Szczerba, Chemical corrosion of basic refractories by cement kiln materials, Ceram. Serena, M. Sainz, and A. Ceylantekin and C. Petkov, P.
Jones, E. Boydens, B. Blanpain, and P. Wollants, Chemical corrosion mechanisms of magnesia—chromite and chrome-free refractory bricks by copper metal and anode slag, J. Karakus, M. Crites, and M.
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Petkov, L. Pandelaers, P. Jones, and B. Blanpain, Degradation mechanisms and use of refractory linings in copper production processes: a critical review, J. Caley, and R. Drew, Copper matte penetration resistance of basic refractories, Metall. Fine alumina and or silica in cement containing compositions are typically added to help and promote good flow properties. Metal powders, such as silicon or aluminum, are also added as antioxidants to protect the carbon particles from oxidation at high temepratures, to aid in dry-out and to enhance the hot strength of the refractory material [2, 1].
Incorporation of all these additive components, mainly present in the matrix phase, increases the corrosion, oxidation and thermal shock resistance of the trough castables [6, 7]. The main trough is usually designed with a zonal lining, which implies that the composition and properties of the refractories in different zones, namely the slag zone and metal zone, are different due to different corrosive environments. Higher amount of SiC improves the corrosion and thermal shock resistances of the compositions but also enhances the chance of oxidation and corrosion by FeO.
Addition of spinel prevents such effect and provides a higher FeO corrosion resistance . SiC is effective to reduce slag penetration and spinel is effective to improve slag corrosion resistance . In the present work, comparison between sol and cement bonding systems is studied for the Al2O3-SiC-C based trough castable with the addition of spinel. Variation in physical and mechanical properties, phase analysis, corrosion resistance against and microstructural developments were studied with the variation in C and spinel content.
Experimental Procedure: The starting materials used in the study are white tabular alumina WTA of different fractions, alumina fines RA , silicon carbide SiC , graphite C , magnesium aluminate spinel, Al metal powder as anti-oxidant and calcium aluminate cement HAC or silica sol as binder. The details of the raw materials are given in Table 1.
In the present work, a q value of 0. All the raw materials were first dry mixed as per batch composition Table 2 in a Hobart mixer.
SiO2-sol or water was added to the dry mixed batches while mixing in the sol or cement-bonded castable compositions respectively at an amount of volume to weight percent. Mixing was continued thoroughly till proper consistency was attained. The castable cube samples were drilled to make cylindrical hole at the center as shown in Figure 2 and fixed weighed amount slag powders were put into the drilled hole and then the samples were fired at oC for 2 h.
Corroded samples after cooling were cut axially and measured for penetration and wear out. Details of the process used in the study are outlined in the flow diagram, given in Figure 3. Phase analysis was done on the powdered samples taken from matrix part only, for better identification of reaction products even formed in a minute amount and to avoid any interference of the coarse granular phase. Detailed corrosion study was also done on the polished samples of the corroded samples.
There is a gradual decrease in the slope with reducing particle size range and sudden change in the slope of the plot below 0. Similar amount of water and silica sol was used 6 to 6. Increase in spinel or graphite content reduces the content of alumina. Here replacing a higher density material alumina by a lower density one graphite or spinel causes the decrease in the density values. At intermediate temperature, oC, de-hydroxylation of the bond systems occurs for all the compositions resulting in a weight loss and corresponding fall in density.
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But on increasing the temperature to oC, densities again increased, due to sintering of the compositions. Strength study: Strength value, measured as cold crushing strength CCS of both sol and cement bonded compositions are shown in Figure 6 and 7 respectively. Dried strength of cement bonded compositions are higher compared to that of the sol bonded ones due to the strong hydraulic bond formation at room temperature compared to that of the coagulation bonding in sol-gel system .
Deterioration of strength was observed at oC due to breaking of hydraulic bonding in cement containing compositions.
Strength development is poor especially for cement bonding with higher non-oxide content. Higher amount of well distributed fine graphite particles in the matrix might have restricted the bonding and strength development even after firing .
