Carbon Bricks Research Articles

Slag – Refractory Interactions During Ilmenite Smelting: Thermodynamic Simulation and Experimental Data

The interaction of four types of commonly used refractories (i.e., burned magnesite brick, magnesia carbon brick, corundum castable, and SiC castable) with slag formed in the smelting of titanium (wt. [TiO2] = 80%) in an electric furnace at the Panzhihuan Iron and Steel plant was studied. Erosion of refractories by titanium slag was calculated using the FactSage software program. The experiment was carried out in an electric furnace based on calculation results. Meanwhile, the results of the thermodynamic simulation showed that the interaction of SiC castable with titanium slag formed TiC with a high melting point, which can prevent the slag from penetrating more deeply into the refractory and exhibits good erosion resistance. In terms of erosion resistance to titanium slag, different refractory materials can be arranged in order from most to least erosion resistant as follows: SiC castable → magnesia carbon brick → magnesite brick → corundum castable. The results of theoretical calculations are in good agreement with the experiment results.

Dissolution Mechanism of Carbon Brick into Molten Iron

Dissolution Mechanism of Carbon Brick into Molten Iron

Raw materials for manufacturing of Superior quality MgO-C bricks

In SAIL Plant, Magnesia carbon (MgO-C) bricks are used as lining material for Metallurgical Vessels like Steel ladles as well as Basic Oxygen Furnaces (BOF). MgO-C bricks are the most suitable refractory in these conditions for slag line as they possess superior slag penetration resistance and excellent thermal shock resistance at elevated temperature. In Iron & Steel Industry, manufacturing processes has changed significantly due to the rising demand of quality steel in the market. Furnace capacities have increased & technological parameters have changed. Plants have been modernized with addition of secondary steel making facilities to meet the stringent quality requirement of newer grades of steel.Refractories in steel ladle are subjected to severe operating conditions like high temperature (1670-1700°C) tapping of liquid steel from BOF, thermal shock, abrasion with molten metal due to stirring during gas purging, localized heating in slag zone due to arcing, corrosion with slag, thermo mechanical stress etc. Hence, use of superior quality refractory material with evenly distributed impurities is essential to get an end product of very high corrosion and spalling resistance and high thermo-mechanical properties. Easier application technique is also required for higher lining life with less down time. Various qualities of magnesia carbon refractories are used in different zones of steel ladles & BOF. Magnesia carbon refractories are essentially constitute of two highly refractory components i.e. magnesia and graphite.Sea water magnesia is mainly used in SAIL as the main raw material for manufacturing of magnesia carbon bricks. Fused magnesia has also been tried by partially mixing with sea water magnesia. Although MgO content in magnesia is important up to a certain level, but the type of impurities and their relative proportions plays vital role in achieving good performance. Besides chemical purity, bulk density and crystal size are considered to be very important properties of magnesia for application in BOF and steel ladles. Beside magnesia, graphite of both indigenous and import sources were used in different occasions. Purity of graphite has been reported to have great influence on slag corrosion resistance and hot properties of magnesia carbon bricks. Particle size distribution of graphite influences porosity and thermal shock resistance properties of magnesia carbon bricks.This paper deals with the properties of different raw materials for making of superior quality MgO-C bricks for improved performance in Metallurgical vessels of SAIL plants.

Corrosion mechanism of carbon brick in the blast furnace hearth by potassium

Alkali plays a significant role in the formation of brittle layer of carbon brick in the blast furnace hearth. The brittle layer in a commercial blast furnace hearth was investigated. Large amounts of potassium compounds were found in the brittle layer. Subsequently, the carbon bricks which reacted with potassium in the simulation of blast furnace hearth under different contents of potassium in the brick (0.25, 0.5, 1.0 and 2.0 wt.%) during various reaction times (0.5, 1, 2 and 4 h) were experimentally studied. Finally, the formation mechanism of the brittle layer in carbon brick was clarified. The investigation results show that a large number of cracks are present in the brittle layer. The average potassium content in the brittle layer is 1 wt.%. According to the experimental results, cracks in the carbon brick can be formed by the attack of potassium. The reason for the formation of the brittle layer in the carbon brick is that the liquid potassium permeates into the carbon brick through the pores and cracks, and then reacts with SiO2 and Al2O3 in CO atmosphere. The generated potassium compounds nepheline and leucite lead to the volume expansion and the damage of the carbon brick.

