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The present work reports the SEM, EPMA and TEM examination of reactions at the interface of Al7075 alloy and a 50/50 wt% mixture of BaAl2Si2O8 + CaAl2Si2O8feldspars at 850 °C, 1150 °C and 1250 °C. Sintering of the feldspar mixture at 1450 °C caused dissolution of ~1.0 wt% Ca in BaAl2Si2O8and 0.5 wt% Ba in CaAl2Si2O8. The interaction of the Al alloy with the sintered feldspars shifted the alloy composition to the Al–Si–αBaAl2Si2and Al–Si–βaAl2Si2compatibility triangles. The feldspars underwent a series of phase transformations, leading ultimately to the formation of Al2O3. [ABSTRACT FROM AUTHOR]

A corrosion cup test was undertaken using BaAl2Si2O8 and Al4.1Zn3.2Mg alloy, heated in air for 150 h at 850°C. Electron probe microanalysis, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive spectroscopy were used to identify the mineralogical and microstructural changes at the interfaces. The microstructural results revealed three microstructural areas: (1) Spinel layer with large numbers of Al alloy channels; (2) interfacial area with mainly alumina, spinel, and BaAl2Si2O8; and (3) interdiffusion zone chemically close to barium hexaaluminate. The principal observations are: BaAl2Si2O8 was highly resistant to molten Al alloy corrosion owing to sluggish kinetics, as evidenced by the observation of unreacted BaAl2Si2O8 grains in the interfacial area., The nature of the microstructure, particularly an interdiffusion zone instead of a continuous layer of precipitated alumina at the interface between the Al alloy channels and the unreacted BaAl2Si2O8 supports the conclusion that the corrosion mechanism is governed by interdiffusion (Si/Ba and Al/Mg) and substitution., The formation and limited retention of an MgO layer at the metal-ceramic interface played a critical role in alloy oxidation and the consequent interfacial phenomena. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the effects of AlPO4 addition on the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test (850°C and 1160°C for 150h and 72h, respectively) were conducted to determine the extent of penetration. The addition of AlPO4 was shown to improve the corrosion resistance of the castables in contact with molten Al-alloy. SEM/EDS analyses of the interfacial reaction zone showed the formation of corundum in the interfacial layer, along with a significant decrease in the phosphorus content in the interface. Thermodynamic calculations revealed that reaction with the alloy leads to the formation of corundum as the reaction product along with gaseous products (phosphorus trioxide gas) and small amounts of aluminum phosphide. Corundum formation at the interface enhances the corrosion resistance of sample due to high stability of corundum against molten Al alloy, while the metal quality is enhanced due to absence of dissolved phosphorus in the metal. [Copyright &y& Elsevier]

Abstract: Interfacial reactions between Al-alloy and andalusite low-cement castables (LCC) containing 5wt% V2O5 were analyzed at 850°C and 1160°C using the Alcoa cup test. Interfacial reaction products and phases formed during heat treatment of the refractory samples were characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. V2O5 addition resulted in the formation of glassy phases, which significantly improved the corrosion resistance. These phases were preferentially corroded by the alloy, due to their glassy nature. However, vanadium formed from reduction, formed intermetallic alloys (V–Al–Si–Mg), which formed an interfacial physical barrier to further alloy penetration. [Copyright &y& Elsevier]

Interfacial reactions between Al alloy and andalusite low-cement castables (LCCs) containing 5 wt pct BO, BC, and BN were analyzed at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. The results showed that the addition of boron-containing materials led to the formation of aluminoborate (9AlO.2BO) and glassy phase containing boron in the prefiring temperature (1373 K [1100 °C]), which consequently improved the corrosion resistance of the refractories. The high heat of formation of the aluminoborate phase (which increased its stability to reactions with molten Al alloy) and the low solubility of boron in molten Al were the major factors that contributed to the improvement in the corrosion resistance of B-doped samples. [ABSTRACT FROM AUTHOR]

