scholarly journals High-Temperature Mineral Phases Generated in Natural Clinkers by Spontaneous Combustion of Coal

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 213 ◽  
Author(s):  
Elisa Laita ◽  
Blanca Bauluz ◽  
Alfonso Yuste
Keyword(s):  
High Temperature ◽  
Spontaneous Combustion ◽  
Vitreous Phase ◽  
X Ray Diffraction ◽  
Ceramic Tiles ◽  
Mineral Phases ◽  
Fe Content ◽  
Spontaneous Combustion Of Coal ◽  
Compositional Variations ◽  
Refractory Ceramics

The aim of this study is to analyze natural clinkers (= calcined clays by coal combustion) from a lower Cretaceous coal outcrop in Ariño (Teruel, NE Spain) in order to describe mineral and textural transformations produced during the spontaneous combustion of coal. To achieve this aim, samples were analyzed using X-ray diffraction and optical and electron microscopy. Spontaneous combustion resulted in the melting of the surrounding clays, with the generation of an Al–Si-rich vitreous phase. Subsequently, high-temperature phases crystallized from this vitreous phase. These new minerals are interesting due to their similarity with those formed during ceramic processes, used in the manufacture of stoneware and ceramic tiles, as well as in refractory ceramics, and with natural events such as metamorphic and igneous processes. The studied natural clinkers are composed of vitreous phase mullite, hematite, hercynite, cristobalite, quartz, pyroxenes, cordierite, gypsum, pyrite, and calcium oxides. A trend from hematite to hercynite composition indicates compositional variations at sample scale, which evidence d-spacing differences in hercynite and may be related to the Al and Fe content in hercynite depending on its texture. The mullite shows higher Si/Al ratio (1.21) than the theoretical composition (0.35), indicating that this mullite is more Si-rich. Three pyroxene-type compositions (diopside-type, ferrosilite-type, and a Ca–Al-rich pyroxene) were found. Both the mullite and the pyroxenes are nonstoichiometric.

scholarly journals The Influence of the Sample Preparation on the Result of Coal Propensity to Spontaneous Combustion in the High-temperature Adiabatic Method

2021 ◽  
Vol 1 (2) ◽  
Author(s):  
Dariusz OBRACAJ ◽  
Marek KORZEC ◽  
Tien Tung VU
Keyword(s):  
High Temperature ◽  
Coal Seam ◽  
Spontaneous Combustion ◽  
Spontaneous Heating ◽  
Mine Fire ◽  
Mine Fires ◽  
Technical Factors ◽  
Spontaneous Combustion Of Coal ◽  
Seam Mining ◽  
Very High

The liability of coal to spontaneous combustion is the principal cause of mine fires. Spontaneouscombustion is one of the main threats in Polish and Vietnamese coal mines. The article presents an analysisof the spontaneous combustion of coal in mines of both countries. It is related to the natural prone of coalto spontaneous heating and consequently to its self-ignition. Despite the relevant recognition of themethods of preventing this threat, in mines, spontaneous combustion occurs during the exploitation ofcoal seams with low and very high self-ignition tendency. Apart from the technical factors related to thedesign of coal seam mining, the properties of coal have a significant impact on the occurrence ofspontaneous combustion. Their correct recognition is essential to the precautions against spontaneouscombustion for minimalizing the risk of a mine fire. Therefore, it is necessary to study the factorsinfluencing the propensity of coal to spontaneous heating. A review of the methods used to determine thepropensity of coal to spontaneous combustion is presented in the article. Based on the high-temperaturemethod of determining the propensity of coals to spontaneous combustion, the influence of selectedfactors related to samples' preparation for testing on the determination result was investigated. Theinfluence of the fractional decomposition and the moisture content in the prepared samples on thedetermination result was demonstrated. The presented research results may improve research proceduresfor determining the propensity of coal to spontaneous combustion.

scholarly journals Crystal Chemistry and High-Temperature Behaviour of Ammonium Phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the Burned Dumps of the Chelyabinsk Coal Basin

Minerals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 486 ◽  
Author(s):  
Andrey A. Zolotarev ◽  
Elena S. Zhitova ◽  
Maria G. Krzhizhanovskaya ◽  
Mikhail A. Rassomakhin ◽  
Vladimir V. Shilovskikh ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Coal Basin ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Mineral Phases

