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2 pages, 185 KiB

Open AccessEditorial

Editorial for Special Issue “Clay Minerals and Waste Fly Ash Ceramics”

by Marta Valášková

Minerals 2022, 12(1), 73; https://doi.org/10.3390/min12010073 - 07 Jan 2022

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Abstract

This Special Issue published a collection of eight scientific contributions [...] Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

Research

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14 pages, 6420 KiB

Open AccessArticle

Effects of Kaolin Additives in Fly Ash on Sintering and Properties of Mullite Ceramics

by Marta Valášková, Veronika Blahůšková and Jozef Vlček

Minerals 2021, 11(8), 887; https://doi.org/10.3390/min11080887 - 17 Aug 2021

Cited by 12 | Viewed by 2459

Abstract

The effective utilization of fly ash (FA) as a raw material for ceramics production is performed on the FA-kaolin mixtures containing kaolins 10% by mass. The mixtures in comparison with FA and three raw kaolins were annealed to mullite ceramics at temperatures of [...] Read more.

The effective utilization of fly ash (FA) as a raw material for ceramics production is performed on the FA-kaolin mixtures containing kaolins 10% by mass. The mixtures in comparison with FA and three raw kaolins were annealed to mullite ceramics at temperatures of 1000, 1100, 1200 and 1300 °C. The main aims were to contribute to the discussion on the effect of impurity of Na,K-feldspars in kaolins and Fe₂O₃ in FA on sintering procedure, porous ceramics properties and mullite structural properties. The phases were characterized using X-ray diffraction and thermogravimetry DTA/TGA methods. Mercury intrusion porosimetry was used for characterization of porosity of ceramic samples. Results evidenced the influence of feldspars in kaolins and Fe₂O₃ in FA on the sintering temperatures and properties of mullite ceramics. The fully FA-based ceramic sintered at 1100 °C exhibited post-sintering properties of bulk density 2.1 g/cm³; compressive strength 77.5 MPa; and porosity, 2% in comparison with the FA/kaolin-based ceramics properties of bulk density 2.2 g/cm³; compressive strength, 60–65 MPa; and porosity from 9.3 to 16.4% influenced by Na,K-feldspars. The best structural and mechanical characteristics were found for the FAK3 sample, supported by the high content of kaolinite and orthoclase in the kaolin K3 additive. The FAK3 annealed at 1100 °C exhibited good compressive strength of 87.6 MPa at a porosity of 10.6% and density of 2.24 g/cm³ and annealed at 1300 °C the compressive strength of 41.3 MPa at a porosity of 19.2% and density of 1.93 g/cm³. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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16 pages, 1922 KiB

Open AccessArticle

Alkali-Activated Metakaolin and Fly Ash as Unfired Ceramic Bonding Systems

by Jozef Vlček, Michaela Topinková, Miroslava Klárová, Petra Maierová, Hana Ovčačíková, Vlastimil Matějka, Alexandr Martaus and Veronika Blahůšková

Minerals 2021, 11(2), 197; https://doi.org/10.3390/min11020197 - 13 Feb 2021

Cited by 4 | Viewed by 2251

Abstract

Metakaolin (MK) prepared by the calcination of kaolin at 550 °C and fly ash (FA) from the combustion of black coal in a granulating boiler were used to prepare unfired ceramic bonding systems via the alkali activation process. A long-term stability of the [...] Read more.

Metakaolin (MK) prepared by the calcination of kaolin at 550 °C and fly ash (FA) from the combustion of black coal in a granulating boiler were used to prepare unfired ceramic bonding systems via the alkali activation process. A long-term stability of the mechanical properties of the prepared samples similar to the unfired ceramic systems was observed. The optimal metakaolin and fly ash ratio, the type of the activator (NaOH or water glass) and its concentration were evaluated after the hydration in: a) laboratory conditions; b) hydration box; and c) under the hydrothermal activation. Raw materials and the samples prepared by alkali activation process were characterized by XRD, XRF, TG/DTA, and FTIR methods. The mechanical properties of the prepared samples were tested using a compressive strength test after 2, 28 and 56 days of hydration. The compressive strengths of 16 and 24 MPa after 28 days of hydration were reached for FA samples activated with water glass. The alkali activation of MK was successful in the NaOH solution of the molar concentration above 5 M. The compressive strength values of metakaolin, activated hydrothermally and hydrated at laboratory conditions, reached 11.2 and 5.5 MPa, respectively, for 5 M activator of NaOH. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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14 pages, 2685 KiB

Open AccessArticle

Effect of Talc in Mixtures with Fly Ash on Sintering Crystalline Phases and Porosity of Mullite-Cordierite Ceramics

by Marta Valášková, Veronika Blahůšková, Alexandr Martaus, Soňa Študentová, Silvie Vallová and Jonáš Tokarský

Minerals 2021, 11(2), 154; https://doi.org/10.3390/min11020154 - 01 Feb 2021

Cited by 8 | Viewed by 2556

Abstract

The effect of talc in the two mixtures with the representative sample of fly ash (Class F) was investigated at sintering temperatures of 1000, 1100, and 1200 °C. X-ray diffraction, thermal DTA/TGA, and mercury intrusion porosimetry analyses were applied to characterize the mineral [...] Read more.

