Treballs Finals de Grau (TFG) - Enginyeria de Materials

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/67211

Treballs Finals del Grau d'Enginyeria de Materials de la Facultat de Química de la Universitat de Barcelona.

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Formulation of sodium borosilicate glass inks from ceramic precursors for Direct Ink Writing
(2020-07) Perez Bustos, Kevork; Xuriguera Martín, María Elena
Additive manufacturing (AM) refers to a series of techniques in which, in contrast to traditional manufacturing techniques, the final pieces are achieved by adding material instead of subtracting it. These technologies have been developing for more than 25 years and they are also referred to as Rapid Prototyping, Freeform Fabrication, Layered Manufacturing, 3D Printing and others, being all synonyms. By using these techniques, complex shapes can be produced with practically any material, allowing virtually infinite applications for AM techniques. The way the material is added depends on the specific technique used. Each one has its own characteristics, advantages and limitations. Extrusion processes are the most common ones among AM. To form final pieces with these processes, the material is forced through a nozzle and deposited creating a three dimensional matrix. The need of a post treatment also depends on the technique. Nevertheless, all AM processes produce final or near-final pieces. This work aims to study the possibility of formulating sodium borosilicate glass (NBS) inks for Direct Ink Writing (DIW), an extrusion based AM technique. DIW ceramic inks are highly viscous solutions with specific rheological properties that let them retain its shape after being extruded. These inks are commonly a mixture of ceramic powders and a rheological agent, however, it is also possible to mix ceramic precursors with rheological agents to formulate them. Specifically in the synthesis of silica and silica derivate glasses, the ceramic powder method is the most utilized. In contrast, little information can be found for the ceramic precursors approach. Therefore, a first approach to produce NBS glass from precursors has been studied. Sol-gel method was used as the route to produce NBS glass from precursors. Addition of a poloxamer (Pluronic-F127) was explored to achieve the rheological behaviour desired and different inks where formulated. The rheological properties of the inks formulated were characterized, being the most suitable ones printed and sintered to verify the feasibility of the process developed. Finally, a series of characterization techniques where proposed to fully determine the properties of the material synthesized. Sol-gel method is suitable to form NBS glass from precursors and the optimizations explored gave positive results. Pluronic-F127 as rheological agent in combination with the NBS glass solution behaves as a pseudoplastic non-Newtonian fluid. The highest loaded printable ink is the formulation with a content of 75% PLU-F127 33% (w/w) + 25% NBS-12 by volume. Higher concentrations of NBS-12 cannot retain the given shape after printing. Altogether, is possible to produce printable NBS glass inks as a proof of concept. The sintered samples are unable to retain their given shape and the final appearance is not the expected one, however, the process developed does yield a final NBS glass piece
State-of-the-art of the new alloys in the duplex stainless steel family. Alloy design, manufacturing, post treatments and applications
(2021-06) Ferré Adán, Iván; Llorca i Isern, Núria
Duplex stainless steels have been a big revolution mainly in the offshore oil industries. These alloys have become a very good alternative for dealing very efficiently with stress corrosion cracking (SCC) with a much lower associated cost than nickel base alloys. From their discovery in the late 1920's to the present day, these alloys have been evolving in the form of new duplex alloys which have offered increasingly better corrosion resistance and improved mechanical properties. This paper offers a brief journey through time from the beginning of the Iron Age to the present day, narrating the evolution of the use of iron in the different stages of humanity. Subsequently, all the theoretical principles associated with duplex stainless steels are described, as well as the associated technologies for obtaining and processing them. Finally, the state-of-the-art of the most recent duplex alloys, the super duplex and hyper duplex stainless steels, has been elaborated
Implementation of bioactive glass coatings obtained by thermal spraying to improve the properties of bone implants
(2021-06) Martín Morata, Alejandro; Dosta Parras, Sergi
