Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite
Fly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al<sub>2</sub>O<sub&...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-01-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/11/1/84 |
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| author | Pramod Koshy Naomi Ho Vicki Zhong Luisa Schreck Sandor Alex Koszo Erik J. Severin Charles Christopher Sorrell |
| author_facet | Pramod Koshy Naomi Ho Vicki Zhong Luisa Schreck Sandor Alex Koszo Erik J. Severin Charles Christopher Sorrell |
| author_sort | Pramod Koshy |
| collection | DOAJ |
| description | Fly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al<sub>2</sub>O<sub>3</sub>·2SiO<sub>2</sub>) is the only stable phase in the Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> system and is used in numerous applications owing to its high-temperature chemical and mechanical stabilities. Hence, fly ash offers a potential economical resource for mullite fabrication, which is confirmed by a review of the current literature. This review details the methodologies to utilise fly ash with different additives to fabricate what are described as porous interconnected mullite skeletons or dense mullite bodies of approximately stoichiometric compositions. However, studies of pure fly ash examined only high-Al<sub>2</sub>O<sub>3</sub> forms and none of these works reported long-term, high-temperature, firing shrinkage data for these mullite bodies. In the present work, high-SiO<sub>2</sub> fly ashes were used to fabricate percolated mullite, which is demonstrated by the absence of firing shrinkage upon long-term high-temperature soaking. The major glass component of the fly ash provides viscosities suitably high for shape retention but low enough for ionic diffusion and the minor mullite component provides the nucleating agent to grow mullite needles into a direct-bonded, single-crystal, continuous, needle network that prevents high-temperature deformation and isolates the residual glass in the triple points. These attributes confer outstanding long-term dimensional stability at temperatures exceeding 1500 °C, which is unprecedented for mullite-based compositions. |
| first_indexed | 2024-03-09T04:34:14Z |
| format | Article |
| id | doaj.art-bb4e45aaa7cc419aacf544348cadb950 |
| institution | Directory Open Access Journal |
| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-09T04:34:14Z |
| publishDate | 2021-01-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Minerals |
| spelling | doaj.art-bb4e45aaa7cc419aacf544348cadb9502023-12-03T13:31:13ZengMDPI AGMinerals2075-163X2021-01-011118410.3390/min11010084Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated MullitePramod Koshy0Naomi Ho1Vicki Zhong2Luisa Schreck3Sandor Alex Koszo4Erik J. Severin5Charles Christopher Sorrell6School of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, AustraliaSchool of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, AustraliaSchool of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, AustraliaSchool of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, AustraliaVecor Technologies Pty. Ltd., Sydney, NSW 2039, AustraliaVecor Technologies Pty. Ltd., Sydney, NSW 2039, AustraliaSchool of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, AustraliaFly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al<sub>2</sub>O<sub>3</sub>·2SiO<sub>2</sub>) is the only stable phase in the Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> system and is used in numerous applications owing to its high-temperature chemical and mechanical stabilities. Hence, fly ash offers a potential economical resource for mullite fabrication, which is confirmed by a review of the current literature. This review details the methodologies to utilise fly ash with different additives to fabricate what are described as porous interconnected mullite skeletons or dense mullite bodies of approximately stoichiometric compositions. However, studies of pure fly ash examined only high-Al<sub>2</sub>O<sub>3</sub> forms and none of these works reported long-term, high-temperature, firing shrinkage data for these mullite bodies. In the present work, high-SiO<sub>2</sub> fly ashes were used to fabricate percolated mullite, which is demonstrated by the absence of firing shrinkage upon long-term high-temperature soaking. The major glass component of the fly ash provides viscosities suitably high for shape retention but low enough for ionic diffusion and the minor mullite component provides the nucleating agent to grow mullite needles into a direct-bonded, single-crystal, continuous, needle network that prevents high-temperature deformation and isolates the residual glass in the triple points. These attributes confer outstanding long-term dimensional stability at temperatures exceeding 1500 °C, which is unprecedented for mullite-based compositions.https://www.mdpi.com/2075-163X/11/1/84fly ashmullitehigh temperaturepercolationlong-term heating |
| spellingShingle | Pramod Koshy Naomi Ho Vicki Zhong Luisa Schreck Sandor Alex Koszo Erik J. Severin Charles Christopher Sorrell Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite Minerals fly ash mullite high temperature percolation long-term heating |
| title | Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite |
| title_full | Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite |
| title_fullStr | Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite |
| title_full_unstemmed | Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite |
| title_short | Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite |
| title_sort | fly ash utilisation in mullite fabrication development of novel percolated mullite |
| topic | fly ash mullite high temperature percolation long-term heating |
| url | https://www.mdpi.com/2075-163X/11/1/84 |
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