The effect of talc in the two mixtures with the representative sample of fly ash (Class F) was investigated at sintering temperatures of 1000, 1100, and 1200 °C. X-ray diffraction, thermal DTA/TGA, and mercury intrusion porosimetry analyses were applied to characterize the mineral phase transformation of talc and fly ash in cordierite ceramic. The influence of iron oxide on talc transformation to Fe-enstatite was verified by the simulated molecular models and calculated XRD patterns and the assumption of Fe-cordierite crystallization was confirmed. The fly ash mixtures with 10 mass% of talc in comparison with 30 mass% of talc at 1000 °C and 1100 °C showed higher linear shrinkage and lower porosity. At a temperature of 1200 °C, sintering expansion and larger pores in mullite and cordierite ceramics also containing sapphirine and osumilite demonstrated that magnesium in FA and Tc structure did not react with the other constituents to form crystalline cordierite. The ceramics produced in the present work using fly ash and talc have similar properties to the commercial ceramics produced at sintering temperatures higher than 1250 °C. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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13 pages, 1874 KiB

Open AccessArticle

Quantitative Evaluation of Crystalline and Amorphous Phases in Clay-Based Cordierite Ceramic

by Zdeněk Klika, Marta Valášková, Lucie Bartoňová and Petra Maierová

Minerals 2020, 10(12), 1122; https://doi.org/10.3390/min10121122 - 14 Dec 2020

Cited by 8 | Viewed by 2647

Abstract

An innovative chemical quantitative mineral analysis (CQMA) was successfully tested on a cordierite-based clay ceramic sample to quantify crystalline and amorphous components. The accuracy of this method was demonstrated on an added module to the CQMA program that used oxide formulas of amorphous [...] Read more.

An innovative chemical quantitative mineral analysis (CQMA) was successfully tested on a cordierite-based clay ceramic sample to quantify crystalline and amorphous components. The accuracy of this method was demonstrated on an added module to the CQMA program that used oxide formulas of amorphous phases obtained by energy dispersive X-ray spectroscopy (EDS) microprobe chemical analysis. This CQMA method was tested for three variants calculated using chemical analysis, i.e., X-ray diffraction (XRD) identification of crystalline (cordierite and enstatite) and amorphous phases by scanning electron microscopy (SEM)/EDS texture and microanalyses. The test results from CQMA suggest their application possibilities as well as the limits of their utilization. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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14 pages, 3211 KiB

Open AccessArticle

The Impact of Coal Fly Ash Purification on Its Antibacterial Activity

by Seham Alterary and Narguess H. Marei

Minerals 2020, 10(11), 1002; https://doi.org/10.3390/min10111002 - 11 Nov 2020

Cited by 12 | Viewed by 2761

Abstract

Fly ash (FA) is produced from coal power plants’ combustion. FA is used in the concrete industry, as an ingredient in the brick and paving. Knowledge of the chemical composition and toxic metal content in FA is essential for evaluating its environmental risks. [...] Read more.

Fly ash (FA) is produced from coal power plants’ combustion. FA is used in the concrete industry, as an ingredient in the brick and paving. Knowledge of the chemical composition and toxic metal content in FA is essential for evaluating its environmental risks. This study aimed to assess FA purification effect on its antibacterial activity against Escherichia coli and Bacillus cereus, by calculating percent bacterial reduction. Moreover, centrifugation time effect on the purification process was evaluated. Chemical composition and properties of purified FA were determined and compared with raw FA, using Fourier transform Infrared (FTIR); X-ray diffraction (XRD); X-ray photoelectron spectroscopy (XPS); energy-dispersive X-ray (EDXA); carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis; moisture content; and loss-of-ignition. Particle size was predicted by using dynamic laser scattering, BET and scanning electron microscopy (SEM). The CHNS results showed that purified FA contains the highest carbon content (88.9%), as compared to raw FA (82.1%). The particle size distribution (PSD) of FA microspheres ranges from 48.53 ± 17.9 to 52.98 ± 19.4 µm by using SEM. PSD, using dynamic laser scattering, showed polydispersed and non-uniform size in raw FA, ranging in size from 107.1 to 1027 nm, while purified FA manifests a monodispersed size from 103.3 to 127.3 nm. FA showed the least bacterial growth reduction %, while the purified fly ash (FA2) showed the highest bacterial growth reduction %, as compared to the control bacterial broth culture without fly ash. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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14 pages, 6203 KiB

Open AccessFeature PaperArticle

Up-Cycling of Iron-Rich Inorganic Waste in Functional Glass-Ceramics

by Acacio Rincón Romero, Daniele Desideri, Aldo R. Boccaccini and Enrico Bernardo

Minerals 2020, 10(11), 959; https://doi.org/10.3390/min10110959 - 27 Oct 2020

Cited by 3 | Viewed by 2207

Abstract

The intensive mechanical stirring of suspensions of recycled glass and inorganic waste powders in ‘weakly alkaline’ aqueous solutions (e.g., 2.5–3 NaOH), followed by viscous flow sintering at 800–1000 °C, easily yields highly porous glass-ceramic foams. The firing determines just the consolidation of powders [...] Read more.

