Amélioration de la résistance à la corrosion de réfractaires exposés à des alliages d'aluminium liquide par des revêtements de nitrure d'aluminium synthétisés par suspension plasma

Abstract : The objective of this thesis is to identify and synthesize a corrosion-resistant refractory composition when in direct contact with the chemically aggressive molten Al-5wt%Mg alloy. The reviewed literature suggests solutions for resolving the corrosion issue: (i) the addition of non-wetting agents (NWAs) to the refractory, and (ii) deposition of a protective coating on the refractory surface. The first part of this project aims at finding the NWAs that would protect the white fused mullite (WFM) refractory from corrosion, and the experimental results showed that a mixture of CaF2 and BaSO4 is the most impactful NWA protecting the WFM refractories from corrosion. For solution (ii) i.e., the coating, the existing literature suggests that: a) its melting point should exceed the furnace service point, b) its thermal expansion coefficient should be close to that of the substrate, c) it should be chemically resistant to molten Al alloy. The corrosion-resistant property of the selected coating candidate in contact with molten Al alloy was assessed using FactSage thermochemical software. The results showed that aluminum nitride (AlN) meets the required criteria and its in-situ synthesis and deposition using radio-frequency (RF) induction suspension plasma spray (SPS) technology on various substrates (Ti, Mo, and carbon steel) was performed and studied in the second part of the thesis. The corrosion-resistant performance of hexagonal and cubic phases of AlN in contact with molten Al was studied using the ab initio molecular dynamic (BOMD) simulation module of BIOVIA Materials Studio software. Such analysis was needed for the quantification of corrosion resistance of hexagonal versus cubic phases of AlN which is not possible to get using FactSage software. The results show that both phases have interfacial energy within the physisorption regime confirming that neither cubic nor hexagonal AlN phases are reactive in contact with molten Al. Different parametric studies have been done to understand the most important parameters which affect the cubic AlN coatings synthesis. The main results are: 1) The best particle size distribution ratio by mass is 75% of the (– 5 +1 μm) size range mixed with 25% of (– 35 + 17 μm). Rietveld quantitative analysis (RQA) using X-ray diffraction (XRD) data indicated that the coatings consisted of up to 82% AlN (80% cubic + 2% hexagonal crystal structure). 2) Melamine is advantageous over urea by producing more active nitrogen species in the plasma. 3) Hexadecane suspension carrier outperforms ethylene glycol, light mineral oil, and ethanol in the formation of AlN. 4) The use of promotional additives such as boron, BN, Mo, Y2O3, AlN, or Al4C3 can stimulate the formation of AlN. The optimum amount of promotional AlN was 0.22-wt% of the total suspension mass, producing up to 72% AlN in the coating. 5) Among Ti, Mo, and carbon steel substrates, the formation of AlN was significantly higher with the latter than with the two others. 