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Introduction to the chemical properties and usage of micro silicon powder


Microsilica is also called silica fume or agglomerated silica fume. English is Microsilica or Silica fume. When ferroalloy is used to smelt ferrosilicon and industrial silicon (metal silicon), a large amount of highly volatile SiO2 and Si gas is produced in the ore furnace, and the gas is quickly oxidized and condensed and precipitated after being discharged. It is a by-product of large-scale industrial smelting. The whole process needs to be recycled by dust-removing environmental protection equipment. Because of its lighter quality, it needs to be encrypted with encryption equipment.

First, the chemical properties of micro silicon powder:

1. Silica fume: Appearance is gray or off-white powder, and the refractoriness is >1600 °C. Volume weight: 1600~1700kg/m3. The chemical composition of silica fume is shown in the following table: (The various chemical compositions of silica fume are different and only the following are listed.)

2. Fineness of silica fume: The fineness of silica fume is less than 1 μm, accounting for more than 80%, the average particle size is 0.1-0.3 μm, and the specific surface area is 20-28 m2/g. Its fineness and specific surface area are about 80 to 100 times that of cement and 50 to 70 times that of fly ash.

3, particle morphology and mineral phase structure: in the formation process of silica fume, due to the surface tension in the process of phase change, the formation of amorphous phase spherical particles, and the surface is relatively smooth, and some are multiple circles Agglomerates in which the ball particles stick together. It is a volcanic ash substance with a large specific surface area and high activity. A material containing silica fume, a tiny spheroid can act as a lubricant.

Second, the use of micro-silica powder:

Addition method:

The silica fume concrete and castables shall be constructed and matched by the laboratory. Construction in strict accordance with the mix ratio. In the mixing of silica fume concrete, the silica fume should be added to the mixer immediately after the aggregate is charged. There are two ways to join:

1. Inject the aggregate, then add the silica fume and dry mix of the cement, then add water and other admixtures.

2. Inject coarse aggregate +75% water + silica fume + 50% fine aggregate, stir for 15-30 seconds, then put in cement + admixture + 50% fine aggregate + 25% water, stir until uniform. The mixing time is 20-25% or 50-60 seconds longer than ordinary concrete. Never add silicon powder to the concrete that has been mixed.

Construction method:

There is no significant difference between the construction methods of silica fume concrete and ordinary concrete, but it is necessary to organize and vibrate well in construction. The early strength of the silica fume concrete will make the final setting time advance, and should pay attention when the surface is wiped; at the same time, the addition of silica fume will increase the viscosity of the concrete and greatly reduce the bleeding, making the surface slightly difficult.

construction safety:

The construction safety of silica fume concrete should be strictly in accordance with the relevant national construction specifications of concrete engineering. However, due to the lighter silica fume, it is strictly forbidden to throw materials at high altitude to prevent the flying of silica fume.

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