MAGNESIA REFRACTORIES


Magnesia Refractories
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Non-metallic inorganic substances that can survive extremely high temperatures are known as refractory materials. Refractories are defined as “nonmetallic materials with the chemical and physical qualities that make them applicable for structure or as components of systems exposed to conditions exceeding 1000 °F / 538 °C” according to ASTM C71. Superior mechanical properties at room and high temperatures, the capacity to withstand rapid temperature fluctuations due to repeated heating and cooling during application as a lining material in iron and steel converters, and good resistance to corrosion and erosion due to molten metal, slag, and other contaminants are just a few of the notable characteristics associated with these materials. Magnesia carbon refractory is a composite material made up of MgO and carbon. It can be found in the shape of bricks or in castables.

The primary components of magnesia carbon bricks are magnesia grains, graphite, antioxidants to keep the carbon from oxidizing, and a high carbon-containing pitch or resin as a binder to keep the various parts of the refractory together. Refractories are likewise basic since slag in steelmaking is mostly basic. Steelmaking applications include the lining of basic oxygen furnaces, steel ladles, LD converters, electric arc furnaces, and secondary steelmaking uses. Because of the characteristics given by MgO and carbon, these refractories have been prevalent along the slag line of ladles for at least a decade. Using MgO-C bricks, clean steel can be manufactured with less refractory usage. Because magnesia has a melting point of 2800 degrees Celsius, these refractories have a considerable advantage over Al2O3- and SiO2-based materials.

Furthermore, a reaction between MgO and C results in the embryonic creation of a dense layer of MgO on the MgO-C brick’s working surface. This layer prevents slag and metal from penetrating and improves corrosion resistance. MgO, on the other hand, has a low thermal shock resistance. Graphite, on the other hand, has a high thermal conductivity, a moderate thermal expansion, and a higher resistance to spalling. Graphite was added to the MgO matrix to generate a new high temperature material with superior capabilities, overcoming the drawbacks of MgO. Carbon fills the porous structure of the MgO matrix and helps to increase slag and metal corrosion and penetration resistance due to its non-wetting nature. Due to the presence of weak van der Waals inter-layer connections, graphite possesses lubricating characteristics.

Carbon, on the other hand, has a low resistance to oxidation. It can be oxidized to produce CO or CO2, resulting in a porous structure with low strength and corrosion resistance. Large levels of carbon generate more heat loss through the refractory, as well as higher shell temperatures in steel vessels. As a result, shell deformation increases, reducing ladle life. Steel picks up more carbon when the carbon percentage is higher, which is undesirable because steelmaking is often a decarburization process. More CO and CO2 gas by-products are also a result, posing a growing threat to the global environment. Due of these reasons, attempts have been made to lower the overall quantity of carbon required in MgO-C materials while maintaining their major advantageous features. The use of nano carbon has been discovered to be a viable solution to this issue. Magnesia(MgO) is widely utilized in refractories for basic oxygen and electric arc. The superiority of other materials, such as te refractories, both key raw materials, and graphite, in areas such as the s tal contact is restricted. If brick is mined chemically from grain, the raw materials for MgO refractories in the United States are magnesite or brines or seawater. Their use may result in a reduction in raw materials. By the Bureau of Critical Information Earlier study 1 2 Mines was directed at arties of the is the major factory the prop which were current Bureau dictated that adding metallic salts to low-alumina refractories improved their characteristics. Two commercial MgO refractories (90 and 98 percent) were treated with solutions of 14 different metallic salt and oxide solutions to see if similar property improvements could be made in refractories. They were burnt to 1, C after impregnation to allow salt ion and interaction between the oxide and the refrac in the brick. Sabse Hot Rupture Modulus (MOR).

Deformation under load at high temperatures (hot thermal resistance, and s resistance tests) Energy spectroscopy () was used to determine the distribution of the additives, whereas diffraction (XRD) was employed to determine the mineral phases that were created. This paper summarizes the findings and compares them to untreated properties. The carbon in the MgO-C bricks serves to prevent slag components from penetrating the bricks, but it also has the disadvantage of being oxidized.

The following three types of carbon oxidation phenomena can be distinguished: • Liquid phase oxidation • Gas phase oxidation • Oxidation of carbon by MgO (MgO-C reaction)

  • Iron oxides in the slag are the primary cause of liquid-phase oxidation. The amount of iron oxide in the slag has a significant impact on the wear rate of MgO-C bricks. 10) This effect gasifies the carbon in the brick matrix, causing structural embrittlement, as indicated by the chemical formula FeO(s)+C(s)Fe(s)+CO(g). The presence of very brilliant Fe precipitates in the void layer beneath the working surface or immediately below the void layer has been confirmed.

