Magnesia Spinel Research Articles

Deoxidizing effect on the low-alloyed steel's nonmetallic inclusion's compositions

The investigating results are given in the article for the deoxidizing effect on the non-metallic inclusion compositions tubes steels melted in the vacuum induction furnaces with periclase lining. The oxygen thermodynamic activity was calculated for the lanthanum, cerium, alumina and yttrium melts during four heats. The magnesia spinel inclusion's formation condition was evaluated depending on the deoxidizer's used and on the deoxidizing depth. It was shown how the reduced alumina concentration during the steel ladle treatment governs the non-metal inclusions' compositions and on the possibility of their modification during the commercial tubes steels melting.

Regulation of Ash Fusibility Characteristics for High-Ash-Fusion-Temperature Coal by Bean Straw Addition

The effects of bean straw (BS) on ash fusion behaviors of coals (Jiaozuo (JZ) and Zaozhuang (ZZ)) with high ash fusion temperature (AFT) and the regulating mechanism were investigated from the perspectives of ash chemical composition and mineralogical property. The results showed that the AFT of JZ ash mixture decreased as the BS ash mass ratio increased, while the AFT of the ZZ ash mixture decreased rapidly (0–12%) and then increased slowly (>12%). The existence form of Al2O3 and SiO2 was converted from high-melting-point (high-MP) mullite into low-melting-point (low-MP) aluminosilicates and their eutectics with BS ash addition, leading to a decrease in AFT. With increasing BS ash ratio, the major mineral reducing the AFT was changed from feldspar into leucite. Magnesia spinel had a weaker effect on improving the AFT than that of mullite or quartz, because of their different molecular structures. The experimental ash samples were divided into three categories, based on the total contents of SiO2 and Al2O...

Determination of the fracture behaviour of MgO-refractories using multi-cycle wedge splitting test and digital image correlation

Refractories with reduced brittleness show a pronounced deviation from linear elastic behaviour and an enhanced thermal shock resistance. This paper aims to study the influence of microstructure on the fracture behaviour of magnesia refractories. The wedge splitting test(WST), which enables stable crack propagation for quasi-brittle materials, was used to identify the fracture behaviour and evaluate the energy dissipation. The evaluation of the crack lengths of the magnesia and magnesia spinel materials during the entire cyclic WST is based on the localized strain evaluated using the digital image correlation (DIC). A significant fracture process zone develops in the magnesia spinel material. The relationship between the dissipated energy and the actual crack length, which was used to characterize the crack growth resistance, was determined. The refractory materials that showed reduced brittleness consume a small amount of energy for fracture initiation but a large amount of energy for further crack propagation.

Modelling and inverse investigation of the fracture process for a magnesia spinel refractory using a heterogeneous continuum model

The microcrack network that develops during the cooling stage of magnesia spinel refractories production process contributes to its heterogeneity. To simulate the fracture process of a magnesia spinel refractory subjected to a wedge splitting test, a heterogeneous continuum model with random distribution of the properties was developed. The tortuous crack path and fracture process development were investigated numerically and compared to experimental digital image correlation observation. Bilinear strain softening curves were used to depict the fracture behaviour of the refractories. With an inverse identification approach, the fracture parameters including tensile strength, ultimate displacement, and total specific fracture energy were obtained. The method is the basis for a realistic simulation of crack propagation in refractories used for industrial applications.

Observation and quantification of the fracture process zone for two magnesia refractories with different brittleness

In this paper, the formation of the fracture process zone (FPZ) of industrially produced magnesia spinel and magnesia refractories was analysed using digital image correlation (DIC). Compared to pure magnesia materials, the magnesia spinel materials exhibited a higher amount of microcracks, causing a larger FPZ. A critical displacement, where the cohesive stress between the crack faces decreases to zero, is determined by analysing the development of the localized zone. Critical displacement determined from the changes of the FPZ width and length is used to determine the onset of macro-cracking and locate the crack tip. The development of the fracture process zone for a magnesia spinel initiates before reaching the maximum load, and the onset of the macro-crack is in the post-peak region. The FPZ size increases until the formation of a macro-crack takes place, but decreases afterwards. For the magnesia refractory, no pronounced FPZ could be detected.

Development Concepts for Porous Periclase MgO

The repair of the lining in the sinter zone of the rotary kilns is needy on the constant, single sided exploit on the refractory of high temperatures (1650-1700°C) and the active loads developing during rotation of the kiln. The interrupted factors include changes in temperature and gas atmosphere, linked with the displacement of the material being fired across the surface of the lining. A new age group of porous plugs reduces the require for cleaning via oxygen lancing, improves safety and increases in commission life. Refractory mixes based on low cement or ultra low cement, high technology castables put in to the good performance. The experimental linings made from Periclase Spinel products undergo double testing in the mostbadly wearable (least heated) part of the sinter zone of one of the 90-m rotary kilns effective on the burning of caustic dust.