Influence of TiO2 on the Viscosity of a High Alumina Slag and on Carbon Brick Corrosion

The influence of TiO2 on viscosities of CaO–SiO2–MgO–Al2O3–Cr2O3‐based slags and the corrosion mechanism of carbon brick used in blast furnace hearth by slags was investigated in this work. From the viscosity experimental results, it was found that the viscosity decreased with the addition of TiO2. Furthermore, the critical temperature and activation energy for the viscous flow of slags also decreased with increasing content of TiO2. The corrosion of carbon brick depended on the component of the brick surface in contact to the molten slags. In the region consisting mainly of carbon, the corrosion of carbon brick may be caused by the oxidation of carbon and in lower carbon content area, the corrosion of brick was mainly caused by the dissolution and slag penetration. The corrosion of carbon brick by slags could be a consequence of carbon oxidation, brick dissolution and slag infiltration, and the degradation of carbon brick was accelerated with the addition of TiO2.

Corrosion mechanism research and microstructure analysis of Baosteel No. 3 blast furnace hearth

AbstractBaosteel No. 3 blast furnace hearth was divided into tuyere area, taphole area, taphole upper side wall and taphole lower side wall according to different working situations. Through chemical composition analysis, scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry and other means, chemical composition and microstructure of different parts of hearth carbon brick were analyzed and markedly different corrosion mechanisms of these areas were found. Zn element in form of ZnO mainly deposited on the hot side of carbon brick. There was no obvious evidence that Zn permeates into carbon bricks and erodes them. Except for taphole area, K, Na, and Fe contents from hot side to cold side gradually rise and fall, resulting in the decrease of apparent porosity, the increase of density and the higher thermal conductivity compared with those of new carbon brick. The higher content of Fe in carbon brick leads to more serious erosion because Fe has greatly changed the physical properties of carbon brick. In the taphole area, the contents of Si and Al present obvious concentration gradient because of the mechanical souring of molten iron and slag. The SiO2 and Al2O3 particles that have different expansion factors with carbon brick damaged the carbon substrate because of temperature fluctuation. The graphitized carbon found on H4 where is the most serious corrosion site means that the carbon brick ever directly contacts with molten iron.

The Mechanical Performance Experiments of Blast Furnace Hearth Ramming Material and Carbon Brick Refractory Mortar

In this paper, the mechanical properties experiments of BF hearth ramming material and carbon brick refractory mortar were carried out. The compressive strength experiments of refractory mortar at different curing temperatures and the resin and asphalt combined with ramming material at different molding pressures and curing temperatures were carried out respectively. The conclusions are as follows: (1) In the experiment temperature range, the compressive strength of resin combined with ramming material is significantly higher than that asphalt under the same conditions. (2) With the increase of temperature, the compressive strength of resin combined with ramming material and refractory mortar first increased and then decreased, while the asphalt combined with ramming material increases gradually.

Micro-CaCO3 conformal template synthesis of hierarchical porous carbon bricks: As a host for SnO2 nanoparticles with superior lithium storage performance

We demonstrate a facile conformal template synthesis of hierarchical porous carbon bricks (HPCBs) via chemical vapor deposition (CVD) method using CH4 as carbon source and micro-CaCO3 bricks as a conformal template. The as-prepared HPCBs exhibit abundant interconnected meso/macro-sized cavities, large surface area, high graphitization degree and robust framework, which act as an efficient host to buffer the volume changes of Li-Sn alloying-dealloying when applied in lithium ion batteries. Ultrafine SnO2 nanoparticles are easily loaded onto the inner surfaces of the HPCBs via a facile pyrolysis of tin (II) 2-ethylhexanoate at 300 °C in air. The SnO2/HPCB electrode exhibits superior cycle stability and rate capability, delivering a high reversible capacity of 743.8 mA h/g after 180 cycles at 200 mA/g with capacity retention of 109.5%, which is much higher than that of HPCBs (308.6 mA h/g after 180 cycles at 200 mA/g with capacity retention of 87.7%). The hierarchical porous carbon materials synthesized using micro-CaCO3 as a conformal template can be a promising general host for various electrochemical energy storage applications.

