Magnesia-spinel Bricks Research Articles

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

AbstractMagnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium‐free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite‐ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron‐size whisker network bond domination in their matrix. Such a whisker‐network bond renders the material a successful eco‐friendly alternative to magnesia–chrome refractory.

Design of Magnesia–Spinel Bricks for Improved Coating Adherence in Cement Rotary Kilns

It is well known that doloma bricks present better coating adherence than magnesia–spinel bricks when applied in cement rotary kilns, which is related to the different coating formation mechanism. The coating has an essential role in prolonged operation by protecting the refractory lining; thus, it is important to improve its adherence on magnesia–spinel refractories. The objective of this investigation is to study different compositions of magnesia–spinel bricks, achieved by varying additives used (calcined alumina, limestone, hematite and zirconia) and firing temperature (1500 °C and 1700 °C), to enhance the coating adherence measured by the sandwich test. The results have pointed out that the use of higher firing temperature contributes positively to physical adherence due to well-sintered refractory structure and elevated permeability, attaining coating strength superior to 2 MPa. For the chemical adherence, the addition of 2 wt.% of limestone increased the coating strength to 3 MPa, but resulted in a drop in hot properties. In this context, the most suitable approach to improve adherence of clinker coating and maintain hot properties in suitable levels is to increase the firing temperature.

Qualitative and Quantitative Coating Tests: A Comparison in Magnesia–Spinel Refractory Bricks

In cement processing, which involves the production of clinker in rotary kilns, the main refractories used in the transition and burning zones are magnesia–spinel bricks. These bricks present suitable chemical and thermomechanical properties, not to mention that they can be easily landfilled. Among the main wear mechanisms of these bricks in the kiln, the infiltration of alkaline salts is noteworthy and occurs through the open pores of the refractory. In this way, the coating—a clinker layer adhered to the brick surface—appears as a protection mechanism of the lining against infiltration. Thus, the objective of this investigation is to run a qualitative coating test based on the contact method, and quantitative coating test based on the sandwich method to check the suitability of the methodologies and to evaluate the coating adherence on two different magnesia–spinel bricks. It was possible to distinguish the superior adherence ability of brick B in both coatings due to the higher porosity and the presence of nonreacted ZrO2. Despite the similarity between the test results, the quantitative sandwich-coating test is preferable because it does not depend on subjective analysis.

Investigation of microstructure-property relantionships of magnesia-hercynite refractory composites by a refined digital image correlation technique

Industrial magnesia-spinel bricks destined for thermal shock applications often show more flexibility and improved crack growth resistance. Components from the spinel structure group are usually added to promote microcracking coming from thermal expansion mismatch. This leads to the development of toughening mechanisms that are very effective in improving the crack propagation resistance.Magnesia-hercynite composites were investigated in order to highlight their fracture process, with regard to their microstructure, by using Digital Image Correlation (DIC). The direct measurement of displacement fields between digital images of the reference state and the deformed one has provided valuable information on material deformation during loading. The aim of this work was to investigate the fracture behaviour of refractories through the coupling of the Wedge Splitting Test (WST) and DIC. By using a refined DIC process transformation taking into account a discontinuity of displacement, called 2P-DIC, a more effective characterisation of the fracture behaviour was achieved.

Qualitative and quantitative investigation of post–mortem cement refractory: The case of magnesia–spinel bricks

Post–mortem investigation of damaged refractory bricks remains an essential source of information to predict the reactions responsible for corrosion phenomena. In this context, the corrosion of two post–mortem magnesia spinel bricks, taking from the sintering zone of a rotary cement kiln, was investigated qualitatively and quantitatively. The results of the X-rays diffraction, combined with the Rietveld method supported by heating microscope and elemental analysis, revealed that the sulphur and the high temperature (>1600°C) were the main factors which caused the degradation of the refractory matrix of magnesia–spinel bricks by the infiltrated mineralogical phases of the clinker melt. In fact, the appearance of the merwinite C3MS2, the akremanite Ca2Mg (SiO7), mayenite C12A7 and Yeelimite CAS̅ was the warning of the refractory matrix corrosion. Also, the deterioration rate of MgAl2O4 was more important in the hottest zone and it was deeper in brick 2 than in brick 1. As a result, the elasticity loss in brick 2 was more severe than in brick 1, which explains the length difference after a short duration of service (40 days).

Life Cycle Assessment and Life Cycle Cost Analysis of Magnesia Spinel Brick Production

Sustainable use of natural resources in the production of construction materials has become a necessity both in Europe and Turkey. Construction products in Europe should have European Conformity (CE) and Environmental Product Declaration (EPD), an independently verified and registered document in line with the European standard EN 15804. An EPD certificate can be created by performing a Life Cycle Assessment (LCA) study. In this particular work, an LCA study was carried out for a refractory brick production for environmental assessment. In addition to the LCA, the Life Cycle Cost (LCC) analysis was also applied for economic assessment. Firstly, a cradle-to-gate LCA was performed for one ton of magnesia spinel refractory brick. The CML IA method included in the licensed SimaPro 8.0.1 software was chosen to calculate impact categories (namely, abiotic depletion, global warming potential, acidification potential, eutrophication potential, human toxicity, ecotoxicity, ozone depletion potential, and photochemical oxidation potential). The LCC analysis was performed by developing a cost model for internal and external cost categories within the software. The results were supported by a sensitivity analysis. According to the results, the production of raw materials and the firing process in the magnesia spinel brick production were found to have several negative effects on the environment and were costly.