n experimental study was conducted to investigate the interfacial phenomena between an Al alloy and andalusite low-cement castables (LCCs) containing fixed contents of barium compounds (BaO, BaSO, and BaCO) at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. Interfacial reaction products and phases formed during heat treatment of the refractory samples were characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) and X-ray diffraction analysis (XRD). The addition of both BaO and BaSO led to a significant reduction of alloy penetration into the refractory. Hexa-celsian formation was observed in both these refractories, which drastically increased their corrosion resistance. Barite decomposition was observed at 1373 K (1100 °C) in the presence of alumina and silica, which was the precursor for hexa-celsian formation. Barium silicates were formed in all samples containing additives; however, this did not have any major influence on the corrosion resistance. Solidified eutectics of BaSi and α-BaAlSi formed in all these samples, which acted as an interfacial barrier that prevented additional molten aluminum penetration; however, the positive effect of intermetallic formation was offset by glassy phase formation in samples containing BaCO as the additive. [ABSTRACT FROM AUTHOR]

ndalusite containing low-cement castables (LCCs) have been used in aluminum casthouses for several decades. CaF is commonly added to the refractory to improve its corrosion resistance mainly because of its role in the formation of anorthite (CaAlSiO); the latter has been reported to decrease the penetration of molten aluminum alloys into refractories. This article investigates the effect of the addition of different calcium containing compounds (CaO, CaCO, CaSO, CaF, Clinker white cement, calcia feldspar, wollastonite, and Ca(PO)) on reactions with the refractory constituents to form anorthite as well as the effect of the additives on both the subsequent physical properties and the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test at temperatures (1123 K [850 °C] for 150 hours and 1433 K [1160 °C] for 72 hours) were conducted to determine the extent of penetration, whereas immersion tests in boiling water were conducted to determine the extent of open porosity in the material. Scanning electron microscopy coupled with energy dispersive spectrometer, optical microscopy, and X-ray diffraction techniques were employed to characterize the phase formations in the materials after the tests. The study demonstrated that both calcia feldspar and clinker white cement had the potential to be used as new additives for decreasing the penetration of molten Al-alloy into the refractory materials. Anorthite formation (in the refractory matrix), along with the absence of glassy phases, were responsible for the improvement in the corrosion resistance of the castables containing calcia feldspar. However, in the sample containing cement, the presence of calcium silicate phases were observed to resist reactions with molten aluminum. The observed results were validated using thermodynamic calculations, which indicated that tricalcium silicates (3CaO.SiO) and dicalcium silicate (2CaO.SiO) phases were more resistant than wollastonite (CaSiO) for applications involving contact with molten aluminum. [ABSTRACT FROM AUTHOR]

The performance of high-alumina refractories used for aluminium casting significantly impacts the efficiency of metal production. The interfacial reactions with Al-alloys cause corundum and magnesium spinel deposition on the refractory surface, leading to refractory degradation. An experimental study was conducted to investigate the influence of varying barium sulphate (BaSO) concentrations in a high-alumina refractory on its interfacial reactions with molten Al-alloy in a horizontal tube furnace at 1523 K (1250 °C) under inert conditions. This study showed that the Al-alloy reactions with pure BaSO would form barium aluminates at the interface. However, in the Al-alloy/refractory system, the interfacial behaviour was strongly influenced by the relative amount of BaSO, such that up to 5 wt%, the extent of alloy penetration into the refractory increased with increasing BaSO contents. Electron-probe micro-analyser and X-ray diffraction studies indicated that the composition of the interface for these refractories was augmented with barium silicates and diminishing anorthite phases. In the presence of 10 wt% BaSO, the extent of metal penetration into the refractory decreased, whilst for 20% BaSO, the penetration was higher; these results were attributed to the interfacial presence of celsian (BaAlSiO) and unreacted barium sulphates, respectively. This study suggests that maximising the celsian formation at the interface is critical for optimising the BaSO concentration for improving the refractory's performance for Al-casting. [ABSTRACT FROM AUTHOR]