Nowadays human beings stand out for their increased longevity thanks to scientific and technological advances applied to the field of medicine. One of the most important fields is the replacement or repair of bones and body tissues such as a knee operation or a hip prosthesis. Many of these implants are introduced into the body with the addition of a functional ceramic coating such as hydroxyapatite or bioactive glasses like 45S5 which increase the durability of the prostheses and their replacement time. The main problem that many bioactive glasses suffer comes from their ceramic nature. These materials tend to have a low thermal conductivity, so spraying them becomes a challenge, as they fail to adhere optimally. This work focuses on increasing the adhesion of 45S5 glass sprayed using the Atmospheric Plasma Spray technique on Ti4Al6V substrates using two strategies. The first strategy is to introduce one or more hydroxyapatite interlayers using the demonstrated affinity of HA both 45S5 and substrate in APS. Second strategy, 45S5 agglomerates are produced by using PVA solution to increase the contact area of the particles with the spraying substrate. The mechanical tensile strength of the coatings is evaluated, and the failure mode is characterized by Scanning Electron Microscopy (SEM) to determine which strategy provides the highest adhesion. Finally, to complete the work, an in vitro study of bioactivity and biodegradation of the coatings in body fluids simulated medium is performed to evaluate their compatibility
Study on synthesis, surface derivatization, processing and techno-economic analysis of a PLA – Nanocellulose composite
(2020-06) Geraldo Silva, Gustavo; Fernández González, Javier
As a biodegradable material that can be obtained from sustainable resources, Polylactic acid (PLA) has positioned itself among one of the most prominent materials to substitute petrochemical-based plastics in our quest towards a circular, carbon-neutral economy. On the other hand, Cellulose, a natural polymer found as a reinforcement element in plants, cells and tissue, has a proven record of use not only as paper, but also in many composite applications as a thickening agent, as a binder, or as reinforcement in composite materials. Despite its great prospects, PLA has some serious drawbacks in its mass adoption as a substitute material of mainstream olefins, mainly due to its relatively poor mechanical, thermal and permeability properties. As such, Cellulose, in particular that which is sourced from agricultural waste products, such as Soy Husks, and scaled to its nano-constituent particles, has the potential to be used as a reinforcement and filler material in PLA, improving its weak properties. However, due to their different surface behavior, a mixture of PLA and Nanocellulose is hard to achieve without special processes. The goal of this final degree project is to study the processes in place to individualize the different nano-constituents of Cellulose, namely Cellulose Nanofibers (CNF), modify its surface behavior to make it compatible to PLA and explore the processes to which a PLA – Nanocellulose composite could be produced. This study has been made based on existing bibliography from other research fellows and the most prominent pathway to a PLA – Nanocellulose composite has been presented on this study along with a techno-economic analysis of its viability
Exploring the dynamic of Sn for the synthesis of high efficiency Cu2ZnSnSe4 based solar cells
(2020-07) Navarro Güell, Alejandro; Pérez Rodríguez, Alejandro; Saucedo Silva, Edgardo
The need for new renewable sources of energy has been a reality for several years. Both because our current source of energy, fossil fuels, is limited, and because of the high pollution and problems associated with their use. As a solution to this problem, the development of renewable energies is our best asset. Within the wide range of possibilities, this work focuses on the energy that directly uses the enormous potential of our sun, photovoltaic energy. One of the most promising materials for emerging applications in the field of photovoltaics are the so-called kesterites, formed by the elements: Cu, Zn, Sn and Se; all of which are abundant and of low or null toxicity. The development of high efficiency cells based on kesterite faces several challenges related to the complex nature of this family of materials. Among them, the control of Sn that tends to form liquid and volatile species during the synthesis process having a strong exchange with the annealing atmosphere. In this work, the dynamics of Sn during the synthesis of the photovoltaic absorber, Cu2ZnSnSe4 (CZTSe), is investigated through a sequential process (Sputtering + Annealing). We compare the classical methodology where Sn is already incorporated in the solid precursor with a new and innovative solution in which Sn is partially incorporated in the vapour phase. The impact on the mechanism of CZTSe formation is investigated, as well as the properties of the layers and the characteristics of the finished devices
