Ramp facies in an intracratonic basin: A case study from the Upper Devonian and Lower Carboniferous in central Hunan, southern China

AbstractDetailed studies on Late Devonian to Early Carboniferous carbonate rocks in central Hunan, southern China have led to the recognition of 25 lithofacies which can be grouped into: (1) inner ramp peritidal platform, (2) inner ramp organic bank and mound, (3) mid ramp, (4) outer ramp, and (5) shelf basin facies associations. The peritidal platform facies association dominates the Zimenqiao Formation (Namurian A or late Datangian) and is characterized by gypsum and dolostone-containing sequences, indicating a peritidal platform environment. The other four facies associations dominate the Menggongao Formation (late Famennian), Liujiatang Formation (Tournaisian or Yangruanian), Shidengzi Formations (early Visean or early Datangian). Five upward-shallowing cycles were distinguished in these three Formations. The predominant facies associations developed in each Formation demonstrate an overall transgression–regression cycle in the Late Devonian to Early Carboniferous in central Hunan. The overall transgressive sequence was preserved in the Shaodong, Menggongao, and Liujiatang Formations, and the overall regressive sequence was preserved in the Liujiatang, Shidengzi, Ceshui and Zimenqiao Formations

Fabrication and Properties of (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni Cermets

Abstract(#br)Fine single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders were synthesized through the carbothermal reduction method. (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets were fabricated via vacuum sintering.Micrographs of powders and microstructures of the cermets were observed using transmission electron microscopy and scanning electron microscopy in combination with energy-dispersive spectroscopy. Phase compositions were investigated using x-ray diffraction. The C and N contents were measured using elemental analysis (CHNS/O). The optimized conditions for the synthesis process of single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders with high nitrogen content were 1500 °C for 2 h under a 2 kPa nitrogen atmosphere. Under such conditions, the particle size of the..

Microwave Deposition of Palladium Catalysts on Graphite Spheres and Reduced Graphene Oxide Sheets for Electrochemical Glucose Sensing

This work outlines a synthetic strategy inducing the microwave-assisted synthesis of palladium (Pd) nanocrystals on a graphite sphere (GS) and reduced graphene oxide (rGO) supports, forming the Pd catalysts for non-enzymatic glucose oxidation reaction (GOR). The pulse microwave approach takes a short period (i.e., 10 min) to fast synthesize Pd nanocrystals onto a carbon support at 150 °C. The selection of carbon support plays a crucial role in affecting Pd particle size and dispersion uniformity. The robust design of Pd-rGO catalyst electrode displays an enhanced electrocatalytic activity and sensitivity toward GOR. The enhanced performance is mainly attributed to the synergetic effect that combines small crystalline size and two-dimensional conductive support, imparting high accessibility to non-enzymatic GOR. The rGO sheets serve as a conductive scaffold, capable of fast conducting electron. The linear plot of current response versus glucose concentration exhibits good correlations within the range of 1–12 mM. The sensitivity of the Pd-rGO catalyst is significantly enhanced by 3.7 times, as compared to the Pd-GS catalyst. Accordingly, the Pd-rGO catalyst electrode can be considered as a potential candidate for non-enzymatic glucose biosensor

Thermal Transport on Graphene-Based Thin Films Prepared by Chemical Exfoliations from Carbon Nanotubes and Graphite Powders

Thermal conductivities (k) of different graphene nanosheet (GN)-based heat sinks are investigated within the temperature range of 323–423 K. One- and two-step modified Hummers’ methods are adopted to chemically exfoliate GNs from two kinds of carbon precursors: carbon nanotubes (CNTs) and graphite powders. The two-step method offers an improved exfoliation level of GN products, especially for the CNT precursor. Experimental results show that the GN-based heat sink—exfoliated from graphite powders after the two-step approach—delivers an enhanced k value to 2507 W/m K at 323 K, as compared to the others. The k value is found to be a decreasing function of the porosity of the heat sink, revealing the importance of solid/void fraction (i.e., volumetric heat capacity). The improved thermal efficiency mainly originates from the long phonon mean free path and the low void fraction of GN-based heat sinks, thus inducing highly efficient thermal transport in the GN framework