Thermal shock resistance of magnesia spinel refractories—Investigation with the concept of configurational forces

Thermal shock resistance of magnesia spinel refractories—Investigation with the concept of configurational forces

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.

Thermal shock resistance of magnesia spinel refractories—Investigation with the concept of configurational forces

In magnesia-spinel refractories, spinel inclusions are embedded in a magnesia matrix in order to increase the thermal shock resistance by micro-crack toughening. The paper investigates damage evolution in the material during the cooling at the end of the production process by a sophisticated numerical analysis. After a stress-strain analysis on a large representative volume element, the development of the damage zone between spinel grains is simulated with the concrete damaged plasticity model of ABAQUS. Application of the concept of configurational forces allows the physically correct determination of the driving force for cracks in the elastic quasi-plastic matrix material. The results demonstrate that inherent matrix cracks are unable to grow during the cooling, but they strongly influence the initiation and development of the damage zone. The pronounced damage initiation, in combination with the low crack driving force, is the main reason for the good thermal shock resistance of magnesia spinel refractories.

Processing of High‐Density Magnesia Spinel Electro‐Conducting Ceramic Composite and its Oxidation at 1400°C

Dense conductive ceramic composites of MgAl2O4 and MoSi2 were processed using combustion synthesis under‐load methodology. The starting reactants were blends of MoO3, SiO2, MgO, and Al powders. The study revealed that to obtain dense composite with homogeneous microstructure, 30 wt. % of MoSi2, 18.5 μm Al average particle size, and 175 MPa load are required. The produced dense composite was found to have a low apparent porosity (<1.0 vol. %), moderate density 4.61 g/cm3, and low electrical resistivity 0.3 Ωcm. The dense composite exhibited excellent thermodynamic stability between its phases at 1400°C in open atmosphere.

Simulation of micro-crack formation in a magnesia spinel refractory during the production process

Simulation of micro-crack formation in a magnesia spinel refractory during the production process

Simulation of micro-crack formation in a magnesia spinel refractory during the production process

Refractory brittleness is often reduced by the introduction of micro-cracks during the production process. Using the finite element method, crack initiation and formation in a magnesia-spinel refractory during the cooling stage of the firing process are simulated in a 2D representative volume element. The microstructure is described by a random spatial distribution of spinel and magnesia grains surrounded by a magnesia matrix. The grain size distribution was chosen according to the Dinger–Funk equation. Crack formation due to a thermal misfit between the magnesia and spinel phases was evaluated using the concrete damaged plasticity model in ABAQUS. After cooling, the model displayed reduced brittleness and a crack pattern typical of this type of material. The obtained mechanical properties from the subsequently simulated tensile test were compared with literature values. The simulation provided reasonable values and is capable of reproducing micro-cracking in the presented refractory.

Characterization of the Mechanical Behavior of Magnesia Spinel Refractories Using Image Correlation

The improvement in thermal shock resistance of refractory materials is among the crucial properties that interest researchers and industrials. The “flexibility” in terms of large strain‐to‐rupture is, up to now, an important parameter to develop such characteristic. This can be obtained by generating a network of microcracks within the microstructure of the material under mechanical solicitations. As an outcome, the mechanical behavior can vary from fragile to a large nonlinear one depending on the degree of microcracking present inside the material. In fact, this nonlinear behavior of ceramics related to their microstructure is behind the possibility to enhance the level of strain‐to‐rupture for a better accommodation to the high level of strain induced by thermal shock solicitations. This study is devoted to apply digital imaging correlation method to support mechanical behavior analysis for the evaluation of the thermal shock ability of refractory materials. In this paper, mechanical characterization of magnesia spinel materials has been carried out using different experimental tests. These nonlinear materials are characterized by a mechanical behavior strongly dependent on their microstructure.

Analysis of the parameters affecting energy consumption of a rotary kiln in cement industry

In this study, the effects of refractory bricks and formation of anzast layer on the specific energy consumption of a rotary kiln are investigated. Thermodynamic analysis of the kiln is performed to achieve effective and efficient energy management scheme. Actual data, which are taken from a cement plant located in Gaziantep, Turkey, are used in numerical calculations to obtain energy balance for the system. It is calculated that 12.5 MW of energy is lost from the surface of the kiln which accounts for the 11.3% of the total energy input to the unit. The specific energy consumption for clinker production is determined to be 3735.45 kJ/kg clinker. The formation of anzast layer and the use of high quality magnesia spinel and high alumina refractory bricks provide 7.27% reduction in energy consumption corresponding to a saving of 271.78 MJ per ton of clinker production. It is recognized that the anzast layer has an important role for durability of the refractory bricks and heat transfer out of the kiln. The applications prevent the emission of 1614.48 tons of CO2 per year to the atmosphere.