Development of integrated waste management options for irradiated graphite

Abstract The European Treatment and Disposal of Irradiated Graphite and other Carbonaceous Waste project sought to develop best practices in the retrieval, treatment, and disposal of irradiated graphite including other irradiated carbonaceous waste such as structural material made of graphite, nongraphitized carbon bricks, and fuel coatings. Emphasis was given on legacy irradiated graphite, as this represents a significant inventory in respective national waste management programs. This paper provides an overview of the characteristics of graphite irradiated during its use, primarily as a moderator material, within nuclear reactors. It describes the potential techniques applicable to the retrieval, treatment, recycling/reuse, and disposal of these graphite wastes. Considering the lifecycle of nuclear graphite, from manufacture to final disposal, a number of waste management options have been developed. These options consider the techniques and technologies required to address each stage of the lifecycle, such as segregation, treatment, recycle, and ultimate disposal in a radioactive waste repository, providing a toolbox to aid operators and regulators to determine the most appropriate management strategy. It is noted that national waste management programs currently have, or are in the process of developing, respective approaches to irradiated graphite management. The output of the Treatment and Disposal of Irradiated Graphite and other Carbonaceous Waste project is intended to aid these considerations, rather than dictate them.

Development of Metallic Fibre-Reinforced MgO-C Brick and its Application at the SAIL Rourkela Steel Plant

Magnesia carbon (MgO-C) bricks are widely used in steel ladles and converters in the iron and steel industry. Bricks of different composition are used depending on the chemical, mechanical and thermal conditions encountered by the converter/ladle. Brick varieties have different erosion behaviour. The critical areas in these iron and steel processing devices are the charge pad area of converters and the impact area of steel ladles, where hot liquid metal or high temperature liquid steel directly strike from a height, causing thermo-mechanical abrasion. A special composition of MgO-C bricks reinforced with stainless steel fibres was developed at the Research and Development Centre for Iron and Steel (RDCIS) and samples were characterised at laboratory scale. The added fibre design was optimised for hot strength properties. Bricks were manufactured at Lime Dolomite Brick Plant (LDBP), a sister plant of Rourkela Steel Plant (RSP), based on laboratory test results. The paper describes the details of brick composition, results of lab testing and the performance of bricks in plant-scale trials at RSP.

Development of Improved Quality Magnesia Carbon Brick by Incorporation of Industrial Grade Functionalised Multi-Walled Carbon Nanotube

A growing requirement to make low or ultra-low carbon steel has resulted in strong demand for lower carbon content in the MgO-C refractory lining materials of metallurgical vessels. Incorporation of carbon nanostructure materials is expected to reduce the total carbon content of refractory bricks due to their very high specific surface area compared to other carbon precursor materials. It will also help to significantly enhance both the corrosion and thermo-mechanical behaviour of refractories. Different compositions were designed to evaluate the effect of using industrial grade functionalised multi-walled carbon nanotube (F-MWCNT) in MgO-C refractory. Samples containing an appropriate combination of graphite and F-MWCNT produced the most impressive results. Based on the study, brick was developed for a panel trial in a 300-t ladle of BSL (Bokaro Steel Plant) at SAIL (Steel Authority of India Limited). The average erosion rate of carbon nanostructure-containing MgO-C brick refractory was observed to be about 28 mass-% less than that of conventional MgO-C bricks.

Residual thickness of carbon brick calculation model and systematic analysis of heat transfer

In order to calculate the hearth carbon brick residual thickness accurately at the end of the blast furnace service, three kinds of carbon brick residual thickness calculation models were established through physical model and equation derivation, and the reliability of calculation models was verified by examples. The heat transfer situation of hearth equipped with cast iron staves which is a widespread technology was systematically analyzed on the basis of analytic hierarchy process, and the distribution of thermal resistance in hearth heat transfer system was analyzed through actual calculation, the results show that total thermal resistance of the hearth heat transfer system is mainly composed of carbonaceous ramming material, the air gap between stave body and the steel water pipe and the stave body. The efforts to resolve the problems of these three sections will be the development direction of long hearth service-life.