Fabrication of La₂O₃ Uniformly Doped Mo Nanopowders by Solution Combustion Synthesis Followed by Reduction under Hydrogen

This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40⁻70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20⁻40 nm in size) with different amounts of La2O3 were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La2O3 doped Mo nanopowders through hydrogen reduction. Thus, the content of La2O3 used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La2O3 into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO2 precursor by the La2O3 doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 °C. As shown by X-ray diffraction, the formation of Mo2C impurity, which usually occurs in the direct H2 reduction process, can be avoided by using the Ar calcination-H2 reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 °C

Characterization of hot-pressed short ZrO2 fiber toughened ZrB2-based ultra-high temperature ceramics

Two different ZrB2-based ultra-high temperature ceramics were produced by hot pressing: ZrB2 + 20 vol.% SiC particle + 15 vol.% ZrO2 fiber and ZrB2 + 20 vol.% SiC whisker + 15 vol.% ZrO2 fiber. The microstructures were analyzed by using transmission electron microscopy and high-resolution transmission electron microscopy. It was shown that a clean interface without any impurities was identified in ZrB 2-based hybrid ceramics with SiC whiskers and ZrO2 fibers, which would significantly improve the toughening mechanism. The results of high-resolution transmission electron microscopy showed that stacking faults in SiC whiskers resulted from an insertion of a (111) layer, which would be one of the main reasons for material anisotropy. However, the interface between the SiC particle and ZrO2 fiber was found to be ambiguous in ZrB 2-based hybrid ceramics with SiC particles and ZrO2 fibers due to the slight reaction. The orientation relationship between t-ZrO 2 and m-ZrO2 phases obeyed the classical correspondence: (100)m//{100}t and [001]m//?001 t, which further verified the feasibility of phase transformation toughening mechanism. ? 2014 Elsevier Inc

Influences of Ultrafine Ti(C, N) on the Sintering Process and Mechanical Properties of Micron Ti(C, N)-Based Cermets

For investigating the influence mechanism underlying ultrafine Ti(C, N) within micron Ti(C, N)-based cermets, three cermets including diverse ultrafine Ti(C, N) contents were employed. In addition, for the prepared cermets, their sintering process, microstructure, and mechanical properties were systematically studied. According to our findings, adding ultrafine Ti(C, N) primarily affects the densification and shrinkage behavior in the solid-state sintering stage. Additionally, material-phase and microstructure evolution were investigated under the solid-state stage from 800 to 1300 °C. Adding ultrafine Ti(C, N) enhanced the diffusion and dissolution behavior of the secondary carbide (Mo2C, WC, and (Ta, Nb)C) under a lower sintering temperature of 1200 °C. Further, as sintering temperature increased, adding ultrafine Ti(C, N) enhanced heavy element transformation behaviors in the binder phase and accelerated solid-solution (Ti, Me) (C, N) phase formation. When the addition of ultrafine Ti(C, N) reached 40 wt%, the binder phase had increased its liquefying speed. Moreover, the cermet containing 40 wt% ultrafine Ti(C, N) displayed superb mechanical performances

Microstructures and hardness prediction of an ultrafine-grained Al-2024 alloy

High-pressure torsion (HPT) is a high efficiency processing method for fabricating bulk ultrafine-grained metallic materials. This work investigates microstructures and evaluates the corresponding strengthening components in the center of HPT disks, where effective shear strains are very low. An Al-4.63Cu-1.51Mg (wt. %) alloy was processed by HPT for 5 rotations. Non-equilibrium grain and sub-grain boundaries were observed using scanning transmission electron microscopy in the center area of HPT disks. Solute co-cluster segregation at grain boundaries was found by energy dispersive spectrometry. Quantitative analysis of X-ray diffraction patterns showed that the average microstrain, crystalline size, and dislocation density were (1.32 ± 0.07) × 10−3, 61.9 ± 1.4 nm, and (2.58 ± 0.07) × 1014 m−2, respectively. The ultra-high average hardness increment was predicted on multiple mechanisms due to ultra-high dislocation densities, grain refinement, and co-cluster–defect complexes