129,896 research outputs found
Recycled Glass Mixtures as Cast Glass Components for Structural Applications, Towards Sustainability
No full textThe problem of sustainability represents one of the most important issues that the world has to face nowadays, not only in terms of energy consumption and of the consequent CO2 emissions, but also in terms of material waste streams that end in landfill. 38 million tons of glass waste are produced every year in the European Union and new targets have been set for 2020 towards a more sustainable management of such wastes. Nowadays, only the container glass industry has reached a considerable recycling rate, while for all the other sectors we are still witnessing downgrading processes. Looking at the world of construction, glass has been more and more employed as a structural material thanks to its high transparency and compression strength. Although the use of glass can be attractive under multiple aspects and its production is continuously increasing, once employed as a construction element, it is rarely reused or recycled due to the high-quality requirement demanded to the industry of production. Nevertheless, besides its main applications as a 2-dimensional element, the new technology of cast glass has been recognised as a potential mean of glass recycling. Here, glass is designed and used under the form of repetitive 3-dimensional units assembled in a whole geometrical shape. In fact, thanks to its higher load-bearing capacity under monolithic shapes, this glass can admit less restrictions and potentially incorporate different types of waste. For this reason, the aim of this experimental work is to find a possible combination between glass families, specifically soda-lime, borosilicate and lead-crystal glass, to be recycled as cast glass components. Each type of glass was powdered or grinded under the form of cullet and different mixtures were prepared to be melted at temperatures of 970°C, 1120°C and 1200°C through the kiln-cast tecnique. Finally, an experimental splitting test was performed to define a force trend and a fracture behaviour for each sample. Some preliminary results have been achieved drawing the guidelines for a further investigation. Soda-lime-silica glass and lead-crystal glass mixture revealed to be the most compliant glass recipe with the required physical and mechanical properties, when reheated at 1120°C. The decrease in the melting temperature of the compound and the higher transparency given by the addition of lead glass revealed the potential benefit, in terms of sustainability, for future projects
On Kolmogorov entropy compactness estimates for scalar conservation laws without uniform convexity
No full textIn the case of scalar conservation laws u_t +f(u)_x = 0; t > 0; x in R, with uniformly strictly convex flux, quantitative compactness estimates-in terms of Kolmogorov entropy in L^1_{loc}- were established in [C. De Lellis and F. Golse, Comm. Pure Appl. Math., 58 (2005), pp. 989{998; F. Ancona, O. Glass, and K. T. Nguyen, Comm. Pure Appl. Math., 65 (2012), pp. 1303{1329] for sets of entropy weak solutions evaluated at a fixed time t > 0, whose initial data have a uniformly bounded support and vary in a bounded subset of L1. These estimates reflct the irreversibility features of entropy weak discontinuous solutions of these nonlinear equations. We provide here an extension of such estimates to the case of scalar conservation laws with a smooth flux function f that either is strictly (but not necessarily uniformly) convex or has a single inflection point with a polynomial degeneracy
Production and Testing of Kiln-cast Glass Components for an Interlocking, Dry-assembled Transparent Bridge
No full textA pedestrian glass bridge, located at the TU Delft campus site, is being designed by the TU Delft Glass & Transparency Lab. Specifically, the arch-formed bridge consists of cast glass, dry-assembled, interlocking components. To validate the shape of the components, glass mock-ups in 1:2 scale are kiln-cast and tested. This paper follows the elements’ production process from the 3D milled MDF model and the construction of disposable moulds via the lost-wax technique, to the kiln-casting at 940ºC with the “flowerpot method”. Steps are taken towards the refinement of the production technique, with emphasis in minimizing the occurrence of air bubbles, surface flaws and internal stresses that can reduce the load-bearing capacity of the components. Polarisation techniques are employed to define the residual stress distribution of the cast elements as well as to map the consolidated flow of molten glass and the areas of inhomogeneity or non-cohesion. The structural performance of the components and their interlocking behaviour are studied by conducting shear tests on three series comprising three glass bricks with a transparent PU interlayer in-between. The fracture patterns of the specimens are analysed and correlated with the flaws and internal stresses resulting from the kiln-casting process
The dependence of the weathering of soda–lime–silica glass on environmental parameters: a preliminary investigation
No full textThe chemical resistance (durability) of glass depends both on its chemical composition and on the chemical (type and
amount of the molecules interacting with the glass surface) and physical (temperature, humidity, time, etc.) environmental
parameters. A wide literature is available concerning glass weathering mechanisms, mainly involving leaching processes,
