Silicate bonded silicon carbide refractories have a series of excellent properties such as high strength, good thermal shock resistance, erosion resistance, etc. They are widely used in metallurgical industrial bricks, muffle furnaces, slabs, tiles, crucibles, kiln furnaces, etc. And other places that meet the needs. The mechanical properties of this refractories have been extensively studied, and the corrosion and thermal expansion behavior of such refractories has been compared with nitrides and oxynitrides combined with silicon carbide refractories. However, the effect of adding molybdenum disilicide infiltrant on the mechanical and chemical properties of silicate-bonded silicon carbide refractories has not been reported. This work studied the preparation of silicate-bonded silicon carbide refractories with molybdenum disilicide as infiltrant and studied the effect of infiltrant on modulus of rupture, thermal expansion, and erosion behavior.

experiment. Molybdenum silicide infiltrant An electric furnace using a graphite electrode as a heating element was used for experiments at high temperatures. Commercial silicon carbide powders of different particle sizes, mullite and sillimanite powders, and key infiltrant of disilicide are used as the initial ingredients. The proportion of silicate binder is between 15% and 30% (mass). By pressure molding, the shape of the prepared sample is determined by dipping method to determine the bulk density and porosity of the sample. The modulus of rupture at room temperature was measured by an Instron Universal Tester. The test sample was measured using a rectangular spline (101.6 mm x l9.0 mm x l2.7 mm) D. The mechanical properties of the sample were measured using a three-point bending method with a span of 25 mm and a crosshead loading speed of mmmin. The average of 10 samples was measured to obtain a data.

The coefficient of thermal expansion can be measured at room temperature. Corrosion resistance was studied by dipping experiments. The microstructure was analyzed by SEM, and the phase composition was analyzed using a Siemens X-ray powder diffractometer with diafiltered Cuka rays.

3 Results and discussion The bulk density and porosity are shown in Table 1 and Table 2. It can be seen that the mullite-bonded silicon carbide refractories, when containing 4% centistokes, have a density of 2.42 g-cm -3 increased to 2.71g.cm-3, and porosity decreased from 16% to 10%. Without MoSh, the density and porosity were 2.23 ~ 2.44g.cm-3 and 20% ~ 14%, respectively. between. Obviously, when MSI2 was added, the density increased and the porosity rate dropped significantly.

The room temperature fracture modulus data are listed in Table 1 and Table 2. From the table, it can be seen that the silicon carbide refractories with mullite as the bonding agent are more effective than the silicon carbide bonded silicon carbide refractories. High modulus of rupture. Moreover, the modulus of rupture increases with the increase in the proportion of sillimanite or silica binder, but the increase in fracture modulus does not exceed 25% of the silicate bond. In addition, with the addition of MSl2 The modulus of rupture also increases.

When the addition ratio of mullite was increased from 15% to 30%, the fracture modulus of the refractory material with MSi2 as infiltrant also increased from 32 MPa to 44 MPa. Carbonization of 20% to 25% of silicate binder was added. Silicon refractories are particularly suitable for high temperature applications in the metallurgical industry. From the above results, it can also be seen that the addition of MSi2 infiltrant is very important in order to increase the strength of the silicon carbide refractories.

Table 1 Properties of sillimanite-bonded silicon carbide refractories Sillimanite (mass) Bulk density/(gcm"3) Porosity/% fracture modulus M Table 2 Properties of mullite-bonded silicon carbide refractories Rheology/% (mass) bulk density/(g'cm-3) Porosity modulus/MPa XRD analysis shows that the sample contains mainly SiC, and there are traces of silicate binder phase. MoSh infiltration agent is added because The amount is too small to show on the XRD pattern.

When the osmotic infiltration dose increases, the coefficient of thermal expansion decreases.

For samples not added with MoSb, castables with a rheological and particle size distribution with similar flow values ​​ranging from 4.2xl-6 pumped castables may exhibit different rheological properties, between pseudoplastic and expansive properties. Variety. Therefore, rheological properties are necessary to design pumping castables.

Introduction The pumping technology for refractory castables has been successfully applied to places that are difficult to get in or out of the mixer. This possibility stems from high masonry speeds and minimal material loss.

In this process, special pumps pump materials from the mixer directly into the mold at high flow rates through the tubes. However, pumping refractory castables is a complex process because these dense materials have a large particle size distribution (0.1 to 8000 Lm). In the matrix (small particles + water) and in the aggregate (large particles) have different properties of force.

100 (xm particles are mainly affected by gravity or mass-related forces. Therefore, the coexistence of the two force domains causes the castable to be defined as a two-phase material whose rheological properties are caused by the interaction between large particles and the fluid matrix. Decision.

The rheological pumping process for pumping castables can be divided into three stages: mixing, transport, and forming.

2.1 The first stage of the hybrid pumping process involves the mixing of dry castable powder and water. The force applied at this stage determines the degree of homogeneity, dispersion state, shear curve, and initial heating of the material.

High mixing energy can lead to undesirable heating, which can reduce the potting material's cure time and/or increase the required pump pressure. The mixing energy level is often associated with the total surface area of ​​the castable and/or the expansion behavior in the composition.

2.2 After the transportation materials are mixed, the pipelines are pumped at high flow rates (turbulent flow) and subjected to a strong shear stress in a limited range. Therefore, the pumped castables should exhibit pseudoplasticity, and also due to their presence in the material. With the increase of the flow rate, the shear resistance decreases.

Pseudo-plasticity and ultra-fine particles in the matrix (thus, castables containing lesser amounts of matrix tend to separate.

There are several ways to avoid phase separation. The difference in density between the matrix and the aggregate must be reduced to a minimum, which can be demonstrated by increasing the solid concentration in the former and/or decreasing the SEM image. Large and small grains are SiC. Small white spots surrounded by a silicate bound phase indicate the presence of MSl2. The silicate bound phase is shown as a matrix surrounding the SiC grains. Erosion experiments with MSi2 and MoSh-free refractories have shown that the refractories are resistant to molten lead and zinc, but are easily attacked by sodium sulfate and carbonates. From the above studies, it can be seen that the strength of the silicon carbide refractories containing the MSi2 impregnation agent is greatly increased, and the thermal expansion coefficient is greatly reduced. This material is particularly suitable for use as a high temperature material in the metallurgical industry.

(February 2001)

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