Development of magnesium phosphate cement mortars formulated with reactive silica
(2018-06) Cosialls Borràs, Eduard; Formosa Mitjans, Joan; Maldonado Alameda, Alex
The construction sector has been in upwgrowing these last years and consequently the contamination is at a level that takes society to concern. That is why nowadays it is a challenge for engineers and scientists to develop sustainable and eco-friendly construction materials. This research project aims to replace portland cement (OPC) using Chemically Bonded Phosphate Ceramics (CBPC). This cement is characterized by having a spontaneous and highly exothermic reaction that leads to a very fast setting. It also uses by-products such as magnesium oxide (Lg-MgO) and Ceramic, Stone and Porcelain (CSP) to make the material more sustainable and at the same time have a more competitive price in the market. It is wanted to analyze if the CSP reacts with the structure of the MPC known as k-struvite. To reach the optimal formulation, different influence factors are determined in the mortar and they are assigned important values through an Experiment Design (DoE). The results show that an increase of CSP increases mechanical and physical properties, but reactivity with k-struvite is unclear. The resulting MPC can be used as a repairing mortar.
Selection of thermoplastic materials for application in mixer cartridges based on the tribological properties between polymeric pairs
(2018-06) Sabaté Rovira, David; García Cano, Irene; Alcaine Santamaría, Manuel
The performance of the mixer cartridges that regulates the temperature and the water flow in most of the daily use faucets is based on the movement and geometry of two ceramic discs, whose relative position is set by moving the handle. During the transmission of the movement to the discs, we also submit relative movement to three thermoplastic pieces called ceramic holder, racord and housing, which are in permanent contact and compressed. The tribological behaviour of this system is crucial for the cartridge’s performance. Even if different greases are used as lubricants between the pieces, the raw material of these polymers is fundamental in terms of the generated friction and wear. In the present project, a selection process aimed at enhancing the thermoplastic combination currently used for the components has been done. A first selection phase, in where parameters such as dimensional stability associated to moisture absorption, thermal expansion, mechanical properties, availability or cost have been studied, has been done in order to choose potential substitutes. In a second selection phase, using a ball-on-disk device, tribological tests have been done to those combinations worthwhile to the project. In the final count, the results show that the current combination can be improved; being the use of polyoxymethylene (POM) in the ceramic holder, polyphthalamide (PPA) filled with 40% glass fibre in the racord and polybutylene terephthalate (PBT) filled with 15% glass fibre in the housing the best combination among those studied
Study of the ballistic limit of carbon fiber laminates throughout MEF and neural networks methodologies combined
(2016-01) Martin Montal, Jordi; Fernández Renna, Ana Inés; Artero Guerrero, José Alfonso; Pernas Sánchez, Jesús
Nowadays composite materials are widely used in aeronautics due to its high resistance-density relation. However, one of its main drawbacks is its elevated vulnerability against perpendicular impacts. The ballistic limit value of each laminate is a critical variable playing an integral role in the aforementioned impacts. The aim of this project is to analyze the influence of the laminates stacking sequence in its ballistic limit values. To this end, a numerical model through a commercial code of finite elements in LS-DYNA® will be developed and implemented to be compared and validated through an previous experimental model from [López-Puente et al., 2003][1]. The experimental model was carried out with impact trials of high and low velocity of spherical projectiles on carbon fiber test tubes with specific geometries and boundary conditions. The composite material utilized is AS4 carbon fiber and 8552 epoxy matrix, an amply used material in aeronautics. For a thorough interpretation and analysis of the influence between both parameters it is intended the usage of a new technology based in neural artificial networks through a code implemented in Python. These computational tools are increasing in use in the engineering industry due to its features of behavior prediction between variables without an apparent either particular or mathematizable physical relation.