Influence of magnesia in the infiltration of magnesia-spinel refractory bricks by different clinkers

In cement production, which involves the production of cement clinker in rotary kilns, the main refractories used are magnesia-spinel bricks. These bricks may suffer infiltration by the clinker liquid phase, resulting in the corrosion of the spinel and the formation of low refractoriness mineralogical phases, such as the Q phase (C 20 A 13 M 3 S 3 ), which compromises refractory performance. Thus, the aim of this work is to correlate the infiltration resistance of magnesia-spinel bricks made from different grades of magnesia by clinker collected in three different cement plants (A, B and C). The purity of magnesia, besides its physical properties, strongly influences the proper ties and the infiltration resistance of magnesia-spinel bricks; as such the use of high grade magnesia is essential for producing high performance refractories.

OS1329-351 非線形弾性挙動を有するマグネシア・スピネル質れんがのR曲線評価

OS1329-351 非線形弾性挙動を有するマグネシア・スピネル質れんがのR曲線評価

The Development of Free of Chrome of Basic Refractory Materials for Cement Kiln and its Applications in Engineering

This paper introduces the domestic and international evolution of refractory for cement rotary kiln and the situation of development for basic refractory. Also it introduces the usage and advantages and disadvantages of the high alumina brick, magnesia chrome brick, dolomite brick, magnesia spinel brick, magnesia zirconia brick. Refractory for cement kiln develops towards the direction of free of chromium, and it points out the development prospect of re-bonded magnesium zirconium refractory material .

Optimizing Performance of Magnesia-Spinel Brick Used at Cement Rotary Kiln

Using high pure magnesia and magnesia-spinel as the main raw material, keeping the same quantity of spinel, specimens were made with different spinel size distribution (≤0.044mm, 1-0mm, 2-1mm, 3-2mm and 3-1mm). Dextrin and brine are the binder. Specimens were dried at the temperature of 110°C for 24 hours, sintered at the temperature of 1680°C holding 8 hours in a tunnel kiln. The properties and microstructure of the specimens were analyzed. The results are shown that the addition of spinel with grain size of 3-1mm improves sintering of magnesia-spinel brick, with the thermal shock resistance reaching 18 cycles, the cold crushing strength reaching 54 MPa, improving the comprehensive performance of the magnesia-spinel brick.

Phase Relations in the MgO-Rich Region of the System MgO-Fe2O3

Fe2O3-added magnesia-spinel brick, in replacing magnesia-chrome brick, has been recently used as a basic refractory for the burning zone in cement rotary kiln. According to the system MgO-Fe2O3 phase diagram, the phase change and the separation with temperature fluctuation in the kiln may damage the microstructure of the magnesia-spinel brick, which leads to the quality deterioration. The MgO-rich region of this system has been investigated by using a high-temperature X-ray diffraction (XRD) apparatus in air. The change from MgOss to MgO accompanied by the exsolution of Fe3+ occurs possibly around 1010°C based on the phase diagram. However, MgOss was found to still exist at room temperature in this study. Also, it was proved that the formation temperature of the solid-solution including 5-20mass%Fe2O3 shifted to a higher temperature compared to the conventional result. The unknown edge of the boundary line between MgOss and MgOss+MgFe2O4 on the MgO-Fe2O3 composition line was estimated in the system MgO-FeO-Fe2O3 phase diagram by considering the oxygen partial pressure of the atmosphere as 0.1MPa. The lattice constant of MgOss was altered by the change of the electronic spin state of Fe3+ from low-spin state to high-spin state around 1100°C on a temperature-elevated process, together with the solution quantity of Fe3+ and heating temperature. Furthermore, the crystal strain of MgOss and MgFe2O4 increased remarkably upon this spin alternation. However, the reverse-change of the spin state could not be recognized on a cooling process, then MgOss was considered to be metastable due to this slow reverse-change. The existence of MgOss single phase in the system MgO-Fe2O3 became clear under expanded conditions, which certainly contributes to the realization of the long life time of magnesia-spinel bricks.

The “Direct Bond” in Magnesia Chromite and Magnesia Spinel Refractories

The microstructures of several commercial refractory bricks have been characterized using scanning and transmission electron microscopy. The “direct bond” is shown to be direct at the level of resolution attainable (∼0.3 nm), and a significant number of such direct contacts occur between non‐silicate phases in the microstructures of magnesia‐chromite bricks. However, attempts to examine the direct bond in magnesia‐spinel bricks were unsuccessful due to nonuniform ion thinning of TEM specimens.

Chemical Resistance of Refractories to AI and AI‐Mg Alloys

The chemistry of the reaction between molten aluminum alloys and some refractory oxides is discussed. High‐alumina brick containing 85, 94, and 99% Al2O3 periclase brick, and magnesia spinel brick were immersed for 48 hours in three aluminum alloys containing 0, 2.4, and 7.7% magnesium, respectively. All brick were discolored, although most of the discoloration disappeared after reheating at 1000°C in an oxidizing atmosphere. Only the 85 and 94% brick, which contained silica, showed permanently darkened reaction rims. X‐ray diffraction analysis of these darkened areas showed that the alloy containing 7.7% magnesium caused periclase formation in the rim whereas the alloy containing 2.4% magnesium produced spinel. Commercial aluminum caused only a decrease in the mullite content of the darkened area. Magnesia spinel and periclase were unaffected by all the alloys tested.