Cândida Vilarinho

Kinetics of thermal de-chlorination of PVC under pyrolytic conditions.

Although PVC-containing wastes are an important potential source of energy they are frequently disposed in landfill. In thermal treatment processes such as pyrolysis and gasification, the presence of poly(vinyl chloride) (PVC), a compound with 56.7% of chlorine, may cause problems concerned with environmental protection, as consequence of the formation of hydrochloric acid, chlorine gas and dioxins, as well as corrosion phenomena of the reactor/equipment materials. Thus, a possible solution may involve a previous removal of the chlorine from PVC containing waste through a pyrolysis process at low temperatures before the material being submitted to a subsequent thermal treatment, for energetic valorization. In this work, a kinetic model for the thermal decomposition of PVC has been developed, in view of its de-chlorination. DTA/TGA testing at different temperatures indicated a first order reaction and an activation energy of 133,800J/mol. An almost completed de-chlorination reaction was obtained at 340°C under an inert atmosphere. The resulted material is a C(n)H(n) type polymer with potential to be used in an energy recovery process. Validation test performed at laboratory scale indicate that the temperature of 340°C enables the removal of ∼99.9% of the chlorine present in PVC. The chloride can be fixed in the form of an aqueous solution of HCl or calcium chloride, driving to an alternative full process with environmental benefits and reduction of the costs associated to the PCV - containing materials/wastes management.

Utilisation of pulp and paper industry wastes as raw materials in cement clinker production

The present work assesses the incorporation of grits and dregs, both wastes from cellulose and paper making industry, in cement clinker production. Industrial trials were developed with conventional raw clinker, used as a reference material and with the addition of grits and dregs, 0.25% and 0.13%, respectively. All raw meals were fired at 1400?1500°C. Chemical composition of the final mixtures, gaseous emissions quality during clinker production and leaching behaviour of the final products were evaluated. The results show that such incorporation could be an effective process for waste management from both the environmental and economic points of view.

Contribution to the knowledge of the Cu‐Zn‐Ti system for compositions close to brass alloys

The effect of tin content in the equilibrium phases of the Cu–Zn-based alloys, within the range of chemical compositions with interest to brass producers is described. For this purpose, ternary alloys with copper contents between 55.4 and 67.5 wt.% and tin contents up to 5.30 wt.% have been studied. The chemical composition of each alloy has been determined by X-ray fluorescence spectrometry (XRF). Isothermal homogenization, followed by rapid cooling, has been employed to determine the equilibrium phases at different temperatures. The homogenized alloys have been observed by scanning electron microscopy and the respective chemical analysis of the phases determined by electron probe microanalysis (EPMA). The statistical analysis of the obtained results enable to correlate the chemical composition of equilibrium phases with temperature. The chemical composition of the three-phase field, for the studied temperatures, has also been determined.

Effect of the Bi content on the mechanical properties of a Sn-Zn-Al-Bi solder alloy

Because of environmental and health concerns, some alternative solder alloys, named lead-free ones, are being developed. Among them, the Sn-Zn-Al system has been studied and reveals promising properties. Selection of the solder alloys, for the electronic industry applications, is conditioned by their mechanical properties due to the stress produced in service. The studied alloys were produced by melting the pure elements in a resistance furnace, under inert atmosphere, and pouring in a steel mould. The samples were heat treated for homogenization of the microstructure. The produced alloys were analyzed by XRF spectrometry and Scanning Electronic Microscopy (SEM/EDS) for chemical and microstructural characterization. In this work the presence of bismuth, in the range of 0-7 weight %, was evaluated in what concerns to the as-cast and homogenized microstructures and mechanical properties. The mechanical properties of the produced alloys, in the as-cast and homogenized conditions, have been determined by tensile strength and hardness tests. The results obtained showed that bismuth has an important effect on the mechanical behavior of the alloys, namely, in the transition from ductile to brittle behavior. This behavior was correlated with the samples microstructures.

EFFECT OF TRACE ELEMENTS ON THE INTERFACE REACTIONS BETWEEN TWO LEAD-FREE SOLDERS AND COPPER OR NICKEL SUBSTRATES

Traditional Sn-Pb solder alloys are being replaced, because of environmental and health concerns about lead toxicity. Among some alternative alloy systems, the Sn-Zn and Sn-Cu base alloy systems have been studied and reveal promising properties. The reliability of a solder joint is affected by the solder/substrate interaction and the nature of the layers formed at the interface. The solder/substrate reactions, for Sn-Zn and Sn-Cu base solder alloys, were evaluated in what concerns the morphology and chemical composition of the interface layers. The effect of the addition of P, at low levels, on the chemical composition of the layers present at the interface was studied. The phases formed at the interface between the Cu or Ni substrate and a molten lead-free solder at 250o C, were studied for different stage times and alloy compositions. The melting temperatures, of the studied alloys, were determined by Differential Scanning Calorimetry (DSC). Identification of equilibrium phases formed at the interface layer, and the evaluation of their chemical composition were performed by Scanning Electron Microscopy (SEM/EDS). Different interface characteristics were obtained, namely for the alloys containing Zn. The obtained IML layer thickness was compared, for both types of alloy systems.

