2,544 research outputs found

    Effect of raw materials on the performance of 3D printing geopolymer: A review

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    Traditional construction materials such as cement products release a significant amount of carbon dioxide during their preparation and usage, negatively impacting on the environment. In contrast, 3D printing (3DP) with geopolymer materials utilises renewable and low-carbon emission raw materials. It also exhibits characteristics such as energy efficiency and resource-efficient utilisation, contributing to reduction in carbon emissions and an improvement in sustainability. Therefore, the development of 3DP geopolymer holds great significance. This paper provides a comprehensive review of 3DP geopolymer systems, examining the effect of raw materials on processability, including flowability and thixotropy, and microstructure. The study also delves into sustainability and environmental impact. The evaluation highlights the crucial role of silicon, aluminium, and calcium content in the silicate raw material, influencing the gel structure and microstructural development of the geopolymer. Aluminium promotes reaction rate, increases reaction degree, and aids in product formation. Silicon enhances the mechanical properties of geopolymer, while calcium facilitates the formation and stability of the three-dimensional network structure, further improving material strength and stability. Moreover, the reactivity of raw materials is a key factor affecting interlayer bonding and interface mechanical properties. Finally, considering sustainability, the selection of raw materials is crucial in reducing carbon emissions, energy consumption, and costs. Compared to Portland cement, 3DP geopolymer material demonstrate lower carbon emissions, energy consumption, and costs, thus making it a sustainable material

    Insights on numerical models to predict potential recyclability of spent refractories from steel making industry

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    The present study is part of the CESAREF (Concerted European action on Sustainable Applications of REFractories) doctoral network, started in late 2022. The aim of the consortium is the contribution to scientific breakthroughs inherent to refractories for steel making sector thanks to transversal competences deriving from academic and industrial realities. European green deal and circular economy targets set by EU for 2025 are also related to the massive consumption of refractory materials in the steel industry. Operative lifetimes of refractories range from hours to several months depending on their role. As a result of increasingly tightened policies and disposal costs, and due to recent supply chain shortages, end-of-life refractories recovery and recycling practices are receiving great attention. Some of the core requirements for sustainability and circularity are the reduction of open-loop and down scaling strategies, to maintain refractory materials value as long as possible, of the end-of-life materials. Over the years application of numerical models has proved to be a useful strategy for researchers facing in-use issues related to refractory materials. In this study, different finite element models (FEM) applied to end-use refractories are discussed to understand their suitability for potential recyclability prediction. Thermomechanical characterization of prior- and post-use materials allow to identify the critical issues related to numerical models' development. The comparison between empirical results and the appropriate numerical model allow us to identify suitable pathways to improve refractories sustainability

    Derivation and application of the stream of variation model to the manufacture of ceramic floor tiles

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    One of the main problems in the manufacture of floor tiles is the dimensional variability of the ceramic product, which leads to the product having to be classified into different dimensional qualities with an increase in cost. In this paper we propose a novel way of modelling the dimensional variability of ceramic floor tiles by the adaptation of the Stream of Variation model. The proposed methodology and its potential applicability contributes to the integration of process knowledge in the ceramic tile industry and allow tile manufacturers have a new methodology for process improvement, variation reduction and dimensional control

    A review of alternative approaches to the reduction of CO2 emissions associated with the manufacture of the binder phase in concrete

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    In this review we discuss a wide range of alternative approaches to the reduction of CO2 emissions associated with the manufacture of the binder phase in concrete. They are classified broadly as follows: (1) Use alternative fuels and/or alternative raw materials in the manufacture of Portland-based cements. (2) Replace Portland clinker with “low-carbon” supplementary cementitious materials (SCMs) in concrete. (3) Develop alternative low-carbon binders not based on Portland clinkers. The first approach mainly represents incremental improvements that can be achieved fairly easily and cheaply as long as suitable raw materials can be found. The second approach ranges from incremental improvements, if low levels of SCM substitution are used, all the way to major innovations for binders with very high Portland clinker replacement levels. The third approach is the most risky but also holds the greatest promise for truly significant CO2 reductions if it can be implemented on a large scale

    Multi-scale modeling of the additive manufacturing of ceramics by vat photopolymerization

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    Advanced Technology of Waste Treatment

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    The protection of human health and the environment (representing the main reason for waste management), as well as the sustainable use of natural resources, requires chemical, biological, physical and thermal treatment of wastes. This refers to the conditioning (e.g., drying, washing, comminution, rotting, stabilization, neutralization, agglomeration, homogenization), conversion (e.g., incineration, pyrolysis, gasification, dissolution, evaporation), and separation (classification, direct and indirect (i.e., sensor-based) sorting) of all types of wastes to follow the principles of the waste hierarchy (i.e., prevention (not addressed by this issue), preparation for re-use, recycling, other recovery, and disposal). Longstanding challenges include the increase of yield and purity of recyclable fractions and the sustainable removal or destruction of contaminants from the circular economy.This Special Issue on “Advanced Technology of Waste Treatment” of Processes collects high-quality research studies addressing challenges on the broad area of chemical, biological, physical and thermal treatment of wastes

    Experimental extrusion of tubular multilayer materials for Oxygen Transport Membranes

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    Investigation of the use of microwave image line integrated circuits for use in radiometers and other microwave devices in X-band and above

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    Program results are described in which the use of a/high permittivity rectangular dielectric image waveguide has been investigated for use in microwave and millimeter wavelength circuits. Launchers from rectangular metal waveguide to image waveguide are described. Theoretical and experimental evaluations of the radiation from curved image waveguides are given. Measurements of attenuation due to conductor and dielectric losses, adhesives, and gaps between the dielectric waveguide and the image plane are included. Various passive components are described and evaluations given. Investigations of various techniques for fabrication of image waveguide circuits using ceramic waveguides are also presented. Program results support the evaluation of the image line approach as an advantageous method for realizing low loss integrated electronic circuits for X-band and above

    DEVELOPMENT OF EXPERIMENTAL FACILITIES FOR INVESTIGATIONS OF VORTEX MACHINING

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    This dissertation presents work done in investigation of a novel polishing process called Vortex Machining. Vortex Machining uses an oscillating probe to induce vortices in a polishing slurry above a workpiece, thereby removing material in regions measuring micrometers laterally. The probe features a high-aspect ratio geometry that enables it to reach into (and potentially polish) complex geometries such as small holes and deep channels. The probe can also be used for force and displacement feedback, providing potential for in situ measurement. Throughout this research two test facilities have been developed; a low-power facility utilizing a 7 ?m diameter probe oscillating at 32.7 kHz with amplitudes in the tens of micrometers, and a high-power facility utilizing a 500 µm diameter probe oscillating at several kHz with amplitudes of several hundred micrometers. The facilities control probe position to 0.5 µm, slurry depth to 10 µm, and probe phase to 2.5°; and have demonstrated machining capabilities used in preliminary studies of the process. Analysis software was developed to characterize process footprints. While substantial variability in footprints is observed, material removal rates of the order 10-8 and 10-4 mm3·hr-1 have been measured on silicon. Surface finish values of footprints are typically sub-nanometer and thus comparable to traditional polishing
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