6) Between the range of 6 to 10 cm, the standoff distance of 8 cm provides a residence time long enough for the reaction of Al and nitrogen active species, maximizing the formation of AlN. Finally, the plasma synthesized AlN coating was tested for corrosion resistance by direct contact with molten Al-5wt%Mg alloy at 1123 K and found to be stable after the test.L'objectif de cette thèse est d'identifier et de synthétiser un matériau réfractaire résistant à la corrosion lorsqu'il est en contact direct avec l'alliage Al-Mg fondu qui est très agressif chimiquement. La revue de littérature suggère des solutions pour résoudre le problème de la corrosion : (i) l'ajout d'agents non mouillants (NWA) au réfractaire, et (ii) le dépôt d'un revêtement protecteur sur la surface réfractaire. La première partie de ce projet vise à trouver les NWA qui protégeraient le réfractaire de mullite fondue blanche (WFM) de la corrosion, et les résultats expérimentaux ont montré qu'un mélange de CaF2 et de BaSO4 est le NWA le plus efficace pour protéger ces réfractaires de la corrosion. Pour la solution (ii) c'est-à-dire le revêtement, la littérature existante suggère que : a) son point de fusion doit dépasser la température de service du four, b) son coefficient de dilatation thermique doit être proche de celui du substrat, et c) il doit être chimiquement résistant à l’alliages d'Al fondu. La propriété de résistance à la corrosion du revêtement candidat sélectionné en contact avec l'alliage d'Al fondu a été évaluée à l'aide du logiciel thermochimique FactSage. Les résultats ont montré que le nitrure d’aluminium (AlN) répond aux critères requis. Sa synthèse et déposition in situ à l'aide de la technologie de projection par plasma de suspension par induction radiofréquence (RF) sur divers substrats (Ti, Mo et acier au carbone) a été réalisée et étudiée dans la deuxième partie de la thèse. Les performances de résistance à la corrosion des phases hexagonales et cubiques d'AlN en contact avec l'Al fondu ont été étudiées à l'aide du module de simulation de dynamique moléculaire ab initio (BOMD) du logiciel BIOVIA Materials Studio. Une telle analyse était nécessaire pour la quantification de la résistance à la corrosion des phases hexagonales par rapport aux phases cubiques d'AlN, ce qui n'est pas possible avec le logiciel FactSage. Les résultats montrent que les deux phases ont une énergie interfaciale dans le régime de physisorption confirmant que ni les phases AlN cubique ni hexagonale ne sont réactives au contact de l'Al fondu. Différentes études paramétriques ont été réalisées pour comprendre les paramètres les plus importants qui affectent la synthèse des revêtements d'AlN cubique. Les principaux résultats sont : 1) Le meilleur ratio de distribution granulométrique en masse est de 75 % de la gamme granulométrique (– 5 +1 µm) mélangé à 25 % de (– 35 + 17 µm). L'analyse quantitative de Rietveld (RQA) utilisant des données de diffraction des rayons X (XRD) a indiqué que les meilleurs revêtements étaient constitués de 82 % d'AlN (80 % cubique + 2 % de structure cristalline hexagonale). 2) La mélamine est avantageuse par rapport à l'urée en produisant plus d'espèces azotées actives dans le plasma. 3) Le liquide de suspension d'hexadécane surpasse l'éthylène glycol, l'huile minérale légère et l'éthanol dans la formation d'AIN. 4) L'utilisation d'additifs promotionnels tels que le bore, le BN, le Mo, le Y2O3, l'AlN ou l'Al4C3 peut stimuler la formation d'AlN. La quantité optimale d'AlN promotionnel est de 0,22 % en poids de la masse totale de la suspension, produisant jusqu'à 72 % d'AlN dans le revêtement. 5) Parmi les substrats en Ti, Mo et acier au carbone, la formation d'AlN est significativement plus élevée avec ce dernier que pour les deux autres. 6) Entre 6 et 10 cm, la distance de déposition de 8 cm fournit un temps de séjour suffisant pour la réaction d'Al et des espèces actives d'azote, maximisant ainsi la formation d'AlN. Enfin, le revêtement AlN synthétisé par plasma a été testé pour sa résistance à la corrosion par contact direct avec un alliage fondu Al-5wt%Mg à 1123 K et s'est avéré stable après le test

