concentrated in metals. The present work aimed at the physical and chemical characterisation of spent cylindrical and thin prismatic Ni-MH batteries, contributing for a better definition of the recycling process of these spent products. The electrode materials correspond to more than 50% of the batteries weight and contain essentially nickel and rare earths (RE), and other secondary elements (Co, Mn, Al). The remaining components are the steel parts from the external case and supporting grids (near 30%) containing Fe and Ni, and the plastic components (<10%). Elemental quantitative analysis showed that the electrodes are highly concentrated in metals. Phase identification by X-ray powder diffraction combined with chemical analysis and leaching experiments allowed advancing the electrode materials composition. The cathode is essentially constituted by 6% metallic Ni, 66% Ni(OH)₂, 4.3% Co(OH)₂ and the anode consists mainly in 62% RENi₅ and 17% of substitutes and/or additives such as Co, Mn and Al.

Abstract: Galvanic coating processes are based on metal plating baths and are responsible for the production of large amounts of wastewaters. Subsequent physical-chemical treatment of the wastewaters generates solid wastes called galvanic sludges. These sludges have a hazardous character and are often disposed, mainly on landfills, without any economical or environmental benefits. The development of alternatives and viable ways to reduce the environmental impact and recover the valuable metals contained in those sludges such as copper, chromium, nickel or zinc, which content might reach 30% (wt.%, dry weight) are of utmost importance. The present work has been developed in the aim of the project VALMETAIS and proposes a hydrometallurgical process for copper recovery from galvanic sludges produced by Ni/Cr plating plants. This procedure has been developed on laboratory scale and is based on leaching of sludges in sulphuric acid solution followed by copper cementation step, using iron scrap as a precipitating agent. The sludge has been characterized for its chemical and physical properties. Chemical analysis showed a copper concentration of more than 10% (dry base). Preliminary leaching tests in both sulphuric acid and ammoniacal media were performed in order to determine the best operating conditions for this step of the process and to assure the best metal recovery conditions in subsequent separation methods. Sulphuric acid yielded much higher metal ion dissolution when compared with ammoniacal leaching. Optimal experimental leaching parameters were defined as follows: sulphuric acid solution 100 g/l, a solid to liquid ratio of 1:10, stirring speed of 400 rpm at room temperature and under atmospheric pressure. It was found that metals dissolution was almost complete in 30 minutes of reaction time. Extraction rates of 99% for Cu and Ni were obtained under the leaching conditions above mentioned. The solid residue separated from the leaching solution is mostly constituted by gypsum (CaSO₄), and presents a metal content below 1%. The subsequent extraction of cooper from the obtained solution is achieved by a cementation step with iron scrap. Copper precipitation was performed at a pH of 2 which was achieved through adding new sludge to the filtered leaching solution. Such pH level led to insignificant precipitation of other metals present in the leaching solution, namely chromium. The recovery rate of copper is about 90% and the purity grade of the resulting copper cement enables its application as a commercial product.

Abstract: Concrete is one of the most widely used construction materials in the world. However, the production of Portland cement as the essential constituent of concrete requires a considerable energy level. Also releases a significant amount of chemical carbon dioxide emissions and other greenhouse gases (GHGs) into the atmosphere. Global demand will increase almost 200 % by 2050 from 2010 levels. Thus, seeking an eco-efficient and sustainable concrete may be one of the main roles that the construction industry should play in sustainable construction. Portland cement can be partially replaced by cementitious and pozzolanic materials, especially those of industry by-products such as fly ash, GGBS, silica fume, ceramic waste powder and metamorphic rock dust from stone cutting industry. The aggregates are also conserved by replacing them with recycled or waste materials (among which recycled concrete), ceramic waste, post-consumer glass, and recycled tires. All of the previous alternatives are, currently, the most used. This paper summarizes current knowledge about eco-efficient concrete, by reviewing previously published work.

