An efficient stabilized boundary element formulation for 2D time-domain acoustics and elastodynamics

International audienceThe present paper describes a procedure that improves efficiency, stability and reduces artificial energy dissipation of the standard time-domain direct boundary element method (BEM) for acoustics and el-astodynamics. Basically, the developed procedure modifies the boundary element convolution-related vector, being very easy to implement into existing codes. A stabilization parameter is introduced into the recent-in-time convolution operations and the operations related to the distant-in-time convolution contributions are approximated by matrix interpolations. As it is shown in the numerical examples presented at the end of the text, the proposed formulation substantially reduces the BEM computational cost, as well as its numerical insta-bilities

Production of metallic nanoparticles, from industrial residues, by the use of different types of reduction gases

The need to enhance and reuse existing materials on secondary sources of metals has had quite an impact in recent times. Several processes and technologies had being studied for recovery of raw materials from industrial waste generated. This study focuses on the possibility of waste reducing, from the galvanic floor covering industry, with the aim of obtaining micro or nano-particles of nickel or a nickel based alloy. Sludges from one galvanic treatment plant were used as base material in two conditions: as produced and after a hydrometallurgical treatment for metal concentration. Several reducing agents were used in this study: a synthesis gas from a polymer pyrolysis and solid polymer agents (PVC, HDPE and PP residues). Obtained products were characterised in terms of metallic particles production during the reduction treatment and by SEM/EDS analysis on the final products. A simultaneous differential thermal and thermogravimetric equipment (DSC/TGA) was used for the study of the reduction process with a reduction gas obtained from the pyrolysis of chlorine free PVC derived char. The obtained results show that it is possible to obtain small metallic particles, in the range of 60 to 240 nm, at 800 ºC. Reduction tests, by the use of a solid residue, were made in a laboratorial furnace with two independent heating zones. Best results were obtained with de-chlorinated PVC as a reduction agent with the production of metallic particles, in the range of 150 to 600 nm, at 800 ºC. For all the tested conditions the metallic particles were constituted by Ni and Cu with variable chemical composition

Gestão de resíduos industriais por incorporação em materiais para construção civil

Nesta apresentação abordar-se-á a problemática da gestão de resíduos industriais da indústria metalúrgica e de processamento de materiais, por via da sua inertização durante o processo de fabricação de materiais para a construção civil. Referir-se-á, em particular, a experiência de valorização de resíduos da indústria metalúrgica no processo de fabricação de cerâmicos, de clinquer, de misturas cimentosas e de agregados betuminosos. Todos estes materiais, largamente utilizados pela indústria de construção civil, constituem boas opções para o escoamento de resíduos industriais, de forma ambientalmente correcta. Cada um dos materiais de construção civil testados apresenta características físicas, químicas e de processamento distintas. Esta especificidade implica diferentes aptidões para a inertização de resíduos, o que, globalmente, se apresenta como vantajoso. Os resultados obtidos até ao presente apontam genericamente para a elevada capacidade de valorização de resíduos das indústrias metalúrgicas e de processamento de materiais, por via da sua incorporação na produção de materiais para construção civil.In this presentation, the management of metal and materials processing industrial wastes, by its incorporation in civil construction products will be reviewed. In particular, the incorporation of metallurgical wastes in the fabrication of red ceramics, clincker, cement mortars and bituminous aggregates will be presented. All these materials are commonly used by construction industry and are hence good options for the management of industrial wastes, in a environmentally correct way. Each of the construction materials shows different and specific physical characteristics and properties. This is an important factor for wastes management, taking into account the variability of physical properties of the wastes themselves. Results obtained in research, both at laboratory and industrial environment, show that this is a very promising way of giving value to wastes from metallurgical and materials processing activitie

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

The effect of aluminium in the equilibrium phases of the Cu-Zn alloys, within the range ofchemical compositions of interest to brass producers, has been studied. Ternary alloys werecasted by melting two Cu-Zn base alloys (with ~59.5% and ~61.2 wt.% of Cu) followed by theaddition of aluminium up to 3.68 wt.%. Isothermal homogenization, followed by rapid cooling,has been employed to determine the equilibrium phases at different temperatures. The alloys have been observed by scanning electron microscopy (SEM) and the respective chemicalanalysis determined by electron probe microanalysis (EPMA). The statistical analysis of theobtained results enable to correlate the chemical composition of equilibrium phases withtemperature, for the range of compositions studied

Interactions of Cu substrates with titanium-alloyed Sn-Zn solders

The interactions of copper substrate with titanium-alloyed Sn-Zn eutectic solders have been studied. Two series of experiments have been performed. The first one consisted in differential thermal analyses of Sn-Zn nearly eutectic alloys containing from 1.3 to 2.2 wt. % Ti. Diffusion couples consisted of Cu-wires and Sn-Zn-Ti liquid solders, produced at 250 and 275 OC have been prepared in the second series,. The contact times were up to 3600 s. The contact zones have been characterized by optical and scanning electron microscope. Two layers have been found along the interfaces solid/liquid. The first and the second layers are identical, respectively, with γ and ε phases of the Cu-Zn system. No changes of the chemical compositions were detected for the tested temperatures and reaction times. Continuous parabolic growth of the total diffusion zone thickness with the time of diffusion is observed. The growth is due mainly to one the formed layers (γ ) while the thickness of the ε-phase layer, stays almost constant for all tested diffusion times and temperatures

