Phosphorus recovery from a pilot-scale grate furnace: influencing factors beyond wet chemical leaching conditions

Phosphorus is a non-renewable resource going to exhaustion in the future. Sewage sludge ash is a promising secondary raw material due to its high phosphorus content. In this work, the distribution of 19 elements in bottom and cyclone ashes from pilot-scale grate furnace have been monitored to determine the suitability for the phosphorus acid extraction. Moreover, the influence of some parameters beyond wet chemical leaching conditions were investigated. Experimental results showed that bottom ash presented lower contamination in comparison to cyclone ash and low co-dissolution of heavy metals (especially Cr, Pb and Ni), while high phosphorus extraction efficiencies (76-86%) were achieved. High Al content in the bottom ash (9.4%) negatively affected the phosphorus extraction efficiency as well as loss on ignition, while the particle size reduction was necessary for ensuring a suitable contact surface. The typology of precipitating agents did not strongly affect the phosphorus precipitation, while pH was the key parameter. At pH 3.5-5, phosphorus precipitation efficiencies higher than 90% were achieved, with a mean phosphorus content in the recovered material equal to 16-17%, comparable to commercial fertilizers. Instead, the co-precipitation of Fe and Al had a detrimental effect on the recovered material, indicating the need for additional treatments

Insight into the Cycling Behaviour of Metal Anodes, Enabled by X-ray Tomography and Mathematical Modelling

This work tackles the methodological challenge of rationalizing symmetric-cell cycling data from a materials-science perspective, through experiment replication, mathematical modelling, and tomographic imaging. Specifically, we address Zn electrode cycling in alkaline electrolyte with and without adding tetrabutylammonium bromide (TBAB). This additive is known from literature, but its practical impact is jeopardized by lack of in-depth understanding of its behaviour. Electrochemical testing was carried out at practically relevant current densities and the effect of variations of operating conditions was taken into account. The physical chemistry underlying cell potential profiles, has been modelled mathematically, accounting for: electrokinetics, mass-transport, electrode shape change and passivation. In particular, we disclosed an unexpected joint effect of TBAB and current density on passivation time: tomography allowed to rationalise this behaviour in terms of precipitate morphology

Danneggiamento per pitting di acciai bonificati, cementati e nitrurati

La comprensione dei meccanismi di danneggiamento che portano al manifestarsi dell’usura per faticaè di fondamentale importanza per l’ottimizzazione dei materiali e dei trattamenti termici.Il presente lavoro ha previsto l’esecuzione di prove di rotazione disco su disco (rolling disc-on-disc test).Questo metodo si basa sulla rotazione simultanea di una coppia di dischi sagomati in modo da simulareil contatto tra superfici sferiche. Le prove sono state eseguite su tre differenti tipi di acciaio:• UNI EN 42CrMo4 bonificato; • UNI EN 18NiCrMo5 cementato; • UNI EN 42CrMo4 nitruratoLo scopo del presente lavoro è quello di identificare i meccanismi di danneggiamento coinvoltinella fase di innesco del fenomeno di usura per fatica e durante la sua evoluzione.A tal proposito sui campioni ottenuti dalle prove di rotazione disco su disco sono state condotte numerose analisifrattografiche sia ad occhio nudo, che mediante l’utilizzo del microscopio elettronico a scansione (SEM).Sono stati identificati differenti meccanismi di danneggiamento a seconda del tipo di acciaio:• UNI EN 42CrMo4 bonificato: pitting dovuto a cricche originate negli strati superficialifortemente incruditi. • UNI EN 18NiCrMo5 cementato: pitting originato dagli ossidi depositati a bordo granodurante la fase di carburazione. • UNI EN 42CrMo4 nitrurato: pitting dovuto a cricche che siinnescano e propagano all’interno della coltre bianca

What Happens to MnO2 When It Comes in Contact with Zn2+? An Electrochemical Study in Aid of Zn/MnO2-Based Rechargeable Batteries

In the science and technology of electrochemical energy storage, different allotropes of MnO2, fabricated with a variety of methods, are assembled into electrodes, playing the role of cathode or oxygen reduction reaction (ORR) electrocatalyst. Often, MnO2-based cathodes are combined with Zn anodes into different types of batteries, resulting in contact between MnO2 and its electrochemical reaction products, and Zn2+. Awareness is growing that this interaction adversely affects the functional performance of MnO2, but no definitive understanding has been reached for this issue. This study contributes, through electrochemical measurements accompanied by microscopy and Raman spectroscopy, to a better understanding of the way the electrochemical behavior of two technologically representative types of manganese dioxide - hydrothermally grown α-MnO2 and electrodeposited γ-MnO2 (EDM) - is degraded when these materials are exposed to neutral and alkaline aqueous solutions, containing Zn2+. Specifically, we highlighted different types of irreversible changes in electrochemical response, which can be interpreted with phase-formation processes. Such changes result in the deactivation of α-MnO2 as ORR electrocatalyst, and of both α-MnO2 and EDM as zinc-ion battery (ZIB) cathodes. The electroactivity of EDM for ZIB operation can be restored if Mn2+ is added to the neutral electrolyte, because a phase, active in discharge, is electrodeposited during charging