Wear and Dissolution of MgO–C Refractory Lining in Belly and Top Cone Regions of BOF Vessel

The MgO–carbon bricks of varying carbon concentration are used as refractory lining material in BOF. Laser profiling of the lining is done at regular intervals to keep track of refractory wear in different parts of vessels. The main factors which affect the kinetics of dissolution of graphite flakes lying between the MgO grains in the belly region are attack by CO2 in gas and FeO in slag, and temperature. FeO can easily penetrate the MgO grains along grain boundaries and reach those places where graphite flakes are present. Kinetic models of refractory wear are analyzed on the basis of data obtained from actual laser profile measurements. The bricks salvaged from the top cone region at the end of the campaign have been subjected to scanning electron microscope (SEM) and electron probe micro analyzer (EPMA) investigations. The possible cause of wear in top cone region is also the oxidation of carbon in the brick by CO2 gas and direct attack by FeO thrown from the jet impact region.

Reactions of Secondary Phases with Carbon in Magnesia‐Carbon Bricks

Despite the excellent thermochemical properties of magnesia carbon bricks, these exhibit one weak characteristic during their use: their carbothermally induced wear. Carbon has a high affinity to oxygen, which leads to a reaction between magnesia and carbon, forming gaseous products at very low oxygen partial pressures in the surrounding atmosphere. When magnesia carbon material is furthermore applied at negative pressures, the precited carbothermic reduction processes effect an internal decomposition or even degradation of the bricks. Mostly, high‐purity magnesia varieties (MgO ≥ 96 wt%) are used for the production of magnesia carbon bricks because the low‐melting calcium silicate secondary phases in magnesia impair the high‐temperature resistance of these bricks. The fundamental question if and to which extent secondary phases react with carbon and which impact they have on the carbothermally induced wear of bricks has been unsolved so far. The following paper presents which influence the mineral secondary phases, monticellite, merwinite, and belite that are most commonly occurring in magnesia, have on the carbothermally induced wear. The respective studies were conducted by means of thermogravimetric and microstructural analyses. The results of these studies show that monticellite in the MgO–C microstructure brings about an increase in weight loss on account of carbothermic reduction processes. On the contrary, belite and merwinite in the MgO–C structure do not exhibit any negative impact on the thermal stability of the microstructure.

Oxidation behavior and kinetics of Al2O3-SiC-SiO2-C refractories in CO2 atmosphere

Al2O3-SiC-SiO2-C refractories are widely used as blast furnace hearth lining but have low oxidation resistance in the presence of CO2. Carbon composite brick is a newly developed Al2O3-SiC-SiO2-C refractory that may function better in the blast furnace hearth due to improved erosion-resistance and high thermal conductivity. In this study, the oxidation behavior and kinetics of carbon composite brick, carbon brick, and corundum brick were investigated in CO2 atmosphere. The results show the oxidation resistance of carbon composite brick was better than that of carbon brick but worse than that of corundum brick. SiC functions as an antioxidant to play an important role in the oxidation process. For carbon composite brick, the oxidation activation energy was 141.72kJ/mol at the step controlled by the interface reaction and 161.24kJ/mol at the step controlled by gas diffusion. Carbon composite brick exhibits improved thermal conductivity and oxidation resistance relative to carbon brick and corundum brick that should allow improved performance in blast furnace hearth lining.

Mg(OH)2 Nucleation and Growth Parameters Applicable for the Development of MgO‐Based Refractory Castables

MgO is a very attractive raw material for refractory applications. However, its use has been mainly aimed at developing high‐magnesia and magnesia–carbon bricks due to the marked hydration likelihood of this oxide and the related drawbacks (volumetric expansion, crack formation) associated with this transformation. This work aims to evaluate some critical aspects that affect the MgO reaction with water (magnesia source, particle size, concentration of available sites for brucite nucleation, influence of a hydrating additive – acetic acid, and others) during the curing and drying steps of Al2O3–MgO binder‐free refractory castables. The attained experimental results were associated with the boundary nucleation and growth model proposed in the literature. According to the in situ elastic modulus measurements carried out at 110°C, the MgO particle size and reactivity present an important effect on the nucleation and growth of brucite crystals, highlighting that a proper site activation should be induced during the castables' curing process in order to effectively allow the use of magnesia as a binder source for refractories. Faster Mg(OH)2 nuclei generation also helps to minimize further growth of these crystals, leading to a decrease in the samples' porosity and, consequently, a continuous increase in the overall refractory stiffness (E values).