Abstract: Energy is a key issue for Portugal, it is responsible for the higher part of its imports and since almost 30% of Portuguese energy is generated in power stations it is also responsible for high CO₂ emissions. Between 1995 and 2005 Portuguese GNP rise 28%, however the imported energy in the same period increased 400%, from 1500 million to 5500 million dollars. As to the period between 2005 and 2007 the energy imports reach about 10,000 million dollars. Although recent and strong investments in renewable energy, Portugal continue to import energy and fossil fuels. This question is very relevant since a major part of the energy produced in Portugal is generated in power plants thus emitting greenhouse gases (GHGs). Therefore, investigations that could minimize energy use are needed. This paper presents a case study of a 97 apartment-type building (27.647 m²) located in Portugal, concerning both embodied energy as well as operational energy (heating, hot water, electricity). The operational energy was an average of 187,2 MJ/m²/yr and the embodied energy accounts for aprox. 2372 MJ/m², representing just 25,3% of the former for a service life of 50 years. Since Portuguese energy efficiency building regulation made under the Energy Performance Building Directive (2002/91/EC-EPBD) will lead to a major decrease of operational energy this means that the energy required for the manufacturing of building materials could represent in a near future almost 400% of operational energy. Replacement up to 75% of Portland cement with mineral admixtures could allow energy savings needed to operate a very high efficient 97 apartment-type building during 50 years.

Abstract: Among the solid wastes produced by textile industry, there is a significant amount of wastes with energetic value and which are usually sent to controlled landfills, without any recovery. This traditional route corresponds to high economical and environmental costs, since wastes can be used as a source of energy and/or materials. With the recycling route strongly restricted due to the presence of mixtures of different types of polymeric compounds, some of them not biodegradable, the study of the feasibility of energy recovery from such wastes is of upmost importance and the aim of the present work. Most of the wastes are valuable resources that can be used as raw materials or as an energy source to produce heat or electricity. In this work the potentiality of energy recovery from solid wastes of some of the Vale do Ave textile units was investigated. For that purpose, wastes have been characterized for their weight loss at 105°C, calorific value and ashes content (after burning out at 850°C). The chemical composition of the ashes was determined by X-Ray fluorescence spectrometry. DSC-TGA tests were performed in two different atmospheres, air and argon, in order to evaluate the thermal behavior of the studied wastes. The characterized wastes showed calorific values not negligible, varying from 3500 to10400 kcal/kg (at dry base), similar to the results obtained by others authors and comparable to solid materials which are traditionally considered as fuels (sugar cane, lignite, etc). A weight loss at (105°C) lower than 6.5% and a maximum ashes content of 15% was achieved. However, some ashes present high contents of heavy metals, which can drives to environmental concerns. By the analysis of the thermal profiles it was found that wastes decomposition takes place at low temperatures (< 600°C) resulting in a small amount of the final solid fraction. Concerning the obtained results, the solid wastes collected from different textile units show high potential for energy recovery.

Abstract: Lime mortars can suffer alterations when subjected to gaseous pollutants. Particulate air pollutants can also be deposited and incorporated to the mortar surfaces. Thus, they can be used as pollution tracers allowing us to measure deposition rates of pollutants to compare pollution loads. To calculate deposition rates the absolute age of the studied mortars must be known. Luminescence dating allows estimating the age of lime mortars but involves some partially unsolved problems. Luminescence yields the age of an object from the ratio between paleodose or cumulative radiation dose in the minerals of that object and the annual dose rate of ionizing radiation. The development of optically stimulated luminescence (OSL) in the last years and the application of statistical tools have resulted in the first dating of lime mortars. In this work mortars from old buildings and have been collected from two urban sites (A Coruña, Spain, and Braga, Portugal) to estimate their ages by luminescence. Thus, the mortars could be used as passive samplers to calculate deposition rates and relate these to different pollution loads. Results show partial successful estimates and some related problems in younger mortars are discussed.