Wetting of Pure Aluminium on Filter Materials Graphite, AlF 3 and Al 2 O 3 (original) (raw)
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Wetting of pure aluminium on graphite, SiC and Al2O3 in aluminium filtration
Transactions of Nonferrous Metals Society of China, 2012
The wettability of pure aluminium on filter materials and on inclusions is believed to be an important factor affecting the filtration of aluminium. The contact angles of molten aluminium on alumina, SiC and graphite were measured under 10 −8 bar high vacuum in the temperature range of 1000−1300 °C. To describe the wetting behaviour of the Al on ceramic at lower temperatures used in filtration and casting aluminium, a semi-empirical calculation was employed. The calculated contact angles at 700 °C were around 97° for alumina, 92° for vitreous graphite, 126° for single-and poly-crystal graphite, and 79° for single crystal SiC, respectively. This indicates that aluminium does not wet alumina or graphite (or Al 4 C 3 ) around the casting temperature, but wets SiC at this temperature. Thus a priming height is required for aluminium to infiltrate an alumina filter. Increasing temperature can also improve the wettability of Al on ceramic.
Aluminum Melt Filtration with Carbon Bonded Alumina Filters
Materials
The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 °C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 °C and 30 min). The conventional test yielded contact angles of around 92°, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157°. Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thi...
Wettability of Aluminum on Alumina
Metallurgical and Materials Transactions B, 2011
The wettability of molten aluminum on solid alumina substrate has been investigated by the sessile drop technique in a 10 À8 bar vacuum or under argon atmosphere in the temperature range from 1273 K to 1673 K (1000°C to 1400°C). It is shown that the reduction of oxide skin on molten aluminum is slow under normal pressures even with ultralow oxygen potential, but it is enhanced in high vacuum. To describe the wetting behavior of the Al-Al 2 O 3 system at lower temperatures, a semiempirical calculation was employed. The calculated contact angle at 973 K (700°C) is approximately 97 deg, which indicates that aluminum does not wet alumina at aluminum casting temperatures. Thus, a priming height is required for aluminum to infiltrate a filter. Wetting in the Al-Al 2 O 3 system increases with temperature.
Influence of Grain Refiners on the Wettability of Al2O3 Substrate by Aluminum Melt
Metallurgical and Materials Transactions B
It is well known that grain refiner additions in aluminum melts significantly reduce the filtration efficiency of ceramic foam filters (CFF). However, the mechanism remains unclear. In this work, the influence of grain refiners on the wettability of alumina substrate by aluminum melt was studied by both conventional sessile drop and improved sessile drop methods at different temperatures and vacuums. Commercial purity aluminum (CP-Al) and grain refiner master alloys Al-3Ti-1B, Al-5Ti-1B, Al-3Ti-0.15C were used. It is found that master alloy melts wet alumina substrate better than CP-Al. Generally, a lower temperature or lower vacuum results in a higher contact angle. The roles of grain refiner particles in improving the wettability were studied by analyzing the solidification structure of post wetting-test droplets using SEM. Strong sedimentation of grain refiner particles at the metal-substrate interface was observed, which is attributed to the higher density of grain refiner parti...
Wetting ofAl2O3by Molten Aluminum: The Influence ofBaSO4Additions
Journal of Nanomaterials, 2008
The effects ofBaSO4additions on the wetting of alumina by molten aluminum were studied by the sessile drop technique. To study the effect ofBaSO4decomposition(1100–1150∘C), the additions were treated at two temperatures700∘C(973 K) and1450∘C(1723 K), respectively.BaSO4additions at low and high temperatures did not improve the nonwetting character of these compositions. However, at higher firing temperature, the formation ofBA6 (BaO•6Al2O3)has a nonwetting trend with increasing its content. To address theBA6specifically a pureBaO•6Al2O3was produced and tested. It was more nonwetting than the pure alumina. After the analysis of the contact angles for theBaSO4and theBA6 (BaO•6Al2O3), it was concluded that these additions to alumina do not inhibit wetting by molten aluminum. In fact, at the addition levels common for refractories, the wetting tendency of molten aluminum is enhanced. Alternative explanations for the effectiveness ofBaSO4additions to alumina refractories are discussed.