The technogenic mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the burned dumps of the Chelyabinsk coal basin have been investigated by single-crystal X-ray diffraction, scanning electron microscopy and high-temperature powder X-ray diffraction. The NH4MgCl3·6H2O phase is monoclinic, space group C2/c, unit cell parameters a = 9.3091(9), b = 9.5353(7), c = 13.2941(12) Å, β = 90.089(8)° and V = 1180.05(18) Å3. The crystal structure of NH4MgCl3·6H2O was refined to R1 = 0.078 (wR2 = 0.185) on the basis of 1678 unique reflections. The (NH4)2Fe3+Cl5·H2O phase is orthorhombic, space group Pnma, unit cell parameters a = 13.725(2), b = 9.9365(16), c = 7.0370(11) Å and V = 959.7(3) Å3. The crystal structure of (NH4)2Fe3+Cl5·H2O was refined to R1 = 0.023 (wR2 = 0.066) on the basis of 2256 unique reflections. NH4MgCl3·6H2O is stable up to 90 °C and then transforms to the less hydrated phase isotypic to β-Rb(MnCl3)(H2O)2 (i.e., NH4MgCl3·2H2O), the latter phase being stable up to 150 °C. (NH4)2Fe3+Cl5·H2O is stable up to 120 °C and then transforms to an X-ray amorphous phase. Hydrogen bonds provide an important linkage between the main structural units and play the key role in determining structural stability and physical properties of the studied phases. The mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O are isostructural with natural minerals novograblenovite and kremersite, respectively.

scholarly journals Chemical and mineralogical characterization of portuguese ceramic tiles in the historic center of São Luís do Maranhão (Brazil): an approximation of the mineralogy and firing temperature of the raw materials

2013 ◽  
Vol 66 (1) ◽  
pp. 91-98 ◽  
Author(s):  
José Manuel Rivas Mercury ◽  
Domingos de Jesus Costa Pereira ◽  
Nazaré do Socorro Lemos Silva Vasconcelos ◽  
Aluísio Alves Cabral Jr. ◽  
Romulo Simões Angélica
Keyword(s):  
Firing Temperature ◽  
Raw Materials ◽  
X Ray Diffraction ◽  
Ceramic Tiles ◽  
Mineralogical Characterization ◽  
Calcium Carbonates ◽  
Historic Center ◽  
Mineral Phases ◽  
Materials Used

This work involved the first-ever characterization of antique Portuguese ceramic wall tiles in the Historic Center of São Luis do Maranhão, Brazil. The tiles were characterized by optical microscopy, X-ray diffraction (XRD) and chemical analysis to identify the possible raw materials used in the fabrication process, as well as the firing temperature of these materials. The results indicate that the microstructure of these materials consists of pores of varying sizes with calcite incrustations and quartz grain sizes smaller than 500 µm distributed in a pinkish yellow matrix, which were identified by XRD as calcite, gehlenite, wollastonite, quartz, and amorphous mineral phases. Based on this information, it can be inferred that the original raw materials probably consisted of a mixture of kaolinitic clays (Al2O3·2SiO2·2H2O) rich in calcium carbonates and quartz, or mixtures of kaolinitic clays, quartz and calcite, which did not reach the pre-firing temperature of 950ºC.

Chemical-Mineralogical and Microscopic Characterization of Clay Used as Raw Materials in Santa Gertrudes' Ceramic Pole

2016 ◽  
Vol 869 ◽  
pp. 191-194
Author(s):  
Carolina del Roveri ◽  
R.A. Cunha ◽  
Antenor Zanardo ◽  
Letícia Hirata Godoy ◽  
Maria Margarita Torres Moreno ◽  
...  
Keyword(s):  
Raw Materials ◽  
Microscopic Analysis ◽  
Major Elements ◽  
X Ray Diffraction ◽  
Ceramic Tiles ◽  
X Ray ◽  
Mineral Phases ◽  
Icp Ms ◽  
Materials Used

The Santa Gertrudes ́ Ceramic Polo is the Brazilian region with national and international prominence in the manufacturing of ceramic tiles. Some raw materials used by ceramic industry and coatings industries in this region were characterized in terms of chemical-mineralogical and microscopic view, in order to promote the best technological characterization of them. For this, chemical analysis of major elements and trace X-ray diffraction and microscopic analysis by SEM, TEM and Electron microprobe were performed by ICP-MS. The results showed that the raw materials commonly referred to as "clays" are actually constituted by various mineral phases, which directly influence the properties of the same ceramics. Also showed that, by virtue of this constitution, different formulations can be developed, using the best raw materials found in the region of Santa Gertrudes, SP.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

Microdomains in BaFeO3-y (0.35 < y < 0.50)

