ABSTRACT
The visualisation and quantification of pore networks and main phases have been critical research topics in cementitious materials as many critical mechanical and chemical properties and infrastructure reliability rely on these 3D characteristics. In this study, we realised the mesoscale serial sectioning and analysis up to â¼80 µm by â¼90 µm by â¼60 µm on portland cement mortar using plasma focused ion beam (PFIB) for the first time. The workflow of working with mortar and PFIB was established applying a prepositioned hard silicon mask to reduce curtaining. Segmentation with minimal human interference was performed using a trained neural network, in which multiple types of segmentation models were compared. Combining PFIB analysis at microscale with X-ray micro-computed tomography, the analysis of capillary pores and air voids ranging from hundreds of nanometres (nm) to millimetres (mm) can be conducted. The volume fraction of large capillary pores and air voids are 11.5% and 12.7%, respectively. Moreover, the skeletonisation of connected capillary pores clearly shows fluid transport pathways, which is a key factor determining durability performance of concrete in aggressive environments. Another interesting aspect of the FIB tomography is the reconstruction of anhydrous phases, which could enable direct study of hydration kinetics of individual cement phases.
ABSTRACT
By finding appropriate recycling approaches, the volume of wastes, corresponding disposal cost, and the pollution of environment could be diminished. Also, such promising approaches can result in the conservation of natural sources and economic benefits. Aluminum dross as a hazardous solid waste in aluminum production industries has caused serious environmental and public health challenges. Various methods have been introduced for management, utilization, and recycling of the waste. The present review describes, firstly, different types of aluminum dross, their environmental and health hazards, composition, and production process and then focuses on the direct and indirect recycling approaches and recovery strategies.
Subject(s)
Aluminum , Hazardous Waste , Recycling , Environmental Pollution , Humans , Public Health , Refuse DisposalABSTRACT
The numerous ecological problems caused by the accumulation of secondary aluminum dross (SAD) as a hazardous waste generated in aluminum castings have necessitated a need for a sustainable recycling solution. This study proposes a novel and green leaching-based process for recovery of nano-alumina as a highly valuable material from SAD. The leaching phase was performed at atmospheric pressure and low temperature. To obtain optimum conditions for the recovery process, the dissolution kinetics and mechanism of SAD in hydrochloric acid were initially studied under a given liquid-to-solid ratio of 20â¯ml/g, various reaction temperatures and times. It was found that the dissolution of SAD in HCl was controlled by layer diffusion with an apparent activation energy of around 10.49â¯kJ/mol. Alumina in the form of a high purity nanostructured powder from SAD was then recovered under optimum conditions of 85⯰C, acid concentration of 5â¯mol/l, and reaction time of 120â¯min by the proposed process. Characterization of nano-alumina was performed using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and transmission electron microscopy (TEM) techniques. The results revealed that the as-produced alumina had a nano-crystalline structure, having the crystal size of 15.90â¯nm and consisting mainly of gamma phase. The microstructural studies disclosed the aggregations of rounded-corner shaped particles. Also, wet chemical analysis showed a purity of more than 98% for the produced alumina.