Acta Materialia, 2011
Filters coated with AlF 3 can be used to filter molten aluminum to simultaneously remove nonmetallic inclusions and dissolved alkali and alkaline earth metal impurities. Coating experiments were carried out in which anhydrous HF gas was generated from reactions involving NaF or CaF 2 and concentrated H 2 SO 4 , and used in a reaction with Al 2 O 3 ceramic foam filter to produce a layer of AlF 3 coating on the surface of the Al 2 O 3 filter. Samples from these experiments were studied by X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Preliminary results of the coating experiments showed that it is possible to coat Al 2 O 3 filters with AlF 3 by this method. Increasing the pressure of HF gas increased the yield of AlF 3 in the filter. Theoretical evaluation of the removal efficiency of dissolve impurity elements showed that dissolved calcium can be removed up to 99.8% within 30 s of contact time between the filter material and the molten aluminum.
Aluminium Filtration by Bonded Particle Filters
Light Metals 2019, 2019
Non-metallic inclusions such as oxides, borides and carbides in aluminium melts are a major cause of product failure during both processing and use. To remove these inclusions, molten aluminium is usually filtered through a mechanical filter such as deep bed-filter, ceramic foam filter or Bonded Particle Filter (BPF). In this study three BPF from Pyrotek have been tested at Hydro’s reference centre in Sunndalsora. The filters had different grit sizes; 6, 10, and 14 (equivalent to 30, 50, and 70 ppi). The filters were mounted in the patent pending Drain Free filter box developed by Hycast. LiMCA was used at the up-stream side of the two coarsest filter (Grit 6 and 10) and both up-stream and down-stream for the finest filter (Grit 14). Three samples from each of the filters have been studied in a light microscope, and inclusions have been counted using image analysis. In addition, PoDFA samples from the test with the finest filter were also analysed and discussed.
Production of Foundry Filters Using Al2O3 from the Al-Anodizing Process
Advances in Science and Technology, 2010
The manufacturing and materials transformation industries generate residues, which do not always have an adequate ecological destination. In many cases, however, these secondary products can be directly re-used as raw materials in other industrial processes. In this context, this article presents the characterization of the sludge generated in the aluminum anodizing process and emphasizes the application potential of this residue as a raw material for the production of industrial ceramic filters. Results show that the high alumina contents (89-96 wt%) and composition constancy, as well as the low particle size (~1 m) after calcination and milling, render this residue a suitable raw material to produce alumina filters with optimized properties for casting engineering metal components with better performance.
Role of Ash Impurities in the Depletion of Carbon from Alumina-Graphite Mixtures in to Liquid Iron
ISIJ International, 2007
Due to their excellent thermal shock and slag resistance at high temperatures, alumina-graphite refractories are used extensively in the steel industry. The degradation of carbon based refractories through carbon depletion is an important issue and a fundamental understanding of refractory behaviour at high temperatures is crucially important. Natural flake graphite, with ash impurity levels ranging from 1 to 10%, is used extensively in the commercial preparation of alumina-carbon refractories. This study investigates the role played by ash impurities in the depletion of carbon from the refractory composite. Two natural graphites, respectively containing 2.1 % and 5.26 % ash, were used in this study. Substrates were prepared from mixtures of alumina and carbon over a wide concentration-range. Using a sessile drop arrangement, carbon pickup by liquid iron from alumina-natural graphite mixtures was measured at 1 550°C and was compared with the carbon pickup from alumina-synthetic graphite mixtures. These studies were supplemented with microscopic investigations on the interfacial region. Very high and similar levels of carbon dissolution were however observed from both alumina-natural graphite mixtures, with carbon pickup by liquid iron from mixtures with up to 30 wt% alumina reaching saturation. A sharp reduction to near zero levels was observed in the 30 to 40 wt% alumina range. Along with implications for commercial refractory applications, these results are discussed in terms of poor wettability between alumina and liquid iron, interactions between ash impurities and alumina, and formation of complexes in the interfacial region.
Metals, 2020
Smelter grade alumina (SGA) plays multiple roles in the Hall–Héroult process for primary aluminum production. Given its very porous nature, one major role of SGA is to adsorb toxic hydrogen fluoride (HF) in the dry scrubber. However, also because of its porous nature, SGA inevitably adsorbs ambient moisture. This paper discusses the influence of alumina properties, including pore size distribution and specific surface area, on the physical adsorption of water vapor on SGA, as well as the adsorption kinetics. The result shows that the adsorption enthalpy of moisture on SGA is in the range of 4–13 kJ/mol. The adsorption capacity increases significantly with the particle specific surface area and total pore volume. A higher adsorption temperature indicates a much faster adsorption rate but corresponds to a lower equilibrium adsorption capacity.