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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 14896

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Prof. Dr. Qinfu Liu

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School of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
Interests: graphite and graphene; mineralogy and mineral materials; clay mineralogy and application
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Dr. Kuo Li

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School of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
Interests: coaly graphite; mineralogy; organic-inorganic interaction
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Dr. Shuai Zhang

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School of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
Interests: graphite; clay mineralogy; molecular dynamics simulations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Graphite generally occurs in three forms: microcrystalline, crystalline lump or vein, and crystalline flake. The microcrystalline graphite is formed through contact metamorphism of coal by large scale igneous intrusion. Flake graphite is assumed to form from ancient organic matters during long period of high-grade regional metamorphism. Vein graphite is assumed to be crystallized from thermal fluid. Graphite is a layered mineral with strong sp² hybridization carbons within each graphene layer, and these graphene layers are bonded by the weak van der Waals interaction forces. The structural features endow graphite great physical and chemical properties, such as lubricity, conductivity, anti-corrosion, high melting point in non-oxidizing conditions, etc. The traditional applications of graphite are in the refractories industry, friction materials, lubricants, etc. Graphite consumption has increased with the rapid development of electric cars and energy storage power stations in recent years, because large amounts of graphite were used as anodes of lithium–ion batteries. With the depletion of high-quality graphite resource, demand for synthetic graphite derived from petroleum or coal-based byproducts under high temperature increases dramatically. People also try to synthesize graphite directly from coal to reduce dependence on petroleum and lower the cost. Meanwhile, the graphene first obtained by simply peeling off graphite with tape was found to be a fantastic two-dimensional material; its exceptionally high tensile strength, electrical conductivity, transparency, and being the thinnest 2D material in the world will significantly impact the future semiconductor, electronics, electric batteries, sensors, and composites industry. Considering the applications in future cutting edge techniques of graphite, many countries view natural graphite as a strategic non-metallic mineral material.

This Special Issue “graphite minerals and graphene” welcomes original research articles and reviews on the following:

(1) ore occurrences of graphite minerals, and their exploration, exploitation, and separation and purification;

(2) structural evolution during graphitization, and the structural properties, surface activity, and modification of different type graphite;

(3) synthesized graphite under high temperature, the graphene preparation, and applications of graphite and graphene are also welcomed.

This Special Issue aims to contribute our knowledge on graphite minerals and its value-added utilizations.

Prof. Dr. Qinfu Liu
Dr. Kuo Li
Dr. Shuai Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

graphite ores
graphite crystal growth
graphitic carbon
graphite structural properties
graphene preparation
applications of graphite and graphene

Related Special Issue

Graphite Minerals and Graphene, 2nd Edition in Minerals

Published Papers (9 papers)

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Research

13 pages, 4723 KiB

Open AccessArticle

Constraints on Crystallinity of Graphite Inclusions in Nephrite Jade from Xinjiang, Northwest China: Implications for Nephrite Jade Formation Temperatures

by Jifei Zheng, Lei Chen, Cun Zhang, Yue Liu, Ruicong Tian, Jinlin Wu, Yu Wu and Shouting Zhang

Minerals 2023, 13(11), 1403; https://0-doi-org.brum.beds.ac.uk/10.3390/min13111403 - 01 Nov 2023

Cited by 1 | Viewed by 1125

Abstract

Graphite usually occurs in mineral/rock associations in the form of solid inclusions and plays an important role in tracing regional metamorphic degree, ore-forming temperature, fluid evolution, as well as the deep carbon cycle of the Earth. In this study, we investigate the placer black nephrite jade where the co-occurrence of abundant graphite inclusions and jade remains extraordinary. By employing petrographic, mineral-chemical, and Raman spectroscopic methods, we characterize the textures and crystallinity of graphite inclusions that exist in nephrite jade. EPMA and petrological data indicate that the main constituents of black jade are tremolite and graphite, with minor phases of diopside, calcite, dolomite, epidote, and apatite. Micro-Raman spectroscopic thermometry of carbonaceous material shows that most of the formation temperatures of graphite inclusions are between 378 and 556 °C, and only a few temperatures may be above 650 °C, indicating that graphite inclusions were formed at medium- to high-temperature metamorphic facies. The petrologic and spectral investigations of graphite inclusions in these nephrite jade samples show major metamorphic signatures with mixed features associated with fluid precipitation. Our results allow us to propose that primary nephrite jade was formed under multi-stage tectonic evolution conditions, and regional temperatures were predominately driven by the late continent–continent collision, while the ore-controlling temperatures of nephrite jade formation were found in a medium- to high-temperature environment. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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20 pages, 6285 KiB

