What Is Silica Fume?

Silicon fume (Microsilica or Silica Fume), also called micro-silica fume, scientific name "silica ash", is an industrial electric furnace in the process of high-temperature melting of industrial silicon and ferrosilicon. Made. The scientific name "silica ash", Microsilica or Silica Fume, is an industrial electric furnace that collects and processes the fume and dust that escape with the exhaust gas through a special capture device during the high temperature melting of industrial silicon and ferrosilicon. In the escaping soot, the SiO2 content accounts for about 90% of the total soot. The particle size is very small, and the average particle size is almost nanometer level, so it is called silicon powder.

Silicon powder

For the design of the mix ratio of silica fume concrete, it is mainly based on the design requirements to determine the blending method of silica fume, the optimum blending amount of silica fume, the optimum blending amount of water reducing agent and the adjustment of sand and gravel.

Although HPC with compressive strength of up to 100 MPa can be made using pure cement, it will be much easier when using silica fume. For the preparation of concrete with a strength exceeding 100 MPa, the use of silica fume is almost indispensable. Silica fume is used as both a filler and pozzolanic material in concrete. After the use of silicon powder, the pore size in the hydrated slurry is greatly reduced, and the pore size distribution is improved, so that the strength is increased and the permeability is reduced. For example, the research results show (CEB2FIP1988) that in order to obtain the concrete strength of 70 MPa, the application of pure cement requires a water-binder ratio of 0.35, and when 8% silicon powder is added, the water-binder ratio can be 0.50. Because the silicon powder particles are very fine, they can react with volcanic ash in the early hours. According to Carette and Malhotra (1992), the contribution of silica fume to concrete strength is mainly before 28d. So, just

The durability of concrete includes its frost resistance, impermeability, chemical resistance, resistance to reinforcement corrosion and erosion resistance. Here we only talk about its frost resistance, impermeability and chemical resistance. Erosive effect.

a) Frost resistance: When the amount of silica fume is small, the frost resistance of silica fume concrete is basically the same as that of ordinary concrete. When the amount of silica fume exceeds 15%, its frost resistance is poor. Through a large number of experiments, this view has been basically confirmed. The main reason is that when the silica fume exceeds 15%, the concrete expansion increases, the relative dynamic elastic modulus decreases, and the compressive strength decreases sharply. From the perspective of the internal characteristics of concrete, , Small specific surface area, large spacing coefficient.

b) Impermeability: Because the silica powder particles are small, 20 to 100 times smaller than the cement particles, they can be filled into the voids between the cement particles to make the concrete dense. At the same time, the secondary hydration of the silica powder will block new products The concrete penetrates the channel, so the silica fume concrete has a strong impermeability. The permeability of the concrete increases with the increase of the water-binder ratio. This is because water-cement is relatively poorer than concrete.

c) Chemical resistance: Adding silica fume to concrete can reduce the content of Ca (OH) 2, increase the compactness of concrete, and effectively improve the ability of weak acid corrosion, but not in strong acid or high depth weak acid. CSH decomposes in acid. In addition, it can resist salt corrosion, especially to chloride and sulfate. The reason why it can resist salt erosion is that the silica fume concrete is denser and the pore structure is improved, which reduces It has reduced the rate of harmful ion transmission and reduced the formation of soluble Ca (OH) 2 and ettringite (3CaO · Al2O3 · 3CaSO4 · 32H2), and increased the result of hydrated calcium silicate crystals.

The fineness specifications of the silicon powder required in the domestic and international markets are as follows:

Specification (2mm-10mm) Screening weight (weight)

500um-180um (30 mesh-80 mesh) + 500um3% -180um10%

425um-150um (40 mesh-100 mesh) + 425um5% -150um15%

250um-140um (60 mesh-110 mesh) + 250um3% -140um10%

125um-74um (120 mesh-200 mesh) + 125um3% -74um10%

-74um (-200 mesh) + 74um5%

-45um (325 mesh) + 45um5%

5um-1um (2500 mesh-12500 mesh) + 5um5%

due to

There are many ways to make silicon powder from silicon blocks. Among them, the Raymond method, the roller method, the disc grinding method, and the punching method are more effective and applied more often. The equipment used is the Raymond method, the roller mill, the disc mill (also known as the vertical mill), and the punching method. In terms of the principle of milling, the first three are crushing and crushing, and the latter is impact crushing. According to their structure, they are very different, each has its own characteristics, and each has its own advantages and disadvantages.

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1 Silica powder performance and application Silica powder is finely processed with silicon dioxide (SiO ₂ ), also known as quartz, through crushing, purification, grinding, classification and other processes. It has high purity, white color, and reasonable particle grading. Unique performance and wide range of uses.
1. 1 Silicon fine powder performance (1) has good insulation properties: due to the high purity of silicon fine powder, low impurity content, stable performance, excellent electrical insulation performance, so that the cured product has good insulation performance and arc resistance.
(2) It can reduce the exothermic peak temperature of the epoxy resin curing reaction, reduce the linear expansion coefficient and shrinkage of the cured product, thereby eliminating the internal stress of the cured product and preventing cracking.
(3) Corrosion resistance: silicon powder is not easy to react with other substances, and it can not react with most acids and alkalis. Its particles cover the surface of the object uniformly, and it has strong corrosion resistance.
(4) The particle gradation is reasonable, which can reduce and eliminate precipitation and delamination when used; it can increase the tensile and compressive strength of the cured product, improve the wear resistance, and increase the thermal conductivity of the cured product and increase resistance. Flammability.
(5) The silicon fine powder treated with a silane coupling agent has good wetting properties for various resins, good adsorption performance, easy mixing, and no agglomeration.
(6) The silicon fine powder is used as a filler and added to the organic resin, which not only improves the properties of the cured product, but also reduces the product cost.
1.2 Physical and Chemical Indexes of Several Kinds of Silicon Silica Powder 1.2.1 Silicon Silica Powder for Electronics and Electrical Industry Silicon Silica Powder for Electronics and Electrical Industry (SJ / T10675-2002) Product Classification and Code: General Silicon Silica Powder (PG) for electrical industry , Ordinary active silicon fine powder (PGH), electrical grade silicon fine powder (DG), electrical grade active silicon fine powder (DGH). Used in the electronics industry include electronic grade crystalline silicon fine powder (JG), electronic grade crystalline active silicon fine powder (JGH), electronic grade fused silicon fine powder (RG), and electronic grade fused active silicon fine powder (RGH). Product specifications are the number of product meshes, divided into 300, 400, 600, and 1000 meshes . ^[2]