Synthesis of Cubic Aluminum Nitride (AlN) Coatings through Suspension Plasma Spray (SPS) Technology

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic substrates. The effects of the nitriding agent, the suspension liquid carrier, the substrate materials and the standoff distance during deposition by SPS were investigated. The plasma-synthesized coatings were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show higher AlN content in the coatings deposited on a carbon steel substrate (~82%) when compared to titanium substrate (~30%) or molybdenum (~15%). Melamine mixed with pure aluminum powder produced AlN-richer coatings of up to 82% when compared to urea mixed with the Al (~25% AlN). Hexadecane was a relatively better liquid carrier than the oxygen-rich liquid carriers such as ethanol or ethylene glycol. When the materials were exposed to a molten aluminum–magnesium alloy at 850 °C for 2 h, the corrosion resistance of the AlN-coated carbon steel substrate showed improved performance in comparison to the uncoated substrate

Proven Anti-Wetting Properties of Molybdenum Tested for High-Temperature Corrosion-Resistance with Potential Application in the Aluminum Industry

The behavior of Mo in contact with molten Al was modelled by classical molecular dynamics (CMD) simulation of a pure Mo solid in contact with molten Al at 1200 K using the Materials Studio®. Results showed that no reaction or cross diffusion of atoms occurs at the Mo(s)–Al(l) interface, and that molten Al atoms exhibit an epitaxial alignment with the exposed solid Mo crystal morphology. Furthermore, the two phases {Mo(s) and Al(l)} are predicted to interact with weak van der Waals forces and give interfacial energy of about 203 mJ/m2. Surface energy measurements by the sessile drop experiment using the van Oss–Chaudhury–Good (VCG) theory established a Mo(s)–Al(l) interface energy equivalent to 54 mJ/m2, which supports the weak van der Waals interaction. The corrosion resistance of a high purity (99.97%) Mo block was then tested in a molten alloy of 5% Mg mixed in Al (Al-5 wt.%Mg) at 1123 K for 96 h, using the ALCAN’s standard “immersion” test, and the results are presented. No Mo was found to be dissolved in the molten Al-Mg alloy. However, a 20% mass loss in the Mo block was due to intergranular corrosion scissoring the Mo block in the ALCAN test, but not as a result of the reaction of pure Mo with the molten Al-Mg alloy. It was observed that the Al-Mg alloy did not stick to the Mo block

The addition of synthesized hydroxyapatite and fluorapatite nanoparticles to a glass-ionomer cement for dental restoration and its effects on mechanical properties

The objective of this study was to evaluate the effect of the addition of synthesized hydroxyapatite (HA) and fluorapatite (FA) nanoparticles to a glass-ionomer cement (GIC) on the mechanical properties, while preserving their unique and potent clinical properties. Bioceramics, such as HA and FA, have been recognized as restorative materials (e.g. GICs) in dentistry due to their chemical and biological compatibility with human hard tissues, which are considered calcium phosphate complexes. In this study, both of these inorganic nanoparticles (HA and FA) were synthesized via a wet-chemical precipitation method. The obtained nanoparticles were characterized with X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) Theory. Then, HA and FA were incorporated into the powder component of the resin-modified cement (Fuji II, GC gold label, GC international, Tokyo, Japan) at 5% and 8 wt%, and unblended powder was employed as control. Compressive strength (CS) and diametral tensile strength (DTA) before and after 1, 7 and 28 days of storage in distilled water were evaluated using a universal testing machine. Surface microhardness after 1 and 7 days of storage in distilled water was determined using Vickers microhardness tester. Setting and working time was measured as specified in the ASTM standard. The surface morphology of the modified GICs was examined using SEM observations. The morphology of the synthesized HA and FA nanoparticles was hexagonal, and their average sizes were about 25 nm and 30 nm, respectively. The mechanical results of the modified GICs ascertained addition of HA and FA (5 and 8 wt%) into the glass ionomer cement after 7 days of storage in distilled water exhibited statistically higher CS of about 107–113.6 MPa and 111–117.8 MPa, respectively, and also higher DTS, 13–16 MPa and 14–19 MPa, respectively. The hardness of the glass ionomers containing HA and FA nanoparticles (5 wt%) were increased by 2.21% and 11.77%, respectively. In addition, working time and setting time by adding the 5% nanoparticles were reduced about 8.5% and 13.23% for HA and 10.63% and 19.11% for FA, respectively. It was concluded that glass ionomer cements containing nanobioceramics (HA and FA) are promising restorative dental materials with improved mechanical properties. These experimental GICs may be potentially employed for higher stress-bearing site restorations, such as Class I and II restoration