Open AccessArticle

Effects of Minerals Type and Content on the Synthetic Graphitization of Coal: Insights from the Mixture of Minerals and Anthracite with Varied Rank

by Peng Luo, Yuegang Tang, Ruiqing Li and Minmin Ju

Minerals 2023, 13(8), 1024; https://0-doi-org.brum.beds.ac.uk/10.3390/min13081024 - 31 Jul 2023

Viewed by 884

Abstract

The challenge of how to effectively treat minerals in coal before synthetic graphitization is a practical problem. It is unrealistic to remove minerals completely via physical or chemical methods. So, it is essential to clarify the role of minerals in the synthetic graphitization of coal. Based on the complex mineral composition, the mixture samples consisting of coal and mineral are used to obtain the effect of minerals type and content on the synthetic graphitization of coal. The role of minerals in synthetic graphitization is closely associated with the mineral content and type, as well as the rank. As to the lower-rank anthracite, quartz, kaolinite, and calcite have the role of inhibitor for the yields and defect degrees of corresponding samples after synthetic graphitization derived from the mixtures, but the role of catalyzer for their crystal structure (the degree of graphitization, stacking height, lateral size). The increasing content of quartz, kaolinite, and calcite is harmful for the yield, but useful for the crystal structure and defect degrees; the increasing content of pyrite is harmful for the yield, degree of graphitization, and stacking height, and it is useful for defect degrees. As to the higher-rank anthracite, quartz, kaolinite, and calcite have the role of inhibitor for the yield of corresponding samples after synthetic graphitization, catalyzer for their crystal sizes (stacking height, lateral size), and inertia for their degrees of graphitization. The increasing content of quartz, kaolinite, calcite, and pyrite is harmful for the yield and crystal size. A lower coal rank indicates being more prone to positive mineral effects on synthetic graphitization. The role of minerals in the synthetic graphitization of coal is complex and also represents a coupling relationship with the thermal transformation of anthracite. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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16 pages, 7664 KiB

Open AccessArticle

Experimental Verification for the Graphitization of Inertinite

by Zhifei Liu, Daiyong Cao, Gaojian Chen, Zhongwei Bi and Qingtong Chen

Minerals 2023, 13(7), 888; https://0-doi-org.brum.beds.ac.uk/10.3390/min13070888 - 29 Jun 2023

Cited by 4 | Viewed by 898

Abstract

In order to explore the graphitization of inertinite, this paper conducted high-temperature thermal simulation experiments (HTT) and high-temperature high-pressure simulation experiments (HTHP) on isolated samples enriched in inertinite. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used to analyze the graphitization process of inertinite. ① Results of HTT: the graphitization of inertinite has a “threshold condition” with the temperature threshold ranging between 2100 °C and 2400 °C. Below this threshold, the d₀₀₂ value of the samples remains above 0.342 nm. ② Results of HTHP: (i) External forces have a significant positive effect on the graphitization of inertinite. Compared to the HTT, the addition of external forces significantly reduces the temperature required for inertinite graphitization. (ii) Proper combinations of temperature and pressure conditions are crucial for efficiently promoting the graphitization of inertinite. Changes in pressure, either increasing or decreasing from the optimal pressure, have a suppressive effect on the graphitization of inertinite. ③ The mechanism of external forces on the graphitization of inertinite was analyzed. Shear stress promotes the rotation and orientation of aromatic layers, while static hydrostatic pressure contributes to the contraction and reduction of interlayer spacing in carbon layers. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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19 pages, 4267 KiB

