The Al2O3-SiC-C or ASC castables are used in the main runners of blast furnaces. Most of the papers published to date focus on laboratory corrosion tests because access to the post-mortem samples of ASC castables is difficult. However, investigation of post-mortem samples is crucial in reducing the wear of ASC castables. The main runner is divided into the turbulence, middle, and non-turbulence zones. The microstructures of post-mortem samples located in working linings of different zones were investigated by SEM/EDS technique. The thermodynamic simulations were carried out in different systems, such as slag/refractory and iron/refractory, using the FactSage software. The SEM/EDS results showed the formation of phases with low melting points, such as gehlenite and anorthite, together with spinel solid solutions in the matrix and calcium dialuminate near the alumina aggregates. The thermodynamic simulations showed that slag and iron tend to react with alumina and silicon carbide, respectively.

Damage of SiC oxide bonded refractories in waste-to-energy facilities (WtE) has been characterized. Different phenomena were observed: wear by slag phases, volume expansion of tiles and fracture in different locations. These results are in agreement with laboratory experiments. The role of gas composition and tiles temperature profile on deposit composition, on condensation of gaseous alkali chloride and on formation of liquid phase inside the porosity of the refractories has been emphasized. Gaseous alkali species are involved, not only in the formation of liquid phases, but also as a precursor of cristoballite formation around the SiC grains as well as in the rich alumina-silica matrix. On the hot face of the refractories, oxo-reduction reactions produce the formation of wollastonite. Post-mortem analysis after several thousand hours of operation point to three main corrosion mechanisms:

Corrosion tests of oxide-bonded SiCbased refractory cylinders by molten salts (mainly CaSO4, K2SO4) were performed at high temperature to better understand the corrosion mechanisms operating in these materials. Salt pellets were placed on the upper surface of small refractory cylinders. After melting, the corrosive product soaked into the pores of the refractory cylinders and partially corroded the SiC phase. SEM-EDS analyses showed that CaSiO3 was the main new phase formed, growing from SiC aggregates into the pores. The shapes of the initial and corroded cylinders were measured at room temperature using a 3D coordinate measuring machine equipped with a laser-plane sensor. These measurements allowed for the monitoring of the evolution of the residual radial deformation versus the depth from the surface in contact with the salt pellets and consequently the characterisation of the local volume expansion induced by the phase change. Coupling SEM-EDS analyses with 3D digitising revealed the link between the corrosion product and the volume expansion.

The biomass gasification process is devoted to the production of electricity from waste and biomass. The gas, obtained by this technique, cannot be used efficiently if it contains tars. A new type of installation has been developed to purify the gas produced by gasification with the help of a plasma torch. There is actually no functioning equivalent and no industrial experience. So it is necessary to define the operating conditions, the design of the reactor and the refractory materials used for the walls. These materials must be chosen wisely to ensure the integrity and durability of the lining, according to the solicitations and the chemical environment inside the reactor. The design and thermal profile of the reactor was determined using computational fluid dynamics. A thermo-chemical simulation was conducted to determine the chemical environment of the reactor. Finally these theoretical data were used to carry out laboratory corrosion tests on different selected refractories in order to determine which one was best suited for this application.

This study investigated oxide bonded SiC refractories lining failure in Waste-to-Energy boilers taking into account SiC material description and operating conditions. SiC tiles located at different elevations are instrumented with thermocouples. Hot side temperatures range from 900°C to 700°C depending on flue gas temperature at corresponding elevations. On-site tile observation showed: (i) wear by slag phases, (ii) swelling and cracks of tiles and (iii) fractures. Post-mortem analysis after several thousand hours of operation revealed three main corrosion mechanisms: molten salt/slag attack (Na, K, Ca sulphate phases), salt condensation inducing new phase formation (SiO2–CaSO4–K2SO4) and SiC oxidation. The relative contributions of chemical degradation mechanisms are discussed and tile deformation is related to thermo-chemo-mechanical coupled effect.

Refractory castables containing alumina-magnesia/self-forming spinel (MgAl2O4) are used in impact pads of steel ladles in steelmaking processes. In order to understand the wear mechanisms of refractory materials, several recipes were tested from a corrosion, slag resistance and thermal shock point of view. The results show that the corrosion is extremely limited at the slag/refractory interface for all cases. Nevertheless, for higher cement alumina content castables, the formation of cracks is observed in refractory castables into which slag can penetrate. The slag reacts with the alumina to form a new phase such as hibonite (CA6) and calcium dialuminate (CA2). The volumetric change of these reactions involving CA2 and CA6 lead to the apparition of macro-cracks. Thus, the penetration of slag and steel are increased, causing hot mechanical properties to degrade. For lower cement alumina castables, the formation of micro-cracks is avoided by controlling volume expansion. Thus, the slag deposit reacts with alumina grains and the matrix at the slag/refractory interface to produce a monomineral layer of hibonite. In this way, the monomineral layer acts as a barrier and limits the penetration of slag and steel into the refractory lining. Thus, to increase the lifetime of refractory castables containing alumina-magnesia/ self-forming spinel, it is advised to control volume expansion in order to avoid the formation of cracks and limit the penetration of secondary metallurgy steel ladle slag.