The intensive mechanical stirring of suspensions of recycled glass and inorganic waste powders in ‘weakly alkaline’ aqueous solutions (e.g., 2.5–3 NaOH), followed by viscous flow sintering at 800–1000 °C, easily yields highly porous glass-ceramic foams. The firing determines just the consolidation of powders with concurrent incorporation of pollutants from iron-rich waste, such as fly ash from coal combustion (FA). Engineered mixtures allow for the obtainment of chemically stable foams from treatments in air. Treatments in nitrogen are even more significant since they extend the conditions for stabilization and promote novel functionalities. In addition, the change in the atmosphere favors the formation of magnetite (Fe₃O₄), in turn enabling ultra-high dielectric permittivity and semiconductivity. Such a condition was further evidenced by preliminary tests on recycled glass combined with residues from the Bayer processing of aluminum ores or red mud (RM). Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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12 pages, 6025 KiB

Open AccessArticle

The Influence of Fly Ash on Mechanical Properties of Clay-Based Ceramics

by Tomáš Húlan, Igor Štubňa, Ján Ondruška and Anton Trník

Minerals 2020, 10(10), 930; https://doi.org/10.3390/min10100930 - 21 Oct 2020

Cited by 11 | Viewed by 2373

Abstract

Elastic properties of mixtures of illitic clay, thermal power plant fly ash (fluidized fly ash—FFA and pulverized fly ash—PFA), and grog were investigated during the heating and cooling stages of the firing. The grog part in the mixtures was replaced with 10, 20, [...] Read more.

Elastic properties of mixtures of illitic clay, thermal power plant fly ash (fluidized fly ash—FFA and pulverized fly ash—PFA), and grog were investigated during the heating and cooling stages of the firing. The grog part in the mixtures was replaced with 10, 20, 30, and 40 mass% of the fly ash, respectively. The temperature dependence of Young’s modulus was derived using the dynamical thermomechanical analysis, in which dimensions and mass determined from thermogravimeric and thermodilatometric results were used. Flexural strength was measured at the room temperature using the three-point bending test. The following results were obtained: (1) Bulk density showed a decreasing trend up to 900 °C and a steep increase above 900 °C. During cooling, the bulk density slightly increased down to the room temperature. (2) Young’s modulus increased significantly during heating up to ~300 °C. Dehydroxylation was almost not reflected in Young’s modulus. At temperatures higher than 800 °C, Young’s modulus began to increase due to sintering. (3) During cooling, down to the glass transformation, Young’s modulus slightly increased and then began to slightly decrease due to microcracking between phases with different thermal expansion coefficients. (4) Around the β→α quartz transition, radial stresses on the quartz grain altered from compressive to tensile, creating microcracks. Below 560 °C, the radial stress remained tensile, and consequently, the microcracking around the quartz grains and a decreasing Young’s modulus continued. (5) With a lower amount of PFA and FFA, a higher Young’s modulus was reached after sintering. The final values of Young’s modulus, measured after firing, show a decreasing trend and depend linearly on the part of fly ash. (6) The flexural strength measured after firing decreased linearly with the amount of the fly ash for both mixtures. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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14 pages, 2680 KiB

Open AccessArticle

Phase Transformations in Fly Ash-Based Solids

by Ivana Perná, Tomáš Hanzlíček, Monika Šupová and Martina Novotná

Minerals 2020, 10(9), 804; https://doi.org/10.3390/min10090804 - 11 Sep 2020

Cited by 1 | Viewed by 2097

Abstract

The presented article describes the phase transformations in solid bodies based on fluid fly ash (FFA) over eight years from the initial to the final phases. FFA has been selected as a type of industrial waste whose amount has been growing in recent [...] Read more.

The presented article describes the phase transformations in solid bodies based on fluid fly ash (FFA) over eight years from the initial to the final phases. FFA has been selected as a type of industrial waste whose amount has been growing in recent years. This type of ash has self-hardening properties when watered because of the conditions of its origin. The specific temperature of fluid burning and the addition of calcium carbonate into the burning zone create a mixture of phases which are, even when solidified, ready to form new crystal phases, especially alumina-silicates, relicts of coal clay minerals. For experiments, bricks from the mixture of FFA and quartz sand were industrially produced and left outside. Subsequent mineralogical analyses of samples of various ages confirmed differences in phase compositions. It is supposed that the main role in the presented changes is played by the content of the roentgen-amorphous part of alumina-silicates because they are likely to be transformed into a stable form of feldspar. In addition to that, this article presents the hypothesis of a moving agent, which could explain the transformations in the final bodies. Full article

(This article belongs to the Special Issue Clay Minerals and Waste Fly Ash Ceramics)

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