Open AccessArticle

Preparation and Characterization of Asphalt Pitch-Derived Activated Carbons with Enhanced Electrochemical Performance as EDLC Electrode Materials

by Ju-Hwan Kim, Young-Jun Kim, Seok-Chang Kang, Hye-Min Lee and Byung-Joo Kim

Minerals 2023, 13(6), 802; https://0-doi-org.brum.beds.ac.uk/10.3390/min13060802 - 12 Jun 2023

Cited by 2 | Viewed by 1385

Abstract

This study used a physical activation method to prepare asphalt-pitch-derived activated carbon (Pitch AC) for an electric double-layer capacitor (EDLC) electrode. X-ray diffraction analysis and Raman spectroscopy were used to estimate the change in the crystal structure of Pitch AC with activation time. In addition, the textural properties of Pitch AC were studied by Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR) and non-localized density functional theory (NLDFT) equations with N₂/77K isotherm adsorption-desorption curves. The electrochemical performance of the Pitch AC was analyzed using a coin-type EDLC with 1 M SBPBF₄/PC via galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area and total pore volume were 990–2040 m²/g and 0.42–1.51 cm³/g, respectively. The pore characteristics of the Pitch AC varied according to the activation time and changed from a microporous structure to a micro-mesoporous structure as the activation time increased. The electrochemical performance analysis also found that the specific capacity was increased from 43.6 F/g to 84.5 F/g at 0.1 A/g as activation time increased. In particular, Pitch AC-9 exhibited the best electrochemical performance (rectangular CV curve, reversible GCD, lowest ion charge transfer resistance and Warburg impedance). In addition, Pitch AC-9 was confirmed to have a specific capacitance similar to commercial activated carbon for EDLC (YP-50F). Therefore, it was considered that Pitch AC could replace commercial activated carbon for EDLC because it has excellent pore characteristics and electrochemical performance despite being manufactured through a very low-cost precursor and a simple process (physical activation method). Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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18 pages, 9235 KiB

Open AccessArticle

Investigation on the Mineral Catalytic Graphitization of Anthracite during Series High Temperature Treatment

by Haiyue Cao, Kuo Li, Hao Zhang and Qinfu Liu

Minerals 2023, 13(6), 749; https://0-doi-org.brum.beds.ac.uk/10.3390/min13060749 - 31 May 2023

Cited by 3 | Viewed by 1374

Abstract

Graphite can be artificially converted from anthracites under high temperatures; however, the exact mechanism through which inorganic minerals contribute to the graphitization process is still unknown. In light of this, several selected minerals in different amounts were added to demineralized anthracite coal. The anthracite–mineral mixtures were subjected to artificial graphitization experiments under temperatures ranging from 1700 to 2900 °C in the laboratory. The obtained series of coal-based graphites with various levels of graphitization were characterized by X-ray diffraction (XRD), and the derived structural parameters, such as d₀₀₂ and FWHM (002), La, and Lc were used to compare the carbon structural evolution during the high temperature treatment and mineral catalytic graphitization. Moreover, the amorphous carbon of anthracite is eventually transformed into the highly ordered crystalline carbon of coal-based graphite. The five added minerals show interesting structural variation during the graphitization process, in which pyrite is decomposed into iron (Fe), illite, quartz, and kaolinite, which can react with disordered carbon in organic matter to form moissanite (SiC), while dolomite seems to react with sulfur to form oldhamite (CaS). At temperatures less than 2300 °C, the minerals could significantly enhance the catalytic effect. There is a clear difference in the catalytic effect of different minerals on graphitization. Kaolinite exhibits the strongest catalytic effect. The minerals dolomite, illite, and quartz only show a certain degree of catalysis. Pyrite, however, only has a limited effect on improving the degree of graphitization at a temperature of 1700 °C. However, once the temperature exceeds 2300 °C, the dominant factor controlling the graphitization of anthracite appears to be the temperature. According to the growth pattern at microcrystalline sizes (La and Lc), the minerals’ catalytic effects can be classified into three groups. The first group includes minerals that preferentially promote La growth, such as pyrite, illite, and quartz. The second group includes minerals that preferentially promote Lc growth, such as dolomite. Finally, kaolinite is in a separate group that promotes microcrystal growth in both the lateral and vertical directions simultaneously. The mechanisms of the minerals’ catalytic graphitization are discussed in this paper. The promotion role of minerals in the artificial graphitization process may help to optimize the graphitization process and reduce the process cost in the future. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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20 pages, 15743 KiB