but only few investigate the effects of each critical parameter. This study considers the dependence of soda–lime–silica
glass alteration on temperature, relative humidity and time in the case of glass in a confined environment. The aim is to
simulate the experimental conditions related to the weathering of the inner surface of empty glass containers that occurs
during the storage in industrial pallets. A low cost experimental apparatus was set up, in which humidity and temperature
were controlled by high performance homemade devices. The dependences of humidity, temperature and time on the
glass leaching and on the formation of weathering products of low durability soda–lime–silica glass was investigated
by optical and electronic microscopy (SEM), x-ray microanalysis and micro-infrared reflectance spectroscopy (IRRS)
Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic
No full textCooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined
Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic
No full textCooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined
Clinopyroxene based glasses and glass-ceramics for functional applications
No full textDoutoramento em Ciência e Engenharia de MateriaisAs piroxenas são um vasto grupo de silicatos minerais encontrados em muitas rochas ígneas e metamórficas. Na sua forma mais simples, estes silicatos são constituídas por cadeias de SiO3 ligando grupos tetrahédricos de SiO4. A fórmula química geral das piroxenas é M2M1T2O6, onde M2 se refere a catiões geralmente em uma coordenação octaédrica distorcida (Mg2+, Fe2+, Mn2+, Li+, Ca2+, Na+), M1 refere-se a catiões numa coordenação octaédrica regular (Al3+,
Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), e T a catiões em coordenação tetrahédrica (Si4+, Al3+, Fe3+). As piroxenas com estrutura monoclínica são designadas de clinopiroxenes. A estabilidade das
clinopyroxenes num espectro de composições químicas amplo, em conjugação com a possibilidade de ajustar as suas propriedades físicas e químicas e a durabilidade química, têm gerado um interesse mundial devido a suas
aplicações em ciência e tecnologia de materiais. Este trabalho trata do desenvolvimento de vidros e de vitro-cerâmicos baseadas de clinopiroxenas
para aplicações funcionais. O estudo teve objectivos científicos e tecnológicos; nomeadamente, adquirir conhecimentos fundamentais sobre a formação de fases cristalinas e soluções sólidas em determinados sistemas vitro-cerâmicos, e avaliar a viabilidade de aplicação dos novos materiais em diferentes áreas tecnológicas, com especial ênfase sobre a selagem em células de combustível de óxido sólido (SOFC). Com este intuito, prepararam-se vários vidros e
materiais vitro-cerâmicos ao longo das juntas Enstatite (MgSiO3) - diopsídio (CaMgSi2O6) e diopsídio (CaMgSi2O6) - Ca - Tschermak (CaAlSi2O6), os quais foram caracterizados através de um vasto leque de técnicas. Todos os vidros
foram preparados por fusão-arrefecimento enquanto os vitro-cerâmicos foram obtidos quer por sinterização e cristalização de fritas, quer por nucleação e cristalização de vidros monolíticos. Estudaram-se ainda os efeitos de várias substituições iónicas em composições de diopsídio contendo Al na estrutura, sinterização e no comportamento durante a cristalização de vidros e nas propriedades dos materiais vitro-cerâmicos, com relevância para a sua aplicação como selantes em SOFC. Verificou-se que Foi observado que os vidros/vitro-cerâmicos à base de enstatite não apresentavam as características necessárias para serem usados como materiais selantes em SOFC, enquanto as melhores propriedades apresentadas pelos vitro-cerâmicos à base de
diopsídio qualificaram-nos para futuros estudos neste tipo de aplicações. Para além de investigar a adequação dos vitro-cerâmicos à base de clinopyroxene como selantes, esta tese tem também como objetivo estudar a influência dos
agentes de nucleação na nucleação em volume dos vitro-cerâmicos resultantes á base de diopsídio, de modo a qualificá-los como potenciais
materiais hopedeiros de resíduos nucleares radioactivos.The pyroxenes are a wide spread group rock-forming silicate minerals found in many igneous and metamorphic rocks. They are silicates that, in their simplest form, contain single SiO3 chains of linked SiO4 tetrahedra. The general chemical formula for pyroxenes is M2M1T2O6, where M2 refers to cations in a generally distorted octahedral coordination (Mg2+, Fe2+, Mn+, Li+, Ca2+, Na+), M1 to cations in a regular octahedral coordination (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), and T to tetrahedrally coordinated cations (Si4+, Al3+, Fe3+). Monoclinic pyroxenes are called clinopyroxenes. The stability
of clinopyroxenes over a broad spectrum of chemical compositions, in conjunction with the possibility of achieving desired physical properties and high chemical durability, has generated a worldwide interest due to their applications in material science and technology. The present work deals with the development of clinopyroxene based glasses and glass-ceramics for functional applications. The objective of the study was dual, both scientific and technological; particularly to gain fundamental knowledge on the formation of
crystalline phases and solid solutions in selected glass-ceramic systems, and to evaluate the feasibility for application of new materials in different
technological areas with emphasis on sealing in solid oxide fuel cells (SOFC).