FORENSIC ENGINEERING SURVEYS WITH UAV PHOTOGRAMMETRY AND LASER SCANNING TECHNIQUES

This work aims at presenting the use of new technologies in the field of forensic engineering. In particular, the use of UAV photogrammetry and laser scanning is compared with the traditional methods of surveying an accident site. In this framework, surveys must be carried out promptly, executed in a short time and performed so that the greatest possible amount of information is collected with sufficient accuracy to avoid the possibility of neglecting details once that the scene is no longer preserved. The combination of modern surveying techniques such UAV photogrammetry and laser scanning can properly fulfill these requirements. An experimental test has been arranged and instruments, procedures, settings, practical limits and results have been evaluated and compared with respect to the usual way of performing the survey for forensic purposes. In particular, both qualitative and quantitative considerations are given, assessing the completeness of the reconstructed model, the statistical evaluation of the errors and the accuracy achieved

Spontaneous sparse learning for PCM-based memristor neural networks

Neural networks trained by backpropagation have achieved tremendous successes on numerous intelligent tasks. However, naive gradient-based training and updating methods on memristors impede applications due to intrinsic material properties. Here, we built a 39nm 1Gb phase change memory (PCM) memristor array and quantified the unique resistance drift effect. On this basis, spontaneous sparse learning (SSL) scheme that leverages the resistance drift to improve PCM-based memristor network training is developed. During training, SSL regards the drift effect as spontaneous consistency-based distillation process that reinforces the array weights at the high-resistance state continuously unless the gradient-based method switches them to low resistance. Experiments show that the SSL not only helps the convergence of network with better performance and sparsity controllability without additional computation in handwritten digit classification. This work promotes the learning algorithms with the intrinsic properties of memristor devices, opening a new direction for development of neuromorphic computing chips

Metallurgical Analysis as a Useful Method for Fire Investigation: the Case of Galvanized Steel Sheets

In this work, fire simulations were carried out on zinc-coated steel sheets usually employed for the structural parts of furniture, transformer rooms and aeration pipes. The thermal alteration induced by the fire was simulated by heating samples at 13 different temperatures (from 20° C to 1050° C) and for different exposure times (1 h and 6 h) in a laboratory furnace. The metallurgical investigation concerned the surface coloring by photographic analysis, the morphology and chemical composition of the surface oxides by SEM and EDS and the microstructure modifications as a function of the temperature by LOM. The influence of the different parameters was discussed by a statistical approach. The obtained results allowed to associate the temperature to one or more alteration of the steel microstructure and of the color, the morphology and the chemical composition of the surface oxides

Dai reperti in metallo la radiografia dell'incendio

L'analisi metallurgica di questi materiali rappresenta un utile metodo di indagine per individuare le temperature sviluppate durante un incident

La ricostruzione dello scenario di incendio parte dall'analisi dei reperti in metallo

Le potenzialità dell’analisi metallurgica e metallografica dei reperti provenienti dalle zone coinvolte in un incendio. Dalle simulazioni d’incendio su componenti, realizzati in lega d’alluminio, in rame o lega di rame, sono stati ottenuti dei campioni, poi esaminati in laboratorio tramite microscopia ottica e microscopia elettronica a scansione (SEM) con microsonda a dispersione d’energia (EDS)

The effect of nitriding, severe shot peening and their combination on the fatigue behavior and micro-structure of a low-alloy steel

Fatigue strength of mechanical components can be greatly enhanced by generating compressive residual stress, increasing the hardness and reducing the grain size. It is well known that while the use of mechanical treatments is able to generate an effective field of compressive residual stresses and, if severe parameters are used, to cause grain refinement, thermochemical treatments are able to increase the surface hardness. This justifies the interest in developing combined treatments, able to achieve all the just mentioned factors. In this study, the effect of combination of severe shot peening and nitriding on the fatigue limit of a low-alloy steel is investigated. Severe shot peening was conducted by using particular processing parameters to obtain ultra-fine/nano-structured surface layers. Micro-structural observation, micro-hardness, surface roughness and XRD measurement of residual stress were performed on single and hybrid surface treated specimens including nitrided, severely shot peened, nitrided plus severely shot peened and severely shot peened plus nitrided specimens. The fatigue limit of all series was experimentally determined and compared with the as-received specimens. Severe shot peening and Nitriding improved the fatigue limit by 11.6% and 51.3% respectively. Combination of severe shot peening and nitriding improved hardening, residual stress and nitrogen diffusion with respect to the single treatment. Nevertheless, it could not guarantee further improvement in the fatigue limit as compared with the nitrided smooth specimens. The results are critically assessed by considering the local fatigue limit concept