Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

Schramm, Alina; Bock, Benjamin; Schmidt, Anne; Zienert, Tilo; Ditze, André; Scharf, Christiane; Aneziris, Christos G.

doi:10.1016/j.ceramint.2018.06.207

Cited by 8 publications

(12 citation statements)

References 27 publications

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“…Alumina and silica sol have been applied to fabricate protective coatings to enhance the anticorrosion or thermal stability properties of base materials. [ 23–28 ] For the ZnO microparticles used for Mg refinement, an alumina–silica coating can be prepared on the ZnO surface using the sol–gel method, which may improve the thermal stability and slow down the reduction reaction of ZnO in molten Mg. [ 29,30 ] Based on thermodynamics principles (Equation ), magnesia is one of the most stable oxides, and there is driving force for Mg to react with alumina or silica as follows [ 28,31–34 ]

Mg (l) + \frac{1}{3} {Al}_{2} {normalO}_{3} (s) \to MgO (s) + \frac{2}{3} Al (l) Δ G_{1000}^{θ} = - 39 kJ {mol}^{- 1}

Mg (l) + \frac{1}{2} {SiO}_{2} (s) \to MgO (s) + \frac{1}{2} Si (s) Δ G_{1000}^{θ} = - 128 kJ {mol}^{- 1}

MgO (s) + {SiO}_{2} (s) \to {MgSiO}_{3} (s) Δ G_{1000}^{θ} = - 34 kJ {mol}^{- 1}

…”

Section: Introductionmentioning

confidence: 99%

“…properties of base materials. [23][24][25][26][27][28] For the ZnO microparticles used for Mg refinement, an alumina-silica coating can be prepared on the ZnO surface using the sol-gel method, which may improve the thermal stability and slow down the reduction reaction of ZnO in molten Mg. [29,30] Based on thermodynamics principles (Equation 2-4), magnesia is one of the most stable oxides, and there is driving force for Mg to react with alumina or silica as follows [28,[31][32][33][34]…”

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The Refinement Effect of Alumina–Silica Sol‐Coated ZnO Particles for Cast Magnesium

Cao

Meng

2020

Adv Eng Mater

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Grain refinement is a practical method to improve the mechanical properties of magnesium alloys, and relevant research demonstrates that inoculation is an effective method of melt treatment to achieve grain refinement. [1-5] Thus, the development of efficient and reliable refiners for Mg alloys is technologically important and necessary. According to the crystallographic perspective-based edge-to-edge matching model, Zhang and co-workers predicted and explained a series of currently available grain refiners for Al and Mg alloys. [2,6,7] Combining the crystallographic database and edge-to-edge matching model calculation, a series of potential grain refiners for Mg alloys have been predicted, such as Al 2 Ca, AlN, Al 2 Y, CaO, AlMn, and ZnO, and experimental results match well with the theoretical predictions. [8-14] Based on edge-to-edge crystallographic matching calculation, ZnO is predicted to be one of the most effective candidates for Mg refinement, as it has an hexagonal close-packed (HCP) structure and belongs to the P63mc space group. The lattice parameters of ZnO are a ¼ 0.3265 nm and c ¼ 0.5219 nm, which are very close to those of the Mg matrix, i.e., a ¼ 0.320936 nm, and c ¼ 0.521123 nm. This prediction was based on the lattice parameters of ZnO and Mg at room temperature, which are expected to vary slightly at higher temperatures. However, some previous work showed that a small variation in lattice parameters between room temperature and solidification temperature does not affect the refining results. [15-17] Therefore, based on the success of previous applications of the edge-to-edge crystallographic matching model to the crystallographic understanding of grain refinement, these small misfits suggest that ZnO is likely to be an efficient grain refiner for Mg alloys. This prediction has been supported by preliminary results from other researchers. [18,19] However, according to thermodynamic data, ZnO particle reduction in molten Mg could occur as follows [7] MgðlÞ þ ZnOðsÞ ! MgOðsÞ þ ZnðlÞ ΔG θ 1000 ¼ À236.7 kJ mol À1 (1) ZnO would be reduced into Zn solute in contact with molten Mg, which would damage the crystallographic structure of the ZnO particles, affecting its use as a refiner for Mg. As the separation of inclusion and casting processes usually takes time, it is difficult to completely prevent the reduction between ZnO and Mg. At the same time, a reduction that generates Zn solute and native MgO could also lead to grain refinement for Mg alloys. [20] Although there is a reduction reaction between the added ZnO particles and molten Mg, the grain refinement achieved by ZnO particles is still better than that achieved with the equivalent addition of pure Zn. Saha and Ravindran and Ohtomo et al. suggested that ZnO acts as a heterogeneous nucleation before the ZnO particle is totally reduced to Zn solute by the molten Mg. [21,22] However, the refinement effect of ZnO on Mg may still be compromised because of the reduction reaction. Alumina and silica sol have been applied to fabricate protective coat...

