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Geopolymers are green and sustainable cementitious materials that are a possible alternative to cement due to lower energy consumption and emissions. Volcanic ash can be used as raw material to prepare geopolymers by alkali activation owing to its high silica and alumina content. However, research on volcanic-ash-based geopolymers is still limited and no consensus on the optimal alkali activator and reaction mechanism has been obtained. This study investigates the effect of alkali activators with different cations on the mechanical properties and microstructure of volcanic-ash-based geopolymers. The flexural and compressive strengths were evaluated. X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy coupled with energy-dispersive spectroscopy and silicon-29 (29Si) magic-angle spinning nuclear magnetic resonance were used to characterise the microstructural properties. The results showed that the alkali activation effect of sodium hydroxide (NaOH) on volcanic ash was superior to those of lithium hydroxide (LiOH) and potassium hydroxide (KOH), particularly at a concentration of 8 mol/l, with 28-day flexural and compressive strengths of 3.0 and 28.3 MPa, respectively. Microstructural results indicated that the sodium hydroxide-activated geopolymers formed dense, continuous, highly polymerised silica–aluminate gels. This paper provides a proper ratio scheme for activating the volcanic ash from similar deposits and promoting practical applications conducive to sustainable engineering development in the future. [ABSTRACT FROM AUTHOR]

Using the Moon's natural resources to build infrastructure is the first step toward lunar colonization. Lunar regolith, rich in aluminosilicate, has the potential to prepare geopolymer for construction. In this paper, carbon nanofibers (CNFs) were added to geopolymers based on lunar regolith simulant, aiming at reinforcing mechanical and microstructural properties. A ball-milling method of CNF dispersion into the lunar regolith simulant was evaluated. The mechanical properties of the resulting geopolymer nanocomposites was investigated. X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, and mercury intrusion porosimetry were used to characterize the microstructural properties. The results indicated that the mechanical properties were improved by CNFs and that the optimal content was 0.3% by weight. Also, flexural strength, Young's modulus, flexural toughness, peak displacement, and compressive strength were reinforced by 34.8%, 7.5%, 83.9%, 21.4%, and 13.1%, respectively. Microstructural results suggested that the CNFs acted as nucleation, fillers, and bridges in the nanocomposites, leading to lower porosity, higher energy requirement for failure, and higher mechanical properties, which are considerable for lunar-based construction. [ABSTRACT FROM AUTHOR]

• Geopolymer can be synthesis using lunar in-situ high temperature. • Time-varying curing temperature influences the strength development. • Lunar extreme temperature causes deterioration in the mechanical properties. • Zeolitic phase materials are products of geopolymerization reaction. Lunar base construction is of great importance for deep space exploration, and the establishment of lunar pavements for the movement of machinery and transportation of materials is essential to improve construction efficiency. Lunar regolith as an in-situ resource has been demonstrated to be used as raw materials to prepare geopolymers for lunar pavements. In this paper, geopolymers based on lunar regolith simulant with different concentrations of alkali activator were synthesized using the natural high-temperature of the lunar surface. Then, the durability of the resulting geopolymer under lunar high and cryogenic temperature was investigated. The flexural and compressive strength was tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si MAS-NMR), and Mercury Intrusion Porosimetry (MIP). The results of the curing section showed that the geopolymer with 8 mol/L sodium hydroxide (NaOH) generated high strength and dense structure, and the period of 420 h–492 h of a lunar day corresponding to a temperature variation from 84.5 °C to 33.5 °C in 72 h was suitable for preparation, with 5.7 MPa and 31.2 MPa 72-h flexural and compressive strength. Three test points were selected on the lunar 30° latitude temperature curve, corresponding to before and after the cryogenic attack, and after high temperature again to investigate the durability of the geopolymer, and the degradation was found noticeable. The flexural strength decreased about 49% and 70%, and the compressive strength decreased about 15% and 18% after the cryogenic temperature and high temperature again, respectively. Microscopic observations revealed that the geopolymer structure was significantly granulated with obvious cracks and increased porosity. In addition, the formation of the zeolitic phase was unexpectedly found, leading to interfacial cracks and mechanical strength reduction of the geopolymer. This paper will be beneficial to explore the evolution of properties of lunar pavement construction materials in the lunar environment. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of polyaniline films with different microstructures were prepared and investigated. One of the films was prepared with polyaniline having nanofiber structure, which was synthesized by rapidly mixed reaction; and the other was prepared with polyaniline having granular particle structure, synthesized by conventional chemical oxidation method. The spectroscopic, electrochemical, and transport properties of the two kinds of films were studied with an interest in an influence of film microstructure on mobilities of charge carriers in polymer films. A clear difference was observed in the mobility versus oxidation level plot between the two kinds of polyaniline films. The results show that nanofiber structure of polyaniline film enhances mobilities, but affect little features of the mobility change induced by oxidation, which implies that although the nanofibers structure facilitates the charge transport in neutral or oxidized films, but it is irrelevant to the evolution of metallic conduction in polyaniline films. [Copyright &y& Elsevier]