Open AccessArticle

Computed Tomography of Flake Graphite Ore: Data Acquisition and Image Processing

by Leonard T. Krebbers, Bernd G. Lottermoser and Xinmeng Liu

Minerals 2023, 13(2), 247; https://0-doi-org.brum.beds.ac.uk/10.3390/min13020247 - 09 Feb 2023

Cited by 3 | Viewed by 2512

Abstract

A solid knowledge of the mineralogical properties (e.g., flake size, flake size distribution, purity, shape) of graphite ores is necessary because different graphite classes have different product uses. To date, these properties are commonly examined using well-established optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and SEM-based automated image analysis. However, these 2D methods may be subject to sampling errors and stereological effects that can adversely affect the quality of the analysis. X-ray microcomputed tomography (CT) is a nondestructive imaging technique allowing for examination of the interior and exterior of solid materials such as rocks and ores in 3D. This study aimed to explore whether CT can provide additional mineralogical information for the characterisation of graphite ores. CT was used in combination with traditional techniques (XRD, SEM-EDS, OM) to examine a flake graphite ore in 3D. A scanning protocol for the examined graphite ore was established to acquire high-quality CT data. Quantitative mineralogical information on key properties of graphite was obtained by developing a deep learning-based image processing strategy. The results demonstrate that CT allows for the 3D visualisation of graphite ores and provides valid and reliable quantitative information on the quality-determining properties that currently cannot be obtained by other analytical tools. CT allows improved assessment of graphite deposits and their beneficiation. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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15 pages, 4548 KiB

Open AccessArticle

The Effect of Silicon-Containing Minerals on Coal Evolution at High-Temperature Pre-Graphitization Stage

by Yan Shao, Shaoqing Wang and Xueqi Li

Minerals 2023, 13(1), 20; https://0-doi-org.brum.beds.ac.uk/10.3390/min13010020 - 23 Dec 2022

Cited by 4 | Viewed by 1403

Abstract

Coal is a carrier of carbon enrichment, so it has the potential for the preparation of coal-based carbon materials. In this paper, LT anthracite and TSG bituminous coal were selected, and the corresponding graphitized samples were prepared from high-temperature treatment. The effects of silicon-containing minerals on coal evolution during the high-temperature pre-graphitization stage were investigated by XRD, Raman spectroscopy, and SEM. The results showed that with increasing temperature, the silicon-containing samples showed smaller d₀₀₂ and ID₁/IG, and higher L_c, while L_a presented a slight increase. It was found by SEM that the micromorphology of all samples was mainly massive structures. Meanwhile, irregular polyhedral structures also were observed in silicon-containing samples at 1300 °C, which were related to the formation and deposition of SiC. The carbothermal reactions of silicon-containing minerals continued to generate SiC and precipitate with increasing temperature, resulting in the gradual transformation of the needle-like structures into polyhedral structures. However, SiC was completely decomposed at 2800 °C. These changes indicated that during the pre-graphitization stage, silicon-containing minerals form SiC to advance the reduction of the interlayer spacing and the increase of longitudinal layer stacking height, thereby enhancing structural ordering and graphitization degree, while it had less effect on the lateral size. This will help to further understand the role of silicon-containing minerals in the coal pre-graphitization stage and also provide useful information about synthetic coal-based graphite. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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19 pages, 9133 KiB

Open AccessArticle

A High-Temperature Thermal Simulation Experiment for Coal Graphitization with the Addition of SiO₂

by Gaojian Chen, Daiyong Cao, Anmin Wang, Yingchun Wei, Zhifei Liu and Meng Zhao

Minerals 2022, 12(10), 1239; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101239 - 28 Sep 2022

