Experimental investigation and evaluation of influence of oxygen concentration on characteristic parameters of coal spontaneous combustion

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Magnetic and Electrical Properties of high-entropy rare-earth manganites

ABSTRACT The methane contained in a coal seam is closely related to the oxidative properties of the coal and serves as an important basis for accurately evaluating the coal spontaneous combustion (CSC) behavior. In this paper, programmed temperature rise experiments were conducted on three coal samples with different methane contents. The sensitivity of oxidation products, olefin products, and their production rates to methane content were investigated. Also, the contribution made by methane content to the characteristic temperature point and CSC limit parameters were qualitatively assessed. When the methane content is 2.7 cm3/g, 4.5 cm3/g, and 6.8 cm3/g, the critical temperatures (CT) are 70°C, 80°C, and 100°C, respectively, and the dry cracking temperatures (DCT) are 100°C, 110°C, and 130°C, respectively. The higher the methane content, the greater the CT and DCT points during coal oxidation, which is because high concentration of methane will inhibit coal oxygen chemical reaction. The methane content is positively correlated with the minimum floating coal thickness (h min) and the lower limit oxygen concentration (C min), while the upper limit air leakage intensity (Q max) decreases with the increasing methane content. Coal samples with high methane content can withstand higher safe float thicknesses and oxygen concentrations and require less air leakage to carry away the heat accumulated by the residual coal in the mining area, making the CSC risk lower.

Experimental investigation of methane content on the oxidation characteristics and spontaneous combustion limit parameters of coal

High-entropy materials defy historical materials design paradigms by leveraging chemical disorder to kinetically stabilize novel crystalline solid solutions comprised of many endmembers. Formulational diversity results in local crystal structures that are seldom found in conventional materials that can strongly influence macroscopic physical properties. Thermodynamically prescribed chemical flexibility provides a means to tune such properties. Additionally, kinetic metastability results in many possible atomic arrangements, including both solid-solution configurations and heterogeneous phase assemblies, depending on synthesis conditions. Local disorder induced by metastability, and extensive cation solubilities allowed by thermodynamics combine to give many high-entropy oxide systems utility as electrochemical, magnetic, thermal, dielectric, and optical materials. Though high-entropy materials research is maturing rapidly, much remains to be understood and many compositions still await discovery, exploration, and implementation. This article is protected by copyright. All rights reserved 

High‐entropy oxides: Harnessing crystalline disorder for emergent functionality

ABSTRACT The fundamental reason for coal’s spontaneous combustion is that the amount of generated heat by oxidation exceeds that of heat dissipated. Therefore, the generated heat by oxidation and the amount of consumed oxygen are major indexes to evaluate coal’s spontaneous combustion propensity (CSCP). In this study, a method to simultaneously measure the consumed oxygen and generated heat was established by using constant temperature difference guiding method. On this basis, the relationship between the oxygen consumption and heat generation during low-temperature oxidation of four types of coal from six mines was studied. It was found that this method can quickly and efficiently obtain oxygen consumption and heat generation of coal during the low-temperature oxidation. The results reveal that the oxygen consumption of all the test samples are positively and linearly correlated with their heat generation. On this basis, with the aid of the oxygen consumption (to replace the heat generation), a theoretical basis for judging CSCP was obtained, which supports the identification of CSCP based on oxygen consumption.

Study on Coal’s Spontaneous Combustion Propensity based on the Correlation between Oxygen Consumption and Heat Generation

Technologically relevant strongly correlated phenomena such as colossal magnetoresistance (CMR) and metal‐insulator transitions (MIT) exhibited by perovskite manganites are driven and enhanced by the coexistence of multiple competing magneto‐electronic phases. Such magneto‐electronic inhomogeneity is governed by the intrinsic lattice‐charge‐spin‐orbital correlations, which, in turn, are conventionally tailored in manganites via chemical substitution, charge doping, or strain engineering. Alternately, the recently discovered high entropy oxides (HEOs), owing to the presence of multiple‐principal cations on a given sub‐lattice, exhibit indications of an inherent magneto‐electronic phase separation encapsulated in a single crystallographic phase. Here, the high entropy (HE) concept is combined with standard property control by hole doping in a series of single‐phase orthorhombic HE‐manganites (HE‐Mn), (Gd0.25La0.25Nd0.25Sm0.25)1‐xSrxMnO3 (x = 0–0.5). High‐resolution transmission microscopy reveals hitherto‐unknown lattice imperfections in HEOs: twins, stacking faults, and missing planes. Magnetometry and electrical measurements infer three distinct ground states—insulating antiferromagnetic, unpercolated metallic ferromagnetic, and long‐range metallic ferromagnetic—coexisting or/and competing as a result of hole doping and multi‐cation complexity. Consequently, CMR ≈1550% stemming from an MIT is observed in polycrystalline pellets, matching the best‐known values for bulk conventional manganites. Hence, this initial case study highlights the potential for a synergetic development of strongly correlated oxides offered by the high entropy design approach.

Z. Zhao

Papers

Study on Coal’s Spontaneous Combustion Propensity based on the Correlation between Oxygen Consumption and Heat Generation

High Entropy Approach to Engineer Strongly Correlated Functionalities in Manganites