  • Gas phase oxidation refers to the burning of the carbon in the brick matrix. The presence of oxygen and carbon dioxide in the atmosphere causes it. Gas-phase oxidation is likely to become an issue in general converters if the converter cone is not adequately coated by slag and is exposed to air.

  • The MgO-C reaction is similar to the wear mechanism of MgO-C bricks in terms of its occurrence. The damage mechanism, frequency, and amount of the various lining areas differ in the design of the converter refractory lining. To make the entire damage equilibrium as uniform as possible across the converter refractory lining, zoned lining is commonly used to change the thickness and quality of MgO-C bricks in different lining locations. Damage to the converter throat and cone includes gas phase oxidation, physical impact during de-slagging, and cracks caused by barrel thermal expansion. Adding SiC as an antioxidant, using anchors drilled into the steel shell to attach the bricks, and using metal casings for fusion bonding all help to prevent brick dislodgment. Abrasion by molten steel flow is the most common cause of damage to the tap hole sleeve, which is thought to be enhanced by frequent heating and cooling during operation, as well as gas phase oxidation. Adjusting the antioxidant addition and boosting the hot modulus of rupture improves the tap hole sleeve’s durability. In the slag line, trunnion, and steel bath areas, slag corrosion is the most common. Densification by modifying particle size composition and binder type, suppression of structural deterioration owing to cyclic thermal loading, and the utilization of CaO-containing clinker with high slag coating qualities have all been made improvements. When hot metal is received from the hot metal ladle and scrap is charged as a cold iron source, the charging pad is subjected to mechanical impact.

The charging pad area MgO-C bricks are strengthened by lowering the carbon concentration and increasing the metal addition content. Another issue is spalling damage. There have been reports of improving spalling resistance by changing the binder and flake graphite types. Graphite oxidation, slag corrosion, and spalling are some of the factors that cause damage to the bottom tuyeres. Another factor is mechanical damage caused by the bottom blown gas’s rearward attack and the molten steel’s flow abrasion. The MgO-C bricks used in the lower tuyere area have a higher graphite concentration than the bricks used in the walls. These bottom tuyere MgO-C bricks also contain additives that prevent graphite oxidation and boost strength.

Nippon Steel Corporation invented the MultiRefining Converter (MURC) method in recent years, which combines dephosphorization and decarburization in a single converter. The penetration of low-basicity slag into refractories and the corrosion of refractories by low-basicity slag had noticeable consequences on the MURC converter as the new process became more frequently used throughout the industry. The impurity in high temperature strength and abrasion resistance rose when the quality of iron ore, coke, and other steel raw materials deteriorated. In the BOF Zone of BOF, there is a case of wear and the required attributes of each part.

The main source of wear Is properties that are mostly necessary Corrosion Oxidation Abrasion Spalling Upper cone, mouth removal of the cranium causes mechanical harm. Air oxidation is a type of oxidation that occurs when substances are exposed to drilling a hole Abrasion by molten steel stream Oxidation by air Line of slag Slag corrosion is a type of corrosion that occurs when metals come into contact with each other. Side of the charger Scrap charging causes mechanical harm. Hot metal stream abrasion Thermal spalling is a term that refers to the process of a material. As a result, the operating severity of converters was aggravated, the corrosion rate of MgO-C bricks rose, and the necessity for greater MgO-C brick durability was emphasized.

Compilation of a systematic commissioning plan divided into distinct commissioning phases, with each phase defining the criteria that must be met before moving on to the next. These criteria also serve as a set of clear objectives. Gathering information (conducting a literature study on typical preheating practices, as described earlier in this paper, will add tremendous value) and thoroughly evaluating ‘what if’ scenarios outside of the pressurized commissioning environment are both facilitated by compiling this plan well in advance. Problem fixing should be undertaken with the intention of not causing further issues while resolving existing ones.

Every opportunity to learn from earlier experiences, whether from experienced persons, previously collected internal reports, or outside sources, must be taken advantage of. Every encounter provides an opportunity to add to the company’s knowledge base. A daily journal of critical factors, thought processes, and justifications can be useful for future work. A delicate balance must be struck between driving for a quick start and minimizing the risk of irreversible harm. The commissioning team’s energy levels, motivational state, and alertness should all be considered as part of this risk assessment. These qualities have a big impact on risk recognition. Conclusion Despite the fact that Southern African businesses commercially produce nineteen different commodities at over sixty smelters25, there is very little literature on furnace start-up for any type of lining.

Because furnace start-up events are not common in continuous smelting operations, sharing experiences and, more importantly, the lessons learnt from these experiences, would allow for productive debate on best practices in furnace dry out and heat up. Best practices in furnace start-up are something the pyro metallurgical industry could greatly benefit from, especially given the high costs of a failed start-up.