Synthesis and characterization of Alkali Activated Cements based on Bottom Ash and Paval
(2018-06) Mañosa Bover, Jofre; Chimenos Ribera, Josep Ma.; Maldonado Alameda, Alex
One of the most important challenges of European Union (EU) is to reduce the amount of municipal waste and industrial by-products generated since they are one of the main threats to the environment. For this reason, the valorisation of this waste and by-products has emerged, to produce compatible and viable products. If we focus on construction materials, some of these waste and by-products that have a large SiO2, Al2O3 and CaO content can be used to produce cements. Alkali Activated Cements (AAC) stands out as one of the best choices to produce this cements, since they can compete with Portland cements and they are also more sustainable. The main purpose of this project is to synthetize and study AAC based in two by-products: municipal waste incineration bottom ash and Paval, an industrial by-product generated in aluminium production, by using as alkaline activators NaOH and Na2SiO3. The results obtained in this project demonstrate that with this two by-products it is possible to synthetize AAC, and that their mechanical properties are good enough to study them in more detail to make them a real alternative to Portland cements. Different formulations have been considered by changing the proportions of this by-products and the alkali activators to determine which formulation gives rise to best results. It has been concluded that the AAC synthetized with bottom ash and 10% of Paval and activated with NaOH 6M are the formulations that give rise to better properties
Design of a Lab-scale system for the study of dry desulfurization process
(2018-06) Gil Sáenz, Raúl; Formosa Mitjans, Joan; Huete Hernández, Sergio
Sulphur dioxide (SO2) is a major contributor to contamination and environmental degradation. The limit emission values are becoming tighter and nowadays, the Industrial Emissions Directive (EID) of the European Union has been demanding the cement, lime, and magnesium oxide industries to reduce their SO2 emissions by means of sustainable methods. The main industrial activity of Magnesitas Navarras S.A. (MAGNA), Company located in Zubiri (Navarra, Spain), is obtaining magnesium oxide, MgO, from calcination of natural magnesite MgCO3. Emissions of SOX are mainly in the form of sulfur dioxide (SO2), whose emission concentration directly depend on the amount of sulphur contained in the raw material and more importantly in the type of fuel used during the firing process. The reuse of by-products like Low Grade Magnesium Oxide (LG-MgO) during the calcination of magnesite for flue gas desulfurization (FGD) can generate a loop process optimizing the efficiency and revaluating those by-products. FGD is the widest applied measure for SO2 reduction. It allows an industrial plant to reduce its emission by up to 99%. Essentially, is an acid-base reaction in wet or dry conditions. Although wet methods present many advantages such as their high desulfurization efficiency and low economic cost, the conclusions also brought up the fact that the large amounts of liquid effluents produced at the end of the process require a proper management. After research work in wet conditions, MAGNA requested DIOPMA to start a study of Dry FGD. The first benefit of using the dry method is wastes, which are easier to handle than wet flue gas desulfurization. Moreover, requires less energy inputs and lower operation costs. The scope of this project is the lab-scale design to achieve the study of the LG-MgO performance as a desulfurization agent.There are different considerations to take into account for the design of the lab-scale experiment for the dry desulfurization process: gas composition, flow rate, heat flow, corrosion resistance, among others, in order to achieve the company conditions for a reliable study. The process of heat exchange becomes the core of the project since the bottles with the gas composition and the particulate solid have been provided by the company. The design requires heating the gas from room temperature to 200ºC before putting it in contact with the LG-MgO. The calculation to determine the fluid flow conditions has been made in order to use the best correlations to approximate the heat transfer system for the project. The laboratory system designed includes a 1m length furnace and a pipe that goes through to reach the working temperature. Additionally the minimum radius of insulation has been calculated to avoid the heat losses between the exit of the furnace and the the reactor input. Boundary conditions of energy-efficient walls, for furnace and maximum service temperature or durability for pipe have been studied in order to select the best materials for each one using Granta CES EduPack software. As a main conclusions for this work, it has been determined that the flow conditions directly influences the convection heat transfer, suggesting a turbulent flow as a better ally for its optimization. On the other hand, another configuration can be made and allows to use a resistance instead of a furnace. Therefore, and an external insulation should be used in order to ensure that all the heat generated is absorbed by the fluid