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This effect is less prominent for sol containing compositions may be due to better coating of sol particles over non-oxide components and resulting in better sintering and strength development. No deterioration in strength values were found for the sol containing compositions at oC. The CCS values for sol bonded castables are higher compared to cement bonded ones after sintering because the gel have high surface area and contain finer particles, thus exhibit better sintering . Phase analysis: Phase analysis study of the matrix phases of the fired samples of different compositions show corundum as the major phase with SiC, C, spinel and mullite as the minor phases in both the bonding systems.
Mullite is the reaction product formed at high temperature in the matrix part of the castables due to reaction between silica from sol and fine alumina particles in sol containing compositions and between fume silica and alumina fines in cement-bonded ones. This lime bearing phase was formed due to the reaction between calcium aluminate phases of cement with fume silica present in the matrix part. Corrosion resistance: The rate of corrosion was found to decrease with the increase in the amount of carbon and spinel in the composition, as can be seen from Table 4 and Figure Inherent non-wetting character of carbon helps to avoid adhesion and coating of slag to the castable samples  and high melting point and excellent resistance against chemical attacks of magnesium aluminate spinel [15, 16] help to improve the corrosion resistance.
Here also, sol bonded compositions show better corrosion resistance compared to that of the cement bonded ones. Formation of lower melting lime bearing compound, like anorthite as observed in phase analysis in cement containing compositions results in faster corrosion of the samples and showing poor corrosion resistance of the castables. Microstructural and EDX analysis: The microstructural evolution of the castable samples fired at oC was studied using field emission scanning electron microscopy on representative regions.
The microstructural images are provided with the support of EDX analysis, given in Figure This low magnification photomicrograph shows well compact dense microstructure of the unreacted refractory left side of the photograph but a corroded and porous structure right side of photomicrograph due to the reaction of the sample with the slag. Corroded and reacted portion of the same area is further enlarged in Figure 14, which clearly shows porous structure of the refractory due to the reaction eating away of slag and some chipping of refractory particles, due to loosening of grains caused by corrosion of slag, during polishing and sample preparation.
Elemental analysis confirms the presence of silicon, aluminium, magnesium, calcium and some iron with oxygen and carbon in the porous region. Hence the main components of slag that are reacting with the refractory are silica, calcia and iron oxide. Presence of Au gold in elemental analysis is due to the coating used for microstructural study. Enlarged view of the unreacted refractory portion of sol bonded batch 4 with EDX analysis of a grain marked area in the micrograph is shown in Figure Dense well compact grains with nearly no porosity was observed in the unaffected portion of the castable.
Aluminium was found to be the only prominent element with oxygen and carbon and nearly no trace of any other impurity element phase was observed. In addition, the compressive strength of castables containing obtained aluminous cements increase obviously with the content of CA rising or the curing time increasing. Abstract: Magnesium aluminate spinel specimens with various Al 2 O 3 content were prepared.
Sintering performance and microstructure of different kinds of MgAl 2 O 4 spinel were studied. It is found that the sintering of materials becomes more difficult with the increase in their Al 2 O 3 contents. However, with further increase in the sintering temperature, the corundum dissolves into magnesium aluminate spinel above The precipitation and solid solution of corundum hinder the sintering of materials. In alumina-rich spinel, if the content of Al 2 O 3 in alumina-rich spinel materials is more and the content of CA 6 is also more.
Effect of spinel content on the properties of Al2O3–SiC–C based trough castable
At the same time CA 6 crystal is bigger in the alumina-rich spinel. Abstract: Cements have been used to encapsulate low and intermediate level radioactive wastes. Here, phosphate-modified calcium aluminate CAP cement is explored as an encapsulant for strontium radioanuclide-containing wastes.
Electron microscopy indicates strontium chloride, used in place of strontium radionuclides, increases porosity in CAP possibly due to increased viscosity of CAP cement during mixing. Added To Cart.
Related Effect of spinel content on the properties of magnesia–spinel composite refractory
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