Thermo‐mechanical modelling of cellular ceramic composites by a multiphase approach of porous media

AbstractRefractory materials have a wide range of applications in the steel‐making industry for example as lining of furnaces, oxygen converters or for ladles. Often, magnesia carbon bricks (MgO‐C) are used. These are made of a periclase phase (MgO) with carbon inclusions and pores. In their applications, refractories are subjected to thermal and mechanical loads causing damage. The thermo‐mechanical behaviour of MgO‐C composites and hence their thermal stability could be improved significantly using cellular MgO‐C composites based on carbon foams [1, 2]. The present contribution focuses on the development of a fully coupled phenomenological thermo‐mechanical continuum model based on the theory of porous media (TPM) with a new kinematic coupling of the displacement field of all constituents. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental study on the adsorption and desorption of tritium in the graphite materials for HTR-PM

Tritium behavior in the reactor such as production, diffusion and release are accompanied by their adsorption and desorption in graphite materials, which are essential to the safety of high temperature gas cooled reactor (HTGR). In order to study this important issue, hydrogen instead of tritium is experimentally used in this work and justified viable by theory. By performing multiple sets of comparative experiments, the features of hydrogen adsorption and desorption behavior changing by adsorption temperature and time in typical graphites used in HTR-PM (High Temperature Gas Cooled Reactor – Pebble Bed Module), i.e. reflective layer, fuel element and boron carbon bricks, have been observed and analyzed. Furthermore, the adsorption rates of hydrogen in the three materials as above at different conditions are also given. Based on the experimental results, tritium behavior in the HTR-PM was inferred and estimated, which is significant for the further study on the mechanism of tritium transport.

Comparison of the chemical corrosion resistance of magnesia-based refractories by stainless steelmaking slags under vacuum conditions

This study evaluates commercially available magnesia–chromite, magnesia–carbon and magnesia–doloma bricks for their use in a Vacuum Oxygen Decarburisation ladle. The corrosion behaviour of these bricks by stainless steelmaking slags is, therefore, investigated through crucible tests in a vacuum induction furnace at elevated temperatures (1650 and 1750°C) and low oxygen partial pressures (5.3 and 3.0×10−11atm). The results reveal that magnesia–carbon bricks are severely corroded due to the high dissolution of MgO, while magnesia–chromite and magnesia–doloma refractories exhibit an excellent corrosion resistance. The MgO enrichment in the slag is believed to be the reason of the low wear rate of the MgO–doloma refractories. Rebonded and direct-bonded MgO–chromite refractories show similar corrosion resistance against the slags because of the ‘secondary chromite inactivation’. Decreasing the slag basicity enhances the dissolution of MgO into the slag, thereby increasing the corrosion of the magnesia-based refractories.

Critical Heat Flux of Blast Furnace Hearth in China

The critical heat flux surveys of thirteen Chinese blast furnaces were carried out. The mathematical model of hearth bottom was established and the temperature field was simulated by utilizing the method of inverse problem based on the collected parameters and temperature data. The critical heat flux and dangerous critical heat flux of hearth were defined and analyzed as well as the initial and investigative critical heat flux of hearth, and the influences of thermal conductivity and residual thickness of carbon bricks on critical heat flux were discussed. The relationships between critical heat flux of stave and hearth bricks were also compared. It is found that the dangerous critical heat flux of these blast furnaces ranged from 9.38 to 57 kW/m2. Therefore, there was no uniform critical heat flux of hearth due to the structure design, refractory materials selection, construction quality of hearth and other factors. The heat flux should be lower than the critical heat flux with corresponding thickness of carbon bricks to control the erosion of hearth. The critical heat flux of stave would be much lower than that of hearth bricks with the air gap. However, the critical heat flux of stave should be higher than that of hearth bricks when gas existed between furnace shell and staves.