An investigation on mechanical properties of Alumina–Zirconia–Magnesia spinel composite ceramics fabricated by gel-casting using solution combustion synthesized powder

Addition of spinel (MgAl2O4) to Al2O3–ZrO2 composite inhibits alumina grain growth and produces phase boundaries that leads to formation of a ceramic matrix composite with special mechanical properties such as high temperature superplastic deformation. However, the room temperature mechanical properties of Alumina–zirconia–magnesia spinel composite (AZM) such as fracture toughness were rarely investigated by researchers. In this research the AZM nanocomposite powders were synthesized via the solution combustion method. The dense AZM composite samples were fabricated through gelcasting process. Phase analysis studies were performed on both powder and sintered samples and the effects of spinel and zirconia contents on mechanical properties as well as microstructure of AZM composite samples were investigated. The maximum Vickers hardness (18.83±1.86GPa) and flexural strength (563.74±23.38MPa) were achieved in the sample with 10vol% spinel and 10vol% zirconia. The sample with 10vol% spinel and 20vol% zirconia had the maximum fracture toughness (6.67±0.81MPa√m).

Service characteristics of granular periclase–spinel vibration castables for the production of melting crucibles

Granular periclase–spinel vibration castables are studied. The range of their service characteristics (vibrating activity not less than 3 h) is determined depending on the type of dispersant: flow is 80–190% at 4.5–6.2% castable moisture for polyethyleneglycol dispersant, 80–180% at 5.2–6.5% castable moisture for polycarboxylic acid dispersant, and 80–190% at 5.5–7.0% castable moisture for polyelectrolyte dispersant. The range of service characteristics is assessed taking into account quality of the effective (melting) crucible surface. The studies have allowed the minimization of possible rejects during vibration casting and the production of high-refractory crucibles with smooth surface without defects to be used for induction melting of oxidation- and heat-resistant alloys.

New periclase-magnesium aluminate spinel refractories from sintered high-purity dead burned magnesite and new various presynthesized spinel-based compositions. II. Compositional variation between coexisting spinel, periclase, and Ca-silicate and Ca-aluminate phases in magnesia spinel refractories and in their spinel-based precursors

The chemistry and distribution of phases formed in a set of six laboratory-prepared magnesia-magnesium aluminate spinel ceramics and in three of their precursor spinel-based compositions, sintered at 1600°C and 1760°C respectively, are examined and compared. The evaluation of the results is the basis for the industry design of magnesia spinel refractories for new advanced applications. In each type of the materials, the spinel phases formed under their firing temperatures seem to have a strong preference for the normal structure. Cracked and noncracked domains in periclase crystals from spinel-based compositions is probably facilitated by differences in the thermal expansion coefficient of periclase crystals having domains differing in their Al2O3 contents. Periclase and spinel mixtures at lower temperatures (1600°C) involved reactions leading to the formation of different periclase s.s and spinel s.s, which depart clearly from equilibrium assemblages. Minor amounts of stoichiometric Ca-silicate and Ca-aluminate phases were formed in all materials.

Strength Behavior of Magnesia‐Based Refractories after Thermal Cycling

The thermal shock resistance of four commercially available magnesia‐based refractory bricks mainly used in furnace linings were investigated. Thermal stability of the bricks was tested using the water‐quench method. The experimental damage was characterised by visual inspection and determining some residual physical and mechanical properties. Cracks were observed after thermal cycling resulting in loss of strength and materials degradation. The results show that thermal stability of magnesia‐based refractories depends strongly on their chemical composition. The addition of chrome and spinel improved the thermal stability of magnesia bricks with magnesia–spinel (MgAl2O4) having better thermal stability than the magnesia–chrome bricks.

New periclase-spinel refractories from densely sintered high purity magnesite and new synthetic compositions based on spinel. Part 1. Study of mineral composition, microstructure, thermal expansion, and ultimate strength in compression

Six specimens of magnesia-spinel material are made under laboratory conditions. Specimens are prepared at 1600°C from sintered magnesite and three different compositions based on spinel, previously synthesized at 1760 °C. Sintered magnesite and synthesized spinel properties are provided. Raw material properties in relation to different spinel content within them, apparent density, additions introduced, and also their effect on final product, are shown. Three forms of final product contain 8 – 11 wt.% Al2O3, and the rest contain from 19 – 21 wt.% Al2O3. Photographs taken in a scanning electron microscope, and results of microstructural analysis of raw material and final product, point to formation of direct periclase–periclase and periclase–spinel bonds, and also secondary calcium aluminate and calcium silicate phases. Secondary spinel is detected in the form of a solution within periclase, and also at grain boundaries within magnesia-spinel refractories. On the basis of petrographic criteria (mineral composition, microstructure), and also linear thermal expansion coefficient (LTEC) and ultimate strength in compression for final materials, the authors of this article propose a most suitable material with respect to quality for testing in high-temperature branches of industry.