Freeform fabrication of aluminum metal-matrix composites

This study continues the investigation into the ash cenosphere formation mechanism using a series of narrow size-fractioned ash cenosphere samples separated from the fly ash of an Australian coal-fired power station. The gas products locked inside various ash cenosphere size fractions are dominantly CO2 and some N2. With increasing ash cenosphere particle size from 63–75 μm to 150–250 μm, the average gas pressure decreases from 0.227 atm (at normal temperature and pressure, NTP) to 0.172 atm while the amount of CO2 and N2 locked in ash cenospheres increases significantly. The SiO2/Al2O3 ratio decreases with increasing ash cenosphere size, accompanied with an increase in the sum of TiO2 and Fe2O3 contents. Thermomechanical analysis further shows that ash cenospheres of different size fractions cannot achieve full melting at 1600 °C, suggesting that the formation of these ash cenospheres requires higher temperatures. Further analysis based on ash chemistry of individual cenospheres suggests that the optimum particle temperature for cenosphere formation is ∼1640–1850 °C. The growth of cenosphere precursors is governed by a wide range of viscosity of molten cenosphere precursors together with the force of surface tension, which is inversely proportional to the viscosity of molten droplets, producing ash cenospheres with various wall thicknesses. The data suggest that, apart from Fe2O3, TiO2 may play an important role in the formation of ash cenospheres.

Section: Introductionmentioning

confidence: 99%

Further Investigation into the Formation Mechanism of Ash Cenospheres from an Australian Coal-Fired Power Station

Gao

2013

“…Previous studies ,,,− showed that the shells of ash cenospheres may compose of mineral phases, including aluminosilicate glass, mullite, quartz, calcite, iron oxides, calcium silicates and sulfates. It is well-known that ash cenospheres have superior physical, chemical, mechanical, and thermal properties such that the materials are widely used for manufacturing various value-added products, such as lightweight construction products and lightweight composites. − …”

Section: Introductionmentioning

confidence: 99%

Ash Cenosphere from Solid Fuels Combustion. Part 1: An Investigation into Its Formation Mechanism Using Pyrite as a Model Fuel

2011

This paper reports a systematic investigation into the fundamental formation mechanism of ash cenosphere during solid fuels combustion using pyrite as a model fuel. The combustion of pulverized pyrite particles (38–45 μm) was carried out in a laboratory-scale drop-tube furnace at furnace temperatures of 530–1100 °C. The formation of ash cenosphere commences at 580 °C. At temperatures ≥600 °C, the ash products of pyrite combustion consist of dominantly large ash cenospheres (up to 130 μm in diameter) with thin shells (1–3 μm) and ash cenosphere fragments of various sizes. An increase in the temperature results in enhanced ash cenosphere fragmentation. The formation of molten Fe–S–O droplets during pyrite combustion is essential to ash cenosphere formation. The Fe–S–O melts inflate and expand into cenospheric forms (that may also burst into smaller fragments) via sulfur oxide gas generation inside the molten droplets as oxidation reactions progress. Further oxidation and resolidification transforms these cenospheric precursors into final ash cenospheres that also experience fragmentation and contain dominantly iron oxides.

“…11 They have also found extensive applications in manufacturing lightweight composites, including polyurethane composites, 12 polyester composites, 13 functionally gradient materials, 14 poly(vinyl chloride) composites, 15 PCV-U composite, 16 nylon composites, 17 syntactic polymer foam, [18][19][20][21] (7) Lilkov, V.; Djabarov, N.; Bechev, G.; Petrov, O. Cem. Concr metal-matrix composites, [22][23][24] glass fiber/epoxy resin composites, 25 and conducting polymers. [26][27][28] The properties and performance of the lightweight products utilizing ash cenospheres depend largely on ash cenosphere characteristics, particularly ash cenosphere physical structure such as diameter, particle size distribution, wall thickness, and shape.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Ash Cenospheres in Fly Ash from Australian Power Stations

Ngu¹,

Wu²,

Zhang³

2007

120

Ash cenospheres in fly ashes from five Australian power stations have been characterized. The experimental data show that ash cenosphere yield varies across the power stations. Ash partitioning occurred in the process of ash cenosphere formation during combustion. Contradictory to conclusions from the literature, iron does not seem to be essential to ash cenosphere formation in the cases examined in the present work. Further investigation was also undertaken on a series of size-fractioned ash cenosphere samples from Tarong power station. It is found that ∼70 wt% of ash cenospheres in the bulk sample have sizes between 45 and 150 µm. There are two different ash cenosphere structures, that is, single-ring structure and network structure. The percentage of ash cenospheres of a network structure increases with increasing ash cenosphere size. Small ash cenospheres (in the size fractions <150 µm) have a high SiO 2 /Al 2 O 3 ratio, and the majority of the ash cenospheres are spherical and of a single-ring structure. Large ash cenosphere particles (in the size fractions of 150-250 µm and >250 µm) have a low SiO 2 /Al 2 O 3 ratio, and a high proportion of the ash cenospheres are nonspherical and of a network structure. A novel quantitative technique has been developed to measure the diameter and wall thickness of ash cenospheres on a particle-to-particle basis. A monolayer of size-fractioned ash cenospheres was dispersed on a pellet, which was then polished carefully before being examined using a scanning electron microscope and image analysis. The ash cenosphere wall thickness broadly increases with increasing ash cenosphere size. The ratios between wall thickness and diameter of ash cenospheres are limited between an upper bound of ∼10.5% and a lower bound of ∼2.5%, irrespective of the ash cenosphere size.