1990 ◽  
Vol 48 (4) ◽  
pp. 780-781
Author(s):  
M. Vallet-Regí ◽  
M. Parras ◽  
J.M. González-Calbet ◽  
J.C. Grenier
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Monoclinic Phase ◽  
Orthorhombic Phase ◽  
Total Iron ◽  
Zone Axis ◽  
Electron Micrograph ◽  
X Ray Diffraction ◽  
X Ray ◽  
Compositional Variations

BaFeO3-y compositions (0.35<y<0.50) have been investigated by means of electron diffraction and microscopy to resolve contradictory results from powder X-ray diffraction data.The samples were obtained by annealing BaFeO2.56 for 48 h. in the temperature range from 980°C to 1050°C . Total iron and barium in the samples were determined using chemical analysis and gravimetric methods, respectively.In the BaFeO3-y system, according to the electron diffraction and microscopy results, the nonstoichiometry is accommodated in different ways as a function of the composition (y):In the domain between BaFeO2.5+δBaFeO2.54, compositional variations are accommodated through the formation of microdomains. Fig. la shows the ED pattern of the BaFeO2.52 material along thezone axis. The corresponding electron micrograph is seen in Fig. 1b. Several domains corresponding to the monoclinic BaFeO2.50 phase, intergrow with domains of the orthorhombic phase. According to that, the ED pattern of Fig. 1a, can be interpreted as formed by the superposition of three types of diffraction maxima : Very strong spots corresponding to a cubic perovskite, a set of maxima due to the superposition of three domains of the monoclinic phase along [100]m and a series of maxima corresponding to three domains corresponding to the orthorhombic phase along the [100]o.

High temperature X-ray diffraction investigation of an aluminium-silicon-corundum system

2007 ◽  
Vol 2007 (suppl_26) ◽  
pp. 369-374 ◽  
Author(s):  
D. Garipoli ◽  
P. Bergese ◽  
E. Bontempi ◽  
M. Minicucci ◽  
A. Di Cicco ◽  
...  
Keyword(s):  
High Temperature ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals High-pressure synthesis and crystal structure of the mixed-cation borate Ga4In4B15O33(OH)3

2019 ◽  
Vol 74 (4) ◽  
pp. 357-363
Author(s):  
Daniela Vitzthum ◽  
Hubert Huppertz
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
High Temperature ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Synthesis And Crystal Structure ◽  
X Ray ◽  
Mixed Cation ◽  
High Pressure High Temperature ◽  
Pressure Synthesis

AbstractThe mixed cation triel borate Ga4In4B15O33(OH)3 was synthesized in a Walker-type multianvil apparatus at high-pressure/high-temperature conditions of 12.5 GPa and 1300°C. Although the product could not be reproduced in further experiments, its crystal structure could be reliably determined via single-crystal X-ray diffraction data. Ga4In4B15O33(OH)3 crystallizes in the tetragonal space group I41/a (origin choice 2) with the lattice parameters a = 11.382(2), c = 15.244(2) Å, and V = 1974.9(4) Å3. The structure of the quaternary triel borate consists of a complex network of BO4 tetrahedra, edge-sharing InO6 octahedra in dinuclear units, and very dense edge-sharing GaO6 octahedra in tetranuclear units.

The Application of X-Ray Diffraction at Elevated Temperatures to Study the Mechanism of Formation of Sodium Tripolyphosphate

1961 ◽  
Vol 5 ◽  
pp. 276-284
Author(s):  
E. L. Moore ◽  
J. S. Metcalf
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Amorphous Phase ◽  
Elevated Temperatures ◽  
Sodium Tripolyphosphate ◽  
X Ray Diffraction ◽  
Mechanism Of Formation ◽  
X Ray ◽  
Temperature Form ◽  
High Temperature Form

AbstractHigh-temperature X-ray diffraction techniques were employed to study the condensation reactions which occur when sodium orthophosphates are heated to 380°C. Crystalline Na4P2O7 and an amorphous phase were formed first from an equimolar mixture of Na2HPO4·NaH2PO4 and Na2HPO4 at temperatures above 150°C. Further heating resulted in the formation of Na5P3O10-I (high-temperature form) at the expense of the crystalline Na4P4O7 and amorphous phase. Crystalline Na5P3O10-II (low-temperature form) appears after Na5P3O10-I.Conditions which affect the yield of crystalline Na4P2O7 and amorphous phase as intermediates and their effect on the yield of Na5P3O10 are also presented.

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

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