Materials Science Forum Vol. 1167

Abstract: In this work, the liquid phase exfoliation (LPE) method was investigated to produce a large quantity of 2D MoS₂. The introduction of ultrasound into IPA and IPA/DI solutions containing MoS₂ resulted in fragmentation and exfoliation of the MoS₂. The determination of the layers of LPE-MoS₂ was performed by optical microscopy, atomic force microscopy, non-resonant Raman spectroscopy and XRD. Flakes with few layers were detected by AFM and resonant Raman investigations.

Abstract: In this work, an investigation of the mechanically exfoliated MoS₂ under the influence of heat treatment was carried out. Optical and atomic force microscopy techniques were applied to determine the number of layers. Resonant Raman investigation was performed, which clearly showed systematic layer-dependent spectral features. The surface morphology of MoS₂ was investigated with the STM. Atomic-resolution images of MoS₂ is were obtained. Three types of atomic defects were identified as substitutions of donor and acceptor atoms in the Mo atomic layer below the topmost sulfur layer.

Abstract: The carbon aerogels (CA) with different precursor concentration ratios were successfully prepared using the sol-gel method and vacuum freeze-drying technique, using formaldehyde and resorcinol as precursor materials. The crystal structure of the samples was analyzed by X-ray diffraction (XRD), the microstructure was characterized by scanning electron microscopy (SEM), the specific surface area was measured by Bruner-Emmett-Teller (BET) and the pore volume and pore size distribution of the sample was analyzed by Barrett-Joyner-Halenda (BJH). The results show that the microstructure of carbon aerogel is mainly microporous and mesoporous with a loose network pore structure. The microstructure and morphology of carbon aerogel changed significantly with the increase in precursor concentration. When the precursor concentration reaches 10 wt. %, the mesoporous microstructure of carbon aerogel is the best, the specific surface area reaches 970.51 m²/g, and a mesoporous material with good gel skeleton strength and toughness is formed.

Abstract: Depending on the collecting methods, coal combustion by-products are usually divided into fly ash, bottom ash, and flue gas desulfurization product. Because they are a hazardous dust source, they are often stored underwater in ponds or lagoons and are called pond ash. In this investigation, the pond ashes from Ulaanbaatar's 4^th TPS (thermal power station) and Erdenet’s TPS were characterized by XRF, XRD, BET, PSD, SEM and TEM. The pond ash of the 4^th TPS contains more than 20% calcium oxide, while Erdenet’s TPS contains around 4% calcium oxide. PSD of the 4^th TPS shows a bimodule distribution with a maximum of 36 and 260 mm, while Erdenet's pond ash shows an unimodal distribution with a maximum of 74 mm. The main crystalline compounds of the 4^th TPS pond ash were quartz, calcite, hematite, albite, while in the Erdenet pond ash were quartz, mullite, magnetite, and calcite. The mineralogical composition of the pond ashes depends on the used coal type, the power plant’s working principle and the duration of time inside the ash pond. The alkali-activated binder prepared from these pond ashes demonstrated a weak compressive strength of around 1.5-2.5 MPa after 7 days. Notably, the high-calcium pond ash-based alkali-activated paste exhibited slightly higher mechanical properties than the low-calcium pond ash-based paste. The weak mechanical properties of the pond ash-based alkali-activated materials are related to both pond ashes’ porous and high-surface microstructure. High calcium pond ashes could exhibit a partial calcium silicate formation reaction, which is the reason for the higher mechanical properties than low calcium pond ash-based alkali-activated pastes. Furthermore, a brief mechanical activation of these pond ashes for 20 min slightly improved their mechanical properties, reaching up to 3.75 MPa.