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Mg (l) + \frac{1}{3} {Al}_{2} {normalO}_{3} (s) \to MgO (s) + \frac{2}{3} Al (l) Δ G_{1000}^{θ} = - 39 kJ {mol}^{- 1}

Mg (l) + \frac{1}{2} {SiO}_{2} (s) \to MgO (s) + \frac{1}{2} Si (s) Δ G_{1000}^{θ} = - 128 kJ {mol}^{- 1}

MgO (s) + {SiO}_{2} (s) \to {MgSiO}_{3} (s) Δ G_{1000}^{θ} = - 34 kJ {mol}^{- 1}

…”

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

The Refinement Effect of Alumina–Silica Sol‐Coated ZnO Particles for Cast Magnesium

Cao

Meng

2020

Adv Eng Mater

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“…In the last 5 years, the usage of carbon‐bonded ceramic foams instead of oxidic ones has been the topic of extensive research in the field of metal‐melt filtration . Although the filtration of steel melts using carbon‐bonded alumina filters has become state of the art, these filters also showed promising reactions during immersion tests in an AZ91 magnesium alloy melt, as well as in ongoing aluminum filtration experiments. Carbon‐bonded ceramic foams have the advantage of a lower manufacturing temperature, as well as a higher resistance toward thermal shock and creep deformation and a lower wettability, which is advantageous for their application in filtering metal melts .…”

Section: Introductionmentioning

confidence: 99%

Influence of the Manufacturing Technique on the Macro‐ and Microstructure of Reticulated Carbon‐Bonded Alumina Foams

et al. 2019

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Carbon‐bonded alumina foams, prepared by means of the replica technique, are typically used as metal melt filters for the filtration of steel due to their low wettability and their good resistance towards thermal shock and corrosion. According to literature, there are different process routes for the preparation of carbon‐bonded alumina foams, for example, dipping/rolling, spray‐ and dip/centrifugation coating. The influence of such process variations on macro‐ and microstructure and mechanical properties of carbon‐bonded ceramic foams has not been analyzed fully yet. Herein, carbon‐bonded alumina foams are manufactured by applying varying process routes regarding slurry preparation and coating steps. The macrostructure of the foams is analyzed by computer tomography, and for evaluating the microstructure, mercury intrusion porosimetry, optical microscopy, and scanning electron microscopy are applied. The determination of the cold‐crushing strength of the carbon‐bonded alumina foams allows the correlation of the structure and mechanical properties.

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“…[14] After carbon-bonded alumina filters showed promising results in the filtration of steel melts, [15] short-term immersion tests in AZ91 have been carried out to evaluate their applicability in a magnesium alloy melt. Interface reactions between the AZ91 melt and variously coated ceramic Al 2 O 3 -C filters have been investigated after immersion times of 10-120 s. [16] The investigated filter coatings consisted of Al 2 O 3 , MgO-C, MgAl 2 O 4 , or carbon nanotubes/ alumina nanosheets. The formation of MgO in situ layers was shown on filter surfaces containing Al 2 O 3 or MgAl 2 O 4 .…”

mentioning

confidence: 99%

“…The formation of MgO in situ layers was shown on filter surfaces containing Al 2 O 3 or MgAl 2 O 4 . [16] Therefore, the next step toward assessing the applicability of oxidic as well as carbon-bonded ceramic foam filters in the field of magnesium melt filtration is the evaluation of their long-term resistance toward the magnesium melt, with a special regard toward melt contamination and inclusion content.In this study, additional ceramic foam filter materials, namely ZrO 2 [13] and MgAlON, [17] were added to the selected materials…”

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confidence: 99%

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

et al. 2021

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Due to its low density, high specific strength, and resource availability, magnesium and its alloys, such as AZ91, have a high potential for various lightweight applications. [1][2][3] A major hindrance for its widespread processing and use is its high reactivity, contributing to high dross-and sludge formation in the melt, which results in the metal being prone to corrosion and containing high quantities of nonmetallic inclusions, if the handling of the melt has not been accurate. The inclusions can be divided into oxide films, lumps, and clusters, as well as intermetallic particles; gas-and shrinkage pores, may also be present. [1][2][3][4][5] While measures are taken to protect and cleanse magnesium melts on industrial scale, such as gas purging treatments by Ar, N 2 , or Cl 2 , the usage of a variety of possible cover gases or fluxes and the optimization of the casting system toward a high grade of enclosure, [1,6] the application of ceramic foam filters is seen as a promising method for cleansing the melt and improving the mechanical properties of the casting. [7][8][9] Ideally, an auxiliary addition of fluxes would be avoided, while delivering the same quality of melt cleanliness. [10][11][12] Wu et al. emphasized the effectiveness of ceramic foam filters made from MgO or Al 2 O 3 in AZ91, improving the elongation-to-failure of cast samples up to relative 58%. [13] In contrast to oxidic, sintered filters, carbon-bonded ceramic foam filters show higher resistance toward thermal shock and creep deformation, as well as lower energy consumption during their manufacture, due to their lower manufacturing temperature. [14] After carbon-bonded alumina filters showed promising results in the filtration of steel melts, [15] short-term immersion tests in AZ91 have been carried out to evaluate their applicability in a magnesium alloy melt. Interface reactions between the AZ91 melt and variously coated ceramic Al 2 O 3 -C filters have been investigated after immersion times of 10-120 s. [16] The investigated filter coatings consisted of Al 2 O 3 , MgO-C, MgAl 2 O 4 , or carbon nanotubes/ alumina nanosheets. The formation of MgO in situ layers was shown on filter surfaces containing Al 2 O 3 or MgAl 2 O 4 . [16] Therefore, the next step toward assessing the applicability of oxidic as well as carbon-bonded ceramic foam filters in the field of magnesium melt filtration is the evaluation of their long-term resistance toward the magnesium melt, with a special regard toward melt contamination and inclusion content.In this study, additional ceramic foam filter materials, namely ZrO 2 [13] and MgAlON, [17] were added to the selected materials

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Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

Cited by 8 publications

References 27 publications

The Refinement Effect of Alumina–Silica Sol‐Coated ZnO Particles for Cast Magnesium

The Refinement Effect of Alumina–Silica Sol‐Coated ZnO Particles for Cast Magnesium

Influence of the Manufacturing Technique on the Macro‐ and Microstructure of Reticulated Carbon‐Bonded Alumina Foams

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

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