In this pursuit, various glasses and glass-ceramics along Enstatite (MgSiO3) - Diopside (CaMgSi2O6) and Diopside (CaMgSi2O6) – Ca – Tschermak
(CaAlSi2O6) joins have been prepared and characterized by a wide array of characterization techniques. All the glasses were prepared by melt-quenching technique while glass-ceramics were produced either by sintering and crystallization of glass powders or by nucleation and crystallization in monolithic glasses. Furthermore, influence of various ionic substitutions/additions in Alcontaining
diopside on the structure, sintering and crystallization behaviour of glasses and properties of resultant glass-ceramics has been investigated, in relevance with final application as sealants in SOFC. It has been observed that enstatite based glasses/glass-ceramics do not exhibit requisite characteristics in order to qualify for the job of sealing in SOFC while the superior properties
exhibited by diopside based glass-ceramics qualify them for further experimentation as SOFC sealants. Apart from investigating the suitability of
clinopyroxene based glass-ceramics as sealants, this thesis also aims to study the influence of nucleating agents on the volume nucleation in the resultant diopside based glass-ceramics so as to qualify them for further experimentation as hosts for radioactive nuclear wastes
Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic
No full textCooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.UNESP, Inst Quim, BR-14800900 Araraquara, SP, BrazilUniversidade Federal Rural de Pernambuco (UFRPE), Dept Fis, BR-52171900 Recife, PE, BrazilUNESP, Inst Quim, BR-14800900 Araraquara, SP, Brazi
Thermal, optical and mechanical properties of new glass compositions containing fly ash
No full textThe investigation of new compositions is crucial for the expansion of possible applications of glass, from the typical applications for building engineering, in the form of cast blocks or float glass, to more advanced technologies, such as 3D-printed glass or glass-to-metal connections. Since high melting temperatures and brittleness are two important drawbacks of glass, this work aims to improve both properties. Characterisation techniques, such as thermal analysis, nano-indentation, and UV/VIS spectroscopy, are used to evaluate the properties of the samples. The modification of the properties is achieved via changes in the composition of the glass, using compounds such as phosphorus pentoxide, aluminium oxide and boron oxide. Then, the choice of different glass formers and modifiers contributes to the development of compositions with lower melting and glass transition temperatures. The reduction of the melting temperature allows a saving of energy during the manufacturing. The structures of the glasses differ from the standard soda–lime–silica and borosilicate glasses, leading to a different mechanical behaviour. Furthermore, these new compositions incorporate up to 35% of fly ash in their formulas. The valorisation of these by-products reduces costs and gas emission.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and EnvironmentStructural Design & MechanicsApplied Mechanic
Cast Glass Components out of Recycled Glass: Potential and Limitations of Upgrading Waste to Load-bearing Structures
No full textAlthough in theory glass can be endlessly remelted without loss in quality, in practice only a small percentage gets recycled, mainly by the packaging industry. Most of the discarded glass fails to pass the high quality standards of the prevailing glass industry -due to coatings, adhesives, other contaminants or incompatibility of the recipe- and ends up in the landfill. However, employing discarded glass in cast components for building applications can be a way to reintroduce this waste to the supply chain. Such components can tolerate a higher percentage of inclusions, without necessarily compromising their mechanical or aesthetical properties. This paper explores the potential but also the limitations of recycling glass in order to obtain load-bearing components. First, an overview is provided regarding which types of glass reach the recycling plants and the which not, arguing on the reasons behind this selection. Afterwards, a series of experiments is presented, exploring the possibilities of recycling everyday glass waste, from beer bottles and Pyrex® trays to mobile phone screens. Each type of glass waste is initially cast separately to define its flow capability and risk of crystallization. The above information is linked to the X-ray fluorescence (XRF) analyses of the samples prior to recycling. Then, the possibility to mix different glass recipes without fracturing is evaluated. The results point out the types of glass with potential in structural applications, and the overall feasibility of the concept.Applied MechanicsStructural Design & MechanicsOLD Structural Desig
- …