Effects of the Use of Master Alloys on the Sintering of Mn Steels
(2019-06) Fernández Perucho, Iu-Aran; Fernández González, Javier; Calero Martínez, José Antonio
When manufacturing sintered steel parts there is the option of adding alloying elements that improve the mechanical, functional, dimensional and wear properties of the component. This is the case of elements such as Mn or Si, which can provide a substantial improvement of the mechanical properties of a steel while maintaining a low cost given the abundance of these in the Earth's crust. Their use, however, is conditioned in the pulvimetallurgy industry given the affinity for oxygen shown by both elements, producing oxides that weaken the sintered components. One of the solutions developed to incorporate these elements into powder mixtures for sintering is the use of master alloys that allow the reduction of the chemical activity of the elements thus avoiding the formation of oxides. In this study, tests were carried out with four master alloys with different compositions of Mn and Si in order to study their behaviour during sintering and the properties they bring to sintered steel. With this objective, several mixtures containing different master alloys are prepared to produce sintered specimens at temperatures normally used in the manufacturing of sintered components. These specimens were used for the mechanical, chemical and microstructural characterization of steels, which will allow the study in greater depth the processes and changes that master alloy particles suffer during sintering, as well as understanding how these processes affect the properties obtained. A range of graphite additions were used in combination with the different master alloys in order to see how the presence of carbon in varying amounts affects the sintering mechanisms. The conclusions of this project paint a bigger picture of the behaviour of Mn and Si introduced in the form of master alloys and their interaction with the rest of the elements of the mixture. In addition, the manufacture of these specimens in industrial sintering conditions allows a first look at the viability of these master alloys for use in the manufacturing of sintered components
Thermal and mechanical study of chemically bonded phosphate cements formulated with magnesium by-product incorporating phase changing materials.
(2015-06) Maldonado Alameda, Alex; Formosa Mitjans, Joan
Magnesium Phosphate Cements (KMgPO4·6H2O; k-struvite), that are known as MPC, part of the family of Chemically Bonded Phosphate Ceramics (CBPC), widely used in the field of biomaterials. These cements are obtained from the acid-base reaction on an aqueous medium between pure MgO and mono-potassium phosphate. It is a spontaneous and highly exothermic reaction that leads to a very fast setting of the material. The main disadvantage of these cements compared with others such as Portland is the high cost of raw materials that are necessary to elaborate the MPC. In the present study we use a by-product called LG-MgO (low magnesium oxide), supplied by the company Magnesitas Navarras, S.A., with the aim to reduce the final cost of MPC and promote aspects such as sustainability and green environment as a consequence of the reduction of the pure MgO mining activity. The research presented here consists in the exhaustive characterization of different dosages of MPC elaborated with magnesium by-product that incorporate air entraining additive and Phase Changing Materials (PCM) to improve the thermal behavior of material when there are thermal oscillations, and thus reduce the use of cooling and heating systems helping to the decrease of CO2 emissions and increasing energy efficiency on the buildings. Moreover, mechanical properties such as elastic modulus, compressive strength and flexural strength are analyzed to test the feasibility of the use of these cements as a passive cooling and heating system. Finally, the degradation of MPC when subjected to thermal cycles is analyzed (thermal durability). Results show that k-struvite is the major product formed in the MPC, although there are also inert phases of magnesium by-product that act as reinforcement. It is verified that the increase of PCM and additive in the content reduces the mechanical properties due to their contribution to increase the porosity and decrease the density. Moreover, we demonstrated that MPC and PCM do not suffer degradation after 750 thermal cycles equivalent to a year.

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