As early as the 1920s, people had the actual use of refractory concrete. But it was not until the late 1950s that microsilica was used in products. The standard combination of low-cement pouring compound oxidation system is composed by the calcium aluminate cement, silicon powder and alumina calcined poured dispersant with fine grinding.
At the base of bonding system, people can conduct a variety of improvements and increasing. Because particles of silica powder in the combination system is usually the smallest and its specific surface area is about 20m2 / g, therefore its surface characteristics and impurity content determines the pouring material placement and condensation performance. In some mixtures, microsilica’s influence on whole particle surface area is more than 50%.
When the microsilica aluminum pouring material containing is heated, the complex combination of phase will react with calcium ternary low cement and ultra-pouring of the cement content of the compound of the reaction. It is found in low cement containing 5% manganese powder and 7% cement pouring compound that generated below 1200 there is anorthite. When above 1200 , anorthite liquid is found. Ultra-low cement containing 6% silica fume and 1.5% of cement pouring compound found in the 1300 ° C mullite (A3S2). When microsilica increase to 3%, did not produce mullite.
Microsilica at least plays dual roles in the fresh pouring compound. Once the appropriate dispersion, silica powder particle size is small, an important performance is to reduce the refractory pouring cement content of the compound. Provincetown Manchester and patent, by using the particle size gradually carefully graded until the particle size of submicron particles, refractory pouring cement content of the compound can be reduced to about 1%. The application of ultra-fine powder is based on the assumption that the pouring compound in the standard particle size distribution, its density is in the construction process of filling intergranular voids of the excess moisture is limited. Fill these voids by progressively finer particles, which will replace the water. The rest of the lag body of porous hydrated cement fills. It is based on this principle, which leads to low water consumption, material technology of high-density placement applications. The microsilica pouring material after calcination at 1000 , pouring the compound of the porosity rate of about 20-30% to 8-16% decline in temperature experienced by the mechanical strength of ordinary pouring turned to become a steady increase in. Thus, the beneficial effects of the silica powder in the compound of pouring in the theory and practice to be fully established. Close packing can be achieved, the amount of boron powder cement can reduce large. Resulting in 2.5-1% of the lime content of cement content is now classified as low-cement pouring material, the lime content of 1-0.2% for ultra-low cement pouring material.
The effect of super-filler in the refractory pouring compound is not the only function that microsilica can play in the pouring compound. Research shows that a certain percentage of silica fumes react with cement, in addition to generate the CAH and AH of hydrated cement, but also generate CASH phase. CASH-phase has nature of the zeolite. The amount of these hydration products depends on the amount of the silica powder. In addition, people also found that adding microsilica can make the distribution apertured towards the small hole. It is not only a chemical reaction but also a physical reaction. In the heating process, CASH is converted to CAS2. Then the CAS2 is converted to cristobalite or quartz. The excess silica powder can be crystallized.Source:http://www.mhcmp.com
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