Oxide bonded silicon carbide refractories are used successfully in solid waste-to-energy facilities (WtE). They are submitted to severe thermo-chemical stresses that limit their performance. Even if the corrosion resistance of silicon carbide is high, wear and failure of refractory lining are currently observed.For a better understanding of corrosion mechanisms, oxide bonded silicon carbide refractories, collected in the combustion chamber of several WtE facilities, were examined. The main mechanisms of corrosion, according to the environment of refractories, were determined. The chemical composition and the nature of the corrosive agents were calculated from the thermo-chemical modeling. They are mainly condensed phases of sulfates and chlorides (CaSO4, K2SO4, Na2SO4, KCl, and NaCl). In service conditions, these molten salts react with the SiC aggregates and the matrix of the refractories to form low melting compounds.The post-mortem analyses showed the formation of para-wollastonite in the porosity and around the SiC grains, on the hot face of refractory tiles. Other phases such as cristobalite and microline (KAlSiO8) were also formed down to the core of refractories. The volume expansion created by the formation of new mineral phases (cristobalite, para-wollastonite) causes the formation of micro cracks in the refractory lining.In this paper, the degradation mechanisms of oxide bonded silicon carbide refractories are presented and the main research developments for the future are discussed.

The chemical attack of alumina refractories by sodium vapours is far from been completely understood. In order to contribute to a better knowledge of this attack, a laboratory test was developed to simulate the sodium gaseous corrosion of different raw materials and refractories.

Refractory castables containing alumina-magnesia/self-forming spinet (MgAl2O4) are used in impact pads of steel ladles in steelmaking processes. In order to understand the wear mechanisms of refractory materials, several recipes were tested from a corrosion, slag resistance and thermal shock point of view. The results show that the corrosion is extremely limited at the interface slag/refractory for all cases. Nevertheless, for higher cement alumina content castables, the formation of micro cracks is observed in refractory castables into which slag deposit can penetrate. The slag reacts with alumina to form a new phase such as hibonite (CA6) and calcium dialuminate (CA2). The expansive reactions involving CA2 and CA6 lead to macro-cracks. Thus, the penetration of slag and steel are increased causing hot mechanical properties to degrade. For lower cement alumina castables, the formation of micro cracks is avoided by controlling volume expansion. Thus, the slag deposit reacts with alumina grains and the matrix at the slag/refractory interface to produce a monomineral layer of hibonite. In this way, the monomineral layer acts as a barrier and limits the penetration of slag and steel into the refractory lining. Thus, to increase the life time of refractory castables containing alumina-magnesia/self-forming spinet it is advisable to control volume expansion in order to avoid the formation of cracks and to limit the penetration of secondary metallurgy steel ladle slag.

In the past, the mechanisms of corrosion in refractory materials used in the flue wall of anode baking furnaces have been poorly understood. To better understand the processes of degradation, a study of corroded refractories from anode baking furnaces was conducted. This study found that all refractory bricks contain fine andalusite particles in the matrix and fireclay as aggregates. The first stage of corrosion is the penetration of gaseous sodium, coming from recycled anodes, through the porosity of materials. Then, at high temperature, sodium becomes oxidized and is included in the liquid phase. The sodium-rich liquid phase corrodes the refractory material, in particular mullite networks. To understand why the andalusite mineral is used in the refractory materials, a corrosion test able to simulate the gaseous corrosion of materials at laboratory scale was developed. Several recipes, composed of andalusite or fireclay, were submitted to the corrosion test. The microstructural observations showed that the matrix is more sensitive to corrosion. Thus, the use of a raw material such as andalusite in the matrix is advised in order to reduce the gaseous sodium corrosion of fireclay based bricks.

Alumina magnesia in situ spinel castables are used as ladle refractory lining in the steel industry. In contact with slag, they suffer degradations which limits their performance. The purpose of this article is to predict the thermochemical attack of a slag on alumina magnesia refractory using Factsage® thermodynamic modeling. To evaluate the reliability of the thermodynamic results, a validation step was carried out, which supported that the database was well adapted to the alumina magnesia spinel system. The corrosion phenomenon was then computed for a simple to a complete system to understand the mechanism and the influence of specific oxides. The model was also compared to corroded microstructures from a steel ladle to evaluate the contribution of each constituent in the castable. The aggregates of alumina react with slag to produce monomineral layers of lime aluminates (CA6 and CA2), while complex spinels (Mg, Fe, Mn)O (Fe2, Al2)O3 are formed from the reaction of the slag with the matrix of the castable. Several oxides (MnO, FeO, Fe2O3) from the slag contribute to the formation of the spinel structures. The microstructures of refractories used in steel ladles confirm the main conclusions and the thermodynamic approach.

This paper deals with the development of a fatigue crack growth model for high temperature complex loading and application to turbine disc conditions. The proposed model is based on an extensive experimental study performed on Astroloy at 650-degrees-C, which comprises fatigue with or without hold times, special tests with holds at intermediate loads, fast-slow or slow-fast triangular waves, sequence tests, etc.The crack growth model is built up in the framework of classical linear elastic fracture mechanics. Its structure is quite simple and is supported by previously developed fatigue crack growth models and a companion study made at Ecole des Mines de Paris (EMP) for the oxidation processes on Astroloy.