Influence of chemical composition and volume fraction of phases on the dezincification resistance of brasses

Although brasses are resistant to several forms of corrosion, they are susceptible to dezincification – selective dissolution of zinc – which may be responsible for failures in service of casting brass products. The effect of the chemical composition on dezincification resistance of brasses has been investigated. This study includes both commercial alloys and alloys prepared in laboratory in order to evaluate the specific effect of alloying elements such as lead, silicon, aluminium, iron, tin, nickel and arsenic upon the dezincification resistance. The effect of the volume fraction of α phase in the dezincification behaviour has also been studied. Dezincification tests have been carried out according to the ISO 6509 standard. The influence of the various alloying elements in the depth of the dezincificated layer, has been evaluated. The statistic treatment of results enable to the establishment of correlationship between the studied properties and the contents of some elements present in the chemical composition of brasses

Coupled Numerical Methods to Analyze Interacting Acoustic-Dynamic Models by Multidomain Decomposition Techniques

In this work, coupled numerical analysis of interacting acoustic and dynamic models is focused. In this context, several numerical methods, such as the finite difference method, the finite element method, the boundary element method, meshless methods, and so forth, are considered to model each subdomain of the coupled model, and multidomain decomposition techniques are applied to deal with the coupling relations. Two basic coupling algorithms are discussed here, namely the explicit direct coupling approach and the implicit iterative coupling approach, which are formulated based on explicit/implicit time-marching techniques. Completely independent spatial and temporal discretizations among the interacting subdomains are permitted, allowing optimal discretization for each sub-domain of the model to be considered. At the end of the paper, numerical results are presented, illustrating the performance and potentialities of the discussed methodologies

Desenvolvimento e caracterização de latões ecológicos

O chumbo é um elemento de liga normalmente presente na composição química dos latões conferindo-lhes boa maquinabilidade. Todavia, sendo um elemento tóxico, a sua presença é possível fonte de contaminação de águas, com eventuais danos para a saúde pública e para o ambiente. Por essa razão, a legislação publicada em vários Países tem vindo a demonstrar a sua preocupação neste domínio, restringindo ou eliminando o teor deste elemento nos latões, particularmente nos produtos que estão em contacto directo com a água para consumo humano, como torneiras, acessórios de canalização e tubagens

Recuperação de compostos clorados e energia a partir de resíduos contendo PVC

Os resíduos são considerados uma fonte atrativa para a produção de energia, principalmente os de base polimérica. Várias são as técnicas de valorização térmica e energética, como a pirólise, que constituem alternativas com elevado potencial no que concerne à produção de combustíveis alternativos e energia. Estas técnicas, quando aplicadas a resíduos, favorecem a formação de produtos com valor acrescentado. A utilização de resíduos como matéria-prima é uma das mais-valias associadas ao processo, constituindo uma alternativa à sua eliminação em aterro sanitário através do reaproveitamento dos mesmos em processos energéticos. Quando está considerado um processo de tratamento térmico, a presença de PVC, um composto com 56.7% de cloro na sua composição, pode comprometer a integridade ambiental, em consequência da formação de ácido clorídrico, gás de cloro e dioxinas, bem como provocar a corrosão dos materiais constituintes dos equipamentos utilizados. Assim, uma possível solução para o seu tratamento consiste na remoção do cloro contido na molécula de PVC, recorrendo a um processo de pirólise a baixa temperatura, a montante de um processo de valorização energética. O interesse no desenvolvimento deste processo resulta do facto desta tipologia de resíduo apresentar grande potencial para valorização energética, possível através de um processo de pirólise aplicado ao material (resíduo carbonoso) obtido após a remoção do cloro nele contido. O presente trabalho contemplou o estudo do processo de remoção do cloro contido nos resíduos com PVC na sua constituição, através da técnica de pirólise a baixa temperatura, com recuperação do cloro através da sua fixação na forma de solução aquosa de ácido clorídrico ou, alternativamente, na forma de cloreto de cálcio ou sódio. Posteriormente, o resíduo carbonoso desclorado resultante é submetido a um processo de valorização energética, produzindo-se um gás de elevado poder calorifico, com consequente potencial de aplicação. Com este processo, a aplicação do tratamento constitui uma alternativa à deposição em aterro deste tipo de resíduos, solução de menor prioridade em termos de política ambiental. Paralelamente, promovendo a redução dos custos inerentes à sua gestão, com vantagens económicas expectáveis

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 133,800 J/mol. An almost completed de-chlorination reaction was obtained at 340 C under an inert atmosphere. The resulted material is a CnHn 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