Influence of the content of silica fume on the properties of castables

At present, silica fume is commonly used in low cement castables to reduce product water addition, reduce porosity and increase product strength. Since silica fume is an industrial by-product produced in the smelting process, the content of silica fume and the impurities contained therein are uncertain, and the presence of impurities has a significant influence on the production performance of the castable.

Through the test description:

The main raw materials for the test are brown corundum, white corundum, silicon carbide, spherical asphalt, a alumina powder, silica fume, pure calcium aluminate cement, and the like. The above are the main refractory materials.

Based on a low cement castable of Al2O3, SiC and C, according to the design comparison test, the ingredients are poured into a cement mortar mixer, and then mixed with clean tap water, and stirred for about 3 minutes until the mixture is plastic. First, measure the flow value of the castable under the same amount of water by using a cone mold with a height of 50 mm, a lower mouth diameter of 100 mm and an upper mouth diameter of 70 mm, and place the cone mold on the vibrating table to fill the castable. After vibrating for 15 s at 0.5 mm amplitude, the diameter of the circle is measured with a micrometer. Secondly, the physical properties under the same flow value are measured by pouring the mixed mixture into 40 mm & time; 40 mm & time; 160 mm steel mold, in the cement mortar shaking table After shaking for 1 min, it is demolded after curing, cured for 24 h, dried at 110 ° C for 24 h, and then tested in air at 110 ° C & time; 24 h, 1100 ° C & times; 3 h, 1450 ° C & times; 3 h heat treatment after normal temperature bending , pressure resistance, line change rate and 1450 ° C & times; 3h high temperature bending strength.

Effect of different content of silica fume on material flow properties

Comparison of the effects of three kinds of silica fume on material flow values under the same amount of water added. It can be seen that the content of silica fume has a direct influence on the fluidity of the material, and the flow value increases with the increase of the silica fume content under the same water addition amount. Since silica fume contains a large amount of active ultrafine silicon micropowder, it is considered that these active ultrafine silicon micropowders form a colloid in water, and the colloidal particles adsorb a dispersant around them to form a solvent layer, thereby increasing the fluidity of the castable and reducing The amount of water used has improved its liquidity.

Effect of different content of silica fume on physical properties of materials

The samples are in the air at 110 ° C & times; 24 h, 1100 ° C & times; 3 h, 1450 ° C & times; 3h heat treatment after the normal temperature flexural and compressive strength diagram, we can know that the content of silica fume has a certain resistance to the room temperature flexural strength The influence, especially at 110 ° C and 1100 ° C, increases the flexural strength with the increase of silica fume grade, and the compressive strength of the sample after treatment with 110 ° C, 1100 ° C and 1450 ° C is also with silicon. The gray grade rises and rises.

Since silica fume has a direct influence on the fluidity of the castable, the high content of silica fume is beneficial to the increase of the fluidity of the material. Under the premise of the same flow value, it will inevitably lead to an increase in the amount of water added with a low content of siliceous castable. Excessively high water content leads to an increase in the porosity of the castable after drying, the porosity of the sample increases, and the bulk density decreases, resulting in a decrease in the physical strength of the product. To ensure the same flow value, the material is required to be added. The water volume and the bulk density of the sample after heat treatment at 1100 °C, under the premise of ensuring the same flow value, the water addition amount of the castable increases with the decrease of the silica ash content, and the bulk density also decreases.

Since silica fume contains active ultrafine silicon micropowder, and the particles are fine, the specific surface area is large (20-28 m2/g), the activity is high, and the solid phase sintering reaction is relatively easy to occur at medium and high temperature and in the high alumina refractory. Al2O3 generates a mullite phase, which increases the physical strength of the product. At the same time, the low content of silica in the low content of silica fume, the low melting point phase produced by the material reduces the high temperature flexural strength of the material.

Through the above experiments, we can know:

The content of silica fume has a direct influence on the fluidity of the castable. Under the premise of consistent water addition, the higher the SiO2 content, the greater the flow value. Due to the presence of the active ultrafine silicon micropowder in the silica fume, a colloid is formed in the water, and the colloidal particles adsorb the dispersant around it to form a solvent layer, which increases the fluidity of the castable, reduces the water consumption, and improves the pouring. The fluidity of the material.

The main physical properties of the castable increase with increasing silica ash content, as higher levels of silica fume provide superior flow. Therefore, in the case of ensuring the same flow value, the higher content of silica fume requires less water, and the reduction of water addition is beneficial to the reduction of the porosity of the product. At the same time, a higher amount of active ultrafine silicon micropowder in high content of silica fume can more easily undergo solid phase sintering reaction at medium and high temperatures, and mullite phase is formed with Al2O3 in high alumina refractories to improve the physical properties of the product. strength.

Remarks: The above information is about “the effect of the level of silica fume on the properties of castables”, provided by Zibo Yuneng Kiln Co., Ltd. (http://test1.zbyuneng.com).