Information for the microstructure of soil aggregates is crucial for understanding the mechanisms of various soil processes. The quantification of complex aggregate microstructure and its relationship to vegetative restoration, however, remains elusive. The objective of this study was to evaluate the impact of natural revegetation on aggregate microstructure using synchrotron-based X-ray micro-computed tomography and image analysis. Soil samples were collected from an active cropland and from four former croplands that have been abandoned for 6, 12, 23, and 32 years on the Loess Plateau, China. Soil aggregates (3–5 mm) were scanned at a voxel resolution of 3.25 μm, and the aggregate pore structure was visualized and quantified with ImageJ software. The stability of wet aggregates and other soil properties were also evaluated. The amount of soil organic carbon increased significantly and soil bulk density decreased significantly with abandonment age. Aggregate water stability was higher after revegetation but did not differ significantly among the abandoned sites. Total porosity, percentage of pores >75 μm, and the fraction of elongated pores increased, but the number of pores, percentage of pores <75 μm, and fractions of regular and irregular pores decreased after the croplands were abandoned. The fractal dimension, degree of anisotropy and the Euler number all indicated that aggregate microstructures were more connected and developed at all abandoned sites than in the active cropland, but the fractal dimension was more sensitive for monitoring the quality of the soil structure. The results from this study can help to improve our understanding of the soil processes during natural vegetative succession and of the importance of pore morphology in monitoring the quality of soil structure. [ABSTRACT FROM AUTHOR]

Al x CoCrFeNiCu (x = 0.5, 1.0, 1.5, 2.0) high entropy alloy was prepared by powder metallurgy method.The effect of Al content x on microstructure and corrosion properties of high entropy alloy was systematically studied. The results show that the high entropy alloy has a simple crystal structure and the distribution of components is uniform. The increase of Al content promotes the formation of the BCC structural phase. When the Al mole content is less than 1.0, the main phase is FCC and the dendrite is FCC2 and the interdendritic is FCC1. When the Al mole content is higher than 1.0, the main phase is BCC and the second phase is FCC1. The electrochemical corrosion properties of Al 1.0 CoCrFeNiCu high entropy alloy is good, and the corrosion mainly starts in the form of spot corrosion. In general, the alloy has poor resistance to nitric acid corrosion, and FCC structural phase has better resistance to nitric acid corrosion than BCC structural phase. • The increase of Al content promotes the formation of BCC structural phase in Al x CoCrFeNiCu high entropy alloy. • FCC second phase particles exist in Al x CoCrFeNiCu high entropy alloy and change with the increase of Al content. • Al 1.0 CoCrFeNiCu high entropy alloy has the best electrochemical corrosion performance. • Al x CoCrFeNiCu high entropy alloy FCC structure shows better resistance to nitric acid corrosion than BCC structure phase. [ABSTRACT FROM AUTHOR]