Cited by 4 | Viewed by 1573

Abstract

The effect of SiO₂ on coal graphitization was investigated by adding SiO₂ as an additive to vitrinite in coal from the Gemudi mining area in Guizhou province (SW China) via a high-temperature heating treatment. The graphitization products of the samples were analyzed by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM), and the influence of the SiO₂ additive on the process of coal graphitization was investigated. The results showed that, with the temperature increases, the graphitization degree of all samples was promoted, and the orderliness of the microcrystalline structure in the vitrinite increased. Compared with the samples without additives, the graphitization degree, graphite lamellae ductility, and stacking degree of the samples with SiO₂ additives were higher, and the carbon layer spacing reached 0.3379 nm at 3000 °C, entering the graphite stage. The Raman spectra showed that the peak intensities of the defect structures (D1 and D2) in the samples with SiO₂ were lower than those of the samples without additives, exhibiting fewer in-plane and interlayer defects in the samples with SiO₂. The microstructures of the experimental samples were observed by HRTEM; at the same temperature, the carbon layer stacking degree of the samples with the SiO₂ additives was higher than that of the samples without SiO₂, and large graphite lamellae with smoother and clearer edges were observed. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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15 pages, 3780 KiB

Open AccessArticle

Microstructural Characteristics of Graphite Microcrystals in Graphitized Coal: Insights from Petrology, Mineralogy and Spectroscopy

by Jiuqing Li, Yong Qin, Yilin Chen and Jian Shen

Minerals 2022, 12(10), 1189; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101189 - 22 Sep 2022

Cited by 6 | Viewed by 1604

Abstract

Graphite microcrystals are the product of coal graphitization and widely exist in the graphitized coal of Yongan Coalfield, Fujian Province, China, which is direct mineralogical evidence for the transformation of coal to graphite. Optical microscopy, scanning electron microscopy (SEM) and micro-Raman spectroscopy were used to detect the morphology and microstructure of the in situ graphite microcrystals. The results show that the volume proportion of graphite microcrystals in graphitized coal samples is between 2.39% and 7.32%, and the optical anisotropy of graphite microcrystals is stronger than that of coal macerals. Graphite microcrystals show the occurrence of attached microcrack inner walls or infilling the cell cavity, with several forms of flakes, needles or aggregates. Under optical microscopy of polarized light and with a retarder plate of 1λ, graphite microcrystals show the color of primary yellow and secondary blue, and the two kinds of colors appear alternately when the microscope is rotating. Additionally, flake-like graphite microcrystals with an isochromatic zone diameter of 10−50 μm are the most widely distributed in graphitized coal. Under SEM, graphite microcrystals show a rough and irregular edge and are characterized by flow or bubble film structures along with several pores, which is the product of cooling crystallization after the softening and melting of carbon-containing substances. Moreover, flake-like graphite microcrystals developed interlayer pores with a clear outline of loose stacking and were almost entirely composed of pure carbon; a small amount of oxygen is related to oxygen-containing functional groups or structural defects. The micro-Raman spectra of graphite microcrystals in the first-order region are characterized by low-intensity D1 and D2 bands and a high-intensity G band, and the parameters R1 and R2 vary from 0.21–0.39 and 0.60–0.74, respectively. The second-order micro-Raman spectra of graphite microcrystals are characterized by a higher intensity of the 2D1 band and a lower intensity of the other three bands. The parameter R3, derived from the area ratio of the 2D1 band to all the bands in the second-order region, was proposed. The value of R3 ranges between 0.78 and 0.86, and both of them indicate a higher percentage of graphene plane with a highly internal crystallographic structure. Similar to the parameters R1 and R2 in the first-order micro-Raman spectrum, the parameter R3 is an effective parameter to characterize the ordering degree of the microstructure, which may be used to evaluate the graphitization degree of graphitization coal. Full article

(This article belongs to the Special Issue Graphite Minerals and Graphene)

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