Phase equilibria of the Al-Cu-Zn system for compositions close to brass alloys

The effect of aluminium on the equilibrium phases of the Cu-Zn alloys has been studied within the range of chemical compositions of interest to brass producers. Ternary alloys were cast by melting two Cu-Zn base alloys (with ∼59.5% and ∼61.2 wt.% Cu) followed by the addition of aluminium up to 3.68 wt.%. Isothermal homogenization, followed by rapid cooling, has been used to determine the equilibrium phases at different temperatures. The alloys have been observed by scanning electron microscopy (SEM) and the respective chemical analysis determined by electron probe microanalysis (EPMA). Statistical analysis of the results enables a correlation of the chemical compositions of the equilibrium phases with temperature within composition range of the study.

Leaching of brasses in long-term direct contact with water

Copper-zinc alloys (alfa-beta brasses) are currently used to produce house water piping and further parts, that might be in direct contact with drinking water. Lead is added to these alloys in order to improve their machinability. It is well known that lead is unhealthy for humans and, according to EU Council Directive 98/83/EC on the quality of water for human consumption, the admissible Pb content in drinking water has to decrease during the next years because of its high toxicity. The interest in improving public health evocated the need of developing new ecological materials for application on water piping and systems because extensive research indicates that the occurrence of increased Pb content in drinking water can be due to the release (leaching) of Pb from leaded copper alloys. As a consequence of such findings, the dissolution /erosion behaviour of a commercial sanitary brass tap, submitted to a dynamic test simulating the service conditions, has been studied. For that purpose an equipment that enables a long ‐ term direct contact with water has been designed and developed. The chemical composition of the tap and of the final residue produced during the test have been determined by XRF spectrometry and the solutions analysed by atomic absorption spectrometry. Results concerning metal values dissolution have been compared with the limit values established by the legislation. For the experimental conditions, results show that Pb level in leaching solution is lower than the admissible value indicated for the quality of water for human consumption.

Removal of Chromium and Aluminum from Aqueous Solutions Using Refuse Derived Char

Refuse derived fuel (RDF) was subject to torrefaction in order to produce a char with higher homogeneity and lower moisture content than the RDF raw materials. The resulting product, RDF char, showed increased fixed carbon and ash contents, decreased moisture and volatile matter contents, and a very significant increase in density. The torrefaction of RDF may therefore contribute to reduce the landfill volume needed to accommodate these materials to one third of the presently used. This new char material was also tested for its adsorption capacities and the results show that it could be used for the removal of chromium and aluminum from aqueous solutions.

Development of Bioplastic Film for Application in the Footwear Industry

There is a growing interest in the use of biodegradable polymers that can help minimize the environmental impact of plastics. Biopolymers have been considered the most promising materials for this purpose. However, they generally have poorer mechanical properties. Starch is a low-cost polysaccharide derived from agricultural plants. To improve starch processing, the molecular order within the granules must be destroyed. This is generally achieved by heating the granular starch mixed with plasticizers. With this process, a conversion of the biopolymer’s molecular structure into thermoplastic starch is obtained. In this way, much of the starch changes from a crystalline structure to an amorphous structure. Of the various plasticizers used, the most common are polyols, in which glycerol is included, allowing a good structuring, although it induces the phenomenon of recrystallization. Four bioplastics were developed, based on corn flour, which differed in thickness (0.25 mm and 0.45 mm, on average), with and without a natural pine resin. Regarding the tests carried out in bioplastics, it was concluded that the bioplastic with 0.25 mm and with resin is the one that presents a greater transparency and a greater tensile strength. In turn, the bioplastic with the highest elongation was the one presenting 0.45 with resin. It was also concluded that up to a certain thickness of bioplastic (0.34 mm), the resin adds a certain resistance, from which it withdraws. Through the FTIR analysis, it was confirmed that the resin provides transparency to the bioplastic and that it causes interference in the bonds between the starch and the glycerol.

A Brief Assessment on the Application of Torrefaction and Carbonization for Refuse Derived Fuel Upgrading

Refuse derived fuel (RDF) represents a very robust and endogenous resource that has the potential to minimize landfilling of solid waste, reduce greenhouse gas emissions through its biogenic component and contribute to national energy provision whilst diversifying solid fuel supplies. This waste derived fuel can be produced from different waste streams after significant mechanical and biological processing. In spite of their processing, these waste derived fuels still have a high degree of heterogeneity, presenting variable fuel properties and some negative characteristics such as high moisture, ash and chlorine contents. Although RDF is used for energy generation in some high energy demanding industrial applications or dedicated energy recovery facilities, its physical-chemical characteristics can result in significant technical and environmental problems that may benefit from an upgrading treatment. Torrefaction and carbonization are thermal treatments that have the potential to upgrade RDF, producing a waste derived char with reduced moisture and chlorine contents, more homogeneous and friable, which are characteristics of great importance for feeding systems in gasification and combustion facilities. Using waste derived chars could result in major environmental and waste management advantages, with potential to help with the waste management crisis, reducing waste volume and corresponding to the present European guidelines for energy recovery from wastes, fitting perfectly in the concept of circular economy.