1,721,062 research outputs found
High porous yttria-stabilized zirconia with aligned pore channels: Morphology directionality influence on heat transfer
No full textHigh porous yttria stabilized zirconia with unidirectionally aligned channels is used in engineering applications with extremely low thermal conductivity. This property is strongly influenced by microstructure features such as pore volume fraction, pore size distribution, random porous microstructure and pore morphology directionality. Although several models are reported in the available literature, but their analytical formulas are formalised for homogeneous structures or they are based on proportion between solid and fluid phases. These differences from real microstructures cause significant computational errors especially when thermal conductivity changes as the function of the measurement direction (parallel or perpendicular). In this context, the application of an intermingled fractal unit's procedure capable of reproducing porous microstructure as well as predicting thermal conductivity has been proposed. The results are in agreement with experimental ones measured for parallel and perpendicular directions and suggest improving the formalisation of fractal modelling in order to obtain an instrument of microstructure design
Fluid flow in complex porous media: Experimental data and IFU model predictions for water vapour permeability
No full textIn this research work, an Intermingled Fractal Units' model (IFU's model) has been proposed with the aim of predicting water vapour permeability characteristics of porous rock, normally studied in gas reservoir field. IFU modelling approach commences with the reproduction of experimental pore size distribution with the help of diverse fractal base units mixed together. This procedure allows simulating the porous microstructure in terms of pore cumulative curve or pore size distribution. An analytical procedure is used for obtaining the permeability values. The studied rocks include limestone from South Sardinia quarries and have similar characteristics of those studied in gas reservoir field. They have been taken from four different parts (systems A, B, C and D) of the quarry for the assessment of the heterogeneity of this rock. From the experimental tests, the average water vapour permeability values are equal to 7.22 ± 1.22, 4.21 ± 1.51, 10.09 ± 1.11 and 10.12 ± 2.4210−12 kg m−1 s−1 Pa−1 respectively for systems A, B, C and D, whereas predictions by IFU are respectively equal to 7.15 ± 1.55, 4.25 ± 1.45, 10.12 ± 1.22 and 9.98 ± 2.1810−12 kg m−1 s−1 Pa−1. The comparison shows a good capacity of IFU procedure to predict water vapour permeability values
Nanoporous Au: Statistical analysis of morphological features and evaluation of their influence on the elastic deformation behavior by phenomenological modeling
No full textThis work investigates the relationship between the morphology of nanoporous (NP) Au metal foams and their response to elastic deformation. A detailed statistical analysis of scanning electron micrographs has been performed to obtain a quantitative description of ligaments and nodes in terms of characteristic lengths. The thickness of ligaments is shown to vary along their length according to a quadratic function. The relatively broad distribution of ligament length and thickness indicates that local structures can be significantly different from each other. Invariably, nodes are quite massive. Based on this experimental evidence, a phenomenological model of the NP Au structure has been developed to describe its mechanical response within the elastic deformation range. The elementary structural unit consists of a cubic node connecting with six half ligaments with a square cross-section and a parabolic thickness profile. The model predicts that the bending behavior is restricted to the central portion of the ligaments, the effective response being modulated by the ligament characteristic lengths. Model predictions are found to agree fairly well with experimental data
Surface stresses and Young’s modulus in nanoporous Au foams
No full textA theoretical model is developed to relate structure and mechanical properties in nanoporous metals. It is shown that undercoordinated surface atoms generate surface stresses that enhance the Young’s modulus of individual ligaments and of the nanoporous metal. The model perfectly reproduces the experimental Young’s modulus of nanoporous Au if ligaments are allowed to bend over an effective length shorter than the nominal one. The effective bending length is roughly 2/3 the nominal one over two orders of magnitude
Sustainable earthen plasters: surface resistance enhancement via thermal treatments
Full text linkThe construction sector contributes approximately 37 % of global embodied carbon from materials. Earth-based materials offer a more sustainable alternative, and using recycled aggregates as sand substitutes further reduces environmental impact by limiting raw material extraction. However, these materials are often vulnerable to erosion and water action. This study investigates low-temperature thermal treatments (200–600 °C) of 10 and 60 min and bio-based polymer coatings to enhance the durability of clay-based mixtures with recycled aggregates. Treatments at 500–600 °C significantly improved resistance, with short treatments at 600 °C performing comparably to longer ones. In contrast, bio-based coatings were less effective due to superficial application and film discontinuities. Results highlight the potential of in situ thermal stabilization as a sustainable and efficient method to improve the durability of earthen construction materials and promote their use as a viable alternative in sustainable building practices
A phenomenological approach to yield strength in nanoporous metal foams
No full textThis work discusses a phenomenological model enabling the estimation of yield strength for nanoporous metal foams. A regular lattice of relatively massive cubic junctions joining six thick ligaments with square cross section is used to describe the foam structure. The characteristic lengths of ligaments and nodes are estimated from experimental data. The yield strength of the structure is related to the plastic moment of individual ligaments. Model predictions are in fairly good agreement with experimental findings
Mechanical behavior of nanoporous Au with fine ligaments
No full textA theoretical model relating the overall mechanical behavior of NP metals to the bending response of thick ligaments is developed based on an idealized regular lattice of massive cubic nodes and thick ligaments with square cross section. The model predictions are compared with the Young's modulus and yield strength of nanoporous Au with ligaments a few nanometers in size obtained by numerical simulation and available in literature. It is shown that the model provides a quantitative description of the elastic and plastic deformation of nanoporous Au, reproducing to a considerable extent the numerically estimated Young's modulus and yield strength values
Sustainable clay-based materials stabilised by low-temperature treatments: Salt degradation and chemomechanical approach
Full text linkEarthen materials represent a low environmental impact alternative, but they are inherently vulnerable to water exposure and degradation processes. For this reason, they often require stabilization through thermal treatments. In this study, temperatures lower than those typically used for ceramic firing were applied, with the aim of preserving the sustainability of the final products. However, while the treated structures exhibit improved water resistance, new degradation mechanisms typical of construction materials, such as salt crystallization, may arise. To investigate this aspect, an experimental campaign has been carried out to assess the resistance to sodium sulfate salt crystallisation. The results have been compared with predictions from a chemomechanical model, which has been adapted in this work through the introduction of a porosity activation factor. The model has been shown to be effective in predicting the onset cycle of degradation, offering a valuable tool for the design of more durable and resilient materials
Coarsening of nanoporous Au: Relationship between structure and mechanical properties
No full textChemical dealloying was used to fabricate nanoporous Au samples with fine ligaments. The samples were subjected to isothermal annealing at relatively low temperature to induce slow, limited coarsening. This allowed obtaining a sequence of progressively coarsened nanoporous Au samples with correlated structure. Scanning and transmission electron microscopies were utilized to measure the characteristic lengths of nanoporous Au and investigate accurately its coarsening kinetics. Nanoindentation experiments were also performed to estimate Young’s modulus and yield strength. It is shown that mechanical properties undergo a gradual variation related to structural evolution. The observed mechanical behavior is tentatively rationalized by a simplified model able to describe the mechanical response of nanoporous metal structures with thick ligaments and massive nodes
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