1,720,993 research outputs found
Thermal behaviour of geopolymer materials: Influence of temperature on mineralogical composition and microstructure of sodium-potassium polysialates
No full textDSC, TGA, XRD, SEM and mechanical tests were used to characterize geopolymer materials based on Na2O-K2O-Al 2O3-SiO2 system up to 1300°C. For all compositions, sodium silicate was used as binder. The samples of geopolymer which were cured at room temperature demonstrated dimensional stability up to 1200°C, with exception of samples with K which was stable up to 1300°C, retaining their predominant x-ray-amorphous tetrahedral Al and Si network (polysialates). The four point flexural and compressive strengths test demonstrated a slight decrease of mechanical properties up to 700°C followed by an exponential increase up to the melting temperature
Battery design based upon life cycle statistics
No full textBattery Life Cycle modelling and estimation are key challenges in the modern electric systems, also due to the development of renewable energy and electrified transportation systems exploitation: in such fields indeed the battery has emerged as the most prominent energy storage device, attracting a significant amount of studies. It is however well known that battery lifetime depends on many parameters, such as power density, specific power, energy density, operating environment, etc., so that an accurate methods to analyze this dependence, also taking into account the randomness of the above parameters in real operating conditions, is a necessary even if difficult task. In this framework, in the paper, after a thorough statistical data analysis, a probabilistic method for battery design is proposed which ensures the optimization of a suitable cost function which has the expected lifetime as a basic input. The method takes properly into account, in particular, the random variations in specific power experienced by a lead-acid battery. The statistical features of lifetime are also explored by means of a large series of numerical simulations based upon suitable probability distributions which may characterize the above operating conditions, in order to obtain an efficient estimation of the above lifetime distribution
Ageing effects on batteries of high discharge current rate
No full textAmong the various stress factors determining the ageing of the battery when cycled at high discharge currents, the temperature increase was identified as the main operating mechanism. In order to quantify the improvement of the battery pack cycle life with load levelling, a model was developed to calculate the temperature inside the battery. A curve correlating the battery cycle number with the internal temperature of the battery was designed. As a result, it was calculated that the differential temperature decreased from 11°C in the high stressed battery down to 1.5 °C in the load-levelled system. © 2017 MOBI -Mobility, Logistics and Automotive Technology Research Centre
Experimental investigation of the overcharge effects on commercial li-ion batteries with two different anode materials
No full textLithium-ion batteries are now a widespread technology in automotive applications. Together with the life of the batteries and their performance, safety plays a fundamental role in ensuring the spread of electromobility in our society. Overcharge is one of the most severe safety problems for the large-scale application of lithium-ion batteries. In this work the results of the overcharge tests performed on Lithium Ion cells with different anode materials are presented: A comparison was made between graphite-based anode Li-ion batteries and Lithium Titanate Oxide (LTO)-based anode Li-ion batteries. Experimental tests were performed with different current intensities: it was thus possible to analyze the effects of an overcharge as the current supplied varies. The graphite-based anode Li-Ion batteries are equipped with protection devices which act by blocking the passage of current in the cell and avoiding venting and/or explosion phenomena; on the other hand, LTObased anode Li-Ion Batteries, although considered intrinsically safer batteries, experienced thermal runaway during the overcharge tests. Increasing the overcharge current, the effects of the electrical abuse are more destructive. © 2021 Italian Association of Chemical Engineerin
Electric field-assisted ion exchange strengthening of borosilicate and soda lime silicate glass
Full text linkIn this study, we investigate the effects of electric field-assisted ion exchange (EF-IE) on potassium for sodium ion exchanges of soda borosilicate and soda lime silicate glasses. The results show that applying an electric field (E-field) with the intensity of 1000 V cm-1 for few minutes produces an exchanged layer with a thickness comparable to the conventional chemical strengthening for 4 hours. There is a critical E-field that increases the mobility and, therefore, the diffusion coefficient of the potassium ions in the glasses. The increase is, perhaps, related to the evolution of the glass structure due to the penetration of potassium ions under an E-field. Vickers indentations showed that strong compression is generated in the glass by EF-IE; however, the bending strength improvement is limited because of the presence of large surface defects and the stress distribution inhomogeneit
Mechanical Properties of Phosphate Glass Optical Fibers
No full textIn this work, step-index 40/125 μm diameter optical fibers produced from two slightly different lithium phosphate glasses were subjected to mechanical characterization. Tensile tests were carried out on fibers with gage length from 10 to 150 mm, allowing for the determination of the failure stress (ranging from ≈200 to 400 MPa) and the elastic modulus (60 GPa). Some tests were also performed with the fiber "immersed" in water; an important subcritical crack growth effect was pointed out, and a fatigue susceptibility parameter (n) equal to 11.4 was determined. The analysis of fracture mirror allows an estimated fracture toughness equal to 0.5 MPa m^0.
Bi-axial four points flexural and compressive strength of geopolymer materials based Na2O-K2O-Al2O 3-SiO2 systems
No full textBi-axial four point flexural and compressive strength tests were used for the assessment of mechanical properties of geopolymer material-based, calcined kaolin and kaolinitic clays. Various activating solutions which consist in the mixture of potassium and sodium hydroxide, water and sodium silicate were designed and tested. Six specimens, over a wide number of investigated compositions, were selected with SiO2/Al2O3 varying from 1:1 to 3:1, The compositions 1:1 and 2:1 were obtained by using two different grades of kaolin as raw materials (standard and sand-rich), while the 3:1 was obtained by adding required amounts of silica to either kaolin or kaolinitic clay, All the samples were prepared by slip casting, using density (≈1,5 g/cm3) as indicator of the optimum viscosity for shaping geopolymer pastes, and cured at room temperature for different periods. The bi-axial four points flexural strength values vary from 13 to 21 MPa while the compressive strength vary from 45 to 67 MPa, being essentially influenced by curing time, SiO2/Al2O3 and K 2O/Na2O/H2O ratios, Increasing the SiO 2/Al2O3 ratio from 1:1 to 3:1, the mechanical properties increase but longer setting and curing times were required, Low SiO2/Al2O3 ratio results the appearance of micro cracks and deformations during curing. The flexural and compressive behaviour of the specimens studied were directly correlated to the porosity, density and the final product microstructure. The chemical behaviour of the six compositions is discussed with respect to basic dissolution-hydrolysis- polycondensation processes that occur in Na2O-K2O-Al 2O3-SiO2 systems
Analysis of the Effects of Overcharging Lithium Ion Cells with Graphite Anode: Efficiency of Protection Devices Integrated into the Cells
No full textLithium ion batteries are currently the main technology for storing energy in electric vehicles thanks to their high power density and energy density. Among the many challenges, safety related aspects must be faced. The thermal runaway caused by overcharge is one of the main weak points to be addressed to ensure a proper level of safety, necessary for the diffusion of this technology.Nowadays, many cells have integrated protection devices that reduce the risk of thermal runaway triggered by overcharging. In this study, the efficiency of devices used to prevent the thermal runaway, caused by overcharging cylindrical 18650 lithium-ion cells with graphite anode, is evaluated. Experimental tests were carried out at different ambient temperatures and overcharge currents.In all the cases the intervention of the Current Interrupt Device avoids the thermal runaway occurrence, preventing the intervention of the others protection devices such as the Positive Temperature Coefficient device and the safety vent
- …
